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   239585篇
  免费   1875篇
  国内免费   1071篇
化学   112224篇
晶体学   3254篇
力学   14027篇
综合类   20篇
数学   47430篇
物理学   65576篇
  2020年   1417篇
  2019年   1540篇
  2018年   12237篇
  2017年   12063篇
  2016年   8926篇
  2015年   2596篇
  2014年   2991篇
  2013年   6838篇
  2012年   8974篇
  2011年   16686篇
  2010年   10171篇
  2009年   10585篇
  2008年   12633篇
  2007年   14531篇
  2006年   5980篇
  2005年   6541篇
  2004年   6257篇
  2003年   6387篇
  2002年   5396篇
  2001年   6184篇
  2000年   4528篇
  1999年   3445篇
  1998年   2506篇
  1997年   2547篇
  1996年   2451篇
  1995年   2220篇
  1994年   2149篇
  1993年   2024篇
  1992年   2481篇
  1991年   2582篇
  1990年   2424篇
  1989年   2379篇
  1988年   2314篇
  1987年   2356篇
  1986年   2168篇
  1985年   2659篇
  1984年   2681篇
  1983年   2167篇
  1982年   2190篇
  1981年   1998篇
  1980年   2007篇
  1979年   2320篇
  1978年   2410篇
  1977年   2340篇
  1976年   2332篇
  1975年   2189篇
  1974年   2182篇
  1973年   2236篇
  1972年   1583篇
  1971年   1279篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Summary This paper studies the flow of an incompressible, constant density micropolar fluid past a stretching sheet. The governing boundary layer equations of the flow are solved numerically using a globally convergent homotopy method in conjunction with a least change secant update quasi-Newton algorithm. The flow pattern depends on three non-dimensional parameters. Some interesting results are illustrated graphically and discussed.
Résumé Nous étudions l'écoulement d'un fluid micropolaire et incompressible, de densité constante, le long d'une surface qui l'étend. Les équations de la couche limite qui régissent l'écoulement sont résolues numériquement. On utilise un algorithme quasi-Newtonien de type least change secant update avec une méthode homotopique /`a convergence globale. Certains résultats intéressants sont discutés et illustrés graphiquement.


This work performed at Sandia National Laboratories supported by the U. S. Department of Energy under contract number DE-AC04-76DP00789.  相似文献   
992.
993.
The finite temperature and density QED and QCD are discussed from the perturbative viewpoint. A comparison between Abelian QED and non-Abelian QCD is made at every step. The calculation of the thermodynamic potential is performed up to 2 In, allowing the masses of the fermions to be arbitrary. The equation of state for QCD plasma is obtained and the phase transition to the hadronic phase is discussed.  相似文献   
994.
Starting from a quantum state represented by its wave function (x), satisfying the Schrödinger equation, we determine stochastic processes which provide the same time evolution for the probability density(x)=¦(x2. The transition probabilities of these processes are explicitly built in two circumstances: in the general case, but in an expansion in the time difference, and exactly, but for Gaussian processes. This allows us to discuss the correspondence between quantum states and stochastic processes, which appears not to be one-to-one, but, on the contrary, to associate with the same state an infinity of processes which differ in the fluctuation correlations of the random variable.  相似文献   
995.
996.
Polymeric dicyanoketene acetals (DCKA) were synthesized by copolymerization of styrene and divinylbenzene or ethylene glycol dimethacrylate. These novel polymers could be used successfully as recyclable pi-acid catalysts in monothioacetalization or carbon-carbon bond forming reaction of acetals.  相似文献   
997.
998.
The N-linked oligosaccharides from human urinary trypsin inhibitor were purified and their structures were investigated by compositional analysis, the two-dimensional sugar map method and 500 MHz 1H-NMR. The results revealed that they were composed of disialosyl, monosialosyl and asialosyl oligosaccharides, which have the common biantennary core structure; Gal1-4GlcNAc1-2Man1-3(Gal1-4GlcNAc1-2Man1-6)M an1-4GlcNAc1-4GlcNAc.  相似文献   
999.
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, p. 1432, October, 1993.  相似文献   
1000.
The polymerization of organic compounds in glow discharge (plasma polymerization) was investigated by using pulsed R.F. discharge (100 μsec on, 900 μsec off). The effects of pulsed discharge on polymer deposition rate, pressure change in plasma, ESR signals of free spins in both plasma polymer and substrate, and the contact angle of water on the plasma polymer surface were investigated for various organic compounds. The results are correlated to the mechanisms of polymer formation in plasma (plasma polymerization) which has been postulated as repeating processes of stepwise (propagation) reactions. The effect of the pulse is different from one group of organic compounds to another depending on whether or not they contain an olefinic double bond and/or a triple bond. The main difference seems to be the addition polymerization which can occur exclusively during the off-period of pulsed discharge. Ultraviolet emission from pulsed discharge is much less than from continuous discharge. Consequently, the fragmentation of the monomer and the free-radical formation in the substrate are less with the pulsed discharge. Properties of polymers from some organic compounds formed in continuous and in pulsed discharge were found to be significantly different, and the differences were postulated from the changes of polymerization mechanisms in the pulsed discharge.  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