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   118564篇
  免费   8381篇
  国内免费   12546篇
化学   70965篇
晶体学   1155篇
力学   2428篇
综合类   843篇
数学   12824篇
物理学   19744篇
无线电   31532篇
  2024年   341篇
  2023年   1439篇
  2022年   2573篇
  2021年   2534篇
  2020年   2960篇
  2019年   2884篇
  2018年   2693篇
  2017年   3854篇
  2016年   3884篇
  2015年   3708篇
  2014年   4764篇
  2013年   8103篇
  2012年   7936篇
  2011年   7074篇
  2010年   5656篇
  2009年   7234篇
  2008年   7592篇
  2007年   8155篇
  2006年   7510篇
  2005年   6395篇
  2004年   5849篇
  2003年   4790篇
  2002年   5727篇
  2001年   3452篇
  2000年   3094篇
  1999年   2836篇
  1998年   2528篇
  1997年   2019篇
  1996年   1725篇
  1995年   1650篇
  1994年   1406篇
  1993年   1140篇
  1992年   1052篇
  1991年   751篇
  1990年   608篇
  1989年   555篇
  1988年   406篇
  1987年   304篇
  1986年   285篇
  1985年   227篇
  1984年   244篇
  1983年   144篇
  1982年   211篇
  1981年   176篇
  1980年   196篇
  1979年   183篇
  1978年   169篇
  1977年   122篇
  1976年   112篇
  1973年   68篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
为促进互联网的良性发展,要使设备制造商、电信运营商、虚拟运营商/集团用户、内容提供商和最终用户构成一条互联网业务价值链,价值链的创建对互联网接入设备提出了更高的要求,华为公司的Quid-wayTMA8010Expert多业务综合接入平台可构建宽带城域网分组语音解决方案、可平滑演进为下一代网络中的媒体网关、提供窄带价值链、提供唯一号码业务以及实现多业务综合接入。  相似文献   
102.
The feature scale planarization of the copper chemical mechanical planarization (CMP) process has been characterized for two copper processes using Hitachi 430-TU/Hitachi T605 and Cabot 5001/Arch Cu10K consumables. The first process is an example of an abrasive-free polish with a high-selectivity barrier slurry, while the second is an example of a conventional abrasive slurry with a low-selectivity barrier slurry. Copper fill planarization has been characterized for structures with conformal deposition as well as with bumps resulting from bottom-up fill. Dishing and erosion were characterized for several structures after clearing. The abrasive-free polish resulted in low sensitivity to overpolish and low saturation levels for dishing and erosion. Consequently, this demonstrated superior performance when compared to the International Technology Roadmap for Semiconductors (ITRS) 2000 roadmap targets for planarization. While the conventional slurry could achieve the 0.13-μm technology node requirements, the abrasive-free polish met the planarization requirements beyond the 0.10-μm technology node.  相似文献   
103.
By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems  相似文献   
104.
We prove that to most of the known hypercyclic operators A on separable Banach spaces there exist compact (compact convex, compact connected) subsets K of E such that each compact (compact convex, compact connected) subset of E can be approximated with respect to Hausdorff's distance by for suitable . Received July 8, 1997, in final form October 17, 1997  相似文献   
105.
106.
Boundedness of commutators on homogeneous Herz spaces   总被引:9,自引:0,他引:9  
The boundedness on homogeneous Herz spaces is established for a large class of linear commutators generated by BMO(R n ) functions and linear operators of rough kernels which include the Calderón-Zygmund operators and the Ricci-Stein oRfiUatory singular integrals with rough kernels. Project supponed in pan by the National h’atural Science Foundation of China (Grant No. 19131080) and the NEDF of China.  相似文献   
107.
Summary. The analytic treatment of problems related to the asymptotic behaviour of random dynamical systems generated by stochastic differential equations suffers from the presence of non-adapted random invariant measures. Semimartingale theory becomes accessible if the underlying Wiener filtration is enlarged by the information carried by the orthogonal projectors on the Oseledets spaces of the (linearized) system. We study the corresponding problem of preservation of the semimartingale property and the validity of a priori inequalities between the norms of stochastic integrals in the enlarged filtration and norms of their quadratic variations in case the random element F enlarging the filtration is real valued and possesses an absolutely continuous law. Applying the tools of Malliavin’s calculus, we give smoothness conditions on F under which the semimartingale property is preserved and a priori martingale inequalities are valid. Received: 12 April 1995 / In revised form: 7 March 1996  相似文献   
108.
无线局域网安全问题研究   总被引:10,自引:0,他引:10  
为了提供相当于有线局域网的数据安全,IEEE802.11定义了有线等价保密(WEP)协议。然而,最近的研究发现WEP存在严重的缺陷。介绍了无线局域网存在的安全隐患,分析了WEP的结构以及WEP协议的缺陷以及可能遭受的攻击,并探讨了改进方案。  相似文献   
109.
基于数字机顶盒的电子选单的设计和实现   总被引:1,自引:0,他引:1  
基于CATV和PSTN的VOD多媒体数字机顶盒,提出了几种实现双向通信以完成电子节目指南的设计方案,对各种方案的优缺点进行了详细的讨论,并介绍了所采用方案的实现方法。  相似文献   
110.
本文从小卫星、星座飞速发展以及对测控通信系统新的要求出发,介绍了综合基带、连续波多波束相控阵天线的功能、特点及工作原理,提出了建立新型多功能智能化测控通信站的设想。  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