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   13479篇
  免费   1774篇
  国内免费   609篇
化学   453篇
晶体学   10篇
力学   854篇
综合类   133篇
数学   4980篇
物理学   2853篇
无线电   6579篇
  2024年   26篇
  2023年   156篇
  2022年   220篇
  2021年   252篇
  2020年   317篇
  2019年   285篇
  2018年   336篇
  2017年   456篇
  2016年   548篇
  2015年   508篇
  2014年   876篇
  2013年   920篇
  2012年   883篇
  2011年   934篇
  2010年   761篇
  2009年   765篇
  2008年   854篇
  2007年   947篇
  2006年   778篇
  2005年   707篇
  2004年   599篇
  2003年   590篇
  2002年   469篇
  2001年   443篇
  2000年   378篇
  1999年   324篇
  1998年   252篇
  1997年   225篇
  1996年   179篇
  1995年   176篇
  1994年   95篇
  1993年   82篇
  1992年   83篇
  1991年   63篇
  1990年   46篇
  1989年   33篇
  1988年   36篇
  1987年   34篇
  1986年   20篇
  1985年   47篇
  1984年   26篇
  1983年   17篇
  1982年   12篇
  1981年   14篇
  1980年   22篇
  1979年   19篇
  1978年   9篇
  1977年   8篇
  1976年   9篇
  1973年   4篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
采用信息融合技术的IR/MMW复合导引头的目标跟踪   总被引:2,自引:0,他引:2  
从误差测量环节入手,基于IR/MMW双模结构,采用信息融合处理技术提高其估计跟踪精度,最终达到降低制导误差,提高武器性能的目的,仿真结果验证了该方法的有效性。  相似文献   
142.
This paper analyses the HIPERLAN channel access mechanism. Both a purely mathematical and a simulation model are built in order to evaluate the two successive phases of the contention scheme. Several optimisations, based on the choice of parametric values, are proposed, evaluated and compared.  相似文献   
143.
1 Introduction The calling dwell time characteristic is critical for the user network planning and deployment, e.g., global system for mobile communications (GSM), as well as the next generation wireless multimedia networks, such as, the currently standar…  相似文献   
144.
静电驱动悬臂梁数模转换器设计、分析与模拟   总被引:1,自引:0,他引:1  
提出了一种新型的微电子机械数模转换器 (MEMDAC)———静电驱动悬臂梁数模转换器 .与传统的静电驱动悬臂梁执行器相比 ,新的结构能更精确地控制梁的挠度 .文中给出了此MEMDAC的设计、分析和模拟过程 .有限元(FEA)分析表明此MEMDAC的最大输出位移为 1 5 1μm ,分辨率为 0 1μm ,其最大非线性误差为 0 0 3μm .  相似文献   
145.
对数正态概率纸的自动生成和分布参数的自动提取   总被引:1,自引:0,他引:1  
采用对数正态概率纸可以直观地判断一组数据是否服从对数正态分布,而且还可以得到对数正态分布参数,即对数均值和对数标准差。介绍对数正态概率纸自动生成和分布参数自动提取的方法以及据此开发的软件。与手工使用概率纸的常规方法相比,采用所开发的软件不但使用简单、方便,而且能提高计算结果的精度。  相似文献   
146.
有序分组资料的线性趋势检验主要用于检验几个二项总体反应率的线性趋势;在医学与生物学中最典型的用途是研究剂量和反应的关系. 如果用Z检验来代替通常在本检验中所用的卡方检验,就可容易地导出本检验的确切概率计算方法,和其他2×C有序列联表有着相同的形式.本文给出了该检验的确切概率计算方法.  相似文献   
147.
The wide production of biomolecular data of the last 30 years, mainly due to the rapid evolving of technologies as well as to the accomplishment of the Genome Projects, led to the necessity of appropriate computational approaches for data storage, manipulation and analyses, giving place to a fast evolving area of Biology: Computational Biology or Bioinformatics.We propose here a new method for the storage of the sequences and their analyses using the C + + programming language, checking the effectiveness of an object oriented approach for new models, suitable to manage data representation and analyses, to improve the efficiency of computational methodologies to solve problems of general interest in bioinformatics. We developed a framework with the aim to decrease the computational costs for the storage and some basic manipulations of nucleic acid sequences. The remarkable reduction of memory requirements with no loss of efficiency makes this approach a first well promising step in order to get a more efficient environment for the manipulation and the management of nucleic acid data sets, in a field of research with hard challenges for Computer and Life Sciences.Mathematics Subject Classification: 68U99G. Toraldo, via Universita’ 100, 80055 Portici, Napoli, Italy  相似文献   
148.
Inexact Newton methods for the nonlinear complementarity problem   总被引:2,自引:0,他引:2  
An exact Newton method for solving a nonlinear complementarity problem consists of solving a sequence of linear complementarity subproblems. For problems of large size, solving the subproblems exactly can be very expensive. In this paper we study inexact Newton methods for solving the nonlinear, complementarity problem. In such an inexact method, the subproblems are solved only up to a certain degree of accuracy. The necessary accuracies that are needed to preserve the nice features of the exact Newton method are established and analyzed. We also discuss some extensions as well as an application. This research was based on work supported by the National Science Foundation under grant ECS-8407240.  相似文献   
149.
在传统光调制器驱动电路中,所用HBT截止频率的大小要达到驱动电路传输速率的4倍以上.文中在输出级采用共射共基HBT形式后,其器件的截止频率只需大于电路传输速率的2倍即可,从电路设计的角度降低了对所用器件的要求.文中分析了新的电路结构提高传输速率的原因并给出了模拟结果.同时新的电路结构也具有良好的热稳定性.  相似文献   
150.
In this paper, a generalized multiple-input multiple-output (MIMO) antenna system that can be fitted to the uplink of a wireless communication system is considered for the general case of multi-user. At the transmitter, the information bits are Turbo coded, then interleaved and passed through a serial-to-parallel converter. The channel is assumed bad urban suffering from multipath Rayleigh fading resulting in inter-symbol and multiple access interferences (ISI and MAI). At the front-end of the receiver, a number of receiving antennas are used followed by a joint multi-user estimator based on the Minimum Mean Square Error Block Linear Equalizer (MMSE-BLE).Computer simulations demonstrate a significant performance improvement in both single user and multi-user cases.This paper depends in parts on that presented at the 11th European Wireless Conference, Cyprus, Nicosia, pp. 187–192, April 2005. Yasmine A. Fahmy was born in Guiza, Egypt, on June 4, 1976. She received the B.Sc., M.Sc. and Ph.D. degrees in Communication and Electronics engineering from Cairo University, Egypt on 1999, 2001 and 2005 respectively. She is presently an assistant professor at Cairo University, Egypt. Her current field of interest is wireless communication and channel estimation. Hebat-Allah M. Mourad received her B.Sc., M. Sc. and Ph.D. degrees in electrical communication engineering from Cairo University, Egypt, in 1983, 1987 and 1994 respectively. Since 1983, she has been with the Department of Electronics and Communications, Faculty of Engineering, Cairo University, and is currently associate professor there. Her research interests include optical fiber communications, mobile and satellite communications. Emad K. Al-Hussaini received his B.Sc degree in Electrical Communication Engineering from Ain-Shams University, Cairo, Egypt, in 1964 and his M.Sc and Ph.D. degrees from Cairo University, Giza, Egypt, in 1974 and 1977, respectively. From 1964 to 1970, he was with the General Egyptian Aeroorganization. Since 1970, he has been with the Department of Electronics and Communications, Faculty of Engineering, Cairo University, and is currently professor there. He was a research fellow at Imperial College, London, UK, and at the Moore School of Electrical Engineering, University of Pennsylvania, Philadelphia, PA, USA, in the academic years 1976/1977 and 1981/1982, respectively. In 1990, he received the Egyptian national encouragement award for outstanding engineering research. He has written several papers for technical international journals and conferences. His research interests include signal processing, fading channel communication, modulation, and cellular mobile radio systems. Dr Al-Hussaini is a senior member of IEEE. He is listed in Marquis Whos Who in the World and in the IBC (International Biographical Center, Cambridge) for outstanding people of the 20th century.  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