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   105036篇
  免费   573篇
  国内免费   885篇
  106494篇
  2021年   104篇
  2020年   100篇
  2019年   127篇
  2018年   11991篇
  2017年   10800篇
  2016年   7699篇
  2015年   880篇
  2014年   660篇
  2013年   790篇
  2012年   4627篇
  2011年   13229篇
  2010年   12265篇
  2009年   8410篇
  2008年   10096篇
  2007年   11684篇
  2006年   650篇
  2005年   880篇
  2004年   1261篇
  2003年   1357篇
  2002年   1074篇
  2001年   541篇
  2000年   394篇
  1999年   201篇
  1998年   98篇
  1992年   258篇
  1991年   259篇
  1990年   183篇
  1989年   226篇
  1988年   252篇
  1987年   253篇
  1986年   218篇
  1985年   253篇
  1984年   210篇
  1983年   187篇
  1980年   85篇
  1979年   238篇
  1978年   160篇
  1977年   139篇
  1976年   137篇
  1975年   176篇
  1974年   272篇
  1973年   260篇
  1972年   499篇
  1971年   522篇
  1970年   263篇
  1969年   246篇
  1968年   194篇
  1967年   197篇
  1966年   173篇
  1965年   142篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
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   
2.
3.
4.
5.
6.
7.
IN addition to its well known antiviral activity, interferon has recently been shown to inhibit the multiplication of tumour and mammalian cells in cell culture1–6. We report here the inhibition by interferon of DNA synthesis induced in mouse spleen lymphocytes by the non-viral stimuli phytohaemagglutinin (PHA) and allogeneic lymphocytes. These findings are in accord with our contention that interferon affects cell function and, furthermore, they suggest that by acting on lymphocytes, interferon plays a role in the immunological response of the host.  相似文献   
8.
9.
The effects of different concentrations of L-ascorbic acid (Asc) on Na+-dependent binding of 3H-GABA and 3H-DL-glutamic acid to rat brain cortical synaptosomes were studied. Asc, at a concentration nearly equal to brain extracellular one (3 X 10(-4) M), had no effect on specific and nonspecific 5H-GABA binding. At higher concentrations (10(-3) M) Asc strongly inhibited, and at lower concentrations (10(-6) M) considerably stimulated 3H-GABA binding. At a concentration of 10(-5)-10(-3) M Asc tended to decrease 3H-DL-glutamic acid binding.  相似文献   
10.
CHLOROPLASTS are more permeable to amino-acids1,2 than are cell membranes3 and also discriminate between their optical isomers2. This has led to the suggestion that the passage of amino-acids through the limiting membranes of chloroplasts is facilitated by carriers2. Using the additional criteria of saturation and competition, we support this suggestion and show that at least two carriers are probably involved.  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