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   163698篇
  免费   1831篇
  国内免费   386篇
化学   90012篇
晶体学   2093篇
力学   6843篇
综合类   7篇
数学   16904篇
物理学   50056篇
  2020年   1291篇
  2019年   1353篇
  2018年   1585篇
  2017年   1568篇
  2016年   2859篇
  2015年   1947篇
  2014年   2853篇
  2013年   7131篇
  2012年   5832篇
  2011年   7036篇
  2010年   4764篇
  2009年   4649篇
  2008年   6436篇
  2007年   6467篇
  2006年   6106篇
  2005年   5631篇
  2004年   4931篇
  2003年   4295篇
  2002年   4274篇
  2001年   4478篇
  2000年   3463篇
  1999年   2658篇
  1998年   2303篇
  1997年   2254篇
  1996年   2082篇
  1995年   1967篇
  1994年   1943篇
  1993年   1806篇
  1992年   2054篇
  1991年   2162篇
  1990年   1963篇
  1989年   1953篇
  1988年   1893篇
  1987年   1792篇
  1986年   1749篇
  1985年   2274篇
  1984年   2389篇
  1983年   1933篇
  1982年   2133篇
  1981年   2017篇
  1980年   1946篇
  1979年   2077篇
  1978年   2248篇
  1977年   2105篇
  1976年   2158篇
  1975年   2046篇
  1974年   2097篇
  1973年   2085篇
  1972年   1363篇
  1971年   1218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