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   39854篇
  免费   1255篇
  国内免费   85篇
化学   26654篇
晶体学   346篇
力学   767篇
数学   5729篇
物理学   7698篇
  2023年   304篇
  2022年   335篇
  2021年   532篇
  2020年   675篇
  2019年   676篇
  2018年   872篇
  2017年   790篇
  2016年   1475篇
  2015年   1226篇
  2014年   1251篇
  2013年   2572篇
  2012年   2713篇
  2011年   2898篇
  2010年   1748篇
  2009年   1445篇
  2008年   2467篇
  2007年   2324篇
  2006年   2153篇
  2005年   1925篇
  2004年   1571篇
  2003年   1193篇
  2002年   1107篇
  2001年   792篇
  2000年   698篇
  1999年   539篇
  1998年   389篇
  1997年   296篇
  1996年   452篇
  1995年   326篇
  1994年   320篇
  1993年   331篇
  1992年   311篇
  1991年   218篇
  1990年   210篇
  1989年   165篇
  1988年   166篇
  1987年   156篇
  1986年   149篇
  1985年   241篇
  1984年   209篇
  1983年   171篇
  1982年   166篇
  1981年   151篇
  1980年   133篇
  1979年   143篇
  1978年   140篇
  1977年   131篇
  1976年   151篇
  1975年   132篇
  1973年   132篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
The work is devoted to the analysis of the surface photometric observations of two total lunar eclipses in 2004. The lunar surface relative brightness distribution inside the umbra was used to retrieve the vertical distribution of aerosol extinction of the solar radiation expanding by a tangent path and its dependence on the location at the limb of the Earth. The upper altitude of troposphere aerosol layer was estimated for different latitude zones. The correlation between additional aerosol extinction in the upper troposphere and cyclones was investigated.  相似文献   
52.
53.
Book reviews     
Ohne Zusammenfassung
Book reviews
  相似文献   
54.
Dislocation motion in the real lattice of alloys is highly complex. In a certain temperature range the dynamic strain ageing phenomena have been reported. In this paper the influence of mobile solute atoms (as obstacles) on the motion of dislocation is analysed. Both processes are assumed to be thermally activated. A new model based on this assumption is proposed. The dislocation velocity and the friction stress (due to solute-dislocation interactions) are calculated. A change in the friction stress caused by solute mobility is discussed.  相似文献   
55.
We consider a sequence of curved rods which consist of isotropic material and which are clamped on the lower base or on both bases. We study the asymptotic behaviour of the stress tensor and displacement under the assumptions of linearized elasticity when the cross‐sectional diameter of the rods tends to zero and the body force is given in the particular form. The analysis covers the case of a non‐smooth limit line of centroids. We show how the body force and the choice of the approximating curved rods can affect the strong convergence and the limit form of the stress tensor for the curved rods clamped on both bases. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
56.
57.
A combined approach based on solid-phase optosensing and multicommutation principles has been applied to develop a method for the simultaneous analysis of two pharmaceuticals (naproxen and salicylic acid) in biological fluids. The multicommuted flow-through optosensor was based on direct native fluorescence measurements of both analgesics using a non-polar sorbent (C18 silica gel) as a solid sensing zone. The flow system was controlled by Java-written home-made software and designed using three-way solenoid valves for an independent automated manipulation of sample and carrier solutions. Using an optimized sampling time, the method was calibrated in the range of 1 - 25 and 5 - 200 ng mL(-1). The obtained detection limits were 0.3 and 1.3 ng mL(-1) for naproxen and salicylic acid, respectively, with RSD (%) values of better than 2% for both analytes. The proposed methodology was successfully applied to urine, serum and pharmaceutical preparations. Recovery percentages ranging from 96.1 to 104% were obtained for both analytes.  相似文献   
58.
In this article we prove a local existence and uniqueness theorem for the Kadomtsev-Petviashvili Equation (u t +u xxx +uu x ) x −u yy =0) in the Sobolev spaces of orders≥3, with initial values in the same spaces, and periodic boundary conditions. This theorem improves previous results based upon the application of singular perturbation techniques.  相似文献   
59.
Ferric ferrocyanides synthesized from different sources of ferric cations and ferrocyanide anions and those derived from ferrous ferricyanide, ferrous ferrocyanide and ferric ferricyanide have been studied using Mössbauer and XRD techniques. Structural information of the effect of the provenance on the properties of the final compound is obtained. Significant correlations between isomer shift and quadrupole splitting of inner and outer iron cations have been observed.  相似文献   
60.
Using the time differential perturbed angular correlation technique, the hyperfine interactions as titanium sites in ZnTiF6·6H2O and its decomposition products were determined between room temperature (300 K) and 1273 K. The different steps in the decomposition pattern were identified and a simple model is given for it.  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