全文获取类型
收费全文 | 2687篇 |
免费 | 4篇 |
国内免费 | 7篇 |
专业分类
航空 | 1253篇 |
航天技术 | 943篇 |
综合类 | 9篇 |
航天 | 493篇 |
出版年
2021年 | 20篇 |
2019年 | 17篇 |
2018年 | 60篇 |
2017年 | 36篇 |
2016年 | 41篇 |
2015年 | 12篇 |
2014年 | 63篇 |
2013年 | 92篇 |
2012年 | 63篇 |
2011年 | 94篇 |
2010年 | 77篇 |
2009年 | 127篇 |
2008年 | 144篇 |
2007年 | 66篇 |
2006年 | 68篇 |
2005年 | 69篇 |
2004年 | 66篇 |
2003年 | 89篇 |
2002年 | 46篇 |
2001年 | 96篇 |
2000年 | 49篇 |
1999年 | 67篇 |
1998年 | 72篇 |
1997年 | 67篇 |
1996年 | 68篇 |
1995年 | 94篇 |
1994年 | 86篇 |
1993年 | 44篇 |
1992年 | 51篇 |
1991年 | 17篇 |
1990年 | 24篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 23篇 |
1986年 | 31篇 |
1985年 | 81篇 |
1984年 | 75篇 |
1983年 | 43篇 |
1982年 | 73篇 |
1981年 | 68篇 |
1980年 | 20篇 |
1978年 | 32篇 |
1977年 | 12篇 |
1975年 | 24篇 |
1974年 | 18篇 |
1973年 | 16篇 |
1972年 | 17篇 |
1969年 | 13篇 |
1968年 | 12篇 |
1966年 | 11篇 |
排序方式: 共有2698条查询结果,搜索用时 578 毫秒
671.
A. Chilingarian V. Babayan T. Karapetyan B. Mailyan B. Sargsyan M. Zazyan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(10):2680-2696
The Space Environment Viewing and Analysis Network (SEVAN) aims to improve the fundamental research on particle acceleration in the vicinity of the sun, on space weather effects and on high-energy physics in the atmosphere and lightning initiation. This new type of a particle detector setup simultaneously measures fluxes of most species of secondary cosmic rays, thus being a powerful integrated device for exploration of solar modulation effects and electron acceleration in the thunderstorm atmosphere. The SEVAN modules are operating at the Aragats Space Environmental Center (ASEC) in Armenia, in Croatia, Bulgaria, Slovakia, the Czech Republic (from 2017) and in India. In this paper, we present the most interesting results of the SEVAN network operation during the last decade. We present this review on the occasion of the 10th anniversary of the International Heliophysical Year in 2007. 相似文献
672.
Based on the experimental data, a dependence of the minimal friction losses in cascades was obtained. A turbine stage efficiency
gain as a result of cascade improvement over the last three decades of the 20th century was estimated by this dependence. 相似文献
673.
B. B. Kreisman 《Cosmic Research》2016,54(6):475-482
Horseshoe orbits in the restricted three-body problem have been mostly considered in the Sun–Jupiter system and, in recent years, in the Sun–Earth system. Here, these orbits have been used to find asteroids that have orbits of this kind. We have built a planar family of horseshoe orbits in the Earth–Moon system and determined the points of planar and 1/1 vertical resonances on this family. We have presented examples of orbits generated by these spatial families. 相似文献
674.
In this paper, a model of heat exchange and resistance in the channels with cylindrical grooves on the walls is presented. We compare the calculated data with the experimental results and give some recommendations for designers of power plants. 相似文献
675.
Atmospheric gravity wave (AGW) is a typical phenomenon in the upper atmosphere. At mid/low latitudes, climatological sources such as unstable barometric activity in the troposphere play an important role to generate AGWs in the thermosphere. While these sources are also important at high latitudes, energy input from the magnetosphere has additional large contributions to AGW generation. This paper reviews previous studies of AGWs associated with auroral activity at high latitudes. Theoretical studies have indicated that Joule/particle heating and the Lorentz force are major processes for generating AGWs in the thermosphere. Many observations show that AGWs can propagate horizontally for thousands of km from the source region. The paper summarizes equations regarding AGW generation by Joule/particle heating and the Lorentz force, and discusses the relative importance of these two processes. 相似文献
676.
677.
Geochemistry of Carbonates on Mars: Implications for Climate History and Nature of Aqueous Environments 总被引:1,自引:0,他引:1
Paul B. Niles David C. Catling Gilles Berger Eric Chassefière Bethany L. Ehlmann Joseph R. Michalski Richard Morris Steven W. Ruff Brad Sutter 《Space Science Reviews》2013,174(1-4):301-328
Ongoing research on martian meteorites and a new set of observations of carbonate minerals provided by an unprecedented series of robotic missions to Mars in the past 15 years help define new constraints on the history of martian climate with important crosscutting themes including: the CO2 budget of Mars, the role of Mg-, Fe-rich fluids on Mars, and the interplay between carbonate formation and acidity. Carbonate minerals have now been identified in a wide range of localities on Mars as well as in several martian meteorites. The martian meteorites contain carbonates in low abundances (<1 vol.%) and with a wide range of chemistries. Carbonates have also been identified by remote sensing instruments on orbiting spacecraft in several surface locations as well as in low concentrations (2–5 wt.%) in the martian dust. The Spirit rover also identified an outcrop with 16 to 34 wt.% carbonate material in the Columbia Hills of Gusev Crater that strongly resembled the composition of carbonate found in martian meteorite ALH 84001. Finally, the Phoenix lander identified concentrations of 3–6 wt.% carbonate in the soils of the northern plains. The carbonates discovered to date do not clearly indicate the past presence of a dense Noachian atmosphere, but instead suggest localized hydrothermal aqueous environments with limited water availability that existed primarily in the early to mid-Noachian followed by low levels of carbonate formation from thin films of transient water from the late Noachian to the present. The prevalence of carbonate along with evidence for active carbonate precipitation suggests that a global acidic chemistry is unlikely and a more complex relationship between acidity and carbonate formation is present. 相似文献
678.
V.V. Paznukhov V.G. Galushko B.W. Reinisch 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
A technique for studying ionospheric wavelike phenomena, primarily AGW/TID events, is developed based on the solution of the problem of radio wave propagation in ionospheric plasma disturbed by wavelike processes. A perfectly reflecting surface model is used for representing TIDs propagating at ionospheric heights. This technique is a generalization of the Frequency-and-Angular Sounding (FAS) method developed earlier for oblique TID diagnostics using transmitters of opportunity. Trial measurements were made in November 2003 with two DPS-4 systems at Millstone Hill Observatory, providing experimental validation of the developed method by comparing the results of disturbance diagnostics to those simultaneously obtained with the original (oblique) FAS method. The TID parameters recovered during the November 2003 campaign suggest that the observed disturbances predominately propagated equatorward which likely indicates their sources to be in the auroral region. The equatorward propagating AGW/TIDs are typical for disturbed geomagnetic conditions which were observed during the campaign. Implementation of the generalized FAS technique in the DPS sounder allowed development of a dedicated data acquisition system for ionospheric disturbance diagnostics. Routine measurements with the developed technique using the existing world-wide network of Digisondes (GIRO) will make it possible to conduct large-scale studies of the AGW/TID phenomena. 相似文献
679.
Numerical results obtained based on the equations for the general theory of physically orthotropic shells are presented. These results illustrate the influence of anisotropy for mechanical and physical characteristics of material on stressed state. 相似文献
680.
In order to realize the operational and service cost savings through the use of rechargeable batteries, the dismounted soldier is burdened with the weight, volume and/or charging logistics of the batteries. By providing the soldier with a high energy density source and a lightweight compact battery charger, the burden imposed by rechargeable batteries in the forward field can be minimized. Zinc-air batteries have the potential for meeting the energy demands of forward battlefield charging. They are attitude insensitive, have a high specific energy and are inherently inexpensive, lightweight and safe 相似文献