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   22652篇
  免费   812篇
  国内免费   23篇
化学   14931篇
晶体学   163篇
力学   367篇
数学   3867篇
物理学   4159篇
  2023年   145篇
  2022年   127篇
  2021年   255篇
  2020年   331篇
  2019年   346篇
  2018年   457篇
  2017年   409篇
  2016年   841篇
  2015年   660篇
  2014年   689篇
  2013年   1457篇
  2012年   1434篇
  2011年   1454篇
  2010年   879篇
  2009年   822篇
  2008年   1271篇
  2007年   1318篇
  2006年   1184篇
  2005年   1085篇
  2004年   981篇
  2003年   763篇
  2002年   658篇
  2001年   519篇
  2000年   468篇
  1999年   361篇
  1998年   242篇
  1997年   232篇
  1996年   305篇
  1995年   219篇
  1994年   237篇
  1993年   200篇
  1992年   192篇
  1991年   179篇
  1990年   181篇
  1989年   154篇
  1988年   143篇
  1987年   136篇
  1986年   135篇
  1985年   193篇
  1984年   196篇
  1983年   126篇
  1982年   129篇
  1981年   143篇
  1980年   138篇
  1979年   95篇
  1978年   96篇
  1977年   103篇
  1976年   84篇
  1975年   88篇
  1973年   71篇
排序方式: 共有10000条查询结果,搜索用时 115 毫秒
31.
In this paper, an MILP formulation is proposed for the design of a reverse logistics network based on a warehouse location–allocation model, which optimizes, simultaneously, the forward and reverse networks. A single product model with unlimited capacity is first defined. Subsequently, the model is extended to a multi-product capacitated recovery network model, where capacity limitations and a multi-product system can be considered. The proposed model is compared to published work in the field, where different model assumptions have been proposed. Two cases are described so as to gain a better insight into the model and allow a comparative analysis.  相似文献   
32.
On some convexities   总被引:3,自引:0,他引:3  
  相似文献   
33.
Regioselective demethylation of 3,4-dihydropapaveraldine (2a) at 7 and 3' positions affords a properly substituted diphenolic key intermidiate (2d) for the synthesis of reticuline and N-norreticuline.  相似文献   
34.
The extents of the protective effects of coating films on the surface of crystals were determined. Three different samples were made with different quantities of coating fluid (Sepifilm LP 010 in 10% aqueous solution). Since the atomizing rate was constant, the coating time increased in parallel with the volume of coating fluid applied. The direct measurement of film thickness and smoothness is very difficult, and therefore indirect methods were used. Dimenhydrinate was chosen as model drug; this is a heat-sensitive antihistamine with a low melting point. This temperature can be reached during the tableting process. The behaviour of samples on exposure to heat was examined by differential scanning calorimetry. The water uptakes of the samples were determined with an Enslin apparatus. Plasticity was studied with an instrumented tablet machine. These indirect methods (thermal conductivity, water uptake and plasticity measurements) revealed connections between the results of the various experiments. An overlong coating time decreased the protective effect of the coating film. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
35.
In the present Note we introduce an extension of the conservative space–time mesh refinement method presented by Fouquet et al. We also propose a post-treatment of the solution that reduces the spurious phenomena due to the non-conformity between the time meshes. A reinterpretation of the equations in terms of new unknowns leads to a new scheme with second order consistent coupling equations. Numerical experiments in 2D and a plane wave analysis for the 1D model show that the method is second order accurate for an arbitrary refinement. To cite this article: J. Rodríguez, C. R. Acad. Sci. Paris, Ser. I 339 (2004).  相似文献   
36.
Sauer, Shelah, Vapnik and Chervonenkis proved that if a set system on n vertices contains many sets, then the set system has full trace on a large set. Although the restriction on the size of the groundset cannot be lifted, Frankl and Pach found a trace structure that is guaranteed to occur in uniform set systems even if we do not bound the size of the groundset. In this note we shall give three sequences of structures such that every set system consisting of sufficiently many sets contains at least one of these structures with many sets.  相似文献   
37.
The distribution of mono- poly- and unlabelled protein molecules in the radiolabelling mixture was calculated from probability point of view as a function of the radioiodine/protein ratio.  相似文献   
38.
In order to study the influence of seeded impurities on ITER like reactor operation the COREDIV code has been extended to include the transport of several sputtered and/or injected impurities. In the COREDIV code the core plasma is treated in the frame of 1D radial transport model whereas in the edge the 2D multifluid code EPIT is used. The EPIT code solves in the slab geometry the MHD equations for densities and velocities for all ions species as well as for electron and ion temperatures. The iteration scheme in the code leads to steady state solution of coupled core and SOL system. The numerical results for Carbon and Nickel plate and seeded impurities Silicon and Neon are presented.  相似文献   
39.
Ohne Zusammenfassung Die mitgeteilten Untersuchungen haben wir mit Unterstützung der Ungarischen wissenschaftlichen „Széchenyi“-Gesellschaft durchgeführt.  相似文献   
40.
Summary This article provides a glimpse of some of the highlights of the joint work of Endre Csáki and Pál Révész since 1979. The topics of this short exploration of the rich stochastic milieu of this inspiring collaboration revolve around Brownian motion, random walks and their long excursions, local times and additive functionals, iterated processes, almost sure local and global central limit theorems, integral functionals of geometric stochastic processes, favourite sites--favourite values and jump sizes for random walk and Brownian motion, random walking in a random scenery, and large void zones and occupation times for coalescing random walks.  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