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   528095篇
  免费   24178篇
  国内免费   12111篇
电工技术   20121篇
技术理论   31篇
综合类   17680篇
化学工业   85032篇
金属工艺   27163篇
机械仪表   25304篇
建筑科学   29005篇
矿业工程   10002篇
能源动力   14051篇
轻工业   40578篇
水利工程   6587篇
石油天然气   21511篇
武器工业   2236篇
无线电   61798篇
一般工业技术   77677篇
冶金工业   64811篇
原子能技术   6633篇
自动化技术   54164篇
  2023年   5058篇
  2022年   8713篇
  2021年   12945篇
  2020年   9518篇
  2019年   8628篇
  2018年   10329篇
  2017年   11320篇
  2016年   10334篇
  2015年   12964篇
  2014年   16762篇
  2013年   26866篇
  2012年   22942篇
  2011年   26827篇
  2010年   22730篇
  2009年   22565篇
  2008年   22691篇
  2007年   22459篇
  2006年   22761篇
  2005年   20473篇
  2004年   15087篇
  2003年   14001篇
  2002年   13404篇
  2001年   12712篇
  2000年   12766篇
  1999年   14802篇
  1998年   23206篇
  1997年   17253篇
  1996年   14276篇
  1995年   11121篇
  1994年   9597篇
  1993年   8313篇
  1992年   6155篇
  1991年   5562篇
  1990年   4731篇
  1989年   4415篇
  1988年   4182篇
  1987年   3422篇
  1986年   3226篇
  1985年   3668篇
  1984年   3228篇
  1983年   2862篇
  1982年   2675篇
  1981年   2653篇
  1980年   2497篇
  1979年   2295篇
  1978年   2237篇
  1977年   2808篇
  1976年   4171篇
  1975年   1899篇
  1974年   1795篇
排序方式: 共有10000条查询结果,搜索用时 23 毫秒
41.
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   
42.
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   
43.
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   
44.
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   
45.
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   
46.
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   
47.
48.
研究了两种比活度的131Ⅰ-MIBG在正常及利血平抑制后在鼠体内的分布,结果表明:注射后4h,正常鼠心肌对3.22TBq/g的MIBG摄取为9.08%ID/g,明显高于对18.5GBq/g的摄取(4.87%ID/g)。计算表明,比活度主要影响了鼠心肌交感神经囊泡内摄取,而与囊泡外摄取无关.当MIBG用于心肌显像时,高比活度的MIBG有利于诊断。  相似文献   
49.
50.
Carboxyl-terminated butadiene-acrylonitrile-rubber decreases modulus and yield stress of the studied epoxy but increases fracture toughness. The addition of glass bead compensates for the loss in modulus but has little effect on yield stress. However, it significantly contributes to the fracture toughness by providing additional mechanisms for toughening of both the unmodified and rubber-modified epoxy. For the toughened epoxies studied, fracture surfaces gave only limited information on fracture mechanisms since significant energy absorption also occurs in the material below the fracture surface. Suggestions for suitable material compositions for fiber composite matrices are given.  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