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   477707篇
  免费   52452篇
  国内免费   205篇
  530364篇
  2018年   4554篇
  2016年   6290篇
  2015年   8578篇
  2014年   10126篇
  2013年   13792篇
  2012年   16095篇
  2011年   16550篇
  2010年   11285篇
  2009年   10448篇
  2008年   14997篇
  2007年   15663篇
  2006年   14770篇
  2005年   14049篇
  2004年   14116篇
  2003年   13336篇
  2002年   12973篇
  2001年   17958篇
  2000年   17807篇
  1999年   14514篇
  1998年   5750篇
  1997年   5808篇
  1996年   5431篇
  1995年   5116篇
  1994年   4941篇
  1993年   5054篇
  1992年   12081篇
  1991年   11916篇
  1990年   11695篇
  1989年   11296篇
  1988年   10870篇
  1987年   10443篇
  1986年   9730篇
  1985年   9662篇
  1984年   8259篇
  1983年   7170篇
  1982年   5745篇
  1981年   5262篇
  1980年   5044篇
  1979年   7785篇
  1978年   6259篇
  1977年   5785篇
  1976年   5544篇
  1975年   5897篇
  1974年   6654篇
  1973年   6483篇
  1972年   5982篇
  1971年   5424篇
  1970年   4842篇
  1969年   4775篇
  1968年   4595篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Experiments on conscious rabbits were made to elaborate motor conditioned reflexes through pairing stimuli with electrocutaneous reinforcement applied every 30 s. Neuronal activity in the sensorimotor cortex and putamen was recorded during formation and reproduction of the conditioned reflexes before and after haloperidol injection (0.2 mg/kg i. v.). In the putamen, haloperidol increased the number of neurons exhibiting trace conditioned activity and made the intensity and duration of these processes rise. The changes seen in the sensorimotor cortex were opposite in nature. Inhibition of trace conditioned activity in the sensorimotor cortex depended mainly on the decreased amplitude of the reaction conditioned component. The role of the dopaminergic system in the interaction of the neostriatum and sensorimotor cortex and in formation and reproduction of trace conditioned activity of both the structures is discussed.  相似文献   
22.
23.
24.
The Fis protein: it''s not just for DNA inversion anymore   总被引:36,自引:0,他引:36  
  相似文献   
25.
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   
26.
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   
27.
28.
29.
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   
30.
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