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   156462篇
  免费   4775篇
  国内免费   2736篇
电工技术   5052篇
技术理论   5篇
综合类   3124篇
化学工业   21946篇
金属工艺   12479篇
机械仪表   10217篇
建筑科学   5703篇
矿业工程   2610篇
能源动力   3236篇
轻工业   6096篇
水利工程   2178篇
石油天然气   5662篇
武器工业   401篇
无线电   16059篇
一般工业技术   33803篇
冶金工业   13092篇
原子能技术   2093篇
自动化技术   20217篇
  2024年   248篇
  2023年   942篇
  2022年   1740篇
  2021年   2496篇
  2020年   1819篇
  2019年   1689篇
  2018年   11221篇
  2017年   12033篇
  2016年   7143篇
  2015年   3018篇
  2014年   3333篇
  2013年   4655篇
  2012年   7026篇
  2011年   13973篇
  2010年   12934篇
  2009年   11492篇
  2008年   11144篇
  2007年   13305篇
  2006年   4060篇
  2005年   7456篇
  2004年   4592篇
  2003年   3929篇
  2002年   2728篇
  2001年   1790篇
  2000年   2034篇
  1999年   2210篇
  1998年   2640篇
  1997年   2043篇
  1996年   1918篇
  1995年   1457篇
  1994年   1180篇
  1993年   864篇
  1992年   625篇
  1991年   563篇
  1990年   396篇
  1989年   365篇
  1988年   302篇
  1987年   197篇
  1986年   152篇
  1985年   122篇
  1984年   93篇
  1968年   129篇
  1967年   117篇
  1966年   149篇
  1965年   126篇
  1960年   89篇
  1957年   130篇
  1956年   119篇
  1955年   140篇
  1954年   153篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
We perform a systematic measurement of the degree-of-polarization (DOP) and eye-closure penalty for optical signals with orthogonal polarizations. We find that the symmetry of DOP is maintained for the orthogonal polarizations under both first and higher order polarization-mode dispersion (PMD), whereas the symmetry of eye-closure penalty is broken under second-order PMD. An orthogonal polarization pair can have large disparity of eye-closure penalty despite an identical DOP. We also demonstrate a novel approach to estimate the maximum eye-closure penalty asymmetry with three orthogonal polarizations on the Poincare/spl acute/ sphere.  相似文献   
32.
Minimum variance beamformers are usually complemented with diagonal loading techniques in order to provide robustness against several impairments such as imprecise knowledge of the steering vector or finite sample size effects. This paper concentrates on this last application of diagonal loading techniques, i.e., it is assumed that the steering vector is perfectly known and that diagonal loading is used to alleviate the finite sample size impairments. The analysis herein is asymptotic in the sense that it is assumed that both the number of antennas and the number of samples are high but have the same order of magnitude. Borrowing some results of random matrix theory, the authors first derive a deterministic expression that describes the asymptotic signal-to-noise-plus-interference ratio (SINR) at the output of the diagonally loaded beamformer. Then, making use of the statistical theory of large observations (also known as general statistical analysis or G-analysis), the authors derive an estimator of the optimum loading factor that is consistent when both the number of antennas and the sample size increase without bound at the same rate. Because of that, the estimator has an excellent performance even in situations where the quotient between the number of observations is low relative to the number of elements of the array.  相似文献   
33.
This paper describes the methodology for simulating a reprographic ink with a ceramic ink based on a commercially available zirconia powder for direct ceramic ink-jet printing. Of over-riding importance was matching viscosity and this was tested systematically by using a mineral oil–hexane binary system. Of secondary importance was adjustment of the pressure defect behind the nozzle to compensate for small differences in surface tension. The inks tested in the wide array print-head were based on low electrical conductivity liquids to avoid damage to the electroding system. The organic binder for the zirconia ink was paraffin wax and the dispersant was a hydroxystearic acid based polyester.  相似文献   
34.
A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented that, coupled with a standard Monte Carlo algorithm, provides an accurate modeling of quantum noise. As a test, the standard results of noise in tunneling junction devices are reproduced within this approach.  相似文献   
35.
DSP--数字化时代的基因芯片   总被引:3,自引:0,他引:3  
DSP是当今发展最为迅速的和最有发展前景的技术之一。与普通CPU和MCU相比 ,DSP在数字信号处理方面有着无可比拟的优势 ,特别适合网络、通信、控制等需要进行大量数字信号处理的应用场合。今天DSP已经成为通信、计算机、网络、工业控制以及家用电器等电子产品中不可或缺的基础器件 ,DSP在通信、计算机、网络、工业控制以及消费类电子产品等领域有着非常广泛的应用 ,本文阐述了DSP的特点、应用和市场以及DSP技术的发展前景。  相似文献   
36.
High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009. Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev.  相似文献   
37.
38.
游梁式抽油机间歇供电装置的研制与应用   总被引:1,自引:0,他引:1  
针对游梁抽油机电动机效率低和井场窃电问题,研制了具有节电和防井场窃电功能的游梁抽油机调压+间歇供电装置。该装置通过控制可控硅的导通角实现在电动机做功期调压供电,在电动机发电期不供电。分析了间歇供电对电动机、抽油机和电网的影响;根据现场实测数据分析了该装置的节电效果及现场应用情况。该装置节电效果显著,能防止井场窃电,可用于对游梁抽油机电动机的长期驱动。  相似文献   
39.
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate.  相似文献   
40.
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