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51.
David A. Clague Alice S. Davis James L. Bischoff Jacqueline E. Dixon Renee Geyer 《Bulletin of Volcanology》2000,61(7):437-449
Glassy bubble-wall fragments, morphologically similar to littoral limu o Pele, have been found in volcanic sands erupted
on Lō'ihi Seamount and along the submarine east rift zone of Kīlauea Volcano. The limu o Pele fragments are undegassed with
respect to H2O and S and formed by mild steam explosions. Angular glass sand fragments apparently form at similar, and greater, depths
by cooling-contraction granulation. The limu o Pele fragments from Lō'ihi Seamount are dominantly tholeiitic basalt containing
6.25–7.25% MgO. None of the limu o Pele samples from Lō'ihi Seamount contains less than 5.57% MgO, suggesting that higher
viscosity magmas do not form lava bubbles. The dissolved CO2 and H2O contents of 7 of the limu o Pele fragments indicate eruption at 1200±300 m depth (120±30 bar). These pressures exceed that
generally thought to limit steam explosions. We conclude that hydrovolcanic eruptions are possible, with appropriate pre-mixing
conditions, at pressures as great as 120 bar.
Received: 22 December 1998 / Accepted: 16 July 1999 相似文献
52.
Surface exposure dating of boulders on an exceptionally well‐preserved sequence of moraines in the Peruvian Andes reveals the most detailed record of glaciation heretofore recognised in the region. The high degree of moraine preservation resulted from dramatic changes in the flow path of piedmont palaeoglaciers at the southern end of the Cordillera Blanca (10° 00′ S, 77° 16′ W), which, in turn, generated a series of cross‐cutting moraines. Sixty 10Be surface exposure ages indicate at least four episodes of palaeoglacier stabilisation (>65, ca. 65, ca. 32 and ca. 18–15 ka) and several minor advances or stillstands on the western side of the Nevado Jeulla Rajo massif. The absence of ages close to the global Last Glacial Maximum (ca. 21 ka) suggests that if an advance culminated at that time any resulting moraines were subsequently overridden. The timing of expanded ice cover in the central Peruvian Andes correlates broadly with the timing of massive iceberg discharge (Heinrich) events in the North Atlantic Ocean, suggesting a possible causal connection between southward migration of the Intertropical Convergence Zone during Heinrich events and a resultant increase in precipitation in the tropical Andes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
53.
ArcGIS to Unity: a design pipeline for creation of 3D terrain in serious egames for geology
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Annabeth Robinson Clare E. Gordon Jacqueline Houghton Geoffrey E. Lloyd Daniel J. Morgan 《Geology Today》2015,31(6):237-240
One of the key challenges during the development of the Virtual World Project ‘egame environment’ discussed in this issue was the creation of the digital virtual landscape from an original 2002 base map of a field area. In this [online] paper we will walk through the design pipeline that was developed by the virtual worlds project team, and discuss some of the issues that were discovered when translating from a 2D map to a 3D environment using available software, for others interested in replicating this work. 相似文献
54.
Y. H. Jonathan Tan Jacqueline K. Q. Tham Aayush Paul Umair Rana Hui Ping Ang Nhung T. H. Nguyen Alex T. K. Yee Bryan P. I. Leong Simon Drummond Karenne P. P. Tun 《Singapore journal of tropical geography》2023,44(1):130-148
Rapid urbanization has resulted in the loss of coastal and marine habitats in cities worldwide. The effective conservation of urban coastal ecosystems requires detailed knowledge of their spatial distribution, necessitating high-resolution mapping. Our study produces a high-resolution coastal and marine habitat map and shoreline map for the tropical city-state of Singapore created through pixel-based supervised classification of satellite imagery, bathymetry data and expert ground knowledge. These maps can be used as a base reference for multiple applications including ecological research, conservation and urban planning. They also help identifiy trends in the extent of key coastal habitats, providing insight into their differing levels of vulnerability to loss and potential for restoration to ensure long-term resilience. The method used for mapping shoreline typologies and resulting insights gained, can guide other rapidly urbanizing coastal cities on strategies to assemble useful spatial knowledge for effective conservation of their urban coastal ecosystems. 相似文献
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Many sapphire and ruby occurrences are spatially linked with orogenic belts such as the Pan-African Orogen, the Himalayas, and regions of active or former subduction along the western margin of the Pacific Ocean. These gemstones have oxygen isotope compositions (δ18O) that span >45‰, reflecting the wide range of environments and conditions involved in corundum (Al2O3) formation. We compiled a global data base of sapphire and ruby δ18O, from which the following major groups of gemstones emerge: a dominant population of sapphires with δ18O centred around 5.5‰ (the mantle value) that is spatially related to regions of former subduction; a lesser population of sapphires and rubies with slightly higher δ18O that are associated with skarn and pegmatite; rubies with relatively low δ18O of 0‰–7‰ that occur in hydrothermally altered ultramafic metamorphic rocks in collision zones; and rubies with high δ18O of 14‰–25‰ that are found, almost exclusively, in Himalayan marble. The spatial distribution of the δ18O groups relative to plate boundaries provides insight into the two major periods of continental collision involved in sapphire and ruby formation: the Ediacaran collision of East and West Gondwana (the East African Orogeny) and the Cenozoic collision of India and Asia. 相似文献
58.
This paper explores how changes in sea level and biome distribution may have affected the habitats occupied by hunter‐gatherers in East Asia. Using a model‐based reconstruction of changing sea level from the Last Glacial Maximum (LGM) to present day, our analysis reveals that the exposure of a large continental shelf during the LGM sea level lowstand created a wealth of wooded, estuarine, and coastal biomes that could have been exploited intensively by Late Pleistocene hunter‐gatherers. Models explaining hunter‐gatherer subsistence changes and migrations in this period should take into account the large area that has been lost to rising sea level since the LGM. 相似文献
59.
In the study, we establish centennial records of anthropogenic lead pollution at different locations in the North Atlantic (Iceland, USA, and Europe) by means of lead deposited in shells of the long-lived bivalve Arctica islandica. Due to local oceanographic and geological conditions we conclude that the lead concentrations in the Icelandic shell reflect natural influxes of lead into Icelandic waters. In comparison, the lead profile of the US shell is clearly driven by anthropogenic lead emissions transported from the continent to the ocean by westerly surface winds. Lead concentrations in the European North Sea shell, in contrast, are dominantly driven by local lead sources resulting in a much less conspicuous 1970s gasoline lead peak. In conclusion, the lead profiles of the three shells are driven by different influxes of lead, and yet, all support the applicability of Pb/Ca analyses of A. islandica shells to reconstruct location specific anthropogenic lead pollution. 相似文献
60.
Sarah R. Hall Daniel L. Farber Joan M. Ramage Donald T. Rodbell Robert C. Finkel Jacqueline A. Smith Bryan G. Mark Christopher Kassel 《Quaternary Science Reviews》2009,28(25-26):2991-3009
The Cordillera Huayhuash in the central Peruvian Andes (10.3°S, 76.9°W) is an ideal mountain range in which to study regional climate through variations in paleoglacier extents. The range trends nearly north-south with modern glaciers confined to peaks >4800 m a.s.l. Geomorphology and geochronology in the nearby Cordillera Blanca and Junin Plain reveal that the Peruvian Andes preserve a detailed record of tropical glaciation. Here, we use ASTER imagery, aerial photographs, and GPS to map and date glacial features in both the western and eastern drainages of the Cordillera Huayhuash. We have used in situ produced cosmogenic 10Be concentrations in quartz bearing erratics on moraine crests and ice-polished bedrock surfaces to develop an exposure age chronology for Pleistocene glaciation within the range. We have also collected sediment cores from moraine-dammed lakes and bogs to provide limiting 14C ages for glacial deposits. In contrast to the ranges to the north and south, most glacial features within the Cordillera Huayhuash are Lateglacial in age, however we have identified features with ages that span 0.2 to 38 ka with moraine sets marking the onset of glacier retreat at 0.3 ka, 9–10 ka, 13–14 ka, 20–22 ka, and >26 ka. The range displays a pronounced east-west variation in maximum down-valley distance from the headwall of moraine crests with considerably longer paleoglaciers in the eastern drainages. Importantly, Lateglacial paleoglaciers reached a terminal elevation of 4000 m a.s.l. on both sides of the Cordillera Huayhuash; suggesting that temperature may have been a dominant factor in controlling the maximum glacier extent. We suggest that valley morphology, specifically valley slope, strongly influences down-valley distance to the maximum glacier extent and potential for moraine preservation. While regionally there is an extensive record of older (>50 ka) advances to the north (Cordillera Blanca) and to the south (Junin region), the apparent lack of old moraines in this locality may be explained by the confined morphology of the Cordillera Huayhuash valleys that has inhibited the preservation of older glacial geomorphic features. 相似文献