全文获取类型
收费全文 | 452篇 |
免费 | 125篇 |
国内免费 | 96篇 |
专业分类
航空 | 397篇 |
航天技术 | 90篇 |
综合类 | 75篇 |
航天 | 111篇 |
出版年
2024年 | 4篇 |
2023年 | 27篇 |
2022年 | 24篇 |
2021年 | 33篇 |
2020年 | 25篇 |
2019年 | 24篇 |
2018年 | 21篇 |
2017年 | 20篇 |
2016年 | 22篇 |
2015年 | 32篇 |
2014年 | 40篇 |
2013年 | 32篇 |
2012年 | 35篇 |
2011年 | 48篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 28篇 |
2007年 | 28篇 |
2006年 | 23篇 |
2005年 | 19篇 |
2004年 | 20篇 |
2003年 | 18篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 6篇 |
1999年 | 4篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 6篇 |
1990年 | 3篇 |
1989年 | 6篇 |
排序方式: 共有673条查询结果,搜索用时 46 毫秒
291.
292.
翼盒结构复杂,航行中承载条件恶劣,利用有限测点信息重构其它位置响应对于实时健康监测具有很强的现实意义。通过误差反向传播神经网络训练得到响应之间的非线性关系,建立基于神经网络的响应重构方法,开展有限元分析对其进行数值仿真验证,并将该方法应用于实测随机激励环境下翼盒典型承力结构的响应重构及损伤定位与判断分析。结果表明:采用该方法重构出的预测响应功率谱密度的均方根相对误差不超过1.90 dB,主要频点误差小于10%;判断出翼盒关键测点e 的损伤或故障发生在所截取片段数据3 s 后,其故障特征频率为240 Hz 左右,该方法应用于响应重构预示及健康监测分析具有可行性。 相似文献
293.
R. Hollmann R.W. Mueller A. Gratzki 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,37(12):2166-II
In the phase of redefinition of the EUMETSAT ground segment seven so called Satellite Application Facilities (SAF) each of them serving dedicated user groups have been established in Europe. The SAF on climate monitoring (CM-SAF) will deliver a comprehensive set of climate variables, including from different cloud products, radiation budget at the top of the atmosphere, surface radiation budget and tropospheric humidity. A consistent dataset of cloud and radiation products in a high spatial resolution on a uniform grid is derived. The CM-SAF is a joint project of the German Meteorological Service, EUMETSAT and five other European Meteorological Services. It is dedicated to produce climate datasets using data from instruments onboard of METEOSAT Second Generation and polar orbiting satellites NOAA and METOP. After the development phase, the CM-SAF has started its initial operational phase in the end of 2003. In this context, the algorithms have been implemented at the processing centres and the processing of satellite data from the polar orbiting satellites of NOAA has commenced. This paper gives an overview of the first products of surface radiative fluxes and their validation with selected surface sites. 相似文献
294.
一种新型的分布式数据采集器(一) 总被引:2,自引:0,他引:2
介绍了一种新型的分布式智能数据采集系统──ALPHA900系列数据采集器。该采集器由中国航空工业总公司第三0四研究所与英国ADAS公司联合设计研制。它集中了90年代采集器的优点,如可变字长、可编程智能前端、带温度补偿的连接器、可脱机工作等,并为突出各自功能形成系列。该采集器已成功地投入了工业生产,并且应用于工业过程监测、条件监测或加工监测。该系统使用价格低廉的RS485网络,各种型号模块提供了精确的温度、压力、应变及数字事件和频率等数据的测量及控制,并有相当突出的性能价格比。 相似文献
295.
296.
与传统的射频链路相比,自由空间光通信FSOC(Free Space Optical Communication)系统是对现有无线通信技术的有力补充,为了抑制大气湍流对信号光束带来的相位噪声和强度波动,有必要对通信信道状况进行实时监测。首先介绍了基于光斑质心漂移的大气折射率结构常数测量方法,利用大口径接收靶面和窄带滤光片,结合实时图像处理算法,实现了大气折射率结构常数的全天候实时监测。将大气折射率结构常数和光强闪烁指数进行了比较分析,测量结果表明它们的包络之间具有很好的线性关系,进一步验证了实时测量系统的可靠性。 相似文献
297.
GNSS用户端自主完好性监测研究综述 总被引:5,自引:1,他引:4
随着全球卫星导航系统的快速发展,对航空安全提出了挑战,完好性监测问题愈发凸显,用户端自主完好性监测(RAIM)是研究的重点之一。针对RAIM问题,首先介绍了所需导航性能的4个重要参数:精度、完好性、可用性和连续性。从单卫星故障下的RAIM、多卫星故障下的RAIM、高斯噪声下的RAIM 3个方面,综述了国内外相关的重要研究,主要涉及了3个层次内容:算法、计算保护限值和可用性,并指出了目前研究存在的不足。其次介绍了近期研究的新趋势与取得的成果。最后,展望了未来的研究方向。 相似文献
298.
299.
P.E. Yastika N. Shimizu H.Z. Abidin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(5):1719-1736
Land subsidence is a critical issue that large cities located in coastal areas, such as Semarang, Indonesia, must address. The monitoring of land subsidence is vital for predicting and mitigating the disasters that such subsidence may cause. Therefore, an economical and effective monitoring method, which can continuously provide accurate measurements over extensive areas, is highly required. Differential Interferometry Synthetic Aperture Radar (DInSAR) has the potential to be a powerful technique that can meet the above demands. Actually, DInSAR has been applied to monitor the subsidence in Semarang, but it was for a limited period before 2012.In order to clarify the transition of the long-term subsidence behavior in Semarang, the Small Baseline Subset (SBAS) method, which is one type of time-series DInSAR, is employed in this research. The sets of data of Envisat-ASAR (2003–2007), ALOS-PALSAR (2007–2011), and Sentinel-1A (2015–2017) are employed for the analyses. Then, the validity of the SBAS results is discussed from the viewpoints of both spatial distribution and temporal transition using GPS displacement measurement results and the geological conditions of the ground.On the other hand, as the lifespan of SAR satellites is commonly designed to be around 5–7?years, an appropriate method, which can connect the subsidence provided independently by the unlinked time-series data sets of the three different SAR satellite data, is required. This study uses the Hyperbolic Method (HM) to connect the above unlinked SBAS results. The HM is often used to fit the monitored subsidence in practice as a geotechnical engineering tool. Using this method, 14?years of the temporal behavior of the subsidence in Semarang is evaluated.It is found that the transition of the subsidence is different depending on the location, and that the subsidence rate is still increasing in the north and northeast parts of the coastal area. This study shows that SBAS DInSAR can be a useful tool for long-term continuous subsidence monitoring. 相似文献
300.