全文获取类型
收费全文 | 2202篇 |
免费 | 324篇 |
国内免费 | 598篇 |
专业分类
航空 | 1762篇 |
航天技术 | 425篇 |
综合类 | 401篇 |
航天 | 536篇 |
出版年
2024年 | 14篇 |
2023年 | 43篇 |
2022年 | 56篇 |
2021年 | 107篇 |
2020年 | 89篇 |
2019年 | 105篇 |
2018年 | 107篇 |
2017年 | 117篇 |
2016年 | 124篇 |
2015年 | 133篇 |
2014年 | 138篇 |
2013年 | 138篇 |
2012年 | 164篇 |
2011年 | 180篇 |
2010年 | 129篇 |
2009年 | 120篇 |
2008年 | 162篇 |
2007年 | 147篇 |
2006年 | 146篇 |
2005年 | 106篇 |
2004年 | 83篇 |
2003年 | 76篇 |
2002年 | 84篇 |
2001年 | 77篇 |
2000年 | 56篇 |
1999年 | 57篇 |
1998年 | 55篇 |
1997年 | 45篇 |
1996年 | 32篇 |
1995年 | 35篇 |
1994年 | 41篇 |
1993年 | 26篇 |
1992年 | 33篇 |
1991年 | 22篇 |
1990年 | 29篇 |
1989年 | 24篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有3124条查询结果,搜索用时 281 毫秒
961.
M.C. Rabello-Soares B.J. Thompson D. Scherrer C. Morrow 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1206-1211
Education and public outreach (EPO) is one of the four components of the International Heliophysical Year (IHY). It is fundamental in achieving one of IHY’s primary objectives which is to “demonstrate the beauty, relevance and significance of Space and Earth science to the world.” 相似文献
962.
根据教育社会学理论分析,班级具有社会化功能、选择功能、个性化功能和保护功能。大学中班级仍然是学生学习知识技能、接受思想道德教育的基本单位,其社会化、选择、个性化和保护功能有独特的内容和作用机制。在班级管理中做到教育管理与学生自治相结合、专业教育与生涯规划相结合、生活指导与心理保健相结合,充分发挥班级社会功能,完善大学班级管理,促进学生全面发展。 相似文献
963.
M.V. Alania K. Iskra M. Siluszyk 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(2):267-274
We find that the soft rigidity spectrum of the Galactic Cosmic Ray (GCR) intensity variations for the maximum epoch and the hard rigidity spectrum for the minimum epoch calculated based on the neutron monitors experimental data (1960–2002) are related with the various dependence of the diffusion coefficient on the GCR particle’s rigidity for different epoch of solar activity. This dependence is stronger in the maximum epoch than in the minimum epoch of solar activity, and is provided by the essential temporal rearrangements of the structure of the Interplanetary Magnetic Field (IMF) turbulence from the maxima to minima epoch of solar activity. We also show that the rigidity spectrum of GCR intensity variations is harder for the effective rigidities ∼(10–15) GV (by neutron monitors data), than for the effective rigidities ∼(25–30) GV (by neutron monitors and muon telescopes data). A general scenario of GCR modulation versus solar activity is settled on the essential temporal rearrangements of the structure of the IMF turbulence. Therefore, the temporal changes of the power law rigidity spectrum exponent can be considered as a vital (new) index to explain the 11-year variations of the GCR intensity. We assume that ∼(70–80)% of the changes of the amplitudes of the 11-year variations of GCR intensity is related with the changes of the IMF turbulence versus solar activity. 相似文献
964.
发扬艰苦奋斗的创业精神目的是为了实现共产主义,创建社会主义和谐社会的方向是通向未来的共产主义社会。艰苦奋斗的创业精神与社会主义和谐社会的创建有着密切的联系。 相似文献
965.
Eduard V. Vashenyuk Yury V. Balabin Leonty I. Miroshnichenko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(6):926-935
In this study we applied again to the outstanding solar particle event of 23 February 1956, the largest one in the entire history of observations of solar cosmic rays. Due to significant improvement of the analysis/modeling techniques and new understanding of physical processes in the solar atmosphere and interplanetary space, a possibility arises to interpret the old data in the light of modern concept of multiple particle acceleration at/near the Sun. In our new analysis the data of available then neutron monitors and muon telescopes are used. The technique of the analysis includes: (a) calculation of asymptotic cones of ground-based detectors; (b) modeling of cosmic ray detector responses at variable parameters of the flux of solar relativistic protons; (c) determination of primary solar proton parameters outside magnetosphere by comparison of computed responses with observations. Certain evidence was obtained that the flux of relativistic solar protons consisted of two distinct components: prompt and delayed ones. The prompt component with exponential energy spectrum caused a giant impulse-like increase at a number of European cosmic ray stations. The delayed component had a power-law spectrum and was a cause of gradual increase at cosmic ray stations in the North American region. A numerical simulation of the proton acceleration in the vicinity of the magnetic reconnection region brings to the proton spectrum with exponential dependence on energy. This agrees with observational data for the prompt component. It is also shown that the huge increase in ∼5000% on neutron monitors was due to the prompt component only with the exponential proton spectrum. The power-law spectrum of comparable intensity gave considerably smaller effect. 相似文献
966.
Electron and proton acceleration by a super-Dreicer electric field is further investigated in a non-neutral reconnecting current
sheet (RCS) with a variable plasma density. The tangential B
z
and transverse magnetic field components B
x
are assumed to vary with the distances x and z from the X nullpoint linearly and exponentially, respectively; the longitudinal component (a ‘guiding field’) is accepted
constant. Particles are found to gain a bulk of their energy in a thin region close to the X nullpoint where the RCS density
increases with z exponentially with the index λ and the tangential magnetic field B
x
also increases with z exponentially with the index α. For the RCS with a constant density (λ = 0), the variations of the tangential magnetic field
lead to particle power-law energy spectra with the spectral indices γ1 being dependent on the exponent α as:
for protons and
for electrons in a strong guiding field (β > 10−2) and
for electrons in a moderate or weak guiding field (β > 10−4). For the RCS with an exponential density increase in the vicinity of the X nullpoint (λ≥ 0) there is a further increase
of the resulting spectral indices γ that depends on the density exponent index λ as
for protons and for electrons in weaker guiding fields and as
for electrons in stronger guiding fields. These dependencies can explain a wide variety (1.5–10) of particle spectral indices
observed in solar flares by the variations of a magnetic field topology and physical conditions in a reconnecting region.
This can be used as a diagnostic tool for the investigation of the RCS dynamics from the accelerated particle spectra found
from hard X-ray and microwave emission. 相似文献
967.
系统科学与民航安全文化建设 总被引:2,自引:0,他引:2
用现代系统理论观战,审视了中国民航安全文化建设的历史经验,得出了有益于安全文化建设的指导思想。首先,通过对安全文化与民航系统的协同问题的分析,探讨了对”安全第一“原则的深层次理解及在实际工作中的把握;其次,研究了系统的运动与安全文化发展的内在关系,提出了保证安全文化建设健康发展的思路。 相似文献
968.
麻智辉 《郑州航空工业管理学院学报(管理科学版)》2007,25(4):1-6
城市群是区域经济的重要增长极。要在中部崛起中加快江西的发展,就必须构建以南昌为中心,九江、景德镇、鹰潭为次中心,涵盖22个县(市)的环鄱阳湖城市群,整合区域内经济、文化、科技和资源优势,加快区域交通、产业、商贸、产权、金融、技术、人才、信息市场一体化进程,使之成为中部地区最具竞争力的经济区。 相似文献
969.
考虑预腐蚀对飞机结构疲劳寿命的影响,建立了疲劳寿命服从Weibull分布的 加速腐蚀因子确定方法.假设预腐蚀疲劳寿命服从Weibull分布,特征寿命随时间呈指数规 律变化,推导得到了以疲劳寿命为腐蚀量的加速腐蚀因子表达式,以及在工程常用的时间范 围内加速腐蚀因子与腐蚀时间无关的结论;进行了相关参数估计,建立了加速腐蚀 因子的估计方法,得到了加速腐蚀因子估计量的近似分布,对其进行了统计分析. 相似文献
970.
飞机大迎角滚转运动频率域建模与稳定性分析 总被引:1,自引:0,他引:1
本文运用频率域建模法,分别建立了飞机大迎角滚转运动的Fourier变换模型及非线性代数模型,并从数学模型中提取动导数。基于非线性非定常数学模型与局部线化的动导数数学模型,计算了飞机滚转运动的稳定性,并运用李雅普诺夫稳定性分析理论,进行飞机滚转运动稳定性分析。结果表明,大振幅非定常滚转运动实验可以用于飞机绕体轴滚转运动的稳定性分析。从大振幅实验数据提取的动导数,基本反映了飞机的非定常气动力特性。通过 相似文献