全文获取类型
收费全文 | 7128篇 |
免费 | 12篇 |
国内免费 | 33篇 |
专业分类
航空 | 3148篇 |
航天技术 | 2611篇 |
综合类 | 23篇 |
航天 | 1391篇 |
出版年
2021年 | 65篇 |
2019年 | 44篇 |
2018年 | 209篇 |
2017年 | 127篇 |
2016年 | 102篇 |
2015年 | 44篇 |
2014年 | 169篇 |
2013年 | 208篇 |
2012年 | 189篇 |
2011年 | 298篇 |
2010年 | 202篇 |
2009年 | 338篇 |
2008年 | 397篇 |
2007年 | 221篇 |
2006年 | 176篇 |
2005年 | 219篇 |
2004年 | 217篇 |
2003年 | 250篇 |
2002年 | 162篇 |
2001年 | 249篇 |
2000年 | 148篇 |
1999年 | 166篇 |
1998年 | 184篇 |
1997年 | 145篇 |
1996年 | 176篇 |
1995年 | 226篇 |
1994年 | 202篇 |
1993年 | 108篇 |
1992年 | 166篇 |
1991年 | 56篇 |
1990年 | 61篇 |
1989年 | 146篇 |
1988年 | 49篇 |
1987年 | 54篇 |
1986年 | 71篇 |
1985年 | 211篇 |
1984年 | 150篇 |
1983年 | 121篇 |
1982年 | 152篇 |
1981年 | 197篇 |
1980年 | 54篇 |
1979年 | 35篇 |
1978年 | 42篇 |
1977年 | 43篇 |
1976年 | 37篇 |
1975年 | 37篇 |
1974年 | 44篇 |
1973年 | 32篇 |
1970年 | 31篇 |
1969年 | 26篇 |
排序方式: 共有7173条查询结果,搜索用时 671 毫秒
561.
M. E. Wiedenbeck 《Space Science Reviews》2013,176(1-4):35-46
The spectra of galactic cosmic rays that are observed inside the heliosphere result from the interaction of the spectra present in the local interstellar medium with the structured but turbulent magnetic field carried by the solar wind. Observational tests of solar modulation theory depend on comparisons between spectra inside and outside the heliosphere. Our knowledge of the local interstellar spectra are indirect, using extrapolations of interplanetary spectra measured at high energies where solar modulation effects are minimal and modeling of the physical processes that occur during particle acceleration and transport in the interstellar medium. The resulting estimates of the interstellar spectra can also be checked against observations of the effects that cosmic rays have on the chemistry of the interstellar medium and on the production of the diffuse galactic gamma-ray background. I review the present understanding of the local galactic cosmic-ray spectra, emphasizing the constraints set by observations and the uncertainties that remain. 相似文献
562.
Alfvén waves are considered to be viable transporters of the non-thermal energy required to heat the Sun’s quiescent atmosphere. An abundance of recent observations, from state-of-the-art facilities, have reported the existence of Alfvén waves in a range of chromospheric and coronal structures. Here, we review the progress made in disentangling the characteristics of transverse kink and torsional linear magnetohydrodynamic (MHD) waves. We outline the simple, yet powerful theory describing their basic properties in (non-)uniform magnetic structures, which closely resemble the building blocks of the real solar atmosphere. 相似文献
563.
Nikolai M. Gavrilov Andrej V. Koval Alexander I. Pogoreltsev Elena N. Savenkova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Parameterization of dynamical and thermal effects of stationary orographic gravity waves (OGWs) generated by the Earth’s surface topography is incorporated into a numerical model of general circulation of the middle and upper atmosphere. Responses of atmospheric general circulation and characteristics of planetary waves at altitudes from the troposphere up to the thermosphere to the effects of OGWs propagating from the earth surface are studied. Changes in atmospheric circulation and amplitudes of planetary waves due to variations of OGW generation and propagation in different seasons are considered. It is shown that during solstices the main OGW dynamical and heat effects occur in the middle atmosphere of winter hemispheres, where changes in planetary wave amplitudes due to OGWs may reach up to 50%. During equinoxes OGW effects are distributed more homogeneously between northern and southern hemispheres. 相似文献
564.
A model of the main support of the aircraft landing gear is presented and its dynamics is studied using the equations for the distributed motion of a wheel equipped with a brake. Stability of the support wheel rolling motion is analyzed and the brake parameter values which may cause stability loss are found. The results of numerical experiments are presented. 相似文献
565.
Three experiments are reported that used an interference paradigm to test the extent to which perceptual orientation to a task environment interfered with retrieval from long-term spatial memory. Visual and spatial sources of interference were tested. The findings were consistent with a spatial locus of interference and showed that orientation to the task environment disrupted the accessibility of relative direction under two retrieval conditions: when the imagined viewpoint was 180 degrees misaligned with the actual viewpoint and when the actual body location was anterior to the imagined body location. While the former finding replicates previous reports of interference in perspective-taking tasks, the latter finding is new and difficult for current models of spatial long-term memory retrieval to explain. More research is needed to articulate further the constraints that perceptual orientation to the task environment place on spatial retrieval and their implications for models of spatial memory. 相似文献
566.
A comparison of temporal profiles of low-energy ion intensity and magnetic field magnitude in different periods of solar activity
in the outer heliosphere is carried out using the data of the Voyager 1 and Voyager 2 spacecraft. It is shown that temporal, spectral, and statistical characteristics of particle fluxes and magnetic field in
the heliospheric regions before and after the terminal shock in 2002–2008 had similar dynamics in different hemispheres. This
similarity allowed one to assume that, in the region of the inner heliospheric boundary, a quasistable spatial structure existed
moving together with the terminal shock in accordance with the solar wind pressure, as well as, probably, under the action
of the interstellar medium. It was revealed that the spatial dimensions of most details of this structure are less on Voyager 2, which, probably, is due to variation of the solar activity level, difference in latitude of spacecraft disposition, and
also the influence of the interstellar magnetic field. 相似文献
567.
I. Antonenko G.R. Osinski M. Battler M. Beauchamp L. Cupelli A. Chanou R. Francis M.M. Mader C. Marion E. McCullough A.E. Pickersgill L.J. Preston B. Shankar T. Unrau D. Veillette 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Remote robotic data provides different information than that obtained from immersion in the field. This significantly affects the geological situational awareness experienced by members of a mission control science team. In order to optimize science return from planetary robotic missions, these limitations must be understood and their effects mitigated to fully leverage the field experience of scientists at mission control. 相似文献
568.
In this paper, we consider some typical values of motion parameters in exceptional situations when approaching to the helicopter critical flight regimes and present a technique for constructing the partial and integral informative functions of hazards at current flight regimes. Also described are the possibilities of their use for solving the problems of warning, informative crew support, and synthesizing the control algorithms to remove helicopter from the exceptional situation occurred. 相似文献
569.
Observations relevant to current models of the solar dynamo are presented, with emphasis on the history of solar magnetic activity and on the location and nature of the solar tachocline. The problems encountered when direct numerical simulation is used to analyse the solar cycle are discussed, and recent progress is reviewed. Mean field dynamo theory is still the basis of most theories of the solar dynamo, so a discussion of its fundamental principles and its underlying assumptions is given. The role of magnetic helicity is discussed. Some of the most popular models based on mean field theory are reviewed briefly. Dynamo models based on severe truncations of the full MHD equations are discussed. 相似文献
570.
I. A. Krivosheev A. G. Godovanyuk V. S. Fatikov G. I. Pogorelov 《Russian Aeronautics (Iz VUZ)》2010,53(1):57-62
A technique for linear interpolation of the multidimensional characteristics of a coaxial propeller fan with opposite rotation
propellers is proposed; the technique makes it possible to simulate the turbofan engine operation in the entire range of flight
conditions and reduce expenses for fullscale tests. The mathematical models obtained meet the requirements imposed in the
semi-full-scale simulation. 相似文献