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   212536篇
  免费   15624篇
  国内免费   7226篇
电工技术   11713篇
技术理论   23篇
综合类   11304篇
化学工业   36329篇
金属工艺   10752篇
机械仪表   12526篇
建筑科学   16560篇
矿业工程   4998篇
能源动力   6259篇
轻工业   13113篇
水利工程   3250篇
石油天然气   11179篇
武器工业   1347篇
无线电   26637篇
一般工业技术   28047篇
冶金工业   10995篇
原子能技术   2358篇
自动化技术   27996篇
  2024年   3156篇
  2023年   3951篇
  2022年   6034篇
  2021年   8350篇
  2020年   6674篇
  2019年   5861篇
  2018年   5598篇
  2017年   6372篇
  2016年   6037篇
  2015年   7410篇
  2014年   9636篇
  2013年   12341篇
  2012年   12232篇
  2011年   13878篇
  2010年   11623篇
  2009年   11469篇
  2008年   10878篇
  2007年   10476篇
  2006年   10863篇
  2005年   9631篇
  2004年   6567篇
  2003年   5773篇
  2002年   5252篇
  2001年   4724篇
  2000年   4865篇
  1999年   5642篇
  1998年   5287篇
  1997年   4357篇
  1996年   3958篇
  1995年   3313篇
  1994年   2768篇
  1993年   2187篇
  1992年   1702篇
  1991年   1280篇
  1990年   1019篇
  1989年   880篇
  1988年   685篇
  1987年   501篇
  1986年   400篇
  1985年   339篇
  1984年   214篇
  1983年   201篇
  1982年   165篇
  1981年   145篇
  1980年   131篇
  1979年   97篇
  1978年   63篇
  1977年   63篇
  1976年   77篇
  1975年   38篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
In this study, it is demonstrated that the incorporation of fluorine can enhance poly-Si/Si interfacial oxide break-up in the poly-Si emitter contacted p+-n shallow junction formation. The annealing temperature for breaking up the poly-Si/Si interfacial oxide has been found to be as low as 900°C. As a result, the junction depth of the BF2-implanted device is much larger than that of the boron-implanted device  相似文献   
82.
83.
IC—V100电台锁相环频率合成器   总被引:2,自引:1,他引:1  
本文从频率合成器的结构、功能入手,详细阐述了频率编程的原理及方法。  相似文献   
84.
85.
Load-capacity interference and the bathtub curve   总被引:1,自引:0,他引:1  
Load-capacity (stress-strength) interference theory is used to derive a heuristic failure rate for an item subjected to repetitive loading which is Poisson distributed in time. Numerical calculations are performed using Gaussian distributions in load and capacity. Infant mortality, constant failure rate (Poisson failures), and aging are shown to be associated with capacity variability, load variability, and capacity deterioration, respectively. Bathtub-shaped failure rate curves are obtained when all three failure types are present. Changes in load or capacity distribution parameters often strongly affect the quantitative behavior of the failure-rate curves, but they do not affect the qualitative behavior of the bathtub curve. Neither is it likely that the qualitative behavior will be affected by the use of nonGaussian distributions. The numerical results, however, indicate that infant mortality and wear-out failures interact strongly with load variability. Thus bathtub curves arising from this model cannot be represented as simple superpositions of independent contributions from the three failure types. Only if the three failure types arise from independent failure mechanisms or in different components is it legitimate simply to sum the failure rate contributions  相似文献   
86.
Design issues of photonic integrated devices for WDM applications based on Rowland circle gratings have been studied. Effects of grating period, diffraction order, grating aperture (size), and Rowland circle size on device performance are discussed. The point spread function of a typical Rowland circle grating is evaluated numerically which yields an optical image (spot) size of several microns in diameter. Our study shows that there is a tradeoff between channel dispersion and feedback efficiency in choosing the grating period when a Rowland circle grating is used as the wavelength-selective element for a parallel-waveguide-type wavelength division multiplexing device  相似文献   
87.
The impacts of CVD tungsten polycide (WSix) on MOSFET performance and reliability are studied in this letter. The WSix process is shown to enhance the S/D lateral extent for both N- and P-channel devices via CGD and Leff measurements, confirming previous suspicion. This enhanced S/D extent is found to be easily modulated by drain-to-gate bias, which is favorable for achieving both higher drive currents and higher S/D punch-through voltages than those of non-WSix devices. Both electron and hole mobility for the WSix device are also slightly higher and closer to the published data compared to the non-WSix case. These effects together yield about >5% improvement for nMOSFET and >10% improvement for pMOSFET in drive current at a given punch-through voltage. The channel hot-electron lifetime for the n-channel WSix device is about 10 times higher than that of the non-WSix one. These enhancements in both performance and reliability make the WSix device very attractive fog VLSI CMOS technologies  相似文献   
88.
89.
In recent years industries have increasingly used customer relationship labor in management as a tool to improve their position in the marketplace. This research involves using a data warehouse, decision-tree-based data mining, and neural network pattern classification analysis to isolate the causes of non-conformity in IC packaging. The correctness of the classification analysis produced using the two methods is compared. Our objective is to establish an information analysis system, that is able to quickly identify the causes of problems thereby reducing the time taken to solve quality-related problems. It is shown that predictions made about the target group using decision tree analysis are more accurate than those made by neural network classification, indicating that decision tree analysis is an effective means of classification analysis of a company's quality problems.  相似文献   
90.
因场地淤泥等软土层深厚,在填方荷载作用下,软弱土层产生固结沉降,引起局部构筑物的不均匀沉降,发生结构破坏。采用微型灌注桩加固满足现场各个限制条件的要求,达到了加固目的。  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