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   578781篇
  免费   6728篇
  国内免费   1858篇
电工技术   9910篇
综合类   2780篇
化学工业   86156篇
金属工艺   24618篇
机械仪表   18225篇
建筑科学   14079篇
矿业工程   3252篇
能源动力   13134篇
轻工业   47381篇
水利工程   6424篇
石油天然气   10295篇
武器工业   83篇
无线电   68143篇
一般工业技术   111998篇
冶金工业   93168篇
原子能技术   11725篇
自动化技术   65996篇
  2021年   3784篇
  2019年   3647篇
  2018年   20179篇
  2017年   19150篇
  2016年   16406篇
  2015年   4994篇
  2014年   7719篇
  2013年   21605篇
  2012年   15018篇
  2011年   25266篇
  2010年   21003篇
  2009年   20205篇
  2008年   22223篇
  2007年   22983篇
  2006年   14262篇
  2005年   14176篇
  2004年   13399篇
  2003年   13132篇
  2002年   12374篇
  2001年   11828篇
  2000年   11361篇
  1999年   11375篇
  1998年   26664篇
  1997年   19478篇
  1996年   15389篇
  1995年   11829篇
  1994年   10637篇
  1993年   10459篇
  1992年   8233篇
  1991年   7852篇
  1990年   7519篇
  1989年   7399篇
  1988年   7222篇
  1987年   6215篇
  1986年   6130篇
  1985年   7161篇
  1984年   6766篇
  1983年   6114篇
  1982年   5779篇
  1981年   6013篇
  1980年   5713篇
  1979年   5486篇
  1978年   5444篇
  1977年   6308篇
  1976年   7995篇
  1975年   5008篇
  1974年   4850篇
  1973年   4889篇
  1972年   4094篇
  1971年   3846篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness.  相似文献   
32.
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon.  相似文献   
33.
We report for the first time optical signal-to-noise penalties which lead to performance degradations in single-fiber long-reach optical access networks when compared to identical dual-fiber systems. A simplified architecture, with reduced optical amplifier count compared to previous work, for single-fiber operation of a symmetrical 10-Gb/s, 1024-way split, 110-km long-reach optical access network is presented and demonstrated. In addition, a possible solution to remove the optical signal-to-noise penalty is suggested  相似文献   
34.
The strong tendency of organic nanoparticles to rapidly self‐assemble into highly aligned superlattices at room temperature when solution‐cast from dispersions or spray‐coated directly onto various substrates is described. The nanoparticle dispersions are stable for years. The novel precipitation process used is believed to result in molecular distances and alignments in the nanoparticles that are not normally possible. Functional organic light‐emitting diodes (OLEDs)—which have the same host–dopant emissive‐material composition—with process‐tunable electroluminescence have been built with these nanoparticles, indicating the presence of novel nanostructures. For example, only changing the conditions of the precipitation process changes the OLED emission from green light to yellow.  相似文献   
35.
An increase in hydrogen evolution from the hydrogen-evolving enzyme in the actinomycete Frankia was recorded in the presence of nickel. Immunogold localisation analysis of the intracellular distribution of hydrogenase proteins indicated that they were evenly distributed in the membranes and cytosol of both hyphae and vesicles. In addition, molecular characterisation of the hydrogen-evolving enzyme at the proteomic level, using two-dimensional gel electrophoresis combined with mass spectrometry, confirmed that the Frankia hydrogen-evolving enzyme is similar to the cyanobacterial bidirectional hydrogenase of Anabena siamensis.  相似文献   
36.
37.
38.
39.
40.
For pt.I see ibid., p.42-55 (2003). The development of a comprehensive decision support system, GMCR II, for the systematic study of real-world interactive decision problems is presented. The companion paper (Part I), discusses how GMCR II elicits, stores, and manages conflict models; here (Part II), the focus is on GMCR IIs analysis and output interpretation subsystems. Specifically, this paper describes the powerful and efficient analysis engine contained in GMCR II, its informative output presentation and interpretation facilities, and a number of follow-up analyses. Furthermore, an illustrative case study is used to demonstrate how GMCR II can be conveniently applied in practice.  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