全文获取类型
收费全文 | 5856篇 |
免费 | 10篇 |
国内免费 | 16篇 |
专业分类
航空 | 2829篇 |
航天技术 | 2026篇 |
综合类 | 189篇 |
航天 | 838篇 |
出版年
2019年 | 35篇 |
2018年 | 85篇 |
2017年 | 44篇 |
2016年 | 47篇 |
2014年 | 109篇 |
2013年 | 141篇 |
2012年 | 122篇 |
2011年 | 199篇 |
2010年 | 140篇 |
2009年 | 227篇 |
2008年 | 296篇 |
2007年 | 153篇 |
2006年 | 126篇 |
2005年 | 148篇 |
2004年 | 148篇 |
2003年 | 180篇 |
2002年 | 203篇 |
2001年 | 239篇 |
2000年 | 90篇 |
1999年 | 148篇 |
1998年 | 174篇 |
1997年 | 129篇 |
1996年 | 174篇 |
1995年 | 208篇 |
1994年 | 165篇 |
1993年 | 108篇 |
1992年 | 156篇 |
1991年 | 68篇 |
1990年 | 59篇 |
1989年 | 135篇 |
1988年 | 53篇 |
1987年 | 50篇 |
1986年 | 57篇 |
1985年 | 185篇 |
1984年 | 170篇 |
1983年 | 105篇 |
1982年 | 153篇 |
1981年 | 171篇 |
1980年 | 57篇 |
1979年 | 53篇 |
1978年 | 47篇 |
1977年 | 40篇 |
1976年 | 34篇 |
1975年 | 51篇 |
1974年 | 45篇 |
1973年 | 31篇 |
1972年 | 44篇 |
1971年 | 36篇 |
1970年 | 33篇 |
1969年 | 39篇 |
排序方式: 共有5882条查询结果,搜索用时 866 毫秒
671.
J. B. Blake B. H. Mauk D. N. Baker P. Carranza J. H. Clemmons J. Craft W. R. Crain A. Crew Y. Dotan J. F. Fennell R. H. Friedel L. M. Friesen F. Fuentes R. Galvan C. Ibscher A. Jaynes N. Katz M. Lalic A. Y. Lin D. M. Mabry T. Nguyen C. Pancratz M. Redding G. D. Reeves S. Smith H. E. Spence J. Westlake 《Space Science Reviews》2016,199(1-4):309-329
672.
Probing the first stars and black holes in the early Universe with the Dark Ages Radio Explorer (DARE) 总被引:1,自引:0,他引:1
Jack O. Burns J. Lazio S. Bale J. Bowman R. Bradley C. Carilli S. Furlanetto G. Harker A. Loeb J. Pritchard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
A concept for a new space-based cosmology mission called the Dark Ages Radio Explorer (DARE) is presented in this paper. DARE’s science objectives include: (1) When did the first stars form? (2) When did the first accreting black holes form? (3) When did Reionization begin? (4) What surprises does the end of the Dark Ages hold (e.g., Dark Matter decay)? DARE will use the highly-redshifted hyperfine 21-cm transition from neutral hydrogen to track the formation of the first luminous objects by their impact on the intergalactic medium during the end of the Dark Ages and during Cosmic Dawn (redshifts z = 11–35). It will measure the sky-averaged spin temperature of neutral hydrogen at the unexplored epoch 80–420 million years after the Big Bang, providing the first evidence of the earliest stars and galaxies to illuminate the cosmos and testing our models of galaxy formation. DARE’s approach is to measure the expected spectral features in the sky-averaged, redshifted 21-cm signal over a radio bandpass of 40–120 MHz. DARE orbits the Moon for a mission lifetime of 3 years and takes data above the lunar farside, the only location in the inner solar system proven to be free of human-generated radio frequency interference and any significant ionosphere. The science instrument is composed of a low frequency radiometer, including electrically-short, tapered, bi-conical dipole antennas, a receiver, and a digital spectrometer. The smooth frequency response of the antennas and the differential spectral calibration approach using a Markov Chain Monte Carlo technique will be applied to detect the weak cosmic 21-cm signal in the presence of the intense solar system and Galactic foreground emissions. 相似文献
673.
According to the Category Adjustment (CA) model, spatial estimates (e.g., of location) involve Bayesian combination across multiple, hierarchical pieces information, each weighted by its relative certainty. Recent work, though, has shown that men and women differ in terms of their certainty regarding fine-grained and categorical information in location memory. Here we demonstrate that this reflects a more general sex difference in visuospatial processing by examining bias patterns in a line angle judgment task (JLAP-15). In addition, the data suggest that multiple, hierarchical levels of categorical information influenced spatial judgments. These results imply that the hierarchical combination outlined by the CA model extends beyond two levels, and that men and women apply differential weighting to these representations. 相似文献
674.
M Andre P Chagvardieff 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(3):265-269
During the past 10 years, the main part of CELSS studies has concerned the exploration of limits of plant productivity. Very high yields were obtained in continuous and high lighting, without reaching any limit. Concepts of mineral nutrition were renewed. CELSS activities now induce a development in the techniques of image processing applied to plants in order to follow the growth, to detect stresses or diseases or to pilot harvesting robots. Notable efforts concern the development of sensors, the study of trace contaminants and the micro-organisms monitoring. In parallel, several instruments for plant culture in closed Systems were developed. The advantages of closure are emphasised in comparison with open flow systems. The concept of Artificial Ecosystems developed for space research is more and more taken into account by the scientific community. It is considered as a new tool to study basic and applied problems related to ecology and not especially concerned with space research. 相似文献
675.
The 1999 Radar Conference banquet address, in which an attempt is made to predict future developments in radar, is presented 相似文献
676.
The Ultra Low Maintenance (ULM) battery technology and its historical performance validation programs are reviewed. Recent military flight test programs are discussed and the growing lists of both military and commercial aircraft flying ULM batteries are presented 相似文献
677.
Gupta Someshwar C. Hall Thomas G. 《IEEE transactions on aerospace and electronic systems》1968,(4):499-504
This paper considers the design of PCM signals with system constraints using Pontryagin's maximum principle. The transmitter signal as well as the correlation signal are determined while maximizing the output signal-to-noise ratio. Both the single and three-pole transmitter filters are considered. An upper bound has been obtained on the performance of PCM signals with constraints. 相似文献
678.
A finite element statement of solving problems on stability of reinforced elliptic cylindrical shells taking into account
momentness and nonlinearity of their subcritical stress strain state is presented. The explicit expressions for displacements
of noncircular cylindrical shell elements as rigid bodies are determined by integrating the equations obtained by equating
the components of linear strains to zero. These expressions were used to construct the form functions for an efficient quadrilateral
finite element of natural curvature. An efficient numerical algorithm of nonlinear deformation and stability of shells was
developed. The stability of reinforced elliptic cylindrical shells under combined loading by bending moment, transverse boundary
force and internal pressure is analyzed. We also examine how the critical loads are affected by the strain nonlinearity and
ellipticity of shell deformation at the subcritical stage. 相似文献
679.
In this paper, a process of flanging to create thin-walled axisymmetrical shells with the shape of truncated cone is analyzed. Also presented are some dependences that make it possible to determine the relative depth of a formed piece at the given piece-blank thickness ratio. 相似文献
680.
Current projects of manned missions to Mars are aimed to their realization in the second-third decades of this century. The purpose of this paper is to determine and review the main biomedical problems, that require a first and foremost decision for safety support of extravehicular activity (EVA) carried out by crewmembers of the Mars expedition. To a number of such problems the authors of the paper attribute a creation of adequate EVA equipment intended, first, for assembly of interplanetary spacecraft on the Earth orbit, performance of maintenance operations and scientific researches on the external surface of spacecraft during interplanetary flight and, secondly, for work on the Mars surface. New generation of space suits with low weight, high mobility and acceptable risk of decompression sickness must be as a central component of EVA equipment. The program for preparation to a Mars expedition also has to include special investigations in order to design the means and methods for a reliable protection of crew against space radiation, to elaborate the approach to medical monitoring and primary medical care during autonomous space mission, to maintain good health condition of crewmembers during EVA under the Mars gravity (0.38 g) after super long-term flight in weightlessness. 相似文献