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   24908篇
  免费   814篇
  国内免费   123篇
化学   16363篇
晶体学   138篇
力学   613篇
综合类   2篇
数学   4436篇
物理学   4293篇
  2023年   142篇
  2022年   129篇
  2021年   395篇
  2020年   430篇
  2019年   409篇
  2018年   780篇
  2017年   549篇
  2016年   728篇
  2015年   620篇
  2014年   668篇
  2013年   1373篇
  2012年   1501篇
  2011年   1638篇
  2010年   1034篇
  2009年   897篇
  2008年   1484篇
  2007年   1448篇
  2006年   1378篇
  2005年   1271篇
  2004年   1027篇
  2003年   937篇
  2002年   778篇
  2001年   381篇
  2000年   412篇
  1999年   236篇
  1998年   219篇
  1997年   236篇
  1996年   311篇
  1995年   197篇
  1994年   208篇
  1993年   192篇
  1992年   179篇
  1991年   167篇
  1990年   177篇
  1989年   147篇
  1988年   151篇
  1987年   118篇
  1986年   125篇
  1985年   190篇
  1984年   224篇
  1983年   138篇
  1982年   181篇
  1981年   184篇
  1980年   157篇
  1979年   123篇
  1978年   160篇
  1977年   135篇
  1976年   140篇
  1975年   122篇
  1973年   99篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
1.
Fuzzy Optimization and Decision Making - Cost-allocation problems in a fixed network are concerned with distributing the costs for use by a group of clients who cooperate in order to reduce such...  相似文献   
2.
3.
Mathematical Programming - Let G be a digraph where every node has preferences over its incoming edges. The preferences of a node extend naturally to preferences over branchings, i.e., directed...  相似文献   
4.
Journal of Analytical Chemistry - The present development involved a flow injection strategy using a mini-column of multiwalled carbon nanotubes and fluorescent detection (λex of 283 nm,...  相似文献   
5.
A CE instrument that can be assembled from commercially available components with minimal construction effort is described. Except for the electronic control circuitry no specially made parts are required. It is based on a flexible design of microfluidic, electropneumatic, and electronic sections and different configurations can easily be implemented. Automated injection into the capillary is performed hydrodynamically by the application of a pressure for a controlled length of time. The performance of the device was tested with a contactless conductivity detector by separating different metal ions. In addition, nine metal cations related to the quality of honey were separated in 2.3 min and four honey samples were analysed quantitatively to demonstrate the applicability of the method.  相似文献   
6.
Motivated by the sizable increase of available computing resources, large-eddy simulation of complex turbulent flow is becoming increasingly popular. The underlying filtering operation of this approach enables to represent only large-scale motions. However, the small-scale fluctuations and their effects on the resolved flow field require additional modeling. As a consequence, the assumptions made in the closure formulations become potential sources of incertitude that can impact the quantities of interest. The objective of this work is to introduce a framework for the systematic estimation of structural uncertainty in large-eddy simulation closures. In particular, the methodology proposed is independent of the initial model form, computationally efficient, and suitable to general flow solvers. The approach is based on introducing controlled perturbations to the turbulent stress tensor in terms of magnitude, shape and orientation, such that propagation of their effects can be assessed. The framework is rigorously described, and physically plausible bounds for the perturbations are proposed. As a means to test its performance, a comprehensive set of numerical experiments are reported for which physical interpretation of the deviations in the quantities of interest are discussed.  相似文献   
7.
A new family of distorted ribbon-shaped nanographenes was designed, synthesized, and their optical and electrochemical properties were evaluated, pointing out an unprecedented correlation between their structural characteristics and the two-photon absorption (TPA) responses and electrochemical band gaps. Three nanographene ribbons have been prepared: a seven-membered-ring-containing nanographene presenting a tropone moiety at the edge, its full-carbon analogue, and a purely hexagonal one. We have found that the TPA cross-sections and the electrochemical band gaps of the seven-membered-ring-containing compounds are higher and lower, respectively, than those of the fully hexagonal polycyclic aromatic hydrocarbon (PAH). Interestingly, the inclusion of additional curvature has a positive effect in terms of non-linear optical properties of those ribbons.  相似文献   
8.
9.
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