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   6312篇
  免费   372篇
  国内免费   21篇
电工技术   125篇
综合类   7篇
化学工业   1389篇
金属工艺   239篇
机械仪表   386篇
建筑科学   113篇
矿业工程   2篇
能源动力   335篇
轻工业   512篇
水利工程   23篇
石油天然气   6篇
武器工业   2篇
无线电   943篇
一般工业技术   1435篇
冶金工业   598篇
原子能技术   65篇
自动化技术   525篇
  2024年   5篇
  2023年   74篇
  2022年   98篇
  2021年   165篇
  2020年   151篇
  2019年   139篇
  2018年   190篇
  2017年   185篇
  2016年   211篇
  2015年   157篇
  2014年   267篇
  2013年   360篇
  2012年   443篇
  2011年   507篇
  2010年   357篇
  2009年   407篇
  2008年   366篇
  2007年   302篇
  2006年   228篇
  2005年   218篇
  2004年   184篇
  2003年   162篇
  2002年   165篇
  2001年   132篇
  2000年   133篇
  1999年   116篇
  1998年   252篇
  1997年   172篇
  1996年   117篇
  1995年   94篇
  1994年   60篇
  1993年   65篇
  1992年   30篇
  1991年   20篇
  1990年   23篇
  1989年   25篇
  1988年   24篇
  1987年   21篇
  1986年   13篇
  1985年   10篇
  1984年   3篇
  1983年   7篇
  1982年   8篇
  1981年   7篇
  1979年   3篇
  1977年   9篇
  1976年   13篇
  1975年   2篇
  1973年   1篇
  1967年   1篇
排序方式: 共有6705条查询结果,搜索用时 15 毫秒
41.
K- and Q-bands CMOS frequency sources with X-band quadrature VCO   总被引:1,自引:0,他引:1  
Fully integrated 10-, 20-, and 40-GHz frequency sources are presented, which are implemented with a 0.18-/spl mu/m CMOS process. A 10-GHz quadrature voltage-controlled oscillator (QVCO) is designed to have output with a low dc level, which can be effectively followed by a frequency multiplier. The proposed multipliers generate signals of 20 and 40 GHz using the harmonics of the QVCO. To have more harmonic power, a frequency doubler with pinchoff clipping is used without any buffers or dc-level shifters. The QVCO has a low phase noise of -118.67 dBc/Hz at a 1-MHz offset frequency with a 1.8-V power supply. The transistor size effect on phase noise is investigated. The frequency doubler has a low phase noise of -111.67 dBc/Hz at a 1-MHz offset frequency is measured, which is 7 dB higher than a phase noise of the QVCO. The doubler can be tuned between 19.8-22 GHz and the output is -6.83 dBm. A fourth-order frequency multiplier, which is used to obtain 40-GHz outputs, shows a phase noise of -102.0 dBc/Hz at 1-MHz offset frequency with the output power of -18.0 dBm. A large tuning range of 39.3-43.67 GHz (10%) is observed.  相似文献   
42.
This paper deals with a stochastic version of the simple facility location problem where the demands of customers are random variables. Under the assumption of step function type distribution of demands, the problem is shown to be approximated by a mixed 0-1 linear programming problem. A heuristic procedure is developed to solve the problem, which successfully extends the well known dual-based approach by Bilde & Krarup, and Erlenkotter. Computational results with 20 test problems are presented to demonstrate the effectiveness of the proposed heuristic.  相似文献   
43.
Changes in the microstructure and dielectric properties with the variation of the donor/acceptor ratio in BaTiO3 ceramics were investigated. In donor-rich specimens, a liquid that appeared during sintering did not penetrate into grain boundaries. However, in the acceptor-rich specimens, the grains were separated by a liquid film during sintering. The much higher mobility of the liquid film than that of the grain boundaries was suggested to cause extensive grain growth in acceptor-rich BaTiO3. The macroscopic homogenization of dopants because of grain growth in acceptor-rich specimens resulted in changes in the dielectric properties.  相似文献   
44.
薄膜晶体管液晶电视(TFT-LCD TV)因为具有薄、轻、紧凑和可随意放置的特点,已经占据了大部分电视机市场。除了这些物理特性以外,最重要的特性是已具有了良好像质的对比度。为了将对比度提高到1:600以上,对偏振片膜、背光源板、滤色片树脂、电极锥角和摩擦条件等都进行了研究。优化的背光板组合,光滑的电极锥角和摩擦方法的控制是提高对比度的主要控制因素。应用新开发的滤色片树脂,对获得高对比度最为有效。  相似文献   
45.
46.
We present a structured procedure for order pick system (OPS) analysis and design that has been established on literature review and interviews with and presentations to OPS experts. In particular, we attempt to include the thinking processes that occur between OPS designers and owners. The design procedure and related issues are discussed in the order of input, selection, and evaluation stages.  相似文献   
47.
48.
To analyze the chatter mechanics, the power spectrum of a time series method was analyzed by considering cutting and structural dynamics. In this study, several time series models such as AR (burg, least square, yule walker, geometric lattice, instrument variable), ARX (arx, iv4), ARMAX, ARMA, Box Jenkins, Output Error were modeled and compared with one another. Finally, it was proved that arx, armax and iv4 are more desirable and reliable algorithms than the others for the calculation of the chatter mode in the endmilling operation. The cutting forces Fx and Fz have more powerful effects on the chatter than Fy in the sense that there is no shifting or pseudo mode in the power spectrum.  相似文献   
49.
Surface and normal ensembles for surface reconstruction   总被引:1,自引:0,他引:1  
The majority of the existing techniques for surface reconstruction and the closely related problem of normal reconstruction are deterministic. Their main advantages are the speed and, given a reasonably good initial input, the high quality of the reconstructed surfaces. Nevertheless, their deterministic nature may hinder them from effectively handling incomplete data with noise and outliers. An ensemble is a statistical technique which can improve the performance of deterministic algorithms by putting them into a statistics based probabilistic setting. In this paper, we study the suitability of ensembles in normal and surface reconstruction. We experimented with a widely used normal reconstruction technique [Hoppe H, DeRose T, Duchamp T, McDonald J, Stuetzle W. Surface reconstruction from unorganized points. Computer Graphics 1992;71-8] and Multi-level Partitions of Unity implicits for surface reconstruction [Ohtake Y, Belyaev A, Alexa M, Turk G, Seidel H-P. Multi-level partition of unity implicits. ACM Transactions on Graphics 2003;22(3):463-70], showing that normal and surface ensembles can successfully be combined to handle noisy point sets.  相似文献   
50.
In this letter, we examined whether the parasitic bipolar junction transistors (BJTs) in the MOSFET fabricated by the standard CMOS process can play a role as a fluorescence detector. To suppress the action of two vertical parasitic BJTs, the gate and n-well were tied in the parasitic BJTs, and the body node was connected to the drain. The proposed device was compared with the inherent and the parasitic diodes in the MOSFET. It had 100 times higher photocurrents than the diodes in the MOSFET. In addition, it was applied for the detection of the fluorescent signal, and could detect near 10 nM of Alexa 546. Therefore, CMOS-process-compatible parasitic BJTs can be used as a photodetector in an integrated fluorescence detector.  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