全文获取类型
收费全文 | 140篇 |
免费 | 20篇 |
专业分类
化学 | 3篇 |
综合类 | 1篇 |
数学 | 1篇 |
物理学 | 16篇 |
无线电 | 139篇 |
出版年
2023年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 4篇 |
2015年 | 10篇 |
2014年 | 15篇 |
2013年 | 9篇 |
2012年 | 19篇 |
2011年 | 7篇 |
2010年 | 6篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 8篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1986年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有160条查询结果,搜索用时 15 毫秒
111.
介绍一个采用国产光电器件研制的微波副载波复用光纤视频传输系统。系统进行了以传输亚洲一号卫星信号地面接收站第一中频多路电视信号为目标的现场实验。信号经过38.78km,1.3μm波长单模光纤传输后,在接收光功率为-22dBm时,载噪比劣化不大于3dB,当接收光功率为-30dBm时。 相似文献
112.
R. T. Hofmeister L. G. Kazovsky C. L. Lu P. Poggiolini F. Yang 《Fiber and Integrated Optics》1997,16(2):199-219
We are implementing and investigating CORD, a 2.5 Gbit/s/λ WDM packet-switched network testbed. CORD features: (i) contention resolution optics (CRO), which consist of optical switches and delay lines to perform all-optical packet contention resolution; (ii) multichannel subcarrier multiplexed (MSCM) signaling to transmit an 80 Mbit/s control channel and 2.5 Gbit/s payload data on the same wavelength; (iii) networkwide distributed slot synchronization technique with maximum slot jitter of ± 6.5 ns; (iv) novel ultrafast signaling synchronization using delay-line phase alignment for data recovery within 4 bits; and (v) pilot-tone payload data synchronization for clock recovery within 16 ns.
In this article, we describe the CORD network testbed and discuss the performance and scaling potential of the technologies developed for CORD. 相似文献
In this article, we describe the CORD network testbed and discuss the performance and scaling potential of the technologies developed for CORD. 相似文献
113.
本文以光纤CATV传输系统为例.研究分析了SCM传输技术中容量的限制。导出了各种副载波调制型式(数字信号的PSK、FSK、ASK,模拟信号的FM、AM和AM-VSB)的容量极限值与系统中主要器件技术参数间的关系。 相似文献
114.
115.
116.
在高频的微波光子学研究的领域中,光载无线(RoF)技术已经成为下一代宽带无线通信技术的发展热点。近年来,支撑RoF技术的新型光电子器件的关键技术有毫米波副载波光学产生技术和接收技术,其中包括外调制器方法、射频上转换法、光学外差法、毫米波调制光脉冲发生器等等。这些技术的突破将促进RoF技术市场化的步伐。 相似文献
117.
Wei Wang Wenbo Wang Qianxi Lu Tao Peng 《International Journal of Communication Systems》2009,22(5):603-623
Cognitive radio makes it possible for an unlicensed user to access a spectrum unoccupied by licensed users. In cognitive radio networks, extra constraints on interference temperature need to be introduced into radio resource allocation. In this paper, the uplink radio resource allocation is investigated for OFDMA‐based cognitive radio networks. In consideration of the characteristics of cognitive radio and OFDMA, an improved water‐filling power allocation scheme is proposed under the interference temperature constraints for optimal performance. Based on the improved water‐filling power allocation, a simple subcarrier allocation algorithm for uplink is proposed. The subcarrier allocation rules are obtained by theoretical deduction. In the uplink subcarrier allocation algorithm, the subcarriers are allocated to the users with the best channel quality initially and then adjusted to improve the system performance. A cursory water‐filling level estimation method is used to decrease the complexity of the algorithm. Asymptotic performance analysis gives a lower bound of the stability of the water‐filling level estimation. The complexity and performance of the proposed radio resource allocation scheme are investigated by theoretical analysis and numerical results. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
118.
An adaptive modulation scheme is presented for multiuser orthogonal frequency‐division multiplexing systems. The aim of the scheme is to minimize the total transmit power with a constraint on the transmission rate for users, assuming knowledge of the instantaneous channel gains for all users using a combined bit‐loading and subcarrier allocation algorithm. The subcarrier allocation algorithm identifies the appropriate assignment of subcarriers to the users, while the bit‐loading algorithm determines the number of bits given to each subcarrier. The proposed bit‐loading algorithm is derived from the geometric progression of the additional transmission power required by the subcarriers and the arithmetic‐geometric means inequality. This algorithm has a simple procedure and low computational complexity. A heuristic approach is also used for the subcarrier allocation algorithm, providing a trade‐off between complexity and performance. Numerical results demonstrate that the proposed algorithms provide comparable performance with existing algorithms with low computational cost. 相似文献
119.
120.
A MAC protocol for new and handoff calls with a finite populationof users, rather than with an infinite user population as indynamic channel reservation scheme (DCRS), is considered. Similarto DCRS, we divide the wireless channels into shared channels andreserved channels. The handoff calls access any available channelwith probability of one, while the new calls access a sharedchannel with probability of one and access a reserved channel witha request probability. We propose three simpler formulae than thatused in the existing DCRS in setting the request probability. Inaddition, the handoff calls in our proposed protocol are allowedto queue in a finite buffer. To evaluate the system performance, amathematical model based on queuing theory, rather than asimulation method used in DCRS, is developed. It is a generalmodel that can be adopted for any types of request probabilitiesincluding DCRS. Suggestions of how to get the optimum values ofthe design parameters are also given. 相似文献