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   2093篇
  免费   42篇
  国内免费   18篇
化学   1423篇
晶体学   23篇
力学   45篇
数学   260篇
物理学   402篇
  2022年   17篇
  2021年   37篇
  2020年   44篇
  2019年   26篇
  2018年   18篇
  2017年   16篇
  2016年   37篇
  2015年   32篇
  2014年   24篇
  2013年   107篇
  2012年   73篇
  2011年   119篇
  2010年   79篇
  2009年   46篇
  2008年   93篇
  2007年   100篇
  2006年   98篇
  2005年   87篇
  2004年   85篇
  2003年   66篇
  2002年   71篇
  2001年   42篇
  2000年   43篇
  1999年   40篇
  1998年   17篇
  1997年   30篇
  1996年   40篇
  1995年   26篇
  1994年   22篇
  1993年   37篇
  1992年   15篇
  1991年   22篇
  1990年   27篇
  1989年   29篇
  1988年   21篇
  1987年   27篇
  1986年   21篇
  1985年   32篇
  1984年   37篇
  1983年   30篇
  1982年   31篇
  1981年   28篇
  1980年   27篇
  1979年   25篇
  1978年   20篇
  1977年   19篇
  1976年   20篇
  1975年   21篇
  1974年   13篇
  1972年   13篇
排序方式: 共有2153条查询结果,搜索用时 31 毫秒
1.
2.
Holographic sensors for monitoring ionic strength have been fabricated from charged sulphonate and quaternary ammonium monomers, incorporated into thin, polymeric hydrogel films which were transformed into volume holograms. The diffraction wavelength or reflected colour of the holograms was used to characterise their swelling or de-swelling behaviour as a function of ionic strength in various media. The effects of co-monomer structure, buffer composition, ion composition, pH and temperature were evaluated, whilst the reversibility and reproducibility of the sensor was also assessed. An acrylamide-based hologram containing equal molar amounts of negatively and positively charged monomers was shown to be able to quantify ionic strength independent of the identity of the ionic species present in the test solution. The sensor was fully reversible, free of hysteresis and exhibited little response to pH between 3 and 9 and temperature within the range 20-45 °C. The system was successfully used to quantify the ionic strength of milk solutions, which contain a complex mixture of ions and biological components.  相似文献   
3.
In the absence of gamma-ray observations from space in the eighties, interest has turned to ground-based observations in the TeV energy region. The best established sources are the Crab Nebula, Cygnus X-3 and Hercules X-1.  相似文献   
4.
Hetero‐bimetallic Fe(II) alkoxide/aryloxides were evaluated as initiators for the ring‐opening polymerization of rac‐lactide. [(THF)NaFe(OtBu)3]2 ( 1 ) and [(THF)4Na2Fe(2,6‐diisopropylphenolate)4] ( 2 ) (THF = tetrahydrofuran) both polymerized lactide efficiently at room temperature, with complex 1 affording better control over the molecular weight parameters of the resultant polymer. At conversions below 70%, a linear increase in molecular weight with conversion was observed, indicative of a well‐controlled polymerization process. Complex 2 is the first example of a dianionic Fe(II) alkoxide and has been structurally characterized to reveal a distorted square planar FeO4 array in which both Na counterions bridge two aryloxide ligands and are further complexed by two THF ligands. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3798–3803, 2003  相似文献   
5.
A special family of partitions occurs in two apparently unrelated contexts: the evaluation of one-dimensional configuration sums of certain RSOS models, and the modular representation theory of symmetric groups or their Hecke algebras Hm. We provide an explanation of this coincidence by showing how the irreducible Hm-modules which remain irreducible under restriction to Hm_1 (Jantzen–Seitz modules) can be determined from the decomposition of a tensor product of representations sln.  相似文献   
6.
7.
We demonstrate that a pair of additive quintic equations in at least 34 variables has a nontrivial integral solution, subject only to an 11-adic solubility hypothesis. This is achieved by an application of the Hardy–Littlewood method, for which we require a sharp estimate for a 33.998th moment of quintic exponential sums. We are able to employ p-adic iteration in a form that allows the estimation of such a mean value over a complete unit square, thereby providing an approach that is technically simpler than those of previous workers and flexible enough to be applied to related problems.  相似文献   
8.
9.
Abstract In [16] a visco-elastic relaxation system, called the relaxed Burnett system, was proposed by Jinand Slemrod as a moment approximation to the Boltzmann equation. The relaxed Burnett system is weaklyparabolic, has a linearly hyperbolic convection part, and is endowed with a generalized eotropy inequality. Itagrees with the solution of the Boltzmann equation up to the Burnett order via the Chapman-Enskog expansion. We develop a one-dimensional non-oscillatory numerical scheme based on the relaxed Burnett system forthe Boltzmann equation. We compare numerical results for stationary shocks based on this relaxation scheme,and those obtained by the DSMC (Direct Simulation Monte Carlo), by the Navier-Stokes equations and bythe extended thermodynamics with thirteen moments (the Grad equations). Our numerical experiments showthat the relaxed Burnett gives more accurate approximations to the shock profiles of the Boltzmann equationobtained by the DSMC, for a range of Mach numbers for hypersonic flows, th  相似文献   
10.
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