全文获取类型
收费全文 | 149篇 |
免费 | 2篇 |
专业分类
大气科学 | 4篇 |
地球物理 | 21篇 |
地质学 | 33篇 |
海洋学 | 10篇 |
天文学 | 79篇 |
自然地理 | 4篇 |
出版年
2022年 | 1篇 |
2020年 | 2篇 |
2018年 | 2篇 |
2016年 | 2篇 |
2015年 | 3篇 |
2014年 | 5篇 |
2013年 | 3篇 |
2012年 | 6篇 |
2011年 | 3篇 |
2010年 | 2篇 |
2009年 | 3篇 |
2008年 | 7篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 11篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有151条查询结果,搜索用时 31 毫秒
61.
Solar Physics - An analytical solution to the magnetohydrostatic equations is presented that generalises a solution due to Birn et al. (1978) to include the effect of gravity. There exist two... 相似文献
62.
63.
S. Vargas Domínguez D. MacTaggart L. Green L. van Driel-Gesztelyi A. W. Hood 《Solar physics》2012,278(1):33-45
Recent studies of NOAA active region 10953, by Okamoto et al. (Astrophys. J. Lett.
673, 215, 2008; Astrophys. J.
697, 913, 2009), have interpreted photospheric observations of changing widths of the polarities and reversal of the horizontal magnetic
field component as signatures of the emergence of a twisted flux tube within the active region and along its internal polarity
inversion line (PIL). A filament is observed along the PIL and the active region is assumed to have an arcade structure. To
investigate this scenario, MacTaggart and Hood (Astrophys. J. Lett.
716, 219, 2010) constructed a dynamic flux emergence model of a twisted cylinder emerging into an overlying arcade. The photospheric signatures
observed by Okamoto et al. (2008, 2009) are present in the model although their underlying physical mechanisms differ. The model also produces two additional signatures
that can be verified by the observations. The first is an increase in the unsigned magnetic flux in the photosphere at either
side of the PIL. The second is the behaviour of characteristic photospheric flow profiles associated with twisted flux tube
emergence. We look for these two signatures in AR 10953 and find negative results for the emergence of a twisted flux tube
along the PIL. Instead, we interpret the photospheric behaviour along the PIL to be indicative of photospheric magnetic cancellation
driven by flows from the dominant sunspot. Although we argue against flux emergence within this particular region, the work
demonstrates the important relationship between theory and observations for the successful discovery and interpretation of
signatures of flux emergence. 相似文献
64.
This paper reviews some of the many 3D numerical experiments of the emergence of magnetic fields from the solar interior and
the subsequent interaction with the pre-existing coronal magnetic field. The models described here are idealised, in the sense
that the internal energy equation only involves the adiabatic, Ohmic and viscous shock heating terms. However, provided the
main aim is to investigate the dynamical evolution, this is adequate. Many interesting observational phenomena are explained
by these models in a self-consistent manner. 相似文献
65.
L. K. Harra V. Archontis E. Pedram A. W. Hood D. L. Shelton L. van Driel-Gesztelyi 《Solar physics》2012,278(1):47-71
In this paper we analyse the flux emergence that occurred in the following polarity area of an active region on 1 – 2 December
2006. Observations have revealed the existence of fast outflows at the edge of the emerging flux region. We have performed
3-D numerical simulations to study the mechanisms responsible for these flows. The results indicate that these outflows are
reconnection jets or pressure-driven outflows, depending on the relative orientation of the magnetic fields in contact (i.e. the emerging flux and the active region’s field which is favourable for reconnection on the west side and nearly parallel
with the pre-existing field on the east side of the emerging flux). In the observations, the flows are larger on the west
side until late in the flux emergence, when the reverse is true. The simulations show that the flows are faster on the west
side, but do not show the east flows increasing with time. There is an asymmetry in the expansion of the emerging flux region,
which is also seen in the observations. The west side of the emerging flux region expands faster into the corona than the
other side. In the simulations, efficient magnetic reconnection occurs on the west side, with new loops being created containing
strong downflows that are clearly seen in the observations. On the other side, the simulations show strong compression as
the dominant mechanism for the generation of flows. There is evidence of these flows in the observations, but the flows are
stronger than the simulations predict at the later stages. There could be additional small-angle reconnection that adds to
the flows from the compression, as well as reconnection occurring in larger loops that lie across the whole active region. 相似文献
66.
Abstract In this paper we study the stability of an idealised magnetostatic coronal loop, incorporating both the effect of line-tying, due to the dense photosphere, and of pressure gradients. The stability equations may be solved analytically for our particular equilibrium. From the marginally stable case, the critical conditions separating instability from stability are derived. It is found that stretching or twisting a loop eventually makes it kink unstable. 相似文献
67.
Semi-arid environments are generally more sensitive to urbanization than humid regions in terms of both hydrologic modifications
and water resources sustainability. The current study integrates hydrologic modeling and land use projections to predict long-term
impacts of urbanization on hydrologic behavior and water supply in semi-arid regions. The study focuses on the Upper Santa
Clara River basin in northern Los Angeles County, CA, USA, which is undergoing rapid and extensive development. The semi-distributed
Hydrologic Simulation Program Fortran (HSPF) model is parameterized with land use, soil, and channel characteristics of the
study watershed. Model parameters related to hydrologic processes are calibrated at the daily time step using various spatial
configurations of precipitation and parameters. Potential urbanization scenarios are generated on the basis of a regional
development plan. The calibrated (and validated) model is run under the proposed development scenarios for a 10 year period.
Results reveal that increasing development increases total annual runoff and wet season flows, while decreases are observed
in existing baseflow and groundwater recharge during both dry and wet seasons. As development increases, medium-sized storms
increase in both peak flow and overall volume, while low and high flow events (extremes) appear less affected. Urbanization
is also shown to decrease natural recharge and, when considered at the regional scale, may result in a loss of critical water
supply to Southern California. The current study provides a coupled framework for a decision support tool that can guide efforts
involved in regional urban development planning and water supply management. 相似文献
68.
W. Gregory Hood 《地球表面变化过程与地形》2010,35(3):319-330
Channel meander dynamics in fluvial systems and many tidal systems result from erosion of concave banks coupled with sediment deposition on convex bars. However, geographic information system (GIS) analysis of historical aerial photographs of the Skagit Delta marshes provides examples of an alternative meander forming process in a rapidly prograding river delta: deposition‐dominated tidal channel meander formation through a developmental sequence beginning with sandbar formation at the confluence of a blind tidal channel and delta distributary, proceeding to sandbar colonization and stabilization by marsh vegetation to form a marsh island opposite the blind tidal channel outlet, followed by narrowing of the gap between the island and mainland marsh, closure of one half of the gap to join the marsh island to the mainland, and formation of an approximately right‐angle blind tidal channel meander bend in the remaining half of the gap. Topographic signatures analogous to fluvial meander scroll bars accompany these planform changes. Parallel sequences of marsh ridges and swales indicate locations of historical distributary shoreline levees adjacent to filled former island/mainland gaps. Additionally, the location of marsh islands within delta distributaries is not random; islands are disproportionately associated with blind tidal channel/distributary confluences. Furthermore, blind tidal channel outlet width is positively correlated with the size of the marsh island that forms at the outlet, and the time until island fusion with mainland marsh. These observations suggest confluence hydrodynamics favor sandbar/marsh island development. The transition from confluence sandbar to tidal channel meander can take as little as 10 years, but more typically occurs over several decades. This depositional blind tidal channel meander formation process is part of a larger scale systemic depositional process of delta progradation that includes distributary elongation, gradient reduction, flow‐switching, shoaling, and narrowing. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
69.
This paper treats the prominence model of Low (1993) to examine more complicated sheet currents than those used in the original model. Nonlinear force-free field solutions, in Cartesian coordinates, invariant in a given direction, are presented to show the possibility of an inverse-polarity prominence embedded in a large twisted flux tube. The force-free solution is matched to an external, unsheared, potential coronal magnetic field. These new solutions are mathematically interesting and allow an investigation of different profiles of the current intensity, magnetic field vector and mass density in the sheet. These prominence models show a general increase in magnetic field strength with height in agreement with observations. Other prominence properties are shown to match the observed values. 相似文献
70.
We suggest that the fibril structure of prominences may be caused by filamentation during its formation by radiative instability. We also discuss the effects of other types of instability and give a mechanism for the formation of vertical threads. The models indicate that highly inhomogeneous density structures can exist in the presence of smooth profiles for the plasma pressure and magnetic field. In our particular models the plasma pressure of a fibril prominence is higher and the vertical magnetical field is weaker than in a uniform prominence model, while the mass is substantially smaller. 相似文献