全文获取类型
收费全文 | 704篇 |
免费 | 251篇 |
国内免费 | 69篇 |
专业分类
航空 | 545篇 |
航天技术 | 195篇 |
综合类 | 28篇 |
航天 | 256篇 |
出版年
2024年 | 6篇 |
2023年 | 13篇 |
2022年 | 23篇 |
2021年 | 22篇 |
2020年 | 28篇 |
2019年 | 24篇 |
2018年 | 18篇 |
2017年 | 18篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 39篇 |
2013年 | 53篇 |
2012年 | 55篇 |
2011年 | 60篇 |
2010年 | 40篇 |
2009年 | 28篇 |
2008年 | 41篇 |
2007年 | 59篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 34篇 |
2003年 | 37篇 |
2002年 | 24篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 30篇 |
1998年 | 29篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 13篇 |
1994年 | 22篇 |
1993年 | 15篇 |
1992年 | 25篇 |
1991年 | 13篇 |
1990年 | 26篇 |
1989年 | 15篇 |
1988年 | 5篇 |
1987年 | 6篇 |
排序方式: 共有1024条查询结果,搜索用时 125 毫秒
701.
发动机整体多级转子盘深内腔加工技术 总被引:1,自引:0,他引:1
为了提高发动机的推重比和可靠性,目前大型航空发动机的风扇盘和压气机盘大多采用整体多级盘结构,整体锻件多级转子盘便是其中的一类。该盘重量轻、性能好,但其深内腔加工是一大技术难点。本文介绍了一种先进的深内腔加工方法和加工中应特别注意的问题,并提出了应用整体锻件机械加工整体多级转子,该转子不仅可以达到发动机结构减化和减重的目的,还可以利用现有设备加工,从而使我们免受诸如线性磨擦焊加工技术和设备等国外对我们在整体叶盘生产技术上的封锁和限制,为此,发动机整体多级转子盘深内腔加工技术应引起我国航空发动机行业相关人员的重视。 相似文献
702.
703.
详细介绍了国军标电磁兼容检测实验室进行实验室间比对的方案,比对器具的选择和比对数据的处理方法,分析了国军标电磁兼容实验室比对的特点,用平均值、数据偏差等参数对国防系统实验室4个比对项目的数据进行了分析,研究实验室间测试结果存在差异的原因,并给出改进建议。 相似文献
704.
705.
热电偶、热电阻自动检定系统的设计与实现 总被引:1,自引:0,他引:1
介绍了热电偶、热电阻系统的工作原理及其硬件组成、软件实现,并简要叙述了其自动检定的过程及方法。 相似文献
706.
707.
P.A. Chaizy T.G. DimbylowP.M. Allan M.A. Hapgood 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
This paper is one of the components of a larger framework of activities whose purpose is to improve the performance and productivity of space mission systems, i.e. to increase both what can be achieved and the cost effectiveness of this achievement. Some of these activities introduced the concept of Functional Architecture Module (FAM); FAMs are basic blocks used to build the functional architecture of Plan Management Systems (PMS). They also highlighted the need to involve Science Operations Planning Expertise (SOPE) during the Mission Design Phase (MDP) in order to design and implement efficiently operation planning systems. We define SOPE as the expertise held by people who have both theoretical and practical experience in operations planning, in general, and in space science operations planning in particular. Using ESA’s methodology for studying and selecting science missions we also define the MDP as the combination of the Mission Assessment and Mission Definition Phases. However, there is no generic procedure on how to use FAMs efficiently and systematically, for each new mission, in order to analyse the cost and feasibility of new missions as well as to optimise the functional design of new PMS; the purpose of such a procedure is to build more rapidly and cheaply such PMS as well as to make the latter more reliable and cheaper to run. This is why the purpose of this paper is to provide an embryo of such a generic procedure and to show that the latter needs to be applied by people with SOPE during the MDP. The procedure described here proposes some initial guidelines to identify both the various possible high level functional scenarii, for a given set of possible requirements, and the information that needs to be associated with each scenario. It also introduces the concept of catalogue of generic functional scenarii of PMS for space science missions. The information associated with each catalogued scenarii will have been identified by the above procedure and will be relevant only for some specific mission requirements. In other words, each mission that shares the same type of requirements that lead to a list of specific catalogued scenarii can use this latter list of scenarii (regardless of whether the mission is a plasma, planetary, astronomy, etc. mission). The main advantages of such a catalogue are that it speeds-up the execution of the procedure and makes the latter more reliable. Ultimately, the information associated to each relevant scenario (from the catalogue or freshly generated by the procedure) will then be used by mission designers to make informed decisions, including the modification of the mission requirements, for any missions. In addition, to illustrate the use of such a procedure, the latter is applied to a case study, i.e. the Cross-Scale mission. One of the outcomes of this study is an initial set of generic functional scenarii. Finally, although border line with the above purpose of this paper, we also discuss multi-spacecraft specific issues and issues related to the on-board execution of the plan update system (PUS). In particular, we show that the operation planning cost of N spacecraft is not equal to N times the cost of 1 spacecraft and that on-board non-synchronised operation will not require inter-spacecraft communication. We also believe that on-board PUS should be made possible for all missions as a standard. 相似文献
708.
军用车辆外部射频干扰试验测试技术研究CSCD 总被引:1,自引:0,他引:1
提出了军用车辆外部射频干扰测试平台的搭建方法,对发射天线的选择、输入功率计算及测试系统匹配进行了详细介绍。给出了相应的测试方法,归纳该方法的技术特点及创新点。结合该测试平台及测试方法对抗干扰指标要求进行了验证。 相似文献
709.
710.