全文获取类型
收费全文 | 6780篇 |
免费 | 1151篇 |
国内免费 | 82篇 |
专业分类
化学 | 11篇 |
晶体学 | 2篇 |
力学 | 25篇 |
综合类 | 68篇 |
数学 | 35篇 |
物理学 | 332篇 |
无线电 | 7540篇 |
出版年
2024年 | 35篇 |
2023年 | 72篇 |
2022年 | 139篇 |
2021年 | 127篇 |
2020年 | 142篇 |
2019年 | 186篇 |
2018年 | 183篇 |
2017年 | 200篇 |
2016年 | 230篇 |
2015年 | 333篇 |
2014年 | 430篇 |
2013年 | 405篇 |
2012年 | 617篇 |
2011年 | 619篇 |
2010年 | 453篇 |
2009年 | 405篇 |
2008年 | 429篇 |
2007年 | 530篇 |
2006年 | 488篇 |
2005年 | 422篇 |
2004年 | 320篇 |
2003年 | 308篇 |
2002年 | 210篇 |
2001年 | 224篇 |
2000年 | 150篇 |
1999年 | 98篇 |
1998年 | 99篇 |
1997年 | 31篇 |
1996年 | 35篇 |
1995年 | 19篇 |
1994年 | 28篇 |
1993年 | 16篇 |
1992年 | 11篇 |
1991年 | 3篇 |
1990年 | 8篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有8013条查询结果,搜索用时 468 毫秒
91.
基于DRFM的脉冲多普勒雷达组合干扰及其效能评估 总被引:2,自引:0,他引:2
脉冲多普勒雷达具有较强的抗干扰能力,对其实施有效干扰有一定的困难。本文仿真研究了两种基于数字射频存储器的脉冲多普勒雷达组合干扰技术,并分别提出了脉冲多普勒雷达压制性干扰和欺骗性干扰的干扰效果度量方法,该方法在具体应用场合更贴近于干扰抗干扰的动态对抗过程。 相似文献
92.
93.
94.
95.
96.
97.
Peeramed Chodkaveekityada Hajime Fukuchi 《International Journal of Satellite Communications and Networking》2017,35(4):281-293
The effects of rain attenuation on communication systems will become more pronounced in future satellite communication systems, especially with the planned use of the 21‐GHz band or higher‐frequency bands. Diversity techniques provide a solution to mitigate rain attenuation effects. This study proposes a time diversity technique, one such technique that is likely to demonstrate high effectiveness. To model the system, rainfall rate statistics are necessary, and reliability is improved as the amount of statistical data increases. This paper derives the cumulative distribution of the rainfall rate across Japan over 4 years using rain radar data from the automated meteorological data acquisition system and ground‐based rain radar network and evaluates the rainfall rate at 23 observation points across Japan. We carry out a performance evaluation for all locations within Japan to confirm the efficiency of the time diversity method. Finally, we propose prediction model of the time diversity gain for Japan and other significant parameter which is time correlation of rainfall rate that was found from the time diversity results for further investigation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
98.
针对雷达天线罩瞄准误差的补偿问题,提出了一种适用于各向同性的天线罩瞄准误差修正方法。构建了基于一维物理光学法的天线罩瞄准误差的数学模型,推导了雷达导引头测量目标角度和角速度的误差修正公式。试验结果表明,该方法有效降低了天线罩瞄准误差对目标角速度性能的影响。 相似文献
99.
We demonstrated a 3D laser imaging system at 1550 nm with a 1.5-GHz sine-wave gated Geiger-mode InGaAs/InP avalanche photodiode (APD). An optical fiber bundle with 100 individual fiber outputs was implemented at the focal plane of the telescope, providing a 2.5-mrad imaging view. The system used single-pixel near-infrared single-photon detector to measure photons at fiber outputs instead of a photon counting array. The 1.5-GHz gated Geiger-mode InGaAs/InP APD with a timing jitter of 290 ps was operated in quasi-continuous mode with detection efficiency of ∼4.3%. We achieved higher than 6-cm surface-to-surface resolution at single-photon level, showing a potential of low-energy and eye-safe laser imaging system for long-distance measurements. 相似文献
100.
A laser coherent detection system of 1550 nm wavelength was presented, and experimental research on detecting micro-Doppler effect in a dynamic target was developed. In this paper, the return signal in the time domain is decomposed into a set of components in different wavelet-scales by multi-resolution analysis, and the components are associated with the vibrational motions in a target. The micro-Doppler signatures are extracted by applying the reconstruction (inverse wavelet transform). During the course of the final data processing frequency analysis and time–frequency analysis are applied to analyze the vibrational signals and estimate the motion parameters successfully. The experimental results indicate that the micro-Doppler information in a moving can be effectively detected, and tiny vibrational signatures also can be acquired effectively by wavelet multi-resolution analysis and time–frequency analysis. 相似文献