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   214943篇
  免费   23647篇
  国内免费   18855篇
化学   136418篇
晶体学   2724篇
力学   12294篇
综合类   1221篇
数学   26810篇
物理学   77978篇
  2023年   2844篇
  2022年   5653篇
  2021年   6202篇
  2020年   6705篇
  2019年   6760篇
  2018年   6898篇
  2017年   6611篇
  2016年   8968篇
  2015年   7886篇
  2014年   10223篇
  2013年   13504篇
  2012年   15344篇
  2011年   15972篇
  2010年   11872篇
  2009年   11591篇
  2008年   12175篇
  2007年   11185篇
  2006年   10388篇
  2005年   8803篇
  2004年   7195篇
  2003年   6032篇
  2002年   5882篇
  2001年   5147篇
  2000年   4310篇
  1999年   3916篇
  1998年   3448篇
  1997年   3062篇
  1996年   2969篇
  1995年   2586篇
  1994年   2531篇
  1993年   2188篇
  1992年   2047篇
  1991年   1966篇
  1990年   1822篇
  1989年   1599篇
  1988年   1340篇
  1987年   1282篇
  1986年   1252篇
  1985年   1212篇
  1984年   1103篇
  1983年   982篇
  1982年   938篇
  1981年   785篇
  1979年   834篇
  1978年   837篇
  1977年   825篇
  1976年   942篇
  1975年   834篇
  1974年   853篇
  1973年   866篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
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   
102.
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   
103.
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   
104.
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   
105.
A Cayley map is a Cayley graph embedded in an orientable surface such that. the local rotations at every vertex are identical. In this paper, balanced regular Cayley maps for cyclic groups, dihedral groups, and generalized quaternion groups are classified.  相似文献   
106.
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   
107.
108.
Wang  Qing-Lun  Zhao  Bin  Liao  Dai-Zheng  Yan  Shi-Ping  Cheng  Peng  Jiang  Zong-Hui 《Transition Metal Chemistry》2003,28(3):326-330
The copper(II) complex Na2[Cu(pba)] · 6H2O has been synthesized and its structure determined. It consists of a novel two-dimensional network of [Cu(pba)]2– anions connected to each other through the sodium ion as a bridge. Spectroscopic and magnetic properties have been measured and a spin distribution calculation has been carried out with the GAUSSIAN-94. Theoretical calculations indicate the rather larger spin density on nitrogen atoms should be responsible for the satellite lines appearing beside the main hyperfine coupling signs of copper(II). The antiferromagnetic interaction may be due to the intermolecular interaction and/or different copper(II) ions through the Na+ bridge in the same layer.  相似文献   
109.
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   
110.
Effects of ion impinging on the microstructure and field electron emission properties of screen-printed carbon nanotube films were investigated. We observed that the plasma treatment modified the microstructure of CNTs along with the remarkable increase of emission site density. With the prolongation of ion impinging time, the emission current falls down first, and then rises up to higher than that of the untreated films. It is proposed that the change of emission characteristics is due to the different emission mechanisms. After the treatment, electrons are emitted predominantly from the nano-nodes on the tube wall instead from the nanotube tips.  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