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   648954篇
  免费   62918篇
  国内免费   210篇
  2018年   7741篇
  2017年   7351篇
  2016年   9851篇
  2015年   12070篇
  2014年   14137篇
  2013年   19768篇
  2012年   22813篇
  2011年   23121篇
  2010年   15664篇
  2009年   13978篇
  2008年   20311篇
  2007年   20910篇
  2006年   19807篇
  2005年   18612篇
  2004年   18698篇
  2003年   17576篇
  2002年   17141篇
  2001年   25089篇
  2000年   24975篇
  1999年   19852篇
  1998年   7091篇
  1997年   7083篇
  1996年   6644篇
  1995年   6251篇
  1994年   5989篇
  1993年   5986篇
  1992年   16181篇
  1991年   16241篇
  1990年   15859篇
  1989年   15505篇
  1988年   14794篇
  1987年   14132篇
  1986年   13096篇
  1985年   13149篇
  1984年   10955篇
  1983年   9287篇
  1982年   6953篇
  1981年   6173篇
  1979年   10292篇
  1978年   8106篇
  1977年   7453篇
  1976年   7174篇
  1975年   8031篇
  1974年   9042篇
  1973年   8835篇
  1972年   8118篇
  1971年   7520篇
  1970年   6623篇
  1969年   6461篇
  1968年   6218篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
31.
Changes in the properties of adenylate cyclase from the lungs of tuberculotic guinea pigs were revealed. The number of beta-adrenergic receptors in the lungs was found to be reduced by 30% at the second and by 70% at the third stage of the disease. The degree and the value of Ka for adenylate cyclase activation by isoproterenol remained thereby unchanged. The basal activity of adenylate cyclase was increased by 20% against the control level at the second stage and decreased by 20% at the third stage of the disease. At these periods, the stimulating effects of guanylyl imidodiphosphate, NaF and forskolin on lung adenylate cyclase were diminished. The experimental results point to the significant role of the enzymes of cAMP metabolism and reflect the course of the tuberculosis process in experimental animals.  相似文献   
32.
The immunization of mice with the protein fraction of B. pertussis strain 305 has made it possible to obtain hybridomas producing monoclonal antibodies to B. pertussis antigens. Ascitic fluids containing monoclonal antibodies react in the ELISA in high titers and actively agglutinate B. pertussis strains 305 and 475.  相似文献   
33.
34.
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures.  相似文献   
35.
36.
Mutants of Bacillus amyloliquefaciens resistant to at least 10 micrograms/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile.  相似文献   
37.
38.
39.
Regulation of many cell systems has been shown to be mediated by Inositol 1,4,5-trisphosphate which causes a release of calcium from intracellular sites. We have shown that release of Ca2+ from sarcoplasmic reticulum microsomes was not stimulated by IP3. The phorbol ester, TPA, also had no effect on Ca2+ release or Ca2+ ATPase activity. Thus, it is unlikely that the breakdown of polyphosphatidylinositides serves as a second messenger to mediate release of Ca2+ in skeletal muscle.  相似文献   
40.
The content of neurospecific proteins S-100, GFA and D2 was measured in malignant cerebral tumors by electrophoresis with the use of monospecific antisera. Concomitant measurement of proteins S-100 and GFA is a more reliable diagnostic criterion as to the tumor histogenesis than study of each protein alone. D2 protein appeared to be the most stable specific marker.  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