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   1434篇
  免费   46篇
  国内免费   5篇
化学   990篇
晶体学   7篇
力学   38篇
数学   234篇
物理学   216篇
  2024年   5篇
  2023年   12篇
  2022年   20篇
  2021年   19篇
  2020年   24篇
  2019年   24篇
  2018年   22篇
  2017年   17篇
  2016年   34篇
  2015年   32篇
  2014年   42篇
  2013年   69篇
  2012年   104篇
  2011年   142篇
  2010年   79篇
  2009年   63篇
  2008年   106篇
  2007年   74篇
  2006年   90篇
  2005年   67篇
  2004年   59篇
  2003年   59篇
  2002年   56篇
  2001年   15篇
  2000年   21篇
  1999年   15篇
  1998年   11篇
  1997年   9篇
  1996年   16篇
  1995年   11篇
  1994年   17篇
  1993年   8篇
  1992年   14篇
  1991年   7篇
  1989年   3篇
  1988年   3篇
  1987年   6篇
  1986年   7篇
  1985年   12篇
  1984年   9篇
  1983年   6篇
  1982年   6篇
  1981年   6篇
  1980年   7篇
  1978年   7篇
  1976年   10篇
  1975年   5篇
  1974年   5篇
  1973年   5篇
  1942年   3篇
排序方式: 共有1485条查询结果,搜索用时 15 毫秒
1.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K.  相似文献   
2.
3.
We prove that four spheres in ℝ3 have infinitely many real common tangents if and only if they have aligned centers and at least one real common tangent.  相似文献   
4.
Packing two disks into a polygonal environment   总被引:1,自引:0,他引:1  
We consider the following problem. Given a polygon P, possibly with holes, and having n vertices, compute a pair of equal radius disks that do not intersect each other, are contained in P, and whose radius is maximized. Our main result is a simple randomized algorithm whose expected running time, on any input, is O(nlogn). This is optimal in the algebraic decision tree model of computation.  相似文献   
5.
We show that open 3-manifolds that have a locally finite decomposition along 2-spheres are characterized by the existence of a Riemannian metric with respect to which the second homotopy group of the manifold is generated by small elements. Received: November 2005 Revision: February 2006 Accepted: May 2006  相似文献   
6.
7.
The performances of two Laser Doppler Velocimetry (LDV) systems adapted for measuring the acoustic particle velocities are assessed in enclosed sound field. This assessment is performed by comparing the acoustic velocities measured by means of LDV to reference acoustic velocities estimated from sound pressure measurements. The two LDV systems are based on a single optical bench which delivers an optical signal called Doppler signal. The Doppler signal, which is frequency modulated, is analyzed by means of two signal processing systems, the BSA (Burst Spectrum Analyser from Dantec) on the one hand, and a system specifically developed for the estimation of the acoustic velocity on the other hand. Once the experimental setup has been optimized for minimizing the errors made on the reference velocities, the assessment is performed and shows that both systems can measure the acoustic velocity in enclosed field in two the frequency ranges [0-4 kHz] and [0-2 kHz] respectively for acoustic velocity amplitudes of 10 mm/s and 1 mm/s.  相似文献   
8.
In this Note, we return to the theory of characteristic modes which was introduced 30 years ago for electromagnetic scattering problems. A simple mathematical framework is proposed and complete definitions are given. The potential interest of this theory in terms of Radar Cross Section (RCS) analysis is then discussed, especially in the low frequency case. Finally, a 3-D example is presented to illustrate the efficiency of this decomposition. To cite this article: Y. Morel et al., C. R. Mecanique 332 (2004).  相似文献   
9.
10.
Reported here is an analytical method enabling the stereochemical resolution of a new antianginal compound possessing two stereogenic centers, leading to four stereoisomers. Only one of these isomers is currently under development as a novel antianginal agent and consequently, the other three isomers are considered as unwanted chiral impurities. Therefore, an enantioselective method is required in order to check its enantiomeric purity. This paper presents a method exploiting the high efficiency of capillary electrophoresis and the complexing properties of cyclodextrins to achieve the separation of the four stereoisomers of this weakly basic compound (pKa = 7.4). For this purpose, the combination of a neutral cyclodextrin, hydroxypropyl-gamma-cyclodextrin (HP-gamma-CD), and an anionic cyclodextrin, carboxymethyl-beta-cyclodextrin (CM-beta-CD), was added to the separation buffer running in an uncoated silica capillary. After selection of the suitable cyclodextrin system, satisfactorily separation conditions were as follows: 30 mM phosphate buffer (pH 6.4) containing 10 mM of HP-gamma-CD and 10 mM of CM-beta-CD, running voltage +30 kV. The resulting run time and resolutions were respectively about 17 min and between 1.95 and 2.84. Linearity curves (0.993 < r2 < 0.998) are also shown.  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