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   1112692篇
  免费   114275篇
  国内免费   436篇
  1227403篇
  2018年   10956篇
  2017年   10433篇
  2016年   14366篇
  2015年   18163篇
  2014年   21561篇
  2013年   31972篇
  2012年   36403篇
  2011年   37751篇
  2010年   25177篇
  2009年   22845篇
  2008年   33584篇
  2007年   35096篇
  2006年   32844篇
  2005年   31291篇
  2004年   31118篇
  2003年   30058篇
  2002年   29180篇
  2001年   45187篇
  2000年   44925篇
  1999年   36069篇
  1998年   13786篇
  1997年   13910篇
  1996年   13303篇
  1995年   12379篇
  1994年   12013篇
  1993年   12047篇
  1992年   30053篇
  1991年   29500篇
  1990年   28846篇
  1989年   28331篇
  1988年   26365篇
  1987年   25143篇
  1986年   23488篇
  1985年   23829篇
  1984年   19838篇
  1983年   17250篇
  1982年   13384篇
  1981年   12071篇
  1980年   11284篇
  1979年   18784篇
  1978年   14838篇
  1977年   13590篇
  1976年   12991篇
  1975年   14354篇
  1974年   15457篇
  1973年   15198篇
  1972年   13956篇
  1971年   12606篇
  1970年   10986篇
  1969年   10828篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A promising producer of bioactive compounds isolated from a Brazilian tropical soil was tested for its range of antimicrobial activities. Strain 606, classified as Streptomyces sp., could not be identified up to species level, suggesting a possible new taxon. The supernatant and 10 extracts and fractions, obtained by extraction and chromatographic techniques, presented antimicrobial activity using antibiograms. The methanolic fraction was highly active against pathogenic bacteria, phytopathogenic fungi and the human pathogenic yeast Candida albicans. It also possessed high antiviral activity inhibiting the propagation of an acyclovir-resistant herpes simplex virus type 1 strain on HEp-2 cells at non-cytotoxic concentration. The strong cytotoxic effect suggests an antitumour action. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
62.
Formation of rings from Drosophila DNA fragments   总被引:1,自引:0,他引:1  
  相似文献   
63.
The literature relating to chemical, biochemical and biological aspects of the steroidal glycoalkaloid, α-tomatine, is reviewed. The alkaloid, which can be used as a starting compound for the synthesis of steroidal hormones, is toxic to a wide range of living organisms. The significance of tomatine to plants which elaborate it is discussed and some possible uses of the compound are mentioned.  相似文献   
64.
65.
Four myeloid cell lines (M1, WEHI-3B D+, FDC-P1, and 32D) were screened for the presence of J11d antigen. One of these cell lines, the myeloid leukemia M1, was found to express a high level of J11d antigen on the cell surface. Recombinant mouse leukemic inhibitory factor (rm-LIF), recombinant human LIF (rh-LIF), and steroids (hydrocortisone and dexamethasone) could induce M1 cells to undergo monocytic differentiation. The level of J11d antigen was greatly reduced after treatment of the cells with LIF or steroids. Western blotting revealed that the apparent molecular weight of the J11d antigen on M1 cells was 45-48 kDa. Furthermore, the level of J11d mRNA was also reduced during LIF-induced differentiation of M1 cells.  相似文献   
66.
67.
Censuses of buffalo and wildebeest in the Serengeti-Mara region have been carried out by various workers at intervals since 1958. The methods of these censuses, which normally employ a total count, are described and the errors inherent in such techniques are analysed in detail. After the appropriate corrections had been made the results showed that both populations have increased considerably over the years 1961–1971.  相似文献   
68.
69.
70.
AAA ATPases form a functionally diverse superfamily of proteins. Most members form homo-hexameric ring complexes, are catalytically active only in the fully assembled state, and show co-operativity among the six subunits. The mutual dependence among the subunits is clearly evidenced by the fact that incorporation of mutated, inactive subunits can decrease the activity of the remaining wild type subunits. For the first time, we develop here models to describe this form of allostery, evaluate them in a simulation study, and test them on experimental data. We show that it is important to consider the assembly reactions in the kinetic model, and to define a formal inhibition scheme. We simulate three inhibition scenarios explicitly, and demonstrate that they result in differing outcomes. Finally, we deduce fitting formulas, and test them on real and simulated data. A non-competitive inhibition formula fitted experimental and simulated data best. To our knowledge, our study is the first one that derives and tests formal allosteric schemes to explain the inhibitory effects of mutant subunits on oligomeric enzymes.  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