全文获取类型
收费全文 | 289285篇 |
免费 | 2353篇 |
国内免费 | 879篇 |
专业分类
化学 | 128846篇 |
晶体学 | 4251篇 |
力学 | 13233篇 |
综合类 | 17篇 |
数学 | 26246篇 |
物理学 | 84458篇 |
无线电 | 35466篇 |
出版年
2021年 | 2621篇 |
2020年 | 2665篇 |
2019年 | 3273篇 |
2018年 | 4494篇 |
2017年 | 4420篇 |
2016年 | 6046篇 |
2015年 | 3069篇 |
2014年 | 5648篇 |
2013年 | 11586篇 |
2012年 | 9436篇 |
2011年 | 11329篇 |
2010年 | 9116篇 |
2009年 | 9769篇 |
2008年 | 11423篇 |
2007年 | 11604篇 |
2006年 | 10512篇 |
2005年 | 9348篇 |
2004年 | 8815篇 |
2003年 | 8051篇 |
2002年 | 7879篇 |
2001年 | 9526篇 |
2000年 | 7299篇 |
1999年 | 5651篇 |
1998年 | 4683篇 |
1997年 | 4802篇 |
1996年 | 4245篇 |
1995年 | 3840篇 |
1994年 | 3854篇 |
1993年 | 3744篇 |
1992年 | 4291篇 |
1991年 | 4404篇 |
1990年 | 4213篇 |
1989年 | 4064篇 |
1988年 | 3865篇 |
1987年 | 3607篇 |
1986年 | 3331篇 |
1985年 | 4226篇 |
1984年 | 4217篇 |
1983年 | 3396篇 |
1982年 | 3323篇 |
1981年 | 3255篇 |
1980年 | 2992篇 |
1979年 | 3427篇 |
1978年 | 3415篇 |
1977年 | 3590篇 |
1976年 | 3510篇 |
1975年 | 3207篇 |
1974年 | 3168篇 |
1973年 | 3237篇 |
1972年 | 2371篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
N. P. Yeliseyeva 《Journal of Communications Technology and Electronics》2006,51(4):380-384
Rigorous analytic expressions for radiation resistance R Σ of an electric dipole are obtained for three mutually orthogonal orientations of the dipole’s axis with respect to a plane metal screen or right-angle corner of infinite dimensions. Radiation resistance R Σ of the dipole oriented arbitrarily in space is calculated and analyzed as a function of the distance from the screen. 相似文献
3.
In this letter, we introduce and investigate a new problem referred to as the All Hops Shortest Paths (AHSP) problem. The AHSP problem involves selecting, for all hop counts, the shortest paths from a given source to any other node in a network. We derive a tight lower bound on the worst-case computational complexities of the optimal comparison-based solutions to AHSP. 相似文献
4.
5.
6.
Kontogiannopoulos N. Psychalinos C. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2006,53(12):1373-1377
In this brief, the well-known switched-current (SI) filtering technique is revisited using the concept of the square-root domain (SRD) filtering. It is proved that SI filters are a subclass of the SRD filters, where sampled-data signal processing is performed. This is achieved by considering typical lossless and lossy SRD sampled-data integrator configurations, using a set of complementary SRD operators which are based on the quadratic I-V relationship of MOS transistor operated in the saturation. Circuit examples are given, where linear-domain integrator and third-order filter configurations were derived using appropriate SRD sampled-data building blocks 相似文献
7.
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
8.
M. N. Levin A. V. Tatarintsev V. A. Makarenko V. R. Gitlin 《Russian Microelectronics》2006,35(5):329-336
A model is formulated that describes how radiation-induced charge accumulates in the gate oxide of a MOS structure and how it decays through tunneling and thermal emission. The model is used in a numerical analysis of the x-ray or UV adjustment of threshold voltage in MOS-circuit manufacture. The limits of this process technique are evaluated. 相似文献
9.
We consider the problem of designing a network of optical cross-connects (OXCs) to provide end-to-end lightpath services to large numbers of label switched routers (LSRs). We present a set of heuristic algorithms to address the combined problem of physical topology design (i.e., determine the number of OXCs required and the fiber links among them) and logical topology design (i.e., determine the routing and wavelength assignment for the lightpaths among the LSRs). Unlike previous studies which were limited to small topologies with a handful of nodes and a few tens of lightpaths, we have applied our algorithms to networks with hundreds or thousands of LSRs and with a number of lightpaths that is an order of magnitude larger than the number of LSRs. In order to characterize the performance of our algorithms, we have developed lower bounds which can be computed efficiently. We present numerical results for up to 1000 LSRs and for a wide range of system parameters such as the number of wavelengths per fiber, the number of transceivers per LSR, and the number of ports per OXC. The results indicate that it is possible to build large-scale optical networks with rich connectivity in a cost-effective manner, using relatively few but properly dimensioned OXCs. 相似文献
10.
J.M. Roth T.G. Ulmer N.W. Spellmeyer S. Constantine M.E. Grein 《Photonics Technology Letters, IEEE》2004,16(9):2009-2011
We demonstrate a novel 40-GHz mode-locked fiber laser that utilizes a single active device to provide both gain and mode-locking. The laser produces pulses as short as 2.2 ps, is tunable over a 27-nm band centered at 1553 nm, and exhibits long-term stability without cavity-length feedback control. The pulse train at 1556 nm was used in a 40-Gb/s transmission experiment over 45 km with a low 0.4-dB power penalty. 相似文献