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   309833篇
  免费   32446篇
  国内免费   52篇
  2021年   3197篇
  2020年   4268篇
  2019年   6040篇
  2018年   8310篇
  2017年   8220篇
  2016年   9487篇
  2015年   9804篇
  2014年   10716篇
  2013年   14150篇
  2012年   14002篇
  2011年   13864篇
  2010年   11242篇
  2009年   8792篇
  2008年   11264篇
  2007年   10987篇
  2006年   10548篇
  2005年   9634篇
  2004年   9736篇
  2003年   9140篇
  2002年   8931篇
  2001年   10872篇
  2000年   10451篇
  1999年   8186篇
  1998年   2657篇
  1997年   2365篇
  1996年   2211篇
  1995年   2011篇
  1992年   6005篇
  1991年   6123篇
  1990年   6057篇
  1989年   6013篇
  1988年   5594篇
  1987年   5210篇
  1986年   4774篇
  1985年   5008篇
  1984年   4031篇
  1983年   3246篇
  1982年   2226篇
  1979年   3520篇
  1978年   2735篇
  1977年   2523篇
  1976年   2441篇
  1975年   2985篇
  1974年   3320篇
  1973年   3286篇
  1972年   2908篇
  1971年   2757篇
  1970年   2357篇
  1969年   2295篇
  1968年   2172篇
排序方式: 共有10000条查询结果,搜索用时 187 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.
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   
14.
15.
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   
16.
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   
17.
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells.  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