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   238035篇
  免费   16541篇
  国内免费   48篇
  2021年   1951篇
  2018年   3298篇
  2017年   3178篇
  2016年   3948篇
  2015年   3672篇
  2014年   4980篇
  2013年   6984篇
  2012年   8296篇
  2011年   8823篇
  2010年   6265篇
  2009年   5382篇
  2008年   7872篇
  2007年   8195篇
  2006年   7819篇
  2005年   7386篇
  2004年   7552篇
  2003年   7167篇
  2002年   7199篇
  2001年   9526篇
  2000年   9196篇
  1999年   7236篇
  1998年   2346篇
  1997年   2077篇
  1996年   1982篇
  1992年   5698篇
  1991年   5865篇
  1990年   5864篇
  1989年   5801篇
  1988年   5390篇
  1987年   5027篇
  1986年   4612篇
  1985年   4831篇
  1984年   3879篇
  1983年   3159篇
  1982年   2170篇
  1981年   1878篇
  1980年   1832篇
  1979年   3482篇
  1978年   2708篇
  1977年   2501篇
  1976年   2462篇
  1975年   2945篇
  1974年   3226篇
  1973年   3192篇
  1972年   2844篇
  1971年   2688篇
  1970年   2281篇
  1969年   2226篇
  1968年   2081篇
  1967年   1841篇
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
11.
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   
12.
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   
13.
This paper is concerned with gene survival in a population which may increase without density dependence according to a generalization of the Moran model for haploid individuals. A selective advantage to one allele and the possibility of differential reproductive rates are allowed. Simple conditions are given for ultimate homozygosity to be certain and for the possibility of ultimate polymorphism. The results complement and extend those of Heyde (1981, 1982).  相似文献   
14.
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   
15.
16.
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   
17.
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   
18.
19.
20.
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