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   246151篇
  免费   3075篇
  国内免费   1230篇
电工技术   4879篇
综合类   269篇
化学工业   35901篇
金属工艺   10936篇
机械仪表   7117篇
建筑科学   6365篇
矿业工程   492篇
能源动力   6322篇
轻工业   24288篇
水利工程   1925篇
石油天然气   1350篇
武器工业   3篇
无线电   31236篇
一般工业技术   45272篇
冶金工业   50778篇
原子能技术   3892篇
自动化技术   19431篇
  2021年   1590篇
  2019年   1447篇
  2018年   2355篇
  2017年   2259篇
  2016年   2488篇
  2015年   1991篇
  2014年   3228篇
  2013年   10941篇
  2012年   5521篇
  2011年   7898篇
  2010年   6350篇
  2009年   7042篇
  2008年   7686篇
  2007年   7741篇
  2006年   7116篇
  2005年   6594篇
  2004年   6319篇
  2003年   6334篇
  2002年   6311篇
  2001年   6415篇
  2000年   5846篇
  1999年   6469篇
  1998年   16656篇
  1997年   11641篇
  1996年   9006篇
  1995年   6733篇
  1994年   5962篇
  1993年   5758篇
  1992年   4100篇
  1991年   4027篇
  1990年   3621篇
  1989年   3538篇
  1988年   3473篇
  1987年   2937篇
  1986年   2870篇
  1985年   3446篇
  1984年   3088篇
  1983年   2779篇
  1982年   2582篇
  1981年   2599篇
  1980年   2459篇
  1979年   2297篇
  1978年   2262篇
  1977年   2838篇
  1976年   4200篇
  1975年   1919篇
  1974年   1821篇
  1973年   1808篇
  1972年   1472篇
  1971年   1330篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The impact of crosstalk in an arrayed-waveguide N×N wavelength multiplexer is investigated precisely in relation to its application to wavelength-routing N×N all optical networks. In such systems multiple crosstalk light which has the same wavelength as the signal results in signal-crosstalk beat noise. We confirm that the noise is Gaussian and obtain the relation between crosstalk and power penalty. It is shown that the crosstalk must be less than -38 dB for a 16×16 system to keep the power penalty below 1 dB at a bit error rate of 10-9  相似文献   
32.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration  相似文献   
33.
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies  相似文献   
34.
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models  相似文献   
35.
Two novel configurations for digitally tunable optical filters based on arrayed-waveguide grating (AWG) multiplexers are described in detail with emphasis on the connection of the AWG multiplexer and optical switches. Performance comparisons show that conventional configurations are disadvantaged by the switch size required and loss imbalance among the optical frequency-division-multiplexed (FDM) channels; the proposed configurations require only O(√(N)) switch elements to select one of N FDM channels, and the loss imbalance is lower by up to 75% in decibel  相似文献   
36.
A new lateral MOS-gated thyristor, called the Base-Current-Controlled Thyristor, is described. This device is designed so that most holes at the on-stage reach the P base through the floating P+ region adjacent to the P base and the on-state MOSFET. At the turn-off stage, the interruption of the hole current to the P base due to switching off the above MOSFET occurs simultaneously with the conventional turn-off operation. The concept of this device is verified experimentally by using the fabricated lateral device with the external MOSFET. This device exhibits a better trade-off relation between the on-state voltage and the turn-off time compared uith the conventional MOS-gated thyristor  相似文献   
37.
A novel monitoring method for plasma-charging damage is proposed. This method performs a quick and accurate evaluation using antenna PMOSFET. It was found that not only hot-carrier (HC) lifetime but transistor parameters such as initial gate current and substrate current were changed according to the degree of plasma-charging damage. However, the present work suggests that monitoring the shift of drain current after a few seconds of HC stress is a more accurate method to indicate plasma-charging damage. The monitoring method using the present test structure is demonstrated to be useful for realizing highly reliable devices  相似文献   
38.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications  相似文献   
39.
40.
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