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   18085篇
  免费   42篇
  国内免费   53篇
系统科学   261篇
丛书文集   444篇
教育与普及   38篇
理论与方法论   66篇
现状及发展   8299篇
研究方法   840篇
综合类   8078篇
自然研究   154篇
  2012年   245篇
  2011年   464篇
  2010年   115篇
  2009年   99篇
  2008年   308篇
  2007年   389篇
  2006年   334篇
  2005年   341篇
  2004年   294篇
  2003年   348篇
  2002年   294篇
  2001年   633篇
  2000年   637篇
  1999年   367篇
  1992年   349篇
  1991年   263篇
  1990年   306篇
  1989年   279篇
  1988年   270篇
  1987年   287篇
  1986年   292篇
  1985年   358篇
  1984年   251篇
  1983年   228篇
  1982年   207篇
  1981年   242篇
  1980年   268篇
  1979年   586篇
  1978年   477篇
  1977年   478篇
  1976年   361篇
  1975年   383篇
  1974年   594篇
  1973年   468篇
  1972年   429篇
  1971年   526篇
  1970年   669篇
  1969年   586篇
  1968年   505篇
  1967年   541篇
  1966年   448篇
  1965年   338篇
  1964年   97篇
  1959年   199篇
  1958年   295篇
  1957年   194篇
  1956年   177篇
  1955年   168篇
  1954年   160篇
  1948年   89篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
String theorists are certain that they are practicing physicists. Yet, some of their recent critics deny this. This paper argues that this conflict is really about who holds authority in making rational judgment in theoretical physics. At bottom, the conflict centers on the question: who is a proper physicist? To illustrate and understand the differing opinions about proper practice and identity, we discuss different appreciations of epistemic virtues and explanation among string theorists and their critics, and how these have been sourced in accounts of Einstein's biography. Just as Einstein is claimed by both sides, historiography offers examples of both successful and unsuccessful non-empirical science. History of science also teaches that times of conflict are often times of innovation, in which novel scholarly identities may come into being. At the same time, since the contributions of Thomas Kuhn historians have developed a critical attitude towards formal attempts and methodological recipes for epistemic demarcation and justification of scientific practice. These are now, however, being considered in the debate on non-empirical physics.  相似文献   
2.
The shrink proofing on wool with treatment of protease named Argaenzyme STL was studied. The various pretreating auxiliaries, different parameters for protease treating process and the effect of stabilizer were discussed in detail. The varieties of some properties before and after protease treatment were also investigated.  相似文献   
3.
Photon emission of phagocytes in relation to stress and disease.   总被引:1,自引:0,他引:1  
E M Lilius  P Marnila 《Experientia》1992,48(11-12):1082-1091
Phagocytes, the first-line cells of the body's defence mechanisms against invading pathogens, kill microorganisms by means of lysosomal degradative enzymes and highly toxic reactive oxygen intermediates. The reactive oxygen compounds are produced, in a process called the 'respiratory burst', by the NADPH oxidase complex in plasma membranes, and by myeloperoxidase in phagolysosomes after degranulation. These processes generate electronically excited states which, on relaxation, emit photons, giving rise to phagocyte chemiluminescence (CL). This paper describes the conditions for the measurement of CL, and reviews the activity of phagocytes from individuals undergoing stress or disease. The capability of phagocytes to emit photons reflects remarkably well the pathophysiological state of the host. In many cases even the magnitude of the stress, the presence of a pathogen in the body, or the activity of the disease can be estimated. Physiological changes, e.g. in the reproductive cycle, can also be predicted.  相似文献   
4.
Summary The authors show the antibiotic activity of water-insoluble salts of hydrosoluble antibiotics in the case of penicillin G (salts of iron, copper, silver, gold, and uranium) and streptomycin (oleate).  相似文献   
5.
1 Results Acid-doped polybenzimidazoles[1] are particularly appealing because of high proton conductivity with no or low humidification and promising fuel cells performances. PBI, in fact, contains basic functional groups which can easily interact with strong oxo-acids, such as H3PO4 and H2SO4. The acid partially protonates the polymer and partially is freely dispersed in the polymer backbone, so allowing proton migration via Grotthuss mechanism along the anionic chains[2]. Anyway, a technological limit...  相似文献   
6.
7.
8.
9.
10.
The three-dimensional crystal structure of the Escherichia coli methionine repressor, MetJ, complexed with a DNA operator fragment is described in an accompanying article. The complex exhibits several novel features of DNA-protein interaction. DNA sequence recognition is achieved largely by hydrogen-bond contacts between the bases and amino-acid side chains located on a beta-ribbon, a mode of recognition previously hypothesized on the basis of modelling of idealized beta-strands and DNA, and mutagenesis of the Salmonella phage P22 repressors Arc and Mnt. The complex comprises a pair of MetJ repressor dimers which bind to adjacent met-box sites on the DNA, and contact each other by means of a pair of antiparallel alpha-helices. Here we assess the importance of these contacts, and also of contacts that would be made between the C-helices of the protein and DNA in a previous model of the complex, by studying mutations aimed at disrupting them. The role of the carboxy-terminal helix face in operator binding was unclear, but we demonstrate that recognition of operator sequences occurs through side chains in the beta-strand motif and that dimer-dimer interactions are required for effective repression.  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