全文获取类型
收费全文 | 211976篇 |
免费 | 2889篇 |
国内免费 | 863篇 |
专业分类
化学 | 96804篇 |
晶体学 | 2531篇 |
力学 | 7861篇 |
综合类 | 7篇 |
数学 | 19294篇 |
物理学 | 55274篇 |
无线电 | 33957篇 |
出版年
2021年 | 1203篇 |
2020年 | 1321篇 |
2019年 | 1296篇 |
2018年 | 1372篇 |
2017年 | 1356篇 |
2016年 | 2735篇 |
2015年 | 2184篇 |
2014年 | 2914篇 |
2013年 | 8765篇 |
2012年 | 7007篇 |
2011年 | 8836篇 |
2010年 | 5708篇 |
2009年 | 6192篇 |
2008年 | 8904篇 |
2007年 | 9287篇 |
2006年 | 9035篇 |
2005年 | 8493篇 |
2004年 | 7585篇 |
2003年 | 6759篇 |
2002年 | 6543篇 |
2001年 | 7526篇 |
2000年 | 5903篇 |
1999年 | 4724篇 |
1998年 | 3849篇 |
1997年 | 3809篇 |
1996年 | 3708篇 |
1995年 | 3328篇 |
1994年 | 3262篇 |
1993年 | 3178篇 |
1992年 | 3403篇 |
1991年 | 3363篇 |
1990年 | 3005篇 |
1989年 | 2896篇 |
1988年 | 2787篇 |
1987年 | 2367篇 |
1986年 | 2266篇 |
1985年 | 3244篇 |
1984年 | 3186篇 |
1983年 | 2603篇 |
1982年 | 2787篇 |
1981年 | 2676篇 |
1980年 | 2621篇 |
1979年 | 2488篇 |
1978年 | 2580篇 |
1977年 | 2494篇 |
1976年 | 2428篇 |
1975年 | 2397篇 |
1974年 | 2277篇 |
1973年 | 2387篇 |
1972年 | 1427篇 |
排序方式: 共有10000条查询结果,搜索用时 623 毫秒
951.
A highly linear electrooptic modulator has been designed, fabricated, and evaluated. The design of this modulator consists of only a simple modification to the directional coupler. Two-tone testing has demonstrated that, for an optical modulation depth of 30% per channel, the third-order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. This improvement was not observed to be accompanied by any increase in second harmonic distortion. Also included are results of two-tone computer simulations which predict the improvement in linearity of this device for a range of modulation depths.<> 相似文献
952.
953.
The pattern synthesis techinque described allows the power pattern to be optimized in a very useful sense over the desired operating band of the antenna array. This is an improvement over previous techniques involving constraints on such artificial parameters as source norm and superdirectivity ratio, which do not, in fact, ensure a useful pattern bandwidth. The procedure described provides minimum mean square error over an arbitrary number of discrete frequencies 相似文献
954.
We introduce and investigate the properties of Hochschild cohomology of algebras in an abelian monoidal category M. We show that the second Hochschild cohomology group of an algebra in M classifies extensions of A up to an equivalence. We characterize algebras of Hochschild dimension 0 (separable algebras), and of Hochschild dimension ≤1 (formally smooth algebras). Several particular cases and applications are included in the last section of the paper. 相似文献
955.
Logic and memory with nanocell circuits 总被引:1,自引:0,他引:1
Husband C.P. Husband S.M. Daniels J.S. Tour J.M. 《Electron Devices, IEEE Transactions on》2003,50(9):1865-1875
Molecular electronics is an emerging field that seeks to build faster, cheaper, denser computers from nanoscale devices. The nanocell is a molecular electronics design wherein a random, self-assembled array of molecules and metallic nanoparticles is addressed by a relatively small number of input/output pins. The challenge then is to program the nanocell post-fabrication. We have previously demonstrated the ability to program individual simulated nanocells as logic gates. In this paper, we further explore the problem of programming nanocells and consider connecting nanocells into circuits using bistable latches at the interconnects. These latches are critical because they permit signal restoration. Simulated nanocell circuits for logic and memory are presented here. 相似文献
956.
Soole J.B.D. Schlax M. Earnshaw M.P. Narayanan C. Pafchek R. 《Electronics letters》2003,39(18):1318-1319
The realisation of a monolithic athermalised variable-optical-attenuator-integrated multiplexer (VMUX) implemented in silica-on-silicon waveguide technology is reported. The VMUX incorporates an athermal arrayed waveguide grating, providing <0.05 nm of peak transmission wavelength shift over 20-70/spl deg/C operating ambient independent of attenuator settings. 相似文献
957.
A design-for-testability scheme for detecting CMOS analog faults was reported by Favalli et al. (see ibid., vol.25, no.5, p.1239-46, 1990). The authors propose two alternative designs, one for small circuits and another for large circuits, which require significantly less area overhead (about 1/4 to 1/3) than that of Favalli's design. With the proposed modification in the first design, the untestable problem, which occurred in Favalli's design, can be alleviated. Furthermore, the proposed schemes are also fit to be implemented in VLSI circuits 相似文献
958.
959.
This paper presents supplier–buyer models to describe the bargaining process between a supplier and a buyer over a long-term replenishment contract. Two different models are developed: one for the situation where the supplier has superior bargaining power over the buyer, and the other for the reverse situation. For each model, a method is derived that employs game theory-based analysis to determine the best strategy for each agent. A computational experiment is conducted to estimate the efficiency of the methods and to determine the economic implications of the results. The result indicates that each algorithm is very efficient compared to other strategies. We also verify that the solutions derived from each model are Nash equilibrium. Significantly improved outcomes are obtained for both agents by agreeing to the terms generated by the algorithms over the terms selected in the usual manner. 相似文献
960.
We consider the method of Poincaré to investigate thelocal index of vector fields in the plane. If m is the degreeof the first non-zero jet, Xm, of the vector field X at an isolatedzero, we explore the geometry of the pencil generated by thecoordinate functions of Xm when the absolute value of the indexof X, |ind (X)|, is m. We also find necessary and sufficientconditions for |ind (X)| to be m. 相似文献