全文获取类型
收费全文 | 400702篇 |
免费 | 3759篇 |
国内免费 | 1470篇 |
专业分类
电工技术 | 7375篇 |
综合类 | 641篇 |
化学工业 | 57100篇 |
金属工艺 | 19555篇 |
机械仪表 | 15073篇 |
建筑科学 | 8917篇 |
矿业工程 | 2593篇 |
能源动力 | 9092篇 |
轻工业 | 28840篇 |
水利工程 | 4656篇 |
石油天然气 | 8592篇 |
武器工业 | 49篇 |
无线电 | 44955篇 |
一般工业技术 | 85205篇 |
冶金工业 | 65872篇 |
原子能技术 | 9802篇 |
自动化技术 | 37614篇 |
出版年
2021年 | 2875篇 |
2020年 | 2175篇 |
2019年 | 2671篇 |
2018年 | 11903篇 |
2017年 | 12367篇 |
2016年 | 9265篇 |
2015年 | 3664篇 |
2014年 | 5662篇 |
2013年 | 14954篇 |
2012年 | 11086篇 |
2011年 | 19026篇 |
2010年 | 16251篇 |
2009年 | 16509篇 |
2008年 | 16781篇 |
2007年 | 18487篇 |
2006年 | 9643篇 |
2005年 | 11760篇 |
2004年 | 10292篇 |
2003年 | 9784篇 |
2002年 | 8639篇 |
2001年 | 8218篇 |
2000年 | 7944篇 |
1999年 | 8053篇 |
1998年 | 19298篇 |
1997年 | 13733篇 |
1996年 | 10538篇 |
1995年 | 8114篇 |
1994年 | 7119篇 |
1993年 | 7106篇 |
1992年 | 5187篇 |
1991年 | 4979篇 |
1990年 | 4901篇 |
1989年 | 4879篇 |
1988年 | 4498篇 |
1987年 | 4032篇 |
1986年 | 4024篇 |
1985年 | 4487篇 |
1984年 | 4083篇 |
1983年 | 3827篇 |
1982年 | 3565篇 |
1981年 | 3596篇 |
1980年 | 3579篇 |
1979年 | 3358篇 |
1978年 | 3362篇 |
1977年 | 3782篇 |
1976年 | 4878篇 |
1975年 | 2906篇 |
1974年 | 2828篇 |
1973年 | 2833篇 |
1972年 | 2420篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
31.
32.
Rankin D.M. Gulliver T.A. Taylor D.P. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(9):2230-2235
This article investigates the asymptotic performance of single parity-check (SPC) product codes (PCs) from a decoding point of view. Specifically, the probability of bit error is bounded before and after the decoding of each dimension, similar to the analysis of "iterated codes" by Elias (1954). It is shown that the asymptotic probability of bit error can be driven to zero as the number of dimensions, and hence the block length, increases at signal-to-noise ratios (SNRs) within 2 dB of capacity over the additive white Gaussian noise (AWGN) channel. 相似文献
33.
High-efficiency LEDs of 1.6–2.4 µm spectral range for medical diagnostics and environment monitoring
N. D. Stoyanov B. E. Zhurtanov A. P. Astakhova A. N. Imenkov Yu. P. Yakovlev 《Semiconductors》2003,37(8):971-984
High efficient LED structures covering the spectral range of 1.6–2.4 μm have been developed on the basis of GaSb and its solid
solutions. The electroluminescent characteristics and their temperature and current dependences have been studied. The radiative
and nonradiative recombination mechanisms and their effect on the quantum efficiency have been investigated. A quantum efficiency
of 40–60% has been obtained in the quasi-steady mode at room temperature. A short-pulse optical power of 170 mW was reached.
__________
Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 8, 2003, pp. 996–1009.
Original Russian Text Copyright ? 2003 by Stoyanov, Zhurtanov, Astakhova, Imenkov, Yakovlev. 相似文献
34.
35.
A fuzzy logic based-method for prognostic decision making in breast and prostate cancers 总被引:1,自引:0,他引:1
Seker H. Odetayo M.O. Petrovic D. Naguib R.N.G. 《IEEE transactions on information technology in biomedicine》2003,7(2):114-122
Accurate and reliable decision making in oncological prognosis can help in the planning of suitable surgery and therapy, and generally, improve patient management through the different stages of the disease. In recent years, several prognostic markers have been used as indicators of disease progression in oncology. However, the rapid increase in the discovery of novel prognostic markers resulting from the development in medical technology, has dictated the need for developing reliable methods for extracting clinically significant markers where complex and nonlinear interactions between these markers naturally exist. The aim of this paper is to investigate the fuzzy k-nearest neighbor (FK-NN) classifier as a fuzzy logic method that provides a certainty degree for prognostic decision and assessment of the markers, and to compare it with: 1) logistic regression as a statistical method and 2) multilayer feedforward backpropagation neural networks an artificial neural-network tool, the latter two techniques having been widely used for oncological prognosis. In order to achieve this aim, breast and prostate cancer data sets are considered as benchmarks for this analysis. The overall results obtained indicate that the FK-NN-based method yields the highest predictive accuracy, and that it has produced a more reliable prognostic marker model than both the statistical and artificial neural-network-based methods. 相似文献
36.
The characteristics of pulsation processes in dc plasmatrons with the cathode located in the channel center and the anode in the form of a cylindrical or a conical channel wall are investigated in plasmas of argon and nitrogen at atmospheric pressure. The fast Fourier transform of signals and their subsequent computer processing are used to obtain the dependences of the frequency of fluctuations of the arcing voltage on the working parameters of the plasmatron, namely, the electric arc current, the flow rate of plasma-forming gas, and the channel diameter. For plasmatrons with the self-adjusting length of the electric arc, analysis is performed of the mechanism of reclosing of the anode region of the arc, i.e., of the electric arc shunting associated with the stretching of the current filament by a flow of gas and with the electrodynamic interaction of different filament regions. A formula is derived which defines the dependence of the characteristic frequency of fluctuations of the arcing voltage on the external parameters of the problem, namely, the arc current, the flow rate of the working gas, and the characteristic channel diameter. It is demonstrated that the pattern of the dependence of the frequency of voltage fluctuations on the gas flow rate may vary with the values of the parameter of magnetohydrodynamic interaction. The formula generalizes the experimental results of numerous researchers obtained in a wide range of variation of the external parameters. 相似文献
37.
Why does it pay to be selfish in a MANET? 总被引:2,自引:0,他引:2
Younghwan Yoo Dharma P. Agrawal 《Wireless Communications, IEEE》2006,13(6):87-97
Routing protocols for a mobile ad hoc network have assumed that all mobile nodes voluntarily participate in forwarding others' packets. This was a reasonable assumption because all MNs in a MANET belonged to a single authority. In the near future, however, a MANET may consist of MNs that belong to many different organizations since numerous civilian applications are expected to crop up. In this situation, some MNs may run independently and purposely decide not to forward packets so as to save their own energy. This could potentially lead to network partitioning and corresponding performance degradation. To minimize such situations in MANETs, many studies have explored the use of both the carrot and the stick approaches by having reputation-based, credit-payment, and game theory schemes. This article summarizes existing schemes, identifies their relative advantages, and projects future directions 相似文献
38.
S. P. Skobelev 《Journal of Communications Technology and Electronics》2006,51(7):748-758
A recent approach to solution of 2D scattering problems for electromagnetic waves scattered by thin screens is analyzed. With the use of examples of scattering by a strip and an unclosed cylindrical surface, it is shown that the proposed approach has no advantages in terms of the efficiency of numerical solution over a well-known approach based on exact integral equations for currents that have singular kernels and that are solved with the Krylov-Bogoliubov method. 相似文献
39.
Pallem C. Chowdhuri P. Demko J.A. Gouge M.J. 《Applied Superconductivity, IEEE Transactions on》2006,16(1):31-37
The objective of this work was to determine the significant parameters of a 3-GW 200-kV dc superconducting cable system which influence the transient voltage distribution in the various parts of the cable. The cable system consists of four coaxial metallic cylinders. It was found that the dielectric constant and the electrical resistivity of the soil significantly affect the severity of the transient voltages; lower dielectric constant and higher resistivity of the soil will increase the magnitudes of the transient voltages by increasing the earth-return impedance. It was also found that the effect of the conductor internal impedances of the cable is insignificant. Shorting the coaxial cylinders of the cryogen flow and the cryostat will lessen the severity of the transient voltages. Grounding the second, third, and fourth cylinders at regular intervals with low-impedance grounding impedance will also improve the transient performance of the cable. More research is needed to evaluate these procedures. 相似文献
40.
Nonlinear dynamics of crack propagation are investigated experimentally and theoretically with the goal of clarifying the nature of limiting crack velocity, the transition from steady state to branching regimes of crack dynamics, and the dynamics of crack arrest. The theoretical explanation of limiting steady-state crack velocity and the transition to a branching regime was proposed due to the study of collective behavior of a microcrack ensemble at the crack tip area. The experimental study of crack dynamics was carried out in a preloaded plate PMMA specimen using the high-speed camera coupled with the photo-elasticity method, the point stress recording with a laser system, and the failure surface roughness measurement. 相似文献