全文获取类型
收费全文 | 472513篇 |
免费 | 7454篇 |
国内免费 | 2713篇 |
专业分类
电工技术 | 9626篇 |
技术理论 | 5篇 |
综合类 | 1388篇 |
化学工业 | 72448篇 |
金属工艺 | 20305篇 |
机械仪表 | 13816篇 |
建筑科学 | 12172篇 |
矿业工程 | 2104篇 |
能源动力 | 11116篇 |
轻工业 | 45853篇 |
水利工程 | 4469篇 |
石油天然气 | 7118篇 |
武器工业 | 246篇 |
无线电 | 54509篇 |
一般工业技术 | 87466篇 |
冶金工业 | 93224篇 |
原子能技术 | 8846篇 |
自动化技术 | 37969篇 |
出版年
2021年 | 3755篇 |
2019年 | 3284篇 |
2018年 | 5324篇 |
2017年 | 5201篇 |
2016年 | 5726篇 |
2015年 | 4414篇 |
2014年 | 7177篇 |
2013年 | 20739篇 |
2012年 | 12189篇 |
2011年 | 16646篇 |
2010年 | 13432篇 |
2009年 | 14620篇 |
2008年 | 15804篇 |
2007年 | 16026篇 |
2006年 | 14369篇 |
2005年 | 12880篇 |
2004年 | 11909篇 |
2003年 | 11595篇 |
2002年 | 11563篇 |
2001年 | 11746篇 |
2000年 | 10908篇 |
1999年 | 11514篇 |
1998年 | 27934篇 |
1997年 | 19973篇 |
1996年 | 15359篇 |
1995年 | 11522篇 |
1994年 | 10335篇 |
1993年 | 10133篇 |
1992年 | 7504篇 |
1991年 | 7269篇 |
1990年 | 6976篇 |
1989年 | 6878篇 |
1988年 | 6585篇 |
1987年 | 5639篇 |
1986年 | 5593篇 |
1985年 | 6471篇 |
1984年 | 6033篇 |
1983年 | 5511篇 |
1982年 | 5005篇 |
1981年 | 5184篇 |
1980年 | 4836篇 |
1979年 | 4858篇 |
1978年 | 4734篇 |
1977年 | 5425篇 |
1976年 | 7545篇 |
1975年 | 4118篇 |
1974年 | 3905篇 |
1973年 | 3875篇 |
1972年 | 3295篇 |
1971年 | 2951篇 |
排序方式: 共有10000条查询结果,搜索用时 453 毫秒
991.
992.
R. L. Williamson J. J. Beaman D. K. Melgaard G. J. Shelmidine A. D. Patel C. B. Adasczik 《Journal of Materials Science》2004,39(24):7161-7168
A particularly challenging problem associated with vacuum arc remelting occurs when trying to maintain accurate control of electrode melt rate as the melt zone passes through a transverse crack in the electrode. As the melt zone approaches the crack, poor heat conduction across the crack drives the local temperature in the electrode tip above its steady-state value, causing the controller to cut back on melting current in response to an increase in melting efficiency. The difficulty arises when the melt zone passes through the crack and encounters the relatively cold metal on the other side, giving rise to an abrupt drop in melt rate. This extremely dynamic melting situation is very difficult to handle using standard load-cell based melt rate control, resulting in large melt rate excursions. We have designed and tested a new generation melt rate controller that is capable of controlling melt rate through crack events. The controller is designed around an accurate dynamic melting model that uses four process variables: electrode tip thermal boundary layer, electrode gap, electrode mass and melting efficiency. Tests, jointly sponsored by the Specialty Metals Processing Consortium and Sandia National Laboratories, were performed at Carpenter Technology Corporation wherein two 0.43 m diameter Pyromet® 718 electrodes were melted into 0.51 m diameter ingots. Each electrode was cut approximately halfway through its diameter with an abrasive saw to simulate an electrode crack. Relatively accurate melt rate control through the cuts was demonstrated despite the observation of severe arc disturbances and loss of electrode gap control. Subsequent to remelting, one ingot was sectioned in the “as cast” condition, whereas the other was forged to 0.20 m diameter billet. Macrostructural characterization showed solidification white spots in regions affected by the cut in the electrode. 相似文献
993.
Input error sensitivity of hardness and elastic modulus evaluated from indentation load-displacement records by Oliver and Pharr method 总被引:1,自引:0,他引:1
L. Prchlik 《Journal of Materials Science》2004,39(4):1185-1193
Due to its straightforwardness and the ease of implementation the Oliver-Pharr method [1] has been used in the analysis of load-displacement records for more than a decade now. This paper provides analytical expressions relating the errors in the hardness and elastic modulus obtained by this method to systematic calibration errors of measured depth, force and frame compliance for spherical and sharp indentation. While in systems with zero frame compliance the sensitivity ratios for depth and force measurement were found to be constant, in systems with a finite frame compliance the error sensitivity changes with the absolute values of applied force and measured depth. The analytical predictions are compared with the true variation in derived materials parameters and the ranges of validity of the expressions are established. The error sensitivity with respect to different input variables and its implications for the actual measurement are discussed. 相似文献
994.
I. Kasatkin F. Girgsdies T. Ressler R. A. Caruso J. H. Schattka J. Urban K. Weiss 《Journal of Materials Science》2004,39(6):2151-2157
The orientation relations m(100) || t(001), m[001] || t[110]; m(011) || t(100), m[100] || t[001]; m(100) || t(110), m[001] || t[001]; m(013) || t(116), m[001] || t[001] (indices for the primitive tetragonal cell) have been found between the tetragonal (t) and monoclinic (m) domains during the electron irradiation-induced m-t phase transition observed in-situ with HREM within isolated zirconia nanoparticles. Geometric models of the m-t interfaces are proposed. 相似文献
995.
996.
997.
998.
999.
1000.
The hydrogen gas pick-up problem that can occur during Lost Foam Casting was investigated with reduced pressure tests and real castings.The initial hydrogen concentration of the melt and the contact time between melt and polystyrene had a main effect on the hydrogen gas pick-up of Al melt. The hydrogen gas pick-up of Al alloy depended also on pouring temperature and a proper metal front temperature gave the minimum hydrogen pick-up. At a low pouring temperature, the hydrogen went into the melt mainly from entrapped liquid product of polystyrene but at high pouring temperature it was by the gas as well as the liquid product. The mold flask evacuation down to 710 torr decreased the gas porosity down by around 0.4 vol%. The permeability of coating thickness had a great effect because it affects the filling time and the easy removal of liquid polystyrene. 相似文献