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   7691篇
  免费   662篇
  国内免费   4篇
  2023年   59篇
  2022年   142篇
  2021年   274篇
  2020年   149篇
  2019年   178篇
  2018年   200篇
  2017年   161篇
  2016年   336篇
  2015年   510篇
  2014年   526篇
  2013年   535篇
  2012年   764篇
  2011年   654篇
  2010年   380篇
  2009年   368篇
  2008年   493篇
  2007年   425篇
  2006年   380篇
  2005年   295篇
  2004年   292篇
  2003年   267篇
  2002年   243篇
  2001年   54篇
  2000年   33篇
  1999年   41篇
  1998年   60篇
  1997年   30篇
  1996年   22篇
  1995年   27篇
  1994年   23篇
  1993年   27篇
  1992年   24篇
  1991年   22篇
  1990年   18篇
  1989年   21篇
  1988年   15篇
  1987年   12篇
  1986年   12篇
  1985年   18篇
  1984年   18篇
  1983年   25篇
  1982年   10篇
  1981年   18篇
  1980年   15篇
  1979年   13篇
  1978年   16篇
  1977年   11篇
  1976年   10篇
  1975年   11篇
  1974年   10篇
排序方式: 共有8357条查询结果,搜索用时 15 毫秒
21.
Specific and nonspecific T-cell invasion into cerebrospinal fluid has been investigated in the nonfatal viral meningoencephalitis induced by intracerebral inoculation of mice with vaccinia virus. At the peak of the inflammatory process on Day 7 approximately 5 to 10% of the Lyt 2+ T cells present are apparently specific for vaccinia virus. Concurrently, in mice primed previously with influenza virus, 0.5 to 1.0% of the appropriate T-cell set located in cerebrospinal fluid is reactive to influenza-infected target cells. This vaccinia virus-induced inflammatory exudate may thus contain as many as 500 influenza-immune memory T cells. These findings are discussed from the aspect that such nonspecific T-cell invasion into the central nervous system during aseptic viral meningitis could result in exposure of potentially brain-reactive T cells to central nervous system components.  相似文献   
22.
Summary Kinetic studies of the uptake of hydroquinone--D-glucoside (arbutin) by excised roots of barley demonstrated that this compound is actively transported. Similar studies on the uptake of hydroquinone indicated that the latter compound enters the root tissues by diffusion. A concentration gradient favouring diffusion is maintained for at least three hours by the conversion of the aglucone to its correspondings glucoside. Hydroquinone, at a concentration of 5 mM, reduced uptake of 86rubidium ion by approximately 30%.This work was supported by a grant from the National Research. Council of Canada  相似文献   
23.
The enzymic estimation of glutamate and glutamine   总被引:2,自引:1,他引:1  
A method of estimating glutamic acid is described, based on its dehydrogenation by glutamate dehydrogenase coupled, by means of N-methylphenazine methosulphate, to the reduction of tetrazolium salts. The method is suitable for the estimation of 0-0.3mumole of glutamic acid. The response is linear, but not stoicheiometric: possible reasons for this are discussed. If suitable precautions are taken, the use of a partially purified preparation of glutaminase makes it possible to estimate glutamine also.  相似文献   
24.
Studies on Chrysophyceae from some ponds and lakes in Alaska   总被引:2,自引:1,他引:1  
Summary A new variety, Mallomonopsis elliptica var. salina, of M. elliptica var. elliptica Matwienko is described as seen in the living state in the light microscope, and in the electron microscope. The locality in which it was found is described.
Zusammenfassung Eine neue Varietät, Mallomonopsis elliptica var. salina, von M. elliptica var. elliptica Matwienko wird beschrieben. Sie wurde in lebendiger Gestalt in dem Lichtmikroskop and in dem Elektronenmikroskop beobachtet. Der Fundort wird beschrieben.
  相似文献   
25.
26.
27.
Eighty-two percent of a group of rhesus monkeys removed from Cayo Santiago were seropositive for B virus (Herpesvirus simiae) antibodies. Similar results were obtained from the Cayo Santiago macaque population two decades ago and from feral Indian rhesus monkeys. Thus it is likely that B virus has been enzootic in the Cayo Santiago population since 1938, when the colony was established with stock imported from India.  相似文献   
28.
29.
30.
Effects of gene products on reproductive behavior which are relatively direct include those of the estrogen receptor and progesterone receptor. For example, work with estrogen receptor-deficient (ERKO) female mice has extended previous evidence contributing to the neurochemical analysis of lordosis behavior. On the other hand, sex differences in behavior present a classic example of indirect effects of genes on behavior. Work with ERKO male mice shows the necessity of ER gene expression for normal masculinization of the brain. In particular, behavioral assay results distinguish apparent motivational performance of ERKO males from male mating reflexes: the former is similar to that of wild-type males in important respects, while the latter are deficient in ERKO males. The present paper first reviews a small number of clear genetic contributions to reproductive behaviors, and then reports one experiment pertinent to the interpretation of the behavioral status of ERKO male mice.  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