全文获取类型
收费全文 | 795篇 |
免费 | 323篇 |
国内免费 | 137篇 |
专业分类
航空 | 713篇 |
航天技术 | 182篇 |
综合类 | 91篇 |
航天 | 269篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 74篇 |
2021年 | 82篇 |
2020年 | 81篇 |
2019年 | 54篇 |
2018年 | 69篇 |
2017年 | 73篇 |
2016年 | 60篇 |
2015年 | 54篇 |
2014年 | 59篇 |
2013年 | 66篇 |
2012年 | 79篇 |
2011年 | 55篇 |
2010年 | 64篇 |
2009年 | 60篇 |
2008年 | 46篇 |
2007年 | 48篇 |
2006年 | 43篇 |
2005年 | 39篇 |
2004年 | 30篇 |
2003年 | 13篇 |
2002年 | 21篇 |
2001年 | 14篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 4篇 |
1987年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1255条查询结果,搜索用时 234 毫秒
991.
992.
This article presents a new multichannel medium access control (MAC) protocol to solve the exposed-terminal (ET) problem for efficient channel sharing in multi-hop wireless networks. It uses request-to-send and clear-to-send (RTS/CTS) dialogue on a common channel and flexibly opts for conflict-free traffic channels to carry out the data packet transmission on the basis of a new channel selection scheme. The acknowledgment (ACK) packet for the data packet transmission is sent back to the sender over another common channel thus completely eliminating the exposed-terminal effects. Any adjacent communication pair can take full advantage of multiple traffic channels without collision and the spatial reuse of the same channel is extended to other communication pairs which are even within 2 hops from them. In addition, the hidden-terminal effect is also considerably reduced because most of possible packet collisions on a single channel are avoided due to traffic load balance on multichannels. Finally, a performance comparison is made between the proposed protocol and other typical MAC protocols. Simulation results evidence its obvious superiority to the MAC protocols associated with other channel selection schemes and traditional ACK transmission scheme as well as cooperative asynchronous multichannel MAC (CAM-MAC) protocol in terms of four performance indices: total channel utilization, average channel utilization, average packet delay, and packet dropping rate. 相似文献
993.
994.
Hirokazu Hoshino Yukio Yamamoto Shin-ichi Sobue Katsuhide Yonekura Mina Ogawa Yasunori Iwana Kai Matsui Hayato Okumura Manabu Kato 《Space Science Reviews》2010,154(1-4):317-342
The functions of KAGUYA(SELENE) Operation and Analysis Center (SOAC) are to operate three satellites: the main orbiter KAGUYA and two small satellites, Relay satellite OKINA and VRAD (VLBI (Very Long Baseline Interferometry) RADio source) satellite OUNA; and to process, archive and provide mission data. SOAC has two main functional areas, “Tracking and Control system” and “Mission Operation and Data Analysis system.” The former is for operational planning of bus and mission instruments including satellite navigation, and for the implementation of those plans and for the evaluation of satellite conditions. The latter is the system that processes, archives and provides mission data, and which principal investigators use to generate higher-level data products. Data up to the end of the operation in June 2009 have been processed and the total amount of Level-2 data products reaches about 50 TB. The data products have been released to the public since November 2009. 相似文献
995.
本文介绍一种便携式X射线机无线遥控装置,该装置采用MCS51系列单片机构成。利用单片机的串行通讯口、调制解调和无线电话实现数据通讯功能,该遥控器能够显示X射线机的工作状态,能够无线遥控开、关射线机的高压开关。 相似文献
996.
空间目标RCS动态测量及特性分析 总被引:7,自引:0,他引:7
本文探讨了适用于某型窄带雷达的RCS相对测量法,对部分空间目标进行了RCS测量。利用随机游程检验法对实测的空间目标RCS时间序列进行了随机性检验,得到了与实际情况相符的结果。 相似文献
997.
998.
简要介绍了角速度波动率校准技术在国内外的现状及其发展趋势,阐述了开展此项研究的目的和意义,并结合现有设备和技术,介绍了几种实现角速度波动率校准的方法。 相似文献
999.
1000.
张凯%傅强%黄渝鸿%周德惠 《宇航材料工艺》2004,34(6):1-5
在总结近年来国内外有关磁性高分子微球研究成果的基础上,对磁性高分子微球的四种制备方法,即共混包埋法、界面沉积法、活化溶胀法和单体聚合法的工艺过程及优缺点进行了概述。对磁性高分子微球的各项特征(如平均粒径、粒径分布、磁含量、磁响应性及耐酸碱性等)的表征方法进行了介绍。 相似文献