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   332776篇
  免费   15426篇
  国内免费   865篇
  349067篇
  2021年   1835篇
  2018年   15853篇
  2017年   14739篇
  2016年   11821篇
  2015年   3955篇
  2014年   4870篇
  2013年   6786篇
  2012年   12341篇
  2011年   22487篇
  2010年   19051篇
  2009年   14527篇
  2008年   18604篇
  2007年   20988篇
  2006年   7656篇
  2005年   7862篇
  2004年   8225篇
  2003年   8214篇
  2002年   7939篇
  2001年   9598篇
  2000年   9245篇
  1999年   7022篇
  1998年   2143篇
  1997年   1985篇
  1996年   1850篇
  1992年   5493篇
  1991年   5738篇
  1990年   5663篇
  1989年   5638篇
  1988年   5230篇
  1987年   4880篇
  1986年   4444篇
  1985年   4679篇
  1984年   3710篇
  1983年   3052篇
  1982年   2030篇
  1981年   1725篇
  1980年   1728篇
  1979年   3340篇
  1978年   2579篇
  1977年   2376篇
  1976年   2332篇
  1975年   2839篇
  1974年   3117篇
  1973年   3084篇
  1972年   3428篇
  1971年   3244篇
  1970年   2220篇
  1969年   2158篇
  1968年   2031篇
  1967年   1797篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A study was made of the effect of T-activin on the biosynthesis of immune gamma-interferon. It was shown that in 27% of patients with chronic nonspecific pulmonary diseases, production of gamma-interferon by lymphocytes was substantially reduced during exacerbation of inflammatory process in the lungs. It was discovered that T-activin was not an interferon inductor but enhanced its synthesis in patients with a low capacity of producing immune interferon even at small doses of interferon inductor. The preparation does not produce any effect on this process in normal subjects and in patients showing the normal level of gamma-interferon. Thus T-activin can be used for stimulation of interferonogenesis.  相似文献   
992.

Background  

Chow and Liu showed that the maximum likelihood tree for multivariate discrete distributions may be found using a maximum weight spanning tree algorithm, for example Kruskal's algorithm. The efficiency of the algorithm makes it tractable for high-dimensional problems.  相似文献   
993.
994.
In the experiment performed on 175 white male rats by means of a complex of morphological, biochemical and biomechanical methods peculiarities of structure, growth, outline formation and mineralization of the skeletal bones have been investigated under a toxic lesion of the organism with pesticides (chlorophose and keltan) and at a simultaneous administration of antioxidants of various groups (tocopherol, ionol, sodium selenit). Osteotoxic effect of the pesticides, manifested as an inhibition of bone growth, as a disbalance of mineral saturation and their composition, as a decrease in indices of firmness is leveled by means of therapeutic doses of the antioxidants. The stabilizing effect of the antioxidant applied correlates to the manifestation of the pesticides osteotoxic effect, to the ability of their cumulation in the organism and is directly connected with the supposed mechanism of damaging effect to the organism and/or cell. The expressiveness of the toxic effect of the chemical poison, in its turn, is defined not only by the dose, mechanism and duration of the effect, but by age peculiarities of the organism and by functional state of its reactivity. When the poisons are applied for a long time, in order to level their osteotoxic effect, a multiple increase of therapeutic doses of the antioxidants and a combined potentiation of their effect are necessary.  相似文献   
995.
996.
997.
Principal component (PCA) and factor analysis (FA) are widely used in animal behaviour research. However, many authors automatically follow questionable practices implemented by default in general‐purpose statistical software. Worse still, the results of such analyses in research reports typically omit many crucial details which may hamper their evaluation. This article provides simple non‐technical guidelines for PCA and FA. A standard for reporting the results of these analyses is suggested. Studies using PCA and FA must report: (1) whether the correlation or covariance matrix was used; (2) sample size, preferably as a footnote to the table of factor loadings; (3) indices of sampling adequacy; (4) how the number of factors was assessed; (5) communalities when sample size is small; (6) details of factor rotation; (7) if factor scores are computed, present determinacy indices; (8) preferably they should publish the original correlation matrix.  相似文献   
998.
999.
Production of cholinesterase by a pyocyanin-producing strain of Pseudomonas aeruginosa, isolated from a patient and grown in the presence of acetylcholine as the main source of carbon, was described. The enzyme activity was detected in suspensions of intact bacteria and in their subcellular preparations. Like the acetylcholinesterase of the electric eel, as opposed to that of the erythrocytes, this bacterial enzyme was inhibited by specific antiserum produced against it in rabbits. The production of the enzyme was found to be sensitive to catabolite repression and to require external cyclic AMP, but not 5′-AMP for the elimination of this repression. Cyclic AMP alone, without the inducer, did not stimulate the production of the enzyme.  相似文献   
1000.
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