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   419089篇
  免费   4086篇
  国内免费   981篇
电工技术   7075篇
综合类   272篇
化学工业   65537篇
金属工艺   19227篇
机械仪表   13044篇
建筑科学   9349篇
矿业工程   3258篇
能源动力   8989篇
轻工业   33000篇
水利工程   5294篇
石油天然气   13191篇
武器工业   24篇
无线电   42852篇
一般工业技术   86934篇
冶金工业   73560篇
原子能技术   12289篇
自动化技术   30261篇
  2021年   3370篇
  2018年   5980篇
  2017年   6038篇
  2016年   6474篇
  2015年   3815篇
  2014年   6538篇
  2013年   17132篇
  2012年   10217篇
  2011年   13460篇
  2010年   11013篇
  2009年   12472篇
  2008年   12870篇
  2007年   12723篇
  2006年   11089篇
  2005年   10304篇
  2004年   9709篇
  2003年   9387篇
  2002年   9378篇
  2001年   9236篇
  2000年   8892篇
  1999年   8825篇
  1998年   20659篇
  1997年   15271篇
  1996年   11721篇
  1995年   8912篇
  1994年   7998篇
  1993年   7965篇
  1992年   6224篇
  1991年   6213篇
  1990年   6116篇
  1989年   6055篇
  1988年   5985篇
  1987年   5212篇
  1986年   5260篇
  1985年   5904篇
  1984年   5619篇
  1983年   5247篇
  1982年   4885篇
  1981年   5196篇
  1980年   4899篇
  1979年   5066篇
  1978年   5209篇
  1977年   5754篇
  1976年   7371篇
  1975年   4784篇
  1974年   4675篇
  1973年   4713篇
  1972年   4210篇
  1971年   3834篇
  1970年   3343篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Exact pairwise error probability of space-time codes   总被引:9,自引:0,他引:9  
We describe a simple technique for the numerical calculation, within any desired degree of accuracy, of the pairwise error probability (PEP) of space-time codes over fading channels. This method applies also to the calculation of E[Q(√ξ)] for any nonnegative random variable ξ whose moment-generating function Φξ(s)=E[exp(-sξ)] is known. Its application to the multiple antenna independent Rayleigh-fading channel and to the Rayleigh block fading channel is discussed, and illustrated by two simple examples  相似文献   
112.
Efficient numerical solution techniques have been developed and used to examine the electromagnetic fields that can be developed in the working volume of the CW Ellipticus antenna operated at frequencies from 100 kHz to 1 GHz. An exponentially tapered transition section is designed to obtain the desired illumination pattern in the working volume. The input transition section is needed for impedance matching and to drive efficiently the Ellipticus antenna. A parametric study is performed to ascertain the performance of the Ellipticus antenna for frequencies up to 1 GHz  相似文献   
113.
114.
115.
An instrument is proposed for continuously tracking the Sun and measuring its height by the use of a laser gyrometer as measuring converter. The accuracy in photoelectric sighting on the Sun is improved by greatly reducing the light fluxes to be compared by screening out the central part of the Sun's image in the focal plane. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 7–9, March, 1994.  相似文献   
116.
A method is given for calculating the monitoring reliability parameters (MRP) for an engineering system with allowance for the drift in the measurement error of the means of measurement (MM). The approach is based on introducing a biased MM error distribution into the traditional formulas for the conditional probabilities of spurious and unobserved failure. The bias at the center of the distribution is determined by the systematic error at the given instant. An example is given to illustrate the performance in MRP calculation.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 12–13, January, 1994.  相似文献   
117.
The mass and charge identification of secondary particles with Z < 4 by a large CsI(T1) scintillation detector is performed using pulse shape analysis and time-of-flight methods. The dependence of the light output on E, A and Z is studied in the energy range of 1–20 MeV/A and special attention is paid to the integration time of the photomultiplier anode signal. It is found that the behaviour of the calibration curves strongly depends on the choice of the integration time interval.  相似文献   
118.
This paper presents a high-speed, small-area circuit specifically designed to identify the levels in the read out operation of a flash multilevel memory. The circuit is based on the analog computation of the Euclidean distance between the current read out from a memory cell and the reference currents that represent the different logic levels. An experimental version of the circuit has been integrated in a standard double-metal 0.7-μm CMOS process with a die area of only 140×100 μm2. Operating under a 5-V power supply, this circuit identifies the read-out current of a memory cell, and associates it with the appropriate logic level in 9 ns  相似文献   
119.
A modification to the `shape-invariant' sinusoidal speech model is proposed, whereby the phases of the component sinewaves used for the excitation are made to add coherently at each glottal closure. Applied to pitch and time-scale modification, higher quality synthetic speech is produced when large changes are required  相似文献   
120.
The authors report the design of a new current-mode A/D converter, based on a modified successive-approximations model, in 1.2 μm CMOS technology. The proposed circuit is characterised by good accuracy and fast dynamic performance, low power consumption and small occupation area. SPICE simulations allow the design approach to be validated and the electrical performance of the ADC to be predicted  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