全文获取类型
收费全文 | 3809篇 |
免费 | 3篇 |
国内免费 | 9篇 |
专业分类
航空 | 1712篇 |
航天技术 | 1402篇 |
综合类 | 10篇 |
航天 | 697篇 |
出版年
2021年 | 28篇 |
2018年 | 56篇 |
2017年 | 51篇 |
2016年 | 47篇 |
2014年 | 65篇 |
2013年 | 104篇 |
2012年 | 88篇 |
2011年 | 153篇 |
2010年 | 107篇 |
2009年 | 150篇 |
2008年 | 197篇 |
2007年 | 111篇 |
2006年 | 78篇 |
2005年 | 112篇 |
2004年 | 127篇 |
2003年 | 123篇 |
2002年 | 81篇 |
2001年 | 117篇 |
2000年 | 60篇 |
1999年 | 86篇 |
1998年 | 107篇 |
1997年 | 77篇 |
1996年 | 70篇 |
1995年 | 109篇 |
1994年 | 125篇 |
1993年 | 64篇 |
1992年 | 76篇 |
1991年 | 32篇 |
1990年 | 42篇 |
1989年 | 68篇 |
1988年 | 30篇 |
1987年 | 26篇 |
1986年 | 38篇 |
1985年 | 125篇 |
1984年 | 111篇 |
1983年 | 91篇 |
1982年 | 77篇 |
1981年 | 155篇 |
1980年 | 31篇 |
1979年 | 34篇 |
1978年 | 37篇 |
1977年 | 34篇 |
1976年 | 29篇 |
1975年 | 34篇 |
1974年 | 29篇 |
1973年 | 31篇 |
1972年 | 41篇 |
1971年 | 22篇 |
1970年 | 22篇 |
1969年 | 21篇 |
排序方式: 共有3821条查询结果,搜索用时 406 毫秒
371.
V.E. Zuev S.I. Kavkyanov G.M. Krekov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1985,5(6):81-85
A single-frequency lidar, using aerosol scattering as an informative component, is the simplest and reliable facility for remote sensing of the atmosphere. The information on vertical distribution of atmospheric aerosol which can be obtained using such a lidar is necessary for investigating the physics of atmospheric processes and forecast of optical state of the atmosphere. At the same time, the interpretation of data on single-frequency sounding is associated with some difficulties of fundamental character, mainly due to insufficient software of the experiment. Under such conditions the problems of optimal processing of lidar returns aiming at extracting the useful information on aerosol are of great importance, especially if one takes into account the hindering effects of atmospheric background and optical noises. This paper presents a statistical approach to this problem, and the possibilities of single-frequency sounding from space are analyzed. 相似文献
372.
G R Petersen P K Seshan E H Dunlop 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1989,9(8):185-193
The operation and evaluation of a bioreactor designed for high intensity oxygen transfer in a microgravity environment is described. The reactor itself consists of a zero headspace liquid phase separated from the air supply by a long length of silicone rubber tubing through which the oxygen diffuses in and the carbon dioxide diffuses out. Mass transfer studies show that the oxygen is film diffusion controlled both externally and internally to the tubing and not by diffusion across the tube walls. Methods of upgrading the design to eliminate these resistances are proposed. Cell growth was obtained in the fermenter using Saccharomyces cerevisiae showing that this concept is capable of sustaining cell growth in the terrestrial [correction of terrestial] simulation. 相似文献
373.
G.J. Nagy D.N. Severov V.A. Pshennikov M. De los Santos J.J. Lagomarsino K. Sans E.G. Morozov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(11):1876-1881
This paper deals with the application of SeaWIFS images to characterize spatial and temporal variability of fronts in the Rio de la Plata estuarine system over the period 2000–2003. We aim to depict the relationship between river outflow and variability of fronts’ loci on monthly to ENSO-related timescales and the influence of the winds along Rio de la Plata (axial winds) on the abrupt changes in frontal dynamics over synoptic timescales. During the studied period both La Niña (July 1999–June 2000) and El Niño (April 2002–May 2003) events induced significant displacements of fronts. Three distinct fronts were analyzed between river, estuarine, coastal and marine waters of the Rio de la Plata: Main Turbidity Front, Main Marine Front, and Secondary Marine Front. Their number, location and separation seem to be mainly related to river outflow and second, to fresh (>8 m/s) axial winds. During low discharge periods (i.e. summer time and/or La Niña events) these winds induce abrupt changes in the location of fronts (100–200 km) and greater separation between them over synoptic timescale, whereas during high river discharge or ENSO years some of the variability of fronts location is explained by the river’s outflow fluctuations, especially by the high variability of the River Uruguay discharge. 相似文献
374.
Benchmark for radar allocation and tracking in ECM 总被引:4,自引:0,他引:4
375.
E.G. Berezhko 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(3):429-441
We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ∼1017 eV. 相似文献
376.
M.B. Moldwin D. Fiello E. Harter G. Holman N. Nagumo A. Pryharski C. Takunaga 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
An elementary science education professional development partnership between Culver City Unified School District teachers and UCLA has been formed. The project was designed to assist teachers to comfortably present introductory space science concepts, to support them in their efforts, and to aid them in encouraging their students to develop inquiry skills related to space sciences. The project encourages teacher use of observational science techniques in their classrooms, the use of NASA solar mission images and enhanced use of astronomical observation to facilitate discovery learning. The integrated approach of the project has fostered collegial learning activities among the participating teachers and offered them opportunities for continued renewal and professional development of teacher competencies in astronomy and space science. The activities used in the classroom were developed by others, classroom tested, and specifically address National Science Education and California Science Content Standards. These activities have been sustained through on-going collaboration between the scientist and the teachers, a summer Research Experience for Teachers program, and on-going, grade-specific, district-sponsored workshops. Assessment of the value of the program is done by the school district and is used to continuously improve each workshop and program component. Culver City (California) Unified School District is a small urban school district located on the Westside of Los Angeles. This paper describes the program and the plans for incorporating IHY-themed science into the classroom. 相似文献
377.
Yihua Zheng Anthony T.Y. Lui Mei-Ching Fok Brian J. Anderson Pontus C. Brandt Donald G. Mitchell 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(8):1234-1242
One essential component of magnetosphere and ionosphere coupling is the closure of the ring current through Region 2 field-aligned current (FAC). Using the Comprehensive Ring Current Model (CRCM), which includes magnetosphere and ionosphere coupling by solving the kinetic equation of ring current particles and the closure of the electric currents between the two regions, we have investigated the effects of high latitude potential, ionospheric conductivity, plasma sheet density and different magnetic field models on the development of Region 2 field-aligned currents, and the relationship between R2 FACs and the ring current. It is shown that an increase in high latitude potential, ionospheric conductivity or plasma sheet density generally results in an increase in Region 2 FACs’ intensity, but R2 FACs display different local time and latitudinal distributions for changes in each parameter due to the different mechanisms involved. Our simulation results show that the magnetic field configuration of the inner magnetosphere is also an important factor in the development of Region 2 field-aligned current. More numerical experiments and observational results are needed in further our understanding of the complex relationship of the two current systems. 相似文献
378.
Stephen W. Bougher Pierre-Louis Blelly Michael Combi Jane L. Fox Ingo Mueller-Wodarg Aaron Ridley Raymond G. Roble 《Space Science Reviews》2008,139(1-4):107-141
Numerical modeling tools can be used for a number of reasons yielding many benefits in their application to planetary upper atmosphere and ionosphere environments. These tools are commonly used to predict upper atmosphere and ionosphere characteristics and to interpret measurements once they are obtained. Additional applications of these tools include conducting diagnostic balance studies, converting raw measurements into useful physical parameters, and comparing features and processes of different planetary atmospheres. This chapter focuses upon various classes of upper atmosphere and ionosphere numerical modeling tools, the equations solved and key assumptions made, specified inputs and tunable parameters, their common applications, and finally their notable strengths and weaknesses. Examples of these model classes and their specific applications to individual planetary environments will be described. 相似文献
379.
Algorithms for determining fixed-pitch propeller parameters and some flight characteristics of a superlight aircraft at the early stage of designing are described. 相似文献
380.
Richard G. Lugar 《Space Policy》1985,1(3):231-236
Senator Lugar argues that a better European appreciation of the SDI is essential to try to define the roles of the US allies in the programme. A number of guidelines for allied participation should be applied, covering mode of participation, areas for participation, responsibilities under treaty provisions, technology transfer and security safeguards. Bilateral agreements are viewed as the mode for proceeding, but it is incumbent on the US government to outline the next steps it evisages to come to grips with the political considerations that will influence allied calculations on whether and under what circumstances to participate in SDI research. 相似文献