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   109331篇
  免费   12257篇
  国内免费   8755篇
化学   37323篇
晶体学   1306篇
力学   16002篇
综合类   1802篇
数学   38055篇
物理学   35855篇
  2024年   217篇
  2023年   1020篇
  2022年   2977篇
  2021年   2999篇
  2020年   2700篇
  2019年   2604篇
  2018年   2412篇
  2017年   3047篇
  2016年   3509篇
  2015年   3022篇
  2014年   4846篇
  2013年   7331篇
  2012年   5383篇
  2011年   6379篇
  2010年   5603篇
  2009年   6695篇
  2008年   6683篇
  2007年   6856篇
  2006年   6039篇
  2005年   4954篇
  2004年   4374篇
  2003年   4179篇
  2002年   6353篇
  2001年   3718篇
  2000年   3051篇
  1999年   2748篇
  1998年   2521篇
  1997年   2075篇
  1996年   1845篇
  1995年   1519篇
  1994年   1382篇
  1993年   1243篇
  1992年   1275篇
  1991年   877篇
  1990年   752篇
  1989年   624篇
  1988年   555篇
  1987年   439篇
  1986年   376篇
  1985年   550篇
  1984年   445篇
  1983年   277篇
  1982年   454篇
  1981年   583篇
  1980年   524篇
  1979年   590篇
  1978年   451篇
  1977年   365篇
  1976年   288篇
  1973年   209篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results.  相似文献   
3.
High-energy assisted extraction techniques, like ultrasound assisted extraction (UAE) and microwave assisted extraction (MAE), are widely applied over the last years for the recovery of bioactive compounds such as carotenoids, antioxidants and phenols from foods, animals and herbal natural sources. Especially for the case of xanthophylls, the main carotenoid group of crustaceans, they can be extracted in a rapid and quantitative way with the use of UAE and MAE.  相似文献   
4.
5.
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557  相似文献   
6.
We give a sheaf theoretic interpretation of Potts models with external magnetic field, in terms of constructible sheaves and their Euler characteristics. We show that the polynomial countability question for the hypersurfaces defined by the vanishing of the partition function is affected by changes in the magnetic field: elementary examples suffice to see non-polynomially countable cases that become polynomially countable after a perturbation of the magnetic field. The same recursive formula for the Grothendieck classes, under edge-doubling operations, holds as in the case without magnetic field, but the closed formulae for specific examples like banana graphs differ in the presence of magnetic field. We give examples of computation of the Euler characteristic with compact support, for the set of real zeros, and find a similar exponential growth with the size of the graph. This can be viewed as a measure of topological and algorithmic complexity. We also consider the computational complexity question for evaluations of the polynomial, and show both tractable and NP-hard examples, using dynamic programming.  相似文献   
7.
8.
采用DIS数字信息化系统,对不同浓度的蓝墨水溶液在激光光源照射下的透射平均照度及照度分布图像进行实验研究,得到了平均照度值随溶液浓度变化的规律。对不同颜色塑料膜片对白炽灯光源透过照度值及照度分布图像进行实验研究得到及其相关之规律。  相似文献   
9.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point.  相似文献   
10.
In this paper we study constant mean curvature compact surfaces with two Jordan curves in parallel planes as boundary and we investigate the point at which the surface inherits the symmetries of its boundary.  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