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   586224篇
  免费   8499篇
  国内免费   2070篇
电工技术   10599篇
综合类   527篇
化学工业   87399篇
金属工艺   19595篇
机械仪表   16609篇
建筑科学   16285篇
矿业工程   1275篇
能源动力   16244篇
轻工业   62028篇
水利工程   4656篇
石油天然气   3384篇
武器工业   16篇
无线电   76634篇
一般工业技术   106311篇
冶金工业   111541篇
原子能技术   7685篇
自动化技术   56005篇
  2021年   3968篇
  2020年   2856篇
  2019年   3622篇
  2018年   5622篇
  2017年   5707篇
  2016年   6203篇
  2015年   4928篇
  2014年   8248篇
  2013年   27696篇
  2012年   14703篇
  2011年   21223篇
  2010年   16349篇
  2009年   18615篇
  2008年   19828篇
  2007年   20156篇
  2006年   18316篇
  2005年   16868篇
  2004年   16306篇
  2003年   15981篇
  2002年   15253篇
  2001年   15589篇
  2000年   14318篇
  1999年   15325篇
  1998年   36185篇
  1997年   25906篇
  1996年   20005篇
  1995年   15499篇
  1994年   13691篇
  1993年   13314篇
  1992年   9720篇
  1991年   9258篇
  1990年   8747篇
  1989年   8378篇
  1988年   8087篇
  1987年   6708篇
  1986年   6558篇
  1985年   8081篇
  1984年   7473篇
  1983年   6626篇
  1982年   6100篇
  1981年   6164篇
  1980年   5742篇
  1979年   5455篇
  1978年   5063篇
  1977年   6151篇
  1976年   8129篇
  1975年   4267篇
  1974年   4044篇
  1973年   3969篇
  1972年   3121篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Thrombin-induced platelet malondialdehyde (MDA) formation and plasma malondialdehyde-like material (MDA-LM) were evaluated in 12 healthy subjects before and after 1 and 7 days from aspirin (1 g) ingestion. 24 hr after aspirin administration, platelet MDA was almost abolished while MDA-LM showed a 23% decrease. Platelet MDA and plasma MDA-LM returned to baseline values 7 days after aspirin ingestion. These data suggest that platelet cyclooxygenase pathway affects only in part plasma MDA-LM. The evaluation of plasma MDA-LM before and after aspirin could be useful for evaluating in vivo platelet cyclooxygenase activation.  相似文献   
992.
993.
A very broad framework for control system design is considered that encompasses frequency-response methodologies for H optimization that solve various aspects of the control design problem and that are less well known that state-space methods. The focus is on linear programming, Lawson's algorithm, and Trefethen's algorithm. A modified Lawson's algorithm is proposed and related to Trefethan's method. The modified algorithm is shown to be significantly faster than linear programming and Lawson's algorithm. It is also shown how to extend the modified Lawson's algorithm so as to handle time-domain constraints in addition to frequency-domain specifications, which distinguishes it from other H optimization methods. Some steps are taken toward dealing with time domain constraints within an H optimization framework  相似文献   
994.
This paper discusses the successful application of the Acoustic Emission Technique (AET) for detection and location of leak paths present on the inaccessible side of an end shield of a Pressurised Heavy Water Reactor (PHWR). The methodology was based on the fact that air and water leak AE signals have different characteristic features. Baseline data was generated from a sound end-shield of a PHWR for characterizing the background noise. A mock up end-shield system with saw cut leak paths was used to verify the validity of the methodology. It was found that air leak signals under pressurisation (as low as 3 psi) could be detected by frequency domain analysis. Signals due to air leaks from various locations of a defective end-shield were acquired and analysed. It was possible to detect and locate leak paths. Presence of detected leak paths were further confirmed by alternate test.  相似文献   
995.
Summary The flow pattern of the slosh motion of a homogeneous, nonviscous (inviscid) and incompressible fluid with a free surface, contained in a rigid circular canal, has been dealt with analytically and experimentally. The axis of the canal is perpendicular to the direction of gravity. Considered are transverse (lateral to axis) oscillations of the liquid. The shape of the free liquid surface is determined numerically by means of a simple procedure. Theoretically calculated streamlines (path lines) are found to be in good qualitative agreement with experimentally observed trajectories of small spheres, made of plastic material and immersed in the liquid. The plastic particles and the liquid (water with a solution of salt added) have the same density.  相似文献   
996.
997.
The growth kinetics, crystal structure, and morphology of the intermetallic compounds formed between nickel, electroless Ni-P and electroless Ni-B coatings with tin at 453 to 493 K for times up to 506 h have been determined by microscopical and X-ray diffraction techniques. The compound Ni3Sn4 was formed. All kinetics followed as parabolic law with activation energies of 128.0, 130.4, and 122.3 kJ mol–1 for the Ni/Sn, Ni-P/Sn and Ni-B/Sn systems, respectively. The rate of growth of Ni3Sn4 in the Ni/Sn and Ni-P/Sn systems were similar but the rate of growth in the Ni-B/Sn system was five times faster. Pores occurred in the intermetallic compound formed in the Ni-P/Sn system and these are discussed in relation to the density of the phases.  相似文献   
998.
999.
1000.
This paper derives two fuzzy financial profitability models, namely, a least cost solution model and a cost-benefit analysis model, to evaluate the fuzzy financial profitability of load management alternatives. A straightforward vertex parameters' fuzzy mathematics operation using the function principle is derived as an alternative to the traditional extension principle and is applied to evaluate a number of different financial decision indexes. Compared to the extension principle, the function principle is simple to implement and is conceptually straightforward. The geometric moments of the fuzzy financial indexes are established in order to determine their relative ranking as part of a decision-making process. The performances of the proposed fuzzy financial models are verified by considering their application to two practical load management programs in Taiwan, namely, a cooling energy storage air conditioner and a cogeneration project. These investigations not only confirm that the results of the fuzzy financial models are consistent with those of the conventional crisp models but also demonstrate that the proposed models are more flexible, intelligent, and computationally efficient compared to the extension principle fuzzy mathematics approach. The developed models represent readily implemented possibility analysis tools for use in the arena of uncertain financial decision-making.  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