全文获取类型
收费全文 | 111篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
航空 | 79篇 |
航天技术 | 24篇 |
航天 | 11篇 |
出版年
2021年 | 3篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 1篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 6篇 |
2008年 | 5篇 |
2007年 | 2篇 |
2006年 | 2篇 |
2005年 | 4篇 |
2004年 | 3篇 |
2003年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有114条查询结果,搜索用时 0 毫秒
101.
102.
Tim Van Hoolst Frank Sohl Igor Holin Olivier Verhoeven Véronique Dehant Tilman Spohn 《Space Science Reviews》2007,132(2-4):203-227
This review addresses the deep interior structure of Mercury. Mercury is thought to consist of similar chemical reservoirs
(core, mantle, crust) as the other terrestrial planets, but with a relatively much larger core. Constraints on Mercury’s composition
and internal structure are reviewed, and possible interior models are described. Large advances in our knowledge of Mercury’s
interior are not only expected from imaging of characteristic surface features but particularly from geodetic observations
of the gravity field, the rotation, and the tides of Mercury. The low-degree gravity field of Mercury gives information on
the differences of the principal moments of inertia, which are a measure of the mass concentration toward the center of the
planet. Mercury’s unique rotation presents several clues to the deep interior. From observations of the mean obliquity of
Mercury and the low-degree gravity data, the moments of inertia can be obtained, and deviations from the mean rotation speed
(librations) offer an exciting possibility to determine the moment of inertia of the mantle. Due to its proximity to the Sun,
Mercury has the largest tides of the Solar System planets. Since tides are sensitive to the existence and location of liquid
layers, tidal observations are ideally suited to study the physical state and size of the core of Mercury. 相似文献
103.
Tom Van Helleputte Eelco Doornbos Pieter Visser 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1890-1896
Current and planned Earth observation missions are equipped with highly sensitive accelerometers. Before using the data, the instrument has to be calibrated by determining scale and bias parameters for each axis. Here, the accelerometer measurements are used in a GPS-based reduced-dynamic orbit determination approach, replacing the non-gravitational force models, and nominally daily calibration parameters are estimated. Additional empirical accelerations are estimated to account for deficiencies in the applied force models. This method is applied to 5 years of CHAMP and GRACE data, resulting in an orbit precision at the level of a few centimeters. In along-track direction the calibration parameters can be estimated freely, scale factors of 0.96 ± 0.014 and 0.95 ± 0.015 are obtained for GRACE A and B, and 0.85 ± 0.024 for CHAMP. A constant scale factor results in the smoothest bias series, with clear trends and occasional jumps. In radial and cross-track direction tight constraints to a priori biases have to be applied. Furthermore, the determined orbits are analyzed with respect to reference trajectories, and SLR, phase and KBR residuals are presented. 相似文献
104.
Sugitani K Lepot K Nagaoka T Mimura K Van Kranendonk M Oehler DZ Walter MR 《Astrobiology》2010,10(9):899-920
Morphologically diverse structures that may constitute organic microfossils are reported from three remote and widely separated localities assigned to the ca. 3400?Ma Strelley Pool Formation in the Pilbara Craton, Western Australia. These localities include the Panorama, Warralong, and Goldsworthy greenstone belts. From the Panorama greenstone belt, large (> 40?μm) lenticular to spindle-like structures, spheroidal structures, and mat-forming thread-like structures are found. Similar assemblages of carbonaceous structures have been identified from the Warralong and Goldsworthy greenstone belts, though these assemblages lack the thread-like structures but contain film-like structures. All structures are syngenetic with their host sedimentary black chert, which is associated with stromatolites and evaporites. The host chert is considered to have been deposited in a shallow water environment. Rigorous assessment of biogenicity (considering composition, size range, abundance, taphonomic features, and spatial distributions) suggests that cluster-forming small (<15 μm) spheroids, lenticular to spindle-like structures, and film-like structures with small spheroids are probable microfossils. Thread-like structures are more likely fossilized fibrils of biofilm, rather than microfossils. The biogenicity of solitary large (>15?μm) spheroids and simple film-like structures is less certain. Although further investigations are required to confirm the biogenicity of carbonaceous structures from the Strelley Pool Formation, this study presents evidence for the existence of morphologically complex and large microfossils at 3400?Ma in the Pilbara Craton, which can be correlated to the contemporaneous, possible microfossils reported from South Africa. Although there is still much to be learned, they should provide us with new insights into the early evolution of life and shallow water ecosystems. 相似文献
105.
T. Beuselinck C. Van Bavinchove V. I. Abrashkin A. E. Kazakova V. V. Sazonov 《Cosmic Research》2010,48(3):246-259
The results of reconstruction of rotational motion of the Foton M-3 satellite during its uncontrolled flight in September 2007 are presented. The reconstruction was performed by processing
the data of onboard measurements of the Earth’s magnetic field obtained by the DIMAC instruments. The measurements were carried
out continuously throughout the flight, but the processing technique dealt with the data portions covering time intervals
of a few orbital revolutions. The data obtained on each such interval were processed jointly by the least squares method with
using integration of the equations of satellite motion relative to its center of mass. When processing, the initial conditions
of motion and the used mathematical model’s parameters were estimated. The results of processing 16 data sets gave us complete
information about the satellite motion. This motion, which began at a low angular velocity, had gradually accelerated and
in five days became close to the regular Euler precession of an axisymmetric solid body. At the end of uncontrolled flight
the angular velocity of the satellite relative to its lengthwise axis was 0.5 deg/s; the angular velocity projection onto
the plane perpendicular to this axis had a magnitude of about 0.18 deg/s. 相似文献
106.
W F Dempster M Van Thillo A Alling J P Allen S Silverstone M Nelson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(7):1477-1482
Laboratory Biosphere is a 40 m3 closed life system that commenced operation in May 2002. Light is from 12,000 W of high pressure sodium lamps over planting beds with 5.37 m2 of soil. Water is 100% recycled by collecting condensate from the temperature and humidity control system and mixing with leachate collected from under the planting beds. Atmospheric leakage was estimated during the first closure experiment to be 0.5-1% per day in general plus about 1% for each usage of the airlock door. The first trial run of 94 days was with a soybean crop grown from seeds (May 17, 2002) to harvest (August 14, 2002) plus 5 days of post-harvest closure. The focus of this initial trial was system testing to confirm functionality and identify any necessary modifications or improvements. This paper describes the organizational and physical features of the Laboratory Biosphere. 相似文献
107.
Van Hagan T.H. Smith J.N. Jr. Schuller M. 《Aerospace and Electronic Systems Magazine, IEEE》1997,12(7):10-15
This paper presents trade studies that address the use of the thermionic/AMTEC cell-a cascaded, high efficiency, static power conversion concept that appears well-suited to space power applications. Both the thermionic and AMTEC power conversion approaches have been shown to be promising candidates for space power. Thermionics offers system compactness via modest efficiency at high heat rejection temperatures, and AMTEC offers high efficiency at modest heat rejection temperature. From a thermal viewpoint, the two are ideally suited for cascaded power conversion: thermionic heat rejection and AMTEC heat source temperatures are essentially the same. In addition to realizing conversion efficiencies potentially as high as 35-40% such a cascade offers the following perceived benefits: Survivability-capable of operation in the Van Allen belts; Simplicity-static conversion, no moving parts; Long lifetime-no inherent life-limiting mechanisms identified; Technology readiness-Large thermionic database; AMTEC efficiencies of 18% currently being demonstrated, with more growth potential available; and Technology growth-applicable to both solar thermal and reactor-based nuclear space power systems. Mechanical approaches and thermal/electric matching criteria for integrating thermionics and AMTEC into a single conversion device are described. Focusing primarily on solar thermal space power applications, parametric trends are presented to show the performance and cost potential that should be achievable with present-day technology in cascaded thermionic/AMTEC systems 相似文献
108.
V. Icke K. F. Wakker A. Journet P. C. van der Kruit H. Nieuwenhuijzen R. Mewe 《Space Science Reviews》1992,62(1-2):205-212
109.
G Van Hoven D.L Hendrix 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,19(12):1865-1869
The excitation (flares, ejections, heating, …) of the corona can be understood in terms of the dynamics of the confectively driven magnetized plasma. In particular, anomalous ohmic heating may be a consequence of the formation and rapid dissipation of small-scale magnetic fields in the corona. We have performed numerical simulations of the loop heating model proposed by Parker (1972, 1994), and have studied its dynamics and global power balance in order to assess its viability as a coronal heating candidate, with promising results. Our results suggest the following view of the small-scale dynamics of coronal loops. First of all, photospheric granular motions quasi-statically twist the magnetic field of the corona in a random-walk fashion. In topologically closed structures, the perpendicular magnetic energy increases, causing magnetic shear to build up at the quasi-separatrices of the resulting close-packed magnetic flux tubes. At some point, the boundary driving causes this stressed configuration to cross the threshold of an ideal time-scale MHD instability (possibly magnetic coalescence or resistive tearing) or a point of nonequilibrium and the field lines pinch toward a small-scale sheared configuration. It then becomes energetically favorable for dynamic reconnection to occur, producing narrow current sheets and an Ohmic heating rate sufficient to balance the input Poynting flux. 相似文献
110.
J.E. Wiik L. Van Driel-Gesztely B. Schmieder P. Heinzel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1997,20(12):2345-2349
Observations in X-rays (Yohkoh/SXT) and in H of a system of post-flare loops which developed after a flare on 25 June 1992 provide a unique set of data for a study of the relationship between the hot and cool post-flare loops as they evolve. Through a study of the magnetic configuration in which the flare occurred, we are able to reconstruct the true, 3D geometry of the loops. We derive the bulk-flow velocities along the loop as a function of height using Doppler velocities and the results from the loop reconstruction. We also provide a set of relative altitude data. These results are used to check the validity of the reconnection model in the frame of the cooling time needed to cool X-ray loops to H temperature. 相似文献