全文获取类型
收费全文 | 1207篇 |
免费 | 82篇 |
国内免费 | 50篇 |
专业分类
航空 | 192篇 |
航天技术 | 937篇 |
综合类 | 24篇 |
航天 | 186篇 |
出版年
2023年 | 31篇 |
2022年 | 15篇 |
2021年 | 61篇 |
2020年 | 32篇 |
2019年 | 45篇 |
2018年 | 41篇 |
2017年 | 15篇 |
2016年 | 12篇 |
2015年 | 21篇 |
2014年 | 82篇 |
2013年 | 66篇 |
2012年 | 71篇 |
2011年 | 88篇 |
2010年 | 69篇 |
2009年 | 100篇 |
2008年 | 106篇 |
2007年 | 66篇 |
2006年 | 40篇 |
2005年 | 77篇 |
2004年 | 30篇 |
2003年 | 17篇 |
2002年 | 22篇 |
2001年 | 23篇 |
2000年 | 25篇 |
1999年 | 18篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 11篇 |
1995年 | 20篇 |
1994年 | 33篇 |
1993年 | 12篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 3篇 |
1987年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1339条查询结果,搜索用时 15 毫秒
101.
S. W. Kahler 《Space Science Reviews》2007,129(4):359-390
Electrons with near-relativistic (E≳30 keV, NrR) and relativistic (E≳0.3 MeV) energies are often observed as discrete events in the inner heliosphere following solar transient activity. Several
acceleration mechanisms have been proposed for the production of those electrons. One candidate is acceleration at MHD shocks
driven by coronal mass ejections (CMEs) with speeds ≳1000 km s−1. Many NrR electron events are temporally associated only with flares while others are associated with flares as well as with
CMEs or with radio type II shock waves. Since CME onsets and associated flares are roughly simultaneous, distinguishing the
sources of electron events is a serious challenge. On a phenomenological basis two classes of solar electron events were known
several decades ago, but recent observations have presented a more complex picture. We review early and recent observational
results to deduce different electron event classes and their viable acceleration mechanisms, defined broadly as shocks versus
flares. The NrR and relativistic electrons are treated separately. Topics covered are: solar electron injection delays from
flare impulsive phases; comparisons of electron intensities and spectra with flares, CMEs and accompanying solar energetic
proton (SEP) events; multiple spacecraft observations; two-phase electron events; coronal flares; shock-associated (SA) events;
electron spectral invariance; and solar electron intensity size distributions. This evidence suggests that CME-driven shocks
are statistically the dominant acceleration mechanism of relativistic events, but most NrR electron events result from flares.
Determining the solar origin of a given NrR or relativistic electron event remains a difficult proposition, and suggestions
for future work are given. 相似文献
102.
Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure
formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification
and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat transport and the dissipative
processes in the hot intra-cluster plasma. The acceleration, transport and interactions of non-thermal energetic particles
are essential for modelling the observed emissions. Therefore, the inclusion of the non-thermal components will be mandatory
for simulating accurately the global dynamical processes in clusters. In this review, we summarise the results obtained with
the simulations of the formation of galaxy clusters which address the issues of shocks, magnetic field, cosmic ray particles
and turbulence. 相似文献
103.
综述了当前国际空间太阳能电站技术的研究进展与发展趋势。重点介绍了空间太阳能电站系统方案新构思“太阳塔”和“太阳盘”的特点;介绍了空间太阳能电站的主要相关技术———无线电能传输技术、太阳能转换技术和空间运输技术等的发展趋势;最后简要介绍了月球电站的进展情况。 相似文献
104.
F. Dalla Vedova H. Henrion M. Leipold Th. Girot R. Vaudemont Th. Belmonte K. Fleury O. Le Couls 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
SSM (Solar Sail Materials) is an on-going project for the European Space Agency (ESA) relying on past and recent European solar sail design projects. It aims at developing and testing future technologies suitable for large, operational solar sailcrafts. 相似文献
105.
Liming He Lixin Wu Sergey Pulinets Shanjun Liu Fan Yang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
A precise determination of ionospheric total electron content (TEC) anomaly variations that are likely associated with large earthquakes as observed by global positioning system (GPS) requires the elimination of the ionospheric effect from irregular solar electromagnetic radiation. In particular, revealing the seismo-ionospheric anomalies when earthquakes occurred during periods of high solar activity is of utmost importance. To overcome this constraint, a multiresolution time series processing technique based on wavelet transform applicable to global ionosphere map (GIM) TEC data was used to remove the nonlinear effect from solar radiation for the earthquake that struck Tohoku, Japan, on 11 March, 2011. As a result, it was found that the extracted TEC have a good correlation with the measured solar extreme ultraviolet flux in 26–34 nm (EUV26–34) and the 10.7 cm solar radio flux (F10.7). After removing the influence of solar radiation origin in GIM TEC, the analysis results show that the TEC around the forthcoming epicenter and its conjugate were significantly enhanced in the afternoon period of 8 March 2011, 3 days before the earthquake. The spatial distributions of the TEC anomalous and extreme enhancements indicate that the earthquake preparation process had brought with a TEC anomaly area of size approximately 1650 and 5700 km in the latitudinal and longitudinal directions, respectively. 相似文献
106.
A. Gil M.V. Alania 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
We study the temporal evolution of the power rigidity spectrum of the first (27 days) and the second (14 days) harmonics of the 27-day variation of the galactic cosmic ray intensity measured by neutron monitors in the period of 1965–2002. The rigidity spectrum of these variations can be approximated by a power law. We show the rigidity spectra of the first and the second harmonics of the 27-day variation of the galactic cosmic ray intensity have similar time profiles. These spectra are hard (γ ≈ 0.5 ± 0.1) and soft (γ ≈ 1.1 ± 0.2) during solar maximum and minimum activity, respectively. We ascribe this to the alternation of the sizes of the modulation regions responsible for the 27-day variation of the galactic cosmic ray intensity in different epochs of solar activity. Especially, the average radial sizes of the modulation regions of the 27-day variation and the heliolatitudinal extension of the heliolongitudinal asymmetry are smaller during solar minimum than during solar maximum. We show also, that the temporal changes of the power rigidity spectra of the first and the second harmonics of the 27-day variation of the galactic cosmic ray intensity are in a negative correlation with the changes of the rigidity spectrum of the corresponding 11-year variation. 相似文献
107.
Monika E. Kress Alexander G.G.M. Tielens Michael Frenklach 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Interstellar material is highly processed when subjected to the physical conditions that prevail in the inner regions of protoplanetary disks, the potential birthplace of habitable planets. Polycyclic aromatic hydrocarbons (PAHs) are abundant in the interstellar medium, and they have also been observed in the disks around young stars, with evidence for some modification in the latter. Using a chemical model developed for sooting flames, we have investigated the chemical evolution of PAHs in warm (1000–2000 K) and oxygen-rich (C/O < 1) conditions appropriate for the region where habitable planets may eventually form. Our study focuses on (1) delineating the conditions under which PAHs will react and (2) identifying the key reaction pathways and reaction products characterizing this chemical evolution. We find that reactions with H, OH and O are the main pathways for destroying PAHs over disk timescale at temperatures greater than about 1000 K. In the process, high abundances of C2H2 persist over long timescales due to the kinetic inhibition of reactions that eventually drive the carbon into CO, CO2 and CH4. The thermal destruction of PAHs may thus be the cause of the abundant C2H2 that has been observed in disks. We propose that protoplanetary disks have a ‘soot line’, within which PAHs are irreversibly destroyed via thermally-driven reactions. The soot line will play an important role, analogous to that of the ‘snow line’, in the bulk carbon content of meteorites and habitable planets. 相似文献
108.
109.
Panagiotis K. Marhavilas 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The analysis of energetic particles and magnetic field measurements from the Ulysses spacecraft has shown that in a series of events, the energy density contained in the suprathermal tail particle distribution is comparable to or larger than that of the magnetic field, creating conditions of high-beta plasma. In this work we analyze periods of high-beta suprathermal plasma occurrences (βep > 1) in interplanetary space, using the ratio (βep) of the energetic particle (20 keV to ∼5 MeV) and magnetic field energy densities from measurements covering the entire Ulysses mission lifetime (1990–2009) in order to reveal new or to reconfirm some recently defined interesting characteristics. The main key-results of the work are summarized as follows: (i) we verify that high-beta events are detected within well identified regions corresponding mainly to the vicinity of shock surfaces and magnetic structures, and associated with energetic particle intensity enhancements due to (a) reacceleration at shock-fronts and (b) unusually large magnetic field depressions. (ii) We define three considerable features for the high-beta events, concentrated on the next points: (a) there is an appreciable solar-activity influence on the high-beta events, during the maximum and middle solar-cycle phase, (b) the annual peak magnitude and the number of occurrences of high events are well correlated with the sunspot number, (c) the high-beta suprathermal plasma events present a spatial distribution in heliographic latitudes (HL) up to ∼±80°, and a specific important concentration on the low (−25° ? HL < −6°, 6° < HL ? 25°) and median (−45° ? HL < −25°, 25° < HL ? 45°) latitudes. We also reconfirm by a statistical analysis the results of Marhavilas and Sarris (2011), that the high-beta suprathermal plasma (βep > 1) events are characterized by a very large parameter βep (up to 1732.5), a great total duration (406 days) and a large percentage of the Ulysses-mission lifetime (which is equal to 6.34% of the total duration with usable measurements, and 11.3% of the duration in presence of suprathermal particles events). 相似文献
110.
A. Shalchi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
A heuristic derivation of an improved nonlinear guiding center theory for perpendicular diffusion of charged particles is presented. This new derivation complements previous work which is based on an indirect solution of the Fokker–Planck equation. The new derivation confirms the improved theory for diffusion of charged particles and makes the validity of the theory plausible. 相似文献