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   809051篇
  免费   83380篇
  国内免费   269篇
  2018年   8418篇
  2017年   8009篇
  2016年   11194篇
  2015年   14144篇
  2014年   16801篇
  2013年   24067篇
  2012年   26991篇
  2011年   27586篇
  2010年   18837篇
  2009年   17415篇
  2008年   24493篇
  2007年   25464篇
  2006年   23750篇
  2005年   22852篇
  2004年   22601篇
  2003年   21712篇
  2002年   21194篇
  2001年   34938篇
  2000年   34379篇
  1999年   27722篇
  1998年   10260篇
  1997年   10351篇
  1996年   9908篇
  1995年   9131篇
  1994年   8789篇
  1993年   8812篇
  1992年   22445篇
  1991年   22005篇
  1990年   21442篇
  1989年   20886篇
  1988年   19159篇
  1987年   18395篇
  1986年   17148篇
  1985年   17017篇
  1984年   13990篇
  1983年   12227篇
  1982年   9273篇
  1981年   8409篇
  1980年   7777篇
  1979年   12985篇
  1978年   10242篇
  1977年   9221篇
  1976年   8831篇
  1975年   9851篇
  1974年   10520篇
  1973年   10392篇
  1972年   9494篇
  1971年   8477篇
  1970年   7400篇
  1969年   7277篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
841.
Diagnostic test systems for the detection of IgG and IgM to Mycobacterium leprae in the blood sera of leprosy patients and armadillos experimentally infected with M. leprae have been developed on the basis of the indirect immunoperoxidase assay. The possibility has been shown of prognosing the activity of the leprotic process in leprosy patients and the results of the experimental infection of armadillos by the dynamic increase of antibody reactions with the development of the infection.  相似文献   
842.
New olean-18(19)-ene triterpenoids were effectively synthesized by the interaction of allobetulin or its acetate with phosphorous oxychloride in refluxing pyridine. The structures of the synthesized 17-chloromethyloleane-18(19)-enes were confirmed by NMR spectroscopy and X-ray analysis.  相似文献   
843.
Two methods for the calculation of optimal trajectories for the input variables of a fed-batch culture of hybridoma cells are compared. It pointed out that a gradient method based on Pontryagins' minimum principle based yields a significant better performance with respect to computational effort and the calculated minimum than a dynamic programming approach which has been presented in a previous paper [1] as the most suitable method.  相似文献   
844.
The in vitro treatment of membranes isolated from different rat organs with a water-soluble synthetic antioxidant has resulted in the change of basal and stimulus-induced adenylate cyclase activity. It is believed that the antioxidant effect is realized rather at the level of signal transfer from activated receptor to adenylate cyclase than at the level of agonist-receptor interaction.  相似文献   
845.
As the result of the study of tetanolysin-producing Clostridium tetani strains, their populations have been found to be markedly heterogeneous with respect to the hemolytic activity of clone cultures. On the basis of normal and dialyzed cultures of selected variants with maximum activity the preparations of tetanolysin have been obtained, and their hemolytic activity and antigenic properties have been studied. Antihemolytic rabbit sera have also been obtained and characterized. Partially purified preparations of tetanolysin with high hemolytic activity have been obtained by the fractionation of C. tetani dialyzed cultures with ammonium sulfate.  相似文献   
846.
Abstract The natural product cyanobacterin has been shown to be toxic to most cyanobacteria at a concentration of approx. 5 μM. We demonstrate here that cyanobacterin will also inhibit the growth of most eukaryotic algae at a similar concentration. Some algae, such as Euglena gracilis , are resistant because they are able to maintain themselves by heterotrophic nutrition. Others, such as Chlamydomonas reinhardtii , can apparently induce a detoxification mechanism to maintain photosynthesis in the presence of low concentrations of the inhibitor. Non-photosynthetic microorganisms are not affected by cyanobacterin.  相似文献   
847.
848.
Hybrid protein, cancer necrosis factor thymosin-α1 (TNF-T), when synthesizing in strain-producer of Escherichia coli SG200-50 with plasmid pThy315, was a part of “inclusion bodies” mostly in the form of a high-molecular complex with other proteins due to the S-S bonds formation. An approach of purification of TNF-T has been proposed, which is based on the destruction of the complex in the presence of sodium dodecylsulfate (DDS-Na) and dithiotreitol (DDT) followed by gel-filtration on Sephadex G-100 and renaturation by ultrafiltration on hollow fibers. The method allows the isolation of electrophoretically homogeneous TNF-T containing no DDS-Na and having high cytotoxic activity against cancer cells of mouse adenocarcinome L-929. The yield of TNF-T achieved 80% relative its content in biomass and 30% relative the total protein.  相似文献   
849.
Immediate fragmentation of parental DNA by near-ultraviolet irradiation at 313 nm was measured in cultured skin fibroblasts from normal individuals, patients with Xeroderma pigmentosum of complementation group A (XPA) and Xeroderma pigmentosum variants (XPV) by the alkaline elution procedure. For a dose of 2.25 KJm?2 given at Oo fragmentation was comparable in all cell strains. However, fragmentation was strongly increased relative to Oo in XPV but not in normal fibroblasts and the XPA strains when irradiation was carried out at 37o. From our results it appears that a step in the repair of parental DNA is abnormal in XPV.  相似文献   
850.
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