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   19381篇
  免费   58篇
  国内免费   57篇
系统科学   295篇
丛书文集   444篇
教育与普及   36篇
理论与方法论   100篇
现状及发展   9203篇
研究方法   888篇
综合类   8326篇
自然研究   204篇
  2012年   289篇
  2011年   545篇
  2010年   149篇
  2009年   110篇
  2008年   347篇
  2007年   410篇
  2006年   368篇
  2005年   373篇
  2004年   352篇
  2003年   386篇
  2002年   322篇
  2001年   635篇
  2000年   627篇
  1999年   362篇
  1992年   343篇
  1991年   268篇
  1990年   315篇
  1989年   280篇
  1988年   270篇
  1987年   296篇
  1986年   295篇
  1985年   357篇
  1984年   261篇
  1983年   227篇
  1982年   221篇
  1981年   252篇
  1980年   284篇
  1979年   625篇
  1978年   506篇
  1977年   518篇
  1976年   368篇
  1975年   400篇
  1974年   641篇
  1973年   518篇
  1972年   485篇
  1971年   566篇
  1970年   721篇
  1969年   635篇
  1968年   541篇
  1967年   591篇
  1966年   501篇
  1965年   369篇
  1964年   100篇
  1959年   204篇
  1958年   301篇
  1957年   198篇
  1956年   172篇
  1955年   173篇
  1954年   164篇
  1948年   92篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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   
2.
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   
3.
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   
4.
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   
5.
6.
7.
8.
9.
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   
10.
Linear models are invariant under non-singular, scale-preserving linear transformations, whereas mean square forecast errors (MSFEs) are not. Different rankings may result across models or methods from choosing alternative yet isomorphic representations of a process. One approach can dominate others for comparisons in levels, yet lose to another for differences, to a second for cointegrating vectors and to a third for combinations of variables. The potential for switches in ranking is related to criticisms of the inadequacy of MSFE against encompassing criteria, which are invariant under linear transforms and entail MSFE dominance. An invariant evaluation criterion which avoids misleading outcomes is examined in a Monte Carlo study of forecasting methods.  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