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   53021篇
  免费   11967篇
  国内免费   3056篇
化学   53547篇
晶体学   545篇
力学   1357篇
综合类   73篇
数学   3743篇
物理学   8779篇
  2024年   61篇
  2023年   346篇
  2022年   628篇
  2021年   767篇
  2020年   1870篇
  2019年   3190篇
  2018年   1609篇
  2017年   1180篇
  2016年   4103篇
  2015年   4263篇
  2014年   4407篇
  2013年   5315篇
  2012年   4471篇
  2011年   3817篇
  2010年   3974篇
  2009年   3768篇
  2008年   3535篇
  2007年   2794篇
  2006年   2416篇
  2005年   2472篇
  2004年   2055篇
  2003年   1872篇
  2002年   2476篇
  2001年   1706篇
  2000年   1625篇
  1999年   635篇
  1998年   294篇
  1997年   272篇
  1996年   253篇
  1995年   192篇
  1994年   229篇
  1993年   190篇
  1992年   173篇
  1991年   139篇
  1990年   132篇
  1989年   134篇
  1988年   76篇
  1987年   58篇
  1986年   65篇
  1985年   59篇
  1984年   47篇
  1983年   29篇
  1982年   34篇
  1981年   38篇
  1980年   35篇
  1979年   27篇
  1977年   22篇
  1976年   29篇
  1974年   28篇
  1973年   19篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The fuzzification of convex sets in median algebras is considered, and some of their properties are investigated. A characterization of finite valued fuzzy convex set is given.  相似文献   
82.
The energy loss effect in nuclear matter, which is a nuclear effect apart from the nuclear effect on the parton distribution as in deep-inelastic scattering process, can be measured best by the nuclear dependence of the high energy nuclear Drell-Yan process. By means of the nuclear parton distribution studied only with lepton deep-inelastic scattering experimental data, the measured Drell-Yan production cross sections for 800 GeV proton incident on a variety of nuclear targets are analyzed within the Glauber framework which takes into account the energy loss of the beam proton. It is shown that the theoretical results with considering the energy loss effect are in good agreement with the FNAL E866 data.Arrival of the final proofs: 24 June 2003  相似文献   
83.
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   
84.
85.
86.
A graph G is N2locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005  相似文献   
87.
A Promising MoO_x-based Catalyst for n-Heptane Isomerization   总被引:1,自引:0,他引:1  
The increasing demand for higher-octane gasoline and the regulations limiting the amount of aromatics in the fuel motivate the interest in catalytic isomerization of n-alkanes. In the last ten years, transition metal oxides or oxycarbides based on molybdenum or tungstate have attracted much attention due to their high activity and isomerization selectivity compared to the conventional bifunctional supported platinum catalyst and high resistance to sulphur and nitrogen catalyst poisons1-5. Ma…  相似文献   
88.
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting,  相似文献   
89.
In the title compound, catena‐poly[lithium‐μ3‐ethyl­ene­diphos­phon­ato], [Li(C2H7O6P2)]n, the supra­molecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethyl­ene­diphosphon­ate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand.  相似文献   
90.
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced.  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