全文获取类型
收费全文 | 65624篇 |
免费 | 3312篇 |
国内免费 | 2663篇 |
专业分类
电工技术 | 2814篇 |
综合类 | 2642篇 |
化学工业 | 8997篇 |
金属工艺 | 4713篇 |
机械仪表 | 3128篇 |
建筑科学 | 2590篇 |
矿业工程 | 1309篇 |
能源动力 | 1960篇 |
轻工业 | 4856篇 |
水利工程 | 1207篇 |
石油天然气 | 2363篇 |
武器工业 | 488篇 |
无线电 | 6372篇 |
一般工业技术 | 12590篇 |
冶金工业 | 8193篇 |
原子能技术 | 1178篇 |
自动化技术 | 6199篇 |
出版年
2023年 | 455篇 |
2022年 | 1215篇 |
2021年 | 1582篇 |
2020年 | 1235篇 |
2019年 | 999篇 |
2018年 | 1299篇 |
2017年 | 1322篇 |
2016年 | 1334篇 |
2015年 | 1584篇 |
2014年 | 2137篇 |
2013年 | 3963篇 |
2012年 | 3435篇 |
2011年 | 3967篇 |
2010年 | 3448篇 |
2009年 | 3659篇 |
2008年 | 3639篇 |
2007年 | 3580篇 |
2006年 | 2953篇 |
2005年 | 2563篇 |
2004年 | 2144篇 |
2003年 | 1660篇 |
2002年 | 1601篇 |
2001年 | 1609篇 |
2000年 | 1298篇 |
1999年 | 1139篇 |
1998年 | 2161篇 |
1997年 | 1676篇 |
1996年 | 1463篇 |
1995年 | 1001篇 |
1994年 | 771篇 |
1993年 | 783篇 |
1992年 | 606篇 |
1991年 | 578篇 |
1990年 | 531篇 |
1989年 | 487篇 |
1988年 | 372篇 |
1987年 | 405篇 |
1986年 | 367篇 |
1985年 | 386篇 |
1984年 | 305篇 |
1983年 | 303篇 |
1982年 | 303篇 |
1981年 | 301篇 |
1980年 | 360篇 |
1979年 | 346篇 |
1978年 | 296篇 |
1977年 | 415篇 |
1976年 | 629篇 |
1975年 | 308篇 |
1973年 | 312篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A wideband orthogonal-mode junction (OMJ) using a quad-ridged circular coaxial waveguide and four single-ridged sectoral waveguides is described. The new structure is used for extracting a wide lower band signal from a coaxial dual-band feed. Theoretical results show that the broadband incoming signal in the quad-ridged coaxial waveguide can be coupled to four single-ridged sectoral waveguides with low reflection. The new structure transforms a complex system to a simple single-ridged sectoral waveguide where multi-band separation can be accomplished by a number of means. The transformation eliminates the interference among the excitation sources and enables the accurate mathematical modeling of the complete system possible 相似文献
102.
103.
104.
105.
106.
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
107.
In Malaysia, no long-term daylight data are measured. It was only recently that the need to measure the availability of daylight became urgent when the importance of daylighting in buildings was rediscovered. The hourly daylight availability has been simulated for the Malaysian sky using daylight modelling techniques based on empirical and measured solar irradiation and cloud cover data. This paper presents the techniques involved in producing exterior illuminance data. These data were then compared with measured illuminance at Shah Alam and Bangi, Malaysia. The global illuminance levels are generally high, with values exceeding 80,000 lux at noon during the months when solar irradiation is highest. Even during the months when the ground receives less solar irradiation, the peak illuminance can reach 60,000 lux. Applications and uses of such data are in daylighting design, both for visual and thermal comfort, task illuminance and energy-conscious design of buildings. Recommendations are made at the end of the paper on the various climatic data that are required to be measured for overall daylighting design applications. 相似文献
108.
109.
110.
Sung D. Kwon Sung J. Song Dong H. Bae Young Z. Lee 《Journal of Mechanical Science and Technology》2002,16(9):1084-1092
The frequency dependency of Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward
radiation of the incident ultrasonic wave in two kinds of degraded specimens by scuffing or corrosion. Then, the frequency
dependency is compared with the residual stress distribution or the corrosion-fatigue characteristics for the scuffed or corroded
specimens, respectively. The width of the backward radiation profile increases with the increase of the variation in residual
stress distribution for the scuffed specimens. In the corroded specimens, the profile width decreases with the increase of
the effective aging layer thickness and is inversely proportional to the exponent, m, in the Paris’ law that can predict the
crack size increase due to fatigue. The result observed in this study demonstrates high potential of backward radiated ultrasound
as a tool for nondestructive evaluation of subsurface gradient of material degradation generated by scuffing or corrosion. 相似文献