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   351篇
  免费   18篇
林业   17篇
农学   22篇
  41篇
综合类   19篇
农作物   13篇
水产渔业   62篇
畜牧兽医   169篇
园艺   10篇
植物保护   16篇
  2023年   2篇
  2022年   2篇
  2021年   21篇
  2020年   7篇
  2019年   4篇
  2018年   6篇
  2017年   16篇
  2016年   13篇
  2015年   12篇
  2014年   23篇
  2013年   29篇
  2012年   26篇
  2011年   25篇
  2010年   13篇
  2009年   15篇
  2008年   26篇
  2007年   24篇
  2006年   14篇
  2005年   14篇
  2004年   15篇
  2003年   32篇
  2002年   11篇
  2001年   4篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1994年   1篇
  1992年   2篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1984年   1篇
  1981年   1篇
  1963年   1篇
排序方式: 共有369条查询结果,搜索用时 15 毫秒
1.
Dwarf Lulu cattle, the only Bos Taurus type of cattle in Nepal, are raised under severe environments in the mountainous zone of that country. In the present study, the body measurement traits, cytogenetic and molecular genetic characteristics of the Lulu cattle are investigated. Blood samples were collected from 31 animals in four villages (altitudes 2590–3550 m) in the southern part of Mustang. The Lulu cattle had a normal karyotype with 2n = 60, XY or XX. Only one male examined had a large submetacentric X‐chromosome and a small submetacentric taurine type Y‐chromosome. The mitochodrial DNA (mtDNA) genotypes were analyzed by PCR mediated restriction fragment length polymorphisms, displacement (D)‐loop region PCR mediated single strand conformation polymorphisms, and D‐loop region sequences. Many base substitutions were found in the D‐loop region, suggesting that the Lulu cattle originated from at least 10 maternal lines. Three types of mtDNA from these cattle were found, the Bos taurus type (n = 23), the Bos indicus type (n = 6), and the Bos grunniens type (n = 2). In the village at the lowest altitude, four of the five cows were of the Bos indicus type. These results indicated that mtDNA types of the Lulu cattle mostly belong to Bos taurus, but have been hybridized with Bos indicus cattle in lower‐elevation regions in their maternal lineage.  相似文献   
2.
3.
This study aimed to determine the effects of feeding an increased volume of high‐fat milk during the early post‐natal life on metabolite concentrations in the blood, the expression of key genes regulating intermediary metabolism in the skeletal muscles, and the rate of growth of Japanese Black cattle. All calves were fed a high‐fat milk replacer (crude protein, 26%; crude fat, 25.5%; total dissolved nitrogen, 116%). Control calves (n = 4) were nursed with 500 g milk replacer until 3 months of age, whereas calves in the experimental group (n = 4) were nursed with 1800 g milk replacer until 3 months, and then the volume was gradually reduced until 5 months. Body weight was significantly higher in the experimental group than in the control group at 7 months. Plasma glucose concentrations were significantly lower in the experimental group. Expression of glucose‐transporter‐4 messenger RNA (mRNA) was lower, whereas that of glucose transporter 1, cluster of differentiation 36, and carnitine palmitoyltransferase‐1b mRNA was significantly higher in the Longissimus thoracis of the experimental group. Nutritional status during early post‐natal life appears to strongly influence the growth rate and glucose and lipid metabolism in Japanese Black cattle.  相似文献   
4.
MX belongs to a family of type I interferon (IFN)-stimulated genes, and the MX protein has antiviral activity. MX has at least two isoforms, known as MX1 and MX2, in mammals. Moreover, bovine MX1 has been found to have alternative splice variants—namely, MX1-a and MX1B. In ruminants, IFN-τ—a type I IFN—is temporarily produced from the conceptus before implantation and induces MX expression in the endometrium. However, the expression dynamics of MX after implantation are not clear. In the present study, we investigated the expression of MX1-a, MX1B and MX2 in the endometrium and placenta before and after implantation along with the expression of IFN-α, type I receptors (IFNAR1 and IFNAR2) and interferon regulatory factors (IRF3 and IRF9). Pregnant uterine samples were divided into five groups according to pregnancy days 14–18, 25–40, 50–70, 80–100, and 130–150. Tissue samples were collected from the intercaruncular endometrium (IC), caruncular endometrium (C) and fetal placenta (P). Although all the MX expressions were significantly higher in the IC and C at days 14–18, presumably caused by embryo-secreted IFN-τ stimulation, their expressions were also detectable in the IC, C and P after implantation. Furthermore, IFN-α expression was significantly higher in the IC. RT-PCR indicated IFNAR1, IFNAR2, IRF3 and IRF9 mRNA in all the tissues during pregnancy. These results suggest that all the MX genes are affected by the type I IFN pathway during pregnancy and are involved in an immune response to protect the mother and fetus.  相似文献   
5.
Epidemiological and bacteriological survey of buffalo mastitis in Nepal   总被引:2,自引:0,他引:2  
A total of 355 Murrah cross buffaloes, consisting of 23 subclinical and 332 clinical mastitis cases brought to the Veterinary Teaching Hospital, Chitwan, Nepal from 2002 to 2005, were analyzed to determine the organisms involved, the seasonal occurrence of mastitis, and antibiotic susceptibility of mastitis pathogens. Coagulase negative Staphylococci (CNS) such as Staphylococcus albus and S. epidermidis were the predominant organisms associated with subclinical cases, and CNS and Coliforms in clinical cases. The maximum number (16%) of clinical cases of mastitis were observed in the month of July, when temperature and humidity are highest. The incidence of clinical mastitis was higher in animals during 1st calving and during the 1st month of parturition. Resistance to antibiotics was determined for 55, 23 and 149 isolates of Staphylococcus spp., Streptococcus spp. and Coliforms, respectively. In vitro drug sensitivity testing revealed that enrofloxacin had the highest average sensitivity (91%) for all types of bacteria. The effectiveness of other drugs detected were gentamicin (87%), tetracycline (83%) and chloramphenicol (82%). The antibiogram showed that both gentamicin and enrofloxacin are slowly becoming resistant. Mastitis pathogens have developed resistance to ampicillin and penicillin.  相似文献   
6.
7.
In order to identify genetic resources for breeding fragrant petunias for use as bedding plants, volatile compounds released by day from the flowers of 40 commercial Petunia hybrida cultivars were analyzed using a solid-phase micro-extraction technique coupled with GC–MS. The three cultivars with solid deep-blue flowers that accumulate malvidin in corollas with high tissue pH were found to emit abundant iso-eugenol as the principal floral fragrance. Several other cultivars that emitted considerable amounts of methylbenzoate and/or benzylbenzoate from the flower were also identified. Association between the floral fragrance and the other floral traits such as floral anthocyanin composition and corolla-tissue pH was discussed.  相似文献   
8.
Japanese isolates of Verticillium dahliae, a causal agent of wilt disease in many plants, are classifiable into pathotypes based on their pathogenicity. Because these pathotypes are morphologically indistinguishable, establishing a rapid identification method is very important for the control of this pathogen in Japan. For cloning DNA fragments that are useful for identification and specific detection of V. dahliae pathotypes, we performed random amplified polymorphic DNA (RAPD) analyses using various isolates. One polymerase chain reaction (PCR) product, E10-U48, was specific to isolates pathogenic to sweet pepper. The other product, B68-TV, was specific to race 1 of isolates pathogenic to tomato. The specificity of these sequences was confirmed by genomic Southern hybridization. Further analyses revealed that the region peripheral to B68-TV obtained from the genomic DNA library includes the sequence specific to all isolates pathogenic to tomato (races 1 and 2). Moreover, sequence tagged site (STS) primers designed from B68-TV and its peripheral region showed race-specific and pathotype-specific amplification in a PCR assay. The probes and primers obtained in this study are likely to be useful tools for the identification and specific detection of pathotypes and races of V. dahliae. The nucleotide sequence data reported are available in the DDBJ/EMBL/GenBank databases under accession number AB095266.  相似文献   
9.
Previously, we reported that ovarian hormones affect the immune response against E. coli isolated from the dogs affected with pyometra. In order to investigate mechanisms underlying the immune modulation, we examined the effects of ovarian hormones on the generation of dendritic cells (DCs), the most potent antigen presenting cell. DCs were differentiated from peripheral blood monocytes (PBMOs) using a cytokine cocktail. Both estrogen receptor and progesterone receptors were expressed by the PBMOs and immature DCs. When various ovarian hormones were added to the culture for the DC differentiation, progesterone significantly decreased the expression of DC maturation markers, such as CD1a, CD80 and CD86, on mature DCs. Conversely, the addition of estrogen to the cultures increased the expression of CD86, but not other maturation makers. Furthermore, DCs differentiated in the presence of progesterone did not stimulate allogeneic mononuclear cells in PB. Taken together, these results indicate that progesterone diminishes the maturation of DCs, leading to decreased immune responses against invading pathogens.  相似文献   
10.
Mitigation of nitrous oxide (N2O) emission from swine wastewater treatment was demonstrated in an aerobic bioreactor packed with carbon fibers (CF reactor). The CF reactor had a demonstrated advantage in mitigating N2O emission and avoiding NOx (NO3 + NO2) accumulation. The N2O emission factor was 0.0003 g N2O‐N/gTN‐load in the CF bioreactor compared to 0.03 gN2O‐N/gTN‐load in an activated sludge reactor (AS reactor). N2O and CH4 emissions from the CF reactor were 42 g‐CO2 eq/m3/day, while those from the AS reactor were 725 g‐CO2 eq/m3/day. The dissolved inorganic nitrogen (DIN) in the CF reactor removed an average of 156 mg/L of the NH4‐N, and accumulated an average of 14 mg/L of the NO3‐N. In contrast, the DIN in the AS reactor removed an average 144 mg/L of the NH4‐N and accumulated an average 183 mg/L of the NO3‐N. NO2‐N was almost undetectable in both reactors.  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