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   1543191篇
  免费   145210篇
  国内免费   3310篇
  2021年   19005篇
  2019年   17026篇
  2018年   19065篇
  2017年   17628篇
  2016年   29308篇
  2015年   44003篇
  2014年   52336篇
  2013年   78608篇
  2012年   45047篇
  2011年   34972篇
  2010年   46475篇
  2009年   47084篇
  2008年   32109篇
  2007年   30352篇
  2006年   34506篇
  2005年   35371篇
  2004年   34526篇
  2003年   31884篇
  2002年   29684篇
  2001年   42067篇
  2000年   39649篇
  1999年   37629篇
  1998年   26667篇
  1997年   26658篇
  1996年   25996篇
  1995年   24120篇
  1994年   23824篇
  1993年   22996篇
  1992年   32851篇
  1991年   31417篇
  1990年   30037篇
  1989年   30502篇
  1988年   28158篇
  1987年   26873篇
  1986年   25556篇
  1985年   27214篇
  1984年   25913篇
  1983年   23013篇
  1982年   22255篇
  1981年   21177篇
  1980年   19873篇
  1979年   22516篇
  1978年   20454篇
  1977年   19324篇
  1976年   18417篇
  1975年   18645篇
  1974年   19595篇
  1973年   19705篇
  1972年   17058篇
  1971年   15720篇
排序方式: 共有10000条查询结果,搜索用时 359 毫秒
61.
62.
63.
Elevated levels of intracellular calcium are a major cause of myocardial dysfunction. To find possible mediators of the deregulated calcium we searched for EF-hand calcium-binding proteins of the S100 family. By PCR technology we identified three members of the S100 protein family (S100 alpha, CACY, and CAPL) in the human heart. We cloned the corresponding cDNAs and examined their expression levels in various human tissues by Northern blot analysis. All three proteins are expressed at high levels in the human heart. Whereas CACY and CAPL mRNAs are expressed ubiquitously, S100 alpha mRNA is restricted to heart, skeletal muscle, and brain. Interestingly, the expression pattern of S100 alpha, CACY, and CAPL in human tissues differs significantly from that in rodent tissues.  相似文献   
64.
65.
1. Examination of the cerebrospinal fluid (CSF) of head-injured patients reveals that the concentration of intraventricular xanthine is elevated and that of uridine is decreased relative to those of adult lumbar CSF. 2. No correlations were observed between CSF lactate and CSF hypoxanthine, xanthine, or uridine, suggesting that changes in purine metabolites and the pyrimidine nucleoside do not index similar cellular events as does lactic acid production. 3. Ventricular CSF from hydrocephalic infants had uridine and hypoxanthine concentrations not significantly different from those of normal adult lumbar CSF, but xanthine was significantly elevated. 4. Since uridine has anticonvulsant properties and is a crucial substrate for cerebral metabolism, it may be useful to evaluate this pyrimidine for use in the management of patients with head injury.  相似文献   
66.
67.
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   
68.
69.
70.
Studies of association between candidate genes and disease can be designed to use cases with disease, and in place of nonrelated controls, their parents. The advantage of this design is the elimination of spurious differences due to ethnic differences between cases and nonrelated controls. However, several statistical methods of analysis have been proposed in the literature, and the choice of analysis is not always clear. We review some of the statistical methods currently developed and present two new statistical methods aimed at specific genetic hypotheses of dominance and recessivity of the candidate gene. These new methods can be more powerful than other current methods, as demonstrated by simulations. The basis of these new statistical methods is a likelihood approach. The advantage of the likelihood framework is that regression models can be developed to assess genotype-environment interactions, as well as the relative contribution that alleles at the candidate-gene locus make to the relative risk (RR) of disease. This latter development allows testing of (1) whether interactions between alleles exist, on the scale of log RR, and (2) whether alleles originating from the mother or father of a case impart different risks, i.e., genomic imprinting.  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