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   243991篇
  免费   2961篇
  国内免费   1241篇
电工技术   4854篇
综合类   264篇
化学工业   35532篇
金属工艺   10877篇
机械仪表   7071篇
建筑科学   6244篇
矿业工程   481篇
能源动力   6311篇
轻工业   24176篇
水利工程   1838篇
石油天然气   1335篇
武器工业   3篇
无线电   31074篇
一般工业技术   44964篇
冶金工业   50212篇
原子能技术   3867篇
自动化技术   19090篇
  2021年   1571篇
  2019年   1429篇
  2018年   2332篇
  2017年   2234篇
  2016年   2452篇
  2015年   1917篇
  2014年   3162篇
  2013年   10825篇
  2012年   5465篇
  2011年   7805篇
  2010年   6297篇
  2009年   6983篇
  2008年   7580篇
  2007年   7674篇
  2006年   7053篇
  2005年   6542篇
  2004年   6255篇
  2003年   6278篇
  2002年   6251篇
  2001年   6380篇
  2000年   5812篇
  1999年   6429篇
  1998年   16603篇
  1997年   11621篇
  1996年   8967篇
  1995年   6702篇
  1994年   5918篇
  1993年   5737篇
  1992年   4057篇
  1991年   3996篇
  1990年   3589篇
  1989年   3510篇
  1988年   3444篇
  1987年   2915篇
  1986年   2845篇
  1985年   3417篇
  1984年   3051篇
  1983年   2748篇
  1982年   2552篇
  1981年   2573篇
  1980年   2436篇
  1979年   2279篇
  1978年   2236篇
  1977年   2810篇
  1976年   4175篇
  1975年   1901篇
  1974年   1797篇
  1973年   1786篇
  1972年   1462篇
  1971年   1318篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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   
72.
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   
73.
74.
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   
75.
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   
76.
77.
The damage imposed on SiO x deposited nylon 6 films as a result of abrasion with a cotton cloth and Gelboflex testing was examined by evaluating the rate at which copper plates, which were enveloped by the damaged films, were corroded by H2S. Abrasion with a cotton cloth caused some micro-cracking of the SiO x layer and the permeation rate of H2S approached that of the uncoated nylon 6 film. Damage to the SiO x layer by twisting and crushing progressed gradually with the number of Gelboflex test cycles and correspondingly the corrosion rate of the copper plates increased. Comparison of the corrosion rates of the copper plates kept in the pouches made of various commercial films with those obtained for the damaged SiO x deposited nylon 6 films showed a clear relationship between the H2 permeation rate of the films and the corrosion rate of the copper plates by H2S.  相似文献   
78.
79.
80.
A 1 V switched-capacitor (SC) bandpass sigma-delta (/spl Sigma//spl Delta/) modulator is realized using a high-speed switched-opamp (SO) technique with a sampling frequency of up to 50 MHz, which is improved ten times more than prior 1 V SO designs and comparable to the performance of the state-of-the-art SC circuits that operate at much higher supply voltages. On the system level, a fast-settling double-sampling SC biquadratic filter architecture is proposed to achieve high-speed operation. A low-voltage double-sampling finite-gain-compensation technique is employed to realize a high-resolution /spl Sigma//spl Delta/ modulator using only low-DC-gain opamps to maximize the speed and to reduce power dissipation. On the circuit level, a fast-switching methodology is proposed for the design of the switchable opamps to achieve a switching frequency up to 50 MHz. Implemented in a 0.35-/spl mu/m CMOS process (V/sub TP/=0.82 V and V/sub TN/=0.65 V) and at 1 V supply, the modulator achieves a measured peak signal-to-noise-and-distortion ratio (SNDR) of 42.3 dB at 10.7 MHz with a signal bandwidth of 200 kHz, while dissipating 12 mW and occupying a chip area of 1.3 mm/sup 2/.  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