首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1553篇
  免费   81篇
林业   61篇
农学   57篇
基础科学   26篇
  293篇
综合类   130篇
农作物   56篇
水产渔业   116篇
畜牧兽医   765篇
园艺   26篇
植物保护   104篇
  2023年   13篇
  2021年   21篇
  2020年   25篇
  2019年   41篇
  2018年   30篇
  2017年   26篇
  2016年   30篇
  2015年   30篇
  2014年   42篇
  2013年   74篇
  2012年   67篇
  2011年   82篇
  2010年   49篇
  2009年   57篇
  2008年   91篇
  2007年   93篇
  2006年   58篇
  2005年   78篇
  2004年   74篇
  2003年   68篇
  2002年   65篇
  2001年   36篇
  2000年   34篇
  1999年   37篇
  1998年   15篇
  1997年   14篇
  1996年   11篇
  1995年   16篇
  1994年   14篇
  1993年   14篇
  1992年   22篇
  1991年   16篇
  1990年   12篇
  1989年   16篇
  1988年   18篇
  1987年   13篇
  1986年   13篇
  1985年   19篇
  1984年   12篇
  1983年   13篇
  1982年   10篇
  1980年   8篇
  1979年   12篇
  1978年   10篇
  1975年   14篇
  1974年   12篇
  1973年   10篇
  1971年   11篇
  1969年   11篇
  1967年   8篇
排序方式: 共有1634条查询结果,搜索用时 31 毫秒
71.
In a blind test, 344 samples representing 80 bacterial isolates were analyzed by the Brucella abortus species-specific polymerase chain reaction (BaSS PCR) assay for the identification and discrimination of B. abortus field strains (wild-type biovars 1, 2, and 4) from 1) B. abortus vaccine strains, 2) other Brucella species, and 3) non-Brucella bacteria. Identical samples were tested in 2 laboratories. Half the samples were fully viable, and half were bacteria that had been killed by methanol fixation. The results in 1 laboratory correctly identified 100% of the samples, resulting in a predictive value of 100% for all categories and 100% sensitivity and specificity under the prescribed conditions. The second laboratory misidentified 31 samples, resulting in a range of 66.7-100% sensitivity, 93.2-99.7% specificity, and 77.3-98.2% predictive values depending on the category. There was no significant difference in viable versus fixed bacteria for either laboratory. Subsequent review of the protocol indicated that contamination was the likely cause of 26 of the 31 erroneous identifications. The results show that the BaSS PCR assay has the potential to be a very reliable screening tool for B. abortus identification. However, the data also provide a cautionary reminder of the importance of preventing contamination in diagnostic PCR.  相似文献   
72.
Hip dysplasia is an affection of the coxofemoral joint that progresses until stabilization is caused by fibrosis and osteoarthritic changes. This stabilization process can be examined by clinical and radiographic methods. The capability of evaluating the procollagen concentrations in liquids, such as serum and synovial fluid, has further offered the basis for an objective biochemical evaluation of the stabilization process. Our study was performed to evaluate whether determination of procollagen concentrations was suitable for the use in practice. The procollagen type-III aminoterminal peptide (P-III-NP) concentration was measured in serum and in synovial fluid from coxofemoral joints in 20 dogs. Dogs were grouped on the basis of evidence of dysplasia and osteoarthritic changes of the hip: (1) a control group of 6 dogs without clinical or radiographic signs of hip dysplasia, and (2) dysplastic group of 14 dogs, which was further grouped with respect to the coxofemoral joint laxity, as determined by the Ortolani test. Synovial fluid concentration of P-III-NP was significantly (P less than 0.05) higher in fluid from dysplastic joints than in fluid from normal joints. Serum concentrations of P-III-NP were significantly (P less than 0.05) higher in dogs in which results of the Ortolani test were positive.  相似文献   
73.
Plasma and joint fluids from turkeys experimentally inoculated with Chlamydia psittaci strain TT3 were evaluated by immunoblotting to identify antibodies elicited by chlamydial antigens during the course of infection. Protein antigens from elementary bodies of TT3 were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred electrophoretically to nitrocellulose before being probed with plasma or synovial fluid from TT3-inoculated birds. The major outer-membrane protein (MOMP), the 60,000-molecular-weight proteins, and a 97,400-molecular-weight protein were the predominant antigens recognized by IgG in the plasma and joint fluids. Plasma IgG specific for the 97,400 protein band was first detectable at day 10 postinoculation (PI). Antibodies to the 60,000-molecular-weight protein and MOMP were first detected at days 14-17 PI and at days 7-10 PI, respectively, in some birds, and as late as days 36-42 PI and days 42-70 PI in others. The antibodies were still present at day 142 PI. Immunoblotting techniques indicated that the antigens to which these antibodies were reacting were protein. These observations may have implications for the development of serodiagnostic assays as well as the identification of potential proteins for subunit immunogens in birds.  相似文献   
74.
OBJECTIVE: To compare drilling, tapping, and screw-insertion torque, force, and time for the 4.5-mm AO and 6.5-mm Acutrak Plus (AP) bone screws, and to compare the mechanical shear strength and stiffness of a simulated complete lateral condylar fracture of the equine third metacarpal bone (MC3) stabilized with either an AO or AP screw. STUDY DESIGN: In vitro biomechanical assessment of screw-insertion variables, and shear failure tests of a bone-screw-stabilized simulated lateral condylar fracture. SAMPLE POPULATION: Eight pairs of cadaveric equine MC3s METHODS: Metacarpi were placed in a fixture and centered on a biaxial load cell in a materials-testing system to measure torque, compressive force, and time for drilling, tapping, and screw insertion. Standardized simulated lateral condylar fractures were stabilized by either an AO or AP screw and tested in shear until failure. A paired t test was used to assess differences between screws, with significance set at P < .05. RESULTS: Insertion and mechanical shear testing variables were comparable for AO and AP insertion equipment and screws. CONCLUSION: The 6.5-mm tapered AP screw can be inserted in equine third metacarpal condyles and is mechanically comparable with the 4.5-mm AO screw for fixation of a simulated lateral condylar fracture. CLINICAL RELEVANCE: Considering the comparable mechanical behavior, the potential for less-persistent soft-tissue irritation with the headless design, and the ability to achieve interfragmentary compression by inserting the screw in one hole drilled perpendicular to the fracture plane, the 6.5-mm tapered AP screw may be an attractive alternative for repair of incomplete lateral condylar fractures in horses.  相似文献   
75.
Oestrogen is an important regulator of reproduction and growth. The key enzyme of oestrogen biosynthesis, aromatase cytochrome P450, is encoded by the Cyp19 gene. In order to generate genetic markers for the sheep Cyp19 gene, two novel single nucleotide polymorphisms (SNPs), one located in promoter 2 (P2), the other one in intron 9 (I9), were identified by a comparative sequencing approach. The allele distributions of both SNPs were investigated by means of Polymerase chain reaction‐restriction fragment length polymorphism analysis (PCR‐RFLP) in five economically relevant sheep breeds (British Milk Sheep, Carranzana, Latxa Black Face, Latxa White Face, Merino) and three ancient Hungarian breeds kept as gene reserves (Cikta, Racka, Tsigai). In British Milk Sheep, only the intronic SNP was present whereas in Merino, Cikta, Racka, Tsigai, Carranzana, Latxa Black Face and Latxa White Face, both SNPs could be found. This indicates that the newly identified SNPs can be used as markers for the Cyp19 locus in various sheep breeds.  相似文献   
76.
To investigate the microbial and nutritional characteristics of dry feed, liquid feed containing fermented liquid cereal grains, and fermented liquid feed, and their effect on gastrointestinal ecology and growth performance, 120 piglets from 40 litters were used and housed in pens with 5 animals in each. The 3 dietary treatments (all nonheated and nonpelleted diets) were: a dry meal diet (DRY); a fermented, liquid cereal grain feed (FLG); and a fermented liquid feed (FLF). The FLG diet was prepared by storing the dietary cereals (barley and wheat) and water (1:2.5, wt/wt) in a closed tank at 20 degrees C and adding the remaining dietary ingredients immediately before feeding. The FLF diet was prepared by storing compound feed and water (1:2.5, wt/wt) in a closed tank at 20 degrees C. Three times daily, 50% of the fermented cereals or compound feed and water stored in the tanks was removed and replaced with an equal amount of fresh cereals or feed and water. On d 14, 1 piglet from each pen was killed and samples from the gastrointestinal tract were obtained. The pH of the fermented cereals was 3.85 (SD = 0.10), that of the FLG diet was 5.00 (SD = 0.18), and the pH of the FLF diet was 4.45 (SD = 0.11). The dietary concentration of lysine (g/16 g of N) pointed to a decreased concentration in the FLF (5.46, SD = 0.08) compared with the DRY (6.01) and FLG (6.21, SD = 0.27) diets, and the concentration of cadaverine was greater in the FLF diet (890 mg/kg, SD = 151.3) than in the DRY (32 mg/kg) or FLG (153 mg/kg, SD = 18.7) diets. Fermenting only the cereal component of the diet (FLG) promoted the growth of yeasts to a greater extent than fermenting the whole diet (FLF). Terminal RFLP profiles of diets and digesta from the stomach and midcolon showed differences among dietary groups. The number of yeasts able to grow at 37 degrees C in the stomach and caudal small intestine was greatest in the FLG group compared with the other 2 dietary groups (P < 0.01). In the cecum and colon, the differences were only significant between piglets fed the FLG and the FLF diets (P < 0.05). The greatest number of yeasts able to grow at 20 degrees C was detected in the animals fed the FLG diet. However, the values were different from the FLF-fed piglets only in the stomach (P < 0.05) and midcolon (P < 0.05). There was a tendency (P < 0.10) for greater ADG of the piglets fed the FLG compared with the FLF diet. Feeding liquid feed containing fermented, liquid cereal grains as a means of avoiding microbial decarboxylation of free amino acids in the feed and increasing feed intake by improving palatability seems promising but requires further investigation.  相似文献   
77.
78.
Two transgenic Bt rice lines, KMD1 and KMD2, both containing a synthetic cry1Ab gene from Bt, were crossed with conventional rice varieties. The inheritance of resistance to SSB of KMD1 and KMD2was investigated through LSB and field examination of their progenies, e.g. F1, BC1 and F2 populations. In LSBs, 100.0% of newly hatched SSB larvae died on the second day after feeding on leaf tissues of F1 and GUS positive BC1 plants, of which the area of leaf tissues consumed by SSB is also similar to that of transgenic parents. These results imply that the resistance of Bt rice to SSB is dominantly controlled and could be easily exploited in hybrid rice production. Field evaluation showed that segregation ratios for SSB resistance to susceptibility in BC1 populations fit the ratio of 1:1, which was also confirmed by LSBs. However, in F2 populations, the ratio was significantly smaller than 3:1 for resistant to susceptible plants in all 6 indica × japonica (KMD1 and KMD2) crosses, though it fitted 3:1 in all 4 japonica × japonica crosses. The results implied that the resistance of Bt rice to SSB was controlled by a dominant gene which was present in a homozygous condition in both KMD1 and KMD2, but the inheritance could be affected by other factors. Assays for Cry1Ab protein showed that, in most crosses, the content of Cry1Ab is significantly higher in leaves of GUS positive F1, BC1 and F2 plants than that in transgenic Bt parent plants, which accounts for the high resistance observed in these plants to SSB. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
79.
Jens Weibull 《Euphytica》1987,36(2):571-576
Summary Twenty-seven accessions of Hordeum species and interspecific hybrids were screened in a growth chamber for resistance against the aphid Rhopalosiphum padi. Resistance measurement was based on the aphids' population growth during a 16-day period. The mean number of nymphs produced per female was only about 14% of that on the control cv. Tellus. H. bogdani was the most resistant accession. As a group, interspecific F1-hybrids with common barley (H. vulgare × H. sp.) held an intermediate position. Differences in resistance between hybrids as well as between species (H. jubatum and H. lechleri) were observed. The most resistant species were all diploids. No effects of the host plant on formation of alatae or on the within-plant distribution of aphids were found.  相似文献   
80.
A total of 4,681 accessions of Hordeum vulgare landrace material from Ethiopia, East Mediterranean, Near East, Nepal and China were sown in the field and subjected to the natural powdery mildew epidemic in Denmark. Apparently resistant accessions were selected. Selfed progeny from them were retested and reselected in subsequent years at four locations in Denmark. Finally, 16 promising donors of resistance were retained. They were characterized in the field and tested in the seedling stage for reaction to up to 72 different isolates of the powdery mildew fungus. The absence of the corresponding virulences in the Danish airborne powdery mildew population was ascertained in five years. The resistances in the 16 donors are apparently mutually different and from known sources of powdery mildew resistance in barley. This revised version was published online in July 2006 with corrections to the Cover Date.  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