全文获取类型
收费全文 | 161篇 |
免费 | 7篇 |
国内免费 | 8篇 |
专业分类
航空 | 69篇 |
航天技术 | 69篇 |
综合类 | 4篇 |
航天 | 34篇 |
出版年
2021年 | 5篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2014年 | 15篇 |
2013年 | 9篇 |
2012年 | 8篇 |
2011年 | 18篇 |
2010年 | 6篇 |
2009年 | 13篇 |
2008年 | 19篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有176条查询结果,搜索用时 15 毫秒
1.
Mosbeh R. Kaloop Mosaruf Hussan Dookie Kim 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(11):3505-3521
This study aims at assessing the safety behavior of the Incheon long-span bridge using high rate (10?Hz) geodetic monitoring global positioning system (GPS). The time series of wavelet spectrum analysis is utilized to assess the dynamic behavior of the bridge. The coefficients and model errors of the time series autoregressive-moving average (ARMA) model are used to evaluate the movement performances of the bridge. The results show that: (i) the accuracy of GPS measurements to extract the dynamic behavior of the bridge is 97.27% when compared with the design results. (ii) the behavior of the bridge is within the safety limits of the bridge design with minimum observed changes for the historical GPS measurements in time and frequency domains, the mean deflection of bridge deck is 8.26?mm and frequency changes of bridge is 0.004?Hz compared with the design results. (iii) the time series analysis of the wavelet spectrum and ARMA model coefficients can be used to detect the significant frequency changes and study the rigidity of the bridge performance, respectively; and the both methods are found to be suitable techniques to estimate the performance changes of the GPS measurements in the time and frequency domains during the monitoring time period. 相似文献
2.
The South Pole-Aitken basin region,Moon: GIS-based geologic investigation using Kaguya elemental information 总被引:1,自引:0,他引:1
Kyeong Ja Kim James M. Dohm Jean-Pierre Williams Javier Ruiz Trent M. Hare Nobuyuki Hasebe Yuzuru Karouji Shingo Kobayashi Makoto Hareyama Eido Shibamura Masanori Kobayashi Claude d’Uston Olivier Gasnault Olivier Forni Sylvestre Maurice 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Using Geographic Information Systems (GIS), we performed comparative analysis among stratigraphic information and the Kaguya (SELENE) GRS data of the ∼2500-km-diameter South Pole-Aitken (SPA) basin and its surroundings. Results indicate that the surface rock materials (including ancient crater materials, mare basalts, and possible SPA impact melt) are average to slightly elevated in K and Th with respect to the rest of the Moon. Also, this study demonstrates that K and Th have not significantly changed since the formation of SPA. The elemental signatures of the impact basin of Fe, Ti, Si, O through time include evidence for resurfacing by ejecta materials and late-stage volcanism. The oldest surfaces of SPA are found to be oxygen-depleted during the heavy bombardment period relative to later stages of geologic development, followed by both an increase in silicon and oxygen, possibly due to ejecta sourced from outside of SPA, and subsequent modification due to mare basaltic volcanism, which increased iron and titanium within SPA. The influence of the distinct geologic history of SPA and surroundings on the mineralogic and elemental abundances is evident as shown in our investigation. 相似文献
3.
Jizhang Sang James C. Bennett Craig H. Smith 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
This paper presents a new method for estimating ballistic coefficients (BCs) of low perigee debris objects from their historical two line elements (TLEs). The method uses the drag perturbation equation of the semi-major axis of the orbit. For an object with perigee altitude below 700 km, the variation in the mean semi-major axis derived from the TLE is mainly caused by the atmospheric drag effect, and therefore is used as the source in the estimation of the ballistic coefficient. The method is tested using the GRACE satellites, and a number of debris objects with external ballistic coefficient values, and agreements of about 10% are achieved. 相似文献
4.
E.S. Seo T. Anderson D. Angelaszek S.J. Baek J. Baylon M. Buénerd M. Copley S. Coutu L. Derome B. Fields M. Gupta J.H. Han I.J. Howley H.G. Huh Y.S. Hwang H.J. Hyun I.S. Jeong D.H. Kah K.H. Kang D.Y. Kim H.J. Kim K.C. Kim M.H. Kim K. Kwashnak J. Lee M.H. Lee J.T. Link L. Lutz A. Malinin A. Menchaca-Rocha J.W. Mitchell S. Nutter O. Ofoha H. Park I.H. Park J.M. Park P. Patterson J.R. Smith J. Wu Y.S. Yoon 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The Cosmic Ray Energetics And Mass (CREAM) instrument is configured with a suite of particle detectors to measure TeV cosmic-ray elemental spectra from protons to iron nuclei over a wide energy range. The goal is to extend direct measurements of cosmic-ray composition to the highest energies practical, and thereby have enough overlap with ground based indirect measurements to answer questions on cosmic-ray origin, acceleration and propagation. The balloon-borne CREAM was flown successfully for about 161 days in six flights over Antarctica to measure elemental spectra of Z = 1–26 nuclei over the energy range 1010 to >1014 eV. Transforming the balloon instrument into ISS-CREAM involves identification and replacement of components that would be at risk in the International Space Station (ISS) environment, in addition to assessing safety and mission assurance concerns. The transformation process includes rigorous testing of components to reduce risks and increase survivability on the launch vehicle and operations on the ISS without negatively impacting the heritage of the successful CREAM design. The project status, including results from the ongoing analysis of existing data and, particularly, plans to increase the exposure factor by another order of magnitude utilizing the International Space Station are presented. 相似文献
5.
6.
7.
We optimize the performance of multiframe target detection (MFTD) schemes under extended Neyman-Pearson (NP) criteria. Beyond the per-track detection performance for a specific target path in conventional MFTD studies, we optimize the overall detection performance which is averaged over all the potential target paths. It is shown that the overall MFTD performance is limited by the mobility of a target and also that optimality of MFTD performance depends on how fully one ran exploit the information about the target dynamics. We assume a single target situation and then present systematic optimization by formulating the MFTD problems as binary composite hypotheses testing problems. The resulting optimal solutions suggest computationally efficient implementation algorithms which are similar to the Viterbi algorithm for trellis search. The optimal performances for some typical types of target dynamics are evaluated via Monte-Carlo simulation 相似文献
8.
This paper describes the experimental and computational analyses of a high velocity aluminum projectile impact on an Al6061-T6 spacecraft inner wall at different oblique angles. Al2017-T4 spherical projectiles of 5.56 mm in diameter and 0.25 g in weight were chosen within the velocity range of 1000±200 m/s due to the limitation of the light gas gun. The energy absorbed was calculated by measuring the velocities before and after impact on the inner wall. The energy absorbed by the wall and the remaining energy carried by the projectile helped to estimate the severity of further damage to inner components. Afterwards, validation was done by using the commercially available software LS-DYNA with a dedicated SPH. On average, a 10% energy absorption difference between experimentation and simulation was found. By using C-SCAN, the damage area proportion of the total inner wall to impact penetration hole area was found to be on average 6%, 26% and 53% greater than the projectile cross sectional area for the oblique angle impacts of 30°, 45°, and 60°, respectively. These findings helped to understand the relationship between the oblique impact event and the damage area on a spacecraft inner wall along with space debris cloud propagation and comparison with experimental results using LS-DYNA. 相似文献
9.
Dong-Yoon Kim Byoungsam Woo Sang-Young Park Kyu-Hong Choi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,44(11):1257-1269
A hybrid optimization method is developed for fuel-optimal reconfigurations of a group of satellites flying in formation. The genetic algorithm performs a global search to find two-impulse trajectories, and primer vector analysis finds multiple-impulsive local optimal trajectories with the two-impulse trajectories as initial guesses. Hybrid optimization finds globally optimal trajectories for formation reconfigurations, including formation resizing, reassignment and reorientation maneuvers. Multiple-impulse trajectories reduce the fuel consumption from the two-impulse trajectories by up to 4.4% for those maneuvers. In real missions, satellites can follow two-impulse trajectories to gain the advantage of a smaller number of impulses, with the cost of slightly more propellant. The qualitative characteristics of the optimal trajectories are analyzed from the number of optimal trajectories found by hybrid optimization. 相似文献
10.
介绍了虚拟现实技术及VRML虚拟现实建模语言的概念,提出了用VRML虚拟现实建模语言设计软件时应该注意的一些问题,说明了用VRML虚拟现实建模语言设计的软件适用的范围,探讨了解决虚拟现实技术中存在问题的方法. 相似文献