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   1653篇
  免费   41篇
  国内免费   7篇
化学   1019篇
晶体学   6篇
力学   50篇
数学   128篇
物理学   282篇
无线电   216篇
  2021年   17篇
  2020年   18篇
  2019年   18篇
  2018年   9篇
  2017年   16篇
  2016年   26篇
  2015年   27篇
  2014年   23篇
  2013年   59篇
  2012年   85篇
  2011年   100篇
  2010年   58篇
  2009年   48篇
  2008年   89篇
  2007年   107篇
  2006年   116篇
  2005年   94篇
  2004年   90篇
  2003年   53篇
  2002年   51篇
  2001年   25篇
  2000年   37篇
  1999年   26篇
  1998年   15篇
  1997年   15篇
  1996年   30篇
  1995年   18篇
  1994年   15篇
  1993年   33篇
  1992年   27篇
  1991年   24篇
  1990年   18篇
  1989年   12篇
  1988年   13篇
  1987年   15篇
  1986年   17篇
  1985年   15篇
  1984年   16篇
  1983年   10篇
  1982年   17篇
  1981年   9篇
  1980年   11篇
  1979年   17篇
  1978年   13篇
  1977年   15篇
  1976年   12篇
  1975年   14篇
  1974年   15篇
  1973年   15篇
  1972年   9篇
排序方式: 共有1701条查询结果,搜索用时 578 毫秒
1.
2.
3.
4.
如今的汽车电子系统越来越复杂。同时,汽车环境对任何电子产品来说都是很大的挑战,因为汽车电子系统要求运行电压很宽,并且有很大的瞬态电压和温度变化。另外,性能要求也越来越高,需要多个供应电压以满足系统的不同要求。典型的  相似文献   
5.
许多微处理器和数字信号处理器(DSP)需要一个核心电源和一个在启动期间必须进行排序的输入/输出(I/O)电源。如果未经过适当的电源排序,可能发生闭锁或过流,从而损害微处理器的I/O端口或诸如存储器、逻辑电路、现场可编程门阵列(FPGA)或数据转换器之类支持设备的I/O端口。为了确保在主电源电压未被适当偏置之前I/O负载不被驱动,对核心电源电压和I/O电源电压进行跟踪是必要的。  相似文献   
6.
This paper introduces a novel approach for extracting the maximum number of non-overlapping test forms from a large collection of overlapping test sections assembled from a given item bank. The approach involves solving maximum set packing problems (MSPs). A branch-and-bound MSP algorithm is developed along with techniques adapted from constraint programming to estimate lower and upper bounds on the optimal MSP solution. The algorithm is general and can be applied in other applications including combinatorial auctions. The results of computer simulations and experiments with an operational item bank are presented. An erratum to this article is available at .  相似文献   
7.
For a conformal manifold we introduce the notion of an ambient connection, an affine connection on an ambient manifold of the conformal manifold, possibly with torsion, and with conditions relating it to the conformal structure. The purpose of this construction is to realise the normal conformal Tractor holonomy as affine holonomy of such a connection. We give an example of an ambient connection for which this is the case, and which is torsion free if we start the construction with a C-space, and in addition Ricci-flat if we start with an Einstein manifold. Thus, for a C-space this example leads to an ambient metric in the weaker sense of Čap and Gover, and for an Einstein space to a Ricci-flat ambient metric in the sense of Fefferman and Graham. Current address for first author: Erwin Schr?dinger International Institute for Mathematical Physics (ESI), Boltzmanngasse 9, 1090 Vienna, Austria Current address for second author: Department of Mathematics, University of Hamburg, Bundesstra?e 55, 20146 Hamburg, Germany  相似文献   
8.
Two machine learning techniques were evaluated for automatic design of a rule-based control of functional electrical stimulation (FES) for locomotion of spinal cord injured humans. The task was to learn the invariant characteristics of the relationship between sensory information and the FES-control signal by using off-line supervised training. Sensory signals were recorded using pressure sensors installed in the insoles of a subject's shoes and goniometers attached across the joints of the affected leg. The FES-control consisted of pulses corresponding to time intervals when the subject pressed on the manual push-button to deliver the stimulation during FES-assisted ambulation. The machine learning techniques used were the adaptive logic network (ALN) and the inductive learning algorithm (IL). Results to date suggest that, given the same training data, the IL learned faster than the ALN while both performed the test rapidly. The generalization was estimated by measuring the test errors and it was better with an ALN, especially if past points were used to reflect the time dimension. Both techniques were able to predict future stimulation events. An advantage of the ALN over the IL was that ALN's can be retrained with new data without losing previously collected knowledge. The advantages of the IL over the ALN were that the IL produces small, explicit, comprehensible trees and that the relative importance of each sensory contribution can be quantified  相似文献   
9.
10.
We present an overview of some of our work on transmission properties and mode characteristics of layered metamaterials and their potential applications. In particular, we will show how layered metamaterials exhibit unusual transmission properties and unconventional features of guided modes, such as resonance-induced transparency in multilayer structures and slope reversal of dispersion curves in coupled waveguides. PACS 78.67.-n; 73.21.Ac; 61.46.+w; 42.25.Bs; 42.82.Et  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