全文获取类型
收费全文 | 58055篇 |
免费 | 1751篇 |
国内免费 | 204篇 |
专业分类
电工技术 | 718篇 |
综合类 | 671篇 |
化学工业 | 8280篇 |
金属工艺 | 1010篇 |
机械仪表 | 1296篇 |
建筑科学 | 1617篇 |
矿业工程 | 424篇 |
能源动力 | 931篇 |
轻工业 | 3401篇 |
水利工程 | 742篇 |
石油天然气 | 106篇 |
武器工业 | 5篇 |
无线电 | 3422篇 |
一般工业技术 | 6192篇 |
冶金工业 | 22675篇 |
原子能技术 | 285篇 |
自动化技术 | 8235篇 |
出版年
2023年 | 348篇 |
2022年 | 492篇 |
2021年 | 724篇 |
2020年 | 369篇 |
2019年 | 392篇 |
2018年 | 951篇 |
2017年 | 1117篇 |
2016年 | 1581篇 |
2015年 | 1189篇 |
2014年 | 1043篇 |
2013年 | 1491篇 |
2012年 | 2979篇 |
2011年 | 3502篇 |
2010年 | 1448篇 |
2009年 | 1572篇 |
2008年 | 1388篇 |
2007年 | 1343篇 |
2006年 | 1134篇 |
2005年 | 3794篇 |
2004年 | 2984篇 |
2003年 | 2452篇 |
2002年 | 1156篇 |
2001年 | 1001篇 |
2000年 | 516篇 |
1999年 | 817篇 |
1998年 | 6460篇 |
1997年 | 4092篇 |
1996年 | 2689篇 |
1995年 | 1612篇 |
1994年 | 1228篇 |
1993年 | 1251篇 |
1992年 | 354篇 |
1991年 | 413篇 |
1990年 | 413篇 |
1989年 | 386篇 |
1988年 | 372篇 |
1987年 | 286篇 |
1986年 | 268篇 |
1985年 | 242篇 |
1984年 | 150篇 |
1983年 | 150篇 |
1982年 | 186篇 |
1981年 | 231篇 |
1980年 | 248篇 |
1979年 | 106篇 |
1978年 | 137篇 |
1977年 | 656篇 |
1976年 | 1385篇 |
1975年 | 148篇 |
1973年 | 92篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
64.
65.
66.
Thin films on aluminum-tungsten alloys were prepared by co-deposition of pure aluminum and pure tungsten, each sputtered by an independently controlled magnetron source, on glass and sapphire substrates. Completely amorphous films were obtained in the Al80W20-Al67W33 composition range. Passivity and corrosion behavior of amorphous Al-W alloys were investigated in 1 M deaerated hydrochloric acid solution using polarization and impedance spectroscopy measurements and have been correlated with the properties of pure alloy components. Tungsten and sputter-deposited Al-W thin films are inherently passive materials while aluminum undergoes pitting corrosion in hydrochloric acid solution. The passive film formed at the OCP on each alloy possesses excellent electric and dielectric properties comparable to those of the isolating film on tungsten. The absolute impedance increases with increasing tungsten content in the alloy. According to electrochemical polarization measurements, alloying Al with W in solid solution significantly enhances the material's resistance to pitting corrosion by shifting the breakdown potential above 2000 mV (Al67W33) and lowering the corrosion rate at the OCP by more than two orders of magnitude. The most likely mechanism explaining the passivity of amorphous Al-W alloys, the Solute Vacancy Interaction Model (SVIM), involves the formation of complexes between highly oxidized solute atoms (W+6) and mobile cation vacancies, which restrict the transport of Cl− through the oxide film and inhibit its breakdown in hydrochloric acid solution. The role that film stress relaxation effects and microscopic defects in amorphous Al-W films, of the some composition, and deposited on various substrates play in their corrosion resistance is discussed. 相似文献
67.
Utilities in the sky?: 《Refocus》2002,3(6):54-57
Could huge arrays of space-based solar power systems one day supply utility scale electricity to the electric power grid on earth? How realistic a possibility is this option for alternative energy supply at the moment? Finley R. Shapiro, USA compares space-based and terrestrial solar power systems. 相似文献
68.
Studied the representational structure of process verbs among preschool children and adults. Three experiments were conducted with a total of 80 French preschool children (5–6 yrs) and 80 French university students. In Exp 1, Ss were presented with 12 verbs and were asked to speak a sentence using the verbs. Use of the verbs as a completed action or as a circumstance was recorded. In Exp 2, the Ss were asked to act out or to mark the action/circumstance of the verb on a drawing representing the verb in a sentence. In Exps 3 and 4, Ss were presented with a list of verbs and asked to indicate whether they represented finished actions or uncompleted actions/circumstances. The number of responses indicating a completed or an uncompleted action/circumstance was compared. (English abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
69.
70.
An extended model and calculus, called RasterCalc, is presented for operations on discrete graphics rasters, including their colour functions. The operations are separated into two main categories: operations on domains, and operations on colour functions. The operations are further classified as local and remote, depending on the correspondence between destination and source pixels. The new raster element or pixel can be a function of a single element from one or more rasters, a function of a small area from other rasters, or a function of entire rasters. Local operations have their main applications in computer graphics, while remote operations are more oriented towards image processing. A mathematically oriented notation is used to define and represent the operations included. RasterCalc has been implemented as a procedure package in Pascal, to be used on a powerful, yet expensive display. Recently a C version has been completed for a personal colour computer with a special chip for raster operations. The work reported in this paper is partially supplied by the Dutch Technical Sciences Foundation, under project number LWI 14.0130: “Facilities for raster graphics in programming languages” 相似文献