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   76271篇
  免费   5039篇
  国内免费   13篇
  2023年   498篇
  2022年   630篇
  2021年   1343篇
  2020年   1076篇
  2019年   1245篇
  2018年   2272篇
  2017年   2100篇
  2016年   2765篇
  2015年   3629篇
  2014年   3764篇
  2013年   4988篇
  2012年   5921篇
  2011年   5373篇
  2010年   3453篇
  2009年   2803篇
  2008年   4113篇
  2007年   3880篇
  2006年   3693篇
  2005年   3135篇
  2004年   3088篇
  2003年   2741篇
  2002年   2511篇
  2001年   1710篇
  2000年   1645篇
  1999年   1306篇
  1998年   664篇
  1997年   486篇
  1996年   475篇
  1995年   447篇
  1994年   344篇
  1993年   341篇
  1992年   669篇
  1991年   586篇
  1990年   531篇
  1989年   512篇
  1988年   492篇
  1987年   444篇
  1986年   419篇
  1985年   411篇
  1984年   419篇
  1983年   295篇
  1982年   278篇
  1981年   209篇
  1980年   218篇
  1979年   268篇
  1978年   252篇
  1975年   223篇
  1974年   260篇
  1973年   255篇
  1972年   217篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
Hostile intercommunity relations, including attacking and killing extra-community infants of both sexes have occurred at most wild chimpanzee sites. We describe three recent cases of intercommunity attacks on infants committed by members of the Ngogo chimpanzee community in Kibale National Park, Uganda. Two of the attacks resulted in confirmed infanticides while a third attack probably resulted in the infant's death. In common with previous accounts of chimpanzee infanticides, the attacks described here occurred during boundary patrols outside the Ngogo community's usual range, adult and adolescent males were the main participants, one infant was cannibalized after being killed, and the victims’ mothers did not accompany the attacking party back to the Ngogo range. However, the patrol parties during each infanticide were larger than before and included females from the Ngogo community. Our observations indirectly support both the range expansion and imbalance of power hypotheses, which address why and under which conditions chimpanzee intercommunity encounters lead to aggression. These cases of intercommunity infanticide add to the growing database of the phenomenon in wild chimpanzees.  相似文献   
3.
4.
5.
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   
6.
7.
8.
The enzyme 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate: NADP+ oxidoreductase, decarboxylating EC 1.1.1.44) from bass liver has been purified to over 95% of homogeneity by gel filtration, affinity and ion exchange chromatographies. The apparent molecular weight was estimated by gel filtration chromatography to about 100,000. Analysis of the enzyme on sodium dodecyl sulphate polyacrylamide gel electrophoresis showed to be a dimeric protein. The effect of pH and kinetic properties were studied.  相似文献   
9.
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   
10.
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