全文获取类型
收费全文 | 2169篇 |
免费 | 4篇 |
国内免费 | 7篇 |
专业分类
航空 | 753篇 |
航天技术 | 762篇 |
综合类 | 8篇 |
航天 | 657篇 |
出版年
2022年 | 6篇 |
2021年 | 23篇 |
2019年 | 7篇 |
2018年 | 73篇 |
2017年 | 58篇 |
2016年 | 56篇 |
2015年 | 20篇 |
2014年 | 69篇 |
2013年 | 68篇 |
2012年 | 66篇 |
2011年 | 109篇 |
2010年 | 80篇 |
2009年 | 125篇 |
2008年 | 144篇 |
2007年 | 81篇 |
2006年 | 51篇 |
2005年 | 66篇 |
2004年 | 70篇 |
2003年 | 83篇 |
2002年 | 53篇 |
2001年 | 90篇 |
2000年 | 38篇 |
1999年 | 41篇 |
1998年 | 43篇 |
1997年 | 34篇 |
1996年 | 49篇 |
1995年 | 40篇 |
1994年 | 33篇 |
1993年 | 20篇 |
1992年 | 35篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 34篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 67篇 |
1984年 | 35篇 |
1983年 | 25篇 |
1982年 | 37篇 |
1981年 | 66篇 |
1980年 | 16篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 13篇 |
1976年 | 9篇 |
1975年 | 14篇 |
1974年 | 15篇 |
1973年 | 8篇 |
1970年 | 4篇 |
排序方式: 共有2180条查询结果,搜索用时 15 毫秒
61.
In this paper, the results of calculating the processes of two fuel mixture combustion in different proportions are presented. The values of temperature, thermal capacity, specific gas constant and isentropic expansion ratio of combustion products are given. Also shown is the distinction of thermodynamic properties from the additivity law. 相似文献
62.
I. S. Akhmed’yanov 《Russian Aeronautics (Iz VUZ)》2010,53(2):230-234
To complete study [1], the procedure of applying the numerical quadrature method to analyzing the shells of revolution under axisymmetrical loading is presented. 相似文献
63.
To calculate the unsteady helicopter motion, we propose a simplifying approach consisting in the fact that the numerical solution of equations of nonlinear nonstationary aerodynamics and flight dynamics are made successively in time intervals. As an example, the results of calculating the helicopter motion in descent are presented. The mathematical model and algorithm can be used for calculating the unsteady motion of different helicopters. 相似文献
64.
65.
Understanding properties of solar energetic particle (SEP) events associated with coronal mass ejections has been identified
as a key problem in solar-terrestrial physics. Although recent CME shock acceleration models are highly promising, detailed
agreement between theoretical predictions and observations has remained elusive. Recent observations from ACE have shown substantial
enrichments in the abundances of 3He and He+ ions which are extremely rare in the thermal solar wind plasma. Consequently, these ions act as tracers of their source material,
i.e.,
3He ions are flare suprathermals and He+ ions are interstellar pickup ions. The average heavy ion composition also exhibits unsystematic differences when compared
with the solar wind values, but correlates significantly with the ambient suprathermal material abundances. Taken together
these results provide compelling evidence that CME-driven shocks draw their source material from the ubiquitous but largely
unexplored suprathermal tail rather than from the more abundant solar wind peak. However, the suprathermal energy regime has
many more contributors and exhibits much larger variability than the solar wind, and as such needs to be investigated more
thoroughly. Answers to fundamental new questions regarding the preferred injection of the suprathermal ions, the spatial and
temporal dependence of the various sources, and the causes of their variability and their effects on the SEP properties are
needed to improve agreement between the simulations and observations. 相似文献
66.
The problem of optimal state estimation of linear discrete-time systems with measured outputs that are corrupted by additive white noise is addressed. Such estimation is often encountered in problems of target tracking where the target dynamics is driven by finite energy signals, whereas the measurement noise is approximated by white noise. The relevant cost function for such tracking problems is the expected value of the standard H/sub /spl infin// performance index, with respect to the measurement noise statistics. The estimator, serving as a tracking filter, tries to minimize the mean-square estimation error, and the exogenous disturbance, which may represent the target maneuvers, tries to maximize this error while being penalized for its energy. The solution, which is obtained by completing the cost function to squares, is shown to satisfy also the matrix version of the maximum principle. The solution is derived in terms of two coupled Riccati difference equations from which the filter gains are derived. In the case where an infinite penalty is imposed on the energy of the exogenous disturbance, the celebrated discrete-time Kalman filter is recovered. A local iterations scheme which is based on linear matrix inequalities is proposed to solve these equations. An illustrative example is given where the velocity of a maneuvering target has to be estimated utilizing noisy measurements of the target position. 相似文献
67.
A. Galli P. Wurz H. Lammer H. I. M. Lichtenegger R. Lundin S. Barabash A. Grigoriev M. Holmström H. Gunell 《Space Science Reviews》2006,126(1-4):447-467
We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m?3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity. 相似文献
68.
69.
T. Van Doorsselaere I. Arregui J. Andries M. Goossens S. Poedts 《Space Science Reviews》2005,121(1-4):79-89
We will discuss the observed, heavily damped transversal oscillations of coronal loops. These oscillations are often modeled
as transversal kink oscillations in a cylinder. Several features are added to the classical cylindrical model. In our models
we include loop curvature, longitudinal density stratification, and highly inhomogeneous radial density profiles.
In this paper, we will first give an overview of recently obtained results, both analytically and numerically. After that,
we shed a light on the computational aspects of the modeling process. In particular, we will focus on the parallellization
of the numerical codes. 相似文献
70.
Yakimenko O.A. Kaminer I.I. Lentz W.J. Ghyzel P.A. 《IEEE transactions on aerospace and electronic systems》2002,38(4):1181-1200
This paper addresses the problem of determining the relative position and orientation of an unmanned air vehicle with respect to a ship using three visible points of known separation. The, images of the points are obtained from an onboard infrared camera. The paper develops a numerical solution to this problem. Both simulation and flight test results are presented. 相似文献