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201.
L. S. Anderson-Huang 《Space Science Reviews》1998,85(1-2):203-213
The chromosphere-corona transition region of the Sun enjoys both simplicities of character and complexities of character which
result from its very thin geometrical extent. The simplicities derive from the reasonably clear view of the energy balance
(both observationally and theoretically), while the complexities derive from both the proximity of the not-so-clearly viewed
regions below and above, and the almost certain convolutions and perhaps discontinuities in the three dimensional geometry
of the transition sheet. While observational resolution and spectral information has improved greatly in recent years, the
problems associated with a single vantage point, the Earth and its environs, have not gone away. To understand the transition
region we must resolve structures radially and temporally as well as in the plane of the sky.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
202.
孙定浩 《空间控制技术与应用》2011,37(5):26-30
用分析法全面讨论脉宽调制器(IC:1842/3/4/5,1842A/3A/4A/5A)中振荡器的振荡特征参数(占空比D和频率f)与外接电阻R和电容C的关系.我们得到以R、C为自变量表达D和f的函数,以D、f为自变量求R、C的函数.并根据这些函数的计算结果绘制描述D、f、R、C(1F)4个参数之间的关系曲线.这些结果,不仅提升了对这类振荡器的认知,而且可供设计时直接引用和参考. 相似文献
203.
Kevin Hurley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The observational properties of the soft gamma repeaters are reviewed briefly, starting with the time histories and energy spectra of their bursts. The short bursts and giant flares are compared. Their quiescent emission is presented, and the context of the magnetar model is discussed. 相似文献
204.
以模糊信息优化处理的观点,研究了信息扩散方式实现非参数输入的途径、方法和效果、本文用正态扩散方式处理知识样本,形成参数概率颁上模式,通过SIMAN仿真语言,对某一高速公路的一部分收费系统进行了仿真研究,结果表明:当人们对系统掌握的资料不多时,新方法有较大的优越性;如有较多的资料,新方法的结果与传统方法一致。 相似文献
205.
Jørgen Christensen-Dalsgaard 《Space Science Reviews》1998,85(1-2):19-36
The ‘standard’ solar model is based on a number of simplifying assumptions and depends on knowledge of the physical properties
of matter in the Sun. Given these assumptions, the constraint that the model have the observed surface luminosity provides
an estimate of the initial solar helium abundance. From helioseismic analyses further information can be obtained about the
present composition, including a fairly precise measure of the envelope helium abundance and an estimate of the hydrogen profile
in the radiative interior. It must be emphasized, however, that these inferences may suffer from systematic error arising
from incomplete knowledge about the equation of state and opacity of the solar interior.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
206.
SOHO/UVCS data indicate that minor ions in the corona are heated more than hydrogen, and that coronal heating results in T⊥ larger than T‖. Analogous behavior has been known from in situ measurements in solar wind for many years. Here we compare and contrast two
mechanisms which have been proposed to account for the above behavior: ion-cyclotron resonance and gravity damping.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
207.
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
208.
砂尘造成韧性材料的冲蚀损伤现象和损伤演化规律是冲蚀机理研究的重要内容,基于相应冲蚀试验和数值仿真的分析
方法是揭示冲蚀机理的重要手段。回顾了砂尘冲蚀损伤研究的缘起和发展经历,在介绍砂尘冲蚀损伤机理的基础上,总结了当前
数值仿真研究的3种主流方法:有限元方法、无网格方法和计算流体动力学方法。从数值仿真角度针对砂尘对韧性材料造成的破
坏模式、砂尘冲击姿态、砂尘冲击速度和形状、砂尘破碎对材料去除机制的影响等4个方面综述了影响冲蚀损伤机理的主要因素
和当前研究进展。砂尘对韧性材料造成的破坏模式通常分为材料凹陷、滑动、犁削、切削等4种不同机制;砂尘的冲击姿态决定了
材料的损伤模式;砂尘的冲击速度和砂尘的形状决定了材料的损伤严重程度;砂尘破碎现象对材料的去除机制有一定影响。 相似文献
209.
210.
Martin Tluczykont Daniel Hampf Dieter Horns Tanja Kneiske Robert Eichler Rayk Nachtigall Gavin Rowell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The question of the origin of cosmic rays and other questions of astroparticle and particle physics can be addressed with indirect air-shower observations above 10 TeV primary energy. We propose to explore the cosmic ray and γ-ray sky (accelerator sky) in the energy range from 10 TeV to 1 EeV with the new ground-based large-area wide angle (ΔΩ ∼ 0.85 sterad) air-shower detector HiSCORE (Hundred∗i Square-km Cosmic ORigin Explorer). The HiSCORE detector is based on non-imaging air-shower Cherenkov light-front sampling using an array of light-collecting stations. A full detector simulation and basic reconstruction algorithms have been used to assess the performance of HiSCORE. First prototype studies for different hardware components of the detector array have been carried out. The resulting sensitivity of HiSCORE to γ-rays will be comparable to CTA at 50 TeV and will extend the sensitive energy range for γ-rays up to the PeV regime. HiSCORE will also be sensitive to charged cosmic rays between 100 TeV and 1 EeV. 相似文献