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   25912篇
  免费   5107篇
  国内免费   3547篇
化学   10727篇
晶体学   230篇
力学   1630篇
综合类   200篇
数学   2244篇
物理学   11304篇
无线电   8231篇
  2024年   107篇
  2023年   511篇
  2022年   698篇
  2021年   992篇
  2020年   1183篇
  2019年   947篇
  2018年   893篇
  2017年   1156篇
  2016年   1297篇
  2015年   1268篇
  2014年   1776篇
  2013年   2112篇
  2012年   1738篇
  2011年   1843篇
  2010年   1516篇
  2009年   1729篇
  2008年   1772篇
  2007年   1668篇
  2006年   1594篇
  2005年   1308篇
  2004年   1137篇
  2003年   1045篇
  2002年   842篇
  2001年   761篇
  2000年   686篇
  1999年   610篇
  1998年   513篇
  1997年   430篇
  1996年   375篇
  1995年   333篇
  1994年   264篇
  1993年   209篇
  1992年   173篇
  1991年   174篇
  1990年   121篇
  1989年   119篇
  1988年   97篇
  1987年   77篇
  1986年   67篇
  1985年   67篇
  1984年   54篇
  1983年   31篇
  1982年   45篇
  1981年   48篇
  1980年   38篇
  1979年   36篇
  1978年   22篇
  1977年   25篇
  1976年   13篇
  1974年   13篇
排序方式: 共有10000条查询结果,搜索用时 843 毫秒
91.
For the Na I2 collision system, theoretical study is performed on the QCISD(T) level by using ab initio method. The ab initio potential energy surfaces are got and on them the long-lived complexes are found and optimized. These results verify the crossed molecule beam experimental phenomenon and the detailed geometry structures are given for the first time. The role of the complexes in the reaction path is also described in detail.  相似文献   
92.
Kinetic parameters of amino acid cations in an MK-40 ion-exchange membrane are calculated from the conductivity data. A theoretical quantum-chemical analysis of experimental activation energies for conduction suggests a mechanism of elementary act of transport of amino acid cations in the membrane.  相似文献   
93.
We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen–Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non‐linear. We employ two‐scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
94.
In this paper low‐gain adaptive stabilization of undamped semilinear second‐order hyperbolic systems is considered in the case where the input and output operators are collocated. The linearized systems have an infinite number of poles and zeros on the imaginary axis. The adaptive stabilizer is constructed by a low‐gain adaptive velocity feedback. The closed‐loop system is governed by a non‐linear evolution equation. First, the well‐posedness of the closed‐loop system is shown. Next, an energy‐like function and a multiplier function are introduced and the exponential stability of the closed‐loop system is analysed. Some examples are given to illustrate the theory. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
95.
96.
We show that, contrary to earlier reports, application of the one-parameter variational technique to the classical (image) model for H in front of an Al surface leads to energy shifts for the ground state which are very close to those obtained numerically with a more sophisticated model of the system.  相似文献   
97.
The conjecture according to which the mean energy of an equilibrium system in quantum theory exceeds the mean energy of the corresponding classical system is considered. It is rigorously proved that the conjecture holds for the potential well. The estimates for the mean energy of the potential well at high and low temperatures are of special interest.  相似文献   
98.
The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia  相似文献   
99.
谐振子薛定谔方程的简单解法   总被引:2,自引:0,他引:2  
物质的许多物理与化学性质都可以用线性谐振子模型解释,本文用简单的数学运算求解线性谐振子的薛定谔方程,避免了特殊函数等复杂的数学运算,得出了量子力学教材完全相同的结果。  相似文献   
100.
The problem of nonparametric stationary distribution function estimation by the observations of an ergodic diffusion process is considered. The local asymptotic minimax lower bound on the risk of all the estimators is found and it is proved that the empirical distribution function is asymptotically efficient in the sense of this bound.  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