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   184223篇
  免费   36928篇
  国内免费   26854篇
化学   121504篇
晶体学   2098篇
力学   12143篇
综合类   848篇
数学   23046篇
物理学   88366篇
  2024年   734篇
  2023年   2792篇
  2022年   4487篇
  2021年   4611篇
  2020年   5048篇
  2019年   5298篇
  2018年   4842篇
  2017年   5145篇
  2016年   6982篇
  2015年   7318篇
  2014年   8166篇
  2013年   11772篇
  2012年   13534篇
  2011年   15100篇
  2010年   15434篇
  2009年   15385篇
  2008年   9764篇
  2007年   8766篇
  2006年   8007篇
  2005年   7561篇
  2004年   7295篇
  2003年   5756篇
  2002年   5281篇
  2001年   5287篇
  2000年   4262篇
  1999年   4748篇
  1998年   3986篇
  1997年   3647篇
  1996年   4027篇
  1995年   4230篇
  1994年   4133篇
  1993年   3924篇
  1992年   3400篇
  1991年   2965篇
  1990年   2494篇
  1989年   2449篇
  1988年   2289篇
  1987年   1577篇
  1986年   1570篇
  1985年   1247篇
  1984年   1231篇
  1983年   600篇
  1982年   1063篇
  1981年   874篇
  1980年   872篇
  1979年   592篇
  1978年   593篇
  1977年   702篇
  1976年   1111篇
  1972年   573篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The semi‐iterative method (SIM) is applied to the hyper‐power (HP) iteration, and necessary and sufficient conditions are given for the convergence of the semi‐iterative–hyper‐power (SIM–HP) iteration. The root convergence rate is computed for both the HP and SIM–HP methods, and the quotient convergence rate is given for the HP iteration. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
92.
在本文中,给定一组有序空间数据点列及每个数据点的切矢向量,利用加权二次有理Bézier曲线对数据点作插值曲线,使该曲线具有C1连续性,并且权因子只是对相应顶点曲线附近产生影响,同调整两个相邻的权因子可以调整这两个相邻顶点之间的曲线和它的控制多边形.  相似文献   
93.
In this paper, both low order and high order extensions of the Iyengar type inequality are obtained. Such extensions are the best possible in the same sense as that of the Iyengar inequality. hzrthermore, the Chebyshev central algorithms of integrals for some function classes and some related problems are also considered and investigated.  相似文献   
94.
Compact, time‐harmonic, acoustic sources produce waves that decay too slowly to be square‐integrable on a line away from the sources. We introduce an inner product, arising directly from Green's second theorem, to form a Hilbert space of these waves and present examples of its computation.1 © 2005 Wiley Periodicals, Inc.  相似文献   
95.
本文利用Banach压缩映射原理,讨论了中立型时滞脉冲微分方程正解的存在性。  相似文献   
96.
    
The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction.  相似文献   
97.
In this paper we will present an overview of the use of photonic crystal fibers as fiber amplifiers. We will describe the basic concepts of optical amplification, and how to do numerical modelling of such components. We will then identify advantages and disadvantages of amplifiers based on PCF technology compared to conventional fibers, and then go into greater detail on some of these specific applications, such as low pump power amplifiers, and high-power double-clad amplifiers and lasers.  相似文献   
98.
In this paper, a very useful numerical technique has been developed for analyzing the transient characteristics of a planar-spiral inductor on-chip. A locally conformal technique and an alternating-direction implicit scheme are applied to the finite-difference time-domain method. A formulation for solving three dimensional Maxwell’s equations is proposed. Using the proposed method, various parameters of the planar-spiral inductors have been analyzed and an equivalent circuit, which includes frequency-independent circuit elements, has been introduced. Highly computational efficiency is implemented. Numerical results show excellent agreement with the measured data over a wide frequency range.  相似文献   
99.
We have conducted a millimeter wave propagation experiment at 103 GHz (2.9 mm) on a propagation path of 390 m. The results were compared with the rain attenuation calculations from the Marshall-Palmer, Best, Joss-Thomas-Waldvogel and Weibull distributions for raindrop-size. It has been shown that the Weibull distribution has a good agreement with the experiments.  相似文献   
100.
Four novel hexadentate imidazolium salts were synthesized from hexakis(bromomethyl)benzene and 1-substituted imidazole. The arylation of aldehydes with arylboronic acids was effected conveniently and in high yields by a catalyst system generated in situ from these hexadentate imidazolium salts, [Rh(COD)Cl]2 and a base.  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