全文获取类型
收费全文 | 5384篇 |
免费 | 9篇 |
国内免费 | 11篇 |
专业分类
航空 | 2362篇 |
航天技术 | 1864篇 |
综合类 | 23篇 |
航天 | 1155篇 |
出版年
2022年 | 17篇 |
2021年 | 47篇 |
2019年 | 28篇 |
2018年 | 198篇 |
2017年 | 148篇 |
2016年 | 127篇 |
2015年 | 53篇 |
2014年 | 148篇 |
2013年 | 178篇 |
2012年 | 157篇 |
2011年 | 232篇 |
2010年 | 179篇 |
2009年 | 282篇 |
2008年 | 302篇 |
2007年 | 172篇 |
2006年 | 110篇 |
2005年 | 145篇 |
2004年 | 149篇 |
2003年 | 184篇 |
2002年 | 119篇 |
2001年 | 206篇 |
2000年 | 80篇 |
1999年 | 134篇 |
1998年 | 137篇 |
1997年 | 94篇 |
1996年 | 101篇 |
1995年 | 158篇 |
1994年 | 151篇 |
1993年 | 72篇 |
1992年 | 96篇 |
1991年 | 30篇 |
1990年 | 45篇 |
1989年 | 90篇 |
1988年 | 31篇 |
1987年 | 52篇 |
1986年 | 33篇 |
1985年 | 132篇 |
1984年 | 92篇 |
1983年 | 86篇 |
1982年 | 92篇 |
1981年 | 145篇 |
1980年 | 49篇 |
1979年 | 39篇 |
1978年 | 35篇 |
1977年 | 32篇 |
1976年 | 28篇 |
1975年 | 32篇 |
1974年 | 23篇 |
1972年 | 29篇 |
1969年 | 18篇 |
排序方式: 共有5404条查询结果,搜索用时 156 毫秒
761.
Vitally important to the success of any mission is the ground support system used for commanding the spacecraft, receiving the telemetry, and processing the results. We describe the ground system used for the STEREO mission, consisting of the Mission Operations Center, the individual Payload Operations Centers for each instrument, and the STEREO Science Center, together with mission support from the Flight Dynamics Facility, Deep Space Mission System, and the Space Environment Center. The mission planning process is described, as is the data flow from spacecraft telemetry to processed science data to long-term archive. We describe the online resources that researchers will be able to use to access STEREO planning resources, science data, and analysis software. The STEREO Joint Observations Program system is described, with instructions on how observers can participate. Finally, we describe the near-real-time processing of the “space weather beacon” telemetry, which is a low telemetry rate quicklook product available close to 24 hours a day, with the intended use of space weather forecasting. 相似文献
762.
The enhancements of solar protons with an energy of more than 30 MeV, originating from flares in one active region and observed simultaneously aboard three spacecraft Vega-1, 2 and Prognoz-10 in July 1985, are analyzed and approximated in this work by using the reflection model [2]. The numerical values of several physical parameters (the parameters of distribution of solar cosmic ray (SCR) particles inside heliosphere traps, the coefficients of trap transparency) that are not observed by direct measurements are estimated. 相似文献
763.
Y Kitaya J Tsuruyama T Shibuya M Yoshida M Kiyota 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,31(1):177-182
To obtain basic data on adequate air circulation to enhance plant growth in a closed plant culture system in a controlled ecological life support system (CELSS), an investigation was made of the effects of the air current speed ranging from 0.01 to 1.0 m s-1 on photosynthesis and transpiration in sweetpotato leaves and photosynthesis in tomato seedlings canopies. The gas exchange rates in leaves and canopies were determined by using a chamber method with an infrared gas analyzer. The net photosynthetic rate and the transpiration rate increased significantly as the air current speeds increased from 0.01 to 0.2 m s-1. The transpiration rate increased gradually at air current speeds ranging from 0.2 to 1.0 m s-1 while the net photosynthetic rate was almost constant at air current speeds ranging from 0.5 to 1.0 m s-1. The increase in the net photosynthetic and transpiration rates were strongly dependent on decreased boundary-layer resistances against gas diffusion. The net photosynthetic rate of the plant canopy was doubled by an increased air current speed from 0.1 to 1.0 m s-1 above the plant canopy. The results demonstrate the importance of air movement around plants for enhancing the gas exchange in the leaf, especially in plant canopies in the CELSS. 相似文献
764.
T.S. Bastian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2003,32(12):2705-2714
The Frequency Agile Solar Radiotelescope (FASR), a telescope concept currently under study, will be a ground based solar-dedicated radio telescope designed and optimized to produce high resolution, high-fidelity, and high-dynamic-range images over a broad frequency range (0.1–24 GHz). As such, FASR will address an extremely broad science program, including the nature and evolution of coronal magnetic fields, the physics of flares, drivers of space weather, and the quiet Sun. An important goal is to mainstream solar radio observations by providing a number of standard data products for use by the wider solar physics community. The instrument specifications and the key science elements that FASR will address are briefly discussed, as well as several operational issues. 相似文献
765.
T. R. Robinson F. Honary A. Stocker T. B. Jones 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(12):41-44
Results are presented from recent ionospheric modification experiments in which the EISCAT UHF radar measured the E-region temperature and density response to high power RF heating above Tromsø. A variety of electrojet conditions were encountered during these experiments. In particular, the electron drift velocity varied considerably allowing the heating efficiency of the RF heater to be investigated as a function of electron flow velocity. These observations constitute the first direct investigation of electrojet temperature modifications by high power radio waves and provide a test of a recent theoretical model in which the combined effects of RF heating and of natural plasma turbulence associated with the Farley-Buneman instability have been considered. 相似文献
766.
The fundamental TPBVP usually underlying true “optimal sensor selection strategy” is revisited to obtain practical real-time mechanizations as a solution to an exclusively initial value problem 相似文献
767.
T H Sweetser C A Halsell R J Cesarone 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):257-260
Planetary protection has been an important consideration during the process of designing the Mars Observer mission. It affected trajectory design of both the interplanetary transfer and the orbits at Mars; these in turn affected the observation strategies developed for the mission. The Project relied mainly on the strategy of collision avoidance to prevent contamination of Mars. Conservative estimates of spacecraft reliability and Martian atmosphere density were used to evaluate decisions concerning the interplanetary trajectory, the orbit insertion phase at Mars, and operations in orbit at Mars and afterwards. Changes in the trajectory design, especially in the orbit insertion phase, required a refinement of those estimates. 相似文献
768.
D. J. McComas J. L. Phillips S. J. Bame J. T. Gosling B. E. Goldstein M. Neugebauer 《Space Science Reviews》1995,72(1-2):93-98
In the 25 months since Jupiter flyby, the Ulysses spacecraft has climbed southward to a heliolatitude of 56°. This transit has been marked by an evolution from slow, dense coronal streamer belt solar wind through two regions where the rotation of the Sun carried Ulysses back and forth between streamer belt and polar coronal hole flows, and finally into a region of essentially continuous fast, low density solar wind from the southern polar coronal hole. Throughout these large changes, the momentum flux normalized to 1 AU displays very little systematic variation. In addition, the bulk properties of the polar coronal hole solar wind are quite similar to those observed in high speed streams in the ecliptic plane at 1 AU. Coronal mass ejections and forward and reverse shocks associated with corotating interaction regions have also been observed at higher heliolatitudes, however they are seen less frequently with increasing southern heliolatitude. Ulysses has thus far collected data from 20° of nearly contiguous solar wind flows from the polar coronal hole. We examine these data for characteristic variations with heliolatitude and find that the bulk properties in general show very little systematic variation across the southern polar coronal hole so far. 相似文献
769.
A discussion of the current and emerging core technologies and philosophies that will enable Air Force personnel to quickly, accurately and intuitively diagnose faults in increasingly complex systems 相似文献
770.
Earp S.L. Hughes E.S. Elkins T.J. Vickers R. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(9):30-39
The suitability of ultra-wideband ground-penetrating radar as a tool for the detection of buried metallic mines is explored in this paper. The analysis centers around a 200-800 MHz, dual-polarized ground penetrating radar (GPR) designed and built by SRI International. The analysis consisted of fusing the images from the dual polarizations into a single image to enhance the target objects and suppress clutter. Results are shown for several variations of a Mahalanobis-based fusion technique, and “soft decision” minefield detection results based upon Monte Carlo statistical techniques are also presented. Although relatively few scenes were analyzed, these results show that the dual-polarized GPR is potentially very effective at finding buried mines and minefields 相似文献