全文获取类型
收费全文 | 6536篇 |
免费 | 6篇 |
国内免费 | 16篇 |
专业分类
航空 | 3266篇 |
航天技术 | 2168篇 |
综合类 | 188篇 |
航天 | 936篇 |
出版年
2021年 | 42篇 |
2018年 | 103篇 |
2017年 | 58篇 |
2016年 | 61篇 |
2014年 | 110篇 |
2013年 | 155篇 |
2012年 | 146篇 |
2011年 | 217篇 |
2010年 | 151篇 |
2009年 | 263篇 |
2008年 | 278篇 |
2007年 | 149篇 |
2006年 | 141篇 |
2005年 | 133篇 |
2004年 | 161篇 |
2003年 | 193篇 |
2002年 | 211篇 |
2001年 | 267篇 |
2000年 | 125篇 |
1999年 | 160篇 |
1998年 | 201篇 |
1997年 | 144篇 |
1996年 | 179篇 |
1995年 | 213篇 |
1994年 | 207篇 |
1993年 | 115篇 |
1992年 | 155篇 |
1991年 | 67篇 |
1990年 | 79篇 |
1989年 | 160篇 |
1988年 | 81篇 |
1987年 | 76篇 |
1986年 | 71篇 |
1985年 | 208篇 |
1984年 | 169篇 |
1983年 | 137篇 |
1982年 | 163篇 |
1981年 | 200篇 |
1980年 | 70篇 |
1979年 | 54篇 |
1978年 | 79篇 |
1977年 | 42篇 |
1976年 | 46篇 |
1975年 | 66篇 |
1974年 | 52篇 |
1973年 | 39篇 |
1972年 | 62篇 |
1971年 | 54篇 |
1970年 | 38篇 |
1969年 | 42篇 |
排序方式: 共有6558条查询结果,搜索用时 15 毫秒
781.
G. Clément D. Hamilton L. Davenport B. Comet 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
This paper reviews the medical operations performed on six European astronauts during seven space missions on board the space station Mir. These missions took place between November 1988 and August 1999, and their duration ranged from 14 days to 189 days. Steps of pre-flight medical selection and flight certification are presented. Countermeasures program used during the flight, as well as rehabilitation program following short and long-duration missions are described. Also reviewed are medical problems encountered during the flight, post-flight physiological changes such as orthostatic intolerance, exercise capacity, blood composition, muscle atrophy, bone density, and radiation exposure. 相似文献
782.
R. Govind J.J. Valette F.G. Lemoine 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The Lambert–Amery System is the largest glacier–ice shelf system in East Antarctica, draining a significant portion of the ice sheet. Variation in ice sheet discharge from Antarctica or Greenland has an impact on the rate of change in global mean sea level; which is a manifestation of climate change. In conjunction with a measure of ice thickness change, ice sheet discharge can be monitored by determining the absolute velocities of these glaciers. 相似文献
783.
A mission template for exploration and damage mitigation of potential hazard of Near Earth Asteroids
D. C. Hyland H. A. Altwaijry R. Margulieux J. Doyle J. Sandberg B. Young N. Satak J. Lopez S. Ge X. Bai 《Cosmic Research》2010,48(5):437-442
The Apophis Exploratory and Mitigation Platform (AEMP) concept was developed as a prototype mission to explore and potentially
deflect the Near Earth Asteroid (NEA) 99942 Apophis. Deflection of the asteroid from the potential 2036 impact will be achieved
using a gravity tractor technique, while a permanent deflection, eliminating future threats, will be imparted using a novel
albedo manipulation technique. This mission will serve as an archetypal template for future missions to small NEAs and could
be adapted to mitigate the threat of collision with other potential Earth-crossing objects. 相似文献
784.
R. Sieradzki Iu. Cherniak A. Krankowski 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Since the early 1990s, global positioning system measurements have been used to study of the state and rapid changes of the Total Electron Content in the ionosphere. Currently, the increasing number of permanent stations makes it possible to generate maps of the irregularities in the ionosphere for specified regions with sub-daily resolution. The main goal of this work was to apply global navigation satellite system observations to obtain information about ionospheric variability around the North Geomagnetic Pole. In order to detect the ionospheric disturbances, 30-s observation data was used. The Rate of Total Electron Content Index was applied as a measure of the variability in the ionosphere. The first analyses were executed using more than 100 permanent stations. The results show two kinds of products: 2-hour maps in spherical geomagnetic coordinates and daily maps presenting the occurrence of the strong Total Electron Content fluctuations as a magnetic local time function, for the most disturbed days of April 2010. Apart from the main product of the algorithm, the Rate of Total Electron Content time series for individual satellite tracks was presented. The results demonstrated very good sensitivity of the obtained maps, which can detect even quite weak disturbances. The presented algorithm developed at the Geodynamic Research Laboratory of the University of Warmia and Mazury, in cooperation with Institute of Terrestrial Magnetism, Ionosphere and Radiowave Propagation, will be applied in the near future to create near-real time service of the conditions in the ionosphere based on the Global Navigation Satellite Systems observations. 相似文献
785.
The measured D/H ratios in interstellar environments and in the solar system are reviewed. The two extreme D/H ratios in solar
system water - (720±120)×10−6 in clay minerals and (88±11)×10−6 in chondrules, both from LL3 chondritic meteorites - are interpreted as the result of a progressive isotopic exchange in
the solar nebula between deuterium-rich interstellar water and protosolar H2. According to a turbulent model describing the evolution of the nebula (Drouart et al., 1999), water in the solar system cannot be a product of thermal (neutral) reactions occurring in the solar nebula. Taking
720×10−6 as a face value for the isotopic composition of the interstellar water that predates the formation of the solar nebula, numerical
simulations show that the water D/H ratio decreases via an isotopic exchange with H2. During the course of this process, a D/H gradient was established in the nebula. This gradient was smoothed with time and
the isotopic homogenization of the solar nebula was completed in 106 years, reaching a D/H ratio of 88×10−6. In this model, cometary water should have also suffered a partial isotopic re-equilibration with H2. The isotopic heterogeneity observed in chondrites result from the turbulent mixing of grains, condensed at different epochs
and locations in the solar nebula. Recent isotopic determinations of water ice in cold interstellar clouds are in agreement
with these chondritic data and their interpretation (Texeira et al., 1999).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
786.
787.
The objective of this work is to explore ways in which performance of battery systems can be enhanced through the use of energy-efficient battery management techniques. The phenomenon of charge recovery that takes place under pulsed discharge conditions is identified as a mechanism that can be exploited to enhance the capacity of a cell in a portable communication device. The bursty nature of many data traffic sources suggests that data transmissions in communication devices may provide natural opportunities for charge recovery. We model the data source as a stochastic process and let the cell discharge be driven by such a process. We use a model of a dual lithium ion insertion cell to identify the improvement to cell capacity that results from the stochastic discharge. The insight from this study leads us to propose discharge shaping techniques that tradeoff energy efficiency with delay in the required current supply 相似文献
788.
789.
790.
A possible variant presented for solving the equation of motion of a rotating flow is more general with respect to the variants known in the literature. On the basis of the simultaneous solution of the equations of motion and energy, the temperature fields are determined under changes of the rotation nature. 相似文献