全文获取类型
收费全文 | 5673篇 |
免费 | 13篇 |
国内免费 | 14篇 |
专业分类
航空 | 2535篇 |
航天技术 | 2139篇 |
综合类 | 194篇 |
航天 | 832篇 |
出版年
2021年 | 41篇 |
2019年 | 39篇 |
2018年 | 103篇 |
2017年 | 50篇 |
2016年 | 65篇 |
2015年 | 29篇 |
2014年 | 120篇 |
2013年 | 144篇 |
2012年 | 130篇 |
2011年 | 191篇 |
2010年 | 128篇 |
2009年 | 233篇 |
2008年 | 312篇 |
2007年 | 159篇 |
2006年 | 141篇 |
2005年 | 144篇 |
2004年 | 148篇 |
2003年 | 182篇 |
2002年 | 212篇 |
2001年 | 238篇 |
2000年 | 101篇 |
1999年 | 136篇 |
1998年 | 166篇 |
1997年 | 112篇 |
1996年 | 154篇 |
1995年 | 183篇 |
1994年 | 153篇 |
1993年 | 92篇 |
1992年 | 134篇 |
1991年 | 63篇 |
1990年 | 55篇 |
1989年 | 122篇 |
1988年 | 47篇 |
1987年 | 52篇 |
1986年 | 55篇 |
1985年 | 184篇 |
1984年 | 158篇 |
1983年 | 116篇 |
1982年 | 146篇 |
1981年 | 169篇 |
1980年 | 54篇 |
1979年 | 52篇 |
1978年 | 43篇 |
1977年 | 36篇 |
1974年 | 38篇 |
1973年 | 30篇 |
1972年 | 32篇 |
1971年 | 30篇 |
1970年 | 32篇 |
1969年 | 31篇 |
排序方式: 共有5700条查询结果,搜索用时 15 毫秒
181.
Semenov Vladimir S. Kubyshkin Igor V. Kiendl Michael T. Biernat Helfried K. Rijnbeek Richard P. Besser Bruno P. 《Space Science Reviews》1997,82(3-4):451-461
In this article we address several criticisms of Petschek-type reconnection models which have recently been raised by Heikkila. We discuss features of the time-dependent Petschek-type models in the context of the solar wind-magnetosphere interaction, and point out that such models can incorporate and reproduce observed features at the magnetopause, such as plasma jets and erosion of the current sheet. We argue that some of Heikkila's criticisms can be attributed to weaknesses in the analysis due to incomplete experimental information, rather than to flaws in the concept of reconnection per se; in this category we include the question of which instability leads to the localised breakup of the magnetopause current sheet. Other criticisms are based on an adherence to steady-state models, and cannot be sustained within the extended time-dependent theory. We discuss, for example, how the time-dependent model can provide a consistent picture of how energy from the incoming solar wind is transferred and converted as it enters the magnetosphere. 相似文献
182.
J. Scudder F. Hunsacker G. Miller J. Lobell T. Zawistowski K. Ogilvie J. Keller D. Chornay F. Herrero R. Fitzenreiter D. Fairfield J. Needell D. Bodet J. Googins C. Kletzing R. Torbert J. Vandiver R. Bentley W. Fillius C. McIlwain E. Whipple A. Korth 《Space Science Reviews》1995,71(1-4):459-495
HYDRA is an experimental hot plasma investigation for the POLAR spacecraft of the GGS program. A consortium of institutions has designed a suite of particle analyzers that sample the velocity space of electron and ions between 2 keV/q – 35 keV/q in three dimensions, with a routine time resolution of 0.5 s. Routine coverage of velocity space will be accomplished with an angular homogeneity assumption of 16°, appropriate for subsonic plasmas, but with special 1.5° resolution for electrons with energies between 100 eV and 10 keV along and opposed to the local magnetic field. This instrument produces 4.9 kilobits s–1 to the telemetry, consumes on average 14 W and requires 18.7 kg for deployment including its internal shielding. The scientific objectives for the polar magnetosphere fall into four broad categories: (1) those to define the ambient kinetic regimes of ions and electrons; (2) those to elucidate the magnetohydrodynamic responses in these regimes; (3) those to assess the particle populations with high time resolution; and (4) those to determine the global topology of the magnetic field. In thefirst group are issues of identifying the origins of particles at high magnetic latitudes, their energization, the altitude dependence of the forces, including parallel electric fields they have traversed. In thesecond group are the physics of the fluid flows, regimes of current, and plasma depletion zones during quiescent and disturbed magnetic conditions. In thethird group is the exploration of the processes that accompany the rapid time variations known to occur in the auroral zone, cusp and entry layers as they affect the flow of mass, momentum and energy in the auroral region. In thefourth class of objectives are studies in conjunction with the SWE measurements of the Strahl in the solar wind that exploit the small gyroradius of thermal electrons to detect those magnetic field lines that penetrate the auroral region that are directly open to interplanetary space where, for example, the Polar Rain is observed. 相似文献
183.
Calculation of optimum gain for minimum distortion due to A/D (analog-to-digital) conversion requires the estimation of the input signal strength. To use a common AGC (automatic gain control) for both the I/Q (in-phase and quadrature) signals, it is efficient to estimate the input signal strength using the quantized A/D output from both channels. Assuming a Gaussian input, the relationship between σ of the input of the A/D converter and E (|x |+|y |) and E (max(|x |,|y |)+1/2 min (|x |,|y |)) for t quantized I/Q output x and y is derived. Numerical results obtained using the derived expression and the statistical data obtained through simulation show excellent agreement. It is concluded that, because of its simplicity, the cubic equation obtained by fitting the numerical results should be useful 相似文献
184.
Corrections of pointing data provided by gimbal readout transducers can be used to compensate for the errors that arise because of gimbal misalignments and inaccuracies in transducer readout. This paper reviews the sources of pointing error in precision gimbaled pointing systems and describes the techniques for determining them. In particular, a method of calibration that is suitable for systems in which constraints on gimbal travel preclude the use of conventional calibration procedures is presented, and the pointing readout accuracy that can be achieved by this method is evaluated. 相似文献
185.
186.
J. P. Cox J. C. Wheeler C. J. Hansen D. S. King A. N. Cox S. W. Hodson 《Space Science Reviews》1980,27(3-4):529-535
The radial pulsations of very luminous, low-mass models (L/M 104, solar units), which are possible representatives of the R CrB stars, have been examined. These pulsations are extremely nonadiabatic. We find that there are in some cases at least one extra (strange) mode which makes interpretation difficult. The blue instability edges are also peculiar, in that there is an abrupt excursion of the blue edge to the blue for L/M sufficiently large. The range of periods of the model encompasses observed periods of the Cepheid-like pulsations of actual R CrB stars. 相似文献
187.
K. Schindler 《Space Science Reviews》1979,23(3):365-374
The present theories of tail structures are reviewed. It is shown that any satisfactory model for the quiet tail has to include at least two space dimensions. Several approaches to two-dimensional structures and some recent results of a study that includes the third dimension are reviewed. It is demonstrated that the observed gross structural properties of the quiet magnetotail can be reasonably well understood from these theories. A brief discussion of selected aspects of tail dynamics is added.Proceedings of the Symposium on Solar Terrestrial Physics held in Innsbruck, May–June 1978. 相似文献
188.
An Adaptive Extended Kalman Filter for Target Image Tracking 总被引:1,自引:0,他引:1
189.
K. G. Ivanov 《Space Science Reviews》1982,32(1-2):49-63
The configuration, and the structure of shock waves from isolated solar flares and from a series of flares are discussed and classified.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia. 相似文献
190.
A conceptual system is proposed and described for the control of a multiplicity of drone aircraft. Each target (drone) aircraft is controlled, during a given mission, over a separate preprogrammed path comprised of straight line and circular arc segments. Full control of each target's altitude, plan position, and velocity is available. Position measurement can be obtained by use of either a radar or a bilateration method where altitude is measured in either case by each aircraft and telemetered to a central control point. Velocity is obtained by smoothing position data in a central computer, which also controls the entire mission complex. 相似文献