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   1485159篇
  免费   138078篇
  国内免费   1463篇
  1624700篇
  2021年   18005篇
  2019年   16233篇
  2018年   18267篇
  2017年   17032篇
  2016年   28456篇
  2015年   42787篇
  2014年   50872篇
  2013年   77096篇
  2012年   39991篇
  2011年   29175篇
  2010年   44812篇
  2009年   45815篇
  2008年   27338篇
  2007年   25712篇
  2006年   30432篇
  2005年   31554篇
  2004年   30734篇
  2003年   28320篇
  2002年   26522篇
  2001年   44117篇
  2000年   41843篇
  1999年   39058篇
  1998年   26560篇
  1997年   26372篇
  1996年   25766篇
  1995年   23876篇
  1994年   23698篇
  1993年   22853篇
  1992年   33559篇
  1991年   31770篇
  1990年   30169篇
  1989年   30788篇
  1988年   28452篇
  1987年   26820篇
  1986年   25108篇
  1985年   26890篇
  1984年   25674篇
  1983年   22696篇
  1982年   22101篇
  1981年   21077篇
  1980年   19701篇
  1979年   22014篇
  1978年   19819篇
  1977年   18908篇
  1976年   17798篇
  1975年   17596篇
  1974年   18229篇
  1973年   18630篇
  1972年   15906篇
  1971年   14670篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
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   
54.
Exposure of male Syrian hamsters (Mesocricetus auratus) for 10 weeks to short photoperiod (SP) providing 10 hr light: 14 hr darkness (10:14 LD) produced a significant reduction in the weights of the reproductive organs, plasma thyroxine (T4) levels and free T4 index (FT4I) compared to the values of animals exposed to long photoperiod (LP, 14:10 LD). C57bl male house mice (Mus musculus) kept in SP (10:14 LD) had reproductive organ weights equivalent to those of mice kept in long days (14:10 LD) and lower T3 uptake (T3U) values. Male gerbils (Meriones unguiculatus) exposed to 13 weeks of SP (10:14 LD) had lower body weights, testes and seminal vesicle weights and higher T3U values compared to LP (14:10 LD) controls. However, no effect was seen on plasma T4 and triiodothyronine (T3) values nor the FT4I and free T3 index (FT3I). White-footed male mice (Peromyscus leucopus) exposed to SP (8:16 LD) had significantly lower testes and seminal vesicle weights while plasma T4 and T3 levels were unaffected. Snell strain house mice (Mus musculus) exposed to SP (8:16 LD) had normal reproductive organ weights compared to the values of LP-exposed (16:8 LD) control animals. However, there was a significant depression in T3 and in the FT3I in the SP animals.  相似文献   
55.
56.
57.
58.
59.
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   
60.
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   
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