全文获取类型
收费全文 | 1425620篇 |
免费 | 25464篇 |
国内免费 | 6901篇 |
专业分类
电工技术 | 33972篇 |
综合类 | 6322篇 |
化学工业 | 267164篇 |
金属工艺 | 63243篇 |
机械仪表 | 39848篇 |
建筑科学 | 44350篇 |
矿业工程 | 11258篇 |
能源动力 | 50085篇 |
轻工业 | 101711篇 |
水利工程 | 14163篇 |
石油天然气 | 37476篇 |
武器工业 | 143篇 |
无线电 | 194039篇 |
一般工业技术 | 270283篇 |
冶金工业 | 124709篇 |
原子能技术 | 33783篇 |
自动化技术 | 165436篇 |
出版年
2021年 | 15406篇 |
2020年 | 11693篇 |
2019年 | 14462篇 |
2018年 | 14607篇 |
2017年 | 13874篇 |
2016年 | 20612篇 |
2015年 | 17132篇 |
2014年 | 28473篇 |
2013年 | 87397篇 |
2012年 | 33135篇 |
2011年 | 44341篇 |
2010年 | 40945篇 |
2009年 | 49845篇 |
2008年 | 41843篇 |
2007年 | 38651篇 |
2006年 | 42598篇 |
2005年 | 37180篇 |
2004年 | 39653篇 |
2003年 | 39659篇 |
2002年 | 39038篇 |
2001年 | 35302篇 |
2000年 | 34128篇 |
1999年 | 32515篇 |
1998年 | 32432篇 |
1997年 | 31638篇 |
1996年 | 30378篇 |
1995年 | 27874篇 |
1994年 | 26486篇 |
1993年 | 26372篇 |
1992年 | 25394篇 |
1991年 | 22357篇 |
1990年 | 22799篇 |
1989年 | 21851篇 |
1988年 | 20315篇 |
1987年 | 18688篇 |
1986年 | 18003篇 |
1985年 | 21360篇 |
1984年 | 21912篇 |
1983年 | 19868篇 |
1982年 | 18984篇 |
1981年 | 19036篇 |
1980年 | 17621篇 |
1979年 | 18247篇 |
1978年 | 17475篇 |
1977年 | 16719篇 |
1976年 | 16733篇 |
1975年 | 15801篇 |
1974年 | 15337篇 |
1973年 | 15391篇 |
1972年 | 12885篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
992.
I. I. Abramov I. A. Goncharenko S. A. Ignatenko A. V. Korolev E. G. Novik A. I. Rogachev 《Russian Microelectronics》2003,32(2):97-104
The concept and structure of the NANODEV simulation software are described. NANODEV deals with nanoelectronic devices that exploit single-electron tunneling, resonant tunneling, or quantum interference. It can use both simplified and sophisticated models and enables one to evaluate a wide variety of devices and configurations. The capabilities of NANODEV are illustrated by examples. 相似文献
993.
A novel driver-assist stability system for all-wheel-drive electric vehicles is introduced. The system helps drivers maintain control in the event of a driving emergency, including heavy braking or obstacle avoidance. The system comprises a fuzzy logic system that independently controls wheel torque to prevent vehicle spin. Another fuzzy wheel slip controller is used to enhance vehicle stability and safety. A neural network is trained to generate the required reference for yaw rate. Vehicle true speed is estimated by a sensor data fusion method. The intrinsic robustness of fuzzy controllers allows the system to operate in different road conditions successfully. Moreover, the ease of implementing fuzzy controllers gives a potential for vehicle stability enhancement. 相似文献
994.
A new dual-quantisation sigma-delta modulator is proposed, which introduces an additional feedback path in the input of the second integrator. In this way, unlike other dual-quantisation architectures, larger signal-to-noise ratios can be obtained by means of aggressive noise-shaping, like in a conventional multibit modulator. The proposed modulator is also shown to be more robust against non-idealities than other dual-quantisation architectures. 相似文献
995.
It is shown that the dominant factor controlling reflectarray bandwidth is the bandwidth of the radiating element, and that the effect of non-constant path delays over the surface of the flat reflector has little significance unless the aperture is electrically very large and the f/D ratio is small. An example of a polarisation-twist reflectarray using aperture coupled elements with time delay lines is used to demonstrate this conclusion. 相似文献
996.
Optimal space-time constellations from groups 总被引:10,自引:0,他引:10
Hughes B.L. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(2):401-410
We consider the design of space-time constellations based on group codes for fading channels with multiple transmit and receive antennas. These codes can be viewed as multiantenna extensions of phase-shift keying (PSK), in the sense that all codewords have equal energy, all are rotations of a fixed codeword, and there is a simple differential transmission rule that allows data to be sent without channel estimates at the transmitter or receiver. For coherent detection, we show that all optimal full-rank space-time group codes are unitary (each code matrix has equal-energy, orthogonal rows). This leads to a simpler code design criterion and suggests that unitary codes may play an important role in coherent as well as noncoherent communication. For any number of transmit antennas t, we then use the design criterion to characterize all full-rank unitary space-time group codes of minimum block length (also t) which have 2/sup p/ codewords. These results allow us to characterize all optimal 2/sup p/-ary unitary group codes with square code matrices. This restricted class of block codes matches the class proposed for differential modulation by Hughes (see IEEE Trans. Inform. Theory, vol.46, p.2567-78, Nov. 2000), and by Hochwald and Sweldens (see IEEE Trans. Commun., vol.48, p.2041-2052, Dec. 2000). 相似文献
997.
998.
Reviews the book by Baruss (see record 2003-02669-000), which reviews the experimental and phenomenological research on alterations of consciousness, ranging from sleep and dreaming to mystical and near-death experience. The reviewer suggests there is a clear agenda announced by the book's subtitle, "An Empirical Analysis for Social Scientists." In the view of Baruss, all too often in states of consciousness research a preoccupation with theory has kept investigators from full engagement with the actual data. The book provides readable and at times appropriately controversial discussions of empirical literature on dreaming and lucid dreams, daydreaming and fantasy proneness, hypnosis, dissociative identity disorder, shamanism and possession states, psychedelic drug research, parapsychology, trance-chanelling and mediumship, the alien abduction syndrome, classical mystical experience, out-of-body and near-death experiences, and recent attempts by MacDonald and others to assess individual differences in spirituality through multifactor questionnaires. However, the reviewer believes that the breadth of coverage of both recent and past research is too often highly selective, and that the author's rejection of theory is both questionable in itself and more illusion than reality. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
Can digital rights management be standardized? 总被引:1,自引:0,他引:1
With increasing use of the Internet as a content-distribution platform, mere interoperability of the codec is no longer sufficient if content owners are not prepared to distribute their content online for fear of piracy. Therefore, one also needs interoperability in the area of managing and protecting related intellectual property rights. To provide interoperability of digital rights management (DRM) systems to protect the content rather than the distribution channel, MPEG has embarked on developing intellectual property management and protection (IPMP) specifications targeted at the content itself that are natively built into its standards. It is the hope that such standards will allow for interoperability of content commerce systems, giving consumers more choice, while providing rights holders with the tools to effectively protect their assets and to develop complex and attractive business offering to tempt consumers. While it remains uncertain whether standardization is in fact the right vehicle to provide the e-content market with an impetus to grow, it appears that MPEG is working on a set of specifications with relatively good chances of helping to achieve this goal. 相似文献
1000.
Low supply voltage high-performance CMOS current mirror with low input and output voltage requirements 总被引:1,自引:0,他引:1
Ramirez-Angulo J. Carvajal R.G. Torralba A. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2004,51(3):124-129
This paper presents a scheme for the efficient implementation of a low supply voltage continuous-time high-performance CMOS current mirror with low input and output voltage requirements. This circuit combines a shunt input feedback and a regulated cascode output stage to achieve low input resistance and very high output resistance. It can be used as a high-precision current mirror in analog and mixed signal circuits with a power supply close to a transistor's threshold voltage. The proposed current mirror has been simulated and a bandwidth of 40 MHz has been obtained. An experimental chip prototype has been sent for fabrication and has been experimentally verified, obtaining 0.15-V input-output voltage requirements, 100-/spl Omega/ input resistance, and more than 200-M/spl Omega/ (G/spl Omega/ ideally) output resistance with a 1.2-V supply in a standard CMOS technology. 相似文献