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   828874篇
  免费   84527篇
  国内免费   264篇
  913665篇
  2018年   8753篇
  2017年   8251篇
  2016年   11764篇
  2015年   15102篇
  2014年   17824篇
  2013年   25631篇
  2012年   28738篇
  2011年   29392篇
  2010年   19931篇
  2009年   18293篇
  2008年   25877篇
  2007年   26816篇
  2006年   24973篇
  2005年   23904篇
  2004年   23605篇
  2003年   22733篇
  2002年   22066篇
  2001年   35013篇
  2000年   34391篇
  1999年   27825篇
  1998年   10498篇
  1997年   10482篇
  1996年   10066篇
  1995年   9259篇
  1994年   8929篇
  1993年   8940篇
  1992年   22458篇
  1991年   22044篇
  1990年   21509篇
  1989年   20916篇
  1988年   19174篇
  1987年   18409篇
  1986年   17160篇
  1985年   17042篇
  1984年   14021篇
  1983年   12250篇
  1982年   9300篇
  1981年   8422篇
  1980年   7828篇
  1979年   12999篇
  1978年   10234篇
  1977年   9239篇
  1976年   8832篇
  1975年   9846篇
  1974年   10513篇
  1973年   10390篇
  1972年   9506篇
  1971年   8479篇
  1970年   7401篇
  1969年   7276篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
131.
Gatewood and the first thenar pedicle   总被引:1,自引:0,他引:1  
  相似文献   
132.
Reactivity of histidine residues in equine growth hormone to ethoxyformic anhydride was studied. The existence of two kinetically different sets was demonstrated: one of them including only the slow reacting histidine 169 (k = 0.164 min-1) and the other containing fast reacting histidines 19 and 21 (k = 0.892 min-1). A correlation between the decrease in the capacity to compete with 125I-labeled hormone for rat liver binding sites and the degree of ethoxyformylation of the fast group was found. Circular dichroism studies indicated no significant conformational changes in the protein with all three residues modified. These results fully agree with those obtained for bovine growth hormone which is further evidence supporting the vinculation of histidines 19 and/or 21 with the binding site of these hormones to their specific receptors.  相似文献   
133.
Mycotoxin production by various toxigenic fungi, growing on a bread analogue, was investigated at various water activities (aw) and pH combinations. Citrinin, ochratoxin A and sterigmatocystin could be detected at aw > 0·80, while patulin was only observed at aw= 0·95. These results show that some toxins may be produced at lower water activities than have been reported on synthetic media and suggest that, where possible, natural substrates should be used to investigate factors affect-ing mycotoxin production in foodstuffs.  相似文献   
134.
135.
The selective action of the antibiotics chloramphenicol and cycloheximide on the synthesis of ferredoxin in liquid cultures of Chlamydomonas reinhardii was studied. Highly specific antibodies raised against Chlamydomonas ferredoxin were used to determine the in vivo synthesis of apoferredoxin and conversion into native protein. The results indicate that 80S ribosomes are involved in the synthesis. Chlamydomonas cells growing in the absence of iron did not synthesize immunologically detectable amounts of ferredoxin. We suggest that this is based upon feed-back inhibition of apoferredoxin synthesis at the translational level.Abbreviations CAP chloramphenicol - CHI cycloheximide - IgG Immunoglobulin G - PBS 140.4 mM NaCl. 9 mM Na2HPO4, 1.3 mM NaH2PO4 (pH 74) - SDS sodium dodecvl sulphate - Fd Ferredoxin - apoFd Apoferredoxin - CM-Fd Scarboxymethylated Fd - TCA-Fd Fd treated with trichloroacetic acid  相似文献   
136.
137.
An apparatus for polyacrylamide slab gel electrophoresis is decribed which combines all parts into one integral unit. It eliminates several steps in the process of sealing, pouring, and setting the gels. Construction is easy with modest workshop facilities and the design easily adapted to suit most requirements. The apparatus provides a high degree of versatility and is suitable for use with many slab gel electrophoretic techniques.  相似文献   
138.
An overview of some mechanisms of bacterial pathogenesis   总被引:1,自引:0,他引:1  
The adherence of microorganisms to host surfaces is highly specific, and in many cases, essential for subsequent pathogenetic events to occur. A dynamic process leading to increased mucosal adherence of gram-negative bacilli to epithelial cell receptors in the oral cavity appears to be the initial step in the development of pneumonia. In infectious processes secondary to Streptococcus pneumoniae, adherence may also play a role in specific syndromes. In many cases, however, colonization of oropharyngeal mucus itself, the presence of capsular polysaccharide, and the release of various cell wall components appear to interact to cause clinical disease. In Neisseria gonorrhoeae infections, adherence is all important and is mediated by a number of cell surface structures. These have been studied extensively. Many of these structures, such as pili and protein II, exhibit great variability both between strains and in the same organism at different stages of infection. Others, such as protein I, are more constant. This information has been used in the production of specific vaccines to more preserved structures to inhibit adherence. These will be tested in the near future. It is our view that a better understanding of the many forms of bacterial adherence will be the key to our designing more effective strategies to detect early infection and to intervene more decisively to limit its spread.  相似文献   
139.
An isoleucine arrest point in G1 was determined by two methods for CHO and 3T3 cells. In the first method the fraction of cells entering S after isoleucine deprivation was assessed by [3H]thymidine labelling and autoradiography. In the second method cells entering S after isoleucine deprivation were identified by double-label autoradiography using [3H] and [14C]thymidine. From the fraction of cells entering S, determined by the two methods, the arrest point in G1 (and entry into G0) is located within the last 40 min of G1.  相似文献   
140.
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