全文获取类型
收费全文 | 1219篇 |
免费 | 39篇 |
国内免费 | 1篇 |
专业分类
化学 | 758篇 |
晶体学 | 7篇 |
力学 | 18篇 |
数学 | 169篇 |
物理学 | 207篇 |
无线电 | 100篇 |
出版年
2023年 | 7篇 |
2022年 | 7篇 |
2021年 | 25篇 |
2020年 | 11篇 |
2018年 | 12篇 |
2016年 | 21篇 |
2015年 | 19篇 |
2014年 | 19篇 |
2013年 | 52篇 |
2012年 | 69篇 |
2011年 | 69篇 |
2010年 | 42篇 |
2009年 | 28篇 |
2008年 | 70篇 |
2007年 | 86篇 |
2006年 | 45篇 |
2005年 | 78篇 |
2004年 | 54篇 |
2003年 | 43篇 |
2002年 | 42篇 |
2001年 | 25篇 |
2000年 | 21篇 |
1999年 | 14篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 29篇 |
1995年 | 16篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 17篇 |
1978年 | 10篇 |
1977年 | 13篇 |
1976年 | 11篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1973年 | 20篇 |
1972年 | 9篇 |
排序方式: 共有1259条查询结果,搜索用时 725 毫秒
1.
In the following we find all of the three-dimensional flat spacetimes which are static and rotationally symmetric. 相似文献
2.
3.
4.
Bart M. J. M. Suijkerbuijk Duncan M. Tooke Anthony L. Spek Gerard van Koten Robertus J. M. Klein Gebbink Prof. Dr. 《无机化学与普通化学杂志》2007,633(15):2649-2653
A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures. 相似文献
5.
Kizilyalli I.C. Rambaud M.M. Duncan A. Lytle S.A. Thoma M.J. 《Electron Device Letters, IEEE》1995,16(10):457-459
The trade-off between threshold voltage (Vth) and the minimum gate length (Lmin) is discussed for optimizing the performance of buried channel PMOS transistors for low voltage/low power high-speed digital CMOS circuits. In a low supply voltage CMOS technology it is desirable to scale Vth and Lmin for improved circuit performance. However, these two parameters cannot be scaled independently due to the channel punch-through effect. Statistical process/device modeling, split lot experiments, circuit simulations, and measurements are performed to optimize the PMOS transistor current drive and CMOS circuit speed. We show that trading PMOS transistor Vth for a smaller Lmin results in faster circuits for low supply voltage (3.3 to 1.8 V) n+-polysilicon gate CMOS technology, Circuit simulation and measurements are performed in this study. Approximate empirical expressions are given for the optimum buried channel PMOS transistor V th for minimizing CMOS circuit speed for cases involving: (1) constant capacitive load and (2) load capacitance proportional to MOS gate capacitance. The results of the numerical exercise are applied to the centering of device parameters of a 0.5 μm 3.3 V CMOS technology that (a) matches the speed of our 0.5 μm 5 V CMOS technology, and (b) achieves good performance down to 1.8 V power supply. For this process the optimum PMOS transistor Vth (absolute value) is approximately 0.85-0.90 V 相似文献
6.
We derive and analyse four algorithms for computing the current induced on a thin straight wire by a transient electric field.
They all involve solving the thin wire electric field integral equations (EFIEs) and consist of a very accurate differential
equations solver together with various schemes to approximate the vector potential integral equation. We carry out a rigorous
numerical stability analysis of each of these methods. This has not previously been done for solution schemes for the thin
wire EFIEs. Each scheme is shown to be stable and convergent provided the radius of the wire is small enough for the thin
wire equations to be a valid model. 相似文献
7.
An algorithm is introduced which labels formants from the peaks of pole-focused spectra. A clustering procedure is first used to produce line segments of possible formants. These can be considered as anchor traces for the later processing. Rule-based labelling is then applied to provide final formant trace estimates. Experimental results show that the proposed algorithm offers improved formant labelling accuracy. 相似文献
8.
W. S. Holland P. A. R. Ade M. J. Griffin I. D. Hepburn D. G. Vickers C. R. Cunningham P. R. Hastings W. K. Gear W. D. Duncan T. E. C. Baillie E. E. Haller J. W. Beeman 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(4):669-692
We describe the design and construction of bolometric detectors for SCUBA - the Submillimetre Common-User Bolometer Array for the James Clerk Maxwell Telescope in Hawaii. The instrument contains 131 individual detectors, in two arrays, optimized for the submillimetre atmospheric transmission windows. The detectors are cooled by dilution refrigeration to a temperature of 100 mK, so that the receiver performance will be limited by photon noise from the sky and telescope background in all wavebands. A future paper will describe the performance of the detectors with reference to typical data obtained during the laboratory commissioning period. 相似文献
9.
Multiple-zero multiple-pole optical filter transfer functions may be implemented more efficiently in an integrated optics architecture if higher order N × M optical couplers are utilized. For example, a coherent ring resonator made from two 3×3 couplers offers some advantages over the three mirror Fabry-Perot etalon, which is its analog. To this end we develop the formalism for obtaining the transfer functions and scattering matrices of ring resonators made from two N × M couplers. We then present a methodology for analyzing serial and parallel systems of N × M optical coupler ring resonators. 相似文献
10.
Georgia Benkart Seok-Jin Kang Duncan Melville 《Transactions of the American Mathematical Society》1998,350(8):3297-3319
We construct quantum deformations of enveloping algebras of Borcherds superalgebras, their Verma modules, and their irreducible highest weight modules.