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   1678150篇
  免费   152529篇
  国内免费   1429篇
  2021年   17990篇
  2019年   16245篇
  2018年   20169篇
  2017年   19001篇
  2016年   29723篇
  2015年   43079篇
  2014年   51213篇
  2013年   77315篇
  2012年   49078篇
  2011年   41339篇
  2010年   48826篇
  2009年   48621篇
  2008年   37707篇
  2007年   37116篇
  2006年   39277篇
  2005年   40562篇
  2004年   39378篇
  2003年   36560篇
  2002年   34591篇
  2001年   51242篇
  2000年   48895篇
  1999年   44784篇
  1998年   27563篇
  1997年   27221篇
  1996年   25041篇
  1995年   24573篇
  1994年   24218篇
  1993年   23439篇
  1992年   37726篇
  1991年   36483篇
  1990年   34937篇
  1989年   35385篇
  1988年   32486篇
  1987年   31125篇
  1986年   29222篇
  1985年   30889篇
  1984年   28602篇
  1983年   25103篇
  1982年   23318篇
  1981年   22163篇
  1980年   20790篇
  1979年   24802篇
  1978年   22038篇
  1977年   20656篇
  1976年   19943篇
  1975年   20371篇
  1974年   21401篇
  1973年   21694篇
  1972年   18742篇
  1971年   17092篇
排序方式: 共有10000条查询结果,搜索用时 171 毫秒
61.
L-lysine-alpha-oxidase, a new fungal enzyme catalyzing oxidative deamination of L-lysine, exerts an inhibitory effect on DNA, RNA and protein synthesis in human cells of carcinoma ovarius (CaOv) in vitro.  相似文献   
62.
63.
64.
65.
As part of a program towards the development of novel antibiotics, a convenient method for solid-phase synthesis of the cyclic cationic peptide polymyxin B1 and analogues thereof is described. The methodology, based on cleavage-by-cyclization using Kenner's safety-catch linker, yields crude products with purities ranging from 37-67%. Antibacterial assays revealed that analogues 23-26, in which the (S)-6-methyloctanoic acid moiety is replaced with shorter acyl chains, exhibit distinct antimicrobial activity. The results suggest that the length of the acyl chain is rather critical for antimicrobial activity. On the other hand, substitution of the hydrophobic ring-segment D-Phe-6/Leu-7 in polymyxin B1 with dipeptide mimics (i.e. analogues 27-33) resulted in almost complete loss of antimicrobial activity.  相似文献   
66.
67.
68.
Experiments on 330 rats were made to study the influence of benzodiazepines (diazepam, dormicum and phenazepam) on 5'-nucleotidase activity in brain homogenates. It was discovered that diazepam and dormicum in doses of 3 and 4 mg, phenazepam in doses of 3.75 and 5 mg per 200 g bw provoked a 16-20% reduction in 5'-nucleotidase activity. The maximal effect of diazepam (3 and 4 mg doses) was attained 1 h after intraperitoneal injection, that of dormicum (3 mg) 30 min and of phenazepam (5 mg) 1 h after intraperitoneal injection. It is assumed that benzodiazepines are involved in AMP metabolism.  相似文献   
69.
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   
70.
The results of the inoculation of material taken from the anterior section of the nasal cavity and from the pharyngeal mucosa of 50 healthy young children and 298 acute pneumonia patients were analyzed. 23 microbial species were isolated. In the samples taken from the anterior section of the nasal cavity, monocultures were detected in 86 samples and 54 variants of associations including 2-4 species, in 139 samples. In the samples taken from the pharynx, monocultures were detected in 59 samples and 180 variants of associations including 2-6 species, in 282 samples. Differences in the contamination of the nasal cavity and the pharynx in healthy children and in pneumonia patients were revealed. These differences were manifested in the structure of the microflora (monocultures, associations, their composition), the assortment of microbial species and their concentration. In young children with pneumonia the microflora of the upper respiratory tract was found to reflect the severity of acute pneumonia and the intensity of the pathological process in the lungs (uncomplicated, pyodestructive pneumonia, pyodestructive pneumonia with fatal termination, acute purulent pleurisy).  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