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   248846篇
  免费   22856篇
  国内免费   288篇
  271990篇
  2018年   2726篇
  2017年   2648篇
  2016年   3537篇
  2015年   3814篇
  2014年   4753篇
  2013年   6753篇
  2012年   7452篇
  2011年   8166篇
  2010年   5526篇
  2009年   4906篇
  2008年   7057篇
  2007年   7249篇
  2006年   6864篇
  2005年   6565篇
  2004年   6451篇
  2003年   6284篇
  2002年   6121篇
  2001年   12096篇
  2000年   12041篇
  1999年   9224篇
  1998年   2725篇
  1997年   2780篇
  1996年   2722篇
  1995年   2505篇
  1994年   2449篇
  1993年   2347篇
  1992年   7243篇
  1991年   7036篇
  1990年   7114篇
  1989年   6891篇
  1988年   6397篇
  1987年   6056篇
  1986年   5399篇
  1985年   5711篇
  1984年   4496篇
  1983年   3895篇
  1982年   2699篇
  1981年   2516篇
  1980年   2330篇
  1979年   4140篇
  1978年   3163篇
  1977年   2918篇
  1976年   2851篇
  1975年   3284篇
  1974年   3522篇
  1973年   3561篇
  1972年   3083篇
  1971年   2868篇
  1970年   2549篇
  1969年   2321篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Close inspection of surface bone in skulls of Neanderthal man reveals weathering cracks extensive enough in one specimen, La Chapelle-aux-Saints, to allow preliminary analysis of major patterns of orientation and to make inferences about functional relationships of structures. The fine structure of the bone of the brow ridges is very different from the rest of the skull in the two adults examined, having a peculiar vermiculate surface pattern. Weathering cracks do not appear in this region. This indicates that Neanderthal brow ridges are not closely related to normal mechanical forces such as chewing exertion. It may, however, give further support to theories of Neanderthal brow ridges as protection for the eyes. The localized structure of bone often differs from region to region, and offers new possibilities for the analysis of both contemporary and fossil forms.  相似文献   
992.
993.
Human metallothionein-specific riboprobes.   总被引:2,自引:1,他引:1       下载免费PDF全文
  相似文献   
994.
995.
996.
Clinical, bacteriological, serological and epidemiological studies of ozena morbidity among the population of Minsk were carried out in 1970-1980. On January 1, 1981, the ozena morbidity rate among the inhabitants of Minsk was 26.72%. Ozena was found to affect mainly children and women. A wide spread of the family foci of this disease (31.68%) was revealed. The results of this study indicate that the source of K. ozaenae is a sick person who begins to excrete the bacteria in the prodromal period of the disease and may continue to excrete them for many years. The transfer of K. ozaenae occurs probably by droplet or contact infection. The droplet infection is less active in the absence of symptoms (coughing, sneezing) facilitating excretion of the infective agent into the air and in cases of the low susceptibility of persons to ozena. The main measures for controlling ozena are the timely detection and sanitation of the sources of ozena, as well as the current disinfection of the infection foci in apartments.  相似文献   
997.
The reactions of NADPH oxidation by quinones and inorganic complexes catalyzed by NADPH: adrenodoxin reductase were studied. The catalytic constant for the enzyme at pH 7.0 is 20-25 s-1; the oxidative constants for the quinones vary from 5 X 10(5) to 1.1 X 10(3) M-1 s-1 and show an increase with a rise in the one-electron acceptor reduction potential. The mode of adrenodoxin reductase interaction with oxyquinones differs from that of the enzyme interaction with alkyl-substituted quinones and inorganic complexes. NADPH competitively inhibits electron acceptors, whereas NADP+ is a competitive inhibitor of NADPH and a uncompetitive inhibitor of electron acceptors. (Ki = 25 microM). The depth of FAD incorporation into the enzyme molecule as calculated according to the outer sphere electron transfer theory is 6.1 A.  相似文献   
998.
The addition of ATP or 3,5-AMP (but not UTP, GTP, CTP, AMP, 2,3-AMP, ADP, inorganic pyrophosphate) at a final concentration of 10(-1) M into streptokinase solution, pH 7.0 or 9.5, causes a dramatic inhibition of streptokinase-induced fibrinolysis. The specificity of ATP effect is fully lost at pH 3.0, when all nucleotides completely inhibit the activating function of streptokinase. Ribose-5-phosphate causes a similar effect at pH 3.0. The character of nucleotide action on the activating function of streptokinase considerably differs from their influence on proteolytic reactions.  相似文献   
999.
The mitogenic response of lymphocytes in mouse spleen cell culture to the action of Salmonella typhi lipopolysaccharide (LPS) and Vi-antigen under different experimental conditions has been studied. The density of the culture has been shown to influence the activation of lymphocytes with Vi-antigen. Thus, macrophages stimulate mitogenesis at the concentration of lymphocytes equal to 1.0-1.2 X 10(6) cells/ml and suppress it when this concentration increases tenfold. The method used for the purification of cell suspension from adhering cells has been shown to influence the level of the mitogenic response of lymphocytes. The cultures, purified from macrophages by filtration through a column packed with cotton wool, have been found to respond to the mitogenic doses of LPS 7-8 times weaker than those purified by adhesion onto plastic. Background and mitogen-induced inclusion of 3H-thymidine into lymphocytic DNA varies in accordance with the presence of adhering cells. For this reason, in the evaluation of the influence of macrophages on mitogenesis it is expedient to consider not only the stimulation index, but also the absolute inclusion of thymidine into cells.  相似文献   
1000.
Phosphorylase kinase was isolated from red and white chicken skeletal muscle in a nearly homogeneous state as judged by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The molecular weight of the native enzyme as determined by gel filtration on Sepharose 4B is close to that of rabbit skeletal muscle phosphorylase kinase (i. e., approximately 1300 000). The molecular weights of the subunits determined by SDS gel electrophoresis are: alpha', 140 000 beta, 129 000; gamma', 44 000; delta, 17 000 (cf. the Mr values of the alpha- and gamma-subunits of the rabbit muscle isoenzyme are 146 000 and 42 000). The four subunits, alpha', beta, gamma' and delta, were found to exist in equimolar amounts as shown by a densitometric analysis of acrylamide gels; hence, the subunit formula of the chicken skeletal muscle isoenzyme is (alpha' beta gamma' delta)4. Rabbit antisera against a mixture of alpha'- and beta-subunits of chicken phosphorylase kinase yield a single precipitin line with this enzyme, do not show cross reactions of identity with the rabbit muscle enzyme but strongly inhibit the activity of the chicken enzyme and partially inhibit the activity of the rabbit muscle isoenzyme.  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