全文获取类型
收费全文 | 5339篇 |
免费 | 25篇 |
国内免费 | 32篇 |
专业分类
航空 | 2608篇 |
航天技术 | 1961篇 |
综合类 | 14篇 |
航天 | 813篇 |
出版年
2021年 | 35篇 |
2019年 | 37篇 |
2018年 | 71篇 |
2017年 | 60篇 |
2016年 | 55篇 |
2014年 | 105篇 |
2013年 | 136篇 |
2012年 | 125篇 |
2011年 | 174篇 |
2010年 | 121篇 |
2009年 | 213篇 |
2008年 | 264篇 |
2007年 | 141篇 |
2006年 | 120篇 |
2005年 | 144篇 |
2004年 | 150篇 |
2003年 | 167篇 |
2002年 | 113篇 |
2001年 | 175篇 |
2000年 | 100篇 |
1999年 | 123篇 |
1998年 | 150篇 |
1997年 | 93篇 |
1996年 | 146篇 |
1995年 | 170篇 |
1994年 | 168篇 |
1993年 | 94篇 |
1992年 | 119篇 |
1991年 | 60篇 |
1990年 | 58篇 |
1989年 | 135篇 |
1988年 | 51篇 |
1987年 | 50篇 |
1986年 | 58篇 |
1985年 | 182篇 |
1984年 | 142篇 |
1983年 | 116篇 |
1982年 | 111篇 |
1981年 | 177篇 |
1980年 | 51篇 |
1979年 | 47篇 |
1978年 | 51篇 |
1977年 | 47篇 |
1975年 | 55篇 |
1974年 | 40篇 |
1973年 | 42篇 |
1972年 | 40篇 |
1971年 | 32篇 |
1970年 | 41篇 |
1969年 | 43篇 |
排序方式: 共有5396条查询结果,搜索用时 218 毫秒
991.
Neurobiological problems in long-term deep space flights. 总被引:1,自引:0,他引:1
M E Vazquez 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,22(2):171-183
Future missions in space may involve long-term travel beyond the magnetic field of the Earth, subjecting astronauts to radiation hazards posed by solar flares and galactic cosmic rays, altered gravitation fields and physiological stress. Thus, it is critical to determine if there will be any reversible or irreversible, detrimental neurological effects from this prolonged exposure to space. A question of particular importance focuses on the long-term effects of the space environment on the central nervous system (CNS) neuroplasticity, with the potential acute and/or delayed effects that such perturbations might entail. Although the short-term effects of microgravity on neural control were studied on previous low earth orbit missions, the late consequences of stress in space, microgravity and space radiation have not been addressed sufficiently at the molecular, cellular and tissue levels. The possibility that space flight factors can interact influencing the neuroplastic response in the CNS looms critical issue not only to understand the ontogeny of the CNS and its functional integrity, but also, ultimately the performance of astronauts in extended space forays. The purpose of this paper is to review the neurobiological modifications that occur in the CNS exposed to the space environment, and its potential consequences for extended deep space flight. 相似文献
992.
N N Gurovsky O G Gazenko B A Adamovich E A Ilyin A M Genin V I Korolkov A A Shipov A R Kotovskaya V A Kondratyeva L V Serova 《Acta Astronautica》1980,7(1):113-121
In the 18.5-day flight of the Soviet biosatellite Cosmos-936 (3-22, August 1977) com-parative investigations of the physiological effects of prolonged weightlessness (20 rats) and artificial gravity of 1 g (10 rats) were carried out. Throughout the flight artificial gravity was generated by means of animal rotation in two centrifuges with a radius of 320mm. Postflight examination of animals and treatment of the flight data were performed by Soviet scientists in collaboration with the specialists from Bulgaria, Czechoslovakia, the German Democratic Republic, Hungary, Poland, Rumania, France and the U.S.A. During the flight the total motor activity of the weightless rats was higher and their body temperature was lower than those of the centrifuged animals. Postflight examination of the weightless rats showed a greater percentage of errors during maze an increase in water intake and a decrease in diuresis; a fall of the resistance of peripheral red cells; an increase in the conditionally pathogenic microflora in the mouth; a decrease of oxygen consumption, carbon dioxide production and energy expenditures; a drop in the static physical endurance; a decline in the capacity to keep balance on the rail; an increase in the latent period of the lifting reflex, etc. The centrifugal animals displayed lesser or no change of the above type. These findings together with the biochemical and morphological data give evidence that during and after flight adaptive processes in the centrifuged rats developed better. 相似文献
993.
Morikawa E. Miura R. Matsumoto Y. Kimura K. Arakaki Y. Ohmori S. Wakana H. 《IEEE transactions on aerospace and electronic systems》1995,31(2):784-794
We developed two types of hybrid terminals that can provide both satellite communication and position determination services in one system. One terminal uses the single channel per carrier (SCPC) technique and the other uses the spread spectrum (SS) technique. To evaluate the performance of the two systems, we carried out experiments in Japan and in the Pacific Ocean using two geostationary satellites, ETS-V (150°E) and Inmarsat (180°E). The ranging accuracy between the mobile terminals and the base station via the satellites was found to be about 200 m using the SCPC system and about 10 m using the SS system. The measured positioning accuracy was about 1 km in the SCPC system and about 600 m in the SS system when experiments were carried out near Japan. The experimental results show that the positioning errors were mainly caused by the orbital determination errors of the two satellites. Presented here are the configurations and features of the SCPC and SS terminals, the experimental system, and the experimental results 相似文献
994.
Merlin C. Köhnke Christian von Savigny Charles E. Robert 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(10):2531-2539
Previous studies have identified solar 27-day signatures in several parameters in the Mesosphere/Lower thermosphere region, including temperature and Noctilucent cloud (NLC) occurrence frequency. In this study we report on a solar 27-day signature in NLC altitude with peak-to-peak variations of about 400?m. We use SCIAMACHY limb-scatter observations from 2002 to 2012 to detect NLCs. The superposed epoch analysis method is applied to extract solar 27-day signatures. A 27-day signature in NLC altitude can be identified in both hemispheres in the SCIAMACHY dataset, but the signature is more pronounced in the northern hemisphere. The solar signature in NLC altitude is found to be in phase with solar activity and temperature for latitudes N. We provide a qualitative explanation for the positive correlation between solar activity and NLC altitude based on published model simulations. 相似文献
995.
Markus J. Aschwanden Felix Scholkmann William Béthune Werner Schmutz Valentina Abramenko Mark C. M. Cheung Daniel Müller Arnold Benz Guennadi Chernov Alexei G. Kritsuk Jeffrey D. Scargle Andrew Melatos Robert V. Wagoner Virginia Trimble William H. Green 《Space Science Reviews》2018,214(2):55
Self-organization is a property of dissipative nonlinear processes that are governed by a global driving force and a local positive feedback mechanism, which creates regular geometric and/or temporal patterns, and decreases the entropy locally, in contrast to random processes. Here we investigate for the first time a comprehensive number of (17) self-organization processes that operate in planetary physics, solar physics, stellar physics, galactic physics, and cosmology. Self-organizing systems create spontaneous “order out of randomness”, during the evolution from an initially disordered system to an ordered quasi-stationary system, mostly by quasi-periodic limit-cycle dynamics, but also by harmonic (mechanical or gyromagnetic) resonances. The global driving force can be due to gravity, electromagnetic forces, mechanical forces (e.g., rotation or differential rotation), thermal pressure, or acceleration of nonthermal particles, while the positive feedback mechanism is often an instability, such as the magneto-rotational (Balbus-Hawley) instability, the convective (Rayleigh-Bénard) instability, turbulence, vortex attraction, magnetic reconnection, plasma condensation, or a loss-cone instability. Physical models of astrophysical self-organization processes require hydrodynamic, magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical formulations of self-organizing systems generally involve coupled differential equations with limit-cycle solutions of the Lotka-Volterra or Hopf-bifurcation type. 相似文献
996.
L. Metcalfe M. Aberasturi E. Alonso R. Álvarez M. Ashman I. Barbarisi J. Brumfitt A. Cardesín D. Coia M. Costa R. Fernández D. Frew J. Gallegos J. J. García Beteta B. Geiger D. Heather T. Lim P. Martin C. Muñoz Crego M. Muñoz Fernandez A. Villacorta H. Svedhem 《Space Science Reviews》2018,214(4):78
The ExoMars Trace Gas Orbiter (TGO) Science Ground Segment (SGS), comprised of payload Instrument Team, ESA and Russian operational centres, is responsible for planning the science operations of the TGO mission and for the generation and archiving of the scientific data products to levels meeting the scientific aims and criteria specified by the ESA Project Scientist as advised by the Science Working Team (SWT). The ExoMars SGS builds extensively upon tools and experience acquired through earlier ESA planetary missions like Mars and Venus Express, and Rosetta, but also is breaking ground in various respects toward the science operations of future missions like BepiColombo or JUICE. A productive interaction with the Russian partners in the mission facilitates broad and effective collaboration. This paper describes the global organisation and operation of the SGS, with reference to its principal systems, interfaces and operational processes. 相似文献
997.
以法向马赫数作为激波强度表征量,对斜激波关系式进行重新推导,得到了穿过激波总压损失率极小值的理论解。控制方程表达式为激波角对物面角的线性函数。依据斜激波总压损失率极小值解析公式,首先,绘制了针对超声速流总压损失率应用的楔形角-激波角-马赫数的斜激波效率图。其次,通过生成斜激波三维总压损失率等值线图,呈现了总压损失率在楔形角-激波角-特征马赫数空间上的分布规律。此外,利用斜激波效率图,揭示了等总压损失率条件下马赫数与激波角的对称双解现象。 相似文献
998.
999.
The retrieval of a tethered satellite system is intrinsically unstable. This paper develops a new control strategy to retrieve the tethered satellite system stably and quickly using the fractional order control theory. The governing equation of the tethered satellite system and classic linear feedback tension control law were first reviewed and examined as a benchmark. Then, a new fractional order tension control law has been to avoid the tethered satellite winds around the main satellite near the end of retrieval by existing integer order tension control laws. The newly proposed control law has been discretized and implemented by the Laplace transform and Tustin operator. Unlike the existing integer order control laws, which are based on the feedback of current state and memoryless, the fractional order control law has the memory of previous states and thus controls the tether retrieval more smoothly while maintaining the retrieving speed. The effectiveness and advantage of the new fractional order tension control law is demonstrated numerically by comparing with its integer order counterpart. The results show that the new control law not only retrieves the subsatellite without winding around the main satellite, but also provides a better control performance with smaller in-plane libration angles. 相似文献
1000.
Wang Xiaoying Dai Ziqiang Zhang Enhong K.E. Fuyang Cao Yunchang Song Lianchun 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Algebraic reconstruction techniques (ART) have been successfully used to reconstruct the total electron content (TEC) of the ionosphere and in recent years be tentatively used in tropospheric wet refractivity and water vapor tomography in the ground-based GNSS technology. The previous research on ART used in tropospheric water vapor tomography focused on the convergence and relaxation parameters for various algebraic reconstruction techniques and rarely discussed the impact of Gaussian constraints and initial field on the iteration results. The existing accuracy evaluation parameters calculated from slant wet delay can only evaluate the resultant precision of the voxels penetrated by slant paths and cannot evaluate that of the voxels not penetrated by any slant path. The paper proposes two new statistical parameters Bias and RMS, calculated from wet refractivity of the total voxels, to improve the deficiencies of existing evaluation parameters and then discusses the effect of the Gaussian constraints and initial field on the convergence and tomography results in multiplicative algebraic reconstruction technique (MART) to reconstruct the 4D tropospheric wet refractivity field using simulation method. 相似文献