全文获取类型
收费全文 | 654547篇 |
免费 | 10852篇 |
国内免费 | 2226篇 |
专业分类
电工技术 | 12001篇 |
综合类 | 1145篇 |
化学工业 | 97087篇 |
金属工艺 | 22541篇 |
机械仪表 | 18705篇 |
建筑科学 | 17627篇 |
矿业工程 | 2071篇 |
能源动力 | 17508篇 |
轻工业 | 62481篇 |
水利工程 | 5660篇 |
石油天然气 | 4971篇 |
武器工业 | 33篇 |
无线电 | 82797篇 |
一般工业技术 | 120316篇 |
冶金工业 | 131299篇 |
原子能技术 | 9919篇 |
自动化技术 | 61464篇 |
出版年
2021年 | 4875篇 |
2020年 | 3522篇 |
2019年 | 4435篇 |
2018年 | 7593篇 |
2017年 | 7830篇 |
2016年 | 8611篇 |
2015年 | 6404篇 |
2014年 | 9787篇 |
2013年 | 29906篇 |
2012年 | 17563篇 |
2011年 | 23983篇 |
2010年 | 17830篇 |
2009年 | 20165篇 |
2008年 | 21348篇 |
2007年 | 21528篇 |
2006年 | 19099篇 |
2005年 | 19870篇 |
2004年 | 18768篇 |
2003年 | 18206篇 |
2002年 | 16372篇 |
2001年 | 16643篇 |
2000年 | 15043篇 |
1999年 | 16111篇 |
1998年 | 41672篇 |
1997年 | 29430篇 |
1996年 | 22654篇 |
1995年 | 17085篇 |
1994年 | 15194篇 |
1993年 | 14753篇 |
1992年 | 10491篇 |
1991年 | 10084篇 |
1990年 | 9643篇 |
1989年 | 9167篇 |
1988年 | 8920篇 |
1987年 | 7515篇 |
1986年 | 7403篇 |
1985年 | 8707篇 |
1984年 | 8021篇 |
1983年 | 7211篇 |
1982年 | 6775篇 |
1981年 | 6733篇 |
1980年 | 6389篇 |
1979年 | 6018篇 |
1978年 | 5616篇 |
1977年 | 7251篇 |
1976年 | 10205篇 |
1975年 | 4688篇 |
1974年 | 4486篇 |
1973年 | 4319篇 |
1972年 | 3623篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
Bound-state beta decay of highly ionized atoms 总被引:1,自引:0,他引:1
994.
Hayashi M. Tanaka H. Ohara K. Otani T. Suzuki M. 《Lightwave Technology, Journal of》2002,20(2):236-242
An all-optical multiplexing technique using wavelength division multiplexing (WDM)-time division multiplexing (TDM) conversion with an electroabsorption wavelength converter has been proposed and demonstrated. The effectiveness of this WDM-TDM conversion technique for various pulsewidth settings was experimentally investigated. The fluctuation of the signal performance, which was inevitably caused by the coherent crosstalk between adjacent pulses in the conventional optical time division multiplexing (OTDM) technique, were successfully suppressed, even in the case of wide pulse duration. High Q-factor performance has been maintained for a wide range of duty ration from 36% to 74%. By introducing this technique to the optical time division multiplexer, a highly stable and high-quality 40-Gb/s optical signal can be effectively produced without generating the short pulse or setting two tributaries at orthogonal polarization states, and without introducing high-speed electronics for signal multiplexing. The WDM-TDM conversion with an electroabsorption wavelength converter was extended to 60-Gb/s operation by using three 20-Gb/s tributaries. A clear eye opening was confirmed for a waveform after the WDM-TDM conversion of the 60-Gb/s signal 相似文献
995.
By using mathematical formulae developed in previous studies, certain pollution parameters of dye effluent obtained from reactive dyeing with a single dye can be predicted with good accuracy. In this study, the degree of pollution of reactive dyeing effluent using dye mixtures was also predicted by other approaches, such as linear and non-linear regression. The prediction accuracy was found to be satisfactory. 相似文献
996.
Anguilla is a UK overseas (non-independent) territory in the Caribbean. It is a small middle-income island with a population of 13 000, and recent statistics indicate that it is more dependent on tourism than any other country or territory in the world. Rapid population growth and development have placed more emphasis on the need for human health and environmental protection. For the first time, a systematic water-quality monitoring programme has been developed, based on the realities of the local situation, e.g. low resource base, limited capabilities, dependence on household rainwater catchment, storage cisterns, and a poor water-supply network. Development of the programme incorporated the key themes of pragmatic, realistic, incremental, responsive, and consultative approaches. 相似文献
997.
M. Liess R. Hua K. Elsenaar 《The International Journal of Advanced Manufacturing Technology》2002,20(1):58-62
Cables to moving parts on a linear actuator in production machines, such as pick-and-place machines, are a source of unreliability
owing to the possible breaking of a cable. They further reduce the positioning precision of the actuator owing to additional
forces. Slotted waveguide systems for rail vehicles based on 2.4 GHz transmission frequency are well known, but transmitters/receivers
and waveguides are bulky. The paper reports on the reduction in size of the equipment, adapted to 5.8 GHz using a commercial
off-the-shelf RadioLan communication module. Further, the efficient termination of the wave-guide and a new way to reduce
standing-wave effects is also discussed. 相似文献
998.
J. Perahia comments on the paper by J. S. Hsu (see ibid., vol.16, p.192-7, 2001) and expands on the case of a two stator three phase squirrel cage induction machine where one stator housing is stationary and other stator housing is mounted on a worm gear assembly. The original author replies to the comments 相似文献
999.
1000.
Determination of the flow stress under metal cutting conditions is difficult because high values of strains, strain rates and temperature exist in practical machining operations. Conventional tests for determining flow stress data cannot duplicate these deformation conditions and therefore, extrapolation will be required. In this study we have investigated critical issues regarding the constitutive equation determination by direct methods such as split Hopkinson's pressure bar bench (SHPB) tests. Quantitative analysis about the suitability of an experimentally determined constitutive equation for different purpose modeling is provided, leading to guidelines for the quality improvement of constitutive law dedicated to cutting, from the points of view of formulation and identification sequence. 相似文献