全文获取类型
收费全文 | 2532篇 |
免费 | 4篇 |
国内免费 | 6篇 |
专业分类
航空 | 1187篇 |
航天技术 | 919篇 |
综合类 | 9篇 |
航天 | 427篇 |
出版年
2021年 | 18篇 |
2019年 | 16篇 |
2018年 | 58篇 |
2017年 | 35篇 |
2016年 | 39篇 |
2015年 | 12篇 |
2014年 | 55篇 |
2013年 | 89篇 |
2012年 | 55篇 |
2011年 | 85篇 |
2010年 | 71篇 |
2009年 | 118篇 |
2008年 | 139篇 |
2007年 | 58篇 |
2006年 | 63篇 |
2005年 | 64篇 |
2004年 | 64篇 |
2003年 | 85篇 |
2002年 | 43篇 |
2001年 | 92篇 |
2000年 | 48篇 |
1999年 | 65篇 |
1998年 | 69篇 |
1997年 | 66篇 |
1996年 | 65篇 |
1995年 | 87篇 |
1994年 | 86篇 |
1993年 | 41篇 |
1992年 | 50篇 |
1991年 | 15篇 |
1990年 | 24篇 |
1989年 | 51篇 |
1988年 | 32篇 |
1987年 | 20篇 |
1986年 | 28篇 |
1985年 | 74篇 |
1984年 | 72篇 |
1983年 | 42篇 |
1982年 | 71篇 |
1981年 | 67篇 |
1980年 | 17篇 |
1979年 | 10篇 |
1978年 | 31篇 |
1977年 | 12篇 |
1975年 | 24篇 |
1974年 | 16篇 |
1973年 | 16篇 |
1972年 | 16篇 |
1970年 | 9篇 |
1969年 | 12篇 |
排序方式: 共有2542条查询结果,搜索用时 937 毫秒
661.
662.
This paper summarizes the results of numerical experiments to determine the sensitivity of the final attitude of an inflatable solar sail with vanes after deployment to various parameters affecting the deployment process. These parameters are: in- and out-of-plane asymmetries during deployment, length inflation profile, and vane deployment failures. We show how robust the sail deployment is to geometric asymmetries before a 35° off-Sun angle is reached. Differential delays in the time to inflate the booms and a boom sweep-back angle affect the stability favorably. Adjacent vane failures to deploy affect the stability unfavorably, while the failure of opposing vanes is acceptable. Realistic boom length rate profiles obtained during ground tests are used in the simulation showing that failing adjacent vanes in conjunction with initial inflation delays in adjacent booms represent the worst case. We also demonstrate that by feeding back attitude and attitude rate measurements so that a corrective action is taken during the deployment, the final attitude can be maintained very close to the initial attitude, thus mitigating the attitude changes incurred during deployment. 相似文献
663.
V. A. Parkhomov G. N. Zastenker M. O. Riazantseva B. Tsegmed T. A. Popova 《Cosmic Research》2010,48(1):86-100
We present the results of studying the magnetospheres’s response to sharp changes of the solar wind flow (pressure) based
on observations of variations of the ions flux of the solar wind onboard the Inreball-1 satellite and of geomagnetic pulsations (the data of two mid-latitude observatories and one auroral observatory are used).
It is demonstrated that, when changes of flow runs into the magnetosphere, in some cases short (duration ~ < 5 min) bursts
of geomagnetic pulsations are excited in the frequency range Δf~ 0.2–5 Hz. The bursts of two types are observed: noise bursts without frequency changes and wide-band ones with changing
frequency during the burst. A comparison is made of various properties of these bursts generated by pressure changes at constant
velocity of the solar wind and by pressure changes on the fronts of interplanetary shock waves at different directions of
the vertical component of the interplanetary magnetic field. 相似文献
664.
E. Bering M. Engebretson R. Holzworth A. Kadokura M. Kokorowski B. Reddell J. Posch H. Yamagishi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The 2nd Polar Patrol Balloon campaign (2nd-PPB) was carried out at Syowa Station in Antarctica during 2002–2003. Identical stratospheric balloon payloads were launched as close together in time as allowed by weather conditions to constitute a cluster of balloons during their flights. A very pronounced negative ion conductivity enhancement was observed at 32 km in the stratosphere below the auroral zone on 27 January 2003 from 1500 to 2200 UT. During this event, the conductivity doubled for an interval of about 7 h. This perturbation was associated with an extensive Pc 1 or Pi 1 wave event that was observed by several Antarctic ground stations, balloon PPB 10, and the Polar spacecraft. No appreciable X-ray precipitation was observed in association with this event, which would point to >60 Mev proton precipitation as a possible magnetosphere–stratosphere coupling mechanism responsible for the conductivity enhancement. Such precipitation is consistent with the wave data. During the latter half of the event, Ez was briefly positive. There was a tropospheric Southern Ocean storm system underneath the balloon during this interval. If the event was associated with this storm system and not energetic proton precipitation, the observations imply an electrified Southern Ocean storm and major perturbations in stratospheric conductivity driven by a tropospheric disturbance. This event represents a poorly understood source for global circuit current. Precipitating energetic proton data from Akebono and NOAA POES spacecraft show significant >16 MeV precipitation was occurring at the location of PPB 8 but not PPB 10, suggesting that proton precipitation was, in fact, the responsible coupling mechanism. 相似文献
665.
E. Möbius H. Kucharek G. Clark M. O’Neill L. Petersen M. Bzowski L. Saul P. Wurz S. A. Fuselier V. V. Izmodenov D. J. McComas H. R. Müller D. B. Alexashov 《Space Science Reviews》2009,146(1-4):149-172
Every year in fall and spring the Interstellar Boundary Explorer (IBEX) will observe directly the interstellar gas flow at 1 AU over periods of several months. The IBEX-Lo sensor employs a powerful triple time-of-flight mass spectrometer. It can distinguish and image the O and He flow distributions in the northern fall and spring, making use of sensor viewing perpendicular to the Sun-pointing spin axis. To effectively image the narrow flow distributions IBEX-Lo has a high angular resolution quadrant in its collimator. This quadrant is employed selectively for the interstellar gas flow viewing in the spring by electrostatically shutting off the remainder of the aperture. The operational scenarios, the expected data, and the necessary modeling to extract the interstellar parameters and the conditions in the heliospheric boundary are described. The combination of two key interstellar species will facilitate a direct comparison of the pristine interstellar flow, represented by He, which has not been altered in the heliospheric boundary region, with a flow that is processed in the outer heliosheath, represented by O. The O flow distribution consists of a depleted pristine component and decelerated and heated neutrals. Extracting the latter so-called secondary component of interstellar neutrals will provide quantitative constraints for several important parameters of the heliosheath interaction in current global heliospheric models. Finding the fraction and width of the secondary component yields an independent value for the global filtration factor of species, such as O and H. Thus far filtration can only be inferred, barring observations in the local interstellar cloud proper. The direction of the secondary component will provide independent information on the interstellar magnetic field strength and orientation, which has been inferred from SOHO SWAN Ly-α backscattering observations and the two Voyager crossings of the termination shock. 相似文献
666.
Design of a three-axial accelerometer-seismometer, constructed on the basis of two-coordinate sensors (sensitive elements)
of high and low accelerations, is considered in the paper. This instrument is applied for gravi-inertial measurements. Basic
characteristics of the instrument are described, as well as the technique and results of its standardization. 相似文献
667.
An analysis of the existing astrometric and radar observations of the Apophis asteroid is performed. On the basis of this
analysis, characteristics of future measurements of the asteroid orbit and limitation on their conduction are accepted. A
proposed launching of a spacecraft to the asteroid in order to obtain high-accuracy measurements of its distance and radial
velocity is also considered. Trajectories of the flight to the asteroid in 2012–2022 are studied. Estimates of the accuracy
of the Apophis position determination at various sets of both available and planned measurements at various numbers of determined
parameters are obtained. The method of estimating accuracy is similar to that used in [1] for the Vega project. 相似文献
668.
The influence of aerodynamic heating of the aircraft skin with a partially damaged thermal insulation on its dynamic behavior is studied numerically. The study is carried out in two steps: the first step is to determine the temperature field in the shell; the second step is to measure the values of structure material characteristics depending on its temperature, to correct the stiffness matrix of the skin, and to solve the dynamics problem. The examples are considered. 相似文献
669.
K. B. Panfilovich 《Russian Aeronautics (Iz VUZ)》2014,57(1):71-74
In this paper, a physical model of gas flows through the channels is refined. The influence of gas absorbed by the walls of a channel on its conductance is shown. The experimentally obtained minimum on the channel conductance-pressure dependence (as the Knudsen paradox) is interpreted. 相似文献
670.
B. V. Nerubailo 《Russian Aeronautics (Iz VUZ)》2014,57(2):127-133
The solution is obtained based on the differential equations for the general theory of shells and approximate equations that are the components of the method of asymptotic synthesis. Numerical results are presented. 相似文献