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   944762篇
  免费   110154篇
  国内免费   588篇
  1055504篇
  2018年   8360篇
  2016年   11208篇
  2015年   14929篇
  2014年   17867篇
  2013年   25801篇
  2012年   28635篇
  2011年   29000篇
  2010年   19366篇
  2009年   18029篇
  2008年   25512篇
  2007年   26665篇
  2006年   24994篇
  2005年   24139篇
  2004年   23872篇
  2003年   22928篇
  2002年   22122篇
  2001年   43326篇
  2000年   43648篇
  1999年   34592篇
  1998年   11806篇
  1997年   12527篇
  1996年   11828篇
  1995年   11181篇
  1994年   10984篇
  1993年   10960篇
  1992年   28809篇
  1991年   28133篇
  1990年   27420篇
  1989年   26756篇
  1988年   24682篇
  1987年   23495篇
  1986年   21927篇
  1985年   22010篇
  1984年   18282篇
  1983年   15807篇
  1982年   12060篇
  1981年   11058篇
  1980年   10459篇
  1979年   17829篇
  1978年   13833篇
  1977年   12743篇
  1976年   11846篇
  1975年   13091篇
  1974年   13872篇
  1973年   13614篇
  1972年   12705篇
  1971年   11351篇
  1970年   9840篇
  1969年   9303篇
  1968年   8615篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Fusarium oxysporum f. sp. lycopersici and Rhizoctonal solani were grown in a complete 1.0 mM nutrient solution, and in solutions where Ca, Fe, K, Mg, N, P, and S were either excluded (0.0 mM) or included at depleted levels (0.1 mM) while all other constituents were maintained at 1.0 mM levels. Dry weight of both fungi were determined. For both fungi some of the lowest dry weights were recorded for samples grown in the complete solution. Exclusion of K, Mg, and S significantly increased dry weight of Fusarium. Inclusion at the 0.1 mM level of most components significantly increased Fusarium dry weight over values for both the complete and corresponding excluded nutrient solutions. The exception was S where there was no difference between excluded and 0.1 mM solutions. For Rhizoctonia dry weights in Fe excluded solutions were less than the complete solution, while dry weights in S excluded solutions were greater than the complete solution. At the 1.0 mM level Fe, K, and Mg dry weights were significantly increased over the dry weights produced in both the complete and deficient solutions.  相似文献   
992.
Beta-adrenoceptors have been discovered on the surface of cells of leukaemia L1210 and its variant resistant to sarcolysine (D, L-melphalan). One type of functionally active receptors with dissociation constant Kd for L-[3H] dihydroalprenolol about 0.02 nM and 360 receptors per cell have been revealed in leukaemia L1210 cells. In the resistant cells two types of functionally inactive receptors with Kd1 approximately 0.02 nM (420 receptors per cell) and Kd2 approximately 2.5 nM (3000 receptors per cell) have been revealed. This property of beta-adrenoceptors may be one of the causes of tumour cell resistance to sarcolysine.  相似文献   
993.
A rapid, sensitive method has been developed to detect antibody-antigen complexes on “Western blots.” The methods of H. Towbin, T. Staehlin, and J. Gordon were used to separate and blot the antigens onto nitrocellulose. The remaining sites of attachment were blocked and the nitrocellulose was washed with polyoxyethylenesorbitan monolaurate (Tween 20). The blot was then reacted with the antiserum or hybridoma supernate to be tested. After the antigen-antibody reaction was completed, the blot was washed and treated with anti-antibody which has been conjugated to alkaline phosphatase. The alkaline phosphatase was detected by the reduction of the tetrazolium salt to diformazan by the hydrogen ions released in the formation of indigo by the reaction of the phosphatase on the indoxyl phosphate. The advantages of this method over previously described techniques are (1) use of Tween 20 allows the blot to be stained with Coomassie blue, (2) the substrates of the alkaline phosphatase reaction are stable for long periods of time, (3) the reaction products form an intense blue color which does not fade, (4) the resolution is extremely good with little to no band broadening, (5) the reaction is sensitive to picogram quantities of antigen, and (6) the reaction is quantitative.  相似文献   
994.
995.
996.
A new mutation, mpo, which affects the synthesis of some membrane proteins and sporulation in Bacillus subtilis was identified. The mpo mutation was tightly linked to the overproduction of membrane proteins MP32 and MP18 (molecular weights of 32,000 and 18,000, respectively) and the temperature-sensitive sporulation phenotype. Genetic analysis showed that the mpo mutation maps between the spoIIIB and lys loci.  相似文献   
997.
998.
Several phenotypic and functional defects have been described within the residual T-lymphocyte population of patients with B-cell chronic lymphocytic leukemia (B-CLL), particularly in those in the more advanced stages of the disease. In this study, we review these abnormalities and discuss their possible effects on the course of the illness. Particular emphasis is devoted to the role of interleukin 2 (IL-2) in B-CLL. Evidence is provided that the IL-2 released by B-CLL T-lymphocytes may be utilized by the neoplastic B-cell clone that expresses the IL-2 receptor and that decreased availability of IL-2 may play a contributory role in some of the T-cell defects encountered in B-CLL.  相似文献   
999.
The isolation of spirochaetes from the rat caecum   总被引:1,自引:1,他引:0  
Spirochaetes indigenous to the conventional rat caecum were cultivated on agar medium using selective isolation techniques. The 27 axenic isolates represented four morphological types of spirochaetes differing in cell size, cell coiling pattern and number of protoplasmic flagella.  相似文献   
1000.
Plasma concentrations of adrenaline and noradrenaline were measured at rest from cannulated fish and following net capture. Adrenaline and noradrenaline concentrations in capture-stressed fish averaged 36,740 pmol l-1 and 38,860 pmol l-1 respectively, whereas resting values were less than 200 pmol l-1 for both amines. Erythrocyte swelling and raised blood lactate were evident in stressed fish. In vitro effects of 5 mmol l-1 adrenaline on erythrocyte suspensions suggested that the catecholamine had a direct effect on erythrocyte volume. The significance of these results is discussed in relation to the oxygen transport properties of the blood.  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