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   27860篇
  免费   1288篇
  国内免费   1023篇
化学   22871篇
晶体学   3篇
力学   279篇
综合类   240篇
数学   6374篇
物理学   404篇
  2024年   12篇
  2023年   260篇
  2022年   424篇
  2021年   354篇
  2020年   520篇
  2019年   583篇
  2018年   585篇
  2017年   803篇
  2016年   872篇
  2015年   792篇
  2014年   830篇
  2013年   1286篇
  2012年   1576篇
  2011年   1443篇
  2010年   1208篇
  2009年   1545篇
  2008年   1098篇
  2007年   1398篇
  2006年   1215篇
  2005年   1184篇
  2004年   1040篇
  2003年   842篇
  2002年   839篇
  2001年   699篇
  2000年   776篇
  1999年   692篇
  1998年   622篇
  1997年   669篇
  1996年   564篇
  1995年   585篇
  1994年   488篇
  1993年   401篇
  1992年   286篇
  1991年   362篇
  1990年   338篇
  1989年   286篇
  1988年   380篇
  1987年   378篇
  1986年   296篇
  1985年   284篇
  1984年   297篇
  1983年   156篇
  1982年   270篇
  1981年   206篇
  1980年   173篇
  1979年   164篇
  1978年   41篇
  1977年   14篇
  1976年   12篇
  1975年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
We first state a uniform convergence theorem for finite-part integrals which are derivatives of weighted Cauchy principal value integrals. We then give a two-stage process to modify approximating splines and optimal nodal splines in such a way that the conditions of this theorem are satisfied. Consequently, these modified splines can be used in the numerical evaluation of these finite-part integrals.  相似文献   
102.
Summary Six commercial hydrogen standards containing helium, oxygen, nitrogen, methane and carbon dioxide at trace levels were analyzed by gas chromatography, for periods up to 105 days. The concentrations, in the range of 0–120 μmol mol−1, were stable (with the exception of oxygen) but often significantly different from the certified values provided by the suppliers, especially for helium, oxygen and nitrogen. Concurrently, some experiments were carried out to verify the stability of gas mixtures based on hydrogen stored in cylinders submitted to different chemical and physical treatments. The causes that led to the deviations observed, as well as the decreases in oxygen, are discussed. Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996.  相似文献   
103.
104.
In this paper, we introduce an affine scaling algorithm for semidefinite programming (SDP), and give an example of a semidefinite program such that the affine scaling algorithm converges to a non-optimal point. Both our program and its dual have interior feasible solutions and unique optimal solutions which satisfy strict complementarity, and they are non-degenerate everywhere.  相似文献   
105.
本文研究由双障碍问题导出的一类B可微函数的性质,并在一定条件下证明了求解相应的B可微方程阻尼牛顿法的全局收效性和二阶收效性.数值例子表明这一算法是有效的.  相似文献   
106.
We consider a composite material composed of fibres included in a resin which becomes solid when it is heated up (reaction of reticulation). The mathematical modelling of the cure process is given by a kinetic equation describing the evolution of the reaction of reticulation coupled with the heat equation. In this paper, we are interested in the computation of approximate solutions. We propose a family of discretized problems depending on two parameters (β1, β2) ε [0, 1]2 which split the linear and non‐ linear terms in implicit and explicit parts. We prove the stability and convergence of the discretization for any (β1, β2) ε [½, 1 ] × [0, 1]. We present also some numerical results. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
107.
Perfluorocarboxylic thioesters RFC(O)SR (RF=CF3(CF2)j, R=CH3(CH2)i, i andj=0–5) were studied for the first time by GLC on packed columns using SE-30, SKTFT-50X, and XE-60 as the stationary phase. The values of thermodynamics functions of sorption were calculated. The correlations between these functions and the molecular structures as well as the conditions of analysis were established. The insertion of the S atom into the molecules of derivatives of perfluorocarboxylic acids causes a decrease in the contribution of the orientation interaction and an increase in the dispersion interaction of thioesters with the stationary phases compared to esters and amides of perfluorocarboxylic acids studied previously. For Part 1, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1168, June, 1997.  相似文献   
108.
The V^t-integral as defined in[2], which is eqnivalent to M^2-integrsl as defined in Trigonometre series by Zygmund is used to sum trigonometric seies in[1]. In this paper, some convergent theorems of V^2-integral are established.  相似文献   
109.
After describing simplified equations exspressing the temparature dependency of the viscosity of carrier gases (helium, nitrogen and hydrogen ) relative to a base value, absolute relationships based on the kinetic theory of gases are discussed. Comparative data obtained using various calculation methods are given and are compared to measured values. Based on the kinetic relationshipsm, of viscosity. Finally, the influence of pressure on the viscosity is also briefly discussed. As a supplement, Viscosity data are tabulated for the three gases in the range of 0°C to 400°C in increments of 2 K, calculated using the kinetic relationships.  相似文献   
110.
研究函数族的正规性定则是复变函数论中的一个重要且有意义的工作.引进多元K-拟全纯函数的定义,并给出了多元K-拟全纯函数族的一个正规定则.  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