全文获取类型
收费全文 | 39篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
大气科学 | 1篇 |
地球物理 | 11篇 |
地质学 | 8篇 |
海洋学 | 2篇 |
天文学 | 17篇 |
自然地理 | 3篇 |
出版年
2021年 | 1篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2011年 | 1篇 |
2010年 | 1篇 |
2009年 | 1篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2005年 | 2篇 |
2004年 | 1篇 |
2003年 | 3篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1985年 | 1篇 |
1979年 | 2篇 |
排序方式: 共有42条查询结果,搜索用时 0 毫秒
11.
12.
13.
Asher Yahalom 《地球物理与天体物理流体动力学》2017,111(2):131-137
Cross helicity is not conserved in non-barotropic magnetohydro-dynamics (MHD) (as opposed to barotropic or incompressible MHD). Here we show that variational analysis suggests a new kind of local cross helicity which is conserved in the non-barotropic case. This local cross helicity can be integrated to a global non-barotropic cross helicity which was suggested in the work of Webb et al. (2014a,b). The non-barotropic cross helicity reduces to the standard cross helicity under barotropic assumptions. The new local cross helicity is conserved even for topologies for which the variational principle does not apply. 相似文献
14.
15.
16.
S.V. Jeffers S.P. Manley M.E. Bailey D.J. Asher 《Monthly notices of the Royal Astronomical Society》2001,327(1):126-132
An Öpik-based geometric algorithm is used to compute impact probabilities and velocity distributions for various near-Earth object (NEO) populations. The resulting crater size distributions for the Earth and Moon are calculated by combining these distributions with assumed NEO size distributions and a selection of crater scaling laws. This crater probability distribution indicates that the largest craters on both the Earth and the Moon are dominated by comets. However, from a calculation of the fractional probabilities of iridium deposition, and the velocity distributions at impact of each NEO population, the only realistic possibilities for the Chicxulub impactor are a short-period comet (possibly inactive) or a near-Earth asteroid. For these classes of object, sufficiently large impacts have mean intervals of 100 and 300 Myr respectively, slightly favouring the cometary hypothesis. 相似文献
17.
18.
19.
The origin of the June Bootid outburst in 1998 and determination of cometary ejection velocities 总被引:2,自引:0,他引:2
Numerical integrations are used to show that the main contribution to the outburst observed in the June Bootid meteor shower in 1998 was a subset of meteoroids released from the parent comet, 7P/Pons–Winnecke, at its 1825 return. A substantial part of the June Bootid stream is in 2:1 resonance with Jupiter. This inhibits chaotic motion, allowing structures in the stream to remain compact enough over centuries that meteor outbursts can still be produced. Circumstances of ejection in 1825 are calculated that exactly result in orbits capable of producing meteors at the observed time in 1998. Required ejection velocities are 10–20 m s-1 . 相似文献
20.
There are too few active comets to account for the observed zodiacal dust. Rather we look to the collisional fragmentation
and erosion of sub-kilometre meteoroids in orbit close to the ecliptic. Since 1975 we have also been aware of an apparently
massive meteoroidal swarm in probable 7:2 mean motion resonance with Jupiter, seemingly at the heart of the Taurid Complex
and connecting therefore with the near-ecliptic system through the so-called Štohl Stream. The notable absence of pre-1786
apparitions of 2P/Encke took on a new significance with the 1983 detection by IRAS of its asymmetric trail inside this resonance.
Thus it was possible all these meteoroidal components were ultimately derived from a continuously eroded, substantially dormant,
librating progenitor within the trail whose more volatile inclusions are exposed from time to time and expelled either singly
or severally as independent comets. A Taurid progenitor of this kind (proto-Encke) dominating the inner Solar System environment
probably then accounts for most of the recorded enhancements of the larger meteoroid flux to Earth, including ‘Tunguska’ bodies
as well. Terrestrial dust insertions which control mean temperature and hence climate are also inferred based upon the libration
and nodal precession half-periods of proto-Encke (∼0.2 kyr, ∼2.5 kyr respectively) albeit the longer of these cycles was not
at first evident in the terrestrial record (Asher & Clube 1993). Recently however this cycle appears to have been confirmed
as a significant (long term) global warming/meridional atmospheric circulation / iceberg calving cycle with the correct phase
producing the so-called mini-Heinrich and Heinrich events of the Holocene and late Upper Pleistocene respectively, i.e., during
the past ∼60 kyr BP. The comparative stability of this terrestrial cycle, in contrast with the weakness of the observed resonance,
suggests a fairly recent diversion therefore from a much stronger sungrazing 7:2 Jovian resonance in which proto-Encke's and
Jupiter's longitudes of perihelion are related by ϖ pE ≈ ϖ J or ϖ J + π. Thus both the Hephaistos Stream and the Taurid Complex
could have formed together during a recent close planetary encounter, say with Mercury ∼5 kyr BP. It follows that we envisage
a single large progenitor in 7:2 Jovian sungrazing resonance for 50 kyr or so which undergoes repeated tidal stress: a continuous
dust-induced major glaciation is thus sustained on Earth for most of this dynamical timescale before a disruptive planetgrazing
event finally brings its sungrazing status to an end and produces the present meteoroidal complex. This evolutionary sequence
almost certainly requires that the original sungrazing stream still exists (without its source): a potentially significant
fact because it may have a direct bearing on both the observed zodiacal bands and the original progenitor orbit as well as
the known periodic variation of solar radiance and convected magnetic field, of possible relevance to the solar cycle. While
these aspects have to be further explored, the purpose of the present investigation is to describe some preliminary modelling
with a view to inferring the likely dynamical history of proto-Encke.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献