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   152835篇
  免费   1351篇
  国内免费   384篇
化学   82029篇
晶体学   2028篇
力学   6660篇
综合类   7篇
数学   15320篇
物理学   48526篇
  2020年   1120篇
  2019年   1173篇
  2018年   1480篇
  2017年   1453篇
  2016年   2479篇
  2015年   1551篇
  2014年   2429篇
  2013年   6332篇
  2012年   4941篇
  2011年   6269篇
  2010年   4281篇
  2009年   4292篇
  2008年   5693篇
  2007年   5767篇
  2006年   5406篇
  2005年   4995篇
  2004年   4412篇
  2003年   3853篇
  2002年   3883篇
  2001年   4333篇
  2000年   3318篇
  1999年   2572篇
  1998年   2243篇
  1997年   2184篇
  1996年   1981篇
  1995年   1898篇
  1994年   1886篇
  1993年   1726篇
  1992年   1992篇
  1991年   2120篇
  1990年   1918篇
  1989年   1916篇
  1988年   1856篇
  1987年   1755篇
  1986年   1693篇
  1985年   2192篇
  1984年   2324篇
  1983年   1897篇
  1982年   2078篇
  1981年   1964篇
  1980年   1888篇
  1979年   2029篇
  1978年   2197篇
  1977年   2067篇
  1976年   2113篇
  1975年   2019篇
  1974年   2072篇
  1973年   2060篇
  1972年   1354篇
  1971年   1210篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A modified criterion of the SM perturbative consistency is proposed. It is based on the analytic properties of the two-loop SM running couplings. Under the criterion adopted, the Higgs mass up to 380 GeV might not give rise to strong coupling prior to the Planck scale. This means that the light Higgs boson is possibly preferred for reasons other than the SM perturbative consistency, i.e., for reasons beyond the SM.  相似文献   
102.
The resonance neutron self-shielding factor, G res, is required in neutron metrology and activation data analysis. In a previous paper, the authors have shown that a dimensionless variable can be introduced which converts the dependence of G res on the physical and nuclear properties of the material samples into an universal curve, valid for the isolated resonances of any nuclide. This work presents a methodology based on the universal curve, which enables to calculate G res for a group of isolated resonances by weighting its individual contributions. A good agreement was reached with results calculated by the MCNP code and with experimental values for Mo foils and wires. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
103.
Microscopic petrified grains were collected from a mafic–ultramafic pipe, NE of Dreikeesh, NW Syria. The grains were identified as anthers/gynoecia in herb/grass flowers. Three of the grains showed evidence of magnetism, two slowly dissolved in concentrated HCl, and three microprobed grains showed a montmorillonitic composition. Iron originating from pyroxene was oxidized to magnetite. Released silica formed the mineral suite agate–chalcedony–opal. Warm/cold paleoclimatic fluctuations, occurring during late Pliocene–Holocene, depended on water vapor, CO2 production, and cinders in the atmosphere. Most of these were associated with changing volcanic/tectonic events. Fluctuations were controlled by heat reflected from the Earth's surface being absorbed by water vapor and CO2, which both re-reflected the heat back to the surface, thus, raising the temperature. This cycle was repeated several times during late Pliocene–Holocene.  相似文献   
104.
105.
The frequency or dispersion relation for the least‐squares mixed formulation of the shallow‐water equations is analysed. We consider the use of different approximation spaces corresponding to co‐located and staggered meshes, respectively. The study includes the effect of Coriolis, and the dispersion properties are compared analytically and graphically with those of the mixed Galerkin formulation. Numerical solutions of a test problem to simulate slow Rossby modes illustrate the theoretical results. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
106.
The basis of the two‐step in–in method is as follows: star polymers with poly(divinyl benzene) cores, synthesized by the arm‐first method, include many unreacted double bonds in their core, and these double bonds can be attacked by the carbanions of some monomers such as styrene and dienes. In this work, linear polyisoprene chains were used to attack the double bonds existing in the poly(divinyl benzene) cores of polystyrene star polymers, so that a heteroarm star polymer with polystyrene and polyisoprene arms was synthesized. It was later well characterized with size exclusion chromatography, light scattering, viscometry, UV spectroscopy, dynamic mechanical thermal analysis, and 1H NMR. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 135–142, 2003  相似文献   
107.
The influence of single- and double-charged cations on degradation of metal 2-acrylamido-2-methylpropanesulfonate-N-vinylpyrrolidine copolymers in aqueous solutions in the presence of potassium peroxodisulfate, K2S2O8, at 50 and 70°C was studied by viscosimetry.  相似文献   
108.
The features of anthracite oxidation as influenced by temperature and time were determined. Physicochemical and sorption characteristics of the resulting cation exchanger were studied.  相似文献   
109.
It is shown that CT (compact tension) specimens known from fracture mechanics are adequate to study the strength of interfaces between polymers. The interface is coplanar with the initial notch. The capability of this method is demonstrated by quantifying: (a) the healing procedure of cracks in polystyrene; (b) by elaborating the influence of powders on the welding process in polystyrene; (c) by measuring the strength of interfaces between the different polymers SAN, PMMA, HIPS, PS, PC, and (d) by characterising the influence of a compatibilizer in the interface between PE and HIPS.  相似文献   
110.
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