全文获取类型
收费全文 | 6221篇 |
免费 | 48篇 |
国内免费 | 33篇 |
专业分类
航空 | 2723篇 |
航天技术 | 2099篇 |
综合类 | 88篇 |
航天 | 1392篇 |
出版年
2022年 | 28篇 |
2021年 | 65篇 |
2018年 | 149篇 |
2017年 | 139篇 |
2016年 | 129篇 |
2015年 | 69篇 |
2014年 | 163篇 |
2013年 | 208篇 |
2012年 | 181篇 |
2011年 | 283篇 |
2010年 | 214篇 |
2009年 | 304篇 |
2008年 | 355篇 |
2007年 | 218篇 |
2006年 | 164篇 |
2005年 | 201篇 |
2004年 | 152篇 |
2003年 | 195篇 |
2002年 | 153篇 |
2001年 | 202篇 |
2000年 | 120篇 |
1999年 | 142篇 |
1998年 | 153篇 |
1997年 | 127篇 |
1996年 | 122篇 |
1995年 | 162篇 |
1994年 | 159篇 |
1993年 | 89篇 |
1992年 | 114篇 |
1991年 | 48篇 |
1990年 | 58篇 |
1989年 | 100篇 |
1988年 | 45篇 |
1987年 | 44篇 |
1986年 | 46篇 |
1985年 | 158篇 |
1984年 | 128篇 |
1983年 | 113篇 |
1982年 | 92篇 |
1981年 | 169篇 |
1980年 | 46篇 |
1979年 | 42篇 |
1978年 | 42篇 |
1977年 | 38篇 |
1976年 | 34篇 |
1975年 | 50篇 |
1974年 | 29篇 |
1972年 | 45篇 |
1971年 | 34篇 |
1967年 | 27篇 |
排序方式: 共有6302条查询结果,搜索用时 937 毫秒
861.
This paper describes the procedure implemented to design, develop and test an aeroelastic control system installed on a forward swept wing of the aeroelastic demonstrator X-DIA. A control method directly based on Nissim aerodynamic energy concept has been chosen. Two different modeling techniques have been adopted for the calculation of generalized aerodynamic forces, such as doublet lattice method and computational fluid dynamics and the obtained results are finally compared. The latter approach, applied to better estimate the control surfaces effectiveness, requires the capability to correctly model the control surface rotation and the grid deformation, usually addressed as non-trivial problems in CFD based aeroelastic analysis. A genetic algorithm optimization technique has been adopted to state and refine all the control gains. 相似文献
862.
Miller D.L. Wolfman G.J. Volanth A.J. Mullins R.T. 《Aerospace and Electronic Systems Magazine, IEEE》1996,11(4):22-26
Tower air traffic control is currently performed using several unintegrated systems. While each of these systems supports performing an isolated task, the compilation of tools presents a number of challenges. This paper reports ways in which the Tower Control Computer Complex (TCCC) will support and enhance user management of numerous systems. Areas that will be notably improved include the consistency in the user interface of the air traffic control toolset, the task of manually integrating tools and information, toolset alert management, and toolset organization and administration 相似文献
863.
864.
V. A. Ryabyi V. A. Obukhov A. P. Kirpichnikov P. E. Masherov A. I. Mogulkin 《Russian Aeronautics (Iz VUZ)》2015,58(4):448-453
A technique of integral diagnostics for an RF inductively coupled plasma gas discharge unit of an ion thruster is proposed. This technique includes a priori measurements of antenna coil electrical parameters in free space and in assembled state as well as experimental determination of the antenna coil currents with and without discharge. 相似文献
865.
G. A. Gusev B. N. Lomonosov K. M. Pichkhadze N. G. Polukhina V. A. Ryabov T. Saito V. K. Sysoev E. L. Feinberg V. A. Tsarev V. A. Chechin 《Cosmic Research》2006,44(1):19-38
An estimate of the feasibility of the ultrahigh-energy cosmic ray and neutrino detection using a lunar satellite-borne radio receiver is presented. The data obtained in the proposed experiment will make resolving the current contradictions in the ultrahigh-energy cosmic ray spectra measured with the major ground-based instruments possible. Moreover, they will enable us to considerably extend the accessible energy range and to check predictions of various models of the origin of the highest-energy particles in the Universe. At the same time the lunar radio detector provides a means of searching for ultrahigh-energy neutrinos with a high sensitivity combined with a very large target effective mass. 相似文献
866.
The Navy Navigation Satellite System (TRANSIT) has provided 100% system reliability since being declared operational October 11, 1968. TRANSIT continues to carry out its function of precise, reliable, all weather navigation for the United States Navy and nearly 80,000 worldwide commercial users. TRANSIT's utility has been expanded to provide precise positioning information to those in the fields of geodesy and doppler surveying. While TRANSIT's history is illustrious, its life is limited. The transition from TRANSIT as the Navy's satellite navigation system to NAVSTAR GPS is planned for the 1990' s, with the result that TRANSIT is now scheduled for phase out by the United States Navy in 1994. This paper (essentially an update of reference [1]) will show the current status and plans for TRANSIT, following a brief historical overview. 相似文献
867.
The testing and evaluation of sophisticated security systems has remained in the domain of governments in national facilities and the commercial security industry through manufacturers and engineering consultants. As well, the production of testing protocols and industry standards has been developed by national organisations, professional security, and engineering bodies in the appropriate security fields. The Security Systems Research and Testing Laboratory in the School of Engineering and Mathematics at Edith Cowan University (ECU), Perth, Western Australia has commenced operations in research, testing, and evaluation of security systems. This paper wir describe the first year of operation of the Security Systems Research and Testing Laboratory, and will describe the role that testing and evaluation of security systems plays in the education and training of Security Science graduates, as well as the benefits that the Laboratory brings to the security industry through its testing programme. 相似文献
868.
V Switzer RC rdBogo G A Mickley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(10):443-451
Application of the degeneration sensitive, cupric-silver staining method to brain sections of male Sprague-Dawley rats irradiated 4 days before sacrifice with 155 Mev protons, 2-8 Gy at 1 Gy/min (N=6) or 22-l0lGy at 20 Gy/min (N=16) or with 18.6 Mev electrons, 32-67 Gy at 20 Gy/min (N=20), doses which elicit behavioral changes (accelerod or conditioned taste aversion), resulted in a display of degeneration of astrocyte-like cell profiles which were not uniformly distributed. Plots of 'degeneration scores' (counts of profiles in 29 areas) vs. dose for the proton and electron irradiations displayed a linear dose response for protons in the range of 2-8 Gy. In the 20-100 Gy range, for both electrons and protons the points were distributed in a broad band suggesting a saturation curve. The dose range in which these astrocyte-like profiles becomes maximal corresponds well with the dose range for the X-ray eradication of a subtype of astrocytes, 'beta astrocytes'. 相似文献
869.
The current status of the theory of a new astrophysical phenomenon, aradiation-driven diskon, is outlined.The cyclotron radiation pressure around sufficiently hot, strongly magnetized white dwarfs and neutron stars is shown to be able to drive a wind from the photosphere and support a plasma envelope in the closed part of the magnetosphere. The magnetohydrostatic configuration of an optically thin, radiatively supported plasma envelope is determined. It consists of an equatorial disk in the region where the cyclotron radiation force exceeds the local force of gravity and a closed shell near the equilibrium surface where the radiation pressure equals gravity. The effects of finite optical depth on the behaviour of the magnetospheric plasma and the influence of the envelope on the observed radiation are discussed.Classes of magnetic degenerate stars are pointed out in which radiation-driven diskons may be found. The best candidates are two individual stars, the strongly magnetized white dwarfs GD 229 and PG 1031+234. Both exhibit broad and deep depressions in the ultraviolet which are explained as a result of cyclotron scattering by an optically thick radiation-driven envelope in the inhomogeneous magnetic field of the star. We predict a temporal and spectral variability of these features due to non-stationary plasma motions in the envelope. 相似文献
870.
J A Guikema L DeBell A Paulsen B S Spooner P P Wong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1994,14(8):173-176
The development of legume root nodules was studied as a model system for the examination of gravitational effects on plant root development. In order to examine whether rhizobial association with clover roots can be achieved in microgravity, experiments were performed aboard the KC-135 parabolic aircraft and aboard the sounding rocket mission Consort 3. Binding of rhizobia to roots and the initial stages of root nodule development successfully occurred in microgravity. Seedling germination experiments were performed in the sliding block device, the Materials Dispersion Apparatus, aboard STS-37. When significant hydration of the seeds was achieved, normal rates of germination and seedling development were observed. 相似文献