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   50883篇
  免费   2780篇
  国内免费   32篇
林业   2624篇
农学   1538篇
基础科学   217篇
  5752篇
综合类   10152篇
农作物   1944篇
水产渔业   2349篇
畜牧兽医   25428篇
园艺   560篇
植物保护   3131篇
  2019年   451篇
  2018年   738篇
  2017年   790篇
  2016年   687篇
  2015年   638篇
  2014年   768篇
  2013年   1760篇
  2012年   1487篇
  2011年   1666篇
  2010年   1076篇
  2009年   1161篇
  2008年   1635篇
  2007年   1647篇
  2006年   1536篇
  2005年   1464篇
  2004年   1379篇
  2003年   1347篇
  2002年   1285篇
  2001年   1529篇
  2000年   1485篇
  1999年   1216篇
  1998年   456篇
  1997年   475篇
  1996年   470篇
  1995年   523篇
  1994年   472篇
  1993年   481篇
  1992年   922篇
  1991年   916篇
  1990年   908篇
  1989年   916篇
  1988年   865篇
  1987年   900篇
  1986年   890篇
  1985年   895篇
  1984年   723篇
  1983年   652篇
  1979年   647篇
  1978年   540篇
  1977年   459篇
  1976年   462篇
  1975年   502篇
  1974年   692篇
  1973年   605篇
  1972年   675篇
  1971年   671篇
  1970年   599篇
  1969年   590篇
  1968年   449篇
  1967年   511篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
32.
33.
34.
35.
36.
37.
38.
Disseminated Aspergillus terreus infection was diagnosed in ten previously healthy adult dogs--nine German shepherds and one dalmatian. The disease was characterized by the presence of multiple granulomas and infarcts in a wide range of organs. The kidney, spleen, and skeletal system were most commonly and severely affected. Fungal hyphae were demonstrated in large numbers within granulomas and thrombi, and A. terreus was readily isolated by culture. This disseminated mycosis appears unique; in this series of cases there was no apparent predisposing factor, portal of entry, or primary focus for dissemination of the infection.  相似文献   
39.
Antiserum to a partially purified neuraminidase fromPasteurella multocida, type A:3, was adsorbed with protease-digestedP. multocida type 3 lipopolysaccharide (LPS) to remove LPS immunoreactivity. The LPS-adsorbed antineuraminidase caused a 77% reduction in the neuraminidase activity of homologousP. multocida in anin vitro enzyme neutralization test. All 14 mice passively immunized with the adsorbed antineuraminidase were protected against challenge infection with homologousP. multocida in a mouse protection test. Ten out of 14 mice in one group that received antisera containing antibodies to both neuraminidase and LPS were protected. In contrast, only 1 out of 14 mice that were immunized with pre-immune serum survived the challenge. These results suggest that antiserum toP. multocida neuraminidase was, at least partly, responsible for the protection observed in this study. Neuraminidase may be one of the immunogenic protective proteins present in aqueous extracts ofPasteurella multocida.  相似文献   
40.
Fetal amino acid nutrition and metabolism have been studied primarily in pregnant sheep. The umbilical uptake of amino acids changes during gestation, but at both mid- and late gestation the total supply exceeds that required for growth. Weight-specific protein synthetic rate decreases with increasing gestational age, and these changes are proportional to the changes in metabolic rate. The use of multiple tracer methodology coupled with measurement of net tracer fluxes into and out of fetal and placental tissues can be used to delineate amino acid metabolism in considerable detail. Such studies demonstrate that even essential amino acids can be oxidized extensively by the fetus. The oxidation rate of leucine exceeds its rate of accretion in tissue proteins. Glycine metabolism is unique in several ways; there is a large umbilical uptake of glycine without a measurable uterine uptake. In late gestation there is no significant umbilical uptake of serine, although there is a significant uterine uptake, suggesting net uteroplacental utilization. Glycine is oxidized within the fetal liver and used for serum production. The interorgan exchange of amino acids between the fetal liver and placenta is clearly of major importance for serine and glycine metabolism and is likely to be of major importance for most nonessential amino acids.  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