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   223529篇
  免费   27105篇
  国内免费   16441篇
化学   153649篇
晶体学   2631篇
力学   11577篇
综合类   957篇
数学   25782篇
物理学   72479篇
  2023年   2571篇
  2022年   5034篇
  2021年   5683篇
  2020年   6834篇
  2019年   7912篇
  2018年   6971篇
  2017年   6415篇
  2016年   10716篇
  2015年   9711篇
  2014年   11752篇
  2013年   15219篇
  2012年   15883篇
  2011年   15777篇
  2010年   12651篇
  2009年   12433篇
  2008年   12446篇
  2007年   11088篇
  2006年   10111篇
  2005年   8956篇
  2004年   7492篇
  2003年   6428篇
  2002年   7000篇
  2001年   5754篇
  2000年   4969篇
  1999年   3844篇
  1998年   3201篇
  1997年   2838篇
  1996年   2768篇
  1995年   2390篇
  1994年   2350篇
  1993年   2049篇
  1992年   1915篇
  1991年   1851篇
  1990年   1726篇
  1989年   1518篇
  1988年   1279篇
  1987年   1234篇
  1986年   1201篇
  1985年   1172篇
  1984年   1088篇
  1983年   970篇
  1982年   921篇
  1981年   779篇
  1979年   826篇
  1978年   834篇
  1977年   823篇
  1976年   941篇
  1975年   834篇
  1974年   852篇
  1973年   864篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The spectral properties of multilayer interference systems formed by multiple replication of the symmetric ternary period ABCBA are investigated. The problem of synthesis of structures with suppression of adjacent bands of high reflection of the fourth, fifth, and sixth orders among their spectral characteristics is solved. It is shown that there are only six variants of selection of the optical thicknesses of layers in a period. When the high reflection bands of the fourth, fifth, and sixth orders are suppressed, the high reflection band of the first order remains in only four cases. The values of refractive indices of layers for which the problem hasa solution are found. The refractive indices of layers in all six cases are described by different relations determining the dependence of the refractive index of one of the components on arbitrarily selected refractive indices of the other two components.  相似文献   
102.
用于机械振动实时监测的光纤光栅有源传感装置   总被引:4,自引:1,他引:3  
把一对中心反射波长分别为1562.11nm和1562.71nm的光纤光栅粘贴在均质、等厚、等腰三角形悬臂梁上下表面作为环形腔光纤激光器端镜,当机械振动激励自由端时,通过观测激光输出脉冲,地施加于自由端的机械振动的频率进行了实时监测;观察两光栅波长漂移量差值的变化,可在0~6.1mm的范围内判断所测振动的振幅。低于100Hz时,实验结果与实际值基本吻合。  相似文献   
103.
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   
104.
Studies of thickness and temperature dependencies of the dielectric susceptibility of nitrobenzene interlayers formed on conductive substrates were carried out. The obtained data were processed under the assumption of the existence of dimers (with opposite directions of molecular dipole moments) in orientationally ordered wall-adjacent layers. The results were treated on the basis of Lifshits theory.  相似文献   
105.
Summary The electronic absorption and e.s.r. spectra of a crystal of the title compound [Cu(H2O)2 (C4H5O5)2] were recorded and experimental results are discussed quantitatively, using ligand field theory and the radial wave function of bound CuII. The electronic structure of the compound is consistent with its crystal structure.  相似文献   
106.
The thermodynamic properties of the Ln2BaO4 phases (Ln = Dy, Ho, Sm) were studied by the electromotive force method with a fluoride electrolyte (890–1180 K), solution calorimetry in 1.07 N hydrochloric acid at 298.15 K, and differential scanning calorimetry (298–860 K). The experimental data were jointly processed, and the thermodynamic functions of the compounds over the temperature range 298–1200 K were calculated.  相似文献   
107.
本文讨论了每个元都有幂等元作为右单位元的左消半群与幂单半群N的Schuzenberger积M◇N的ρ类,证明了这种半群M与N的Schuzenberger积M◇N的ρ类是右E一半适合半群和弱E-headged半群.  相似文献   
108.
109.
The inhomogeneous Dirichlet problems concerning divergence form elliptic equations are studied. Optimal regularity requirements on the coefficients and domains for the W1,p theory, 1 < p < ∞, are obtained. The principal coefficients are supposed to be in the John‐Nirenberg space with small BMO seminorms. The domain is a Reifenberg domain. These conditions for the W1,p theory not only weaken the requirements on the coefficients but also lead to a more general geometric condition on the domains. In fact, these domains might have fractal dimensions. © 2004 Wiley Periodicals, Inc.  相似文献   
110.
The thermal conductivity of crystalline chrysotile asbestos made up of hollow tubular Mg3Si2O5(OH)4 filaments is measured in the range 5–300 K. The paper discusses the possibility of using this material in studies of the thermal conductivity of thin filaments of metals and semiconductors incorporated into the channels of crystalline chrysotile asbestos tubes.  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