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   464341篇
  免费   50171篇
  国内免费   20726篇
电工技术   37620篇
技术理论   21篇
综合类   39865篇
化学工业   60209篇
金属工艺   29179篇
机械仪表   31941篇
建筑科学   34583篇
矿业工程   15776篇
能源动力   13152篇
轻工业   46296篇
水利工程   13130篇
石油天然气   19111篇
武器工业   5073篇
无线电   52046篇
一般工业技术   46139篇
冶金工业   18551篇
原子能技术   7068篇
自动化技术   65478篇
  2025年   3179篇
  2024年   11221篇
  2023年   10648篇
  2022年   17383篇
  2021年   22306篇
  2020年   17419篇
  2019年   13059篇
  2018年   12843篇
  2017年   14644篇
  2016年   13666篇
  2015年   19201篇
  2014年   23782篇
  2013年   28422篇
  2012年   33342篇
  2011年   35015篇
  2010年   32210篇
  2009年   30943篇
  2008年   31017篇
  2007年   30063篇
  2006年   27440篇
  2005年   22776篇
  2004年   16348篇
  2003年   11713篇
  2002年   10541篇
  2001年   9668篇
  2000年   8400篇
  1999年   5869篇
  1998年   3952篇
  1997年   3321篇
  1996年   3001篇
  1995年   2443篇
  1994年   1971篇
  1993年   1497篇
  1992年   1236篇
  1991年   940篇
  1990年   707篇
  1989年   620篇
  1988年   471篇
  1987年   346篇
  1986年   290篇
  1985年   189篇
  1984年   173篇
  1983年   143篇
  1982年   119篇
  1981年   113篇
  1980年   157篇
  1979年   81篇
  1978年   33篇
  1959年   57篇
  1951年   70篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
华风气象影视大楼总面积4万平方米,根据空间功能不同分为办公大楼和商务写字楼两部分,办公大楼是集演播室、制作机房、办公室为一体的九层综合性建筑。设计师杨宇在刚接触到这个项目的时候,面对的是一个既成事实的建筑。  相似文献   
2.
Undoped and phosphorus (P)-doped diamond-clad Si field emitter arrays have been successfully fabricated using microwave plasma chemical vapor deposition (MPCVD) technology. The electron emission from the blunt diamond-clad microtips are much higher than those for the pure Si tips with sharp curvature due to a lower work function. Furthermore, the characteristics of emission current against applied voltage for the P-doped diamond-clad tips show superior emission at lower field to the undoped ones. After the examination of Auger electron spectroscopy (AES) and electrical characteristics of as-grown diamond, such a significant enhancement of the electron emission from the P-doped diamond-clad tips is attributed to a higher electron conductivity and defect densities  相似文献   
3.
The oxygen absorption process in highly aligned YBa2Cu3Ox samples in air and in pure oxygen was studied at several constant temperatures. The process can be expressed in two steps, a chemical reaction controlled step and a diffusion controlled step. The kinetic equations are as follows respectively:
(1 − at) ln(1 − at) + at = kDt

The activation energy was calculated using an Arrhenius equation. The technical conditions of heat treatment for oxygen absorption of highly aligned YBa2Cu3Ox crystals are discussed.  相似文献   

4.
A technique for SiO2 formation by liquid-phase deposition (LPD) at nearly room temperature for low-temperature processed (LTP) polysilicon thin-film transistor (poly-Si TFT) was developed. LPD SiO2 film with a lower P-etch rate shows a dense structure. LPD SiO2 also exhibits good electrical characteristics. LTP poly-Si thin-film transistors (TFTs) with LPD SiO 2 as the gate insulator have been fabricated and investigated. Their characteristics indicate performance adequate for their use as pixel transistors in liquid crystal displays (LCDs)  相似文献   
5.
The use of the analytically decoupled near-tip displacement solutions as an alternative approach, is presented in this paper for the efficient finite element evaluation of the decoupled weight functions for an orthotropic 2-D crack. This alternative approach has been validated by directly comparing the prior weight function results with a symmetric mesh approach in the crack-tip neighborhood, and indirectly by comparing the calculated stress intensity factors (KI(II)) values using the computed weight functions with available KI(II) solutions of the 2-D mixed mode orthotropic cracks. In addition, this approach with analytically decoupled near-tip displacement solutions for calculating weight functions at all locations, can facilitate further extension of weight function evaluations to a more general 2-D anisotropic crack.  相似文献   
6.
There is no good method to measure the shape and the strain distributions of a structure changing with time. We have previously proposed the Fourier transform grid method (FTGM) to measure the three-dimensional shape and surface strain distributions of stationary objects by analysing the two-dimensional grating images recorded with two cameras. In the stereoscopic method, it is very important to determine the accurate geometric parameters of the camera system. In this paper, the positions and the directions of cameras are accurately determined using the FTGM applied to images of a reference object on which a two-dimensional grating is drawn. Applications for analysing shape and strain distributions of vibrating rubber plates and a moving human skin are shown.  相似文献   
7.
An anti-plane, semi-infinite crack in polarized ceramics is analyzed using the theory of elastic dielectrics with electric field gradient. The effects of electric field gradient on electromechanical fields around the crack is examined.  相似文献   
8.
We demonstrate the first programmable group-delay module based on polarization switching. With a unique binary tuning mechanism, the device can generate any differential group delay value from -45 to +45 ps with a resolution of 1.40 ps, or any true-time-delay value from 0 to 45 ps with a resolution of 0.7 ps. The delay varying speeds for both applications are under 1 ms and can be as fast as 0.1 ms. We evaluate both the dynamic and static performances of the device while paying special attention to its dynamic figures of merit for polarization-mode dispersion emulation and compensation applications. Our experiment shows that the device exhibits a negligible transient-effect induced power penalty (<0.2 dB) in a 10-Gb/s nonreturn-to-zero system.  相似文献   
9.
The cellular neural network (CNN) architecture combines the best features from traditional fully-connected analog neural networks and digital cellular automata. The network can rapidly process continuous-valued (gray-scale) input signals (such as images) and perform many computation functions which traditionally were implemented in digital form. Here, we briefly introduce the the theory of CNN circuits, provide some examples of CNN applications to image processing, and discuss work toward a CNN implementation in custom CMOS VLSI. The role of analog computer-aided design (CAD) will be briefly presented as it relates to analog neural network implementation.This work is supported in part by the Office of Naval Research under Contract N00014-89-J1402, and the National Science Foundation under grant MIP-8912639.  相似文献   
10.
This letter discusses the difference between piezoelectric constitutive relations for the case of one-dimensional stress and the case of one-dimensional strain, and its implications in the modeling of Rosen piezoelectric transformers.  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