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   482120篇
  免费   5938篇
  国内免费   1295篇
电工技术   9060篇
综合类   706篇
化学工业   72095篇
金属工艺   17401篇
机械仪表   13976篇
建筑科学   12089篇
矿业工程   2114篇
能源动力   13134篇
轻工业   44817篇
水利工程   4633篇
石油天然气   7225篇
武器工业   15篇
无线电   58708篇
一般工业技术   92695篇
冶金工业   89584篇
原子能技术   9726篇
自动化技术   41375篇
  2021年   4060篇
  2019年   3796篇
  2018年   6195篇
  2017年   6063篇
  2016年   6285篇
  2015年   4268篇
  2014年   7325篇
  2013年   22255篇
  2012年   11803篇
  2011年   16340篇
  2010年   12932篇
  2009年   14730篇
  2008年   15165篇
  2007年   15094篇
  2006年   13243篇
  2005年   12249篇
  2004年   11926篇
  2003年   11566篇
  2002年   11051篇
  2001年   11310篇
  2000年   10888篇
  1999年   11411篇
  1998年   27217篇
  1997年   19589篇
  1996年   15475篇
  1995年   11761篇
  1994年   10765篇
  1993年   10380篇
  1992年   7915篇
  1991年   7577篇
  1990年   7286篇
  1989年   7220篇
  1988年   7024篇
  1987年   5926篇
  1986年   5955篇
  1985年   7002篇
  1984年   6400篇
  1983年   6023篇
  1982年   5371篇
  1981年   5618篇
  1980年   5171篇
  1979年   5160篇
  1978年   5005篇
  1977年   5860篇
  1976年   7657篇
  1975年   4312篇
  1974年   4162篇
  1973年   4194篇
  1972年   3438篇
  1971年   3098篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Computer security issues are normally addressed from a technical perspective. Increasingly, however, organizations and computer specialists are coming to realise that applying more technology as the basis of an answer to a problem that derives from technology cannot, in the long term, be a viable solution. This paper shows how it is important that other considerations are taken into account, such as business and management requirements, and practical user issues. In order for this approach to make any progress, we must first establish the current situation in ordinary organizations. This paper describes key results from research carried out to determine the status of computer security in organizations today.  相似文献   
992.
993.
Dynafill, Dynasan-114, Lutrol-F68, PEG-10000 and PEG-20000 have been examined as potential bases for the preparation of fusion formed solid dispersions for molten filling into hard gelatin capsules. Investigations included, an examination of thermal effects on crystal structure by DSC and XRD, a theological study to evaluate capsule filling characteristics, dissolution studies on drug/base formulations, chemical analysis for free fatty acid impurities in Dynafill and Dynasan-114, and detailed studies on selected drug/base formulations. PEG-20000 and Dynasan-114 were not examined in detail, after preliminary investigations had shown high viscosity and poor filling characteristics for PEG-20000 and poor dissolution characteristics for Dynasan-114. Dynafill provided good release profiles when formulated with a variety of model drugs (Acetohexamide, Ibuprofen, Indomethacin, Quinidine sulphate and Theophylline). Results from hot stage photomicrography supported by DSC and XRD were used to construct a phase diagram of the Ibuprofen/Lutrol-F68 system. The evidence from the phase diagram indicated the formulation of a simple eutectic system with no solid solubility and a eutectic composition at approximately 35% w/w Ibuprofen.  相似文献   
994.
It is shown that vibrational stabilization can be effective for linear systems with large bounded delays. Theorems are given that define the procedures for the search of the stabilizing vibrations. Robust oscillatory stabilization insensitive to the delay size is also shown to take place for some classes of systems  相似文献   
995.
The advantages and disadvantages of electric furnaces for melting frits and enamels and glasses for special applications were examined. It was shown that low-efficiency electric furnaces are more economical than furnaces heated by organic fuel. The main advantage of electric furnaces is the reduction in harmful emissions.Translated from Steklo i Keramika, Nos. 3–4, pp. 8–10, March–April, 1994.  相似文献   
996.
997.
A new three-terminal power switch called the Accumulation Channel driven Bipolar Transistor (ACBT) is proposed and experimentally demonstrated. In the on-state, the characteristics of the ACBT have been found to approach those of a P-I-N rectifier with a MOSFET in series for regulating its current, an equivalent circuit considered to be an ideal for MOS/Bipolar power devices. Unlike previous devices, the high off-state voltage is supported by the formation of a potential barrier to the flow of electrons from the N+ emitter into the N-drift region within a depletion region. The absence of the P-base region within the ACBT cells eliminates the parasitic four layer PNPN thyristor which had limited the performance of previous MOS/Bipolar transistor structures. Consequently, the ACBT structure has large maximum controllable and surge current densities in addition to low on-state voltage drop and high-voltage current saturation capability  相似文献   
998.
A computer simulation is used to study the problem of internal scattering for targets that are imaged using X-ray microtomography. A strategy is outlined for selecting X-ray energy and image resolution based on properties of the material being imaged. The X-ray scanning process is simulated by applying a Monte Carlo technique to a modeled target that emulates the material properties of a microelectronic device. The X-ray photons are subject to photoelectric absorption, Rayleigh scattering, and Compton scattering. The simulation applies a method of high-resolution image reconstruction based on discrete Fourier transforms. Examples of reconstructed images that have 0.5-μm spatial resolution are shown for images of simulated lead and aluminum targets  相似文献   
999.
1000.
An algorithm utilizing the minimal number of integrations for the exact linearization of nonlinear systems to Brunovsky normal form under nonlinear feedback is presented. The tools which are involved are based on classical constructions appearing in the theory of exterior differential systems  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