全文获取类型
收费全文 | 18458篇 |
免费 | 2332篇 |
国内免费 | 516篇 |
专业分类
化学 | 1454篇 |
晶体学 | 25篇 |
力学 | 393篇 |
综合类 | 156篇 |
数学 | 519篇 |
物理学 | 3897篇 |
无线电 | 14862篇 |
出版年
2024年 | 70篇 |
2023年 | 204篇 |
2022年 | 341篇 |
2021年 | 472篇 |
2020年 | 483篇 |
2019年 | 290篇 |
2018年 | 311篇 |
2017年 | 550篇 |
2016年 | 647篇 |
2015年 | 924篇 |
2014年 | 1286篇 |
2013年 | 1165篇 |
2012年 | 1364篇 |
2011年 | 1320篇 |
2010年 | 941篇 |
2009年 | 1004篇 |
2008年 | 1155篇 |
2007年 | 1216篇 |
2006年 | 1089篇 |
2005年 | 983篇 |
2004年 | 861篇 |
2003年 | 819篇 |
2002年 | 596篇 |
2001年 | 514篇 |
2000年 | 441篇 |
1999年 | 374篇 |
1998年 | 333篇 |
1997年 | 271篇 |
1996年 | 224篇 |
1995年 | 217篇 |
1994年 | 173篇 |
1993年 | 170篇 |
1992年 | 119篇 |
1991年 | 66篇 |
1990年 | 57篇 |
1989年 | 41篇 |
1988年 | 45篇 |
1987年 | 28篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 22篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 14篇 |
1979年 | 9篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Mark A. Fleischer 《Journal of Heuristics》1996,1(2):225-246
The convergence of the simulated annealing algorithm is accelerated by a probabilistic feedback control scheme. This scheme uses two or more parallel processors to solve the same or related combinatorial optimization problems and are coupled by a probabilistic measure of quality (PMQ). The PMQ is used to generate an error signal for use in feedback control. Control over the search process is achieved by using the error signal to modulate the temperature parameter. Other aspects of control theory, such as the system gain and its effects on system performance, are described. Theoretical and experimental results show that such a scheme increases the steadystate probability of the globally optimal solutions. 相似文献
992.
一种通用神经网络处理机设计及其VLSI集成化讨论 总被引:6,自引:2,他引:4
本文讨论了通用神经网络处理机的性能要求以及全模拟量处理、全数字量处理和数字模拟混合处理等各种处理方式的优缺点,设计了一种数字模拟混合处理的通用神经网络处理机结构。这种结构在当前VLSI集成工艺的条件下,具有较高的性能价格比。 相似文献
993.
J. Ventura-Traveset I. Stojkovic F. Coromina J. Benedicto F. Petz 《International Journal of Satellite Communications and Networking》1995,13(2):117-135
This paper deals with satellite payload architectures adequate for the provision of universal mobile telecommunication services (UMTS) by medium altitude earth and geostationary orbit (MEO and GEO) satellites. The payload concept introduced is based on a transparent transponder with onboard digital signal processing (DSP) operations and digital beamforming at the traffic carrier level (narrowband beamforming). The emphasis of the paper is on key design aspects and technology considerations of the payload processor unit (PPU), which includes multiplexing/demultiplexing and digital beamforming operations, and on the antenna and RF signal handling subsystems. For completeness, a review on the European digital technology is also presented. The development of such a payload architecture is in line with present and planned activities of the European Space Agency (ESA) for MEO and GEO orbit systems, which are also implicitly discussed in the paper. 相似文献
994.
小波变换——一种新的雷达信号处理方法 总被引:3,自引:1,他引:2
论述了小波变换技术的产生、基本思想、特点,介绍了其在雷达信号处理中的应用前景。 相似文献
995.
This paper analyses the effect of signal combination techniques in videowatermark detection. A spatial spread spectrum based watermarking techique isused as embedding method, in combination with common error correction codes(BCH, Reed-Solomon with multilevel signaling, binary convolutional codes withViterbi decoding). Besides an analytical evaluation of the bit error rate, theeffectiveness of the channel coding and diversity techniques is also assessedexperimentally under MPEG-2 video compression. 相似文献
996.
本文综述多媒体硬件支撑技术有代表性的若干新进展:MPEG音、视频解压缩IC的芯片级集成,突破微机总线和接口传输瓶颈,多媒体板级产品的系统集成和平台硬软件的总体优化,外存储器的高速大容量化。 相似文献
997.
In this paper, we propose a new three-wavelength method for automatic measurement of principal-stress directions over an entire model on the basis of four-step phase shift method. This method uses four fringe patterns captured by a color charge-coupled devices (CCD) camera corresponding to four angular position arrangements of polaroids in a dark-field plane polariscope. The principal-stress directions can be determined by a single calculation. The method is applied to a circular disc under compression. The principal-stress direction distributions obtained from the proposed method are compared with those obtained from a conventional method and theory. It can be obviously seen that the proposed method accurately yields the principal-stress directions compared with the conventional method. 相似文献
998.
Automatic code synthesis from dataflow program graphs is a promising high-level design methodology for rapid prototyping of multimedia embedded systems. Memory efficient code synthesis from dataflow models has been an active research subject to reduce the gap in terms of memory requirements between the synthesized code and the hand-optimized code. However, existent dataflow models have inherent difficulty of efficiently handling data structures. In this paper, we propose a new dataflow extension called fractional rate dataflow (FRDF) in which fractional number of samples can be produced and consumed. In the proposed FRDF model, a constituent data type is considered as a fraction of the composite data type. Existent integer rate dataflow models can be easily extended to incorporate the fractional rates without loosing analytical properties. In this paper, the SDF model is extended to include FRDF, which can reduce the buffer memory requirements significantly, up to 70%, for some multimedia applications. Extended SDF model with fractional rate has been implemented in our system design environment called PeaCE(Ptolemy extension as Codesign Environment). 相似文献
999.
Petter M. Bakken Arne Rnnekleiv 《International Journal of Satellite Communications and Networking》1989,7(4):283-293
This paper reports on the work done at ELAB-RUNIT on surface acoustic wave (SAW) on-board signal processing. The main processing is done by the analogue chirp Fourier transformer (CFT) and its inverse (ICFT). In a CFT, the input signal is transformed from an FDMA format to a TDM format and at the same time filtered by a filter bank. By multiplying and convolving the signal with chirp waveforms, the CFT is implemented by one bandpass cover filter and one chirp filter. The paper demonstrates that SAW reflector array compressors (RAC) built by ELAB-RUNIT have suitable chirp responses and adequate precision for digital satellite communication. Two applications are described. An on-board multicarrier demodulator (MCD) for 9·6 kb/s QPSK carriers and a processor for filtering, routeing and beam steering (FROBE) for flexible transparent repeaters. For MCDs the use of SAW CFTs leads to a power consumption for demultiplexing and A/D conversion of 15 mW per carrier with room for improvements. For transparent paylods, the FROBE leads to more flexibility and narrower guardbands than can be obtained by other analogue processors. 相似文献
1000.