全文获取类型
收费全文 | 770908篇 |
免费 | 8807篇 |
国内免费 | 2840篇 |
专业分类
电工技术 | 13861篇 |
综合类 | 1023篇 |
化学工业 | 115964篇 |
金属工艺 | 30440篇 |
机械仪表 | 23832篇 |
建筑科学 | 17521篇 |
矿业工程 | 4270篇 |
能源动力 | 20111篇 |
轻工业 | 62546篇 |
水利工程 | 8127篇 |
石油天然气 | 15028篇 |
武器工业 | 83篇 |
无线电 | 88597篇 |
一般工业技术 | 151412篇 |
冶金工业 | 147355篇 |
原子能技术 | 17537篇 |
自动化技术 | 64848篇 |
出版年
2021年 | 6582篇 |
2020年 | 4969篇 |
2019年 | 6350篇 |
2018年 | 10748篇 |
2017年 | 10783篇 |
2016年 | 11524篇 |
2015年 | 7441篇 |
2014年 | 12418篇 |
2013年 | 35574篇 |
2012年 | 19948篇 |
2011年 | 27331篇 |
2010年 | 21659篇 |
2009年 | 24593篇 |
2008年 | 25254篇 |
2007年 | 25140篇 |
2006年 | 22378篇 |
2005年 | 20141篇 |
2004年 | 19454篇 |
2003年 | 19094篇 |
2002年 | 18519篇 |
2001年 | 18225篇 |
2000年 | 17244篇 |
1999年 | 18045篇 |
1998年 | 45141篇 |
1997年 | 31613篇 |
1996年 | 24330篇 |
1995年 | 18524篇 |
1994年 | 16270篇 |
1993年 | 16296篇 |
1992年 | 11880篇 |
1991年 | 11149篇 |
1990年 | 11177篇 |
1989年 | 10806篇 |
1988年 | 10233篇 |
1987年 | 9062篇 |
1986年 | 9037篇 |
1985年 | 10205篇 |
1984年 | 9385篇 |
1983年 | 8586篇 |
1982年 | 7975篇 |
1981年 | 8164篇 |
1980年 | 7842篇 |
1979年 | 7462篇 |
1978年 | 7445篇 |
1977年 | 8476篇 |
1976年 | 11132篇 |
1975年 | 6418篇 |
1974年 | 6132篇 |
1973年 | 6287篇 |
1972年 | 5326篇 |
排序方式: 共有10000条查询结果,搜索用时 79 毫秒
941.
An assessment is made of the technical contents of flight-vehicle structures curricula at 41 U.S. universities with accredited aerospace engineering programs. The assessment is based on the technical needs for the new and projected aeronautical and space systems as well as on the likely characteristics of the aerospace engineering work environment. A number of deficiencies and areas of concern are identified and recommendations are presented for enhancing the effectiveness of flight-vehicle structures education. A number of government supported programs that can help aerospace engineering education are listed in the appendix. 相似文献
942.
Z. P. Shul'man B. M. Khusid I. L. Ryklina É. A. Zal'tsgendler O. R. Dornyak É. V. Ivashkevich Z. A. Shabunina 《Journal of Engineering Physics and Thermophysics》1987,53(5):1285-1291
Dynamic processes are studied in media with softly and hardly internal destroyable configurations. A method is examined for the measurement of properties of media with spatial separation of the chemical transformation stages and thermal hydrodynamic measurements.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 5, pp. 781–789, November, 1987. 相似文献
943.
944.
945.
An innovative method for modelling biological processes under anaerobic conditions is presented and discussed. The method is based on titrimetric and off-gas measurements. Titrimetric data is recorded as the addition rate of hydroxyl ions or protons that is required to maintain pH in a bioreactor at a constant level. An off-gas analysis arrangement measures, among other things, the transfer rate of carbon dioxide. The integration of these signals results in a continuous signal which is solely related to the biological reactions. When coupled with a mathematical model of the biological reactions, the signal allows a detailed characterisation of these reactions, which would otherwise be difficult to achieve. Two applications of the method to the enhanced biological phosphorus removal processes are presented and discussed to demonstrate the principle and effectiveness of the method. 相似文献
946.
The paper describes an experimental investigation of the diamond-like carbon deposition process from methane precursor with an innovative high-density inductively coupled plasma source. It appears that a high plasma density allows a fast growth of diamond-like carbon coatings exhibiting a high hardness. In contrast to what is usually found in the literature, it seems that the ion species participate significantly to the growth of the carbon film when exposed to a high ion flux. 相似文献
947.
An efficient algorithm for the computation of the orthogonal Fourier-Mellin moments (OFMMs) is presented. The proposed method computes the fractional parts of the orthogonal polynomials, which consist of fractional terms, recursively, by eliminating the number of factorial calculations. The recursive computation of the fractional terms makes the overall computation of the OFMMs a very fast procedure in comparison with the conventional direct method. Actually, the computational complexity of the proposed method is linear O(p) in multiplications, with p being the moment order, while the corresponding complexity of the direct method is O(p2). Moreover, this recursive algorithm has better numerical behaviour, as it arrives at an overflow situation much later than the original one and does not introduce any finite precision errors. These are the two major advantages of the algorithm introduced in the current work, establishing the computation of the OFMMs to a very high order as a quite easy and achievable task. Appropriate simulations on images of different sizes justify the superiority of the proposed algorithm over the conventional algorithm currently used 相似文献
948.
Y.-Y. Won H.-C. Kwon S.-K. Han 《Optoelectronics, IET》2007,1(2):61-64
A new scheme for reducing optical beat interference (OBI) noise in optical network units is proposed for subcarrier multiplexing-based access network applications. The optical spectrum of the transmit lasers is broadened by using a radio frequency (RF) clipping tone with a modulation depth greater than one. This reduces the impact of the OBI noise. The distortions caused by an RF clipping tone are also suppressed by introducing a gain-saturated reflective optical amplifier, which shows the characteristics of high-pass filter. The proposed scheme has been verified by measuring the error vector magnitude of 16QAM signal with 20 Mbps. Error-free transmission has been achieved even when the light of OBI-noise-causing lasers is stronger than that of the signal laser by 7 dB 相似文献
949.
950.
This paper discusses another generalization of the direct Routh table truncation method for interval systems. It is shown that the existing generalization of the direct Routh table truncation fails to produce a stable system, in contradiction to the equivalent result for fixed-coefficients systems. The present method guarantees a stable reduced order model for interval systems as well. 相似文献