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821.
Pavla Kováříková Wolfgang Siebel Emil Jelínek Miroslav Štemprok Václav Kachlík František V. Holub Vratislav Blecha 《International Journal of Earth Sciences》2010,99(3):545-565
Mafic and intermediate intrusions occur in the Slavkovsky les as dykes, sills and minor tabular bodies emplaced in metamorphic
rocks or enclosed in late Variscan granites near the SW contact of the Western Krušné hory/Erzgebirge granite pluton. They
are similar in composition and textures to the redwitzites defined in NE Bavaria. Single zircon Pb-evaporation analyses constrain
the age of a quartz monzodiorite at 323.4 ± 4.4 Ma and of a granodiorite at 326.1 ± 5.6 Ma. The P–T range of magma crystallization is estimated at ~1.4–2.2 kbar and ~730–870°C and it accords with a shallow intrusion level
of late Variscan granites but provides lower crystallization temperatures compared to the Bavarian redwitzites. We explain
the heterogeneous composition of dioritic intrusions in the Slavkovsky les by mixing between mafic and felsic magmas with
a minor effect of fractional crystallization. Increased K, Ba, Rb, Sr and REE contents compared to tholeiitic basalts suggest
that the parental mafic magma was probably produced by melting of a metasomatised mantle, the melts being close to lamprophyre
or alkali basalt composition. Diorites and granodiorites originated from mixed magmas derived by addition of about 25–35 and
50 vol.%, respectively, of the acid end-member (granite) to lamprophyre or alkali-basalt magma. Our data stress an important
role of mafic magmas in the origin of late Variscan granitoids in NW Bohemian Massif and emphasize the effect of mantle metasomatism
on the origin of K-rich mafic igneous rocks. 相似文献
822.
The Tuolumne batholith, Sierra Nevada, California, consists of several nested granitoid units and is an example of upper-crustal
normally zoned intrusions. The two outermost units of the batholith are separated by a wide gradational contact in what is
interpreted to represent a large magma chamber. In the Potter Point area near the eastern margin of the batholith, the gradational
contact is cross-cut by a network of interconnected mafic–felsic sheets, which grade into zones of magmatic erosion by stoping
where the host granodiorite between the sheets was entirely removed and replaced by younger enclave-rich quartz diorite. We
interpret these features to record disruption of a steep solidification front, which migrated inwards from the eastern batholith
margin and separated the mushy to solidified margin from the remaining active magma chamber. When intersecting the gradational
contact, the solidification front started to break up via a network of tectonically driven fractures accompanied by simultaneous
injection of localized magma pulses. The solidification front break-up is interpreted here as an initial stage of a “recycling”
process, whereby older magma mush is disrupted and incorporated into younger magma batches, a process we propose to have been
widespread along internal contacts in the Tuolumne magma chamber. 相似文献
823.
Geo-risk management for developing countries—vulnerability to mass wasting in the Jemma River Basin,Ethiopia 总被引:1,自引:1,他引:0
A progress report of the M141 IPL project is presented. Conceptual and applied analyses bearing on engineering geological,
hydrogeological mapping, and zoning of vulnerability to mass wasting were conducted for nearly a 16,000-km2 area of the Jemma River basin, central Ethiopian highlands. Work was aimed at the specific modification of current methodology
and its practical field testing, user-oriented information dissemination, and training of Ethiopian staff in geo-hazard assessment.
Also, environmental protection studies and water resources management to improve food and sanitary security were provided.
An alternative, conceptual energy-process and land unit-oriented and satellite images implementing method was developed to
substitute for the inadequacy of information by regular field check and regular inventory of risky phenomena. It is necessary
to implement a novel, complex systems paradigm to tackle vulnerability and risks in couplings of nature and human systems.
This is discussed together with emphasis on user-oriented communication and building of geo-risk warning and management systems
based on bottom-up, contextual approach. 相似文献
824.
Bohdan Kříbek Vladimír Majer František Veselovský Imasiku Nyambe 《Journal of Geochemical Exploration》2010
Samples of topsoil together with reference samples of subsurface soil from a depth of 80–90 cm were collected in the central-northern part of the Zambian Copperbelt to distinguish lithogenic sources of metals from anthropogenic contamination of soils caused by fallout of dust from mining operations, flotation ore treatment plants, tailings dams, smelters and slag dumping grounds. The total sulphur, Cu and Co contents were found to be significantly higher in topsoil relative to subsurface soil over a large part of the surveyed area, and Zn, Pb, As and Hg contents showed a definite increase in the close neighbourhood of smelters and in the direction of prevailing winds. This indicates that the increase of these elements in the topsoil is due to anthropogenic activities. The areal extent and degree of anthropogenic contamination of topsoil can be expressed by an enrichment index (EI) based on the average ratio of the actual and median concentrations of the given contaminants. Although the contamination of soil by dust fallout decreases progressively with depth in the soil profile, in areas strongly affected by mining and mineral processing the anthropogenic contamination by sulphur and copper can be traced to a depth of 80–90 cm. In contrast, the concentration of elements such as Cr, Ni, and V, that show a direct correlation with the content of iron in the soils, increases in the subsurface soil relative to the topsoil. This is particularly evident in areas underlain by rocks of the Katanga Supergroup. 相似文献
825.
Janský Jaromír Horálek Josef Málek Jiří Boušková Alena 《Studia Geophysica et Geodaetica》2000,44(2):158-174
West Bohemian earthquake swarms are used to determine the parameters of simple homogeneous velocity models of the individual subregions of the given area, based on a group of earthquakes that occurred in these subregions. The grid search method is used for location. Models yielding the minimum sum of squares of the travel-time residua in locating the whole group of earthquakes in the given subregion are considered suitable. Relocation obtained by grid search is compared with that obtained by the FASTHYPO method. The computations indicate that the subregions under consideration can be, from the point of view of earthquake location, sufficiently represented by homogeneous models, but the models differ for the data from different subregions. The velocities of these models are given. The models under consideration are compared with some of the previously published 1-D models of the broader region of Western Bohemia. 相似文献
826.
Filip Hartvich Petr Tábořík Miroslav Šobr Bohumír Janský Zdeněk Kliment Jakub Langhammer 《地球表面变化过程与地形》2020,45(14):3463-3474
Lake sediment volume calculation is a challenging task, namely in cases when detailed drilling is complicated, expensive, or impossible, information on the pre-sedimentation surface unavailable, and record of siltation rate non-existent or too short. This study shows how waterborne, non-invasive geophysical survey, such as electrical resistivity tomography (ERT) can be very effective in acquiring the missing data, namely when combined with sound navigation ranging (SONAR) water depth measurements and supported by information from auxiliary sources. However, ERT surveying in water environment requires specific approaches, as we illustrate on the case of the Mladotice lake study. The lake was created after a landslide in May 1872, and since its formation, the depth has gradually decreased due to sedimentation. We have reconstructed the original surface, calculated the sediment volume, and compiled information on sedimentation to estimate its remaining life span. To achieve this, we measured nine waterborne ERT profiles across the lake. To reach the necessary depth, all ERT profiles were extended on land and crossed the lake using custom-built flotation pads. ERT profiling was combined with SONAR depth measurements, historical bathymetric surveys, borehole core analysis, sediment flux measurements, volumetric calculations, and water conductivity probing. The study has achieved three main results. First, practical applicability and advantages of stationary waterborne ERT profiling in combination with bathymetric sounding were demonstrated. Second, the original lake volume and accumulated sediment was calculated. We estimate that the volume of lake sediment is 187 000 m3, two-thirds of the original lake volume (over 275 000 m3). Finally, based on three volumetric data sets from 1972, 2003, and 2017, and recent monitoring of the sediment inflow, we propose scenarios of lake filling and its future development. Most interestingly, the sedimentation rate has decreased significantly in the last 20 years, suggesting that the lake may survive much longer than hitherto expected. © 2020 John Wiley & Sons, Ltd. 相似文献
827.
How well can we simulate complex hydro‐geomorphic process chains? The 2012 multi‐lake outburst flood in the Santa Cruz Valley (Cordillera Blanca,Perú)
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Martin Mergili Adam Emmer Anna Juřicová Alejo Cochachin Jan‐Thomas Fischer Christian Huggel Shiva P. Pudasaini 《地球表面变化过程与地形》2018,43(7):1373-1389
Changing high‐mountain environments are characterized by destabilizing ice, rock or debris slopes connected to evolving glacial lakes. Such configurations may lead to potentially devastating sequences of mass movements (process chains or cascades). Computer simulations are supposed to assist in anticipating the possible consequences of such phenomena in order to reduce the losses. The present study explores the potential of the novel computational tool r.avaflow for simulating complex process chains. r.avaflow employs an enhanced version of the Pudasaini ( 2012 ) general two‐phase mass flow model, allowing consideration of the interactions between solid and fluid components of the flow. We back‐calculate an event that occurred in 2012 when a landslide from a moraine slope triggered a multi‐lake outburst flood in the Artizón and Santa Cruz valleys, Cordillera Blanca, Peru, involving four lakes and a substantial amount of entrained debris along the path. The documented and reconstructed flow patterns are reproduced in a largely satisfactory way in the sense of empirical adequacy. However, small variations in the uncertain parameters can fundamentally influence the behaviour of the process chain through threshold effects and positive feedbacks. Forward simulations of possible future cascading events will rely on more comprehensive case and parameter studies, but particularly on the development of appropriate strategies for decision‐making based on uncertain simulation results. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd. 相似文献
828.
The goal of this paper is to present the finite element scheme for solving the Earth potential problems in 3D domains above
the Earth surface. To that goal we formulate the boundary-value problem (BVP) consisting of the Laplace equation outside the
Earth accompanied by the Neumann as well as the Dirichlet boundary conditions (BC). The 3D computational domain consists of
the bottom boundary in the form of a spherical approximation or real triangulation of the Earth’s surface on which surface
gravity disturbances are given. We introduce additional upper (spherical) and side (planar and conical) boundaries where the
Dirichlet BC is given. Solution of such elliptic BVP is understood in a weak sense, it always exists and is unique and can
be efficiently found by the finite element method (FEM). We briefly present derivation of FEM for such type of problems including
main discretization ideas. This method leads to a solution of the sparse symmetric linear systems which give the Earth’s potential
solution in every discrete node of the 3D computational domain. In this point our method differs from other numerical approaches,
e.g. boundary element method (BEM) where the potential is sought on a hypersurface only. We apply and test FEM in various
situations. First, we compare the FEM solution with the known exact solution in case of homogeneous sphere. Then, we solve
the geodetic BVP in continental scale using the DNSC08 data. We compare the results with the EGM2008 geopotential model. Finally,
we study the precision of our solution by the GPS/levelling test in Slovakia where we use terrestrial gravimetric measurements
as input data. All tests show qualitative and quantitative agreement with the given solutions. 相似文献