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   245015篇
  免费   22456篇
  国内免费   259篇
  267730篇
  2018年   2637篇
  2017年   2580篇
  2016年   3427篇
  2015年   3663篇
  2014年   4580篇
  2013年   6556篇
  2012年   7214篇
  2011年   7906篇
  2010年   5385篇
  2009年   4788篇
  2008年   6873篇
  2007年   7086篇
  2006年   6725篇
  2005年   6414篇
  2004年   6320篇
  2003年   6152篇
  2002年   6013篇
  2001年   12010篇
  2000年   11965篇
  1999年   9144篇
  1998年   2670篇
  1997年   2745篇
  1996年   2692篇
  1995年   2477篇
  1994年   2423篇
  1993年   2317篇
  1992年   7176篇
  1991年   6979篇
  1990年   7059篇
  1989年   6843篇
  1988年   6360篇
  1987年   6010篇
  1986年   5355篇
  1985年   5662篇
  1984年   4465篇
  1983年   3862篇
  1982年   2671篇
  1981年   2493篇
  1980年   2304篇
  1979年   4110篇
  1978年   3136篇
  1977年   2883篇
  1976年   2828篇
  1975年   3270篇
  1974年   3500篇
  1973年   3531篇
  1972年   3059篇
  1971年   2845篇
  1970年   2532篇
  1969年   2299篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
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   
953.
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   
954.
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   
955.
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   
956.
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   
957.
Cultured circular smooth muscle from the rabbit colon   总被引:1,自引:0,他引:1  
Summary Although cultured vascular smooth muscle cells have been extensively characterized and investigated, there are very few studies of cultured intestinal smooth muscle cells. The aim of this study was to culture colonic smooth muscle (CSM) cells from the rabbit colon. Freshly isolated CSM cells from the circular muscle layer of the distal colon were prepared by collagenase digestion. In primary culture, CSM cells attached to the culture vessels by 48 to 72 h, proliferated by 3 to 7 d, and reached confluency by 14 to 17 d with a “hill-and-valley” pattern. Spontaneous contractions were not observed at any time at 21° or 37° C. Confluent primary cultures were greater than 95% CSM cells, as identified by intensely positive immunofluorescent staining to smooth muscle actin-specific CGA7 and muscle-specific HHF-35 monoclonal antibodies. Transmission electron microscopy of freshly isolated and proliferating CSM cells revealed ultrastructural features consistent with smooth muscle cells. We successfully cultured CSM cells of the rabbit from freshly isolated cells and validated these CSM cells by electron microscopy and immunocytochemical staining. These highly pure primary cultures may be used to investigate numerous aspects of CSM cell metabolism and physiology. These studies were supported by the National Institutes of Health grant to the Inflammatory Bowel Disease Center (Bethesda, MD) P30-AM-32200 and R01-DK-31147. Dr. Kao is the recipient of a Research Career Development Award from the National Foundation for Ileitis and Colitis, Inc. A preliminary report of this work was presented at the American Motility Society Meeting, Houston, TX, in October 1986, and appeared in abstract form inGastroenterology 91: 1057; 1986.  相似文献   
958.
959.
We investigated the effect of in vivo hypothyroidism on the sialylation and sulfation of thyroid-stimulating hormone (TSH) secreted by mouse pituitary explants. Oligosaccharides from secreted thyroid-stimulating hormone from hypothyroid animals contained greater sialic acid relative to sulfate in both alpha and beta subunits. Aging per se had little effect on thyroid-stimulating hormone sialylation or sulfation. Variable sialylation and sulfation demonstrates a mechanism for charge microheterogeneity of thyroid-stimulating hormone, and the increasing sialylation observed with hypothyroidism may functionally mediate the prolonged metabolic clearance that has been noted previously.  相似文献   
960.
The 13C NMR spectra of geosmin, selina-4(14),7(11)-diene-99-ol and two dihydroeudesmol isomers have been obtained and the individual resonances assigned. Several different empirical correlations developed by others have been combined in simple calculations to predict chemical shift values for sesquiterpenols of the eudesmane group.  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