全文获取类型
收费全文 | 10154篇 |
免费 | 19篇 |
国内免费 | 43篇 |
专业分类
航空 | 4675篇 |
航天技术 | 3567篇 |
综合类 | 33篇 |
航天 | 1941篇 |
出版年
2021年 | 93篇 |
2019年 | 65篇 |
2018年 | 220篇 |
2017年 | 146篇 |
2016年 | 136篇 |
2015年 | 63篇 |
2014年 | 242篇 |
2013年 | 297篇 |
2012年 | 292篇 |
2011年 | 427篇 |
2010年 | 300篇 |
2009年 | 465篇 |
2008年 | 521篇 |
2007年 | 305篇 |
2006年 | 238篇 |
2005年 | 291篇 |
2004年 | 282篇 |
2003年 | 312篇 |
2002年 | 223篇 |
2001年 | 330篇 |
2000年 | 208篇 |
1999年 | 243篇 |
1998年 | 280篇 |
1997年 | 184篇 |
1996年 | 255篇 |
1995年 | 326篇 |
1994年 | 302篇 |
1993年 | 166篇 |
1992年 | 243篇 |
1991年 | 86篇 |
1990年 | 86篇 |
1989年 | 215篇 |
1988年 | 88篇 |
1987年 | 89篇 |
1986年 | 100篇 |
1985年 | 287篇 |
1984年 | 225篇 |
1983年 | 187篇 |
1982年 | 211篇 |
1981年 | 297篇 |
1980年 | 82篇 |
1979年 | 63篇 |
1978年 | 76篇 |
1977年 | 62篇 |
1976年 | 53篇 |
1975年 | 71篇 |
1974年 | 66篇 |
1973年 | 54篇 |
1972年 | 52篇 |
1970年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
781.
Direct measurements of the geomagnetic field have been made for more than 400 years, beginning with individual determinations of the angle between geographic and magnetic North. This was followed by the start of continuous time series of full vector measurements at geomagnetic observatories and the beginning of geomagnetic repeat stations surveys in the 19th century. In the second half of the 20th century, true global coverage with geomagnetic field measurements was accomplished by magnetometer payloads on low-Earth-orbiting satellites. This article describes the procedures and instruments for magnetic field measurements on ground and in space and covers geomagnetic observatories, repeat stations, automatic observatories, satellites and historic observations. Special emphasis is laid on the global network of geomagnetic observatories. 相似文献
782.
E. M. Korovin 《Russian Aeronautics (Iz VUZ)》2012,55(3):326-331
In this paper, a mathematical model of labor-intensity and a method of searching for optimal control of operating conditions in machining arbitrarily configurated parts with the use of CNC machines are considered. Also given is an example of the process optimization.. 相似文献
783.
The paper presents an improved technique and the results of strength analysis for the aircraft structural elements with a structural defect like an arbitrary shape delamination. 相似文献
784.
We consider in detail the intense Pc5 pulsations of the magnetic field, riometric absorption, and electron fluxes occurred
on the recovery phase of the strong magnetic storm on November 21, 2003. The global structure of these disturbances is studied
using the world network of magnetometers and riometers supplemented by the data of particle detectors onboard the LANL geosynchronous satellites. The local spatial structure is investigated according to data of the regional network of Finnish
vertical riometers and of stations of the IMAGE magnetic network. Though a certain similarity is observed in the frequency
composition and time evolution of the variations of magnetic field and riometric absorption, the local spatial structure of
these oscillations turns out to be different. It is suggested that these variations can be manifestations of oscillatory properties
of two weakly connected systems: the magnetospheric MHD waveguide/resonator and the system cyclotron noise + electrons. The
recorded Pc5 oscillations are, presumably, a result of excitation of the magnetospheric waveguide on the morning and evening
flanks of the magnetosphere. At high velocities of the solar wind this waveguide can appear in a metastable state. Not only
jumps in the solar wind density, but injection of electrons into the magnetosphere as well, can serve as a trigger for the
waveguide excitation. 相似文献
785.
This paper proposes a novel landing gear for spacecraft that allows a weight reduction due to using deformable crash legs. Numerical simulation of the landing process was performed. 相似文献
786.
Dynamics of planets around other stars that demonstrate a variety of possible characteristics is of interest from the point
of view of realization of new scenarios of evolution which have not been realized in the Solar System. We consider the rotational
evolution of exoplanets under the action of gravitational perturbations and magnetic disturbances using the methods of quality
analysis and theory of bifurcation of multiparametric differential equations that describe evolution of non-resonant rotation
of a dynamically symmetric planet magnetized along its symmetry axis. We analyze 64 phase portraits describing the evolution
of angular momentum vector L for all possible values of planet parameters. The values of parameters are determined for the case when the direct rotation
of a planet is changed for its retrograde rotation. 相似文献
787.
A. S. Meshchanov 《Russian Aeronautics (Iz VUZ)》2010,53(4):382-393
The results obtained for the systems with a linear stationary object and scalar control of sliding and switching modes [1]
are further developed. The methods of forming five modes of system operation with discontinuous and linear vector control
at nominal and uncertain limited disturbances are suggested. The necessary quality of transient processes with regard to the
speed of response and zero stationary error at all five modes and also controlled oscillation frequency and amplitude of control
signals at the sliding modes are provided. The effective sequence of switching the modes mentioned during the finite and unlimited
time intervals is proposed. The results are useful for qualitative tracking of programmed motion for flight vehicles, robot
manipulators, and other technical and production systems. 相似文献
788.
Vitali Braun A. LüpkenS. Flegel J. GelhausM. Möckel C. KebschullC. Wiedemann P. Vörsmann 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Today’s space debris environment shows major concentrations of objects within distinct orbital regions for nearly all size regimes. The most critical region is found at orbital altitudes near 800 km with high declinations. Within this region many satellites are operated in so called sun-synchronous orbits (SSO). Among those, there are Earth observation, communication and weather satellites. Due to the orbital geometry in SSO, head-on encounters with relative velocities of about 15 km/s are most probable and would thus result in highly energetic collisions, which are often referred to as catastrophic collisions, leading to the complete fragmentation of the participating objects. So called feedback collisions can then be triggered by the newly generated fragments, thus leading to a further population increase in the affected orbital region. This effect is known as the Kessler syndrome. 相似文献
789.
M. E. Wiedenbeck 《Space Science Reviews》2013,176(1-4):35-46
The spectra of galactic cosmic rays that are observed inside the heliosphere result from the interaction of the spectra present in the local interstellar medium with the structured but turbulent magnetic field carried by the solar wind. Observational tests of solar modulation theory depend on comparisons between spectra inside and outside the heliosphere. Our knowledge of the local interstellar spectra are indirect, using extrapolations of interplanetary spectra measured at high energies where solar modulation effects are minimal and modeling of the physical processes that occur during particle acceleration and transport in the interstellar medium. The resulting estimates of the interstellar spectra can also be checked against observations of the effects that cosmic rays have on the chemistry of the interstellar medium and on the production of the diffuse galactic gamma-ray background. I review the present understanding of the local galactic cosmic-ray spectra, emphasizing the constraints set by observations and the uncertainties that remain. 相似文献
790.
Alfvén waves are considered to be viable transporters of the non-thermal energy required to heat the Sun’s quiescent atmosphere. An abundance of recent observations, from state-of-the-art facilities, have reported the existence of Alfvén waves in a range of chromospheric and coronal structures. Here, we review the progress made in disentangling the characteristics of transverse kink and torsional linear magnetohydrodynamic (MHD) waves. We outline the simple, yet powerful theory describing their basic properties in (non-)uniform magnetic structures, which closely resemble the building blocks of the real solar atmosphere. 相似文献