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   87959篇
  免费   28077篇
  国内免费   24433篇
化学   45208篇
晶体学   938篇
力学   4963篇
综合类   20篇
数学   9444篇
物理学   51969篇
无线电   27927篇
  2024年   776篇
  2023年   1325篇
  2022年   1309篇
  2021年   1253篇
  2020年   1566篇
  2019年   2754篇
  2018年   2645篇
  2017年   3405篇
  2016年   3952篇
  2015年   4640篇
  2014年   4348篇
  2013年   6036篇
  2012年   6372篇
  2011年   7039篇
  2010年   10079篇
  2009年   9930篇
  2008年   3752篇
  2007年   3262篇
  2006年   3080篇
  2005年   3121篇
  2004年   4226篇
  2003年   3360篇
  2002年   3188篇
  2001年   3327篇
  2000年   2579篇
  1999年   2621篇
  1998年   2316篇
  1997年   2116篇
  1996年   2471篇
  1995年   2826篇
  1994年   2904篇
  1993年   3027篇
  1992年   2617篇
  1991年   2283篇
  1990年   1853篇
  1989年   1963篇
  1988年   1864篇
  1987年   1124篇
  1986年   1178篇
  1985年   841篇
  1984年   964篇
  1982年   884篇
  1981年   729篇
  1980年   772篇
  1979年   526篇
  1978年   530篇
  1977年   633篇
  1976年   1041篇
  1972年   539篇
  1971年   442篇
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
971.
The effect of spin relaxation on tunnel magnetoresistance (TMR) in a ferromagnet/superconductor/ferromagnet (FM/SC/FM) double tunnel junction is theoretically studied. The spin accumulation in SC is determined by balancing of the spin-injection rate and the spin-relaxation rate. In the superconducting state, the spin-relaxation time τs becomes longer with decreasing temperature, resulting in a rapid increase of TMR. The TMR of FM/SC/FM junctions provides a useful probe to extract information about spin-relaxation in superconductors.  相似文献   
972.
几种N-取代马来酰胺酸辅酶模型的核磁共振研究   总被引:1,自引:0,他引:1  
我们对8种N-取代马来酰胺酸辅酶模型与不同类型的亲核试剂反应后生成的产物进行了1H、13C NMR的研究, 测得1H、13C谱化学位移,研 究探讨其规律性, 并测试了IR谱和元素分析.  相似文献   
973.
广义Hénon映射的滑模变结构控制同步   总被引:5,自引:1,他引:4       下载免费PDF全文
尹逊和  任勇  山秀明 《物理学报》2002,51(9):1949-1953
基于可线性化的非线性离散变结构跟踪控制方法实现了广义Hénon映射混沌系统的同步.广义Hénon映射的混沌吸引子比Hénon映射的混沌吸引子要复杂得多,对于保密通信来说,这种复杂性正是所期望的.提出的同步方法允许参数有适当的失配程度,这对工程实现是非常有利的,理论分析和仿真结果证实了该方法的有效性 关键词: 广义Hénon映射 混沌 同步 变结构控制  相似文献   
974.
New derivation results for integrands and multifunctions via the Lipschitzean approximations are obtained. Applications to multivalued differential equations on closed convex sets are presented.  相似文献   
975.
This paper describes the fabrication of NMOS-transistors with a geometric gate length of down to 50 nm using conventional optical lithography and a modified sidewall-etchback process. Based on measurements the transistors are characterised and their device parameters are compared to simulations. Finally the procedures for further optimisation of the process will be explained.  相似文献   
976.
We have developed a novel chemically amplified deep-UV photoresist called ARCH2. ARCH2 displays a resolution of<0.23μm with a DOF of 1.0μm at 0.25μm. This material also displays superior time delay stability (>8 hours). The post exposure bake (PEB) temperature was varied from 100°C to 120°C and the PEB time was varied from 60s to 180s. This had very little effect on the CD of the resist profiles. Preliminary etching experiments in a conventional reactive ion etcher were then carried out using CF4 to etch TiN. In these experiments the ARCH2 etched at a similar rate as conventional Novolac.  相似文献   
977.
978.
979.
 For the analysis of infrared spectroscopic bands and complex patterns partial cross correlation functions of a sample spectrum with reference spectra are calculated. The chosen ranges of the spectra are based on empirical knowledge of infrared spectrum structure correlations. The normalised maxima of the partial cross correlation functions are interpreted as fuzzy truth values and are combined by fuzzy logical operators. By application of that procedure larger common substructures will be derived from the reference spectra than by a maximum common substructure search based on the complete spectra. Received: 30 October 1996/Revised: 24 February 1997/Accepted: 26 February 1997  相似文献   
980.
An analysis of resonances of scattering from multi-element grating formed by a finite number of resonant elements is presented. It has been shown that gratings with three and more elements on its period can support the π-mode. The π-mode of a grating is characterized by the existence of the regions in the vicinity of the grating and along its period where the electromagnetic field has opposite phases. The existence and excitation of the π-mode in finite gratings with resonant cells formed by several scatterers having open cavities have been studied. The particular case of the grating with cells formed by three identical slotted cylinders has been considered in detail. An application of gratings which support the π-mode in electron-vacuum oscillators of millimeter waves for efficient deceleration of electrons and extracting energy from electron beam is discussed.  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