全文获取类型
收费全文 | 709554篇 |
免费 | 7349篇 |
国内免费 | 2060篇 |
专业分类
电工技术 | 12748篇 |
综合类 | 744篇 |
化学工业 | 107603篇 |
金属工艺 | 30451篇 |
机械仪表 | 22686篇 |
建筑科学 | 16336篇 |
矿业工程 | 5191篇 |
能源动力 | 16662篇 |
轻工业 | 54231篇 |
水利工程 | 8153篇 |
石油天然气 | 17998篇 |
武器工业 | 73篇 |
无线电 | 78533篇 |
一般工业技术 | 147654篇 |
冶金工业 | 121854篇 |
原子能技术 | 19208篇 |
自动化技术 | 58838篇 |
出版年
2021年 | 5954篇 |
2019年 | 5729篇 |
2018年 | 10249篇 |
2017年 | 10449篇 |
2016年 | 11025篇 |
2015年 | 6784篇 |
2014年 | 11615篇 |
2013年 | 30919篇 |
2012年 | 18063篇 |
2011年 | 24155篇 |
2010年 | 19171篇 |
2009年 | 21900篇 |
2008年 | 22612篇 |
2007年 | 22277篇 |
2006年 | 19147篇 |
2005年 | 17524篇 |
2004年 | 17207篇 |
2003年 | 16833篇 |
2002年 | 16283篇 |
2001年 | 16369篇 |
2000年 | 15620篇 |
1999年 | 15686篇 |
1998年 | 35684篇 |
1997年 | 26178篇 |
1996年 | 20313篇 |
1995年 | 15912篇 |
1994年 | 14297篇 |
1993年 | 14284篇 |
1992年 | 10972篇 |
1991年 | 10797篇 |
1990年 | 10563篇 |
1989年 | 10399篇 |
1988年 | 9939篇 |
1987年 | 8933篇 |
1986年 | 9021篇 |
1985年 | 10108篇 |
1984年 | 9360篇 |
1983年 | 8862篇 |
1982年 | 8093篇 |
1981年 | 8398篇 |
1980年 | 8102篇 |
1979年 | 8026篇 |
1978年 | 8040篇 |
1977年 | 8986篇 |
1976年 | 11185篇 |
1975年 | 7093篇 |
1974年 | 7035篇 |
1973年 | 7095篇 |
1972年 | 6088篇 |
1971年 | 5479篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Long-range prediction of the mobile-radio fading envelope is an enabling technology for many fading compensation approaches. Because the fading envelope is well modeled as a bandlimited process, it has special predictability properties. In this paper, we find a linear predictor that is optimal in the mean-square sense when the predictor impulse response is energy constrained. This solution may be used to determine the minimum mean squared error of a prediction based on past values that are corrupted with estimation errors. 相似文献
62.
63.
It is shown that, for the spectrum analysis of digital quasi-periodic signals, one must use a procedure based on approximating the sequence of data readouts by a first-order trigonometric polynomial with a varying frequency of its harmonic functions. 相似文献
64.
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
65.
Chong D. Y. R. Lim B. K. Rebibis K. J. Pan S. J. Sivalingam K. Kapoor R. Sun A. Y. S. Tan H. B. 《Advanced Packaging, IEEE Transactions on》2006,29(4):674-682
The recent advancement in high- performance semiconductor packages has been driven by the need for higher pin count and superior heat dissipation. A one-piece cavity lid flip chip ball grid array (BGA) package with high pin count and targeted reliability has emerged as a popular choice. The flip chip technology can accommodate an I/O count of more than five hundreds500, and the die junction temperature can be reduced to a minimum level by a metal heat spreader attachment. None the less, greater expectations on these high-performance packages arose such as better substrate real estate utilization for multiple chips, ease in handling for thinner core substrates, and improved board- level solder joint reliability. A new design of the flip chip BGA package has been looked into for meeting such requirements. By encapsulating the flip chip with molding compound leaving the die top exposed, a planar top surface can be formed. A, and a flat lid can then be mounted on the planar mold/die top surface. In this manner the direct interaction of the metal lid with the substrate can be removed. The new package is thus less rigid under thermal loading and solder joint reliability enhancement is expected. This paper discusses the process development of the new package and its advantages for improved solder joint fatigue life, and being a multichip package and thin core substrate options. Finite-element simulations have been employed for the study of its structural integrity, thermal, and electrical performances. Detailed package and board-level reliability test results will also be reported 相似文献
66.
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
67.
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
68.
V. N. Logozinskii 《Journal of Communications Technology and Electronics》2006,51(7):836-840
Optical phase nonreciprocity is found to appear in fiber-optic gyroscopes as a result of a magnetically induced distortion of a propagating fiber mode. It is shown that this nonreciprocity places a limitation on the magnetic stability of a gyroscope. 相似文献
69.
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
70.
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