全文获取类型
收费全文 | 333篇 |
免费 | 113篇 |
国内免费 | 120篇 |
专业分类
航空 | 302篇 |
航天技术 | 60篇 |
综合类 | 53篇 |
航天 | 151篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 37篇 |
2020年 | 16篇 |
2019年 | 32篇 |
2018年 | 14篇 |
2017年 | 22篇 |
2016年 | 33篇 |
2015年 | 22篇 |
2014年 | 38篇 |
2013年 | 33篇 |
2012年 | 23篇 |
2011年 | 39篇 |
2010年 | 28篇 |
2009年 | 29篇 |
2008年 | 28篇 |
2007年 | 17篇 |
2006年 | 28篇 |
2005年 | 17篇 |
2004年 | 11篇 |
2003年 | 13篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有566条查询结果,搜索用时 15 毫秒
531.
J. Barengoltz J. Witte 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
In August 2005 NASA launched a large orbiting science observatory, the Mars Reconnaissance Orbiter (MRO), for what is scheduled to be a 5.4-year mission. High resolution imaging of the surface is a principal goal of the mission. One consequence of this goal however is the need for a low science orbit. Unfortunately this orbit fails the required 20-year orbit life set in NASA Planetary Protection (PP) requirements [NASA. Planetary protection provisions for robotic extraterrestrial missions, NASA procedural requirements NPR 8020.12C, NASA HQ, Washington, DC, April 2005.]. So rather than sacrifice the science goals of the mission by raising the science orbit, the MRO Project chose to be the first orbiter to pursue the bio-burden reduction approach. 相似文献
532.
E. Venkatapathy B. Laub G.J. Hartman J.O. Arnold M.J. Wright G.A. Allen Jr. 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The science community has continued to be interested in planetary entry probes, aerocapture, and sample return missions to improve our understanding of the Solar System. As in the case of the Galileo entry probe, such missions are critical to the understanding not only of the individual planets, but also to further knowledge regarding the formation of the Solar System. It is believed that Saturn probes to depths corresponding to 10 bars will be sufficient to provide the desired data on its atmospheric composition. An aerocapture mission would enable delivery of a satellite to provide insight into how gravitational forces cause dynamic changes in Saturn’s ring structure that are akin to the evolution of protoplanetary accretion disks. Heating rates for the “shallow” Saturn probes, Saturn aerocapture, and sample Earth return missions with higher re-entry speeds (13–15 km/s) from Mars, Venus, comets, and asteroids are in the range of 1–6 KW/cm2. New, mid-density thermal protection system (TPS) materials for such probes can be mission enabling for mass efficiency and also for use on smaller vehicles enabled by advancements in scientific instrumentation. Past consideration of new Jovian multiprobe missions has been considered problematic without the Giant Planet arcjet facility that was used to qualify carbon phenolic for the Galileo probe. This paper describes emerging TPS technologies and the proposed use of an affordable, small 5 MW arcjet that can be used for TPS development, in test gases appropriate for future planetary probe and aerocapture applications. Emerging TPS technologies of interest include new versions of the Apollo Avcoat material and a densified variant of Phenolic Impregnated Carbon Ablator (PICA). Application of these and other TPS materials and the use of other facilities for development and qualification of TPS for Saturn, Titan, and Sample Return missions of the Stardust class with entry speeds from 6.0 to 28.6 km/s are discussed. 相似文献
533.
534.
535.
536.
537.
538.
Pascale Ehrenfreund Chris McKayJohn D. Rummel Bernard H. FoingClive R. Neal Tanja Masson-ZwaanMegan Ansdell Nicolas PeterJohn Zarnecki Steve MackwellMaria Antionetta Perino Linda BillingsJohn Mankins Margaret Race 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012,49(1):2-48
In response to the growing importance of space exploration in future planning, the Committee on Space Research (COSPAR) Panel on Exploration (PEX) was chartered to provide independent scientific advice to support the development of exploration programs and to safeguard the potential scientific assets of solar system objects. In this report, PEX elaborates a stepwise approach to achieve a new level of space cooperation that can help develop world-wide capabilities in space science and exploration and support a transition that will lead to a global space exploration program. The proposed stepping stones are intended to transcend cross-cultural barriers, leading to the development of technical interfaces and shared legal frameworks and fostering coordination and cooperation on a broad front. Input for this report was drawn from expertise provided by COSPAR Associates within the international community and via the contacts they maintain in various scientific entities. The report provides a summary and synthesis of science roadmaps and recommendations for planetary exploration produced by many national and international working groups, aiming to encourage and exploit synergies among similar programs. While science and technology represent the core and, often, the drivers for space exploration, several other disciplines and their stakeholders (Earth science, space law, and others) should be more robustly interlinked and involved than they have been to date. The report argues that a shared vision is crucial to this linkage, and to providing a direction that enables new countries and stakeholders to join and engage in the overall space exploration effort. Building a basic space technology capacity within a wider range of countries, ensuring new actors in space act responsibly, and increasing public awareness and engagement are concrete steps that can provide a broader interest in space exploration, worldwide, and build a solid basis for program sustainability. By engaging developing countries and emerging space nations in an international space exploration program, it will be possible to create a critical bottom-up support structure to support program continuity in the development and execution of future global space exploration frameworks. With a focus on stepping stones, COSPAR can support a global space exploration program that stimulates scientists in current and emerging spacefaring nations, and that will invite those in developing countries to participate—pursuing research aimed at answering outstanding questions about the origins and evolution of our solar system and life on Earth (and possibly elsewhere). COSPAR, in cooperation with national and international science foundations and space-related organizations, will advocate this stepping stone approach to enhance future cooperative space exploration efforts. 相似文献
539.
胡心舟 《长沙航空职业技术学院学报》2013,(3):77-79
耕地保护事关国家粮食安全、生态平衡和社会稳定,为此政府一直实行世界最严格的制度来保护耕地。但发展中国家的快速城市化进程必然导致部分耕地被城市建设用地替代。出于农村经济发展的内在要求及提高土地资源配置效率的需要,在市场经济的条件下,促进农地使用权的流转成为我国耕地保护制度改革过程中的重要环节。 相似文献
540.