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   776184篇
  免费   87985篇
  国内免费   1008篇
  2016年   8518篇
  2015年   12461篇
  2014年   14642篇
  2013年   20386篇
  2012年   23298篇
  2011年   23909篇
  2010年   15905篇
  2009年   14643篇
  2008年   21160篇
  2007年   21990篇
  2006年   20807篇
  2005年   20007篇
  2004年   19973篇
  2003年   18825篇
  2002年   18528篇
  2001年   33397篇
  2000年   33821篇
  1999年   27068篇
  1998年   9664篇
  1997年   9892篇
  1996年   9314篇
  1995年   8906篇
  1994年   8612篇
  1993年   8637篇
  1992年   22365篇
  1991年   21979篇
  1990年   21457篇
  1989年   20751篇
  1988年   19447篇
  1987年   18469篇
  1986年   17529篇
  1985年   17521篇
  1984年   14495篇
  1983年   12482篇
  1982年   9648篇
  1981年   8940篇
  1980年   8186篇
  1979年   13844篇
  1978年   11266篇
  1977年   10160篇
  1976年   9551篇
  1975年   10930篇
  1974年   11959篇
  1973年   11769篇
  1972年   10764篇
  1971年   9847篇
  1970年   8423篇
  1969年   8294篇
  1968年   7593篇
  1967年   6643篇
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
151.

Background  

Recent studies point to a great diversity of non-ribosomal peptide synthesis systems with major roles in amino acid and co-factor biosynthesis, secondary metabolism, and post-translational modifications of proteins by peptide tags. The least studied of these systems are those utilizing tRNAs or aminoacyl-tRNA synthetases (AAtRS) in non-ribosomal peptide ligation.  相似文献   
152.
Systematic analysis of the long-chain components of Eubacterium lentum   总被引:1,自引:0,他引:1  
The cellular long-chain component patterns of 33 strains of Eubacterium lentum were determined by gas chromatography. Two main types of long-chain component patterns were distinguished. The first (26 strains) was characterized by saturated branched-chain fatty acids (br14:0, br15:0, br16:0 and br17:0). The second (7 strains) did not contain branched-chain fatty acids and was characterized by saturated straight-chain fatty acids (11:0, 12:0, 14:0 and 16:0). Both types contained fatty aldehydes and their respective dimethyl acetals (14ald and 14dma, 16ald and 16dma). br16dma was only found in the first type. The G + C content of the DNA (Tm) of the 33 strains varied between 63.7 and 69.1 mol %. Canonical correlation analysis distinguished three subtypes within the first main type.  相似文献   
153.
154.
Antibodies to calcitonin, parathyroid hormone and cortisol are detected in acute stage of infection-caused bronchial asthma. The appearance of antibodies is paralleled by marked hypercalcaemia. The antibodies may bind excessive hormones in the blood, preventing further hormonal imbalance. Ten-day treatment with glucocorticoids decreased the amount of antibodies possibly due to normalization of hormonal secretion and restoration of their balance. As a result, calcium blood levels returned to normal.  相似文献   
155.
156.
157.
158.
159.
Neurospora grows vegetatively as a syncytium in which multiple nuclei exist within a connected cytoplasm. Because of the ability of separate and distinct mycelia to fuse, the possibility exists of generating heterocaryotic cultures in which the nuclei and cytoplasms of two different strains are comingled into the same syncytium. We have used such heterocaryons, in which the component parts differed with respect to their circadian clock phase, to examine whether or not clock-dominant phases exist in the circadian cycle. To this end, the phase subsequent to the formation of heterocaryons by pairs of mycelial discs that are initially at different circadian phases was examined in Neurospora crassa. The resulting phase was an average of the parent phases in many cases, but was sometimes observed to correspond more closely to just one of the original parental phases. In these cases, we did not observe any dominant phases in the circadian cycle; the phase of a particular parent disc was more dominant in the heterocaryon when the proportion of the nuclei from that parent was greater in the heterocaryon. In some instances, which occurred mostly when the difference in phase of the parental discs was large, the resultant phase could not be related in a simple way to the parental phases. An interpretation based on a limit cycle model of the circadian oscillation is possible.  相似文献   
160.
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