全文获取类型
收费全文 | 207295篇 |
免费 | 3597篇 |
国内免费 | 1049篇 |
专业分类
电工技术 | 3959篇 |
综合类 | 584篇 |
化学工业 | 30132篇 |
金属工艺 | 8537篇 |
机械仪表 | 6463篇 |
建筑科学 | 5354篇 |
矿业工程 | 1561篇 |
能源动力 | 5394篇 |
轻工业 | 17842篇 |
水利工程 | 2472篇 |
石油天然气 | 4330篇 |
武器工业 | 72篇 |
无线电 | 24343篇 |
一般工业技术 | 41188篇 |
冶金工业 | 37642篇 |
原子能技术 | 5165篇 |
自动化技术 | 16903篇 |
出版年
2021年 | 1965篇 |
2020年 | 1448篇 |
2019年 | 1828篇 |
2018年 | 2851篇 |
2017年 | 2953篇 |
2016年 | 3107篇 |
2015年 | 2164篇 |
2014年 | 3517篇 |
2013年 | 9583篇 |
2012年 | 5609篇 |
2011年 | 7620篇 |
2010年 | 6103篇 |
2009年 | 6857篇 |
2008年 | 6909篇 |
2007年 | 6939篇 |
2006年 | 6013篇 |
2005年 | 5617篇 |
2004年 | 5266篇 |
2003年 | 5130篇 |
2002年 | 4739篇 |
2001年 | 4830篇 |
2000年 | 4749篇 |
1999年 | 4884篇 |
1998年 | 11511篇 |
1997年 | 8239篇 |
1996年 | 6501篇 |
1995年 | 4750篇 |
1994年 | 4339篇 |
1993年 | 4132篇 |
1992年 | 3253篇 |
1991年 | 3119篇 |
1990年 | 2897篇 |
1989年 | 2974篇 |
1988年 | 2848篇 |
1987年 | 2408篇 |
1986年 | 2316篇 |
1985年 | 2726篇 |
1984年 | 2521篇 |
1983年 | 2351篇 |
1982年 | 2103篇 |
1981年 | 2215篇 |
1980年 | 2040篇 |
1979年 | 2131篇 |
1978年 | 2126篇 |
1977年 | 2373篇 |
1976年 | 3189篇 |
1975年 | 1834篇 |
1974年 | 1765篇 |
1973年 | 1778篇 |
1972年 | 1439篇 |
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
961.
Identification and verification of a video clip via its fingerprint find applications in video browsing, database search and security. For this purpose, the video sequence must be collapsed into a short fingerprint using a robust hash function based on signal processing operations. We propose two robust hash algorithms for video based both on the discrete cosine transform (DCT), one on the classical basis set and the other on a novel randomized basis set (RBT). The robustness and randomness properties of the proposed hash functions are investigated in detail. It is found that these hash functions are resistant to signal processing and transmission impairments, and therefore can be instrumental in building database search, broadcast monitoring and watermarking applications for video. The DCT hash is more robust, but lacks security aspect, as it is easy to find different video clips with the same hash value. The RBT based hash, being secret key based, does not allow this and is more secure at the cost of a slight loss in the receiver operating curves 相似文献
962.
963.
In general, the problems of securing a university network are no different than those of securing any other large corporate network. But when it comes to data security, universities have their own unique problems. It's easy to point fingers at students--a large number of potentially adversarial transient insiders. Yet that's really no different from a corporation dealing with an assortment of employees and contractors--the difference is the culture. 相似文献
964.
P.U. Sharma K.B. Modi V.K. Lakhani K.B. Zankat H.H. Joshi 《Ceramics International》2007,33(8):1543-1546
Compositional dependence of hyperfine parameters, determined through Mössbauer spectral analysis has been studied for Y3−xFe5+xO12 (x = 0.0, 0.1, 0.3 and 0.5) garnet system at 300 K. The Mössbauer spectra have been fitted with three sextets in the ferrimagnetic state corresponding to Fe3+ ions at tetrahedral (d), octahedral (a) and dodecahedral (c) sites of the crystal structure. It is observed that isormershift, quadrupole shift and hyperfine field of d-site show no significant variation with Fe3+ concentration. The change in hyperfine fields of a- and c-sites with composition (x) has been explained on the basis of strength of exchange integrals, change in isomershift can be understood due to s-electron charge distribution and asymmetric displacement of oxygen ions surrounding the a- and c-sites seems to be responsible for observable quadrupole shift. The magneton number values obtained from magnetization and Mossbauer data are in agreement to those calculated using Neel's three sublattice model of ferrimagnetism. 相似文献
965.
966.
M. A. Abroyan S. L. Kosogorov I. V. Nabokova N. A. Uspenskii V. A. Chumichev V. B. Shapiro V. Ya. Shvedyuk 《Instruments and Experimental Techniques》2007,50(4):530-533
A system for real-time measurements of the current-density distribution in electron beams ejected from large-area electron accelerators has been developed. The system, which is based on Faraday cups, a microprocessor, and a PC, is designed for measuring the parameters of the electron beams ejected from large-area accelerators—devices for ionizing electroionization lasers and technological accelerators—and ensures real-time monitoring of the current-density distribution over the electron-beam cross section with a relative measurement accuracy of at least ±2%. 相似文献
967.
968.
An optimization design model for surface termination of off-state semiconductor devices under reverse-bias conditions is presented. The multivariable design model is used to optimize the surface profile shapes for nonplanar devices and the doping profiles of material regions along the surface for planar devices. The effectiveness of the design model in reducing the peak surface electric field to below 50% of the bulk value is demonstrated for two examples of each type of device 相似文献
969.
970.
B. G. Raghavendra 《Holz als Roh- und Werkstoff》1987,45(9):383-388
There are several areas in the plywood industry where Operations Research techniques have greatly assisted in better decision-making. These have resulted in improved profits, reduction of wood losses and better utilization of resources. Realizing these, some of the plywood manufacturing firms in the developed countries have established separate Operations Research departments or divisions. In the face of limited raw-material resources, raising costs and a competitive environment, the benefits attributable to the use of these techniques are becoming more and more significant. 相似文献