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   18274篇
  免费   199篇
  国内免费   1篇
林业   3811篇
农学   1387篇
基础科学   144篇
  3089篇
综合类   838篇
农作物   2193篇
水产渔业   1919篇
畜牧兽医   1855篇
园艺   1144篇
植物保护   2094篇
  2023年   13篇
  2022年   19篇
  2021年   32篇
  2020年   47篇
  2019年   28篇
  2018年   2809篇
  2017年   2772篇
  2016年   1262篇
  2015年   158篇
  2014年   103篇
  2013年   157篇
  2012年   950篇
  2011年   2268篇
  2010年   2168篇
  2009年   1311篇
  2008年   1410篇
  2007年   1660篇
  2006年   121篇
  2005年   197篇
  2004年   178篇
  2003年   224篇
  2002年   117篇
  2001年   42篇
  2000年   90篇
  1999年   35篇
  1998年   20篇
  1997年   8篇
  1996年   6篇
  1995年   13篇
  1994年   9篇
  1993年   17篇
  1992年   25篇
  1991年   6篇
  1990年   15篇
  1989年   22篇
  1988年   23篇
  1987年   13篇
  1986年   9篇
  1985年   8篇
  1984年   6篇
  1983年   6篇
  1979年   7篇
  1978年   5篇
  1977年   7篇
  1975年   4篇
  1972年   5篇
  1969年   10篇
  1968年   9篇
  1966年   4篇
  1958年   5篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
2.
3.
4.
5.
A bacterin containing serotypes 1 and 5 of Haemophilus pleuropneumoniae was developed for the prevention and the control of porcine pleuropneumonia. It was injected intramuscularly into three groups of ten piglets, the first group with one dose, the second one with two doses and the third one with three doses at two-week intervals. Another group of ten piglets did not receive the vaccine. All the piglets were then challenged by an aerosol of mixed suspensions of H. pleuropneumoniae serotypes 1 and 5. Two and three injections of vaccine completely prevented mortality, whereas half of the control piglets and of those receiving only one dose of vaccine died. All surviving piglets, both control and vaccinated, had severe signs of respiratory disease for at least 36 hours after exposure to challenge. Moreover, vaccination did not induce the production of antibodies at high titers. Local reactions were not noted after vaccination and at postmortem; ten weeks after the challenge, there were no signs of abscess formation or induration.  相似文献   
6.
7.
Engineering resistance against various diseases and pests is hampered by the lack of suitable genes. To overcome this problem we started a research program aimed at obtaining resistance by transfecting plants with genes encoding monoclonal antibodies against pathogen specific proteins. The idea is that monoclonal antibodies will inhibit the biological activity of molecules that are essential for the pathogenesis. Potato cyst nematodes are chosen as a model and it is thought that monoclonal antibodies are able to block the function of the saliva proteins of this parasite. These proteins are, among others, responsible for the induction of multinucleate transfer cells upon which the nematode feeds. It is well documented that the ability of antibodies to bind molecules is sufficient to inactivate the function of an antigen and in view of the potential of animals to synthesize antibodies to almost any molecular structure, this strategy should be feasible for a wide range of diseases and pests.Antibodies have several desirable features with regard to protein engineering. The antibody (IgG) is a Y-shaped molecule, in which the domains forming the tips of the arms bind to antigen and those forming the stem are responsible for triggering effector functions (Fc fragments) that eliminate the antigen from the animal. Domains carrying the antigen-binding loops (Fv and Fab fragments) can be used separately from the Fc fragments without loss of affinity. The antigen-binding domains can also be endowed with new properties by fusing them to toxins or enzymes. Antibody engineering is also facilitated by the Polymerase Chain Reaction (PCR). A systematic comparison of the nucleotide sequence of more than 100 antibodies revealed that not only the 3′-ends, but also the 5′-ends of the antibody genes are relatively conserved. We were able to design a small set of primers with restriction sites for forced cloning, which allowed the amplification of genes encoding antibodies specific for the saliva proteins ofGlobodera rostochiensis. Complete heavy and light chain genes as well as single chain Fv fragments (scFv), in which the variable parts of the light (VL) and heavy chain (VH) are linked by a peptide, will be transferred to potato plants. A major challenge will be to establish a correct expression of the antibody genes with regard to three dimensional folding, assembly and intracellular location.  相似文献   
8.
9.
10.
During 1972 to 1974, 112 Escherichia coli strains isolated from diarrheic piglets were recieved from different parts of the Province of Quebec, Canada. Fifty-six strains elicited a positive gut loop response in three week old piglets and were then considered as Moon's class 1 enteropathogens, while four of the 56 remaining strains reacted only in ten day old piglets and were classified as class 2 enteropathogens. Forty-eight strains produced both a heat-labile and a heat-stable enterotoxin, while 12 isolates which included the four class 2 enteropathogens produced only a heat-stable enterotoxin. Fifty-one enterotoxigenic strains could be serogrouped using OK antisera against E. coli strains commonly associated with colibacillosis in piglets. The most common serogroups encountered were O157: K "V17"; 88a,c, O149:K91; 88a.c. O157:K"V1c, O149:K91; 88a.c, O157:K"V17"; 88 a,c or a,b and O45:K"E5"; 88a,c. No significant difference was observed in the fermentation patterns, antibiotic susceptibility, colicin production, production of a filterable hemolysin and transferable tetracycline resistance between the enterotoxigenic and the nonenterotoxigenic strains.  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