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   3130篇
  免费   127篇
  国内免费   7篇
化学   2251篇
晶体学   13篇
力学   63篇
数学   532篇
物理学   405篇
  2023年   28篇
  2022年   44篇
  2021年   56篇
  2020年   62篇
  2019年   50篇
  2018年   56篇
  2017年   37篇
  2016年   126篇
  2015年   102篇
  2014年   104篇
  2013年   205篇
  2012年   230篇
  2011年   202篇
  2010年   134篇
  2009年   90篇
  2008年   190篇
  2007年   212篇
  2006年   177篇
  2005年   162篇
  2004年   131篇
  2003年   120篇
  2002年   120篇
  2001年   49篇
  2000年   37篇
  1999年   24篇
  1998年   34篇
  1997年   35篇
  1996年   37篇
  1995年   20篇
  1994年   19篇
  1993年   23篇
  1992年   30篇
  1991年   22篇
  1990年   23篇
  1989年   17篇
  1988年   12篇
  1987年   8篇
  1986年   12篇
  1985年   20篇
  1984年   21篇
  1983年   15篇
  1982年   18篇
  1981年   18篇
  1980年   20篇
  1979年   7篇
  1978年   8篇
  1977年   13篇
  1976年   9篇
  1974年   8篇
  1934年   11篇
排序方式: 共有3264条查询结果,搜索用时 0 毫秒
1.
2.
Central European Journal of Operations Research - In the past years, the number of patients in need of chemotherapy treatments has been constantly increasing. Chemotherapy treatments must be...  相似文献   
3.
4.
Sensitivity-enhanced 2D IPAP experiments using the accordion principle for measuring one-bond 13C'-13Calpha and 1Halpha-13Calpha dipolar couplings in proteins are presented. The resolution of the resulting spectra is identical to that of the decoupled HSQC spectra and the sensitivity of the corresponding 1D acquisitions are only slightly lower than those obtained with 3D HNCO and 3D HN(COCA)HA pulse sequences due to an additional delay 2Delta. For cases of limited resolution in the 2D 15N-1HN HSQC spectrum the current pulse sequences can easily be modified into 3D versions by introducing a poorly digitized third dimension, if so desired. The experiments described here are a valuable addition to the suites available for determination of residual dipolar couplings in biological systems.  相似文献   
5.
Pentacyclic isoxazolines were obtained by the cycloaddition of benzonitrile oxide to norbornene-azetidinone-fused 3,1-oxazines. The constitutions of two of the isomers obtained, and the configurations and conformations of all products, were determined by means of 1H and 13C NMR spectroscopy and DNOE experiments.  相似文献   
6.
We present a new generic problem solving approach for over-constrained problems based on Max-SAT. We first define a Boolean clausal form formalism, called soft CNF formulas, that deals with blocks of clauses instead of individual clauses, and that allows one to declare each block either as hard (i.e., must be satisfied by any solution) or soft (i.e., can be violated by some solution). We then present two Max-SAT solvers that find a truth assignment that satisfies all the hard blocks of clauses and the maximum number of soft blocks of clauses. Our solvers are branch and bound algorithms equipped with original lazy data structures, powerful inference techniques, good quality lower bounds, and original variable selection heuristics. Finally, we report an experimental investigation on a representative sample of instances (random 2-SAT, Max-CSP, graph coloring, pigeon hole and quasigroup completion) which provides experimental evidence that our approach is very competitive compared with the state-of-the-art approaches developed in the CSP and SAT communities. Research partially supported by projects TIN2004-07933-C03-03 and TIC2003-00950 funded by the Ministerio de Educación y Ciencia. The second author is supported by a grant Ramón y Cajal.  相似文献   
7.
8.
9.
Summary. We introduce linear semi-implicit complementary volume numerical scheme for solving level set like nonlinear degenerate diffusion equations arising in image processing and curve evolution problems. We study discretization of image selective smoothing equation of mean curvature flow type given by Alvarez, Lions and Morel ([3]). Solution of the level set equation of Osher and Sethian ([26], \[30]) is also included in the study. We prove and estimates for the proposed scheme and give existence of its (generalized) solution in every discrete time-scale step. Efficiency of the scheme is given by its linearity and stability. Preconditioned iterative solvers are used for computing arising linear systems. We present computational results related to image processing and plane curve evolution. Received April 25, 2000 / Revised version received June 11, 2001 / Published online November 15, 2001  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