全文获取类型
收费全文 | 47篇 |
免费 | 4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 | 5篇 |
地质学 | 18篇 |
海洋学 | 2篇 |
天文学 | 21篇 |
自然地理 | 3篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2013年 | 3篇 |
2012年 | 2篇 |
2011年 | 5篇 |
2010年 | 3篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2001年 | 1篇 |
1999年 | 1篇 |
1990年 | 1篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1976年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有52条查询结果,搜索用时 15 毫秒
41.
Edward A. Cloutis Frank C. Hawthorne Katherine Krenn Dionne Marcino Johnathon Strong Diana L. Blaney Faith Vilas 《Icarus》2006,184(1):121-157
A suite of sulfate minerals were characterized spectrally, compositionally, and structurally in order to develop spectral reflectance-compositional-structural relations for this group of minerals. Sulfates exhibit diverse spectral properties, and absorption-band assignments have been developed for the 0.3-26 μm range. Sulfate absorption features can be related to the presence of transition elements, OH, H2O, and SO4 groups. The number, wavelength position, and intensity of these bands are a function of both composition and structure. Cation substitutions can affect the wavelength positions of all major absorption bands. Hydroxo-bridged Fe3+ results in absorption bands in the 0.43, 0.5, and 0.9 μm regions, while the presence of Fe2+ results in absorption features in the 0.9-1.2 μm interval. Fundamental SO bending and stretching vibration absorption bands occur in the 8-10, 13-18, and 19-24 μm regions (1000-1250, 550-770, and 420-530 cm−1). The most intense combinations and overtones of these fundamentals are found in the 4-5 μm (2000-2500 cm−1) region. Absorption features seen in the 1.7-1.85 μm interval are attributable to HOH/OH bending and translation/rotation combinations, while bands in the 2.1-2.7 μm regions can be attributed to H2O- and OH-combinations as well as overtones of SO bending fundamentals. OH- and H2O-bearing sulfate spectra are fundamentally different from each other at wavelengths below ∼6 μm. Changes in H2O/OH content can shift SO band positions due to change in bond lengths and structural rearrangement. Differences in absorption band wavelength positions enable discrimination of all the sulfate minerals used in this study in a number of wavelength intervals. Of the major absorption band regions, the 4-5 μm region seems best for identifying and discriminating sulfates in the presence of other major rock-forming minerals. 相似文献
42.
43.
The surface reflectance properties of the irregular outer planets satellites are probed for evidence for the presence of aqueous alteration products on their surfaces using the strong correlation between the 3.0-μm water of hydration absorption feature and the 0.7-μm Fe2+ → Fe3+ oxidized iron feature seen in low-albedo asteroid reflectances, in an effort to expand our understanding of the composition of the precursor bodies from which the dynamical satellite clusters are derived. Equations converting Johnson V and Kron-Cousins RI photometry to Eight Color Asteroid Survey v (0.550 μm), w (0.701 μm), and x (0.853 μm) photometry are derived from relationships defined by Howell (1995, Ph.D. thesis), and coupled with an algorithm previously defined to detect the presence of the 0.7-μm absorption feature in ECAS asteroid photometry [Vilas, F., 1994. Icarus 111, 456-467]. Broadband VRI photometry of Ch-class Asteroid 19 Fortuna acquired during 2004 confirms the efficacy of this method of identifying the presence of the 0.7-μm feature. Photometric observations of many recently discovered irregular outer jovian, saturnian, uranian, and neptunian satellites, coupled with limited asteroid spectroscopy, were examined for the presence of aqueous alteration. The dynamical clusters of outer irregular jovian satellites are mixed between objects that do and do not show this absorption feature. Multiple observations of some objects test both positively and negatively, similar to the surface variegation that has been observed among many C-class asteroids in the main asteroid belt. Evidence for aqueous alteration on these jovian satellites augers for an origin in or near the same location as the asteroids now occupying the aqueous alteration zone (2.6-3.5 AU), at heliocentric distances internal to Jupiter's orbit. Among the saturnian irregular satellites, only S IX Phoebe shows limited evidence of aqueous alteration from ground-based observations. The other satellites show no sign of this feature, and have general reflectance properties very similar to the D-class asteroids, supporting an origin for their precursor bodies in the outer Solar System, perhaps the Centaur region. Only two uranian satellites were tested: U XVII Caliban tests positively for the feature. The differences in surface reflectance properties support the idea that Caliban and U XVI Sycorax derive from separate parent bodies. One observation of neptunian satellite N II Nereid shows no sign of this absorption feature. 相似文献
44.
Chan Faith Ka Shun Gu Xinbing Qi Yunfei Thadani Dimple Chen Yongqin David Lu Xiaohui Li Lei Griffiths James Zhu Fangfang Li Jianfeng Chen Wendy Y. 《Natural Hazards》2022,110(3):2397-2404
Natural Hazards - Frequent typhoons significantly affect many coastal cities via intensive rainstorms, tidal surges and strong wind. Natural factors induced by human disturbance such as climate... 相似文献
45.
J. Tyler Faith 《Quaternary Science Reviews》2011,30(13-14):1675-1680
This study proposes an ecological mechanism for the terminal Pleistocene population collapse and subsequent extinction of North American megafauna. Observations of modern ecosystems indicate that feedback mechanisms between plant nutrient content, nitrogen cycling, and herbivore–plant interactions can vary between a nutrient accelerating mode favoring increased herbivore biomass and a nutrient decelerating mode characterized by reduced herbivore biomass. These alternate modes are determined largely by plant nitrogen content. Plant nitrogen content is known to be influenced by atmospheric CO2 concentrations, temperature, and precipitation. It is argued that Lateglacial climate change, particularly increases in atmospheric CO2, shifted herbivore–ecosystem dynamics from a nutrient accelerating mode to a nutrient decelerating mode at the end of the Pleistocene, leading to reduced megafaunal population densities. An examination of Sporormiella records – a proxy for megaherbivore biomass – indicates that megafaunal populations collapsed first in the east and later in the west, possibly reflecting regional differences in precipitation or vegetation structure. The fortuitous intersection of the climatically driven nitrogen sink, followed by any one or combination of subsequent anthropogenic, environmental, or extra-terrestrial mechanisms could explain why extinctions took place at the end of the Pleistocene rather than during previous glacial–interglacial cycles. 相似文献
46.
47.
The responses of Spartina alterniflora above- and belowground biomass to various combinations of N, P, and Fe were documented in a 1-year field experiment in a
Louisiana salt marsh. Five levels of N additions to 0.25 m2 plots resulted in 18% to 138% more live aboveground biomass compared to the control plots and higher stem densities, but
had no effect on the amount of live belowground biomass (roots and rhizomes; R&R). There was no change in the aboveground
biomass when P or Fe was added as part of a factorial experiment of +P, +N, and +Fe additions, but there was a 40% to 60%
decrease in the live belowground biomass, which reduced the average R&R:S ratio by 50%. The addition of various combinations
of nutrients had a significant affect on the belowground biomass indicating that the addition of P, not N, eased the need
for root foraging activity. The end-of-the-growing-season N:P molar ratios in the live above- and belowground tissues of the
control plot was 16.4 and 32.7, respectively. The relative size of the belowground standing stocks of N and P was higher than
in the aboveground live tissues, but shifted downwards to about half that in fertilized plots. We conclude that the aboveground
biomass was directly related to N availability, but not P, and that the accumulation of belowground biomass was not limited
by N. We suggest that the reduction in belowground biomass with increased P availability, and the lower absolute and relative
belowground standing stocks of P as plant tissue N:P ratios increased, is related to competition with soil microbes for P.
One implication for wetland management and restoration is that eutrophication may be detrimental to long-term salt marsh maintenance
and development, especially in organic-rich wetland soils. 相似文献
48.
Kohei Kitazato Beth E. Clark Shinsuke Abe Takahiro Hiroi Paul A. Abell Faith Vilas 《Icarus》2008,194(1):137-145
A photometric analysis of the S-type Asteroid 25143 Itokawa is performed over multiple wavelengths ranging from 0.85 to 2.10 μm based on disk-resolved reflectance spectra obtained with the Hayabusa near-infrared spectrometer (NIRS). We derive the global photometric properties of Itokawa in terms of Hapke's photometric model. We find that Itokawa has a single-scatter albedo that is 35-40% less than that of Asteroid 433 Eros. Itokawa also has a single-particle phase function that is more strongly back-scattering than that of Eros. Despite its hummocky surface strewn with large boulders, Itokawa exhibits an opposition effect. However, the total amplitude of the opposition surge for Itokawa was estimated to be less than unity while Eros and other S-type asteroids have been found to have model values exceeding unity. The wavelength dependence of the opposition surge width reveals that coherent backscatter contributes to the opposition effect on Itokawa's surface. The photometric roughness of Itokawa is well constrained to a value of 26° ± 1° which is similar to Eros, suggesting that photometric roughness models the smallest surface roughness scale for which shadows exist. 相似文献
49.
James Andrew Griffiths Fangfang Zhu Faith Ka Shun Chan David Laurence Higgitt 《地学前缘(英文版)》2019,10(2):363-372
Urban drainage systems in coastal cities in SE China are characterized by often complex canal and sluicegate systems that are designed to safely drain pluvial flooding whilst preventing tidal inundation.However, the risk of coastal flooding in the region is expected to increase over the next 50-100 years, as urban areas continue to expand and sea-levels are expected to rise. To assess the impact of projected sealevel rise on this type of urban drainage system, a one-dimensional model and decision support tool was developed. The model indicated that although sea-level rise represents a significant challenge, flood probability will continue to be most influenced by rainfall. Events that are significant enough to cause flooding will most likely be minimally impacted by changes to the tidal frame. However, it was found that a sea-level rise of up to 1.2 m by 2010 would result in increased drainage times and higher volumes of over-topping when flooding occurs. 相似文献
50.
Narrowband spectrophotometric observations of outer-belt asteroids (semi-major axis greater than 3.2 AU) have been used to investigate the surface compositions of the D- and P-class asteroids in an effort to learn about their origins and formation conditions. Spectra of 19 outer-belt asteroids and 2 main-belt D-class asteroids were obtained using two charge-coupled device spectrographs. No mineralogical absorption features were evident. The spectra can be divided into four groups based upon four discrete slopes among the spectra. The slope increases (reddens) with increasing heliocentric distance. All of the outer-belt asteroids are locked into orbits controlled by Jupiter's gravitational attraction. The distinct slope changes suggest that these asteroids are the remnants of a gradation in composition of planetesimals in the outer Solar System, which were selectively retained in location when other material was ejected from the Solar System. The spectrophotometry of Iapetus and infrared photometry of quiescent comets of other researchers suggest that this compositional gradation could extend through the orbits of Uranus and Neptune. Two possible explanations for this compositional gradation based upon changes in organic polymer materials are discussed. 相似文献