全文获取类型
收费全文 | 138篇 |
免费 | 2篇 |
专业分类
航空 | 44篇 |
航天技术 | 67篇 |
综合类 | 1篇 |
航天 | 28篇 |
出版年
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 1篇 |
2014年 | 9篇 |
2013年 | 6篇 |
2012年 | 5篇 |
2011年 | 15篇 |
2010年 | 8篇 |
2009年 | 7篇 |
2008年 | 12篇 |
2007年 | 5篇 |
2006年 | 10篇 |
2005年 | 1篇 |
2004年 | 5篇 |
2003年 | 5篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1998年 | 3篇 |
1996年 | 2篇 |
1993年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1970年 | 1篇 |
1968年 | 2篇 |
排序方式: 共有140条查询结果,搜索用时 31 毫秒
71.
Simultaneous determination of aerosol- and surface characteristics from top-of-atmosphere reflectance using MERIS on board of ENVISAT 总被引:1,自引:0,他引:1
Wolfgang von Hoyningen-Huene Alexander A. Kokhanovsky John P. Burrows Veronique Bruniquel-Pinel Peter Regner Frederic Baret 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,37(12):2172-II
The determination of aerosol optical thickness (AOT) from nadir scanning multi-spectral radiometers, like SeaWiFS, MERIS or MODIS, requires the separation of spectral atmospheric and surface properties. Since SeaWiFS and MERIS do not provide information at 2.1 μm, like MODIS, the estimation of the surface reflectance cannot be made by the cross correlation approach described by Kaufman et al., 1997. The BAER approach (Bremen AErosol Retrieval), von Hoyningen-Huene et al., 2003, uses a linear mixing model of spectra for ‘green vegetation’ and ‘bare soil’, tuned by the NDVI, determining an apparent surface to enable this separation of aerosol and surface properties from VIS and NIR channels. Thus AOT can be derived over a wide range of land surfaces for wavelengths <0.67 μm. Using MERIS L1 data over Europe, the AOT retrieved is comparable with ground-based observations, provided by AERONET. Regional variation of AOT can be observed, showing the atmospheric variability for clear sky conditions by: large scale variation of aerosol turbidity, regional pollution, urban regions, effects of contrails and cases of aerosol-cloud interaction. Simultaneously with the spectral AOT also spectral surface reflectance is obtained, where all atmospheric influences have been considered (molecules, aerosols and absorbing gases (O3)) for channels with wavelengths <0.67 μm. The AOT is extrapolated by Angström power law to NIR channels and the atmospheric correction for land surface properties is performed, enabling the further investigation of land use and spectral land properties. 相似文献
72.
Alexander Klippel 《Spatial Cognition & Computation》2013,13(4):233-261
Abstract In this paper, we discuss the role of topology as a predictor for the conceptualization of dynamically changing spatial configurations (referred to as movement patterns). We define meaningful units of movement patterns as paths through a topologically defined conceptual neighborhood graph. Topology plays a central role in formal approaches to human cognition and in predicting cognitive similarity ratings—although primarily for static spatial configurations. Formal specifications of the role of topology for characterizing movement patterns do exist, yet there is paucity of behavioral validation. To bridge this gap, we conducted an experiment based on the grouping paradigm to assess factors that underlie conceptualizations of movement patterns. The experiment was designed such that paths through the conceptual neighborhood graph were distinguished by topologically differentiated ending relations. We believe topology can make an important contribution in explaining movement conceptualizations. One recently formulated topology-based contribution is the endpoint hypothesis, asserting that a cognitive focus is placed on event ending relations. We discuss the results of our experiment in relation to previous experiments targeted toward a framework for modeling the cognitive conceptualization of dynamically changing spatial relations. 相似文献
73.
Dartnell LR Storrie-Lombardi MC Mullineaux CW Ruban AV Wright G Griffiths AD Muller JP Ward JM 《Astrobiology》2011,11(10):997-1016
Primitive photosynthetic microorganisms, either dormant or dead, may remain today on the martian surface, akin to terrestrial cyanobacteria surviving endolithically in martian analog sites on Earth such as the Antarctic Dry Valleys and the Atacama Desert. Potential markers of martian photoautotrophs include the red edge of chlorophyll reflectance spectra or fluorescence emission from systems of light-harvesting pigments. Such biosignatures, however, would be modified and degraded by long-term exposure to ionizing radiation from the unshielded cosmic ray flux onto the martian surface. In this initial study into this issue, three analytical techniques--absorbance, reflectance, and fluorescence spectroscopy--were employed to determine the progression of the radiolytic destruction of cyanobacteria. The pattern of signal loss for chlorophyll reflection and fluorescence from several biomolecules is characterized and quantified after increasing exposures to ionizing gamma radiation. This allows estimation of the degradation rates of cyanobacterial biosignatures on the martian surface and the identification of promising detectable fluorescent break-down products. 相似文献
74.
Alexander I. Kozynchenko 《Acta Astronautica》2009,64(7-8):770-777
The paper concerns the general problem of a bounded final state control of non-linear dynamic systems with reference to near-optimal predictive guidance for low lift-to-drag ratio re-entry vehicles. More specifically, it addresses deriving guidance strategies capable to provide a maximal downrange maneuvrability for a maximal remaining flight time. Such robust, “guaranteed”, or assured, guidance keeps the remaining range-to-go to be coincident with the center of instant attainability domain. The paper discusses the existing guaranteed guidance strategy, and presents more general approach that provides an on-board planning of the entry trajectory, thus giving future state and control profiles. As a consequence the proposed guidance law is able to satisfy not only specified terminal conditions but also typical inequality constraints such as the maximal load factor and heat load. Computer simulations show that the algorithm can generate the feasible trajectories with equal downrange margins, using simple two-parametric families of control functions. 相似文献
75.
Trial of hands-on education of rocket technology for university students using water rocket, which consists of structural study, propulsion system study, aerodynamic study, stability study, and flight trajectory study, has been performed. Integrating each subject into a group of tasks, a hands-on education system of aerospace technology will become feasible. Advantage of the system is that students can verify the theory by hands-on practice. Development of recovery mechanism for water rocket will be a good subject of hands-on innovative design. Although the system has been developed mostly for university students, it can easily be converted to hands-on education system for school children and high school students. 相似文献
76.
Two new long-range US space science strategy studies are notable not only for what the new reports say and do for their respective discipline areas but also for what they demonstrate in terms of shared conclusions and in terms of the feasibility of forging consensus on community priorities. Both studies engaged a broad segment of the research community to survey their respective fields, recommend top priority scientific goals and directions for the next decade, provide recommendations for programmatic directions and explicit priorities for government investment in research facilities, and address issues of advanced technology, infrastructure, interagency coordination, education, and international cooperation. The two studies demonstrate that cross-program priorities can be established when a community sees the effort as being beneficial to the long-term health of the field. 相似文献
77.
Some astrophysical mechanisms responsible for gamma-ray bursts on or near neutron stars are briefly reviewed. 相似文献
78.
Jing Sun Geshi Tang Fengchun Shu Xie Li Shushi Liu Jianfeng Cao Andreas Hellerschmied Johannes Böhm Lucia McCallum Jamie McCallum Jim Lovell Rüdiger Haas Alexander Neidhardt Weitao Lu Songtao Han Tianpeng Ren Lue Chen Mei Wang Jinsong Ping 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(3):823-829
The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10?cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1?s integration time of the correlator output is on the level of 0.1?ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype. 相似文献
79.
Alexander Ruzmaikin Jae N. Lee Dong L. Wu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
We determine the spatial-time patterns of zonally averaged carbon monoxide (CO) in the middle atmosphere by applying Principle Component Analysis to the CO data obtained from the Microwave Limb Sounder (MLS) measurements on the Aura satellite in 2004–2012. The first two principal components characterize more than 90% of the CO variability. Both principal components are localized in the low thermosphere near the mesopause. The first principal component is asymmetric relative to the poles. It has opposite signs in the Northern and Southern Hemisphere at mid to high latitudes and strongly oscillates with an annual periodicity. The second principal component has the same sign in both hemispheres and oscillates mainly with a semi-annual frequency. Both principal components are modulated by the 11-year solar cycle and display short-term variations. To test possible correlations of these variations with the short term solar ultraviolet (UV) variability we use the simultaneous measurements of the UV solar radiance from the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE) on the Solar Radiation and Climate Experiment (SORCE) satellite to investigate the correlation between CO in the middle atmosphere and solar UV in 2004–2012. Using a wavelet coherence technique a weak, intermittent 27-day signal is detected in high-frequency parts of the CO principal components. 相似文献
80.
Alexander Sergeevich KOSOV Vladimir Michailovich GOTLIB Vriiy Alexandrovich KOROGOD Uriiy Alexandrovich NEMLIHER Dmitriy Petrovich SKULACHEV 《深空探测学报》2014,1(3):181-191
俄罗斯航天局正在规划和推进新的月球探测计划,包括月球-资源和月球-全球探测任务,它们搭载了3个无线电科学载荷:2个无线电信标机分别安装在2个着陆器上,1个Ka波段接收机安装在月球-全球轨道器上。信标机发射频率为8.4GHz和32GHz。8.4GHz的微波信号将被发回地球,利用地面VLBI监测网对信号进行测量,其结果可用于精密的天体力学观测及导航,还能用于月球天平动研究;32GHz信号将用于定轨和月球重力场研究。Ka波段信号天线轴指向着陆区天顶方向,信号由轨道器接收。本文基于对Ka波段信号多普勒频移的精确测量,通过研究着陆区附近重力场的微小变化(约3~5mGal精度),探讨月球重力场的不均匀性,其测量数据的空间分辨率约为20km。 相似文献