全文获取类型
收费全文 | 118篇 |
免费 | 16篇 |
国内免费 | 18篇 |
专业分类
大气科学 | 8篇 |
地球物理 | 20篇 |
地质学 | 68篇 |
海洋学 | 31篇 |
综合类 | 1篇 |
自然地理 | 24篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 1篇 |
2017年 | 4篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 7篇 |
2013年 | 10篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 2篇 |
2009年 | 11篇 |
2008年 | 13篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 5篇 |
2004年 | 6篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1984年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有152条查询结果,搜索用时 15 毫秒
141.
圆弧状凹陷地形对平面P波的散射:高频解答 总被引:2,自引:1,他引:1
利用波函数的Fourier-Bessel级数展开,推导了具有不同深宽比的圆弧状凹陷地形对入射平面P波二维散射问题的解析解.与现有解析解不同之处在于,为了使该解析解适用于更高的入射波频率,本文利用了柱函数的渐进性质,使得散射波的待定系数可以直接确定,避免了线性方程组的求解以及相关的数值计算问题,从而拓展了该解析解适用的频带范围.通过与现有解析解的比较,论证了该解析解的正确性,进而在一个较宽的频带范围内分析了圆弧状凹陷地形对入射平面P波的散射效应. 相似文献
142.
利用波函数的Fourier-Bessel级数展开法,推导了具有不同深宽比的圆弧状凹陷地形对入射平面SV波二维散射问题的解析解。区别于现有其他解析解,利用柱函数的渐近性质,使得散射波的待定系数得以直接确定,避免了线性方程组的求解以及相应的高频波入射下的数值计算问题,从而拓展了解析解适用的频带范围。通过与已有解析解的比较论证了该解析解的正确性,并在一个较宽的频带范围内研究了圆弧状凹陷地形对入射平面SV波的散射效应。 相似文献
143.
Macrofaunal nematodes of the deep Whittard Canyon (NE Atlantic): assemblage characteristics and comparison with polychaetes
下载免费PDF全文
![点击此处可从《Marine Ecology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Laetitia M. Gunton Brian J. Bett Andrew J. Gooday Adrian G. Glover Ann Vanreusel 《Marine Ecology》2017,38(2)
Large nematodes form an important component of deep‐sea macrofaunal assemblages, but are often considered to be part of the meiobenthos and are rarely studied. We analysed the standing stocks, diversity, and functional group and genus‐level composition of macrofaunal nematodes at lower bathyal depths (3,500 m water depth) in the Whittard Canyon system (NE Atlantic) and on the adjacent continental slope. Five replicate sample sets were obtained using a Megacorer, at four locations (three canyon branches, one slope). Sediment samples were processed on a 500‐μm mesh to provide both nematode and polychaete data from the same samples. The dominant nematode genera included Paramesacanthion, Metacylicolaimus, Cylicolaimus and Phanodermopsis. Nematode standing stocks (density and biomass) increased significantly from slope to canyon locations. Similarly, nematode dominance increased substantially (and diversity decreased) from slope to canyon locations. Nematode feeding groups and tail shape groups also appeared to exhibit common trends across study locations. Nematode genus‐level faunal composition varied significantly between slope and canyon locations. We describe and discuss the broadly similar trends detected in the matching polychaete data, noting some differences in the polychaete density and diversity responses. We suggest that the similar trends in macrofaunal nematode and polychaete ecology across our four study locations reflect responses to both changing sedimentology and food availability. 相似文献
144.
Thomas M. Church Christopher N.K. Mooers Arthur D. Voorhis 《Estuarine, Coastal and Shelf Science》1984,19(4):393-411
A synoptic oceanographic study was conducted in August 1978 at the Middle Atlantic shelfbreak along the shelf-slope front and over the Wilmington Canyon. Four masses (surface, cold pool, shelf, and slope waters) were identified from nutrients and hydrographic variables. Also identified were two pycnocline mixing regimes; one between cold pool and slope waters across the inverted thermocline at the bottom of the cold bool protruding off the shelf, and the other directly across the summer thermocline between slope and shelf waters seaward of the cold pool. These two distinct mixing regimes appear to provide some of the common means for water exchange across the shelf-slope front. The associated mixing may be promoted by the circulation and mixing anomalies induced over canyon topographies. Physical data suggested a cyclonic flow pattern over the Wilmington Canyon, with warm slope water moving up its axis and cold pool water moving off its southwest flank. The above water masses were best identified chemically on the basis of oxygen saturation due to the high apparent photosynthesis at the shelf-slope front. This high primary productivity at the front seems linked to the cold pool and its nutrient supplies. 相似文献
145.
Folding at upper crustal levels occurs by bending of beds and flexural slip between beds. As a fold's interlimb angle decreases, changes in bed thickness and limb rotation are accommodated by various mechanisms, depending on deformation conditions. In the elastico-frictional (EF) regime, cataclastic flow may be the dominant mechanism for fold tightening. The Canyon Range (CR) syncline, located in the Sevier belt of central Utah, shows this type of deformation. The fold involves three thick quartzite units, with slight lithological variations between them. Fold tightening took place in the EF regime (<2 km overburden) by cataclastic flow, involving collective movement on a distributed network of fractures and deformation zones (DZs) from the micro- to the outcrop-scale. In detail, the degree of cataclastic deformation varies significantly across the fold due to minor variations in initial bedding thickness, grain size, matrix composition, etc. A cooperative relationship exists across different scales, and the fracture networks result in a fracture shape fabric that is relatively homogeneous at the outcrop-scale.The initial outcrop scale fracture/DZ network geometry is a product of the growth and linking of micro-scale cataclasite zones, which in turn is controlled by primary lithological variations. Once a fracture network forms, the material behavior of the fractured rock is unlike that of the original rock, with sliding of fracture-bound blocks accomplishing ‘block-controlled’ cataclastic flow. Thus, initial lithological variations at the micro-scale largely control the final deformation behavior at the largest scale. During progressive fold tightening, additional factors regulate cataclastic flow, such as fracture/DZ reactivation or healing, during folding. Although initial lithological variations in different units may produce unique network geometries, each unit's behavior may also depend upon the behavior of adjacent units. In the CR syncline, during the initial stages of cataclastic flow, the inherent nature of each quartzite unit results in unit-specific fracture network geometries. As deformation progresses, unit-specific networks begin to interact with those in surrounding units, resulting in feedback mechanisms regulating the later stages of network development. Thus, the nature of cataclastic flow changes dramatically from the initial to the final stages of folding. 相似文献
146.
William C. Johnson Karen L. Willey Joseph A. Mason David W. May 《Quaternary Research》2007,67(3):474-486
The middle Wisconsinan Gilman Canyon Formation at the Buzzard's Roost type locality in southwestern Nebraska was investigated to document the stratigraphy and to reconstruct the environmental and climate record. The Gilman Canyon Formation was subdivided into three loess units and three soils, with radiocarbon ages constraining it between about 40 ka and 25 ka. Stable carbon isotope ratios, magnetic susceptibility, and carbon content were used to define and characterize soils within both the Gilman Canyon Formation and underlying Illinoian Loveland Loess. At the height of soil development within the Gilman Canyon Formation, climate was supporting C4-dominated grassland, with July temperatures equal to or exceeding those of today. Soil-forming intervals within the Loveland Loess, including the Sangamon Soil, also exhibited relative increases in C4 biomass. Climate, as recorded in the Gilman Canyon Formation, is corroborated by regional proxy data. The formation accumulated during MIS 3, and concurrent soil formation coincided with a summer insolation maximum. 相似文献
147.
Sea-level and tectonic control of middle to late Pleistocene turbidite systems in Santa Monica Basin, offshore California 总被引:1,自引:0,他引:1
Small turbidite systems offshore from southern California provide an opportunity to track sediment from river source through the turbidity‐current initiation process to ultimate deposition, and to evaluate the impact of changing sea level and tectonics. The Santa Monica Basin is almost a closed system for terrigenous sediment input, and is supplied principally from the Santa Clara River. The Hueneme fan is supplied directly by the river, whereas the smaller Mugu and Dume fans are nourished by southward longshore drift. This study of the Late Quaternary turbidite fill of the Santa Monica Basin uses a dense grid of high‐resolution seismic‐reflection profiles tied to new radiocarbon ages for Ocean Drilling Program (ODP) Site 1015 back to 32 ka. Over the last glacial cycle, sedimentation rates in the distal part of Santa Monica Basin averaged 2–3 mm yr?1, with increases at times of extreme relative sea‐level lowstand. Coarser‐grained mid‐fan lobes prograded into the basin from the Hueneme, Mugu and Dume fans at times of rapid sea‐level fall. These pulses of coarse‐grained sediment resulted from river channel incision and delta cannibalization. During the extreme lowstand of the last glacial maximum, sediment delivery was concentrated on the Hueneme Fan, with mean depositional rates of up to 13 mm yr?1 on the mid‐ and upper fan. During the marine isotope stage (MIS) 2 transgression, enhanced rates of sedimentation of > 4 mm yr?1 occurred on the Mugu and Dume fans, as a result of distributary switching and southward littoral drift providing nourishment to these fan systems. Longer‐term sediment delivery to Santa Monica Basin was controlled by tectonics. Prior to MIS 10, the Anacapa ridge blocked the southward discharge of the Santa Clara River into the Santa Monica Basin. The pattern and distribution of turbidite sedimentation was strongly controlled by sea level through the rate of supply of coarse sediment and the style of initiation of turbidity currents. These two factors appear to have been more important than the absolute position of sea level. 相似文献
148.
149.
An urban canopy model is developed for use in mesoscale meteorological and environmental modelling. The urban geometry is
composed of simple homogeneous buildings characterized by the canyon aspect ratio (h/w) as well as the canyon vegetation characterized by the leaf aspect ratio (σ
l
) and leaf area density profile. Five energy exchanging surfaces (roof, wall, road, leaf, soil) are considered in the model,
and energy conservation relations are applied to each component. In addition, the temperature and specific humidity of canopy
air are predicted without the assumption of thermal equilibrium. For radiative transfer within the canyon, multiple reflections
for shortwave radiation and one reflection for longwave radiation are considered, while the shadowing and absorption of radiation
due to the canyon vegetation are computed by using the transmissivity and the leaf area density profile function. The model
is evaluated using field measurements in Vancouver, British Columbia and Marseille, France. Results show that the model quite
well simulates the observations of surface temperatures, canopy air temperature and specific humidity, momentum flux, net
radiation, and energy partitioning into turbulent fluxes and storage heat flux. Sensitivity tests show that the canyon vegetation
has a large influence not only on surface temperatures but also on the partitioning of sensible and latent heat fluxes. In
addition, the surface energy balance can be affected by soil moisture content and leaf area index as well as the fraction
of vegetation. These results suggest that a proper parameterization of the canyon vegetation is prerequisite for urban modelling. 相似文献
150.