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51.
Consolidation and Break-up of the South American Platform in Southeastern Brazil: Tectonothermal and Denudation Histories 总被引:1,自引:0,他引:1
P.C. Hackspacher L.F.B. Ribeiro M.C.S. Ribeiro A.H. Fetter J.C. Hadler Neto C.E.S. Tello E.L. Dantas 《Gondwana Research》2004,7(1):91-101
The different tectonic stages that occurred at the end of the Proterozoic and during the Phanerozoic have an important bearing on the tectonothermal history of the South American Platform and its consolidation. Geochronological data (U/Pb monazite, 40Ar/39Ar whole rock) and apatite fission-track analysis, from Precambrian rocks of the southeastern Brazilian coastline, permit the modeling of a long-term thermal history of the crust and constrain variable denudation rates.Using these data, a temperature-time diagram reflects a period of accelerated exhumation during the end of the Brasiliano Orogeny, followed by long stability and reactivation of the platform during the Rifting Phase of the South Atlantic Ocean.U/Pb zircon and monazite (blocking temperature of ca. 650° C) data from a series of igneous bodies suggest that a tangential and transpressional tectonic regime occurred between 625 and 610 Ma. During the following escape tectonics, between 610 and 590 Ma the exhumation process indicates cooling rates of ca. 12°C/Ma. 40Ar/39Ar biotite ages between 540 and 510 Ma (ca. 300°C) and a corrected fission-track age on apatites (100°C) of 480 Ma indicate an exhumation event related to block tectonics with huge vertical displacement along shear zones.A long stabilization phase, with low exhumation, and cooling rate around 0.25°C/Ma was recorded from the Cambro/Ordovician to the Mesozoic. At 65 Ma an acceleration of the exhumation through denudation and reworking of the South American surface with cooling rate of 1.5°C/Ma is observed.The uplift of the Mantiqueira and Serra do Mar mountain ranges along the southeast Brazilian coastline works as a climatic barrier provoking lateral erosional processes causing long-term scarp retreat, combined with intense, but progressive denudation towards the continent. A denudation of 2.5 to 4 km was calculated for such processes. This lateral retreat of escarpments and flexural response can provide important insights regarding marginal isostatic uplift and the evolution of offshore sedimentary basins of southeast Brazil. 相似文献
52.
It is well recognized that sea surface temperature (SST) plays a dominant role in the formation and intensification of tropical
cyclones. A number of observational/empirical studies were conducted at different basins to investigate the influence of SST
on the intensification of tropical cyclones and in turn, modification in SST by the cyclone itself. Although a few modeling
studies confirmed the sensitivity of model simulation/forecast to SST, it is not well quantified, particularly for Bay of
Bengal cyclones. The present study is designed to quantify the sensitivity of SST on mesoscale simulation of an explosively
deepening storm over the Bay of Bengal, i.e., Orissa super cyclone (1999). Three numerical experiments are conducted with
climatological SST, NCEP (National Center for Environmental Prediction) skin temperature as SST, and observed SST (satellite
derived) toward 5-day simulation of the storm using mesoscale model MM5. At model initial state, NCEP skin temperature and
observed SST over the Bay of Bengal are 1–2°C warmer than climatological SST, but cooler by nearly 1°C along the coastline.
Observed SST shows a number of warm patches in the Bay of Bengal compared with NCEP skin temperature. The simulation results
indicate that the sea surface temperature has a significant impact on model-simulated track and intensity of the cyclonic
storm. The track and intensity of the storm is better simulated with the use of satellite-observed SST. 相似文献
53.
Simulations and analyses of train-induced ground vibrations in finite element models 总被引:2,自引:0,他引:2
Analyses of the actual vibration measurements and the results from the mathematical and numerical models have been performed in both the frequency and time domains. The conclusions from these analyses were that two-dimensional models could be used in order to study certain effects of train-induced ground vibrations, but that three-dimensional analyses are necessary to achieve a better simulation of the problem. All these analyses were linear elastic. It was, however, found in the three-dimensional analyses that relatively large shear strains existed in the embankment and in the soft soil layers just beneath the railway embankment. These shear strains were taken into consideration through iterative reduction of the shear modulus of the materials where large shear strains were calculated. 相似文献
54.
Lascar Volcano (22°22'S, 67°44'W) is the most active volcano of the central Andes of northern Chile. Activity since 1984
has been characterised by periods of lava dome growth and decay within the active crater, punctuated by explosive eruptions.
We present herein a technique for monitoring the high-temperature activity within the active crater using frequent measurements
of emitted shortwave infrared (SWIR) radiation made by the spaceborne along-track scanning radiometer (ATSR). The ATSR is
an instrument of low spatial resolution (pixels 1 km across) that shares certain characteristics with the MODIS instrument,
planned for use as a volcano monitoring tool in the NASA EOS Volcanology Project. We present a comprehensive time series of
over 60 cloud- and plume-free nighttime ATSR observations for 1992–1995, a period during which Lascar experienced its largest
historical eruption. Variations in short wavelength infrared flux relate directly to changes in high-temperature surfaces
within the active crater. From these data, interpretations can be made that supplement published field reports and that can
document the presence and status of the lava dome during periods where direct, ground-based, observations are lacking. Our
data agree with less frequent information collected from sensors with high spatial resolution, such as the Landsat thematic
mapper (Oppenheimer et al. 1993) and are consistent with field observations and models that relate subsidence of the dome
to subsequent explosive eruptions (Matthews et al., 1997). Most obviously, Lascar's major April 1993 eruption follows a period
in which the magnitude of emitted shortwave infrared radiation fell by 90%. At this time subsidence of the 1991–1992 lava
dome was reported by field observers and this subsidence is believed to have impeded the escape of hot volatiles and ultimately
triggered the eruption (Smithsonian Institution 1993a). Extrapolating beyond the period for which field observations of the
summit are available, our data show that the vulcanian eruption of 20 July 1995 occurred after a period of gradual increase
in short wavelength infrared flux throughout 1994 and a more rapid flux decline during 1995. We attribute this additional,
otherwise undocumented, cycle of increasing and decreasing SWIR radiance as most likely representing variations in degassing
through fumaroles contained within the summit crater. Alternatively, it may reflect a cycle of dome growth and decay. The
explosive eruption of 17 December 1993 appears to have followed a similar, but shorter, variation in SWIR flux, and we conclude
that large explosive eruptions are more likely when the 1.6-μm signal has fallen from a high to a low level. The ATSR instrument
offers low-cost data at high temporal resolution. Despite the low spatial detail of the measurements, ATSR-type instruments
can provide data that relate directly to the status of Lascar's lava dome and other high-temperature surfaces. We suggest
that such data can therefore assist with predictions of eruptive behaviour, deduced from application of physical models of
lava dome development at this and similar volcanoes.
Received: 1 October 1996 / Accepted: 13 January 1997 相似文献
55.
青藏高原高空流型对西太平洋台风路径影响的诊断分析 总被引:8,自引:0,他引:8
利用观测研究,动力诊断分析等手段,从上下游效应、中低纬相互作用的角度来探讨青藏高原高空天气系统的变化与西太平洋台风运动两者之间的关系。1970~1995年25年间的统计结果表明,青藏高原高空流型与台风路径有如下关系:高原高空500 hPa为低值系统控制时,有利于台风西行;反之,高原高空500 hPa为高压时,近海台风往往转向。动力诊断分析的结果揭示了高原上空系统影响下游系统的物理机制,即高原上游扰动动能的传递使得下游的槽发展,并进一步影响台风的引导气流。高原脊的存在,使得涡动动能的输送通道偏北;高原上为槽时,涡动动能的输送通道偏南。高原槽前的南风和台风东侧南风将低纬度的低位涡输入副热带高压,有利于副热带高压的发展,影响台风运动,体现了中低纬相互作用对天气系统的影响。 相似文献
56.
Seth Sadofsky Kaj Hoernle Svend Duggen Folkmar Hauff Reinhard Werner Dieter Garbe-Schönberg 《International Journal of Earth Sciences》2009,98(4):901-913
New geochemical data from the Cocos Plate constrain the composition of the input into the Central American subduction zone
and demonstrate the extent of influence of the Galápagos Hotspot on the Cocos Plate. Samples include sediments and basalts
from Ocean Drilling Program (ODP) Site 1256 outboard of Nicaragua, gabbroic sills from ODP Sites 1039 and 1040, tholeiitic
glasses from the Fisher Ridge off northwest Costa Rica, and basalts from the Galápagos Hotspot Track outboard of Central Costa
Rica. Site 1256 basalts range from normal to enriched MORB in incompatible elements and have Pb and Nd isotopic compositions
within the East Pacific Rise MORB field. The sediments have similar 206Pb/204Pb and only slightly more radiogenic 207Pb/204Pb and 208Pb/204Pb isotope ratios than the basalts. Altered samples from the subducting Galápagos Hotspot Track have similar Nd and Pb isotopic
compositions to fresh Galápagos samples but have significantly higher Sr isotopic composition, indicating that the subduction
input will have a distinct geochemical signature from Galápagos-type mantle material that may be present in the wedge beneath
Costa Rica. Gabbroic sills from Sites 1039 and 1040 in East Pacific Rise (EPR) crust show evidence for influence of the Galápagos
Hotspot ∼100 km beyond the morphological hotspot track. 相似文献
57.
58.
台风“风神”路径、强度及引发江西降水诊断分析 总被引:2,自引:2,他引:0
利用NCEP 1°×1°再分析资料、T213分析资料和常规观测资料,从水汽条件、热力条件、动力条件等方面,对2008年第6号台风“风神”路径、强度变化的原因,及其对江西的影响进行分析。结果表明,台风路径与副高的强度和位置变化密切相关,台风移动方向与风场结构中强风速的风向一致。台风在海上强度减弱主要与水汽来源不足有关,登陆后还与冷空气侵入暖中心有关。由于强度减弱且西南季风不强,造成水汽来源不足,从而导致“风神”没有给江西造成大范围暴雨天气。其中的局地强降水天气发生在台风环流高能梯度锋区,这主要是由于干侵入引发对流性不稳定造成的。 相似文献
59.
60.
On the track keeping and roll reduction of the ship in random waves using different sliding mode controllers 总被引:1,自引:0,他引:1
In the paper, an autopilot system composed of sliding mode controller and line-of-sight guidance technique are adopted to navigate the ship in random waves by altering the rudder deflection. Two kinds of sliding mode controller are considered; one is the separate system including sway–yaw control and roll control, the other is the compact system considering sway–roll–yaw control altogether. Both track keeping and roll reduction are accomplished by rudder control and the design parameters of controller are optimized by genetic algorithm. The present simulation results show both the separate controller and the compact controller work quite well, either for track keeping or roll reduction while the ship is sailing in random waves. However, the separate controller is recommended due to its simplicity. 相似文献