全文获取类型
收费全文 | 233977篇 |
免费 | 2815篇 |
国内免费 | 1062篇 |
专业分类
电工技术 | 3872篇 |
综合类 | 2493篇 |
化学工业 | 35138篇 |
金属工艺 | 10428篇 |
机械仪表 | 7906篇 |
建筑科学 | 6524篇 |
矿业工程 | 932篇 |
能源动力 | 5019篇 |
轻工业 | 20845篇 |
水利工程 | 2380篇 |
石油天然气 | 959篇 |
武器工业 | 5篇 |
无线电 | 29608篇 |
一般工业技术 | 44788篇 |
冶金工业 | 26308篇 |
原子能技术 | 2594篇 |
自动化技术 | 38055篇 |
出版年
2019年 | 837篇 |
2018年 | 15376篇 |
2017年 | 14357篇 |
2016年 | 11115篇 |
2015年 | 1657篇 |
2014年 | 2012篇 |
2013年 | 6746篇 |
2012年 | 6253篇 |
2011年 | 13833篇 |
2010年 | 11706篇 |
2009年 | 9578篇 |
2008年 | 11269篇 |
2007年 | 12497篇 |
2006年 | 4453篇 |
2005年 | 5282篇 |
2004年 | 5094篇 |
2003年 | 5038篇 |
2002年 | 4449篇 |
2001年 | 4071篇 |
2000年 | 3910篇 |
1999年 | 3743篇 |
1998年 | 6679篇 |
1997年 | 5252篇 |
1996年 | 4502篇 |
1995年 | 3717篇 |
1994年 | 3369篇 |
1993年 | 3192篇 |
1992年 | 2794篇 |
1991年 | 2712篇 |
1990年 | 2628篇 |
1989年 | 2614篇 |
1988年 | 2467篇 |
1987年 | 2166篇 |
1986年 | 2115篇 |
1985年 | 2556篇 |
1984年 | 2316篇 |
1983年 | 2195篇 |
1982年 | 2068篇 |
1981年 | 1991篇 |
1980年 | 1860篇 |
1979年 | 1874篇 |
1978年 | 1770篇 |
1977年 | 2085篇 |
1976年 | 2563篇 |
1975年 | 1583篇 |
1974年 | 1430篇 |
1973年 | 1453篇 |
1972年 | 1196篇 |
1971年 | 1115篇 |
1970年 | 948篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Current sanitation concepts of decentralised wastewater treatment and reuse raise the issue of monitoring and maintenance of such systems. To guarantee high quality of the recycled water, systems with high requirements concerning process technology are essential. With increasing numbers of decentralised treatment systems spread over far distances it will become more and more impossible and uneconomic to have expert personnel on site. Therefore, new visualisation and intelligent information systems are necessary. The paper describes the structure and 3D-demonstrations as a base for information visualisation. Up-to-date visualisation techniques, facilitating the cognition of context-adapted information, make it possible to maximise the amount of information presented to the user without overwhelming her or him. Concerning diagnosis and decision support systems in the domain of wastewater treatment, several interesting approaches are presented, estimating their applicability for decentralised wastewater treatment systems. The intelligent decision support system presented here consists of a combined ontology- and case-based reasoning system in addition to a process monitoring system. It is responsible for plausibility checks, error diagnosis, solution proposals, and optimisation suggestions. 相似文献
993.
994.
995.
A study was undertaken to determine the influence of number of blades and their thickness on the performance of the Kramer type shear compression cell Cells with 4, 6, 8, 10 and 12 blades, with corresponding blade thicknesses ranging from 6.4 to 0.4 mm, were manufactured and compared against a standard Kramer shear cell Seven canned vegetables were used in the trials. Maximum force, bio-yield force, firmness and energy to maximum force were recorded and compared in testing these products in the different cell configurations. Very thin blades proved to be a source of mechanical problems when used with firm products and will not be used in any further studies. Readings obtained with the various cell configurations were product dependent and forces with the standard cell were higher. Blade spacing is a critical factor in the cell design. 相似文献
996.
With the “orthogonal experimental design” (OED), the dependence of conductivity and transparency of tin oxide films and open circuit voltage Voc of SIS solar cells on the spray deposition process factors was studied. The OED technique was found to be a powerful method for realizing the best factor combination. Using OED, curves were obtained which clearly depict the effects of each factor on the SIS characteristics. The results of the experiments also illustrate exactly which variation in fabrication technique most affects the sheet resistance, Voc, and film transparency. Under the optimal combination of conditions, a thin film doped with NH4F was obtained, with about 90% transmission and a sheet resistance of about 80 Ω/□, along with an SIS structure with a Voc of about 0.61 V. 相似文献
997.
998.
Dorn R. Baumgartner A. Goth A. Gutu-Nelle A. Koppenborg J. Rehm W. Schneider R. Schneider S. von Wirth J. Weber D. 《Lightwave Technology, Journal of》1991,9(6):709-714
Mechanically shaped preforms (MSP) have been demonstrated to combine economic non-CVD (chemical vapor deposition) processing and low loss, with a published value of 0.63 dB/km and a size of 30 fkm/preform. Improved processing is proposed which results in a minimum loss of 0.27 dB/km at 1550 nm. Preforms capable of yielding 150 fkm have been produced. Reboiling during preform stretching and fiber pulling is identified as the last remaining problem of the process 相似文献
999.
W. Klas U. Herpers M. Reich R. Michel R. Droste R. Holm E.-M. Horn G. Müller 《工业材料与腐蚀》1991,42(11):570-575
The radiotracer technique as a means to investigate the corrosion of zirconium, tantalum, and a Ta-40Nb alloy in fluoride containing azeotropic nitric acid Zirconium and tantalum as well as the tantalum 40% niobium alloy are of considerable technical importance due to their high corrosion resistance against numerous corrosive media. With respect to corrosion testing in analytically pure azeotropic nitric acid in the temperature range between 20 and 121°C, corrosion rates were determined for zirconium: 7 · 10?6 to 5 · 10?4 mm/y, for tantalum: 10?8 to 4 · 10?6 mm/y, and for the Ta-40Nb alloy: 2 · 10?7 to 8 · 10?6 mm/y [1]. These corrosion rates will be markedly increased by adding small amounts of fluorides or by fluoride impurities. The radiotracer method after neutron activation was applied to determine the corrosion rates in azeotropic fluoride containing nitric acid. Even minute additions of fluorides strongly affect the corrosion resistance of zirconium. In the range between 0.15 and 10 ppm F? and at a temperature of 108°C, corrosion rates between 5.3 · 10?3 and 3.1 mm/y were measured. It was impossible to establish a limit for the fluoride concentration, below which the corrosion rate of zirconium will not be adversely influenced. The corrosion rates of tantalum and the Ta-40Nb alloy are considerably increasing above a fluoride concentration of 10 ppm. The highest corrosion rates measured were between 8.4 · 10?3 mm/y at 50°C/280 ppm F? and 1.4 · 10?2 mm/y at 110°C/320 ppm F?. Within the range of this investigation, the corrosion resistance of tantalum was higher than that of the Ta-40Nb alloy by one order of magnitude. The corrosion resistance of zirconium and tantalum was not influenced by any treatment of the samples before testing. 相似文献
1000.