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   60369篇
  免费   3417篇
  国内免费   31篇
林业   3456篇
农学   1901篇
基础科学   263篇
  7772篇
综合类   10358篇
农作物   2317篇
水产渔业   3215篇
畜牧兽医   29735篇
园艺   706篇
植物保护   4094篇
  2021年   524篇
  2020年   510篇
  2019年   591篇
  2018年   1149篇
  2017年   1252篇
  2016年   1127篇
  2015年   952篇
  2014年   1175篇
  2013年   2310篇
  2012年   2155篇
  2011年   2244篇
  2010年   1396篇
  2009年   1468篇
  2008年   2106篇
  2007年   2065篇
  2006年   1896篇
  2005年   1830篇
  2004年   1686篇
  2003年   1635篇
  2002年   1522篇
  2001年   1712篇
  2000年   1660篇
  1999年   1383篇
  1998年   498篇
  1997年   504篇
  1996年   511篇
  1995年   548篇
  1993年   500篇
  1992年   1035篇
  1991年   1021篇
  1990年   1000篇
  1989年   1021篇
  1988年   973篇
  1987年   1007篇
  1986年   994篇
  1985年   986篇
  1984年   797篇
  1983年   715篇
  1979年   746篇
  1978年   625篇
  1977年   539篇
  1976年   505篇
  1975年   543篇
  1974年   781篇
  1973年   670篇
  1972年   758篇
  1971年   747篇
  1970年   625篇
  1969年   621篇
  1967年   538篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
43.
44.
45.
46.
47.
48.
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   
49.
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   
50.
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