全文获取类型
收费全文 | 9196篇 |
免费 | 1517篇 |
国内免费 | 1181篇 |
专业分类
化学 | 4789篇 |
晶体学 | 119篇 |
力学 | 343篇 |
综合类 | 91篇 |
数学 | 849篇 |
物理学 | 2533篇 |
无线电 | 3170篇 |
出版年
2024年 | 52篇 |
2023年 | 215篇 |
2022年 | 264篇 |
2021年 | 356篇 |
2020年 | 348篇 |
2019年 | 314篇 |
2018年 | 291篇 |
2017年 | 309篇 |
2016年 | 366篇 |
2015年 | 399篇 |
2014年 | 476篇 |
2013年 | 662篇 |
2012年 | 816篇 |
2011年 | 790篇 |
2010年 | 673篇 |
2009年 | 639篇 |
2008年 | 662篇 |
2007年 | 609篇 |
2006年 | 523篇 |
2005年 | 422篇 |
2004年 | 328篇 |
2003年 | 308篇 |
2002年 | 347篇 |
2001年 | 325篇 |
2000年 | 243篇 |
1999年 | 196篇 |
1998年 | 157篇 |
1997年 | 112篇 |
1996年 | 120篇 |
1995年 | 91篇 |
1994年 | 70篇 |
1993年 | 66篇 |
1992年 | 52篇 |
1991年 | 52篇 |
1990年 | 40篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 18篇 |
1982年 | 13篇 |
1979年 | 5篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1972年 | 5篇 |
1971年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
Group-blind multiuser detectors for uplink code-division multiple-access (CDMA) were recently developed by Wang and Host-Madsen. These detectors make use of the spreading sequences of known users to construct a group constraint to suppress the intracell interference. However, such techniques demand the estimation of the multipath channels and the delays of the known users. In this paper, several improved blind linear detectors are developed for CDMA in fading multipath channels. The proposed detectors utilize the correlation information between consecutively received signals to generate the corresponding group constraint. It is shown that by incorporating this group constraint, the proposed detectors can provide different performance gains in both uplink and downlink environments. Compared with the previously reported group-blind detectors, our new methods only need to estimate the multipath channel of the desired user and do not require the channel estimation of other users. Simulation results demonstrate that the proposed detectors outperform the conventional blind linear multiuser detectors. 相似文献
24.
J. Chen J. B. Xu K. Xue J. An N. Ke W. Cao H. B. Xia J. Shi D. C. Tian 《Microelectronics Reliability》2005,45(1):137-142
Transition-metal compound TiC60 thin films were grown by co-deposition from two separated sources of fullerene C60 powder and titanium. Study of structural properties of the films, by Raman spectroscopy, atomic force microscopy, and scanning tunneling spectroscopy reveals that the films have a deformed C60 structure with certain amount of sp3 bonds and a rough surface with a large number of nanoclusters. z–V tunnelling spectroscopic measurements suggest that several charge transport mechanisms are involved in as the tip penetrates into the thin film. Conventional field electron emission (FEE) measurements show a high emission current density of 10 mA/cm2 and a low turn-on field less than 8 V/μm, with the field enhancement factors being 659 and 1947 for low-field region and high-field region, respectively. By exploiting STM tunneling spectroscopy, local FEE on nanometer scale has also been characterized in comparison with the conventional FEE. The respective field enhancement factors are estimated to be 99–355 for a gap varying from 36 to 6 nm. The enhanced FEE of TiC60 thin films can be ascribed to structural variation of C60 in the films and the electrical conducting paths formed by titanium nanocrystallites embedded in C60 matrix. 相似文献
25.
变频器在暖通空调行业中的应用 总被引:1,自引:0,他引:1
本文提出中央空调系统的一种变频调速改造方案,介绍了该系统的结构组成及运行原理,对系统各部分的作用进行了讨论。 相似文献
26.
Mid-infrared generation based on a periodically poled LiNbO3 optical parametric oscillator
下载免费PDF全文
![点击此处可从《中国物理》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report a nanosecond Nd:YVO_4-pumped optical parametric oscillator (OPO) based on periodically poled LiNbO_3 (PPLN). Tuning is achieved in this experiment by varying the temperature and period of the PPLN. The design of double-pass singly resonant oscillator (DSRO) and confocal cavity enables the OPO threshold to be lowered considerably, resulting in a simple, compact, all-solid-state configuration with the mid-infrared idler powers of up to 466mW at 3.41μm. 相似文献
27.
Pengbo Jiang Tiexin Cheng Yan Liu Xianghao Cui Yingli Bi Kaiji Zhen 《Reaction Kinetics and Catalysis Letters》2004,82(1):49-56
The novel phase transfer catalysts S-8 [4-(dimethyloctylammonium) propansultan] and DB-X [1,4-bis(triethylmethylammonium)benzene dibromide] were synthesized and employed for high conversion synthesis of dichlorocyclopropane from various olefins.This revised version was published online in December 2005 with corrections to the Cover Date. 相似文献
28.
塔顶放大器在移动通信领域有较为广泛的应用,它通过降低(改善)等效接收噪声系数,从而提高上行接收灵敏度。本文将简要介绍塔顶放大器的应用和提高接收机灵敏度的计算。 相似文献
29.