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   1536篇
  免费   204篇
  国内免费   44篇
化学   175篇
晶体学   7篇
力学   681篇
综合类   13篇
数学   322篇
物理学   586篇
  2024年   2篇
  2023年   13篇
  2022年   18篇
  2021年   16篇
  2020年   35篇
  2019年   30篇
  2018年   24篇
  2017年   29篇
  2016年   34篇
  2015年   46篇
  2014年   69篇
  2013年   84篇
  2012年   65篇
  2011年   79篇
  2010年   63篇
  2009年   71篇
  2008年   82篇
  2007年   119篇
  2006年   109篇
  2005年   101篇
  2004年   78篇
  2003年   91篇
  2002年   53篇
  2001年   49篇
  2000年   47篇
  1999年   48篇
  1998年   54篇
  1997年   57篇
  1996年   37篇
  1995年   28篇
  1994年   19篇
  1993年   17篇
  1992年   24篇
  1991年   17篇
  1990年   22篇
  1989年   6篇
  1988年   4篇
  1987年   8篇
  1986年   5篇
  1985年   5篇
  1984年   2篇
  1982年   4篇
  1981年   7篇
  1980年   2篇
  1979年   2篇
  1978年   3篇
  1975年   1篇
  1974年   1篇
  1959年   1篇
  1957年   1篇
排序方式: 共有1784条查询结果,搜索用时 9 毫秒
1.
张良 《应用光学》2003,24(2):4-6
在二极管泵浦固体激光器耦合光学系统中,柱面透镜起着非常重要的作用。随着系统轻量化、小型化的要求需要用重量轻、尺寸小的光学器件来替代。本文介绍一种用于替代柱面透镜的二元光学元件的设计和制作方法。  相似文献   
2.
Using the DFT/B3LYP method with a 6-31G(d) basis set, the structure, normal vibration frequencies, and the absolute band intensities in the IR spectra of the chlorin molecule and its four symmetric isotopomers have been calculated. Scaling of the force field by the Pulay method in independent and natural coordinates has been carried out. A method for obtaining effective force fields without using experimental data on the fundamental vibration frequencies is proposed. By comparing the vibration modes and constructing special matrices, complete assignment of the fundamental frequencies of porphin and chlorin has been carried out. It has been shown that the majority of porphin macroring vibrations upon pyrrolenine ring hydrogenation are frequency-characteristic and only 12 vibrations change considerably. A frequency correlation with regard for the mode transition between chlorin and all its isotopomers under consideration has been established. Comparative analysis of the force fields of porphin and chlorin in dependent natural coordinates has revealed the unique nonlocal character of the change in force constants of the macroring upon hydrogenation of one pyrrolenine ring. Modeling of the IR spectra of chlorin and its isotopomers has been performed. Assignment and interpretation of the normal vibrations of the molecules under consideration have been carried out.  相似文献   
3.
激光标线的原理和实验   总被引:1,自引:1,他引:0  
根据几何光学知识分析了激光标线原理.理论和实验表明:激光标线长度与激光光束形状、光学元件形状及材料折射率有关.并讨论了激光标线向两侧扩展的原因.  相似文献   
4.
5.
The paper outlines a procedure to identify the space-and time-dependent external nonstationary load acting on a closed circular cylindrical shell of medium thickness. Time-dependent deflections at several points of the shell are used as input data to solve the inverse problem. Examples of numerical identification of various nonstationary loads, including moving ones are presented. The relationship between the external load and the stress-strain state of the shell is described by the Volterra equation of the first kind. The identification problem is solved using Tikhonov's regularization method and Apartsin's h-regularization method __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 7, pp. 91–100, July 2008.  相似文献   
6.
一种新型有机电致微腔结构的双模发射   总被引:4,自引:4,他引:0  
采用结构Glass/DBR/ITO/NPB/NPB:Alq/Alq/Al制作了有机微腔电致发光器件。将空穴传输材料与发光材料以一定比例混合作为发光层,为了便于对比,在不改变有机层的膜厚的情况下同时制作了传统的异质结微腔器件,发现两种器件的发光光谱有很大不同,器件的复合效率与传统的异质结器件相比也得到了很大提高,这是因为将两种有机材料混合能消除界面势垒,提高器件的复合效率,从而提高了器件的发光性能,实现了微腔双模发射,且两个模式的半峰全宽分别为8nm和12nm。通过进一步优化器件结构可以实现微腔白光发射。  相似文献   
7.
In this paper, three-pencil lattices on triangulations are studied. The explicit representation of a lattice, based upon barycentric coordinates, enables us to construct lattice points in a simple and numerically stable way. Further, this representation carries over to triangulations in a natural way. The construction is based upon group action of S 3 on triangle vertices, and it is shown that the number of degrees of freedom is equal to the number of vertices of the triangulation.   相似文献   
8.
Layered double hydroxides with the hydrotalcite-like structures, containing Mg2+ and Al3+, doped with Cr3+ and Y3+, have been prepared by precipitation at constant pH. The weight percentages of Cr3+ and Y3+ were 1, 2, or 3%, and 0.5 or 1%, respectively. Single phases were obtained in all cases, whose crystallinity decreased as the content in Cr and Y was increased. The solids have been characterised by element chemical analysis, powder X-ray diffraction, thermal analyses (differential, thermogravimetric and programmed reduction), FT-IR and UV–vis spectroscopies; the specific surface areas have been determined from nitrogen adsorption isotherms at −196 °C. Upon calcination at 1200 °C for 5 h in air all solids display a mixed structure (spinel and rock salt for MgO); these solids have also been characterised by these techniques and their chromatic coordinates (CIE – L*a*b*) have been determined. Their pink colour makes these solids suitable for being used as ceramic pigments.  相似文献   
9.
应用超球会标表示氦原子和氢负离子的薛定谔方程,将二电子原子在三维空间中的运动转化为单电子原子在六维空间中受广义库仑力作用的运动,我们给出了六维空间广义角动量算符的本征值与本征函数,并以此本征函数微基构造超球波函数,得到超球径微分方程,以广义Laguerre 多项式表示超球径波函数,运用密度矩阵和线性变分法得到非正交基下超球径波函数满足的久期方程,最后求得能量和波函数,计算结果与精确的计算符合良好。  相似文献   
10.
Summary A quantum mechanical calculation of cross sections for the reaction F+H2(v=0,j=0) FH(vj)+H has been performed on the T5A semiempirical potential surface using hyperspherical coordinates. State-to-state integral and differential cross sections converge rapidly with the number of components of the total angular momentum projection onto the axis of least inertia. Thev=3 differential cross section has a forward peak whose magnitude increases with energy whereas thev=2 differential cross section has a backward maximum, in qualitative agreement with cross-beam experiments. Thev=2 andv=3 rotational distributions are in rather good agreement with experiment, but not the vibrational branching ratios.  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