全文获取类型
收费全文 | 290篇 |
免费 | 9篇 |
国内免费 | 3篇 |
专业分类
航空 | 162篇 |
航天技术 | 75篇 |
综合类 | 7篇 |
航天 | 58篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 16篇 |
2012年 | 14篇 |
2011年 | 20篇 |
2010年 | 10篇 |
2009年 | 15篇 |
2008年 | 5篇 |
2007年 | 17篇 |
2006年 | 9篇 |
2005年 | 13篇 |
2004年 | 7篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 8篇 |
2000年 | 11篇 |
1999年 | 8篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 4篇 |
1992年 | 7篇 |
1991年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1985年 | 14篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 14篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1975年 | 3篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1969年 | 2篇 |
1967年 | 1篇 |
1963年 | 2篇 |
排序方式: 共有302条查询结果,搜索用时 531 毫秒
61.
Santiago Laín Martin Sommerfeld 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
In this paper the performance of horizontal pneumatic conveying under different gravity environments is evaluated. An Euler–Lagrange approach validated versus ground experiments is employed to predict the relevant particle variables such as particle mass flux, mean conveying and fluctuating velocities in terrestrial, lunar and micro-gravity conditions. Gravity reduced computations predict a reduction in the global particle–wall collision frequency. Also, in the case of low wall roughness and small particle mass loading, reduction of gravity acceleration implies an increase of particle–wall collision frequency with the upper wall of the channel affecting greatly the particle mass flux profile. In the case of high wall roughness and/or high particle-to-fluid mass loading (i.e., around 1.0) particle conveying characteristics are similar in the three gravity conditions evaluated. This is due to the fact that both, wall roughness and inter-particle collisions reduce gravitational settling. However, the influence of gravity on the additional pressure loss along the channel due to the conveying of the particles is much reduced. 相似文献
62.
Songtao Han Axel Nothnagel Zhongkai Zhang Rüdiger Haas Qiang Zhang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(5):1754-1767
Extracting the group and phase delays of interferometric observations produced in the Very Long Baseline Interferometry (VLBI) measurement concept requires a special fringe fitting and delay search algorithm for the recorded bandwidth. While fringe fitting is in use routinely for several megahertz wide channels in geodetic and astrometric VLBI with quasar observations, fringe fitting for artificial tones of very small bandwidth of artificial signals for Differential One-way Ranging (DOR) requires a different way of handling. In a project called Observing the Chang’E-3 Lander with VLBI (OCEL), the DOR tones emitted by the Chang’E-3 lander were observed in a standard geodetic VLBI mode with 8 or 4?MHz wide channels to maintain compatibility with the corresponding quasar observations. For these observations, we modified the existing fringe fitting program of the Haystack Observatory Processing Software (HOPS), fourfit, to properly handle narrow band DOR tones. The main motivations are that through this modification, the data of quasars and artificial radio sources can be processed in the existing geodetic analysis pipeline, and that the algorithm can be used for similar projects as well. In this paper, we describe the algorithm and show that the new algorithm produces much more reliable group delay results than using the standard fourfit algorithm. This is done by a simulation test and in particular by processing of real observations. It is shown that in many cases, systematic deviations of several nanoseconds, which are seen with the standard fourfit algorithm, can be avoided. The ultimate benefit of the new procedure is demonstrated by reducing the errors in delay triangle closures by at least a factor of 3, which, in the OCEL case, is from ~300 to ~100?ps. 相似文献
63.
64.
65.
66.
Yoshifumi Futaana Jean-Yves Chaufray H. Todd Smith Philippe Garnier Herbert Lichtenegger Magda Delva Hannes Gr?ller Alessandro Mura 《Space Science Reviews》2011,162(1-4):213-266
Our understanding of the upper atmosphere of unmagnetized bodies such as Mars, Venus and Titan has improved significantly in this decade. Recent observations by in situ and remote sensing instruments on board Mars Express, Venus Express and Cassini have revealed characteristics of the neutral upper atmospheres (exospheres) and of energetic neutral atoms (ENAs). The ENA environment in the vicinity of the bodies is by itself a significant study field, but ENAs are also used as a diagnostic tool for the exosphere and the interaction with the upstream plasmas. Synergy between theoretical and modeling work has also improved considerably. In this review, we summarize the recent progress of our understanding of the neutral environment in the vicinity of unmagnetized planets. 相似文献
67.
Bieber John W. Eroshenko Eugenia Evenson Paul Flückiger Erwin O. Kallenbach Reinald 《Space Science Reviews》2000,93(1-2):1-9
Cosmic rays provide a diagnostic tool to analyze processes in interplanetary space and at the Sun. Cosmic rays also directly
affect the terrestrial environment and serve as indicators of solar variability and non anthropogenic climatic changes on
Earth at present and in the distant past.
After the invention of the neutron monitor by John A. Simpson in 1948, an international network of cosmic ray detectors developed
in a cooperative effort to examine temporal and spatial variations in our space environment. The resulting datasets represent
the longest continuous, high time resolution series of particle radiation measurement in space science. At present, the neutron
monitor network is complemented by spacecraft instrumentation to study solar-terrestrial correlated phenomena.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
68.
Terrestrial planets are accreted in a disk orbiting a central star. The basic challenge of their formation consists of assembling
micron-sized or smaller dust grains to bodies with over 104 km in diameter. This formation process, ultimately based on collisions, occurs in three very different physical regimes depending
upon the size of the bodies present: 1) Early on, micron- to mm-sized dust grains, chondrules and chondrites are strongly
coupled to the gas. 2) As they grow larger, gravity increases the collisional cross section allowing runaway growth to occur.
3) After this runaway phase stops from exhaustion of matter in the immediate surroundings of the protoplanets, further growth
occurs on timescales typical of mutual gravitational perturbations. The emphasis of this book is on the timescales corresponding
to these formation phases as well as the characteristic chemical and isotopic composition of the bodies involved.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
69.
The coupling between the ionised plasma and the neutral thermospheric particles plays an important role for the dynamics of the upper atmosphere. Significant progress in understanding the related processes has been achieved thanks to the availability of continuous accurate measurements of thermospheric parameters like mass density and wind by high resolution accelerometers on board the satellites CHAMP and GRACE. Here we present some examples of ionosphere-thermosphere coupling where CHAMP observations contributed considerably to their interpretation. We start with the derived properties of the thermosphere at altitudes around 400 km. A new aspect is the significant control of the geomagnetic field geometry on thermospheric features. Phenomena discussed in some depths are the equatorial mass density anomaly, the cusp-related mass density enhancement and the thermospheric response to magnetospheric substorms. Here we consider both the effect on the density and on the wind. A?long predicted process is the wind-driven ionospheric F region dynamo. The high-resolution magnetic field measurements of CHAMP enabled for the first time a systematic study of that phenomenon considering longitudinal, local time, seasonal and solar flux dependences. Some open issues that require further investigations are mentioned at the end. 相似文献
70.
Jürgen Blum 《Space Science Reviews》2000,92(1-2):265-278
For a better understanding of the processes which lead to the formation of planetesimals in the early solar nebula, we performed
an extensive series of laboratory experiments. We find that the capture velocities in collisions between spherical grains
are more than one order of magnitude higher than predicted by Chokshi et al (1993). In contrast, irregular grains have no
capture threshold and can be better described by a sticking probability which is typically a few 10%, even for velocities
exceeding 10 m/s. However, adhesion forces between spherical, micron-sized particles match the theoretical predictions very
well, although contact areas and deformations are of the order of inter-atomic distances only. Aggregation experiments in
rarefied turbulent gases reveal the fractal nature of dust aggregates. Mass distribution functions are bell-shaped. Similar
behaviour can be found in aggregation experiments with sedimenting particles. Experiments on collision-induced aggregate compaction
and fragmentation match the numerical simulations by Dominik and Tielens (1997) very well if revised experimental values of
the break-up energy (from our impact experiments) and the rolling-friction force (from our AFM measurements on particle chains)
are used.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献