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   89771篇
  免费   5876篇
  国内免费   12篇
  2023年   604篇
  2022年   551篇
  2021年   1523篇
  2020年   1270篇
  2019年   1439篇
  2018年   2651篇
  2017年   2435篇
  2016年   3260篇
  2015年   4348篇
  2014年   4502篇
  2013年   5970篇
  2012年   6933篇
  2011年   6378篇
  2010年   4095篇
  2009年   3280篇
  2008年   4936篇
  2007年   4632篇
  2006年   4355篇
  2005年   3780篇
  2004年   3670篇
  2003年   3324篇
  2002年   3014篇
  2001年   1973篇
  2000年   1871篇
  1999年   1493篇
  1998年   755篇
  1997年   565篇
  1996年   547篇
  1995年   535篇
  1994年   393篇
  1993年   388篇
  1992年   776篇
  1991年   653篇
  1990年   605篇
  1989年   584篇
  1988年   544篇
  1987年   509篇
  1986年   459篇
  1985年   487篇
  1984年   469篇
  1983年   323篇
  1982年   316篇
  1981年   264篇
  1980年   246篇
  1979年   320篇
  1978年   310篇
  1975年   267篇
  1974年   301篇
  1973年   291篇
  1972年   245篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
1.
2.
A comparison was made between a hay fed group, consisting of 23 ewes, and a grass silage fed group of 22 ewes, all pregnant. Excretion of Listeria monocytogenes (Lm) in the faeces and milk, antibody titres in sera and whey and delayed hypersensitivity against Lm, and several blood components were determined. The animals had previously been exposed to Lm, and Lm was isolated from the faeces from several animals when the experiment started. No significant difference in number of excretors between the 2 groups was found during the experimental period. The haemagglutination titres in both sera and whey were low and on the same level in both groups. The titres were higher in animals with 1 foetus than in animals with more than 1 foetus. In the first part of the experimental period the silage group had a reduced number of lymphocytes, lower total serum protein values and higher serum iron values, compared with the hay group. The silage group also had a stronger delayed hypersensitivity reaction against Lm than the hay group, and in the silage group the reaction was significantly stronger in ewes with 3 or more foetuses than in ewes with 1 foetus. In conclusion, the combined effect of some of the changes found in animals fed grass silage may leave them more susceptible to infections.  相似文献   
3.
4.
5.
Four new species ofCayaponia are described and illustrated: three from Brazil (C. cogniauxiana, C. nitida andC. rugosa) and one from Brazil and Bolivia (C. ferruginea).  相似文献   
6.
A formalin-fixed paraffin-embedded (FFPE) sample usually yields highly degraded DNA, which limits the use of techniques requiring high-quality DNA, such as Infinium Methylation microarrays. To overcome this restriction, we have applied an FFPE restoration procedure consisting of DNA repair and ligation processes in a set of paired fresh-frozen (FF) and FFPE samples. We validated the FFPE results in comparison with matched FF samples, enabling us to use FFPE samples on the Infinium HumanMethylation450 Methylation array.  相似文献   
7.
8.
Administration of purified pertussis toxin to rats induced persistent tachycardia, (observed in conscious rats but not after pithing); as little as 0.05 microgram/100 g produced a significant effect. Pertussis toxin-treatment did not affected the pressor response produced in the pithed rats by the alpha 2-adrenergic agonist methoxamine but markedly diminished the pressor effect of the alpha 2-adrenergic agonists clonidine and azepexole. A role of adenylate cyclase inhibition in the action of postsynaptic vascular alpha 2-adrenergic receptors is suggested.  相似文献   
9.
10.
Clostridium thermocellum encodes a cellulosomal, modular, and thermostable serine protease inhibitor (serpin), PinA. PinA stability but not inhibitory activity is affected by the Fn(III) and Doc(I) domains, and PinA is a broad inhibitor of subtilisin-like proteases and may play a key role in protecting the cellulosome from protease attack.  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