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   7848篇
  免费   260篇
  国内免费   61篇
化学   5190篇
晶体学   41篇
力学   277篇
数学   1593篇
物理学   1068篇
  2023年   47篇
  2022年   50篇
  2021年   187篇
  2020年   155篇
  2019年   162篇
  2018年   139篇
  2017年   114篇
  2016年   276篇
  2015年   234篇
  2014年   240篇
  2013年   443篇
  2012年   530篇
  2011年   594篇
  2010年   361篇
  2009年   352篇
  2008年   517篇
  2007年   485篇
  2006年   486篇
  2005年   411篇
  2004年   352篇
  2003年   279篇
  2002年   292篇
  2001年   99篇
  2000年   73篇
  1999年   67篇
  1998年   79篇
  1997年   82篇
  1996年   91篇
  1995年   54篇
  1994年   74篇
  1993年   53篇
  1992年   52篇
  1991年   41篇
  1990年   53篇
  1989年   47篇
  1988年   39篇
  1987年   40篇
  1986年   29篇
  1985年   44篇
  1984年   61篇
  1983年   39篇
  1982年   45篇
  1981年   31篇
  1980年   40篇
  1979年   29篇
  1978年   30篇
  1977年   27篇
  1976年   14篇
  1974年   15篇
  1973年   14篇
排序方式: 共有8169条查询结果,搜索用时 15 毫秒
11.
This paper deals with the Cauchy–Dirichlet problem for the fractional Cahn–Hilliard equation. The main results consist of global (in time) existence of weak solutions, characterization of parabolic smoothing effects (implying under proper condition eventual boundedness of trajectories), and convergence of each solution to a (single) equilibrium. In particular, to prove the convergence result, a variant of the so-called ?ojasiewicz–Simon inequality is provided for the fractional Dirichlet Laplacian and (possibly) non-analytic (but C1) nonlinearities.  相似文献   
12.
13.
14.
In this paper the influence on sound reduction index of the length and the depth of sound leaks at the perimeter of lightweight partitions was examined. It was shown that the most important decrease on sound reduction index is caused by the first slit between lightweight partition and one of the structural members. When the length of the slit is increased, the decrease on sound reduction index is less significative. Calculated results show the same effects as measured ones.  相似文献   
15.
Palladium-containing zeolites catalyze the cycloisomerization of diethyl diallylmalonate to dimethylcyclopentenes. When the reaction is carried out in toluene, the performance of the palladium catalyst depends on the pore size of the zeolites. At 60 °C, palladium adsorbed on large pore size Beta zeolite (pore size ∼7.4 Å) is more active than medium pore size ZSM-5 (pore size ∼5.4 Å). This lower activity of ZSM-5 compared to Beta is attributable to the restricted diffusion of reagent and products through the ZSM-5 channels as compared to Beta zeolite. However, due to the gas-like diffusion characteristic of the supercritical state, the activity of ZSM-5 increases and becomes identical to that of Beta zeolite using supercritical CO2 as medium.  相似文献   
16.
17.
Dynamic stage repair policies where the stage repair probabilities are determined by the number of items in the buffer are examined through a model of a manufacturing system with two unreliable workstages connected by a minimal intermediate storage buffer. Definitions for workstage availability and line balance are extended for sequential manufacturing systems with dynamic repair policies. A measure for stage repair inputs and a general form of dynamic stage repair policies are presented. The steady-state probabilities of the resultant state-inhomogeneous Markov chain are computed by an efficient solution procedure. Insights obtained from extensive numerical studies are illustrated and discussed.  相似文献   
18.
The first method for the synthesis of the title compounds has been established involving a stereoselective electrochemical diacylation process. The cathodic reductions of monothiobenzils in an aprotic medium, under constant potential, in the presence of twofold molecular amounts of aroyl chlorides provide previously unknown (Z)-α-benzoyloxy-β-benzoythiostilbenes in high to quantitative yields.  相似文献   
19.
This work aimed at modeling chromium biosorption using the biomass of seaweed Sargassum sp. in a fixed-bed column. The mathematical model used was obtained from the mass balance of the component in the liquid phase and in the biosorbent material. The effects of both axial dispersion in the column and the resistance to mass transfer in the solid were considered for the solution of the partial differential equations of the model, using the Galerkin method on finite elements. To represent the equilibrium data of the batch system the Langmuir isotherm were used. The chromium ion adsorption capacity of the seaweed Sargassum sp., at a temperature of 30°C and pH 3.5, was 2.61 mmol/g. The model performance was evaluated from experimental data obtained at 30°C for flow rates of 2, 6 and 8 mL/min. The parameters of the model, mass transfer and axial dispersion coefficients, were adjusted from these experimental data. The model proved adequate to describe chromium biosorption dynamics in fixed-bed columns.  相似文献   
20.
A partnership in a cooperative game is a coalition that possesses an internal structure and, simultaneously, behaves as an individual member. Forming partnerships leads to a modification of the original game which differs from the quotient game that arises when one or more coalitions are actually formed. In this paper, the Shapley value is used to discuss the convenience to form either coalitions or partnerships. To this end, the difference between the additive Shapley value of the partnership in the partnership game and the Shapley alliance value of the coalition, and also between the corresponding value of the internal and external players, are analysed. Simple games are especially considered. Research partially supported by Grant BFM 2003-01314 of the Science and Technology Spanish Ministry and the European Regional Development Fund.  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