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1.
Geomagnetic storms driven by solar eruptions are known to have significant effects on the total density of the upper atmosphere
in the altitude range 250–1000 km. This in turn causes a measurable effect on the orbits of resident space objects in this
altitude range. We analyzed a sample of these orbits, both from sensor data and from orbital element sets, during the period
surrounding the 14 July 2000 solar activity. We present information concerning the effects of this event on the orbits of
resident space objects and how well accepted atmospheric models were able to represent it. As part of this analysis, we describe
a technique for extracting atmospheric density information from orbital element sets. On daily time scales, the effect of
geomagnetic activity appears to be more important than that of prompt radiation. However, the limitations in time and amplitude
quantization of the accepted solar indices are evident. A limited comparison is also made with previous solar storm events. 相似文献
2.
Floating and grounded peat plateaus were studied in fens in the Yukon Territory (Canada). The peat deposit may be over 4 m thick and consists of a lower bed of aquatic peat overlain by humic fen peat, mesic fen peat and woody peat. Permafrost in the grounded peat plateaus is older than the 1200 year old White River Ash, whereas permafrost in the floating peat plateau is younger.Peat accumulation rates since 1200 years B.P. were greater in the fens (85–100 cm) than on the surface of the peat plateaus (25–55 cm). Where the peat plateau is free-floating, it will persist until the climate changes, causing the icy core to thaw. Where the peat plateau is frozen to the mineral substrate, it slowly drowns since the fen peat accumulates faster than the woody peat. This drowning results in degradation of the landform independently of the climate. Only degradation of floating peat plateaus can be used to identify climatic changes.This publication is the first paper in a series of papers presented at the session on Past Climatic Change and the Development of Peatlands at the ASLO and SWS Meetings in Edmonton, Canada, May 30–June 3, 1993. Dr. P. Kuhry and Dr S. C. Zoltai are serving as Guest Editors. 相似文献
3.
Matthias J. Raab Roderick W. Brown Kerry Gallagher Andrew Carter Klaus Weber 《Tectonophysics》2002,349(1-4)
Namibia's passive continental margin records a long history of tectonic activity since the Proterozoic. The orogenic belt produced during the collision of the Congo and Kalahari Cratons in the Early Proterozoic led to a zone of crustal weakness, which became the preferred location for tectonism during the Phanerozoic. The Pan-African Damara mobile belt forms this intraplate boundary in Namibia and its tectonostratigraphic zones are defined by ductile shear zones, where the most prominent is described as the Omaruru Lineament–Waterberg Thrust (OML–WT). The prominance of the continental margin escarpment is diminished in the area of the Central and Northern Zone of the Damara belt where the shear zones are located. This area has been targeted with a set of 66 outcrop samples over a 550-km-long, 60-km-broad coast-parallel transect from the top of the escarpment in the south across the Damara sector to the Kamanjab Inlier in the north. Apatite fission track age and length data from all samples reveal a regionally consistent cooling event. Thermal histories derived by forward modelling bracket this phase of accelerated cooling in the Late Cretaceous. Maximum palaeotemperatures immediately prior to the onset of cooling range from ca. 120 to ca. 60 °C with the maximum occurring directly south of the Omaruru Lineament. Because different palaeotemperatures indicate different burial depth at a given time, the amount of denudation can be estimated and used to constrain vertical displacements of the continental crust. We interpret this cooling pattern as the geomorphic response to reactivation of basement structures caused by a change in spreading geometry in the South Atlantic and South West Indian Oceans. 相似文献
4.
Benchmarking the thermomechanical behaviour of clays — a progress report — the CEC interclay project
In 1989 a small-scale exercise conducted by the CEC as part of its research programme into the underground storage of radioactive waste highlighted the difficulty of making accurate predictions a priori, of the geomechanical behaviour of clay. Given source data about the Boom clay from the underground research facility at Mol, three organisations independently performed f.e. analyses of two somewhat hypothetical problems. While the results were very broadly in agreement, they were shown to be sensitive to both the type of constitutive model used and the way data was fitted to the model.
Subsequently, the CEC sponsored a more comprehensive benchmark exercise called INTERCLAY II. This involves eleven organisations from various member states of the EC in a project encompassing the three aspects of software development for predictive modelling: verification, validation on the laboratory scale and the treatment of in-situ tests. The paper briefly describes the exercise currently in progress and presents the main results achieved to date concentrating on validation aspects. 相似文献
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Ian Knowles Michael Teubner Aimin Yan Paul Rasser Jong Wook Lee 《Hydrogeology Journal》2007,15(6):1107-1118
A new inverse technique for modelling groundwater flow, based on a functional minimization technique, has been used to calibrate
a groundwater flow model of a subregion of the Port Willunga aquifer within the Willunga Basin in South Australia. The Willunga
Basin is the location of extensive viticulture, irrigated primarily by groundwater, the levels and quality of which have declined
significantly over the last 40 years. The new method is able to generate estimates of transmissivity, storativity and groundwater
recharge over the whole subregion as a time-varying continuous surface; previous methods estimate local discrete parameter
values at specific times. The new method has also been shown to produce accurate head values for the subregion and very good
estimates of groundwater recharge. Its ultimate goal will be to provide a new and invaluable tool for significantly improved
groundwater resource management.
Supported in part by US National Science Foundation grants, DMS-0107492 and DMS-0079478. 相似文献
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Summary Development benefits from the Channel Tunnel for the British regions beyond London depend largely upon the availability of through rail services to and from Europe. This paper examines the failure of deregulation, privatization and government policy to set up the forecast market in such a way that the British regions are included in the European matrix of high-speed intercity passenger rail services. 相似文献