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   20579篇
  免费   662篇
  国内免费   102篇
化学   13271篇
晶体学   92篇
力学   485篇
综合类   2篇
数学   3900篇
物理学   3593篇
  2023年   122篇
  2022年   116篇
  2021年   394篇
  2020年   372篇
  2019年   340篇
  2018年   741篇
  2017年   508篇
  2016年   612篇
  2015年   541篇
  2014年   555篇
  2013年   1152篇
  2012年   1226篇
  2011年   1307篇
  2010年   853篇
  2009年   756篇
  2008年   1216篇
  2007年   1161篇
  2006年   1082篇
  2005年   1011篇
  2004年   806篇
  2003年   748篇
  2002年   637篇
  2001年   372篇
  2000年   423篇
  1999年   250篇
  1998年   230篇
  1997年   211篇
  1996年   258篇
  1995年   162篇
  1994年   165篇
  1993年   153篇
  1992年   157篇
  1991年   130篇
  1990年   139篇
  1989年   115篇
  1988年   113篇
  1987年   95篇
  1986年   98篇
  1985年   133篇
  1984年   165篇
  1983年   106篇
  1982年   119篇
  1981年   124篇
  1980年   103篇
  1979年   80篇
  1978年   108篇
  1977年   89篇
  1976年   104篇
  1975年   83篇
  1973年   64篇
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
61.
We investigate the basic properties of the different socles that can be considered in not necessarily semiprime associative systems. Among other things, we show that the socle defined as the sum of minimal (or minimal and trivial) inner ideals is always an ideal. When trivial inner ideals are included, this inner socle contains the socles defined in terms of minimal left or right ideals. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
62.
The following generalization of the Hahn-Mazurkiewicz theorem is proved: Let (E,e) be a locally compact locally connected metric space. Let M be a continuum in this space and let d,e∈ M. Then there is a continuous mapping f: [0,1]→E such that f(0) = d, f(1)= e and M⊂f([0,1]). Also some corollaries of this theorem are proved.  相似文献   
63.
We consider a family of spaces wider than r-UNC spaces and we give some fixed point results in the setting of these spaces.  相似文献   
64.
We prove that for damped hyperbolic equations the Morse-Smale property (hyperbolicity of equilibria and transversal intersection of stable and unstable manifolds) is generic. More precisely, we prove that in an appropriate functional space of nonlinear terms in the equation, the set of functions for which the latter has the Morse-Smale property is residual, i.e., it is a countable intersection of open dense sets. The result extends a similar result proved in [1] for reaction diffusion equations. However, because of the absence of knowledge about nodal sets of polutions new ideas were needed in the proof.  相似文献   
65.
We derive the incompressible and compressible kε model for locally homogeneous turbulence. The model is rigorously derived on formal mathematical grounds using the MPP modelling technique. This lets us calculate by either analytical or numerical means the closure constants of the model. To cite this article: T. Chacón Rebollo, D. Franco Coronil, C. R. Acad. Sci. Paris, Ser. I 337 (2003).  相似文献   
66.
In this paper, we investigate symplectic manifolds endowed with a Morse–Bott function with only two critical submanifolds, one of which is Lagrangian while the other one is symplectic.  相似文献   
67.
Hydrogels of N‐vinylimidazole (VI) and sodium styrenesulfonate (SSS) were synthesized in aqueous solution by radical crosslinking copolymerization with N,N′‐methylene‐bis(acrylamide) as crosslinker. Swelling in several saline solutions was measured for hydrogel samples synthesized with different comonomer concentrations (CT = 10, 25, or 40%) and with SSS mole fractions covering a broad range (fSSS = 0–0.7), while the crosslinker ratio was 2 wt % in all cases. The degree of swelling in aqueous solution with a specific ionic strength (μ), plotted versus the SSS composition of the feed, shows a minimum for any set of samples synthesized with a fixed CT. The dependence of swelling on μ shows both polyelectrolyte (fSSS beyond the minimum) and antipolyelectrolyte behaviors (in the low fSSS limit). It was found that the nonGaussian factor of the crosslinking density and the polymer‐solvent interaction parameter increase with fSSS for any CT. Moreover, in the low fSSS limit, the osmotic swelling pressure is governed not only by the ionic contribution, but also by the polymer‐solvent mixing and, the concentration of mobile counterions inside the gel is not proportional to the net fixed charge but to the addition of cationic and anionic side groups, what discards the formation of ionic pairs. The antipolyelectrolyte effect is interpreted as due to the increasing protonation of VI as μ goes up. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1683–1693, 2007  相似文献   
68.
Details are given of a new method allowing an exact calculation of the spontaneous magnetization in the corner as well as along the edge at an arbitrary distance of the corner for a rectangular planar Ising ferromagnet.  相似文献   
69.
This document presents theoretical considerations about the solution of dynamic optimization problems integrating the Benders Theory, the Dynamic Programming approach and the concepts of Control Theory. The so called Generalized Dual Dynamic Programming Theory (GDDP) can be considered as an extension of two previous approaches known as Dual Dynamic Programming (DDP): The first is the work developed by Pereira and Pinto [3–5], which was revised by Velásquez and others [8,9]. The second is the work developed by Read and others [2,6,7].  相似文献   
70.
The n-dimensional cube Qn is the graph whose vertices are the subsets of {1,…n}, with two vertices adjacent if and only if their symmetric difference is a singleton. Clearly Qn has diameter and radious n. Write M = n2n-1 = e(Qn) for the size of Qn. Let Q = (Qt)oM be a random Qn-process. Thus Qt is a spanning subgraph of Qn of size t, and Qt is obtained from Qt–1 by the random addition of an edge of Qn not in Qt–1, Let t(k) = τ(Q;δ?k) be the hitting time of the property of having minimal degree at least k. We show that the diameter dt = diam (Qt) of Qt in almost every Q? behaves as follows: dt starts infinite and is first finite at time t(1), it equals n + 1 for t(1) ? t(2) and dt, = n for t ? t(2). We also show that the radius of Qt, is first finite for t = t(1), when it assumes the value n. These results are deduced from detailed theorems concerning the diameter and radius of the almost surely unique largest component of Qt, for t = Ω(M). © 1994 John Wiley & Sons, Inc.  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