全文获取类型
收费全文 | 221篇 |
免费 | 59篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 38篇 |
综合类 | 19篇 |
机械仪表 | 4篇 |
建筑科学 | 10篇 |
矿业工程 | 1篇 |
轻工业 | 3篇 |
水利工程 | 1篇 |
石油天然气 | 3篇 |
武器工业 | 2篇 |
无线电 | 129篇 |
一般工业技术 | 12篇 |
原子能技术 | 4篇 |
自动化技术 | 64篇 |
出版年
2024年 | 4篇 |
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 5篇 |
2020年 | 18篇 |
2019年 | 23篇 |
2018年 | 13篇 |
2017年 | 10篇 |
2016年 | 8篇 |
2015年 | 18篇 |
2014年 | 14篇 |
2013年 | 23篇 |
2012年 | 24篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有290条查询结果,搜索用时 312 毫秒
141.
142.
提出了1款小型化单极子超宽带天线。该天线印刷在厚度h=1.0mm,介电常数εr=4.4的FR-4环氧树脂介质板上,主要由类似矩形辐射面、阶梯型接地面组成,总尺寸为33mm×28mm×1mm,满足小型化的设计要求。天线具有3.1~12.5GHz的可用超宽工作带宽(相对带宽达到120.5%)、良好的全向辐射特性、较高的增益和较小的群延时。同时,为了抑制来自全球微波互联接入系统(Wimax,3.3~3.6GHz)或无线局域网系统(WLAN,5.15~5.35GHz,5.75~5.825GHz)的干扰,利用在矩形辐射单元上蚀刻不同长度的C型槽的方法,使天线分别在频谱3.16~3.93GHz或5.11~5.89GHz上具有带陷特性。另外,文中给出了超宽带辐射单元尺寸和陷波槽总长度的估算方法。 相似文献
143.
Kunal Srivastava Ashwani Kumar Binod K. Kanaujia Santanu Dwari Sachin Kumar 《国际射频与微波计算机辅助工程杂志》2019,29(2)
This article presents two designs of circularly polarized antenna with simple circular‐shaped radiator and circular slotted ground plane. An arc‐shaped microstrip line coupling feed mechanism is used to excite the circular radiating patch. The 3‐dB axial ratio bandwidth of the proposed antenna‐1 and proposed antenna‐2 are 3.33% and 18%, respectively. The proposed design has several advantages such as easy matching, fabrication simplicity, compact size, and wide axial ratio bandwidth. Both the antennas have been designed on FR‐4 substrate with dielectric constant 4.4 and thickness 1.59 mm. Simulated and measured results are presented to validate the working of the proposed antennas. 相似文献
144.
145.
为了满足某型单兵系统中通信终端对超短波通信与北斗卫星导航定位的需求,设计了兼容导航与超短波通信双模式的新型单兵通信终端天线。通过在印刷折叠四臂螺旋天线(FPQHA)顶部的螺旋臂与折叠臂间加载电容,设计了电容加载的印刷折叠四臂螺旋天线,实现了北斗卫星导航B1、B3双频段覆盖。该天线结构紧凑,且能够通过改变电容值大小便捷地进行调谐优化。根据当前超短波通信终端采用外置单极子鞭状天线的现状,将提出的电容加载FPQHA与原单极子超短波通信天线同轴共置,减小了天线系统在其载体平台上所占的空间。并通过结构优化,尤其是在单极子天线外添加套筒,解决了二者的兼容性问题。该天线便于综合集成现有设备,能够达到实战中对高精度北斗卫星导航的性能要求,同时支持超短波频段通信。 相似文献
146.
147.
Shunshi Zhong Xiaorong Yan Xianling Liang 《Frontiers of Electrical and Electronic Engineering in China》2008,3(2):136-144
Recent developments of the ultra-wideband (UWB) planar antennas are reviewed, where the progress in UWB plate monopole antennas,
UWB printed monopole antennas and the UWB printed slot antennas is introduced and compared. In addition, the UWB printed antennas
with the band-notched functions are also presented.
__________
Translated from Chinese Journal of Radio Science, 2007, 22(2): 308–315 [译自: 电波科学学报] 相似文献
148.
For monopole antennas with cylindrically symmetric structures, a mode‐expansion method is highly time efficient, which is a realistic approach for integrating function‐optimization tools, such as genetic algorithms (GAs), in order to extract the best bandwidth property. In this article, a mode‐expansion method is used to simulate the impedance characteristics of the cylindrical antennas. As examples, two new types of monopole antennas are presented, one of which possesses a two‐step top‐hat structure while the other has an annulus around the stem. After the modeling scheme is examined for convergence and data validity, the associated optimization problem, with dimensions as decision variables, structural limitations as linear constraints, and desired bandwidth performance as an objective function, is solved using GAs. The effects of the geometric parameters on the impedance characteristics are investigated in order to demonstrate the optimality of the calculated solutions. Two optimized practical antennas are designed based on our numerical studies. One has a broad bandwidth of 3 GHz while the other shows a dual‐band property, which can satisfy the bandwidth requirements for both Bluetooth (2.45‐GHz band) and WLAN (5‐GHz band) systems. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005. 相似文献
149.
The propagation of heat pulses originating from sawtooth activity has been studied on the HT-7 tokamak.Two theoretical models are used for determining electron heat diffusivity from the experimental data measured by a diagnostic system of soft x-ray diode-array.The results show that one model caaled dipole model is more suitable for HT-7 tokamak.In order to improve the signal-to-noise(S/N) ratio of the original signals,over a few tens of sawteeth are averaged to generatc nicc wavcforms.The apace-time evolution is found to be diffusive in character,which is consistent with the theoretical model.The electron heat diffusivity determined from heat pulse propagation is larger than determined from background plasma power balance.The variation of Xe in different discharge phases has been also discussed. 相似文献
150.
全桥逆变单极性SPWM控制方式过零点振荡的研究 总被引:1,自引:0,他引:1
单极性全桥逆变相对于双极性逆变损耗低,电磁干扰少,单极性SPWM更适用于逆变控制,但该控制方式存在一个过零点振荡。介绍了单极性逆变中的双边SPWM的控制方法,分析了这种控制方法在正弦波电压过零点附近的振荡现象,提出一种解决过零点振荡的方案,并经实验验证。 相似文献