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   50670篇
  免费   4606篇
  国内免费   31篇
  55307篇
  2022年   362篇
  2021年   762篇
  2020年   460篇
  2019年   575篇
  2018年   712篇
  2017年   652篇
  2016年   1048篇
  2015年   1766篇
  2014年   1955篇
  2013年   2570篇
  2012年   3244篇
  2011年   3303篇
  2010年   2141篇
  2009年   1918篇
  2008年   2720篇
  2007年   2835篇
  2006年   2778篇
  2005年   2657篇
  2004年   2542篇
  2003年   2426篇
  2002年   2318篇
  2001年   558篇
  2000年   468篇
  1999年   625篇
  1998年   744篇
  1997年   555篇
  1996年   486篇
  1995年   436篇
  1994年   418篇
  1993年   448篇
  1992年   493篇
  1991年   436篇
  1990年   425篇
  1989年   411篇
  1988年   375篇
  1987年   334篇
  1986年   357篇
  1985年   389篇
  1984年   462篇
  1983年   379篇
  1982年   494篇
  1981年   502篇
  1980年   398篇
  1979年   333篇
  1978年   342篇
  1977年   299篇
  1976年   335篇
  1975年   230篇
  1974年   283篇
  1973年   287篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
61.
Incubation of [14C] caffeine with hepatic microsomes from male AKR/J mice resulted in the formation of several metabolites including 1, 3, 7-trimethylurate and 6-amino-5-(N-formylmethyl-amino)-1, 3-dimethyluracil. These two compounds comprised about 60% of products and are major urinary metabolites in several animals. When cytosol was included during incubation, there was a 14-fold increase in yield of the uracil at the expense of the urate; the combination of the two metabolites remained about 60% of total products. Cytosol alone was catalytically inert. Glutathione and other sulfhydryl compounds reproduced the effect of cytosol, and the action of cytosol was accounted for quantitatively by its sulfhydryl content. We propose that an oxidized intermediate of caffeine en route to trimethylurate is reduced by glutathione to the ring-opened uracil derivative.  相似文献   
62.
63.
Prostaglandins E1, F and A2 were covalently joined to the surface of Sepharose as carboxamide linkages. The insolubilized prostaglandins were shown to function effectively in the purification of 15(S) -hydroxyprostaglandin dehydrogenase.  相似文献   
64.
Serotyping is the foundation of pathogenic Escherichia coli diagnostics; however, few laboratories have this capacity. We developed a molecular serotyping protocol that targets, genetically, the same somatic and flagellar antigens of E. coli O26:H11 used in traditional serotyping. It correctly serotypes strains untypeable by traditional methods, affording primary laboratories serotyping capabilities.  相似文献   
65.
66.
67.
E. coli cells containing a temperature-sensitivednaE mutation, in the α-subunit of holoenzyme DNA polymerase III, do not survive at the restrictive temperature. Such cells may survive in the presence of thepcbA1 mutation, an allele of thegyrB gene. Such survival is dependent on an active DNA polymerase I. Evidence indicates that DNA polymerase I interacts directly in the replisome (REP·A). Despite normal survival for cells using thepcbA replication pathway after some type of DNA damage, we have noted a failure of damage-induced mutagenesis. Here we present evidence supporting a model of replisome pausing in cells dependent upon thepcbA replication pathway. The model argues that the (REP·A) complex pauses longer at the site of the lesion, allowing excision repair to occur completely. In the normal replication pathway (REP·E) bypass of the lesion occurs, fixing the mutation.  相似文献   
68.
Summary The kinetics of thermal deactivation for thermostable DNA polymerase enzymes were investigated by using the experimental data published elsewhere (Nielson et al. 1996. Strategies. 9, 7–8). The order of deactivation (a) and the deactivation rate constants (k d) were determined for different Taq DNA polymerase enzymes and were found to be of first order.  相似文献   
69.
70.
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