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   449480篇
  免费   55715篇
  国内免费   283篇
  505478篇
  2018年   3823篇
  2017年   3507篇
  2016年   5467篇
  2015年   8180篇
  2014年   9163篇
  2013年   12887篇
  2012年   14864篇
  2011年   14974篇
  2010年   9887篇
  2009年   9143篇
  2008年   13075篇
  2007年   13543篇
  2006年   12250篇
  2005年   12059篇
  2004年   11835篇
  2003年   11276篇
  2002年   10779篇
  2001年   21656篇
  2000年   21786篇
  1999年   17413篇
  1998年   6220篇
  1997年   6478篇
  1996年   6308篇
  1995年   5698篇
  1994年   5754篇
  1993年   5570篇
  1992年   13666篇
  1991年   12979篇
  1990年   12649篇
  1989年   12514篇
  1988年   11173篇
  1987年   10789篇
  1986年   9880篇
  1985年   9656篇
  1984年   8196篇
  1983年   7074篇
  1982年   5525篇
  1981年   5005篇
  1980年   4649篇
  1979年   7689篇
  1978年   5919篇
  1977年   5427篇
  1976年   5069篇
  1975年   5366篇
  1974年   5809篇
  1973年   5662篇
  1972年   5102篇
  1971年   4729篇
  1970年   3922篇
  1969年   3851篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Book review     
  相似文献   
992.
993.
994.
995.
Transcranial Doppler ultrasonographic recordings of the middle cerebral arteries were performed on eight children with autistic behavior compared to eight controls. Blood flow measurements were assessed at rest and during auditory and visual stimulations. The main result was obtained during the auditory stimulations and concerned the left artery blood flow which is lower in autistics than in controls in these conditions (p less than .02). This result confirms the possibility of a left hemisphere dysfunctioning in autistics and may be related to clinical features as language disabilities and paradoxical reactivity to auditory stimuli.  相似文献   
996.
A generalized Morse index theory is used to study travelling waves in a natural selection-migration model for a diploid organism when the selective strength is weak.  相似文献   
997.
Shell shape and growth of two unionacean species, Villosa villosaand Elliptio icterina, are analyzed with univariate and multivariatetechniques. The relationship of shape variables to size variablesis examined. Under the lognormal assumption, parametric testsof these allometric relationships are valid. Variables describingthe ventro-posterior region of the shell are shown to be thebest of those tested for discriminating between the sexes ofboth species regardless of statistical method. Neither speciesexhibits size sexual dimorphism. Shape sexual dimorphism ofV. villosa is constant during adult growth, but the more subtledimorphism of E. icterina changes as adults continue to grow. (Received 20 January 1986;  相似文献   
998.
Certain features of the Olduvai clavicular fragment have been examined in the light of data already existing on the form of the clavicle in primates. Although similar to that of modern man, the fragment exhibits features which suggest that its function may have differed somewhat from that of the clavicle in man. The new information correlates well with that obtained from the fragmentary Sterkfontein scapula.  相似文献   
999.
QSAR studies have been performed on the homologues of 3-triazines, using molecular connectivity index and van der Waal volume as structural parameters. The regression analysis has shown good correlation between antitumour activity and the two structural parameters.  相似文献   
1000.
Possible interactions between calpain II and phospholipids such as phosphatidylinositol, phosphatidylserine and phosphatidylcholine were studied using fluorescence and gel filtration techniques. Changes in fluorescence intensity of purified calpain II show that the enzyme strongly interacts with phosphatidylinositol and phosphatidylserine and to a lesser extent with phosphatidylcholine. These results are corroborated by the gel filtration technique which permits the isolation of the enzyme phospholipid complex. Association between calpain II and various phospholipid vesicles can occur in the absence of calcium. Such binding occurs without any observable change of the molecular mass of the two subunits on SDS-polyacrylamide gel electrophoresis.  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