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51.
52.
Water mass modification in surface-trapped, near-field river plumes is examined using a 1.5-layer reduced gravity model and a three-dimensional numerical model. Solutions to the layer model are shown to be qualitatively similar to previous observations and three-dimensional simulations of near-field plumes. Analytic analysis of the layer model demonstrates how the near-field plume is controlled by the competing processes of mixing and spreading. The two models are then used to explore the parameter space dependence of density changes within the near-field plume and their associated cross-shore length scales. Both the magnitude of density changes and their length scales are proportional to either estuarine discharge or fresh water discharge; density changes are also inversely proportional to the estuary mouth width. One surprising feature of the parameter space solutions is that the density of water exiting the near-field plume, a measure of the net dilution of the entire near-field plume, is shown to be inversely proportional to local mixing rates. This is because when local mixing is lower, the influence of plume spreading becomes greater; this spreading accelerates the plume, requiring more net mixing to bring the plume back to subcritical flow. 相似文献
53.
Uplifted crust in parts of western India 总被引:1,自引:0,他引:1
H. C. Tewari G. Surya Prakasa Rao B. Rajendra Prasad 《Journal of the Geological Society of India》2009,73(4):479-488
During northward movement of the Indian sub-continent, after its breakup from the Gondwanaland in the Late Cretaceous, the
western part of India traversed over the Reunion plume. The Saurashtra peninsula and the Cambay Basin are two important geological
regions in this part. Two and half dimensional density models, based on the crustal seismic structure, were generated to establish
a relationship between these two regions. These models indicate that the crust is 32–33 km thick in the eastern Saurashtra
and the northern part of the Cambay Basin. The shallower crust is in a triangular region formed by the extension of the western
limb of the Proterozoic Aravalli trend in Saurashtra, its eastern limb and the Narmada fault in the south. Compared to 36–37
km thick crust to the west and 38–40 km to the east of this region the crust in the above triangular region is uplifted by
4 to 6 km. This uplift took place either after the deposition of Mesozoic sediments or was concomitant with the rise of Reunion
plume prior to the extrusion of the Deccan volcanics as the region was close to the axis of the plume. 相似文献
54.
A numerical groundwater flow and mass transport model was developed to predict the extent of impact from methyl tertiary butyl
ether (MTBE) release on a down-gradient drinking water well field. An MTBE incident in Pascoag, Rhode Island, was used as
a case study and the plume’s past and future development was simulated using scenario analysis. The numerical code used was
GeoSys/Rockflow, which permits a coupled flow and transport simulation as one object, thus alleviating the need for simulating
the MTBE fate with separate flow and transport codes. The numerical model was built on available hydrogeological and chemical
data as well as on GIS information of the site. By comparing the simulated results with observed field data, it was found
that the model could provide reliable results even when the simulated aquifer was simplified to a two-dimensional flow and
transport domain. Finally, the calibrated model was used for exploring a location that may be suitable for a new well field.
Despite the model limitations associated with uncertainties of data and simplifying assumptions, numerical modeling of this
MTBE contaminated site proved a useful tool and provided guidance for future municipal well field operation strategies and
aquifer remediation alternatives. 相似文献
55.
Mesoscale measurements of the vertical dispersion coefficient 2 by using a composite turbulence water tank were validated through a comparison with CONDORS (Convective Diffusion Observed with Remote Sensors) field data, and were analysed with respect to the intensity of the thermal flux, mechanical turbulence, and plume release height.It seems possible to correct the plume z values for different release heights below 0.5zi (zi is the mixing height) by applying an equation expressing the height dependency of turbulence intensity. The downwind distance where the plume's mass centre height approaches its final level was also analysed with respect to the above three parameters, and an empirical equation to estimate the downwinddistance derived. 相似文献
56.
地震层析成像板块构造及地幔演化动力学 总被引:8,自引:2,他引:8
地震层析成像技术的飞速发展给人类提供了一个探测地球内部结构的强有力的工具,也给人类展示了一片新的天地,使人类更加清晰地在两个层次之上(地球的层圈构造和内部横向不均匀性)了解地球内部,特别是对幔内部非均匀结构,从全球和区域的尺度上揭示出地球内部特别是地壳和上地幔横向不均匀结构。呈现出全新的地球,特别是地幔结构的三维图像框架,很容易理解,这一基本框架正是地幔演化热动力学过程的现代表现,如此,我们可以利用该框架去追溯、探讨全球构造特别是地幔构造演化的历史,从而深化对于我们这个星球演化过程的理解。 相似文献
57.
《地学前缘(英文版)》2020,11(5):1669-1680
Anomalous topographic swells and Cenozoic volcanism in east Africa have been associated with mantle plumes.Several models involving one or more fixed plumes beneath the northeastward migrating African plate have been suggested to explain the space-time distribution of magmatism in east Africa.We devise paleogeographically constrained global models of mantle convection and,based on the evolution of flow in the deepest lower mantle,show that the Afar plume migrated southward throughout its lifetime.The models suggest that the mobile Afar plume provides a dynamically consistent explanation for the spatial extent of the southward propagation of the east African rift system(EARS),which is difficult to explain by the northeastward migration of Africa over one or more fixed plumes alone,over the last≈45 Myr.We further show that the age-progression of volcanism associated with the southward propagation of EARS is consistent with the apparent surface hotspot motion that results from southward motion of the modelled Afar plume beneath the northeastward migrating African plate.The models suggest that the Afar plume became weaker as it migrated southwards,consistent with trends observed in the geochemical record. 相似文献
58.
59.
渤海是中国东部陆缘的一个裂谷型盆地,通过重力、航磁、古地磁、天然地震、地热、应力场、地壳与上地幔结构及地震层析成像等资料,对渤海湾及其周边地带的深部结构、地球物理场效应和深层物理过程进行了综合研究.这一盆地是由NNE-NE向、近EW向和NW向3组断裂组成,这3组断裂与3组地幔隆起带基本相对应,并在渤中坳陷交汇、渤海内部的现代构造运动以水平构造应力场作用下的走滑运动为主要特征,渤海区内地壳厚度仅28-29km,上地幔向上隆起,等温居里面埋深浅(为12km),并为较高区热流值区(56-77mW/m2).该区岩石层厚度变化显著,庙岛西部中地壳中有一近似圆形的低速体,在120km深度仍为低速异常区.深大断裂可为深部热物质与气态物质上涌的通道.通过综合研究,提出渤海湾很可能是一个潜在的、尚在发展中的地幔热柱. 相似文献
60.
Glyn Williams-Jones Keith A. Horton Tamar Elias Harold Garbeil Peter J. Mouginis-Mark A. Jeff Sutton Andrew J. L. Harris 《Bulletin of Volcanology》2006,68(4):328-332
A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately
measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual
plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least
two time-synchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the
time varying structure of SO2 concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on
Kīlauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s−1. Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer
method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic
or industrial gas flux measurements.
Editorial responsibility: A. Woods 相似文献