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   206260篇
  免费   15395篇
  国内免费   7839篇
电工技术   11297篇
技术理论   14篇
综合类   11246篇
化学工业   35750篇
金属工艺   10643篇
机械仪表   12053篇
建筑科学   16472篇
矿业工程   4959篇
能源动力   5862篇
轻工业   12708篇
水利工程   3223篇
石油天然气   11079篇
武器工业   1346篇
无线电   25539篇
一般工业技术   26762篇
冶金工业   10949篇
原子能技术   2121篇
自动化技术   27471篇
  2024年   883篇
  2023年   3266篇
  2022年   5833篇
  2021年   7943篇
  2020年   5808篇
  2019年   5030篇
  2018年   5420篇
  2017年   6212篇
  2016年   5704篇
  2015年   7299篇
  2014年   9541篇
  2013年   12298篇
  2012年   12250篇
  2011年   13904篇
  2010年   11648篇
  2009年   11501篇
  2008年   10914篇
  2007年   10487篇
  2006年   10877篇
  2005年   9651篇
  2004年   6584篇
  2003年   5802篇
  2002年   5260篇
  2001年   4740篇
  2000年   4883篇
  1999年   5655篇
  1998年   5296篇
  1997年   4362篇
  1996年   3976篇
  1995年   3325篇
  1994年   2774篇
  1993年   2191篇
  1992年   1703篇
  1991年   1282篇
  1990年   1019篇
  1989年   879篇
  1988年   683篇
  1987年   501篇
  1986年   395篇
  1985年   334篇
  1984年   214篇
  1983年   198篇
  1982年   163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 11 毫秒
81.
The manufacturing message specification (MMS) is the ISO standard communication protocol specific to manufacturing. To analyze MMS design and performance, service unit automats are introduced to represent individual MMS services, while service connection Petri Nets (PNs) are constructed from these automats to describe MMS service connections and processes. This approach makes MMS protocol specification and analysis possible in terms of well-developed concepts and methods in PN theory. It leads to a distributed and hierarchical model of MMS software system by integrating service connection PNs. A generalized stochastic PN for MMS performance evaluation is obtained by incorporating service parameters and time factors into the model. A technique based on T-invariants is used to simplify the performance analysis  相似文献   
82.
It has been reported that high-temperature (~1100°C) N2 O-annealed oxide can block boron penetration from poly-Si gates to the silicon substrate. However, this high-temperature step may be inappropriate for the low thermal budgets required of deep-submicron ULSI MOSFETs. Low-temperature (900~950°C) N2O-annealed gate oxide is also a good barrier to boron penetration. For the first time, the change in channel doping profile due to compensation of arsenic and boron ionized impurities was resolved using MOS C-V measurement techniques. It was found that the higher the nitrogen concentration incorporated at Si/SiO2 interface, the more effective is the suppression of boron penetration. The experimental results also suggest that, for 60~110 Å gate oxides, a certain amount of nitrogen (~2.2%) incorporated near the Si/SiO2 interface is essential to effectively prevent boron diffusing into the underlying silicon substrate  相似文献   
83.
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   
84.
85.
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   
86.
87.
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   
88.
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   
89.
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   
90.
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