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   10660篇
  免费   1813篇
  国内免费   728篇
化学   6353篇
晶体学   55篇
力学   369篇
综合类   71篇
数学   1566篇
物理学   4787篇
  2024年   27篇
  2023年   131篇
  2022年   263篇
  2021年   306篇
  2020年   304篇
  2019年   315篇
  2018年   279篇
  2017年   390篇
  2016年   354篇
  2015年   375篇
  2014年   467篇
  2013年   795篇
  2012年   701篇
  2011年   739篇
  2010年   570篇
  2009年   649篇
  2008年   549篇
  2007年   740篇
  2006年   629篇
  2005年   533篇
  2004年   474篇
  2003年   474篇
  2002年   349篇
  2001年   322篇
  2000年   303篇
  1999年   220篇
  1998年   237篇
  1997年   195篇
  1996年   211篇
  1995年   151篇
  1994年   155篇
  1993年   109篇
  1992年   150篇
  1991年   85篇
  1990年   84篇
  1989年   84篇
  1988年   73篇
  1987年   62篇
  1986年   52篇
  1985年   55篇
  1984年   59篇
  1983年   32篇
  1982年   37篇
  1981年   30篇
  1980年   23篇
  1979年   28篇
  1978年   15篇
  1977年   4篇
  1976年   4篇
  1974年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
In this paper, by means of a new twin fixed-point theorem in a cone, the existence of at least two positive solutions of m-point boundary value problem for second order dynamic equations on time scales is considered.  相似文献   
52.
A plasma reactor that has a transient traveling arc has been used to study hydrogen in relation to in-flight reduction of metal oxide particles. Experiments were done to determine the nature of the arc and its interaction with the reactor gas. The lifetime of the excited atomic hydrogen was measured and it was found to be more than 4 ms after the arc had ceased. Powders and tablets of oxides were exposed to the pulsed-arc treated hydrogen and found to react much more rapidly and intensely than when exposed to hot molecular hydrogen. The results suggest that atomic hydrogen will exist throughout the volume of such a reactor for a period that is sufficient to reduce particles of FeO, Cr2O3, and TiO2.  相似文献   
53.
用激光溅射 分子束技术研究了气相中Ni的等离子体与甲醇分子团簇的反应 .观察到Ni+ (CH3 OH) n、NiO+ (CH3 OH) n、H+ (CH3 OH) n、H3 O+ (CH3 OH) n 四个种类的团簇正离子和CH3 O-(CH3 OH) n(n≤ 2 5 )一种团簇负离子 .详细考察了激光烧蚀等离子体作用于脉冲分子束的不同位置时 ,对团簇产物种类和团簇尺寸大小的影响 .发现NiO+ (CH3 OH) n 是由Ni+ (CH3 OH) n 团簇内的脱甲烷反应生成的 ,而H+ (CH3 OH) n、H3 O+ (CH3 OH) n主要是激光等离子体中的电子与甲醇团簇碰撞电离产生的  相似文献   
54.
燕飞  张杰  鲁欣 《物理学报》2003,52(9):2200-2205
利用一维拉格朗日流体动力学程序Med103详细研究了产生类镍Ag,Cd,In,Sn, Sb离子和类氖Fe,Co,Ni,Cu,Zn离子的等离子体状态.通过对电子温度、离子丰度、离子数密度等状态参量的分析比较,得到了这两类等离子体状态之间的对应关系.即类镍银的等离子体状态与类氖铁 的相近,类镍镉的与类氖钴的相近,依次类推.利用这一对应关系可以方便地由类氖机理x射线激光的等离子体状态来对相应元素的类镍x射线激光的等离子体状态进行判断. 关键词: 类氖 类镍 等离子体状态 x射线激光  相似文献   
55.
通过对非线性规划问题的K-T点的光滑路径跟踪方法研究,得出一种针对于既有不等式约束条件又有等式约束条件的优化问题光滑路径跟踪方法,证明了光滑跟踪路径的存在性。  相似文献   
56.
The properties of pulsed laser vapor doping on p-Si(1 0 0) with a KrF (248 nm) excimer pulsed laser (248 nm) and BCl3 gas are reported in this paper. The doped samples are characterized by the resistance measured using a four-probe method, since the sheet resistance changes with the carrier concentration of the sample. The doping effects with the variation of laser energy density, pulse number, and the pressure of BCl3 were investigated in terms of the sheet resistance. In this way, the optimized parameters were obtained and used for the positive heavy doping on p-Si(1 0 0) and p-Si(1 1 1). Then, using a square mesh under the above conditions, an image doping was completed. Finally, the metal–semiconductor Ohmic contacts were realized by plating Ag and Cu films on the doped surface.  相似文献   
57.
In this paper, by using the fixed point theory, under quite general conditions on the nonlinear term, we obtain an existence result of bounded positive solutions of Schrödinger equations in two-dimensional exterior domains.  相似文献   
58.
关于《一类奇异边值问题的正解》的注记   总被引:3,自引:0,他引:3  
柴国庆 《数学学报》2003,46(6):1087-109
文[4]通过构造反例断言文[1]中定理的必要性证明有误,本文首先指出文[4] 的这个断言不正确,然后对文[4]中定理2.1作了本质性的改进.  相似文献   
59.
Charge density fluctuation of low frequency in a dusty plasma   总被引:2,自引:0,他引:2  
The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity of the dusty plasma, has been studied by kinetic theory. The results show that theP value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle Ω c , which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation of low frequency. For a dusty plasma ofP≪1, when the charging frequency Ω c , is much smaller than the dusty plasma frequency ωd, there is a strong charge density fluctuation which is of character of dust acoustic eigenwave. For a dusty plasma ofP≫1, when the frequency Ω c , is much larger than ω d there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist.  相似文献   
60.
Capillary gas chromatography coupled to microwave-inducedplasma detection furnishes sensitivity adequate for trace analysis when the signal is monitored at a carbon emission line. Work performed with one of these systems at high electronic gain for the carbon signal has revealed solvent band widths in excess of four minutes; these impeded quantification of peaks eluting after the solvent. This report discusses two phenomena which could be related to the unexpected intensity of this solvent response: photomultiplier tube saturation and carbon deposits in the quartz plasma discharge tube.  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