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   359821篇
  免费   12674篇
  国内免费   6128篇
电工技术   11869篇
技术理论   7篇
综合类   7845篇
化学工业   55521篇
金属工艺   17156篇
机械仪表   14308篇
建筑科学   15833篇
矿业工程   3911篇
能源动力   9718篇
轻工业   31717篇
水利工程   3922篇
石油天然气   8577篇
武器工业   879篇
无线电   44228篇
一般工业技术   58555篇
冶金工业   55415篇
原子能技术   5121篇
自动化技术   34041篇
  2023年   2434篇
  2022年   4334篇
  2021年   6406篇
  2020年   4760篇
  2019年   4537篇
  2018年   5659篇
  2017年   6097篇
  2016年   5696篇
  2015年   6550篇
  2014年   8800篇
  2013年   17444篇
  2012年   12772篇
  2011年   15634篇
  2010年   13148篇
  2009年   13502篇
  2008年   13867篇
  2007年   13630篇
  2006年   13269篇
  2005年   11960篇
  2004年   9930篇
  2003年   9484篇
  2002年   9246篇
  2001年   9119篇
  2000年   8691篇
  1999年   9522篇
  1998年   19144篇
  1997年   13818篇
  1996年   10985篇
  1995年   8468篇
  1994年   7339篇
  1993年   6767篇
  1992年   4904篇
  1991年   4659篇
  1990年   4062篇
  1989年   3930篇
  1988年   3787篇
  1987年   3149篇
  1986年   3007篇
  1985年   3510篇
  1984年   3115篇
  1983年   2789篇
  1982年   2610篇
  1981年   2607篇
  1980年   2465篇
  1979年   2281篇
  1978年   2238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 15 毫秒
31.
We have analyzed degradation of N-channel thin-film-transistor (TFT) under dynamic stress using a pico-second time-resolved emission microscope. We have successfully detected emission at pulse fall edge for the first time. Emission intensity increased with the decrease of pulse fall time. As the degradation depended on the pulse fall time, this dependence clearly illustrates that hot electrons are the dominant cause of the degradation under dynamic stress. Based on these dependences, we proposed a model considering electron traps in the poly-Si.  相似文献   
32.
In this letter, bandpass filters with one or two tunable transmission zeros are proposed. The reconfigurable transmission zeros are implemented through varactors in combination with tapped quarter-wavelength stubs. Based on mixed mode simulations including EM simulation and circuit simulation, the proposed filters were designed and fabricated on low-cost FR4 board. The measurement results verified the design concepts.  相似文献   
33.
Towards intelligent dressing   总被引:1,自引:0,他引:1  
The aim of this article is to state the principles of an intelligent monitoring and control system for the grinding machine, comprising the dressing process as well as grinding stability.  相似文献   
34.
This paper presents a simple alternative for an electronic ballast operating in self-sustained oscillating mode with dimming capability for fluorescent lamps. A simple modification in one of the gate drivers side circuit allows the lamp to dim without compromising the simplicity, reliability, and low cost which characterize the self-oscillating electronic ballast (SOEB). A qualitative analysis is presented to explain the behavior of the proposed self-oscillating electronic ballast with dimming feature. In addition, the stability and the key equations for the design are derived using the extended Nyquist criterion and describing function method. Experimental results from two 40-W electronic ballasts are presented to demonstrate the performance and to validate the analysis carried out.  相似文献   
35.
Over the last five years, many activities have focused on the unexploited field of carrying out reactions on small scales. Due to the rapid development of new components, this paper deals with recent developments only in a compressed form. An important point is the analysis of possible plant concepts for microreactors and whether these are a sensible option. Due to the enormous difference in size between the microchannels and the fluid periphera of possible components this is not just a technical question. It touches on the microtechnology concept as a whole. The direction in which the field should be developed and which measures can be taken to influence its development are questions that are addressed here with respect to the big industrial interest in microreactors.  相似文献   
36.
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   
37.
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   
38.
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   
39.
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   
40.
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   
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