首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1177篇
  免费   220篇
  国内免费   259篇
航空   844篇
航天技术   380篇
综合类   135篇
航天   297篇
  2024年   5篇
  2023年   45篇
  2022年   31篇
  2021年   56篇
  2020年   53篇
  2019年   54篇
  2018年   75篇
  2017年   58篇
  2016年   83篇
  2015年   80篇
  2014年   65篇
  2013年   73篇
  2012年   78篇
  2011年   84篇
  2010年   82篇
  2009年   81篇
  2008年   64篇
  2007年   58篇
  2006年   63篇
  2005年   45篇
  2004年   53篇
  2003年   48篇
  2002年   45篇
  2001年   41篇
  2000年   44篇
  1999年   41篇
  1998年   32篇
  1997年   24篇
  1996年   20篇
  1995年   13篇
  1994年   15篇
  1993年   12篇
  1992年   8篇
  1991年   5篇
  1990年   10篇
  1989年   2篇
  1988年   7篇
  1987年   1篇
  1986年   2篇
排序方式: 共有1656条查询结果,搜索用时 15 毫秒
241.
鲜勇 《飞行力学》2006,24(4):50-52,56
分别讨论了两种通过飞行时间确定爆高的方法:解析计算修正法和时间偏导数法,这两种方法都是通过计算延迟时间来确定爆高,具有自主性强、可靠性高的特点。计算了两种方法在不同干扰条件下的结果,分析了造成计算偏差的原因。计算结果表明,两种方法的计算误差都非常小,均可应用于弹道导弹爆高确定。  相似文献   
242.
高速数据总线(HighSpeedDataBus,HSDB)是新一代航空电子系统的数据总路线,HSDB网络实际上是基于线性令牌总线的一个专用计算机局域网,在网络上负载较重且时间非苛刻的消息到达是一般过程的条件十分别讨论了网络的局域和全域稳定性,并导出了保证整个网络稳定的令牌握有定时器最小值,同时给出了如何根据应用去调整得到的理论值。  相似文献   
243.
针对如何提高机械加工的生产效率,改进生产管理结合实际工作做了论述,提出了自己的观点。  相似文献   
244.
赵广春  才滢  白旭 《航空计测技术》2002,22(6):13-15,20
介绍了维持计量检定工作环境条件保障装置的设计方法,该装置可实现实验室温,湿度的测量与控制,有方便的通讯接口便于与计算机连接,并附加有多点时间控制电路以实现提前预热仪器设备提高工作效率的功能。  相似文献   
245.
在航天应用中,低轨卫星经常会由于原始数据缺失而影响卫星时序数据模式识别结果,降低准确率。针对该问题提出了一种新型MR-GRU模型,可有效处理缺失时序数据,并获得较好的模式识别准确率。区别于传统模型的补全缺失数据的方法,MR-GRU模型直接在缺失时序数据上运用循环神经网络进行训练,对传统门控循环单元结构进行了改进,增加了两个新变量:掩蔽项和衰减项。掩蔽项作用于输入,衰减项作用于输入和隐层单元输出。MR-GRU模型不仅能够保持时序数据固有的时间特性,还能有效提高模式识别精度。在卫星时序数据上的模式识别试验表明,MR-GRU模型准确率优于传统模型。  相似文献   
246.
Performance of SARAL/AltiKa mission has been evaluated within 2016 altimeter calibration/validation framework in Persian Gulf through three campaigns conducted in the offshore waters of Sajafi, Imam Hassan and Kangan Ports, while the altimeter overflew the passes 470, 111 and 25 on 13 Feb, 7 March and 17 June 2016, respectively. As the preparation, a lightweight buoy was equipped with a GNSS receiver/choke-ring antenna and a MEMS-based IMU to measure independent datasets in the field operations. To obtain accurate sea surface height (SSH) time series, the offset of the onboard antenna from the equilibrium sea level was predetermined through surveying operations as the buoy was deploying in the onshore waters of Kangan Port. Accordingly, the double-difference carrier phase observations have been processed via the Bernese GPS Software v. 5.0 so as to provide the GNSS-derived time series at the comparison points of the calibration campaigns, once the disturbing effects due to the platform tilt and heave have been eliminated. Owing to comparing of the SSH time series and the associating altimetry 1?Hz GDR-T datasets, the calibration/validation of the SARAL/AltiKa has been performed in the both cases of radiometer and ECMWF wet troposphere corrections so as to identify potential land contamination. An agreement of the present findings in comparison with those attained in other international calibrations sites confirms the promising feasibility of Persian Gulf as a new dedicated site for calibration/validation of ongoing and future altimetry missions.  相似文献   
247.
Costal monitoring is focused on fast response to illegal immigration and illegal ship traffic. Especially, the illegal ship traffic has been present in media since April 2015, as the number of reported deaths of immigrants crossing the Mediterranean significantly increased. Satellite images provide a possibility to at least partially control both types of events. This paper defines the principal criteria to select the best satellite constellation architecture for maritime and coastal monitoring, filling the gaps of imagery techniques in term of real-time control. The primary purpose of a constellation is to obtain global measurement improving the temporal resolution. The small size and low-cost are the main factors, which make CubeSats ideal for use in constellations. We propose a constellation of 9 Cubesats distributed evenly in 3 different planes. This reduces the revisit time enhancing the coverage duration. In addition, it also allows observing fire, damage on building and similar disasters. In this analysis, the performance criteria were reported such as the revisit time, the vision duration and the area coverage.  相似文献   
248.
We have studied the time delay of ionospheric storms to geomagnetic storms at a low latitude station Taoyuan (25.02°N, 121.21°E), Taiwan using the Dst and TEC data during 126 geomagnetic storms from the year 2002 to 2014. In addition to the known local time dependence of the time delay, the statistics show that the time delay has significant seasonal characteristics, which can be explained within the framework of the seasonal characteristics of the ionospheric TEC. The data also show that there is no correlation between the time delay and the intensity of magnetic storms. As for the solar activity dependence of the time delay, the results show that there is no relationship between the time delay of positive storms and the solar activity, whereas the time delay of negative storms has weakly negative dependence on the solar activity, with correlation coefficient −0.41. Especially, there are two kinds of extreme events: pre-storm response events and long-time delay events. All of the pre-storm response events occurred during 15–20 LT, manifesting the Equator Ionospheric Anomaly (EIA) feature at Taoyuan. Moreover, the common features of the pre-storm response events suggest the storm sudden commencement (SSC) and weak geomagnetic disturbance before the main phase onset (MPO) of magnetic storms are two main possible causes of the pre-storm response events. By analyzing the geomagnetic indices during the events with long-time delay, we infer that this kind of events may not be caused by magnetic storms, and they might belong to ionospheric Q-disturbances.  相似文献   
249.
针对航天器近距离交会段的位置姿态耦合控制问题,假设航天器受外界干扰且目标航天器存在空间自由翻滚情形时,基于固定时间概念设计了一种六自由度位姿终端滑模自适应控制器,通过引入显含正弦函数的切换项来避免奇异问题。此外所设计的控制器含双幂次项,不仅能全局提高姿态和位置的跟踪速度及精度,还能估计系统稳定所需的时间上界,且该上界与状态初始值无关。基于Lyapunov方法分析了闭环系统的固定时间稳定性。仿真结果表明,该控制器能快速实现对航天器近距离交会时相对位置和姿态的控制,具有较高的精度和良好的干扰抑制能力。  相似文献   
250.
本文提出分别研究电池开路电压在充电结束后停置过程和放电结束后停置过程的不同变化规律,并考虑了不同停置时间在两个过程中的作用和影响,从而达到提高开路电压法估算荷电状态精度的效果。实验验证表明,此方法的精度比传统开路电压法更加准确。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号