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   1332篇
  免费   46篇
  国内免费   50篇
化学   588篇
晶体学   20篇
力学   48篇
综合类   5篇
数学   342篇
物理学   425篇
  2024年   6篇
  2023年   44篇
  2022年   8篇
  2021年   20篇
  2020年   27篇
  2019年   40篇
  2018年   30篇
  2017年   22篇
  2016年   33篇
  2015年   31篇
  2014年   43篇
  2013年   144篇
  2012年   70篇
  2011年   63篇
  2010年   56篇
  2009年   74篇
  2008年   68篇
  2007年   68篇
  2006年   63篇
  2005年   42篇
  2004年   40篇
  2003年   42篇
  2002年   40篇
  2001年   36篇
  2000年   30篇
  1999年   33篇
  1998年   22篇
  1997年   20篇
  1996年   23篇
  1995年   27篇
  1994年   21篇
  1993年   15篇
  1992年   9篇
  1991年   9篇
  1990年   6篇
  1989年   5篇
  1988年   7篇
  1987年   5篇
  1986年   5篇
  1985年   11篇
  1984年   4篇
  1983年   7篇
  1982年   6篇
  1981年   6篇
  1980年   9篇
  1978年   5篇
  1977年   5篇
  1976年   5篇
  1974年   4篇
  1973年   10篇
排序方式: 共有1428条查询结果,搜索用时 8 毫秒
1.
Electron beam induced quantitative X-ray mapping has become a very useful characterisation tool for determining the elemental distribution in materials, whether using energy dispersive spectroscopy or wavelength dispersive spectroscopy. The X-ray intensity distributions of the elements from an X-ray map allow us to generate two dimensional and ternary scatter diagrams thus converting spatial information into concentration dimensions, which is an important tool for displaying the spatial relationships of elements or correlated elements (phases) in materials. To best understand how to use this tool, we need to understand the production and features of the scatter diagram. The type of clustering observed in the scatter diagram, whether oval, linear or spherical, can give the major and trace element distributions within phases as well as qualitative and quantitative phase information. This paper demonstrates the generation of scatter diagrams, properties of scatter diagrams, interpretation of scatter diagrams and the advantages of scatter diagrams through the use of examples.  相似文献   
2.
This work is concerned with Pontryagin's maximum principle of optimal control problems governed by some non-well-posed semilinear heat equations. A type of approach to the non-well-posed optimal control problem is given.  相似文献   
3.
基于MATLAB的异步电动机线性化控制系统的仿真   总被引:1,自引:0,他引:1  
从异步电动机在同步旋转坐标系下的状态方程出发,在一定的条件下,对其系数矩阵简化.推出异步电动机的线性化控制模型.并基于该模型得出异步电动机的线性化控制系统.以给定电机为例,对该模型的有效性、响应用MATLAB进行仿真分析.验证的结果说明上述模型具有实用价值.  相似文献   
4.
Multinomial permutations on a circle are considered in the framework of combinatorics. Different cases are presented and shown to agree with previously derived formula for the number of cyclic necklaces. Two applied examples are discussed with a view to illustrate the implications of derived formulas. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
5.
In this paper, the possibility of using the gradients of the temperature and of the internal parameters as additional state variables in Continuum Thermodynamics is considered. The expressions of the two principles are discussed and Clausius–Duhem inequality is derived under an appropriate statement of the internal entropy production. Several formulations are proposed and compared to existing results in the literature. To cite this article: P. Ireman, Q.S. Nguyen, C. R. Mecanique 332 (2004).  相似文献   
6.
研究了CID-ICP-AES检测煤中硫酸盐和硫铁矿形态硫的方法。较现有国标方法快速、简便,常见元素不干扰,加标回收率在98.5%-103.0%之间,10次测定的RSD在0.76%-1.59%之间。  相似文献   
7.
Photonic crystals exhibit band gaps, meaning that electromagnetic fields cannot propagate in them for specific ranges of wavelengths and directions. The calculation of band structure diagrams has been intensively studied and is now well understood. In contrast to that, so-called wave-vector diagrams (i.e. dispersion surfaces, depicting the loci of all relevant wave vectors at a fixed wavelength) are less known and used. In principle, they show how the effective index of the structure depends on the direction of propagation. A method to calculate explicitly wave-vector diagrams for two-dimensional photonic crystals is derived which leads finally to quadratic eigenvalue problems. Results for square and triangular lattices are presented and some applications are discussed.  相似文献   
8.
The problem of finding conditions of the loss of thermodynamic stability by the reaction system was solved on the basis of the developed theory of living free‐radical copolymerization. The spinodal's calculations were carried out for a significant number of systems differing in the values of kinetic, stoichiometric, and thermodynamic parameters. Analysis of the results of such calculations revealed some regularities in the spinodal curves' behavior and permitted us to classify their possible topological types. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 892–902, 2003  相似文献   
9.
We present new results for the virial coefficientsB k for κ<- 10 for hard spheres in dimensionsD = 2,..., 8.  相似文献   
10.
A Kind of direct methods is presented for the solution of optimal control problems with state constraints.These methods are sequential quadratic programming methods.At every iteration a quadratic programming which is obtained by quadratic approximation to Lagrangian function and Linear approximations to constraints is solved to get a search direction for a merit function.The merit function is formulated by augmenting the Lagrangian funetion with a penalty term.A line search is carried out along the search direction to determine a step length such that the merit function is decreased.The methods presented in this paper include continuous sequential quadratic programming methods and discreate sequential quadrade programming methods.  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