全文获取类型
收费全文 | 8386篇 |
免费 | 318篇 |
国内免费 | 254篇 |
专业分类
航空 | 4167篇 |
航天技术 | 2773篇 |
综合类 | 218篇 |
航天 | 1800篇 |
出版年
2022年 | 74篇 |
2021年 | 129篇 |
2020年 | 65篇 |
2019年 | 92篇 |
2018年 | 203篇 |
2017年 | 152篇 |
2016年 | 162篇 |
2015年 | 120篇 |
2014年 | 268篇 |
2013年 | 302篇 |
2012年 | 310篇 |
2011年 | 441篇 |
2010年 | 332篇 |
2009年 | 426篇 |
2008年 | 443篇 |
2007年 | 306篇 |
2006年 | 238篇 |
2005年 | 275篇 |
2004年 | 237篇 |
2003年 | 248篇 |
2002年 | 190篇 |
2001年 | 267篇 |
2000年 | 164篇 |
1999年 | 221篇 |
1998年 | 238篇 |
1997年 | 138篇 |
1996年 | 211篇 |
1995年 | 240篇 |
1994年 | 228篇 |
1993年 | 163篇 |
1992年 | 187篇 |
1991年 | 89篇 |
1990年 | 66篇 |
1989年 | 166篇 |
1988年 | 81篇 |
1987年 | 63篇 |
1986年 | 70篇 |
1985年 | 185篇 |
1984年 | 146篇 |
1983年 | 111篇 |
1982年 | 116篇 |
1981年 | 217篇 |
1980年 | 50篇 |
1979年 | 45篇 |
1978年 | 50篇 |
1977年 | 42篇 |
1975年 | 51篇 |
1974年 | 39篇 |
1971年 | 35篇 |
1970年 | 37篇 |
排序方式: 共有8958条查询结果,搜索用时 15 毫秒
511.
512.
H. Kunow N. U. Crooker J. A. Linker R. Schwenn R. von Steiger 《Space Science Reviews》2006,123(1-3):1-2
513.
A. G. Yahnin I. V. Despirak A. A. Lubchich B. V. Kozelov N. P. Dmitrieva M. A. Shukhtina H. K Biernat 《Space Science Reviews》2006,122(1-4):97-106
Although the auroral substorm has been long regarded as a manifestation of the magnetospheric substorm, a direct relation
of active auroras to certain magnetospheric processes is still debatable. To investigate the relationship, we combine the
data of the UV imager onboard the Polar satellite with plasma and magnetic field measurements by the Geotail spacecraft. The
poleward edge of the auroral bulge, as determined from the images obtained at the LHBL passband, is found to be conjugated
with the region where the oppositely directed fast plasma flows observed in the near-Earth plasma sheet during substorms are
generated. We conclude that the auroras forming the bulge are due to the near-Earth reconnection process. This implies that
the magnetic flux through the auroral bulge is equal to the flux dissipated in the magnetotail during the substorm. Comparison
of the magnetic flux through the auroral bulge with the magnetic flux accumulated in the tail lobe during the growth phase
shows that these parameters have the comparable values. This is a clear evidence of the loading–unloading scheme of substorm
development. It is shown that the area of the auroral bulge developing during substorm is proportional to the total (magnetic
plus plasma) pressure decrease in the magnetotail. These findings stress the importance of auroral bulge observations for
monitoring of substorm intensity in terms of the magnetic flux and energy dissipation. 相似文献
514.
Y. Futaana S. Barabash A. Grigoriev D. Winningham R. Frahm M. Yamauchi R. Lundin 《Space Science Reviews》2006,126(1-4):315-332
As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case
of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board
the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian
exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485
of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed
by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was
most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can
be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation
region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went
out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic
flux variations of the ENA flux at the spacecraft location. 相似文献
515.
We present a brief introduction to the essential physics of coronal mass ejections as well as a review of theory and models
of CME initiation, solar energetic particle (SEP) acceleration, and shock propagation. A brief review of the history of CME
models demonstrates steady progress toward an understanding of CME initiation, but it is clear that the question of what initiates
CMEs has still not been solved. For illustration, we focus on the flux cancellation model and the breakout model. We contrast
the similarities and differences between these models, and we examine how their essential features compare with observations.
We review the generation of shocks by CMEs. We also outline the theoretical ideas behind the origin of a gradual SEP event
at the evolving CME-driven coronal/interplanetary shock and the origin of “impulsive” SEP events at flare sites of magnetic
reconnection below CMEs. We argue that future developments in models require focused study of “campaign events” to best utilize
the wealth of available CME and SEP observations. 相似文献
516.
介绍了飞机采购费用的构成,概述了飞机采购费用的估算方法;简单描述了人工神经网络的基本原理,以此构建了BP网络模型;最后,利用神经网络方法对飞机采购费用进行估算,并用MATLAB进行仿真,取得了比较满意的结果。 相似文献
517.
介绍了第三代战斗机发动机的设计特点和研制规律;综述了F119和F135等第四代战斗机发动机的研制现状,总结了其性能和结构特点;归纳了战斗机发动机性能、结构和材料的发展趋势;展望了未来战斗机发动机的发展。 相似文献
518.
519.
Structure of a two-phase flow of boiling water at low-head adiabatic efflux through the laval nozzle
The critical flow conditions and structural forms of a two-phase flow that is formed during water efflux from the region of moderate and low pressures into a rarefied medium are analyzed. The difference in the structural forms of a flow realized at the low-head efflux from the structure of a flow occurring in the fluid flow with moderate and high initial pressures is established. The critical pressure differential characterizing the establishment of the maximum flowrate is determined and the decisive influence of turbulence on the vapor phase generation and flow conditions of a two-phase medium is shown. 相似文献
520.
D. B. Reisenfeld D. S. Burnett R. H. Becker A. G. Grimberg V. S. Heber C. M. Hohenberg A. J. G. Jurewicz A. Meshik R. O. Pepin J. M. Raines D. J. Schlutter R. Wieler R. C. Wiens T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):79-86
Analysis of the Genesis samples is underway. Preliminary elemental abundances based on Genesis sample analyses are in good
agreement with in situ-measured elemental abundances made by ACE/SWICS during the Genesis collection period. Comparison of
these abundances with those of earlier solar cycles indicates that the solar wind composition is relatively stable between
cycles for a given type of flow. ACE/SWICS measurements for the Genesis collection period also show a continuum in compositional
variation as a function of velocity for the quasi-stationary flow that defies the simple binning of samples into their sources
of coronal hole (CH) and interstream (IS). 相似文献