全文获取类型
收费全文 | 1968篇 |
免费 | 438篇 |
国内免费 | 384篇 |
专业分类
航空 | 1698篇 |
航天技术 | 430篇 |
综合类 | 203篇 |
航天 | 459篇 |
出版年
2024年 | 4篇 |
2023年 | 27篇 |
2022年 | 73篇 |
2021年 | 96篇 |
2020年 | 104篇 |
2019年 | 99篇 |
2018年 | 96篇 |
2017年 | 104篇 |
2016年 | 107篇 |
2015年 | 87篇 |
2014年 | 134篇 |
2013年 | 119篇 |
2012年 | 159篇 |
2011年 | 141篇 |
2010年 | 181篇 |
2009年 | 161篇 |
2008年 | 128篇 |
2007年 | 150篇 |
2006年 | 112篇 |
2005年 | 85篇 |
2004年 | 73篇 |
2003年 | 61篇 |
2002年 | 72篇 |
2001年 | 49篇 |
2000年 | 47篇 |
1999年 | 39篇 |
1998年 | 37篇 |
1997年 | 40篇 |
1996年 | 34篇 |
1995年 | 36篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 26篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 15篇 |
1987年 | 3篇 |
1984年 | 4篇 |
排序方式: 共有2790条查询结果,搜索用时 15 毫秒
951.
952.
高超声速气动热辨识技术实验研究 总被引:1,自引:0,他引:1
为估计高超声速飞行中的气动热流,采用热流辨识技术研究了平板表面的气动热流。首先采用仿真数据对辨识方法进行验证,结果表明,在测量噪声较低时热流辨识结果误差较小。此后,开展了平板的高超声速气动热风洞实验,通过内埋热电偶测量平板内部温度,采用热流辨识法获得平板表面的气动热流,采用辅助测点对比验证了内埋测点辨识结果的可信度。最后将辨识结果与平板边界层热流理论估算结果进行对比,分析了两者产生误差的原因。本文的研究为热流辨识技术的实际应用奠定了基础。 相似文献
953.
954.
Mayte Vasquez Manfred Gottwald Sebastian Gimeno Garcia Eckhart Krieg Günter Lichtenberg Franz Schreier Sander Slijkhuis Ralph Snel Thomas Trautmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This work shows the capability of observing Venus with a sensor originally designed for Earth remote sensing. SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY), onboard ENVISAT, successfully observed visible and near-infrared spectra from the Venusian atmosphere. The Venus spectra were simulated using a line-by-line radiative transfer model. The single scattering approximation was applied in order to consider the effects of an approximately 20 km-thick haze layer above the main cloud deck, which was considered as a reflecting cloud located in the upper atmosphere of the planet. CO2 absorption lines could be distinguished in both observed and simulated spectra and a good agreement between them was also found. 相似文献
955.
基于当前遥感相机谱段数量的不断增加、分辨率的不断提升等方面造成的数据传输问题,分析了目前广泛应用的并行数据传输系统所面临的技术瓶颈,提出采用串行发送/解串(SerDes)方式加以替代的方案,通过对比分析,指出采用该方式传输数据的优点,进而阐述文章所采用的串行发送/解串芯片-TLK2711的工作原理、传输协议等,最终通过试验证明了其在遥感相机系统中应用的可行性,为后续遥感相机研制提供参考。 相似文献
956.
957.
随着航天器热控制的发展,蒸气压缩热泵排热系统等热控方式逐渐受到人们的重视,其中冷凝换热对热泵的性能好坏有重要的影响。为了研究重力场对冷凝换热的影响,将紫铜直管冷凝器置于蒸气压缩热泵系统中,通过改变重力场与流动方向的夹角,测量得到了不同倾角下的冷凝换热系数和压降。实验结果表明,倾角对直管内冷凝换热系数的影响较大,不同倾角下的换热系数差别达30%,远大于不同倾角对直管内蒸发换热的影响;压缩机润滑油对冷凝换热的影响也很大,相比较无润滑油冷凝换热系数低30%以上。随着质量流量的增加,压缩机润滑油的影响逐渐减弱。
相似文献
相似文献
958.
工业生产中经常用饱和蒸汽作为加热介质,其凝结水在回收过程中由于温度高而产生二次汽化,难以回收,造成热能和高品质水的浪费。针对这种现象提出合理、实用的解决方法,深度利用蒸汽的热能,降低凝结水的温度,使凝水更容易回收,减少热能损失,避免环境污染。 相似文献
959.
Li Wei Li Chunsheng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
As a promising new technology emerged in recent years, the Distributed Satellite-borne SAR (DSS) system with Interferometric Synthetic Aperture Radar (InSAR) imaging capability has been recognized by the remote sensing community as an integrated part of the spaceborne earth observation system. However, most researches on DSS were focused on individual aspects of system design/analysis and data processing, while few studies have been dedicated to establishing a standard methodological framework for universal DSS system design. Aiming at this problem, the topics of DSS system error analysis and design method are investigated in this paper. Firstly, a rigorous error propagation model of height measurement is theoretically derived from the DSS InSAR imaging geometry, and the impact of each error sources in this model on the height measurement accuracy is analyzed individually. In particular, the baseline length and its measurement error in the InSAR imaging plane are identified as the dominant factors. Second, a new method for DSS system design is proposed based on our analyses with the error propagation model. This method consists of two important phases, namely collaboration design and monostatic design. The major objective of collaboration design is to determine the configuration and parameters for the coordination between satellites in the DSS system. Afterwards, the key parameters for single satellite and the payload are determined by the monostatic design. Thirdly, a system performance analysis method is developed to comprehensively evaluate the performance of the pre-designed DSS system. In the next section, a typical example of DSS system design is given to demonstrate the effectiveness of the proposed system design and analysis methods. The target DSS system has the same goal and hardware configuration as the TanDEM-X mission. Finally, the conclusion is drawn with our major findings are presented. 相似文献
960.
G. Nath 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012,49(1):108-120
A self-similar solution is obtained for one dimensional adiabatic flow behind a cylindrical shock wave propagating in a rotating dusty gas in presence of heat conduction and radiation heat flux with increasing energy. The dusty gas is assumed to be a mixture of non-ideal (or perfect) gas and small solid particles, in which solid particles are continuously distributed. It is assumed that the equilibrium flow-condition is maintained and variable energy input is continuously supplied by the piston (or inner expanding surface). The heat conduction is expressed in terms of Fourier’s law and the radiation is considered to be of the diffusion type for an optically thick grey gas model. The thermal conductivity K and the absorption coefficient αR are assumed to vary with temperature only. In order to obtain the similarity solutions the initial density of the ambient medium is assumed to be constant and the angular velocity of the ambient medium is assumed to be decreasing as the distance from the axis increases. The effects of the variation of the heat transfer parameters and non-idealness of the gas in the mixture are investigated. The effects of an increase in (i) the mass concentration of solid particles in the mixture and (ii) the ratio of the density of solid particles to the initial density of the gas on the flow variables are also investigated. 相似文献