全文获取类型
收费全文 | 78篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 1篇 |
地球物理 | 22篇 |
地质学 | 22篇 |
海洋学 | 9篇 |
天文学 | 14篇 |
综合类 | 1篇 |
自然地理 | 8篇 |
出版年
2024年 | 1篇 |
2022年 | 2篇 |
2021年 | 1篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 4篇 |
2013年 | 2篇 |
2012年 | 1篇 |
2011年 | 5篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 3篇 |
2007年 | 1篇 |
2006年 | 6篇 |
2005年 | 4篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1988年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有79条查询结果,搜索用时 171 毫秒
61.
A new Silurian palaeolatitude for eastern Avalonia and evidence for crustal rotations in the Avalonian margin of southwestern Ireland 总被引:1,自引:0,他引:1
Conall Mac Niocaill 《Geophysical Journal International》2000,141(3):661-671
Palaeomagnetic data are presented from Mid-Silurian (Homerian, Upper Wenlock, ~425 Ma) sediments from the Dingle Peninsula, SW Ireland, which forms part of the northern margin of the Palaeozoic microcontinent of Avalonia. Three remanence components were recognized. After removal of a low-temperature component ('L'), oriented parallel to the present Earth field at the sampling area, two higher-stability components were isolated: an intermediate-unblocking-temperature component ('I') with mean in situ D = 196.9°, I = 11.0°, α 95 = 10.8, with a corresponding palaeopole at 330.0°E, 30.6°S ( dp = 5.6, dm = 11.0), and a high-unblocking-temperature component ('H') with mean tilt-corrected D = 218.6°, I = 22.1°, α 95 = 7.9, with a corresponding palaeopole at 309.5°E, 18.3°S ( dp = 4.4, dm = 8.4). A primary (Wenlock) age is indicated for the 'H'-component by a positive intraformational conglomerate test, whereas the 'I'-component is thought to be a secondary mid-Carboniferous partial remagnetization.
These data confirm that the sector of the Iapetus Ocean between Avalonia and Laurentia was essentially closed, within the limits of palaeomagnetic resolution, by the Wenlock. There is still, however, a discrepancy between the declinations recorded by similar-aged sequences to the north and south of the Iapetus Suture. These point to either an approximately 30° clockwise rotation of the entire Avalonian microcontinent relative to Laurentia during closure, or local vertical axis rotations of the sampling sites in southern Britain. 相似文献
These data confirm that the sector of the Iapetus Ocean between Avalonia and Laurentia was essentially closed, within the limits of palaeomagnetic resolution, by the Wenlock. There is still, however, a discrepancy between the declinations recorded by similar-aged sequences to the north and south of the Iapetus Suture. These point to either an approximately 30° clockwise rotation of the entire Avalonian microcontinent relative to Laurentia during closure, or local vertical axis rotations of the sampling sites in southern Britain. 相似文献
62.
Non-stationary spatial covariance structure estimation in oversampled domains by cluster differences scaling with spatial constraints 总被引:2,自引:2,他引:0
J. F. Vera R. Macías J. M. Angulo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(1):95-106
In the analysis of spatiotemporal processes underlying environmental studies, the estimation of the non-stationary spatial
covariance structure is a well known issue in which multidimensional scaling (MDS) provides an important methodological approach
(Sampson and Guttorp in J Am Stat Assoc 87:108–119, 1992). It is also well known that approximating dispersion by a non-metric
MDS procedure offers, in general, low precision when accurate differences in spatial dispersion are needed for interpolation
purposes, specially if a low dimensional configuration is employed besides a high number of stations in oversampled domains.
This paper presents a modification, consisting of including geographical spatial constraints, of Heiser and Groenen’s (Psychometrika
62:63–83, 1997) cluster differences scaling algorithm by which not the original stations but the cluster centres can be represented,
while the stations and clusters retain their spatial relationships. A decomposition of the sum of squared dissimilarities
into contributions from several sources of variation can be employed for an exploratory diagnosis of the model. Real data
are analyzed and differences between several cluster-MDS strategies are discussed. 相似文献
63.
A latent class MDS model with spatial constraints for non-stationary spatial covariance estimation 总被引:3,自引:3,他引:0
J. F. Vera R. Macías J. M. Angulo 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(6):769-779
Multidimensional scaling (MDS) has played an important role in non-stationary spatial covariance structure estimation and
in analyzing the spatiotemporal processes underlying environmental studies. A combined cluster-MDS model, including geographical
spatial constraints, has been previously proposed by the authors to address the estimation problem in oversampled domains
in a least squares framework. In this paper is formulated a general latent class model with spatial constraints that, in a
maximum likelihood framework, allows to partition the sample stations into classes and simultaneously to represent the cluster
centers in a low-dimensional space, while the stations and clusters retain their spatial relationships. A model selection
strategy is proposed to determine the number of latent classes and the dimensionality of the problem. Real and artificial
data sets are analyzed to test the performance of the model. 相似文献
64.
Alexander Hubbard Mordecai-Mark Mac Low Denton S. Ebel 《Meteoritics & planetary science》2018,53(7):1507-1515
Meteoritical and astrophysical models of planet formation make contradictory predictions for dust concentration factors in chondrule-forming regions of the solar nebula. Meteoritical and cosmochemical models strongly suggest that chondrules, a key component of the meteoritical record, formed in regions with solids-to-gas mass ratios orders above the solar nebula average. However, models of dust grain dynamics in protoplanetary disks struggle to surpass concentration factors of a few except during very short-lived stages in a dust grain's life. Worse, those models do not predict significant concentration factors for dust grains the size of chondrule precursors. We briefly develop the difficulty in concentrating dust particles in the context of nebular chondrule formation and show that the disagreement is sufficiently stark that cosmochemists should explore ideas that might revise the concentration factor requirements downward. 相似文献
65.
C. Ortega-Obregón L. Solari A. Gómez-Tuena M. Elías-Herrera F. Ortega-Gutiérrez C. Macías-Romo 《International Journal of Earth Sciences》2014,103(5):1287-1300
Undeformed felsic to mafic igneous rocks, dated by U–Pb zircon geochronology between 311 and 255 Ma, intrude different units of the Oaxacan and Acatlán metamorphic complexes in southwestern Mexico. Rare earth element concentrations on zircons from most of these magmatic rocks have a typical igneous character, with fractionated heavy rare earths and negative Eu anomalies. Only inherited Precambrian zircons are depleted in heavy rare earth elements, which suggest contemporaneous crystallization in equilibrium with metamorphic garnet during granulite facies metamorphism. Hf isotopic signatures are, however, different among these magmatic units. For example, zircons from two of these magmatic units (Cuanana pluton and Honduras batholith) have positive εHf values (+3.8–+8.5) and depleted mantle model ages (using a mean crustal value of 176Lu/177Hf = 0.015) (T DMC) ranging between 756 and 1,057 Ma, whereas zircons from the rest of the magmatic units (Etla granite, Zaniza batholith, Carbonera stock and Sosola rhyolite) have negative εHf values (?1 to ?14) and model ages between 1,330 and 2,160 Ma. This suggests either recycling of different crustal sources or, more likely, different extents of crustal contamination of arc-related mafic magmas in which the Oaxacan Complex acted as the main contaminant. These plutons thus represent the magmatic expression of the initial stages of eastward subduction of the Pacific plate beneath the western margin of Gondwana, and confirm the existence of a Late Carboniferous–Permian magmatic arc that extended from southern North America to Central America. 相似文献
66.
Natural Hazards - This paper presents a case study of Robeson County’s challenges in addressing the double-barrel disasters of Hurricane Matthew in 2016 (Category 5) and Hurricane Florence in... 相似文献
67.
James F. J. Bryson Claire I. O. Nichols Conall Mac Niocaill 《Meteoritics & planetary science》2024,59(5):1194-1215
One key feature of our protoplanetary disk that shaped its transformation into a system of planetary bodies was its vast magnetic field. Unique constraints on the properties of this field can be gleaned from paleomagnetic measurements of certain meteorites. Here, we apply this approach to the recent CM chondrite fall Winchcombe with the aim of constructing the most complete and reliable record to date of the behavior of the disk field in the outer solar system. We find that the interior of Winchcombe carries a stable, pre-terrestrial magnetization that likely dates from the period of aqueous alteration of the CM chondrite parent body. This remanence corresponds to a paleointensity of 31 ± 17 μT accounting for the average effect of parent body rotation. Winchcombe is rich in framboids and plaquettes of magnetite, which formed via precipitation following the dissolution of iron sulfide. This contrasts with most other CM chondrites, where magnetite formed predominantly via pseudomorphic replacement of FeNi metal. Accounting for the potential differences in recording fidelities of these types of magnetite, we find that the reported paleointensities from all CM chondrites to date are likely underestimates of the disk field intensity in the outer solar system, and use our measurements to calculate a unified intensity estimate of ~78 μT. This paleointensity is consistent with two independent values from recent studies, which collectively argue that the disk field could have played a larger role in shaping the behavior of the disk in the outer solar system than previously considered. 相似文献
68.
Giovanni Fontana Conall Mac Niocaill Richard J. Brown R. Stephen J. Sparks Matthew Field 《Bulletin of Volcanology》2011,73(8):1063-1083
Palaeomagnetic techniques for estimating the emplacement temperatures of volcanic deposits have been applied to pyroclastic
and volcaniclastic deposits in kimberlite pipes in southern Africa. Lithic clasts were sampled from a variety of lithofacies
from three pipes for which the internal geology is well constrained (the Cretaceous A/K1 pipe, Orapa Mine, Botswana, and the
Cambrian K1 and K2 pipes, Venetia Mine, South Africa). The sampled deposits included massive and layered vent-filling breccias
with varying abundances of lithic inclusions, layered crater-filling pyroclastic deposits, talus breccias and volcaniclastic
breccias. Basalt lithic clasts in the layered and massive vent-filling pyroclastic deposits in the A/K1 pipe at Orapa were
emplaced at >570°C, in the pyroclastic crater-filling deposits at 200–440°C and in crater-filling talus breccias and volcaniclastic
breccias at <180°C. The results from the K1 and K2 pipes at Venetia suggest emplacement temperatures for the vent-filling
breccias of 260°C to >560°C, although the interpretation of these results is hampered by the presence of Mesozoic magnetic
overprints. These temperatures are comparable to the estimated emplacement temperatures of other kimberlite deposits and fall
within the proposed stability field for common interstitial matrix mineral assemblages within vent-filling volcaniclastic
kimberlites. The temperatures are also comparable to those obtained for pyroclastic deposits in other, silicic, volcanic systems.
Because the lithic content of the studied deposits is 10–30%, the initial bulk temperature of the pyroclastic mixture of cold
lithic clasts and juvenile kimberlite magma could have been 300–400°C hotter than the palaeomagnetic estimates. Together with
the discovery of welded and agglutinated juvenile pyroclasts in some pyroclastic kimberlites, the palaeomagnetic results indicate
that there are examples of kimberlites where phreatomagmatism did not play a major role in the generation of the pyroclastic
deposits. This study indicates that palaeomagnetic methods can successfully distinguish differences in the emplacement temperatures
of different kimberlite facies. 相似文献
69.
Chlorophyll a concentrations of net (retained on 30 m mesh net) and total plankton in surface waters were determined along cruise tracks in an area of the northern North Pacific Ocean and the adjacent Bering Sea and the Gulf of Alaska from summer to autumn. Total chlorophyll a concentrations were high with a great areal and temporal variations in the western northern North Pacific compared to the eastern part. Chlorophyll a concentrations of netplankton varied from 0.001 to 0.230 g chl a l–1 (average, 0.029 ± 0.040 g chl a l–1), and showed a positive relation but a weak regression coefficient (r
2 = 0.551) against the "average total chlorophyll a" (average of total chlorophyll a at the beginning and at the end during sampling of netplankton). However there were several data points showing high "average total chlorophyll a" but low netplankton and vice versa. Average percentage share of netplankton in the total chlorophyll a was estimated to be as large as 4.26%. 相似文献
70.
Guillermo García-Segura Mordecai-Mark Mac Low Norbert Langer 《Astrophysics and Space Science》1995,224(1-2):459-460
We follow the interaction of massive stars with their circumstellar gas over their entire life-times by combining hydrodynamic stellar evolution calculations for 35 and 60M
stars and one- and two-dimensional gas dynamical calculations for the circumstellar medium. 相似文献