全文获取类型
收费全文 | 492篇 |
免费 | 61篇 |
国内免费 | 120篇 |
专业分类
航空 | 242篇 |
航天技术 | 213篇 |
综合类 | 17篇 |
航天 | 201篇 |
出版年
2024年 | 4篇 |
2023年 | 15篇 |
2022年 | 6篇 |
2021年 | 22篇 |
2020年 | 34篇 |
2019年 | 17篇 |
2018年 | 24篇 |
2017年 | 14篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 37篇 |
2013年 | 30篇 |
2012年 | 38篇 |
2011年 | 22篇 |
2010年 | 31篇 |
2009年 | 23篇 |
2008年 | 29篇 |
2007年 | 39篇 |
2006年 | 67篇 |
2005年 | 33篇 |
2004年 | 10篇 |
2003年 | 24篇 |
2002年 | 13篇 |
2000年 | 7篇 |
1999年 | 24篇 |
1998年 | 17篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 14篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
排序方式: 共有673条查询结果,搜索用时 31 毫秒
81.
It is generally accepted that the energy that drives coronal mass ejections (CMEs) is magnetic in origin. Sheared and twisted
coronal fields can store free magnetic energy which ultimately is released in the CME. We explore the possibility of the specific
magnetic configuration of a magnetic flux rope of field lines that twist about an axial field line. The flux rope model predicts
coronal observables, including heating along forward or inverse S-shaped, or sigmoid, topological surfaces. Therefore, studying
the observed evolution of such sigmoids prior to, during, and after the CME gives us crucial insight into the physics of coronal
storage and release of magnetic energy. In particular, we consider (1) soft-X-ray sigmoids, both transient and persistent;
(2) The formation of a current sheet and cusp-shaped post-flare loops below the CME; (3) Reappearance of sigmoids after CMEs;
(4) Partially erupting filaments; (5) Magnetic cloud observations of filament material. 相似文献
82.
Marian Karlický 《Space Science Reviews》2006,122(1-4):161-168
An acceleration process in the collapsing magnetic trap, formed in the flare with cusp magnetic field topology, is described.
Computations show that high-energy electrons are accumulated in the central part of the collapsing magnetic trap due to an
increase of their pitch angles. The effect explains in a natural way the formation of X-ray loop-top sources. Then, using
the model with the collapsing trap and considering only the adiabatic heating process, a possible explanation for the motion
of the X-ray loop-top source observed at the beginning of some cusp-type flares is presented. 相似文献
83.
Oxygen Isotopes in the Solar System 总被引:1,自引:0,他引:1
The oxygen three-isotope system has major advantages over the two-isotope systems of hydrogen, carbon, and nitrogen because
different fractionation laws govern intraplanetary and interplanetary processes. This permits discriminating between solar
nebular processes and parent-body processes. Oxygen isotopes also serve as a sensitive natural tracer for meteorite classification.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
84.
The spectral and polarization properties of thermal cyclotron radio emission from a hot coronal loop with a current along the axis are computed. The magnetic field is supposed to have a component along the loop axis as well as a poloidal part due to the current, both components being of comparable magnitude. In this specific configuration a helical magnetic field is present with a remarkable minimum of its absolute value along the loop axis and a maximum at its periphery. The presence of one or two maxima of magnetic field value along the line of sight results in increasing optical thickness of the gyroresonance layers at appropriate frequencies in the microwave band and, therefore, in enhanced radio emission at those harmonics which are optically thin (for example,s=4). These cannot be observed in models with the commonly employed magnetic field configuration (longitudinal along the loop axis).We show that the frequency spectrum of thermal cyclotron radiation from a hot coronal loop with a helical magnetic field differs from that of the standards-component source (with smooth frequency characteristics and polarization corresponding toe-mode) in that plenty of fine structures (line-like features and cut-offs) are present and theo-mode is prevalent in some frequency intervals. The enhanced radio emission at high harmonics and the complicated form of frequency spectrum in the model considered imply that some microwave sources, which are poorly explained in traditional models of solar active regions, may be associated with helical magnetic fields in hot coronal loops. Computations allow one to indicate spectral and polarizational peculiarities of local sources testifying to the presence of a helical magnetic field. 相似文献
85.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献
86.
Wiesław M. Macek 《Space Science Reviews》2006,122(1-4):329-337
The question of multifractality is of great importance because it allows us to investigate interplanetary hydromagnetic turbulence.
The multifractal spectrum has been investigated with Voyager (magnetic field) data in the outer heliosphere and with Helios
(plasma) data in the inner heliosphere. We use the Grassberger and Procaccia method that allows calculation of the generalized
dimensions of the solar wind attractor in the phase space directly from the cleaned experimental signal. We analyze time series
of plasma parameters of the low-speed streams of the solar wind measured in situ by Helios in the inner heliosphere. The resulting spectrum of dimensions shows a multifractal structure of the solar wind
attractor. In order to quantify that multifractality, we use a simple analytical model of the dynamical system. Namely, we
consider the generalized self-similar baker’s map with two parameters describing uniform compression and natural invariant
measure on the attractor of the system. The action of this map exhibits stretching and folding properties leading to sensitive
dependence on initial conditions. The obtained solar wind singularity spectrum is consistent with that for the multifractal
measure on the weighted baker’s map. 相似文献
87.
Traditionally modeling for space science has concentrated on developing simulations for individual components of the solar
terrestrial system. In reality these regions are coupled together. This coupling can be as simple as the driving of the magnetosphere
– ionosphere – thermosphere system by the solar wind or as a complicated as the feedback of the ionospheric conductivity and
currents on the magnetosphere. As part of the CISM project we are beginning a concentrated effort to compressively model the
entire system. This approach includes chains of models. In the first chain physics based numerical models are utilized while
in the second chain empirical models are coupled together. The first half of this paper discusses the numerical modeling approach
by highlighting the coupling of pairs of regions within the system. In the second section we present results from empirical
models which are combined to make long term forecasts of conditions in the geospace environment. It is expected that a validated
and reliable forecast model for space weather can be obtained by combining the strongest elements of each chain. 相似文献
88.
Infrared spectroscopic observations of planets and Saturn's satellite Titan with the Infrared Space Observatory led to many
significant discoveries that improved our understanding on the formation, physics and chemistry of these objects. The prime
results achieved by ISO are: (1) a new and consistent determination of the D/H ratios on the giant planets and Titan; (2)
the first precise measurement of the 15N/14N ratio in Jupiter, a valuable indicator of the protosolar nitrogen isotopic ratio; (3) the first detection of an external
oxygen flux for all giant planets and Titan; (4) the first detection of some stratospheric hydrocarbons (CH3, C2H4, CH3C2H, C4H2, C6H6); (5) the first detection of tropospheric water in Saturn; (6) the tentative detection of carbonate minerals on Mars; (7)
the first thermal lightcurve of Pluto.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
89.
A Class of TVD Type Combined Numerical Scheme for MHD Equations With a Survey About Numerical Methods in Solar Wind Simulations 总被引:3,自引:0,他引:3
It has been believed that three-dimensional, numerical, magnetohydrodynamic (MHD) modelling must play a crucial role in a
seamless forecasting system. This system refers to space weather originating on the sun; propagation of disturbances through
the solar wind and interplanetary magnetic field (IMF), and thence, transmission into the magnetosphere, ionosphere, and thermosphere.
This role comes as no surprise to numerical modelers that participate in the numerical modelling of atmospheric environments
as well as the meteorological conditions at Earth. Space scientists have paid great attention to operational numerical space
weather prediction models. To this purpose practical progress has been made in the past years. Here first is reviewed the
progress of the numerical methods in solar wind modelling. Then, based on our discussion, a new numerical scheme of total
variation diminishing (TVD) type for magnetohydrodynamic equations in spherical coordinates is proposed by taking into account
convergence, stability and resolution. This new MHD model is established by solving the fluid equations of MHD system with
a modified Lax-Friedrichs scheme and the magnetic induction equations with MacCormack II scheme for the purpose of developing
a combined scheme of quick convergence as well as of TVD property. To verify the validation of the scheme, the propagation
of one-dimensional MHD fast and slow shock problem is discussed with the numerical results conforming to the existing results
obtained by the piece-wise parabolic method (PPM). Finally, some conclusions are made.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
90.
Examples of solar microwave precursors and estimates of their energetic characteristics are discussed based on spectral investigations of the preflare activity. 相似文献