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   10448篇
  免费   1967篇
  国内免费   966篇
化学   6942篇
晶体学   83篇
力学   664篇
综合类   85篇
数学   1200篇
物理学   4407篇
  2024年   23篇
  2023年   241篇
  2022年   341篇
  2021年   395篇
  2020年   420篇
  2019年   416篇
  2018年   348篇
  2017年   334篇
  2016年   513篇
  2015年   476篇
  2014年   545篇
  2013年   748篇
  2012年   914篇
  2011年   1018篇
  2010年   637篇
  2009年   669篇
  2008年   667篇
  2007年   576篇
  2006年   530篇
  2005年   440篇
  2004年   342篇
  2003年   282篇
  2002年   256篇
  2001年   210篇
  2000年   219篇
  1999年   206篇
  1998年   213篇
  1997年   192篇
  1996年   154篇
  1995年   196篇
  1994年   168篇
  1993年   125篇
  1992年   103篇
  1991年   85篇
  1990年   91篇
  1989年   65篇
  1988年   44篇
  1987年   33篇
  1986年   35篇
  1985年   21篇
  1984年   18篇
  1983年   21篇
  1982年   12篇
  1981年   8篇
  1980年   10篇
  1979年   2篇
  1978年   4篇
  1975年   3篇
  1974年   2篇
  1957年   3篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
954.
1 Besicovitch Inner ProductIll this paper, we consider Dirichlet serie8where an, tL = 1, 2,' ', are complex nunlbers. They are Besicovitch almost periodic functionsWe see the 8ystenl {e.(t); e.(t) = e--it Iog 1l, 71 = l, 2,' .} fOrnis a1l orthollor11la1 systelll witl1respect to tI1e BesicovitcI1 iIl1ler productThell we call fOrm the gelleralized trigouolnetrical polynolIlialsAccording to tl1e idea developed il1 [l],[2], auy Dirichlet seriesis weakly convergent over K witll respect to …  相似文献   
955.
罗勤 《发光学报》1989,10(1):74-81
本文概述了长春物理研究所为人民大会堂研制的交流(AC)、直流(DC)电致发光(EL)矩阵大屏幕会务信息显示的结果。其中,ACEL矩阵屏幕尺寸为2.5×3m2,由30块0.46×0.46m2的单元屏拼接而成。平均亮度20尼特,对比度10:1;DCEL矩阵屏幕为:1m2,行列数120×144,平均亮度45尼特,对比度大于10:1。在环境照度60lux条件下,观察距离分别为65m、20m。并从分析EL矩阵的显示特性出发,阐明了显示系统的设计要点,控制、匹配电路和亮度、对比度的关系;还给出了部分驱动电路结构和系统的应用结果。  相似文献   
956.
研究了复赋范空间中的同时太阳集对无穷序列的最佳逼近问题,得到了特征及唯一性定理.  相似文献   
957.
A mathematical model is developed to study periodic-impact motions and bifurcations in dynamics of a small vibro-impact pile driver. Dynamics of the small vibro-impact pile driver can be analyzed by means of a three-dimensional map, which describes free flight and sticking solutions of the vibro-impact system, between impacts, supplemented by transition conditions at the instants of impacts. Piecewise property and singularity are found to exist in the Poincaré map. The piecewise property is caused by the transitions of free flight and sticking motions of the driver and the pile immediately after the impact, and the singularity of map is generated via the grazing contact of the driver and the pile immediately before the impact. These properties of the map have been shown to exhibit particular types of sliding and grazing bifurcations of periodic-impact motions under parameter variation. The influence of piecewise property, grazing singularities and parameter variation on the performance of the vibro-impact pile driver is analyzed. The global bifurcation diagrams for the impact velocity of the driver versus the forcing frequency are plotted to predict much of the qualitative behavior of the actual physical system, which enable the practicing engineer to select excitation frequency ranges in which stable period one single-impact response can be expected to occur, and to predict the larger impact velocity and shorter impact period of such response.  相似文献   
958.
This paper is concerned with optimal harvesting policy for an age-dependent n-dimensional food chain model. The existence and uniqueness of non-negative solution of the system are proved using the fixed point theorem. By Mazur's theorem, the existence of optimal control strategy is demonstrated and optimality conditions derived by means of normal cone.  相似文献   
959.
960.
Optical properties of silver nanobowtie with anisotropic topology, which is separated with nanogap that is horizontal (Y direction) and vertical (Z direction) to the line between the two constituent triangles (i.e., the bowtie axis), are studied. A discrete dipole approximation (DDA) method is used to determine the extinction efficiency and the electric field (E-field) distribution, then the corresponding enhancement factor (EF) and the full width half maximum (FWHM) of the E-field are obtained and analyzed. Our results show that the wavelength of localized surface plasmon resonance (LSPR)-induced blue-shifts and the maximum EF decrease were observed with increasing gap size for the parallel polarized (Z-polarized) excitation. It is also found that the light spot at the “hot spot” in the gap becomes larger and deviates from the rectangular pattern with the increase of the gap in the Z direction (Z-gap), and the FWHM in the Z direction of the localized E-field in the gap broadens with either an increase in the gap in the Y direction (Y-gap) or the Z-gap. These behaviors are due to the decrease of the coupling efficiency of near-field plasmon coupling. In contrast, the wavelength of the LSPR and the maximum EF excited by the perpendicularly polarized (Y-polarized) light show less dependence on the gap size than that of the Y-polarized light. PACS  73.20.Mf; 78.67.-n  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