全文获取类型
收费全文 | 10304篇 |
免费 | 1132篇 |
国内免费 | 664篇 |
专业分类
化学 | 5530篇 |
晶体学 | 96篇 |
力学 | 407篇 |
综合类 | 46篇 |
数学 | 691篇 |
物理学 | 2382篇 |
无线电 | 2948篇 |
出版年
2024年 | 18篇 |
2023年 | 211篇 |
2022年 | 221篇 |
2021年 | 423篇 |
2020年 | 367篇 |
2019年 | 354篇 |
2018年 | 278篇 |
2017年 | 291篇 |
2016年 | 405篇 |
2015年 | 383篇 |
2014年 | 465篇 |
2013年 | 677篇 |
2012年 | 826篇 |
2011年 | 835篇 |
2010年 | 606篇 |
2009年 | 580篇 |
2008年 | 707篇 |
2007年 | 593篇 |
2006年 | 556篇 |
2005年 | 512篇 |
2004年 | 428篇 |
2003年 | 372篇 |
2002年 | 355篇 |
2001年 | 240篇 |
2000年 | 197篇 |
1999年 | 168篇 |
1998年 | 154篇 |
1997年 | 130篇 |
1996年 | 127篇 |
1995年 | 114篇 |
1994年 | 80篇 |
1993年 | 73篇 |
1992年 | 67篇 |
1991年 | 64篇 |
1990年 | 35篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 3篇 |
1973年 | 4篇 |
1971年 | 6篇 |
1970年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 158 毫秒
61.
62.
63.
We study the Bloch oscillations of two-component Bose-Einstein condensates trapped in spin-dependent optical lattices. The influence of the intercomponent atom interaction on the system is discussed in detail Accelerated breakdown of the Bloch oscillations and revival phenomena are found respectively for the repulsive and attractive case. For both the cases, the system will finally be set in a quantum self-trapping state due to dynamical instability. 相似文献
64.
掺杂对低压ZnO压敏陶瓷材料显微结构及性能的影响 总被引:1,自引:0,他引:1
本文探讨了多种金属氧化物对ZnO-Bi_2O_3-TiO_2系材料的改性作用和对其微结构的影响,为得到预定性能的材料提供了掺杂方面的实验依据。 相似文献
65.
Keon Woo Kang Jaemin Ann Hwang Soo Lee 《Electronics letters》1994,30(25):2153-2154
The authors propose a method to estimate the synchronisation offset for orthogonal frequency division multiplexing (OFDM) frame alignment without resort to pilot tones. A decision-directed maximum-likelihood estimation of frame synchronisation offset is derived, and the performance of the proposed scheme is confirmed by computer simulation for QAM systems 相似文献
66.
Analysis and characterization of traveling-wave electrode in electroabsorption modulator for radio-on-fiber application 总被引:1,自引:0,他引:1
Jiyoun Lim Young-Shik Kang Kwang-Seong Choi Jong-Hyun Lee Sung-Bock Kim Jeha Kim 《Lightwave Technology, Journal of》2003,21(12):3004-3010
Comparing with a lumped electroabsorption modulator (EAM), we show the merits of a long EAM with traveling-wave electrode with high radio-frequency (RF) gain that could be used in high-frequency analog application. By terminating the RF output port with the characteristic impedance of 30 /spl Omega/, the device exhibited a large enhancement of 6 dB above 10 GHz in the electrical-to-optical response and a wide fractional bandwidth as estimated from simulation. In addition, an input impedance matching circuit of stub embedded on the device chip was found to be very effective for improving RF characteristics in the narrow band of frequency. 相似文献
67.
68.
Sang‐Heung Lee Seung‐Yun Lee Hyun‐Cheol Bae Ja‐Yol Lee Sang‐Hoon Kim Bo Woo Kim Jin‐Yeong Kang 《ETRI Journal》2005,27(5):569-578
The purpose of this paper is to describe the implementation of monolithically matching circuits, interface circuits, and RF core circuits to the same substrate. We designed and fabricated on‐chip 1 to 6 GHz up‐conversion and 1 to 8 GHz down‐conversion mixers using a 0.8 µm SiGe hetero‐junction bipolar transistor (HBT) process technology. To fabricate a SiGe HBT, we used a reduced pressure chemical vapor deposition (RPCVD) system to grow a base epitaxial layer, and we adopted local oxidation of silicon (LOCOS) isolation to separate the device terminals. An up‐conversion mixer was implemented on‐chip using an intermediate frequency (IF) matching circuit, local oscillator (LO)/radio frequency (RF) wideband matching circuits, LO/IF input balun circuits, and an RF output balun circuit. The measured results of the fabricated up‐conversion mixer show a positive power conversion gain from 1 to 6 GHz and a bandwidth of about 4.5 GHz. Also, the down‐conversion mixer was implemented on‐chip using LO/RF wideband matching circuits, LO/RF input balun circuits, and an IF output balun circuit. The measured results of the fabricated down‐conversion mixer show a positive power conversion gain from 1 to 8 GHz and a bandwidth of about 4.5 GHz. 相似文献
69.
beta-Glucosidase and beta-glucuronidase of human and rat fecal bacteria were induced by cultivation in alkaline media although their growths were not affected. When a bacterium isolated from human feces producing each enzyme was cultured in a medium at pH 5 for 12-15 h and then adjusted to pH 8, beta-glucosidase and beta-glucuronidase were induced 9.2-fold and 11.5-fold, respectively. 相似文献
70.
本文描述在CCIR活动中对HDTV统一标准的争论和趋势。有关ETV,D2-MAC及数字电视地面广播系统的CCIR建议书,以及美国全数字HDTV的发展也作了介绍。 相似文献