全文获取类型
收费全文 | 1406篇 |
免费 | 193篇 |
国内免费 | 148篇 |
专业分类
航空 | 967篇 |
航天技术 | 466篇 |
综合类 | 97篇 |
航天 | 217篇 |
出版年
2024年 | 5篇 |
2023年 | 24篇 |
2022年 | 37篇 |
2021年 | 55篇 |
2020年 | 54篇 |
2019年 | 62篇 |
2018年 | 55篇 |
2017年 | 54篇 |
2016年 | 59篇 |
2015年 | 43篇 |
2014年 | 108篇 |
2013年 | 82篇 |
2012年 | 72篇 |
2011年 | 93篇 |
2010年 | 72篇 |
2009年 | 80篇 |
2008年 | 106篇 |
2007年 | 110篇 |
2006年 | 99篇 |
2005年 | 61篇 |
2004年 | 35篇 |
2003年 | 37篇 |
2002年 | 31篇 |
2001年 | 51篇 |
2000年 | 24篇 |
1999年 | 20篇 |
1998年 | 28篇 |
1997年 | 8篇 |
1996年 | 22篇 |
1995年 | 25篇 |
1994年 | 69篇 |
1993年 | 29篇 |
1992年 | 8篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1984年 | 15篇 |
排序方式: 共有1747条查询结果,搜索用时 15 毫秒
21.
Els Peeters Nieves Leticia Martín-HernáNdez Nemesio J. RodríGuez-FernáNdez Xander Tielens 《Space Science Reviews》2005,119(1-4):273-292
An overview is given of ISO results on regions of high excitation ISM and gas, i.e. HII regions, the Galactic Centre and Supernova Remnants. IR emission due to fine-structure lines, molecular hydrogen, silicates,
polycyclic aromatic hydrocarbons and dust are summarised, their diagnostic capabilities illustrated and their implications
highlighted.
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
22.
介绍了逻辑分析仪部分参数测量结果的不确定度分析评定方法,评定过程及结论,可应用在对于计量标准进行相应指标的不确定度评定分析上。 相似文献
23.
The formation of planetary systems is intimately tied to the question of the evolution of the gas and solid material in the
early nebula. Current models of evolution of circumstellar disks are reviewed here with emphasis on the so-called “alpha models”
in which angular momentum is transported outward by turbulent viscosity, parameterized by an dimensionless parameter α. A
simple 1D model of protoplanetary disks that includes gas and embedded particles is used to introduce key questions on planetesimal
formation. This model includes the aerodynamic properties of solid ice and rock grains to calculate their migration and growth.
We show that the evolution of the nebula and migration and growth of its solids proceed on timescales that are generally not
much longer than the timescale necessary to fully form the star-disk system from the molecular cloud. Contrary to a widely
used approach, planet formation therefore can neither be studied in a static nebula nor in a nebula evolving from an arbitrary initial condition. We propose a simple approach to both account for sedimentation
from the molecular cloud onto the disk, disk evolution and migration of solids.
Giant planets have key roles in the history of the forming Solar System: they formed relatively early, when a significant
amount of hydrogen and helium were still present in the nebula, and have a mass that is a sizable fraction of the disk mass
at any given time. Their composition is also of interest because when compared to the solar composition, their enrichment
in elements other than hydrogen and helium is a witness of sorting processes that occured in the protosolar nebula. We review
likely scenarios capable of explaining both the presence of central dense cores in Jupiter, Saturn, Uranus and Neptune and
their global composition.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
24.
A lightning swept stroke model: A valuable tool to investigate the lightning strike to aircraft 总被引:1,自引:0,他引:1
Alain Broc Philippe Lalande Emmanuel Montreuil Jean-Patrick Moreau Alain Delannoy Anders Larsson Pierre Laroche 《Aerospace Science and Technology》2006,10(8):700-708
In the context of lightning strike on the Dassault Falcon family of aircraft, the standard zoning of Falcon 50, 900 and 2000, inferred from FAA and EUROCAE WG31 documents [US Department of Transportation, Federal Aviation Administration, Advisory Circular AC 20-53A, 1985; US Department of Transportation, Federal Aviation Administration, Advisory Circular AC 20-53B, Draft, 1991; EUROCAE WG 31, Aircraft Lightning Zoning Standard, ED-91, 1998], has been presented. Zoning proves to be quite similar between the three types of aircraft. Thanks to the feed-back on lightning strikes to Falcon, lightning traces have been observed on the fuselage for different flight conditions and aircraft. Observations are compared with the zoning performed by Dassault. A physical model, developed by ONERA, was used to simulate the sweeping of lightning on the fuselage of a Falcon 900. The results are in good agreement with the lightning traces observed on the fuselages. 相似文献
25.
基于光滑粒子流体动力学方法(Smoothed Particle Hydrodynamics,SPH),开展了SPH新算法在蒸发燃烧领域的研究。建立了适用于SPH方法的蒸发数值模型,推导了基于傅立叶热传导公式和菲克扩散定律的SPH离散方程;借鉴VOF方法(Volume of Fluid)的思想,提出了SPH粒子的液相质量分数的概念,以有效表征蒸发过程中的相变问题。采用SPH方法对高温环境中单个液滴的蒸发过程进行数值模拟,结果符合D 2 ![]()
![]()
定律,与理论模型相一致;在强迫对流环境中,液滴的蒸发过程受到对流作用及表面张力的影响,蒸发速率加快;进一步对双液滴在静止、对流环境中的蒸发过程进行数值模拟研究。结果表明,液滴的间距、滴径对多个液滴的蒸发过程影响至关重要,液滴间距至少在两倍的液滴直径以上,相互之间的影响才可以近似忽略。通过本文研究,拓宽了SPH方法在蒸发相变领域的应用范围,研究结果也能够为进一步的燃烧问题研究奠定基础。 相似文献
26.
构建高职数控技术应用专业课程体系的改革与实践 总被引:2,自引:0,他引:2
宋文学 《西安航空技术高等专科学校学报》2005,23(3):18-20
课程体系是衡量学校办学水平和教学质量的重要标志,是实现培养目标的基本保证。从构建课程体系前提、人才培养目标、人才培养机制、课程体系构建、课程体系改革的效果等几个方面对数控技术应用专业课程体系建设进行了探讨,初步构建了产学研结合的人才培养途径,建立了理论体系和实践体系相结合的课程体系。 相似文献
27.
28.
Parameters of expanding magnetic loops and arches and of mass flows generated by them in the corona have been computed in a 1D two-fluid approximation. Two possible trigger mechanisms of the coronal transients have been considered: (i) sudden increase of the background magnetic field strength, and (ii) heating and compression plasma inside these magnetic structures. We discuss the formation of shock waves and their dependence on dynamics and geometry of the magnetic structures. 相似文献
29.
30.
R. J. Murphy 《Space Science Reviews》2007,130(1-4):127-138
Interactions of ions accelerated in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain
a rich set of observables that provides information about both the accelerated ions and the environment where the ions are
transported and interact. Ion interactions with the various nuclei present in the ambient medium produce gamma-ray lines at
unique energies. How abundance information is extracted from the measurements is discussed and results from analyses of a
number of solar flares are presented. The analyses indicate that the composition of the ambient gas where the ions interact
(typically at chromospheric densities) is different from that of the photosphere and more like the composition of the corona,
exhibiting low-FIP elemental enhancements that may vary from flare to flare. Evidence for increased Ne/O and the photospheric
3He abundance is also discussed. 相似文献