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   243673篇
  免费   2944篇
  国内免费   1243篇
电工技术   4829篇
综合类   264篇
化学工业   35481篇
金属工艺   10862篇
机械仪表   7066篇
建筑科学   6239篇
矿业工程   481篇
能源动力   6276篇
轻工业   24150篇
水利工程   1837篇
石油天然气   1335篇
武器工业   3篇
无线电   31061篇
一般工业技术   44897篇
冶金工业   50131篇
原子能技术   3860篇
自动化技术   19088篇
  2021年   1566篇
  2019年   1424篇
  2018年   2322篇
  2017年   2223篇
  2016年   2446篇
  2015年   1911篇
  2014年   3163篇
  2013年   10799篇
  2012年   5454篇
  2011年   7796篇
  2010年   6291篇
  2009年   6974篇
  2008年   7563篇
  2007年   7667篇
  2006年   7036篇
  2005年   6526篇
  2004年   6255篇
  2003年   6268篇
  2002年   6246篇
  2001年   6380篇
  2000年   5807篇
  1999年   6418篇
  1998年   16561篇
  1997年   11600篇
  1996年   8952篇
  1995年   6692篇
  1994年   5908篇
  1993年   5732篇
  1992年   4055篇
  1991年   3994篇
  1990年   3585篇
  1989年   3505篇
  1988年   3441篇
  1987年   2909篇
  1986年   2846篇
  1985年   3413篇
  1984年   3053篇
  1983年   2744篇
  1982年   2549篇
  1981年   2572篇
  1980年   2432篇
  1979年   2273篇
  1978年   2238篇
  1977年   2810篇
  1976年   4174篇
  1975年   1902篇
  1974年   1798篇
  1973年   1787篇
  1972年   1461篇
  1971年   1318篇
排序方式: 共有10000条查询结果,搜索用时 13 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