全文获取类型
收费全文 | 196530篇 |
免费 | 2045篇 |
国内免费 | 728篇 |
专业分类
化学 | 89742篇 |
晶体学 | 3060篇 |
力学 | 7219篇 |
综合类 | 10篇 |
数学 | 19717篇 |
物理学 | 55956篇 |
无线电 | 23599篇 |
出版年
2020年 | 1628篇 |
2019年 | 1792篇 |
2018年 | 2234篇 |
2017年 | 2291篇 |
2016年 | 3520篇 |
2015年 | 2100篇 |
2014年 | 3480篇 |
2013年 | 8339篇 |
2012年 | 6278篇 |
2011年 | 7472篇 |
2010年 | 5588篇 |
2009年 | 5803篇 |
2008年 | 7518篇 |
2007年 | 7545篇 |
2006年 | 7207篇 |
2005年 | 6594篇 |
2004年 | 6148篇 |
2003年 | 5566篇 |
2002年 | 5446篇 |
2001年 | 6114篇 |
2000年 | 4759篇 |
1999年 | 3860篇 |
1998年 | 3308篇 |
1997年 | 3152篇 |
1996年 | 3007篇 |
1995年 | 2830篇 |
1994年 | 2726篇 |
1993年 | 2662篇 |
1992年 | 2946篇 |
1991年 | 2871篇 |
1990年 | 2765篇 |
1989年 | 2640篇 |
1988年 | 2610篇 |
1987年 | 2368篇 |
1986年 | 2215篇 |
1985年 | 2877篇 |
1984年 | 2925篇 |
1983年 | 2580篇 |
1982年 | 2666篇 |
1981年 | 2473篇 |
1980年 | 2453篇 |
1979年 | 2562篇 |
1978年 | 2598篇 |
1977年 | 2527篇 |
1976年 | 2597篇 |
1975年 | 2478篇 |
1974年 | 2444篇 |
1973年 | 2635篇 |
1972年 | 1712篇 |
1971年 | 1430篇 |
排序方式: 共有10000条查询结果,搜索用时 47 毫秒
131.
The bit-error rate (BER) performance of new iterative decoding algorithms (e,g,, turbodecoding) is achieved at the expense of a computationally burdensome decoding procedure. We present a method called early detection that can be used to reduce the computational complexity of a variety of iterative decoders. Using a confidence criterion, some information symbols, state variables, and codeword symbols are detected early on during decoding. In this way, the computational complexity of further processing is reduced with a controllable increase in the BER. We present an easily implemented instance of this algorithm, called trellis splicing, that can be used with turbodecoding. For a simulated system of this type, we obtain a reduction in the computational complexity of up to a factor of four, relative to a turbodecoder that obtains the same increase in the BER by performing fewer iterations 相似文献
132.
The authors present a low-voltage BiCMOS dynamic minimum circuit using a parallel comparison algorithm for VLSI implementation of fuzzy controllers. Using low-voltage BiCMOS dynamic circuits and a parallel comparison algorithm, a four-4-bit-input minimum circuit designed, based on a 1μm BiCMOS technology, shows a 9.5ns comparison time, which is a ×2.5 improvement in speed as compared to that based on CMOS technology 相似文献
133.
When hydrogen loading is used to enhance the photosensitivity of silica-based optical waveguides and fibres, the presence of molecular hydrogen dissolved in the glass matrix changes the effective index of propagation of guided optical modes by as much as 0.05%. Real-time monitoring of the reflectivity spectrum of Bragg gratings written in such conditions shows that the centre wavelength follows the changes in hydrogen concentration due to diffusion and reaction with glass defects 相似文献
134.
Durhuus T. Mikkelsen B. Joergensen C. Lykke Danielsen S. Stubkjaer K.E. 《Lightwave Technology, Journal of》1996,14(6):942-954
Following a brief introduction to the applications for wavelength conversion and the different available conversion techniques, the paper gives an in depth analysis of cross gain and cross phase wavelength conversion in semiconductor optical amplifiers. The influence of saturation filtering on the bandwidth of the converters is explained and conditions for conversion at 20 Gb/s or more are identified. The cross gain modulation scheme shows extinction ratio degradation for conversion to longer wavelengths. This can be overcome using cross phase modulation in semiconductor optical amplifiers that are integrated into interferometric structures. The first results for monolithic integrated interferometric wavelength converters are reviewed, and the quality of the converted signals is demonstrated by transmission of 10 Gb/s converted signals over 60 km of nondispersion shifted single mode fiber 相似文献
135.
A new scheme based on using an IIR design algorithm is presented to demultiplex critically sampled QPSK channels for onboard processing (OBP) satellites. Comparisons with an existing nonrecursive (FIR) transmultiplexer (TMUX) show that the presented IIR TMUX is also a suitable candidate for consideration in future OBP applications 相似文献
136.
Maxwell G.D. Kashyap R. Sherlock G. Collins J.V. Ainslie B.J. 《Electronics letters》1994,30(18):1486-1487
The authors report the first demonstration of a semiconductor external cavity waveguide laser, modulated at 2.5 Gbit/s over 100 km of standard optical fibre using a UV written grating in a planar silica waveguide as the feedback element 相似文献
137.
Harame D.L. Comfort J.H. Cressler J.D. Crabbe E.F. Sun J.Y.-C. Meyerson B.S. Tice T. 《Electron Devices, IEEE Transactions on》1995,42(3):455-468
A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented 相似文献
138.
Ferdinand P. Ferragu O. Lechien J.L. Lescop B. Magne S. Marty V. Rougeault S. Kotrotsios G. Neuman V. Depeursinge Y. Michel J.B. Van Uffelen M. Varelas D. Berthou H. Pierre G. Renouf C. Jarret B. Verbandt Y. Stevens W. Voet M.R.H. Toscano D. 《Lightwave Technology, Journal of》1995,13(7):1303-1313
Recent developments of stability control in mines, essentially based on Ge-doped fiber Bragg gratings (FBG) are reported including results about the different aspects of the system: accurate characterizations of FBG, sensor network topology and multiplexing method, user interface design and sensor packaging 相似文献
139.
The high-speed response properties of resonant cavity enhanced (RCE) photodetectors have been investigated. The limitations on the high-speed performance of photodiodes and the advantages of RCE-detection are discussed. Transient response of heterojunction photodiodes under pulsed optical illumination has been simulated using the method described in Part I. Results on conventional AlGaAs/GaAs and RCE GaAs/InGaAs heterojunction p-i-n photodiodes are presented. For small area detectors, almost 50% bandwidth improvement along with a two-fold increase in efficiency is predicted for RCE devices over optimized conventional photodiodes. A nearly three-fold enhancement in the bandwidth-efficiency product was shown 相似文献
140.