首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
The objective of this field study was to evaluate in an endemically porcine reproductive and respiratory syndrome (PRRS) virus-infected farm the reproductive performance of sows after their vaccination with a PRRS attenuated vaccine. In a farrow-to-finish pig farm with history of endemic PRRS virus infection, a total of 200 gilts and sows were used. They were divided in 2 groups of 100 animals. The first group was used as untreated controls, while the animals of the second group were vaccinated against PRRS virus using the attenuated Porcilis PRRS vaccine (Intervet International, The Netherlands) based on European strain. All health and reproductive parameters were recorded from the time of vaccination up to next weaning. No adverse systemic or local reactions or side effects relative to vaccination were noted. Compared to controls, vaccinated sows showed significantly improved farrowing rate (89% versus 78%) and a tendency for fewer returns to oestrus, particularly those at irregular intervals. Fewer sows farrowed prematurely and showed post-partum dysgalactia syndrome, but more live pigs were born and weaned in each litter after vaccination. It was concluded that vaccination of sows with Porcilis PRRS attenuated vaccine in farms with endemic PRRSV infection has beneficial effects on their health and fertility.  相似文献   

2.
The study was conducted to evaluate the effect of the long-term dietary use of a natural zeolite (clinoptilolite, NZ) on health status and reproductive performance of sows/gilts and performance of their litters, along with its compatibility with antibacterials (chlortetracycline, CTC) periodically used in medication programmes. Two hundred and forty sows/gilts and their litters were assigned to two main experimental groups and four subgroups, depending on the inclusion of NZ and CTC in their feed. During the trial, frequent sampling of pregnancy feed for mycotoxicological analysis revealed a high contamination level with zearalenone. No adverse or side effects attributed to NZ were noticed. Furthermore, the combined use of NZ and CTC revealed no clinically apparent interactive effect on the availability of the latter. Reproductive performance was significantly improved by the dietary inclusion of both NZ and CTC. The results also suggested that the beneficial effect of NZ could be additionally considered as an indicator of the amelioration of zearalenone exposure consequences.  相似文献   

3.
The purpose of this study was to investigate the safety and efficacy of a commercial European porcine reproductive and respiratory syndrome virus (PRRSV)‐inactivated vaccine after 18‐month use in gilts/sows at a farm with high seroprevalence. In a farrow‐to‐finish farm with 1100 sows, all sows and gilts were systematically vaccinated with the PRRS‐inactivated PROGRESSIS® vaccine for a period of 18 months. Farm's reproductive and litter characteristics were longitudinally recorded for this period and historically compared with those of the year prior to vaccination. Serology, employing immunoperoxidase monolayer assay, had confirmed a high prevalence of PRRS‐specific antibodies in most age groups within the farm prior to vaccination. Seroprevalence during the experiment ranged between 0% and 100% in weaners and growers, but remained at stable high levels (>93%) in finishing pigs and gilts throughout all 2‐year period of serology measurements. No local or systemic vaccine side effects were noted throughout the trial period. Vaccinations had resulted over time in a significant improvement of sow reproductive performance (e.g. reduction of premature farrowings, abortions and increase of farrowing rate) and litter characteristics (e.g. increase of the number of live born and weaned pigs and decrease of stillborn, mummified, weak and splay‐legged piglets). It has also been observed that the higher the degree of immunization of a sow, the better the improvement of her reproductive parameters. Sows after vaccination have shown improved characteristics compared to homoparous sows prior to the application of vaccinations in the farm.  相似文献   

4.
Porcine reproductive and respiratory syndrome (PRRS) virus infection causes reproductive failures including return to oestrus, abortion, mummified foetuses, stillborn, and weak-born piglets. The objective of the present study was to investigate reproductive performance of sows in PRRS-virus-seropositive herds with and without PRRS modified live virus (PRRS-MLV) vaccination. The study was conducted in 20 PRRS-virus-seropositive commercial swine herds in Thailand. The data included 211,009 mating and 180,935 farrowing records. The analysed variables included farrowing rate (FR), return rate (RR), abortion rate (AR), total number of piglets born per litter (TB), number of piglets born alive per litter (BA), percentage of stillborn (SB), percentage of mummified foetuses (MM), and number of piglets weaned per litter (WP). The results revealed that FR in non-vaccinated sows was lower than that in vaccinated sows (85.0 vs 89.7 %, respectively, P?<?0.001), and RR in non-vaccinated sows was higher than that in vaccinated sows (6.9 vs 3.7 %, respectively, P?<?0.001). AR did not differ significantly between non-vaccinated and vaccinated sows (1.6 and 2.0 %, respectively, P?=?0.964). TB (11.2 and 11.5, respectively, P?<?0.001), BA (10.0 and 10.6, respectively, P?<?0.001), and WP (9.2 and 9.6, respectively, P?<?0.001) in non-vaccinated sows were lower than those in vaccinated sows. SB (6.9 and 5.1 %, respectively, P?<?0.001) and MM (3.2 and 2.2 %, respectively, P?<?0.001) in PRRS-MLV-vaccinated sows were higher than those in non-vaccinated sows. The improvement in sow reproductive performance in PRRS-MLV-vaccinated herds was most pronounced in gilts and primiparous sows.  相似文献   

5.
The first case of porcine reproductive and respiratory syndrome (PRRS) in Denmark was diagnosed in March 1992 by the detection of specific antibodies against PRRS virus in serum samples originating from sows in a herd located on the island of Als. Subsequently, PRRS virus was isolated from a 200-sow farrow-to-finish herd with clinical signs consistent with PRRS. The virus was isolated by inoculation of pleural fluid from a stillborn piglet onto porcine pulmonary alveolar macrophages. The isolate was identified as PRRS virus by staining with a specific antiserum. By electron microscopy, the virus particle was found to be spherical and enveloped, measuring 45–55 nm in diameter and containing a 30–35 nm nucleocapsid. Only minor antigenic differences were found between the Danish and a Dutch isolate. Following intranasal inoculation of 3 pregnant gilts with the Danish isolate transplacental infection was demonstrated by the re-isolation of PRRS virus from approximately 45% of the piglets from the experimentally infected gilts. However, the experimental infection produced no significant reproductive disorders or other clinical signs. At autopsy, histopathological examination revealed slight interstitial pneumonia in a few piglets.  相似文献   

6.
A randomised, double-blinded, placebo-controlled study into the effectiveness and safety of a vaccine against porcine reproductive and respiratory syndrome virus (PRRSV) was carried out on three farms with a history compatible with chronic PRRSV infection; representative groups of sows and gilts were injected with a live vaccine against PRRSV, and during the next six weeks no side effects were observed. The remaining sows and gilts on the three farms were then vaccinated with the same vaccine. Again, no side effects were observed. There were significant reductions in abortion, reproductive disease, returns to oestrus and the numbers of stillborn pigs per sow, and significant increases in the numbers of liveborn pigs per sow and weaned pigs per sow among the vaccinated animals.  相似文献   

7.
Summary

As no systematic study has been done to get an accurate estimate of the incidence of return to oestrus after first insemination in sows in the Netherlands, the objectives of this investigation were:

1) to obtain an estimate of the incidence of return to oestrus after insemination at the herd level;

2) to investigate the association between incidence of return to oestrus after first insemination and reproduction characteristics in order to get an impression of the economic importance of reproductive failure.

These objectives were investigated by using the reproduction results of 240 swine breeding herds in the Southern Netherlands in 1987. This information was obtained from CBK plus computerized herd management records. The average incidence rate of return to oestrus after first insemination at a herd level was 16.9 per 100 first inseminations. The occurrence of return to oestrus after first insemination was distinctly higher in the insemination months July and August compared to the rest of the year. An increased incidence, with 10 returns per 100 first inseminations corrected for confounders in a multiple linear regression model, was associated with a decrease of approximately 0.3 live born piglets/sow/year. A prospective longitudinal study was started in 1988 and 1989 in 37 sow herds. Individual sows were monitored from weaning to first insemination, to the occurrence of return to oestrus, or not, after first insemination, and to farrowing. The investigation focused in particular on the relationship between return to oestrus after first insemination and seroconversion against porcine parvovirus (PPV) and Leptospira interrogans serovar bratislava (L. bratislava). During a number of consecutive farm visits, blood samples were taken from sows at weaning and again 6 weeks later. The final data set analysed consisted of 161 animals that did not return to oestrus and 158 animals that did return to oestrus after first insemination. Seroconversion was defined as a 4‐fold increase in titre between the two successive blood samplings: sera were investigated at dilutions of 1:100 to 1:3200 (L. bratislava) and 1:4 to 1:16384 (PPV).

There was no indication of an association between the occurrence of return to oestrus after first insemination and seroconversion against PPV or L. bratislava with the serodiagnostics used in this study. However, it should be noted that L. bratislava infected sows can have a titre below the widely accepted minimum titre of 1:100 used in laboratories, and recently from sows without a titre L. bratislava was isolated. It is suggested that the most appropriate way to assess the influence of infection with L. bratislava on reproductive failure in swine at this moment is to use culture or other methods (e.g. PCR). Litter size and between‐farrowing time of the last farrowing before the study period was not associated with the occurrence of return to oestrus after first insemination in the study period. However, an increased weaning‐to‐first‐in‐semination interval, a high progesterone level at weaning, a low albumin concentration at weaning, and a decrease in albumin concentration between the consecutive samplings and an increase in gamma globulin concentration between the two blood samplings increased the risk of occurrence of a regular return to oestrus after first insemination.

An increased weaning‐to‐first insemination interval, an increase in leucocyte and gamma globulin concentrations and a reduction in alpha1,2 globulin concentration between the consecutive samplings increased the risk of occurrence of an irregular return to oestrus after first insemination.  相似文献   

8.
The purpose of the study was to investigate whether, on farms with both post-weaning multisystemic wasting syndrome (PMWS) and porcine reproductive and respiratory syndrome (PRRS), the PRRS vaccination of sows and their fattening pigs protects against these syndromes. In a farrow-to-finish pig farm with a history of PRRS and PMWS, 200 gilts and sows were allocated to one of two groups of equal size. The first group (C-sow group) was used as untreated controls, while the animals of the second group (V-sow group) were vaccinated with live Porcilis PRRS vaccine. At the next weaning, all piglets of half the sows of the C sow group were vaccinated once at 35 days of age with the vaccine (CV group), while the offspring of the other half of the unvaccinated sows were left unvaccinated (CC group). Similarly, the offspring of half the sows of the V sow group were vaccinated (VV group), while those of the other half of the vaccinated sows were left unvaccinated (VC group). No significant differences in morbidity were observed between the groups during the nursery and finishing phases, while morbidity in the growers was significantly reduced in the CV- and VV-groups (P < 0.05). Growers' mortality was significantly reduced after piglet vaccination when compared with unvaccinated pigs of unvaccinated dams (P < 0.05). Average daily gain and feed conversion ratio were significantly improved in vaccinated piglets compared with those in the unvaccinated groups (P < 0.05).  相似文献   

9.
OBJECTIVE: To determine whether cell-mediated immunity against porcine reproductive and respiratory syndrome (PRRS) virus is correlated with protection against reproductive failure in sows during clinical outbreaks of PRRS in commercial herds. DESIGN: Outbreak investigation in 4 swine breeding herds. ANIMALS: 97 sows. PROCEDURES: On each farm, blood samples were collected from sows with clinical signs (abortion or increased fetal death; case sows) and from clinically normal sows (control sows). The intensity of the cell-mediated immune (CMI) response was determined by use of an interferon-gamma enzyme-linked immunospot (ELISPOT) assay. Multiple logistic regression analyses and t tests were used to compare ELISPOT assay values between case and control sows. Multiple linear regression was used to investigate associations between cell-mediated immunity and the magnitude of clinical signs. RESULTS: In 2 farms, case sows had lower ELISPOT assay values than control sows. A negative association between the intensity of the CMI response and the number of pigs born dead per litter was detected on 1 farm. In 1 farm, no association was detected between the intensity of the CMI response and protection against reproductive failure. CONCLUSIONS AND CLINICAL RELEVANCE: Evidence that a strong CMI response was correlated with protection against clinical PRRS was detected in 3 of 4 farms. However, farms and sows within farms varied considerably in their immune responsiveness and in the degree to which they were protected clinically. Increasing cell-mediated immunity within infected herds has the potential to decrease clinical reproductive disease, but only if the sources of intra- and interfarm variation in the intensity of cell-mediated immunity to PRRS virus can be identified.  相似文献   

10.
OBJECTIVE: To determine whether 6.5-week-old gilts that have not previously been exposed to porcine reproductive and respiratory syndrome (PRRS) virus can be acclimatized to an endemic strain of the virus by commingling with age-matched gilts inoculated with the endemic PRRS virus strain and whether 10.5-week-old gilts can be acclimatized by commingling with age-matched inoculated or contact-exposed animals. DESIGN: Randomized controlled longitudinal study. ANIMALS: 80 gilts seronegative for PRRS on a farm in the Midwestern United States with a history of PRRS. PROCEDURES: 20 gilts were inoculated with the endemic PRRS virus strain at 6.5 weeks of age (group 1) and were commingled with 20 gilts that were not inoculated (group 2). Four weeks later, the remaining 40 gilts (group 3) were commingled with gilts in groups 1 and 2. Presence of viral RNA in the tonsils, seroconversion rate, serum neutralizing antibody titers, interferon-gamma-mediated cellular immunity, and reproductive outcomes were analyzed. RESULTS: Acclimatization of PRRS virus-na?ve pigs was achieved by means of contact exposure at both 6.5 and 10.5 weeks of age. No differences were observed among the 3 groups with respect to development of anti-PRRS virus-specific immune responses or reproductive outcomes. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that contact exposure of 6.5- to 10.5-week-old pigs that had not previously been exposed to PRRS virus to pigs inoculated with endemic PRRS virus may be an efficient acclimatization strategy for controlling outbreaks on commercial farms on which PRRS is endemic.  相似文献   

11.
Probiotics have gained considerable attention with respect to their beneficial effects on livestock performance and health. The most significant effects of probiotics on the gut microbiota and the host animals take place when they are included in diets during particularly stressful periods such as weaning and/or at the beginning of the lactation period. The probiotics Bacillus mesentericus strain TO‐A at 1 × 108 colony forming units (CFU)/g, Clostridium butyricum strain TO‐A at 1 × 108 CFU/g and Enterococcus faecalis strain T‐110 at 1 × 109 CFU/g were used. Litter weight at delivery and ratio of return to estrous improved significantly (17% and 24% improvement, respectively) by probiotic administration to sows (0.2% (w/w)). Furthermore, the feed intake of the probiotics‐administered sows was greater than that of the control sows during the late lactation period. Post‐weaning diarrheal incidence and growth performance was improved by probiotics administration to neonates (0.02% (w/w)), while the combined use of probiotics in sows and their neonates induced the enlargement of villous height and prevented muscle layer thinning in the small intestine of weaning piglets. The administration of probiotics of three species of live bacteria improved the porcine reproductive performance around stressful periods of sows (farrowing) and piglets (weaning). [Corrections added on 26 April 2016, after first online publication: ‘Enterococcus faecalis strain T‐100’ has been corrected to ‘Enterococcus faecalis strain T‐110’ in the above paragraph and in the ‘Probiotics’ section under the Materials and Methods heading.]  相似文献   

12.
The purposes of this study were to describe the clinical signs observed in PRRS positive herds during a porcine reproductive and respiratory syndrome (PRRS) outbreak in Ontario and to determine associations between these clinical signs and herd demographics and PRRS control strategies. All PRRS polymerase chain reaction-(PCR)-positive submissions to a diagnostic laboratory between September 1, 2004 and August 31, 2007 were identified (n = 1864). After meeting eligibility requirements and agreeing to voluntary study participation, producers from 455 of these submissions were surveyed for information on clinical signs observed in their herds, herd demographics, and PRRS control strategies used in their herds at the time that the PCR-positive samples were taken. Larger herd size was associated with an increased risk of reporting abortion, weakborn piglets, off-feed sows, and sow mortality in sow herds, and with an increased risk of reporting mortality in finishing herds. When disease control strategies were examined, use of a commercial PRRS vaccine in sows and gilts was associated with a decreased risk of reporting weakborn pigs and high pre-weaning mortality, while the use of serum inoculation in breeding animals was associated with an increased risk of reporting off-feed sows and sow mortality. Providing biofeedback of stillborn/mummified piglets, placenta or feces to gilts was associated with an increased risk of reporting respiratory disease and mortality in finishing pigs while all-in/all-out flow in farrowing rooms was associated with an increased risk of reporting sow mortality and weakborn piglets.  相似文献   

13.
猪繁殖与呼吸综合征是由猪繁殖与呼吸综合征病毒（Porcine reproductive and respiratory syndrome virus,PRRSV）引起的一种严重危害养猪业的传染病,主要引起妊振母猪的流产、死产、木乃伊胎、弱仔等繁殖障碍和仔猪的呼吸道疾病。本次调查采用RT-PCR对山东省潍坊市7个县20家猪场的送检样品进行PRRSV检测。结果显示,7个县猪场均检出PRRSV阳性,阳性检出率为35%~82%,平均阳性率为67.9%。流行病学调查结果表明,PRRSV感染已在潍坊市猪群中普遍存在,PRRS已成为危害当地养猪业的重要疫病。但各县市之间PRRSV感染率差异较大,在拥有较多小规模猪场的县市阳性率较高;不同日龄猪之间PRRSV感染率及死亡率差异较大,30~60日龄最高;不同品种猪群对该病毒的易感性和感染阳性率差别不大。  相似文献   

14.
SUMMARY A serious year-round fertility problem on a commercial piggery was investigated. The problem was characterised by a high proportion of non-pregnant sows and gilts which showed a delayed return or failure to return to oestrus after a normal mating to a fertile boar. Several factors were identified that we considered to be placing undue stress on the breeding stock from wearning through mating and early pregnancy. When steps were taken to reduce the influence of these stressors there was a marked improvement in the herd farrowing rate. Across all months this improvement was largely due to a reduction in the number of sows showing delayed return or failure to return to oestrus after mating. There were no concomitant changes in other indices of performance. In conclusion this study has shown that stressful factors other than summer heat stress can cause a syndrome of delayed or failure to return to oestrus, this syndrome is commonly and perhaps wrongly called summer or seasonal infertility. When given the appropriate combination and/or intensity of stressful stimuli, it can be manifest at any time of the year.  相似文献   

15.
The effect of L-carnitine supplementation during pregnancy and lactation on performance parameters of sows was studied. The trial comprised a total of 127 sows (40 gilts, 87 mature sows) which were divided into a control and a treatment group. All animals were fed individually and received basic feed mixtures for pregnancy and lactation with low carnitine concentrations (gestation diet: 4.7 mg/kg feed, lactation diet: 12.5 mg/kg feed). The rations of the sows in the treated group were supplemented with 125 mg L -carnitine per head and day during pregnancy and 250 mg L -carnitine per head and day during lactation. The animals of the control group received identical feed mixtures in identical amounts, but without the L -carnitine supplement. L -carnitine supplementation resulted in higher sow liveweight gains between day 1 and day 85 of pregnancy. The number of piglets per litter and the number born alive did not differ between the control sows and those treated with L -carnitine. However, the L -carnitine-supplemented sows produced only half as many non-viable piglets as the control animals. Moreover, litter weight and mean birth weight of piglets from L -carnitine-treated sows were higher than in the control sows. This effect was more marked in gilts (+8% higher litter weight, +9% higher piglet weight) than in sows (+7% and +6%, respectively). Piglets from sows whose ration was supplemented with L -carnitine showed higher liveweight gains during the suckling period (+12% for gilts, +4% for sows), which is why litter weights post weaning were also higher among the sows treated with L -carnitine than in the control sows (+14% for gilts, +10% for sows). Overall, the study shows that dietary supplementation with L -carnitine during pregnancy and lactation improves the reproductive performance of sows.  相似文献   

16.
The effect of a modified eros centre on weaning to oestrus interval, follicle size, ovulation and farrowing rate and total born litter size was investigated. In modified eros centre 94.4% and in group housing 79.1% of the sows (p < 0.01) expressed oestrus within 10 days post‐weaning. Weaning to oestrus interval was shorter (p < 0.001) for sows kept in modified eros centre. The interval from onset of oestrus to the time of ovulation was longer for sows in group housing (p=0.05). The time of ovulation was negatively correlated (r=?0.50) with the interval from weaning to oestrus (p=0.005). The time of ovulation after onset of oestrus was significantly (p < 0.05) shorter for sows expressing oestrus within 2–4 days of weaning, compared with the animals that expressed oestrus between days 5 and 6 post‐weaning and was shortest for sows expressing oestrus after day 6 post‐weaning. Farrowing rate was not affected by a modified eros centre. Litter size tended to be smaller in group‐housed weaned sows (p=0.10). The timing of last artificial insemination relative to time of ovulation did not affect litter size (p > 0.10). The implication of these results is that a modified eros centre may improve some of the post‐weaning oestrous parameters of the sow.  相似文献   

17.
A system was designed to allow a small swine farm in a northern latitude to use its own boars for artificial insemination (AI) conveniently. Semen was collected twice weekly for 3 day use (days 0, 1 and 2), extended in an egg yolk extender and stored at 5°C. Farm personnel were trained to manage the entire AI programme. For simplicity all semen collected was used for insemination. In the first test 47 gilts and 15 sows were inseminated with semen from four boars. One boar was subfertile with a farrowing rate of 36%. The averages for the other boars ranged from 71 to 100%. Then semen was collected from seven boars and all was used to inseminate 70 gilts and 55 sows with 3 × 109 or more sperm. Overall 63% farrowed an average of 10.1 piglets per litter. Litter size for sows was 1.5 piglets larger than for gilts. There was no difference in farrowing rate when more than 3 × 109 sperm were inseminated. The feasibility of initiating a complete AI programme within a small herd using herd boars was established. However, selection of the boars, use of only high quality semen, and experience with detecting oestrus was required to increase the farrowing rate. The use of various agents to protect sperm against cold shock below 15°C is worthy of further investigation. A new type of electronic probe, which measures the conductivity of cervical mucus, could be helpful if a boar is not available for conventional detection of oestrus.  相似文献   

18.
OBJECTIVE: To document shedding of porcine reproductive and respiratory syndrome (PRRS) virus in mammary gland secretions of experimentally inoculated sows, to evaluate effects of vaccination during gestation on virus shedding during the subsequent lactation, and to evaluate shedding of PRRS virus in milk of sows in commercial herds. ANIMALS: 6 sows seronegative for PRRS virus were used for experiment 1, and 2 sows were retained for experiment 2. For experiment 3, 202 sows in commercial herds were used. PROCEDURE: In experiment 1, 2 sows were inoculated with PRRS virus, 2 sows were vaccinated with modified-live PRRS virus vaccine, and 2 sows served as control pigs. Mammary gland secretions were assayed for PRRS virus. In experiment 2, pregnant vaccinated sows from experiment 1 were vaccinated with another modified-live PRRS virus vaccine. Mammary gland secretions were assayed in the same manner as for experiment 1. For experiment 3, milk collected from 202 sows in commercial herds was assayed for PRRS virus. RESULTS: In experiment 1, PRRS virus was detected in mammary gland secretions of both vaccinated and 1 of 2 virus-inoculated sows. In experiment 2, virus was not detected in samples from either vaccinated sow. In experiment 3, all samples yielded negative results. CONCLUSIONS AND CLINICAL RELEVANCE: Na?ve sows inoculated late in gestation shed PRRS virus in mammary secretions. Previous vaccination appeared to prevent shedding during the subsequent lactation. Results for samples obtained from sows in commercial herds suggested that virus shedding in mammary gland secretions of such sows is uncommon.  相似文献   

19.
In order to increase reproductive performance, sows are usually inseminated several times during oestrus. In practice, this results in a significant number of sows receiving one or more post‐ovulatory inseminations. This study was carried out to determine the percentage of sows that receive one or more post‐ovulatory inseminations and the effect of such treatment on reproductive performance. The results were analysed from a total of 1298 sows on two farms. It was observed that more than 70% of the sows received at least one post‐ovulatory insemination and approximately 20% received two or more. There was no observed effect on the rate of return to oestrus, farrowing rate or litter size (p > 0.05).  相似文献   

20.
猪繁殖与呼吸综合征疫苗研究进展   总被引：1，自引：0，他引：1  
猪繁殖与呼吸综合征是一种引起母猪繁殖障碍和新生仔猪呼吸道症状及高死亡率的传染病。在世界包括中国在内的各养猪国家广泛流行,造成严重经济损失,受到国内外学者的高度重视,对此病的研究特别是对其疫苗的研究正日益受到关注。文章就猪繁殖与呼吸综合征病毒的灭活疫苗、弱毒疫苗和基因工程疫苗的研究进展做了详细的阐述。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号