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501.
The southwestern South China Sea represents an area of continental crust frozen immediately before the onset of seafloor spreading. Here we compile a grid of multichannel seismic reflection data to characterize the continent-ocean transition just prior to full break-up. We identify a major continental block separated from the shelf margin by a basin of hyperextended crust. Oligocene-Early Miocene rifting was followed by mild compression and inversion prior to 16 Ma, probably linked to collision between the Dangerous Grounds, a continental block to the east of the study area, and Borneo. The timing of inversion supports models of seafloor spreading continuing until around 16 Ma, rather than becoming inactive at 20 Ma. The off-shelf banks experienced uplift prior to 16 Ma in an area, which had previously been a depocenter. The off-shelf banks continued to extend after this time when the rest of the region is in a phase of thermal subsidence. Post-rift magmatism is seen in the form of scattered seamounts (~5–10 km across) within or on the edge of the deeper basins, and are dated as Late Miocene and Pliocene. They are not clearly linked to any phase of tectonic activity. Further inversion of the off-shelf banks occurred in the Pliocene resulting in a major unconformity despite the lack of brittle faulting of that age. We speculate that this is part of a wider pattern of scattered magmatism throughout the South China Sea at this time. Prograding clinoforms are seen to build out from the shelf edge in the south of the study area during the Pliocene, after 5.3 Ma, and then more towards the north and east during the Pleistocene. At the same time a trough south of the off-shelf banks is filled with >1.35 km of mostly Pleistocene sediment. While we expect the bulk of the sediment to come from the Mekong River, we also suggest additional sediment supply from Borneo and the Malay Peninsula via the Molengraaff River and its predecessors. 相似文献
502.
A.E. Izokh S.Z. Smirnov V.V. Egorova Tran Tuan Anh S.V. Kovyazin Ngo Thi Phuong V.V. Kalinina 《Russian Geology and Geophysics》2010,51(7):719-733
Study of the chemical composition of clinopyroxene and garnet megacrysts from the Dak Nong sapphire deposit and model calculations have shown that megacrysts originated from the crystallization of alkali basaltoid magma in a deep-seated intermediate chamber at 14–15 kbar, which is close to the Moho depth (50 km) in this part of southeastern Asia. The chamber was a source of heat and CO2 fluids for the generation of crustal syenitic melts producing sapphires and zircons. The formation conditions of sapphires and zircons are significantly different. The presence of jadeite inclusions in placer zircons points to high pressures during their crystallization, which is confirmed by the ubiquitous decrepitation of CO2-rich melt inclusions. Sapphires crystallized from iron-rich syenitic melt in the shallower Earth’s crust horizons with the participation of CO2 and carbonate–H2O–CO2 fluids. The subsequent eruptions of alkali basalts favored the transportation of garnet and pyroxene megacrysts as well as sapphire and zircon xenocrysts to the surface. It is shown that sapphire deposits can be produced only during multistage basaltic volcanism with deep-seated intermediate chambers in the regions with thick continental crust. The widespread megacryst mineral assemblage (clinopyroxene, garnet, sanidine, ilmenite) and the presence of placer zircon megacrysts can be used as indicators for sapphire prospecting. 相似文献
503.
Moisture Movement Through Cracked Clay Soil Profiles 总被引:1,自引:0,他引:1
Delwyn G. Fredlund Sandra L. Houston Quan Nguyen Murray D. Fredlund 《Geotechnical and Geological Engineering》2010,28(6):865-888
A continuum mechanics approach is used for the formulation of unsaturated hydraulic conductivity functions and the water storage
functions for fractured or cracked clay soils in this parametric study. Suggested procedures are based on available research
literature related to the behavior of cracked unsaturated porous media. The soil–water characteristic curve, hydraulic conductivity
and water storage functions take on the character of bi-modal unsaturated soil property functions. The bimodal character arises
out of the independent behavior of the cracks and the intact clay soil. Matric suction changes beneath a slab-on-grade foundation
placed on a cracked clay soil profile are modeled for varied surface flux conditions using the proposed unsaturated hydraulic
conductivity and water storage functions. The impact of various levels of surface cracking on soil suction distributions is
discussed. Suction distribution patterns are dependent on the initial soil surface suction. In particular, the results are
dependent upon whether the initial matric suction is less than or greater than the air entry of the cracked clay. There is
an extremely wide range of possible conditions that could be modeled but the parametric study results presented in this paper
are limited to a series of selected crack widths and densities for an exfiltration case and an infiltration case. 相似文献
504.
Spherical calcium dioleate particles (∼ 10 μm in diameter) were used as AFM (atomic force microscope) probes to measure interaction forces of the collector colloid with calcite and fluorite surfaces. The attractive AFM force between the calcium dioleate sphere and the fluorite surface is strong and has a longer range than the DLVO (Derjaguin–Landau–Verwey–Overbeek) prediction. The repulsive AFM force between the calcium dioleate sphere and the fluorite surface does not agree with the DLVO prediction. Consideration of non-DLVO forces, including the attractive hydrophobic force, was necessary to explain the experimental results. The non-DLVO interactions considered were justified by the different interfacial water structures at fluorite– and calcite–water interfaces as revealed by the numerical computation experiments using molecular dynamics simulation. The density of interfacial water at the fluorite surface is low and the fluorite surface is not strongly wetted by water molecules. In contrast to the water at the fluorite surface, water molecules at the calcite surface form tightly packed monolayer structures and the calcite surface is extensively hydrated by water molecules. The interfacial water structure agrees with the AFM force measurements and the flotation recovery data. The strong attraction between the calcium dioleate colloid and the fluorite surface, and the moderately wetted fluorite surface by water molecules explain the better flotation response of fluorite with the oleate collector colloid. 相似文献
505.
506.
Acta Geotechnica - Wet agglomerates such as iron-ores, tablets, and aggregates are omnipresent in multi–field industries. However, our understanding of the impact dynamics of these materials... 相似文献