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   609426篇
  免费   9129篇
  国内免费   2849篇
电工技术   11941篇
技术理论   5篇
综合类   1501篇
化学工业   94157篇
金属工艺   22784篇
机械仪表   17539篇
建筑科学   16667篇
矿业工程   2435篇
能源动力   15008篇
轻工业   60602篇
水利工程   5600篇
石油天然气   7528篇
武器工业   256篇
无线电   73873篇
一般工业技术   112888篇
冶金工业   113568篇
原子能技术   10024篇
自动化技术   55028篇
  2021年   4639篇
  2019年   4104篇
  2018年   6490篇
  2017年   6527篇
  2016年   7098篇
  2015年   5670篇
  2014年   9163篇
  2013年   27853篇
  2012年   15913篇
  2011年   22162篇
  2010年   17403篇
  2009年   19300篇
  2008年   20800篇
  2007年   21223篇
  2006年   18937篇
  2005年   17263篇
  2004年   16152篇
  2003年   15573篇
  2002年   15258篇
  2001年   15413篇
  2000年   14411篇
  1999年   14799篇
  1998年   33595篇
  1997年   24647篇
  1996年   19322篇
  1995年   14957篇
  1994年   13427篇
  1993年   13049篇
  1992年   9990篇
  1991年   9472篇
  1990年   9213篇
  1989年   8933篇
  1988年   8540篇
  1987年   7214篇
  1986年   7202篇
  1985年   8547篇
  1984年   8162篇
  1983年   7229篇
  1982年   6648篇
  1981年   6799篇
  1980年   6339篇
  1979年   6402篇
  1978年   6033篇
  1977年   6922篇
  1976年   9166篇
  1975年   5175篇
  1974年   4918篇
  1973年   4860篇
  1972年   4008篇
  1971年   3563篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
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   
993.
994.
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   
995.
Ordered mixes were produced using a fructose-based excipient as a coarse carrier component and fine-particle pyridoxine hydrochloride (vitamin B6) as the adherent component. Prior to mixing, the fructose agglomerates were conditioned for 48 h at either 0% RH or 55% RH at 20 °C. Under these conditions, one lot of fructose had a moisture content of 0.24 wt.% and the other lot had a moisture content of 0.74 wt.%. Following mixing, the powders were subjected to vibration at various frequencies in the range 25 to 200 Hz and accelerations in the range 9.81 to 39.24 m/s2. It was found that whilst ordered mixes produced using fructose at 0.24 wt.% moisture content were unstable, those produced using 0.74 wt.% moisture content fructose were extremely stable and segregation resistant.The formation of ordered units with increased adhesion in carriers with higher moisture content suggested that these ordered mixes could be considered as spontaneous granulations.  相似文献   
996.
997.
Practice on addition basic facts and changes in solution strategies were examined in 3rd- and 4th-grade students, practicing over 3 months. Response latencies decreased, indicating positive practice effects. Each of 3 student groups demonstrated different solution–strategy mixtures. Different mixtures led to different practice effects, indexed by shifts to more efficient counting strategies and more direct retrieval. Expectations about effects of practice and instructional strategies for optimizing practice must be sensitive to a child's actual strategy pattern. Most students had decreasing latency practice functions. However, quantitative functions fit to the practice session data indicated a high proportion of cases where the latency pattern over sessions was nonmonotonic. Trends over a small number of practice sessions may be inadequate for decisions about the utility of further practice, because such data may poorly represent long-term, cumulative effects on modifying strategy usage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
999.
This paper draws attention to the basic principles governing reflections in uniform Bragg reflectors (BR) when measured employing optical low coherence reflectometry (OLCR) technique. Using computations based on transfer matrix method (TMM), we first showed a strong spectral dependence of Bragg reflectograms on an OLCR probe spectrum. Later, this dependence is exploited to evaluate, for the first time, the coupling coefficient κ of a Bragg grating in a distributed Bragg reflector (DBR) laser on InP  相似文献   
1000.
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