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   22165篇
  免费   1075篇
  国内免费   1459篇
化学   16398篇
晶体学   232篇
力学   540篇
综合类   12篇
数学   3327篇
物理学   4190篇
  2023年   147篇
  2022年   439篇
  2021年   534篇
  2020年   408篇
  2019年   456篇
  2018年   475篇
  2017年   451篇
  2016年   853篇
  2015年   693篇
  2014年   824篇
  2013年   1869篇
  2012年   1679篇
  2011年   1814篇
  2010年   1134篇
  2009年   1276篇
  2008年   1340篇
  2007年   1277篇
  2006年   1046篇
  2005年   1016篇
  2004年   1277篇
  2003年   920篇
  2002年   845篇
  2001年   435篇
  2000年   351篇
  1999年   267篇
  1998年   248篇
  1997年   218篇
  1996年   230篇
  1995年   186篇
  1994年   139篇
  1993年   162篇
  1992年   134篇
  1991年   92篇
  1990年   100篇
  1989年   87篇
  1988年   81篇
  1987年   73篇
  1986年   82篇
  1985年   121篇
  1984年   121篇
  1983年   88篇
  1982年   80篇
  1981年   88篇
  1980年   68篇
  1979年   50篇
  1978年   39篇
  1977年   46篇
  1976年   44篇
  1975年   33篇
  1974年   46篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The article referenced above was first published online on 30 August 2007 with incorrect pagination; the pagination has now been corrected online and in print. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
52.
This paper deals with modelling the workpiece temperature field produced during the grinding process. The proposed model is given in terms of a two-dimensional boundary-value problem where the interdependence among the grinding wheel, the workpiece and the coolant is described by two variable functions in the boundary condition. An explicit integral form solution is constructed using the Laplace and Fourier transforms and the Green’s function method.  相似文献   
53.

Background  

The aim of the present study was to characterize the activation profiles of 15 opioid ligands in transfected human embryonic kidney cells expressing only δ opioid receptors. Activation profiles of most of these ligands at δ opioid receptors had not been previously characterized in vitro. Receptor activation was assessed by measuring the inhibition of forskolin-stimulated cAMP production.  相似文献   
54.
In the present work, the effect of the oxidizing treatment with nitric acid on three activated carbon samples has been studied. The influence of the acid treatment on the surface groups of the different samples has been investigated by means of FT-IR spectroscopy. The pore size distributions of the different samples were determined by means of the HK and DFT methods. The HK method points out a moderate increment of the microporosity due to the action of the nitric acid, whereas the DFT method shows an increase in the microporosity range above 17 Å. Finally, the values of the fractal dimension reveal that the treatment of the samples with nitric acid leads to chemical reactions of a limited extent.  相似文献   
55.
56.
We define a multifunction F: XY to be upper (lower) D*-supercontinuous if F +(V) (F (V)) is d*-open in X for every open set V of Y. We obtain some characterizations and several properties concerning upper (lower) D*-supercontinuous multifunctions.   相似文献   
57.
Some curvature conditions about the geodesics emanating from a submanifold are obtained. These conditions are used to to study the topological and geometric properties of the ambient spaces which admit some minimal submanifolds.  相似文献   
58.
The properties of cosmic rays with energies above 106 GeV have to be deduced from the spacetime structure and particle content of the air showers which they initiate. In this review we summarize the phenomenology of these giant air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra high energies, and discuss the prospects for insights into forward physics at the LHC. We also describe the main electromagnetic processes that govern the longitudinal shower evolution, as well as the lateral spread of particles. Armed with these two principal shower ingredients and motivation from the underlying physics, we provide an overview of some of the different methods proposed to distinguish primary species. The properties of neutrino interactions and the potential of forthcoming experiments to isolate deeply penetrating showers from baryonic cascades are also discussed. We finally venture into a terra incognita endowed with TeV-scale gravity and explore anomalous neutrino-induced showers.  相似文献   
59.
In this article we analyze the effect of mass‐lumping in the linear triangular finite element approximation of second‐order elliptic eigenvalue problems. We prove that the eigenvalue obtained by using mass‐lumping is always below the one obtained with exact integration. For singular eigenfunctions, as those arising in non convex polygons, we prove that the eigenvalue obtained with mass‐lumping is above the exact eigenvalue when the mesh size is small enough. So, we conclude that the use of mass‐lumping is convenient in the singular case. When the eigenfunction is smooth several numerical experiments suggest that the eigenvalue computed with mass‐lumping is below the exact one if the mesh is not too coarse. © 2003 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 19: 653–664, 2003  相似文献   
60.
We show that the tensor product B-spline basis and the triangular Bernstein basis are in some sense best conditioned among all nonnegative bases for the spaces of tensor product splines and multivariate polynomials, respectively. We also introduce some new condition numbers which are analogs of component-wise condition numbers for linear systems introduced by Skeel.  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