首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6567篇
  免费   16篇
  国内免费   24篇
航空   3043篇
航天技术   2261篇
综合类   24篇
航天   1279篇
  2021年   46篇
  2018年   124篇
  2017年   80篇
  2016年   82篇
  2015年   36篇
  2014年   146篇
  2013年   171篇
  2012年   153篇
  2011年   258篇
  2010年   189篇
  2009年   284篇
  2008年   356篇
  2007年   182篇
  2006年   135篇
  2005年   181篇
  2004年   180篇
  2003年   223篇
  2002年   126篇
  2001年   216篇
  2000年   109篇
  1999年   147篇
  1998年   177篇
  1997年   130篇
  1996年   181篇
  1995年   212篇
  1994年   170篇
  1993年   120篇
  1992年   176篇
  1991年   72篇
  1990年   59篇
  1989年   145篇
  1988年   63篇
  1987年   62篇
  1986年   65篇
  1985年   201篇
  1984年   158篇
  1983年   115篇
  1982年   158篇
  1981年   195篇
  1980年   60篇
  1979年   65篇
  1978年   60篇
  1977年   50篇
  1976年   43篇
  1975年   63篇
  1974年   53篇
  1973年   34篇
  1972年   42篇
  1970年   33篇
  1969年   36篇
排序方式: 共有6607条查询结果,搜索用时 15 毫秒
131.
To meet the significant increase in EVA demand to support assembly and operations of the International Space Station (ISS), NASA and industry have improved the current Shuttle Extravehicular Mobility Unit (EMU), or "space suit", configuration to meet the unique and specific requirements of an orbital-based system. The current Shuttle EMU was designed to be maintained and serviced on the ground between frequent Shuttle flights. ISS will require the EMUs to meet increased EVAs out of the Shuttle Orbiter and to remain on orbit for up to 180 days without need for regular return to Earth for scheduled maintenance or refurbishment. Ongoing Shuttle EMU improvements have increased reliability, operational life and performance while minimizing ground and on-orbit maintenance cost and expendable inventory. Modifications to both the anthropomorphic mobility elements of the Space Suit Assembly (SSA) as well as to the Primary Life Support System (PLSS) are identified and discussed. This paper also addresses the status of on-going Shuttle EMU improvements and summarizes the approach for increasing interoperability of the U.S. and Russian space suits to be utilized aboard the ISS.  相似文献   
132.
The National Space Research Institute (INPE) is developing the first Brazilian Scientific Microsatellite (SACI-1) based on the vanguard technology and on the experience acquired through projects developed by Brazilian Space Program. The SACI-1 is a 750km polar orbit satellite. The spacecraft will combine spin stabilization with geomagnetic control and has a total mass of 60 kg. The overall dimensions are 640×470×470 mm. The SACI-1 satellite shall be launched together with CBERS (China-Brazil Earth Resource Satellite). Its platform is being designed for multiple mission applications. The Brazilian Academy of Sciences has selected four scientific payloads that characterize the mission. The scientific experiments are: ORCAS (Solar and Anomalous Cosmic Rays Observation in the Magnetosphere), PLASMEX (Study of Plasma Bubbles), FOTSAT (Airglow Photometer), and MAGNEX (Geomagnetic Experiment).  相似文献   
133.
The global network of meteorological satellites used different forms of international cooperation during its development, and some of these forms continue. Concern about continued operation of the global network led the WMO to study the issues and to adopt a long-term policy and strategy based on a shared meteorological satellite network. Nations need to consider how to combine their meteorological and space-related organizations in a partnership role, so they can directly contribute to a future global network of meteorological satellites. Some examples are cited to demonstrate that increased direct participation is a valid and feasible objective.  相似文献   
134.
When discussing problems related to medical service in space flight, particular attention should be given to the specific living conditions and changes associated with space flight. In disease and injury, surgery can be provided only after conservative therapy has failed. In this context gnotobiological chambers allowing surgery in aseptic conditions seem promising. A portable set of interchangeable surgical tools should be made of light-weight alloys that can be readily sterilized. Electroanalgesia in combination with auriculoacupuncture as well as peridureal anesthesia may be used as they allow normal operations in autonomous space flight conditions. Changes in the sympatho-adrenal and kallikrein-kinin systems, as well as water-electrolyte balance, should be taken into account in developing methods and means of medical service in critical situations. Special attention should be given to the prevention and treatment of brain edema in view of weightlessness-induced cephalad fluid shifts.  相似文献   
135.
A major problem with operations of lifting reentry vehicle having an aft center-of-gravity location due to large engine mass at the rear is the required hypersonic trim to fight the desired trajectory. This condition is most severe for lifting maneuvers. As a first step toward analyzing this problem, this paper considers the lift requirement for some basic maneuvers in the plane of a great circle. Considerations are given to optimal lift control for achieving the maximization of either the final altitude, speed or range. For the maximum-range problem, phugoid oscillation along an optimal trajectory is less severe as compared to a glide with maximum lift-to-drag ratio. An explicit formula for the number of oscillations for an entry from orbital speed is proposed.  相似文献   
136.
137.
It is well known that the solar wind can significantly affect high-latitude ionospheric dynamics. However, the effects of the solar wind on the middle- and low-latitude ionosphere are much less studied. In this paper, we report observations that large perturbations in the middle- and low-latitude ionosphere are well correlated with solar wind variations. In one event, a significant (20–30%) decrease of the midlatitude ionospheric electron density over a large latitudinal range was related to a sudden drop in the solar wind pressure and a northward turning of the interplanetary magnetic field, and the density decrease became larger at lower latitudes. In another event, periodic perturbations in the dayside equatorial ionospheric E × B drift and electrojet were closely associated with variations in the interplanetary electric field. Since the solar wind is always changing with time, it can be a very important and common source of ionospheric perturbations at middle- and low-latitudes. The relationship between solar wind variations and significant ionospheric perturbations has important applications in space weather.  相似文献   
138.
Engineering concepts for inflatable Mars surface greenhouses.   总被引:1,自引:0,他引:1  
A major challenge of designing a bioregenerative life support system for Mars is the reduction of the mass, volume, power, thermal and crew-time requirements. Structural mass of the greenhouse could be saved by operating the greenhouse at low atmospheric pressure. This paper investigates the feasibility of this concept. The method of equivalent system mass is used to compare greenhouses operated at high atmospheric pressure to greenhouses operated at low pressure for three different lighting methods: natural, artificial and hybrid lighting.  相似文献   
139.
In this work we have tracked coronal mass ejections observed with the ground based Mirror Coronagraph for Argentina (MICA) and the Large Angle and Spectroscopic Coronagraph (LASCO) C2 and C3 on board of the Solar and Heliospheric Observatory (SOHO). The MICA telescope is located at El Leoncito (31.8 S, 69.3 W), San Juan (Argentina), since 1997 as part of a bilateral scientific project between Germany and Argentina. SOHO is a project of international cooperation between ESA and NASA. Together these instruments are able to observe the solar corona ranging from 1.05 to 32 solar radii. MICA images the Fe XIV emission line corona and LASCO coronagraphs observe the Thomson scattered white light corona. We have selected events for which there are observations from the three coronagraphs. Using the composite data we were able to obtain height-time diagrams for the corresponding dynamical coronal features traveling outwards in order to determine some of their kinematical properties, i.e., plane of sky velocity and acceleration.  相似文献   
140.
PLANET-B is the Japanese Mars orbiter program. The primary objective of the program is to study the Martian aeronomy, putting emphasis on the interaction of the Martian upper atmosphere with the solar wind. The launch of the spacecraft is scheduled for August, 1998. The periapsis altitude and the apoapsis are 150 km and 15 Mars radii, respectively. The dry weight of the orbiter is 186 kg including 14 science instruments. Advanced technologies are employed in the design of the spacecraft in order to overcome the weight limitation. This paper describes the scientific objectives of the PLANET-B program and outline of the spacecraft system.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号