全文获取类型
收费全文 | 3578篇 |
免费 | 9篇 |
国内免费 | 7篇 |
专业分类
航空 | 1441篇 |
航天技术 | 1088篇 |
综合类 | 20篇 |
航天 | 1045篇 |
出版年
2022年 | 15篇 |
2021年 | 42篇 |
2019年 | 19篇 |
2018年 | 185篇 |
2017年 | 134篇 |
2016年 | 116篇 |
2015年 | 46篇 |
2014年 | 115篇 |
2013年 | 148篇 |
2012年 | 128篇 |
2011年 | 191篇 |
2010年 | 137篇 |
2009年 | 206篇 |
2008年 | 208篇 |
2007年 | 141篇 |
2006年 | 84篇 |
2005年 | 117篇 |
2004年 | 103篇 |
2003年 | 121篇 |
2002年 | 86篇 |
2001年 | 120篇 |
2000年 | 42篇 |
1999年 | 58篇 |
1998年 | 65篇 |
1997年 | 45篇 |
1996年 | 46篇 |
1995年 | 81篇 |
1994年 | 62篇 |
1993年 | 39篇 |
1992年 | 49篇 |
1990年 | 21篇 |
1989年 | 44篇 |
1988年 | 12篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 78篇 |
1984年 | 63篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 83篇 |
1980年 | 28篇 |
1979年 | 17篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1972年 | 13篇 |
1967年 | 13篇 |
1966年 | 13篇 |
排序方式: 共有3594条查询结果,搜索用时 31 毫秒
951.
Ground level events (GLEs) occupy the high-energy end of gradual solar energetic particle (SEP) events. They are associated with coronal mass ejections (CMEs) and solar flares, but we still do not clearly understand the special conditions that produce these rare events. During Solar Cycle 23, a total of 16 GLEs were registered, by ground-based neutron monitors. We first ask if these GLEs are clearly distinguishable from other SEP events observed from space. Setting aside possible difficulties in identifying all GLEs consistently, we then try to find observables which may unmistakably isolate these GLEs by studying the basic properties of the associated eruptions and the active regions (ARs) that produced them. It is found that neither the magnitudes of the CMEs and flares nor the complexities of the ARs give sufficient conditions for GLEs. It is possible to find CMEs, flares or ARs that are not associated with GLEs but that have more extreme properties than those associated with GLEs. We also try to evaluate the importance of magnetic field connection of the AR with Earth on the detection of GLEs and their onset times. Using the potential field source surface (PFSS) model, a half of the GLEs are found to be well-connected. However, the GLE onset time with respect to the onset of the associated flare and CME does not strongly depend on how well-connected the AR is. The GLE onset behavior may be largely determined by when and where the CME-driven shock develops. We could not relate the shocks responsible for the onsets of past GLEs with features in solar images, but the combined data from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) have the potential to change this for GLEs that may occur in the rising phase of Solar Cycle 24. 相似文献
952.
The ARTEMIS Mission 总被引:2,自引:0,他引:2
V. Angelopoulos 《Space Science Reviews》2011,165(1-4):3-25
The Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon??s Interaction with the Sun (ARTEMIS) mission is a spin-off from NASA??s Medium-class Explorer (MIDEX) mission THEMIS, a five identical micro-satellite (hereafter termed ??probe??) constellation in high altitude Earth-orbit since 17 February 2007. By repositioning two of the five THEMIS probes (P1 and P2) in coordinated, lunar equatorial orbits, at distances of ??55?C65 R E geocentric (??1.1?C12 R L selenocentric), ARTEMIS will perform the first systematic, two-point observations of the distant magnetotail, the solar wind, and the lunar space and planetary environment. The primary heliophysics science objectives of the mission are to study from such unprecedented vantage points and inter-probe separations how particles are accelerated at reconnection sites and shocks, and how turbulence develops and evolves in Earth??s magnetotail and in the solar wind. Additionally, the mission will determine the structure, formation, refilling, and downstream evolution of the lunar wake and explore particle acceleration processes within it. ARTEMIS??s orbits and instrumentation will also address key lunar planetary science objectives: the evolution of lunar exospheric and sputtered ions, the origin of electric fields contributing to dust charging and circulation, the structure of the lunar interior as inferred by electromagnetic sounding, and the lunar surface properties as revealed by studies of crustal magnetism. ARTEMIS is synergistic with concurrent NASA missions LRO and LADEE and the anticipated deployment of the International Lunar Network. It is expected to be a key element in the NASA Heliophysics Great Observatory and to play an important role in international plans for lunar exploration. 相似文献
953.
Colangeli L. Mennella V. Brucato J.R. Palumbo P. Rotundi A. 《Space Science Reviews》1999,90(1-2):341-354
One of the main objectives of modern astrophysics is the characterisation of properties and evolution of materials present
in space. Production, processing and analysis of cosmic dust analogues in the laboratory represents a powerful tool to interpret
astronomical observations and to contribute to the solution of puzzling problems which are so far unsolved. In the present
paper we summarize recent results obtained in our laboratory on carbon-based and silicate materials able to simulate various
types of cosmic grains. The laboratory data are applied to discuss the nature of spectral features observed in the interstellar
medium and in comets.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
954.
W. I. Axford J. F. McKenzie G. V. Sukhorukova M. Banaszkiewicz A. Czechowski R. Ratkiewicz 《Space Science Reviews》1999,87(1-2):25-41
We outline a theory for the origin and acceleration of the fast solar wind as a consequence of network microflares releasing
a spectrum of high frequency Alfvén waves which heat (by cyclotron absorption) the corona close to the Sun. The significant
features of our model of the fast wind are that the acceleration is rapid with the sonic point at around two solar radii,
the proton temperatures are high (~ 5 million degrees) and the minor ions are correspondingly hotter, roughly in proportion
to their mass. Moreover we argue that since the energy flux needed to power the quiet corona in closed field regions is about
the same as that needed to drive the fast solar wind, and also because at deeper levels (< 2 × 105 K) there is no great difference in the properties of supergranules and network in closed and open field regions, the heating
process (i.e., dissipation of high frequency waves) must be the same in both cases.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
955.
Vasiliev I.A. Ivashov S.I. Makarenkov V.I. Sablin V.N. Sheyko A.P. 《Aerospace and Electronic Systems Magazine, IEEE》1999,14(5):25-29
A subsurface radar using a multi-frequency signal has been developed. It is designated for surveying building structures and works. The characteristic feature of this device is the possibility of obtaining sounding plane radio images featuring a high resolution attaining 1…2 cm. The main applications of this device includes the survey of building structures to reveal their heterogeneities and defects and the investigation of premises to detect bugging devices 相似文献
956.
Formation and Evolution of Corotating Interaction Regions and their Three Dimensional Structure 总被引:1,自引:0,他引:1
Corotating interaction regions are a consequence of spatial variability in the coronal expansion and solar rotation, which
cause solar wind flows of different speeds to become radially aligned. Compressive interaction regions are produced where
high-speed wind runs into slower plasma ahead. When the flow pattern emanating from the Sun is roughly time-stationary these
compression regions form spirals in the solar equatorial plane that corotate with the Sun, hence the name corotating interaction
regions, or CIRs. The leading edge of a CIR is a forward pressure wave that propagates into the slower plasma ahead, while
the trailing edge is a reverse pressure wave that propagates back into the trailing high-speed flow. At large heliocentric
distances the pressure waves bounding a CIR commonly steepen into forward and reverse shocks. Spatial variation in the solar
wind outflow from the Sun is a consequence of the solar magnetic field, which modulates the coronal expansion. Because the
magnetic equator of the Sun is commonly both warped and tilted with respect to the heliographic equator, CIRs commonly have
substantial north-south tilts that are opposed in the northern and southern hemispheres. Thus, with increasing heliocentric
distance the forward waves in both hemispheres propagate toward and eventually across the solar equatorial plane, while the
reverse shocks propagate poleward to higher latitudes. This paper provides an overview of observations and numerical models
that describe the physical origin and radial evolution of these complex three-dimensional (3-D) heliospheric structures.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
957.
V.B. Betelin N.N. Smirnov V.F. Nikitin V.R. Dushin A.G. Kushnirenko V.A. Nerchenko 《Acta Astronautica》2012
Computer simulation of liquid fuel jet injection into heated atmosphere of combustion chamber, mixture formation, ignition and combustion need adequate modeling of evaporation, which is extremely important for the curved surfaces in the presence of strong heat and mass diffusion fluxes. Combustion of most widely spread hydrocarbon fuels takes place in a gas-phase regime. Thus, evaporation of fuel from the surface of droplets turns to be one of the limiting factors of the process as well. The problems of fuel droplets atomization, evaporation being the key factors for heterogeneous reacting mixtures, the non-equilibrium effects in droplets atomization and phase transitions will be taken into account in describing thermal and mechanical interaction of droplets with streaming flows. In the present paper processes of non-equilibrium evaporation of small droplets will be discussed. As it was shown before, accounting for non-equilibrium effects in evaporation for many types of widely used liquids is crucial for droplet diameters less than 100 μm, while the surface tension effects essentially manifest only for droplets below 0.1 μm. Investigating the behavior of individual droplets in a heated air flow allowed to distinguish two scenarios for droplet heating and evaporation. Small droplets undergo successively heating, then cooling due to heat losses for evaporation, and then rapid heating till the end of their lifetime. Larger droplets could directly be heated up to a critical temperature and then evaporate rapidly. Droplet atomization interferes the heating, evaporation and combustion scenario. The scenario of fuel spray injection and self-ignition in a heated air inside combustion chamber has three characteristic stages. At first stage of jet injection droplets evaporate very rapidly thus cooling the gas at injection point, the liquid jet is very short and changes for a vapor jet. At second stage liquid jet is becoming longer, because evaporation rate decreases due to decrease of temperature. But combustion of fuel vapor begins which brings to increase of heat flux to droplets and accelerates evaporation. The length of the liquid jet decreases again and remains constant slightly oscillating. 相似文献
958.
I. V. Mingalev N. M. Astaf’eva K. G. Orlov V. M. Chechetkin V. S. Mingalev O. V. Mingalev 《Cosmic Research》2012,50(3):233-248
Mechanisms of formation of cyclonic vortices in the tropical atmosphere of the Earth are investigated in the intratropical
zone of convergence using numerical simulation made with the complete system of equations of gas dynamics taking into account
transport of infrared radiation, phase transitions of water vapor into microdrops of water and ice particles, and sedimentation
of these drops and ice particles in the field of gravity force. Observational data on the structure of dominant air streams,
which are formed in the intratropical zone of convergence over the North Atlantic in the periods of its highest thermodynamic
intensity and instability, are used in the initial and boundary conditions of the model. Formation of cyclonic vortex flows
is obtained numerically at sufficiently strong bending of the intratropical zone of convergence. The results of numerical
modeling are compared with the data of satellite microwave monitoring: global radio thermal fields of the Earth from the electronic
collection GLOBAL-Field allowing one to study the structure of atmospheric motions in a wide range of space-time scales. 相似文献
959.
Statistical studies of properties of the solar wind and interplanetary magnetic field, based on an extended database for the
period 1963–2007 including four solar cycles, show that the Gaussian approximation well suites for some parameters as the
probability distribution of their numerical values, while for others the lognormal law is preferred. This paper gives an interpretation
of these results as associated with predominance of linear or nonlinear processes in composition and interaction of various
disturbances and irregularities propagating and originating in the interior of the Sun and its atmosphere, including the solar
corona and the solar wind running away from it. Summation of independent random components of disturbances leads, according
to the central limit theorem of the probability theory, to the normal (Gaussian) distributions of quantities proper, while
their multiplication leads to the normal distributions of logarithms. Thus, one can discuss the algebra of events and associate
observed statistical distinctions with one or another process of formation of irregularities in the solar wind. Among them
there are impossible events (having null probability) and reliable events (occurring with 100% probability). For better understanding
of the relationship between algebra and statistics of events in the solar wind further investigations are necessary. 相似文献
960.
Robert H. Nichols Jr. 《Space Science Reviews》2000,92(1-2):113-122
Variations in the abundances of short-lived radionuclides such as 26Al (τ1/2 ≈ 0.74 Ma) and 53Mn (τ1/2 ≈ 3.7 Ma) in meteoritic solids may be used to infer relative formation intervals of these solids in the nebula at precisions
of less than 1 Ma. In a strict chronometric interpretation of the isotopic variations, whereby criteria such as spatial and
temporal isotopic homogeneity and closed system isotopic evolution are met, solid formation occurred in the nebula for at
least several million years. This is longer than some theoretical and astronomical estimates for the duration of the active
nebula. The evidence for live 41Ca (τ1/2 ≈ 0.10 Ma) in meteoritic inclusions further indicates that the onset of solid formation occurred quite early, perhaps within
a few hundred thousand years after the onset of the collapse of the sun's parent molecular cloud. Failure of the chronometric
interpretation may arise for a variety of reasons, including but not limited to, the late, inhomogeneous injection of material
from a nearby stellar source or the local production of short-lived radionuclides by an energetic particle irradiation, e. g., from T Tauri (X-wind) or galactic cosmic ray sources. Although some isotopic evidence exists that the criteria required
for a strict chronometric interpretation are not met by each of the short-lived chronometers, there is no compelling reason
to shorten the interval of solid formation in the nebula to less than 1 Ma.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献