全文获取类型
收费全文 | 490903篇 |
免费 | 5699篇 |
国内免费 | 1432篇 |
专业分类
电工技术 | 9018篇 |
综合类 | 322篇 |
化学工业 | 75392篇 |
金属工艺 | 23596篇 |
机械仪表 | 17265篇 |
建筑科学 | 11689篇 |
矿业工程 | 3147篇 |
能源动力 | 11207篇 |
轻工业 | 39986篇 |
水利工程 | 5457篇 |
石油天然气 | 10341篇 |
武器工业 | 18篇 |
无线电 | 53172篇 |
一般工业技术 | 99584篇 |
冶金工业 | 82800篇 |
原子能技术 | 11355篇 |
自动化技术 | 43685篇 |
出版年
2021年 | 3146篇 |
2019年 | 3001篇 |
2018年 | 12445篇 |
2017年 | 12927篇 |
2016年 | 9668篇 |
2015年 | 4228篇 |
2014年 | 6509篇 |
2013年 | 18650篇 |
2012年 | 12683篇 |
2011年 | 21394篇 |
2010年 | 18339篇 |
2009年 | 18989篇 |
2008年 | 19185篇 |
2007年 | 20615篇 |
2006年 | 11871篇 |
2005年 | 13925篇 |
2004年 | 12028篇 |
2003年 | 11325篇 |
2002年 | 10503篇 |
2001年 | 9850篇 |
2000年 | 9454篇 |
1999年 | 9517篇 |
1998年 | 23084篇 |
1997年 | 16877篇 |
1996年 | 13175篇 |
1995年 | 10048篇 |
1994年 | 8876篇 |
1993年 | 8727篇 |
1992年 | 6594篇 |
1991年 | 6504篇 |
1990年 | 6241篇 |
1989年 | 6272篇 |
1988年 | 6180篇 |
1987年 | 5313篇 |
1986年 | 5292篇 |
1985年 | 6072篇 |
1984年 | 5742篇 |
1983年 | 5269篇 |
1982年 | 4955篇 |
1981年 | 5111篇 |
1980年 | 4853篇 |
1979年 | 4808篇 |
1978年 | 4877篇 |
1977年 | 5593篇 |
1976年 | 7197篇 |
1975年 | 4375篇 |
1974年 | 4190篇 |
1973年 | 4263篇 |
1972年 | 3701篇 |
1971年 | 3403篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
D. M. Van Wie D. G. Drewry Jr. D. E. King C. M. Hudson 《Journal of Materials Science》2004,39(19):5915-5924
Hypersonic flight powered by airbreathing engines offers the potential for faster response time at long ranges, and reduced cost for access-to-space. In the present paper the operating environment of typical hypersonic vehicles are discussed, including results for the radiation equilibrium wall temperature of external vehicle surfaces and the flow properties through three sample engines spanning the range of hydrocarbon-fueled Mach 4-8 flight and hydrogen-fueled flight at speeds up to Mach 17. Flow conditions at several locations through the sample engines were calculated to provide indications of the required operating flow environment. Additional system consideration such a seals, joints, vehicle integration and in-service engineering are addressed. 相似文献
993.
The mechanism of thermochemical growth of iron borides on iron was studied by analysing the products which form on samples placed in contact with B4C-base powder mixtures with different boronising potential. The analyses were carried out by means of metallographic and X-ray diffraction techniques. Three subsequent stages of growth were observed which explain the occurrence of typical properties of the thermochemically grown boride coatings, such as preferred crystallographic orientations and textures, as well as mechanical compactness and hardness, which play a determining role in the tribological behaviour of borided components. 相似文献
994.
995.
996.
997.
In the gold wire bonding of aluminum in microelectronic devices the presence of aluminum oxide on the metallization surface may be expected. Electron transparent couples containing an oxide layer at the interface were heated in a TEM to determine the effects of a passivation layer on intermetallic formation. Intermetallic phases were evidenced by changes in sample appearance and their structure was determined by electron diffraction. The presence of an oxide at the interface hindered second phase formation at temperatures at which they were usually expected to form. In aluminum rich couples, the formation of the AuAl2 intermetallic was not observed to form until about 350°C with the oxide present. In a reverse configuration involving a gold rich couple, an amorphous oxide phase was observed between the Al and the advancing Au2Al front. The movement of the reaction front appeared to be controlled by surface diffusion across this phase. 相似文献
998.
TEM observations of microscopic inclusions in synthetic diamond 总被引:1,自引:0,他引:1
999.
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
1000.
The status of mechanochemical processing of aerospace metals (aluminum and titanium) is reviewed. It is demonstrated that the activation of chemical reactions by mechanical energy can lead to many interesting applications including production of advanced materials with novel constitutional and microstructural effects leading to enhanced mechanical properties. 相似文献