全文获取类型
收费全文 | 11017篇 |
免费 | 277篇 |
国内免费 | 94篇 |
专业分类
化学 | 5114篇 |
晶体学 | 76篇 |
力学 | 302篇 |
综合类 | 2篇 |
数学 | 1492篇 |
物理学 | 2074篇 |
无线电 | 2328篇 |
出版年
2023年 | 60篇 |
2021年 | 90篇 |
2020年 | 100篇 |
2019年 | 92篇 |
2018年 | 95篇 |
2016年 | 161篇 |
2015年 | 142篇 |
2014年 | 189篇 |
2013年 | 470篇 |
2012年 | 492篇 |
2011年 | 570篇 |
2010年 | 302篇 |
2009年 | 318篇 |
2008年 | 531篇 |
2007年 | 545篇 |
2006年 | 549篇 |
2005年 | 526篇 |
2004年 | 437篇 |
2003年 | 407篇 |
2002年 | 356篇 |
2001年 | 326篇 |
2000年 | 302篇 |
1999年 | 227篇 |
1998年 | 195篇 |
1997年 | 166篇 |
1996年 | 222篇 |
1995年 | 185篇 |
1994年 | 193篇 |
1993年 | 208篇 |
1992年 | 184篇 |
1991年 | 157篇 |
1990年 | 143篇 |
1989年 | 137篇 |
1988年 | 105篇 |
1987年 | 119篇 |
1986年 | 98篇 |
1985年 | 164篇 |
1984年 | 120篇 |
1983年 | 89篇 |
1982年 | 108篇 |
1981年 | 124篇 |
1980年 | 101篇 |
1979年 | 106篇 |
1978年 | 110篇 |
1977年 | 89篇 |
1976年 | 95篇 |
1975年 | 96篇 |
1974年 | 114篇 |
1973年 | 135篇 |
1972年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
C. A. Johnson 《Acta Mathematica Hungarica》1990,56(3-4):269-282
982.
The Halo structure is usually adopted in deep submicrometer MOS devices for punchthrough prevention. The tilt angle of the Halo implant determines the dopant distribution which induces anti-punchthrough operation. In this paper, we investigate the impact of the tilt angle on the Halo PMOS device performance via two-dimensional (2D) simulations. We find that the ratio of on-current to off-current is constant for all tilt angles of Halo implant, implying an equivalent DC performance for all tilt angles. The equivalence can be traced back to a self compensation between the body factor and source resistance. The result implies that a low tilt angle should be adopted for Halo devices, for it gives a small threshold voltage and thus a high noise margin. The methodology used in analyzing body factor and source resistance can also be applied to analyze other devices. 相似文献
983.
The time averaged frame subtraction technique is improved by subtracting two Bessel fringe patterns at two different force levels. The technique enables significant enhancement of fringe contrast and increased measurement sensitivity. The contrast and sensitivity of the fringes obtained at different force ratios are investigated. Both theoretical and experimental results are presented. 相似文献
984.
Measuring thermal and mechanical stresses on optical fiber in a DC module using fiber Bragg gratings 总被引:1,自引:0,他引:1
Glaesemann G.S. Smith J.A. Clark D.A. Johnson R. 《Lightwave Technology, Journal of》2005,23(11):3461-3468
Fiber Bragg gratings (FBGs) can be used as sensors to monitor stress and test temperature during the processing and handling of optical fiber. As the FBG experiences a combination of mechanical and thermal loading, the return Bragg wavelength will shift proportionately to the magnitude of the load. This paper discusses the use of these sensors in quantifying induced stress on fiber during the packaging of a dispersion-compensating module (DCM) and the ensuing environmental exposure. There are two potential fiber-failure modes for fiber wound in DCMs, namely microbend-induced attenuation and fiber failure from fatigue. The ability to quantify fiber stress provides a useful feedback tool in the design phase of these modules that can aid in reducing the risk of mechanical and optical failure modes. A practical characterization process was developed to decouple thermal and stress effects on FBGs based on results from current literature and from this study. Uncoated Bragg sensors were found to respond linearly between -40 to 80/spl deg/C. Gratings with a protective polymer recoat departed from the linear behavior of the uncoated gratings below -5/spl deg/C. It was determined that the recoat material places less than 25 MPa (3.6 klbf/in/sup 2/) of axial compression on the fiber at -40/spl deg/C. Four gratings with different Bragg wavelengths were spliced into 10 km of fiber and wound into a DCM. The wind-induced stress on all four gratings quickly relaxed. The module was then thermal cycled between -40 and +75/spl deg/C. The overall stress on each grating was acceptably low for reliability purposes. The maximum stress of 17 MPa (2.5 klbf/in/sup 2/) was observed at the lowest temperature. 相似文献
985.
Leung-Pong Wong Cheng D.K.-W. Chow M.H.L. Yim-Shu Lee 《Industrial Electronics, IEEE Transactions on》2005,52(5):1246-1260
An interleaved three-phase forward converter using an integrated transformer is proposed in this paper. This type of converter has the attractive features of flexible voltage conversion ratio, high output current (due to the parallel connection of outputs), near-zero output-current ripple (due to the output-current-ripple cancellation), fast transient response (due to the small effective output-filtering inductance), and is particularly suitable for high-output-current and low-output-voltage applications such as telecommunication and computer systems. The integrated transformer of the proposed converter consists of three step-down transformers on a single magnetic core. The z-parameter (gyrator) model and the equivalent-circuit model of the integrated transformer are derived. Based on the equivalent-circuit model, the principle of operation of the proposed converter is explained. The analysis and design criteria of the basic circuit, the operation of the regenerative LC snubber circuit, the simulation, and experimental verification are also described. 相似文献
986.
Hiu Yung Wong Takeuchi H. Tsu-Jae King Ameen M. Agarwal A. 《Electron Device Letters, IEEE》2005,26(4):234-236
Pulsed excimer laser annealing (ELA) is used to reduce the poly-Si gate depletion effect (to <0.1 nm). Low resistivity (0.58 m/spl Omega//spl middot/cm) and high active boron concentration (4/spl times/10/sup 20/ cm/sup -3/) at the gate-oxide interface are achieved while preserving the gate oxide quality and avoiding boron penetration, to meet International Technology Roadmap for Semiconductors requirements for sub-65-nm CMOS technology nodes. ELA is compatible with high-/spl kappa/ dielectric (HfO/sub 2/) and results in significantly lower gate leakage current density as compared with rapid thermal annealing (RTA). 相似文献
987.
988.
C.F. Tsang C.Y. Li A. Krishnamoorthy Y.J. Su H.Y. Li L.Y. Wong W.H. Li L.J. Tang K.Y. Ee 《Microelectronics Journal》2004,35(9):693-700
Integration of Cu with low k dielectrics provided solution to reduce both resistance-capacitance time delay and parasitic capacitance of BEOL interconnections for 130 nm and beyond technology node. The motivation of this work is to study and improve electrical and reliability performance of two-level Cu/CVD low k SiOCH metallization from the results of diffusion barrier deposition schemes. Barrier deposition schemes are (a) high-density-plasma 250 Å Ta; (b) surface treatment of forming gas followed by high-density-plasma 250 Å Ta and (c) bi-layer of 100 Å Ta(N)/150 Å Ta. In this work, we demonstrated the superior and competency of high-density-plasma Ta deposition for Cu/CVD low k metallization and achieved excellent electrical and reliability results. Wafers fabricated with high-density-plasma Ta barrier scheme resulted in the best electrical yields, >90% for testing vehicles of dense via chains (via size=200 nm) and interspersed comb structures (width/space=200 nm/200 nm). Dielectric breakdown strength of the interspersed comb structures obtained at electric field of 0.3 MV/cm was ∼4 MV/cm. 相似文献
989.
VoIP reliability: a service provider's perspective 总被引:1,自引:0,他引:1
Johnson C.R. Kogan Y. Levy Y. Saheban F. Tarapore P. 《Communications Magazine, IEEE》2004,42(7):48-54
Voice over IP services offer important revenue-generating opportunities, as well as many technical challenges in providing high-quality services. Users have come to expect highly available telecommunications services with high-quality voice. Service providers need reliable high-performance networks to meet user expectations, and must be able to guarantee performance and reliability to their customers. In converged voice and data networks, the network infrastructure must deliver very high quality and availability for some customer needs, while also providing low-cost high-capacity bandwidth for other needs. The use of quality of service mechanisms to provide prioritization for various traffic types is a key element needed for voice and data network convergence. However, it is not sufficient if the underlying networks are unreliable. The focus of this article is to address the reliability aspects of VoIP services, including the underlying IP networks. 相似文献
990.
In this paper, we redefine the Fox torus homotopy groups and give a proof of the split exact sequence of these groups. Evaluation
subgroups are defined and are related to the classical Gottlieb subgroups. With our constructions, we recover the Abe groups
and prove some results of Gottlieb for the evaluation subgroups of Fox homotopy groups. We further generalize Fox groups and
define a group τ = [Σ(V×W⋃ *), X] in which the generalized Whitehead product of Arkowitz is again a commutator. Finally, we show that the generalized Gottlieb
group lies in the center of τ, thereby improving a result of Varadarajan.
__________
Published in Ukrains'kyi Matematychnyi Zhurnal, Vol. 57, No. 3, pp. 320–328, March, 2005. 相似文献