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   520762篇
  免费   61335篇
  国内免费   5132篇
  587229篇
  2021年   6659篇
  2019年   5404篇
  2018年   6582篇
  2017年   5456篇
  2016年   8183篇
  2015年   12510篇
  2014年   14188篇
  2013年   18486篇
  2012年   21291篇
  2011年   20879篇
  2010年   13381篇
  2009年   12290篇
  2008年   16865篇
  2007年   16887篇
  2006年   15146篇
  2005年   14468篇
  2004年   13864篇
  2003年   13005篇
  2002年   12289篇
  2001年   22661篇
  2000年   22835篇
  1999年   18458篇
  1998年   6964篇
  1997年   7177篇
  1996年   7039篇
  1995年   6353篇
  1994年   6369篇
  1993年   6051篇
  1992年   14263篇
  1991年   13474篇
  1990年   13096篇
  1989年   12906篇
  1988年   11472篇
  1987年   11054篇
  1986年   10128篇
  1985年   9887篇
  1984年   8351篇
  1983年   7218篇
  1982年   5604篇
  1981年   5087篇
  1980年   4721篇
  1979年   7792篇
  1978年   5969篇
  1977年   5488篇
  1976年   5111篇
  1975年   5429篇
  1974年   5880篇
  1973年   5702篇
  1972年   5144篇
  1971年   4759篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
9-methoxy ellipticine, an antitumor compound, is O-demethylated in presence of the system peroxidase-H2O2; this reaction yields the corresponding electrophilic quinone-imine and methanol. This O-demethylation reaction is reported for the first time and might be possibly extended to some other antitumor drugs.  相似文献   
942.
Mice have been characterized as either tasters or non-tastersof the bitter compound sucrose octa-acetate(SOA). However, 11of 17 supposedly non-taster inbred strains were found to avoid1 mM SOA. All 17 strains were indifferent to 0.1 mM SOA. Tasterstrains avoided both concentrations. The intermediate phenotypewas dubbed demitaster. A consistent phenotypic dominance orderwas found in crosses among both inbred and outbred strains (taster> non-taster > demitaster). Demitasters were found (withtasters) in an outbred strain showing monogenic segregationfor SOA avoidance. This, plus monogenic segregation in a back-crossof taster to demitaster inbred strains, suggested a third alleleat the Soa locus (Soac). Demitaster allelism was supported bythe strong associations found in 15 strains between the threeSOA phenotypes and HindIII restriction fragment patterns forthe closely linked Prp (proline rich protein) loci. SOA demitasterstrains were also intermediate in raffinose undeca-acetate (RUA)avoidance. Furthermore, B6.SW-Soa2 congenic mice avoided notonly SOA, but RUA and eight other acetylated sugars. A previouslyproposed separate RUA-sensitivity gene (Rua) thus appeared tobe redundant.  相似文献   
943.
Book review     
  相似文献   
944.
945.
946.
947.
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   
948.
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   
949.
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   
950.
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   
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