全文获取类型
收费全文 | 515866篇 |
免费 | 7117篇 |
国内免费 | 1796篇 |
专业分类
电工技术 | 9863篇 |
综合类 | 526篇 |
化学工业 | 78724篇 |
金属工艺 | 17986篇 |
机械仪表 | 15075篇 |
建筑科学 | 14793篇 |
矿业工程 | 1174篇 |
能源动力 | 13708篇 |
轻工业 | 54756篇 |
水利工程 | 4060篇 |
石油天然气 | 2270篇 |
武器工业 | 17篇 |
无线电 | 68022篇 |
一般工业技术 | 95078篇 |
冶金工业 | 93367篇 |
原子能技术 | 7040篇 |
自动化技术 | 48320篇 |
出版年
2021年 | 3216篇 |
2019年 | 3035篇 |
2018年 | 4565篇 |
2017年 | 4654篇 |
2016年 | 4995篇 |
2015年 | 4135篇 |
2014年 | 6911篇 |
2013年 | 23858篇 |
2012年 | 12220篇 |
2011年 | 17677篇 |
2010年 | 13643篇 |
2009年 | 15642篇 |
2008年 | 16906篇 |
2007年 | 17352篇 |
2006年 | 15573篇 |
2005年 | 14562篇 |
2004年 | 14144篇 |
2003年 | 13813篇 |
2002年 | 13428篇 |
2001年 | 13634篇 |
2000年 | 12619篇 |
1999年 | 13152篇 |
1998年 | 28785篇 |
1997年 | 21314篇 |
1996年 | 16987篇 |
1995年 | 13451篇 |
1994年 | 12043篇 |
1993年 | 11493篇 |
1992年 | 8958篇 |
1991年 | 8503篇 |
1990年 | 8114篇 |
1989年 | 7860篇 |
1988年 | 7502篇 |
1987年 | 6414篇 |
1986年 | 6324篇 |
1985年 | 7712篇 |
1984年 | 7148篇 |
1983年 | 6376篇 |
1982年 | 5996篇 |
1981年 | 5879篇 |
1980年 | 5513篇 |
1979年 | 5394篇 |
1978年 | 5024篇 |
1977年 | 6117篇 |
1976年 | 8043篇 |
1975年 | 4261篇 |
1974年 | 4035篇 |
1973年 | 3941篇 |
1972年 | 3177篇 |
1971年 | 2792篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
An UHV surface electron microscope is described which allows the study of surfaces under vacuum conditions common in surface science with the following techniques: LEERM; LEED; photo, thermionic, secondary emission microscopy; absolute micro area work function measurements. In particular, the first LEERM of Mo(110) and Si(111) surfaces are presented. They show monoatomic steps with high contrast due to Fresnel diffraction and structural differences, respectively. Condensed silver crystallites are imaged. Gold adsorption layers on Si(111) show strong contrast in photoemission; the layer thickness is deduced from LEED. 相似文献
942.
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
943.
944.
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
945.
946.
J.N. Staniforth 《Powder Technology》1985,45(1):73-77
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
947.
948.
Goldman Susan R.; Mertz Davis L.; Pellegrino James W. 《Canadian Metallurgical Quarterly》1989,81(4):481
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
949.
950.
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