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251.
Results from a suite of 30-year simulations (after spin-up) of the fully coupled Community Climate System Model version 2.0.1
are analyzed to examine the impact of doubling CO2 on interactions between the global water cycle and the regional water cycles of four similar-size, but hydrologically and
thermally different study regions (the Yukon, Ob, St Lawrence, and Colorado river basins and their adjacent land). A heuristic
evaluation based on published climatological data shows that the model generally produces acceptable results for the control
1× CO2 concentration, except for mountainous regions where it performs like other modern climate models. After doubling CO2, the Northern Hemisphere receives significantly (95% confidence level) more moisture from the Southern Hemisphere during
the boreal summer than under 1× CO2 conditions, and the phase of the annual cycle of net moisture transport to areas north of 60°N shifts to a month later than
in the reference simulation. Precipitation and evapotranspiration in the doubled CO2 simulation increase for the Yukon, Ob, and St Lawrence, but decrease, on average, for the Colorado region compared to the
reference simulation. For all regions, interaction between global and regional water cycles increases under doubled CO2, because the amount of moisture entering and leaving the regions increases in the warmer climate. The degree of change in
this interaction depends on region and season, and is related to slight shifts in the position/strength of semi-permanent
highs and lows for the Yukon, Ob, and St Lawrence; in the Colorado region, higher temperatures associated with doubling CO2 and the anticyclone located over the region increase the persistence of dry conditions. 相似文献
252.
Chronology and extent of the Lofoten–Vesterålen sector of the Scandinavian Ice Sheet from 26 to 16 cal. ka BP
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Tom Arne Rydningen Nicole J. Baeten Jan Sverre Laberg 《Boreas: An International Journal of Quaternary Research》2015,44(3):445-458
The interplay between the onshore and offshore areas during the Last Glacial Maximum and the deglaciation of the Scandinavian Ice Sheet is poorly known. In this paper we present new results on the glacial morphology, stratigraphy and chronology of Andøya, and the glacial morphology of the nearby continental shelf off Lofoten–Vesterålen. The results were used to develop a new model for the timing and extent of the Scandinavian Ice Sheet in the study area during the local last glacial maximum (LLGM) (26 to 16 cal. ka BP). We subdivided the LLGM in this area into five glacial events: before 24, c. 23 to 22.2, 22.2 to c. 18.6, 18 to 17.5, and 16.9–16.3 cal. ka BP. The extent of the Scandinavian Ice Sheet during these various events was reconstructed for the shelf areas off Lofoten, Vesterålen and Troms. Icecaps survived in coastal areas of Vesterålen–Lofoten after the shelf was deglaciated and off Andøya ice flowed landwards from the shelf. During the LLGM the relative sea level was stable until 18.5 cal. ka BP, and thereafter there was a sea‐level drop on Andøya. Thus, relative sea level (i.e. a sea level rise) does not seem to be a driving mechanism for ice‐margin retreat in this area but the fall in sea level may have had some importance for the grounding episodes on the banks during deglaciation. The positions of the grounding zone wedges (GZWs) in the troughs are related to the morphology as they are often located where the troughs narrow. 相似文献
253.
254.
Models of maar volcanoes,Lunar Crater (Nevada,USA) 总被引:2,自引:1,他引:1
Maar volcanoes are generally understood to be the result of highly energetic, explosive interaction between magma and water
(groundwater or surface water). Two end-member conceptual models have been proposed to explain the dimensions (diameter, depth)
of maar craters: (1) an incremental growth model, where a crater grows due to subsidence and ejection of debris over the course
of many explosions, and the final size is an integrated result of multiple explosive events; (2) a model in which the dimensions
of a maar crater are the result of the largest single explosion during the lifetime of the maar (major-explosion dominated
model). In the latter case, the maar size can be used to estimate the energy and depth of the largest explosion, which in
turn allows estimation of the magma mass involved. This paper describes Lunar Crater maar (Nevada, USA) and tests the two
models as explanations for the characteristics of the volcano, in particular the major-explosion dominated model. This model
implies magma mass and supply rates that are unrealistic, and the tephra at the maar do not contain key features observed
in the ejecta at large single-explosion craters. The incremental growth model seems most suitable based upon geological evidence. 相似文献
255.
Michael Haslam Richard G. Roberts Ceri Shipton J.N. Pal Jacqueline L. Fenwick Peter Ditchfield Nicole Boivin A.K. Dubey M.C. Gupta Michael Petraglia 《Quaternary Research》2011,75(3):670-682
Single-grain optically stimulated luminescence dating was applied to Late Quaternary sediments at two sites in the Middle Son Valley, Madhya Pradesh, India. Designated Bamburi 1 and Patpara, these sites contain Late Acheulean stone tool assemblages, which we associate with non-modern hominins. Age determinations of 140–120 ka place the formation of these sites at around the Marine Oxygen Isotope Stage 6–5 transition, placing them among the youngest Acheulean sites in the world. We present here the geochronology and sedimentological setting of these sites, and consider potential implications of Late Pleistocene archaic habitation in north-central India for the initial dispersal of modern humans across South Asia. 相似文献
256.
Darren G. Rumbold David W. Evans Sharon Niemczyk Larry E. Fink Krysten A. Laine Nicole Howard David P. Krabbenhoft Mark Zucker 《Estuaries and Coasts》2011,34(3):494-513
The first advisory to limit consumption of Florida Bay fish due to mercury was issued in 1995. Studies done by others in the
late 1990s found elevated water column concentrations of both total Hg (THg) and methylmercury (MeHg) in creeks discharging
from the Everglades, which had its own recognized mercury problem. To investigate the significance of allochthonous MeHg discharging
from the upstream freshwater Everglades, we collected surface water and sediment along two transects from 2000 to 2002. Concentrations
of THg and MeHg, ranging from 0.36 ng THg/L to 5.98 ng THg/L and from <0.02 ng MeHg/L to 1.79 ng MeHg/L, were elevated in
the mangrove transition zone when compared both to upstream canals and the open waters of Florida Bay. Sediment concentrations
ranged from 5.8 ng THg/g to 145.6 ng THg/g and from 0.05 ng MeHg/g to 5.4 ng MeHg/g, with MeHg as a percentage of THg occasionally
elevated in the open bay. Methylation assays indicated that sediments from Florida Bay have the potential to methylate Hg.
Assessment of mass loading suggests that canals delivering stormwater from the northern Everglades are not as large a source
as direct atmospheric deposition and in situ methylation, especially within the mangrove transition zone. 相似文献
257.
Helga Ferket Nicole GuilhaumouFrançois Roure Rudy Swennen 《Marine and Petroleum Geology》2011,28(4):936-958
Carbonate reservoirs in the Córdoba petroleum system (NE Mexico) passed through a multiphase deformation history complicating the petroleum geology. The area evolved from passive margin and foreland setting to Laramide fold and thrust belt (FTB) that was subsequently buried below the Tertiary-Quaternary Veracruz Basin, which in turn underwent transpressional deformation. Reconstruction of paleo-burial (erosion) and paleo-thermicity through the different zones of the FTB and adjacent foreland is a challenging task since classical calibration tools fail to discriminate between several kinematic and thermal models. In this study results from detailed diagenetic and fluid inclusion (FI) analyses on carbonates from the western part of the Córdoba Platform helped constraining paleo-thermicity. Combined microthermometry, synchrotron FTIR analyses and PVT modeling of cogenetic hydrocarbon-aqueous FI allowed also calculation of absolute pressures. Thermal modeling exercises calibrated with organic maturity parameters, bottom-hole temperatures or temperatures from FI demonstrate that without controlling also paleo-erosion the model results may be misleading. 相似文献
258.
Bert W. Hoeksema Jacob van der Land Sancia E. T. van der Meij Leendert P. van Ofwegen Bastian T. Reijnen Rob W. M. van Soest Nicole J. de Voogd 《Marine Ecology》2011,32(2):135-141
Botanical and zoological collections may serve as archives for historical ecological research on the effects of global change and human impact on coral reef biota. Museum collections may harbour old specimens of reef‐dwelling species that have become locally extinct. Such collections also help to determine whether early records of invasive species can be obtained from times when they were not yet recognized as such. A case study (2006) involving Saba Bank, Caribbean Netherlands (former Netherlands Antilles), suggests that the coral reef fauna here may have become impoverished when compared with data obtained during an earlier expedition in 1972. However, the 1972 sampling may have been incomplete, as it was performed by professional divers who were not trained taxonomists, whereas the collecting in 2006 was done by experienced marine biologists who knew the taxa they were sampling. As Saba Bank has been under stress due to the anchoring of large vessels, and invasive species have been a potential threat as well, future studies are needed to obtain more insights into the changing reef biota of Saba Bank. Using this Saba Bank example, we want to address the importance of natural history collections as reservoirs of valuable data relevant to coral reef biodiversity studies in a time of global change. As such, these collections are still underexplored and underexploited. 相似文献
259.
综合运用正相和反相硅胶柱层析、Sephadex LH-20凝胶柱层析以及制备HPLC等分离方法,从1种中国南海海绵Xestospongia testudinaria中追踪分离抗肿瘤活性次级代谢产物。从95%乙醇提取物中分离获得8个单体化合物,通过NMR,MS等波谱技术鉴定其结构分别为:E-18,18-二溴-9,17-二烯-5,7-二炔硬脂酸甲酯(1),E-18,18-二溴-9,17-二烯-5,7-二炔硬脂酸乙酯(2),麦角甾-5,7,22-三烯-3-醇(3),麦角甾-4,6,8(14),22-四烯-3-酮(4),胆甾-4-烯-3-酮(5),3-吲哚醛(6),3-吲哚酸(7)和5-吲哚醛(8)。其中,化合物2-5和8为首次从该属海绵中分离得到。化合物1对肿瘤细胞株HCT116和A549显示较强的抑制活性。 相似文献
260.
Edward S. Gilfillan Nicole P. Maher Cecile M. Krejsa Mary E. Lanphear Christopher D. Ball Jeremy B. Meltzer David S. Page 《Marine pollution bulletin》1995,30(12):780-787
Image analysis of historical aerial photographs was used to examine the effects of the Amoco Cadiz oil spill and resulting clean-up on marsh ecology. Two heavily oiled marsh systems were compared. The marsh which received no clean-up recovered to its prior condition. The marshes in the system cleaned by sediment removal were extensively altered as a result of changes in intertidal height of the sediment surface. 相似文献