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排序方式: 共有393条查询结果,搜索用时 15 毫秒
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《中国航空学报》2023,36(5):78-95
Both the Active Flow Control (AFC) and the variable-camber technology are considered as efficient ways to enhance the aerodynamic performance of an aircraft. The present study investigated the feasibility of the combination of a Co-Flow Jet (CFJ) airfoil and a parabolic flap, where the Reynolds Average Navier-Stokes (RANS) equations and the Spalart-Allmaras (S-A) turbulence model were exploited for the numerical simulation. Several significant geometric parameters, including the injection slot location, the suction slot location, the injection slot angle, the suction slot angle and the airfoil Suction Surface Translation (SST), were selected to study their effects on the aerodynamics of the proposed configuration. Then, an optimized design was created and compared with the baseline airfoil. The results show that the CFJ airfoil combined with the parabolic flap is more beneficial to the aerodynamic performance enhancement at small angles of attack. It is preferable to locate the injection slot at a 2% chord-wise location and the suction slot at a 75% chord-wise location. Both the decrease of the injection slot angle and the augmentation of the suction slot angle could reduce the drag. Furthermore, the SST of 0.5% chord is selected due to its high gain in the corrected aerodynamic efficiency at small angles of attack. Compared with the baseline, the optimized design could increase the lift coefficient and the corrected lift-to-drag ratio by 32.1% and 93.8% respectively at the angle of attack α = 4°. 相似文献
343.
Yongqiang Qi Yingmin Jia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this paper, the relative position parameters of the target spacecraft are obtained by using the vision measurement and the target maneuver positions are calculated through the isochronous interpolation method. Furthermore, new switch control laws under constant thrust are designed for active collision avoidance maneuver of the chaser along a specified trajectory. The switch control laws are obtained based on the acceleration sequences and the working times of thrusters in three axes which can be respectively computed by the time series analysis method. The perturbations and fuel consumptions are addressed during the computation of the working times. 相似文献
344.
P.A. Higgins P.T. GallagherR.T.J. McAteer D.S. Bloomfield 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
We present an automated system for detecting, tracking, and cataloging emerging active regions throughout their evolution and decay using SOHO Michelson Doppler Interferometer (MDI) magnetograms. The SolarMonitor Active Region Tracking (SMART) algorithm relies on consecutive image differencing to remove both quiet-Sun and transient magnetic features, and region-growing techniques to group flux concentrations into classifiable features. We determine magnetic properties such as region size, total flux, flux imbalance, flux emergence rate, Schrijver’s R-value, R∗ (a modified version of R), and Falconer’s measurement of non-potentiality. A persistence algorithm is used to associate developed active regions with emerging flux regions in previous measurements, and to track regions beyond the limb through multiple solar rotations. We find that the total number and area of magnetic regions on disk vary with the sunspot cycle. While sunspot numbers are a proxy to the solar magnetic field, SMART offers a direct diagnostic of the surface magnetic field and its variation over timescale of hours to years. SMART will form the basis of the active region extraction and tracking algorithm for the Heliophysics Integrated Observatory (HELIO). 相似文献
345.
J. Bolmont A. Jacholkowska 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
Lorentz Invariance Violation (LIV) may be a good observational window on Quantum Gravity physics. Within last few years, all major gamma-ray experiments have published results from the search for LIV with variable astrophysical sources: gamma-ray bursts with detectors on-board satellites and Active Galactic Nuclei with ground-based experiments. In this paper, the recent time-of-flight studies with unpolarized photons published from the space and ground based observations are reviewed. Various methods used in the time delay searches are described, and their performance discussed. Since no significant time-lag value was found within experimental precision of the measurements, the present results consist of 95% confidence level limits on the Quantum Gravity scale on the linear and quadratic terms in the standard photon dispersion relations. 相似文献
346.
Y. Haba Y. Terashima H. Kunieda K. Ohsuga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):174-179
We present the results of a systematic study of narrow-line Seyfert 1 galaxies (NLS1s) observed with XMM-Newton. The 2–12 keV X-ray spectra of NLS1s are well represented by a single power law with a photon index Γ ∼ 2. When this hard power law continuum is extrapolated into the low energy band, we found that all objects in our sample show prominent soft excess emission. This excess emission is well parameterized by the thermal emission expected from an optically thick accretion disk, and we found the following three peculiar features: (1) The derived disk temperatures are significantly higher than the expectation from a standard Shakura-Sunyaev accretion disk, if we assume a central mass of a black hole to be 106–8M⊙. (2) The temperatures are distributed within narrow range (ΔkT ∼ 0.08 keV) with an average temperature of 0.18 keV in spite of the range of four orders of magnitude in luminosity (1041–45 erg s−1). (3) We found a peculiar temperature–luminosity relation, where the luminosity seems to be almost saturated in spite of the significant change in temperature, during the observations of the most luminous NLS1 PKS 0558-504. These results strongly suggest that the standard accretion disk picture is no longer appropriate in the nuclei of NLS1s. We discuss a possible origin for the soft excess component, and suggest that a slim disk may be able to explain the observational results, if the photon trapping effect is properly taken into account. 相似文献
347.
张衍%王井岗%刘育建%李明伟 《宇航材料工艺》2003,33(5):35-39
采用热重和高效液相色谱法对高残碳酚醛树脂的性能进行分析。结果表明,与其它酚醛树脂相比,此树脂具有较高的热分解温度和表观活化能,700℃残碳率大于75%,热性能和耐烧蚀性能优于传统烧蚀酚醛树脂,是良好的耐热、耐烧蚀基体材料;用高效液相色谱(HPLC)初步探讨了树脂的反应机理,得出大分子量组成含量随聚合度变化,应作为树脂质量控制的指标之一。 相似文献
348.
基于加速度测量的柔性智能桁架结构振动主动控制实验研究 总被引:1,自引:0,他引:1
本文在只能获得加速度时,通过改变Leunberger观测器的结构形式,基于模态滤波器技术、最优控制理论和计算机控制系统理论,采用独立模态空间控制策略进行了具有密集模态的空间柔性智能桁架的实时计算机振动主动控制实验研究。实验结果表明这种控制策略是行之有效的。 相似文献
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