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   4801篇
  免费   83篇
  国内免费   8篇
电工技术   182篇
综合类   7篇
化学工业   916篇
金属工艺   88篇
机械仪表   73篇
建筑科学   72篇
矿业工程   2篇
能源动力   112篇
轻工业   368篇
水利工程   22篇
石油天然气   10篇
无线电   528篇
一般工业技术   735篇
冶金工业   1343篇
原子能技术   131篇
自动化技术   303篇
  2023年   20篇
  2022年   78篇
  2021年   86篇
  2020年   35篇
  2019年   45篇
  2018年   49篇
  2017年   43篇
  2016年   75篇
  2015年   36篇
  2014年   91篇
  2013年   175篇
  2012年   126篇
  2011年   178篇
  2010年   123篇
  2009年   152篇
  2008年   155篇
  2007年   134篇
  2006年   124篇
  2005年   116篇
  2004年   114篇
  2003年   114篇
  2002年   103篇
  2001年   128篇
  2000年   96篇
  1999年   138篇
  1998年   561篇
  1997年   338篇
  1996年   242篇
  1995年   130篇
  1994年   136篇
  1993年   114篇
  1992年   67篇
  1991年   56篇
  1990年   55篇
  1989年   53篇
  1988年   55篇
  1987年   51篇
  1986年   51篇
  1985年   46篇
  1984年   37篇
  1983年   38篇
  1982年   40篇
  1981年   45篇
  1980年   25篇
  1979年   28篇
  1978年   23篇
  1977年   31篇
  1976年   54篇
  1975年   15篇
  1973年   15篇
排序方式: 共有4892条查询结果,搜索用时 0 毫秒
41.
引言 凌力尔特公司最新的一组电源监控器(包含三款器件)是6输入电压监视器,对当今那些需要进行准确电源监视的多电压系统提供了一种理想选择.LTC2930、LTC2931和LTC2932能够在-40℃至125℃的温度范围内保持1.5%的门限准确度.  相似文献   
42.
43.
We have developed the advanced performance, small-scale InGaP/GaAs heterojunction bipolar transistors (HBTs) by using WSi/Ti base electrode and buried SiO2 in the extrinsic collector. The base-collector capacitance CBC was further reduced to improve high-frequency performance. Improving the uniformity of the buried SiO 2, reducing the area of the base electrode, and optimizing the width of the base-contact enabled us to reduce the parasitic capacitance in the buried SiO2 region by 50% compared to our previous devices. The cutoff frequency fT of 156 GHz and the maximum oscillation frequency fmax of 255 GHz were obtained at a collector current IC of 3.5 mA for the HBT with an emitter size SE of 0.5×4.5 μm2, and fT of 114 GHz and fmax of 230 GHz were obtained at IC of 0.9 mA for the HBT with SE of 0.25×1.5 μm2. We have also fabricated digital and analog circuits using these HBTs. A 1/8 static frequency divider operated at a maximum toggle frequency of 39.5 GHz with a power consumption per flip-flop of 190 mW. A transimpedance amplifier provides a gain of 46.5 dB·Ω with a bandwidth of 41.6 GHz at a power consumption of 150 mW. These results indicate the great potential of our HBTs for high-speed, low-power circuit applications  相似文献   
44.
A new class of zero-correlation zone sequences   总被引:15,自引:0,他引:15  
In this correspondence, two new methods for constructing sets of zero-correlation zone (ZCZ) sequences are proposed. These methods are based on perfect sequences and unitary matrices. Compared with previous methods, the proposed methods can generate sets of nonbinary ZCZ sequences having a longer zero-correlation zone. The sequences obtained by these methods are suitable for approximately synchronized code-division multiple-access (AS-CDMA) systems.  相似文献   
45.
Optical response of tin nitride (SnNx) films, which were deposited onto quartz substrates by means of atmospheric pressure, halide chemical vapor deposition (AP-HCVD), were examined by pulsed irradiation of a YAG laser (532 nm). It was observed that the transmittance of a light of a He-Ne laser (633 nm) through the SnNx film decreases after the film is irradiated with a YAG laser. The atomic force microscopy (AFM) micrograph observation confirmed that spot-like humps appeared on the SnNx film surface in the regions spotted by the YAG laser. This phenomenon was explained in terms of the laser-assisted thermal decomposition of SnNx to β-tin.  相似文献   
46.
A multiobjective genetic algorithm (GA) based on Fonseca-Fleming's Pareto-based ranking and fitness-sharing techniques has been applied to aerodynamic shape optimization of cascade airfoil design. Airfoil performance is evaluated by a Navier-Stokes code. Evaluation of GA population is parallelized on the Numerical Wind Tunnel, a parallel vector machine. The present multiobjective design seeks high pressure rise, high flow turning angle, and low total pressure loss at a low Mach number. Pareto solutions that perform better than existing control diffusion airfoils were obtained  相似文献   
47.
A feedforward-compensator-design technique is presented for industrial control systems. The proposed feedforward compensator can improve dynamic characteristics of multidimensional systems by modifying the input signals. The multidimensional feedforward-compensator design is based on the pole assignment regulator, the minimal-order observer, and the conversion from a closed-loop system to an open-loop system. The effectiveness of the proposed feedforward compensator is demonstrated by a simulation study of temperature control of a thermal power plant and by experiments of the contour control of an articulated robot arm.  相似文献   
48.
The transmission and radiation characteristics at an acute bend of a transmission line are investigated analytically. First, in consideration of the strong coupling to the adjacent conductor, the current distributions are decomposed into even and odd modes. Applying the traveling-wave mode method to these modes, it is shown that transmission characteristics of the line with an acute bend can be easily obtained. The abrupt variation of the voltage near the bend is noted. Next, the discontinuities of the traveling wave currents are regarded as radiating sources and the radiation field from the bend in the transmission line is derived by the summation of fields created by each of the discontinuities. It is found that there exist the electric field component radiating strongly in the directions of propagation of the current and another electric field component radiating strongly into the intermediate direction. Finally, by comparing with the former method and experimental results, the validity of the method is confirmed  相似文献   
49.
Inclined crystallographic planes of the wurtzite structure were investigated in comparison with the zincblende structure in terms of surface geometry characteristics. The ball–stick model indicates that the semipolar surface possesses a surface polarity resembling the anion polarity, which agrees with the common experimental observations of epitaxial growth preference for the cation-polarity surface over the surface. The wurtzite surface was found to share geometrical similarities with the zincblende {100} surface uniquely among the possible semipolar planes. This finding encourages epitaxial growth on the plane of wurtzite semiconductors, e.g., GaN, with the potential of avoiding atomic step formations typically associated with off-axis crystallographic planes.  相似文献   
50.
A control scheme for accurately optimizing (and also automatically stabilizing) the interferometer phase bias of symmetric-Mach-Zehnder (SMZ)-type ultrafast all-optical switches is proposed. In this control scheme, weak continuous-wave light is used as supervisory input light and its spectral power ratio at the switch output is used as a bipolar error signal. Our experimental results for 168-Gb/s 16:1 demultiplexing with a hybrid-integrated SMZ switch indicate the feasibility and the sensitivity of this control scheme.  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