全文获取类型
收费全文 | 270篇 |
免费 | 20篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 7篇 |
大气科学 | 19篇 |
地球物理 | 72篇 |
地质学 | 93篇 |
海洋学 | 32篇 |
天文学 | 32篇 |
自然地理 | 38篇 |
出版年
2024年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 13篇 |
2015年 | 4篇 |
2014年 | 13篇 |
2013年 | 21篇 |
2012年 | 20篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 22篇 |
2008年 | 8篇 |
2007年 | 13篇 |
2006年 | 9篇 |
2005年 | 14篇 |
2004年 | 8篇 |
2003年 | 7篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 6篇 |
1998年 | 4篇 |
1996年 | 1篇 |
1994年 | 5篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1979年 | 1篇 |
1973年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有293条查询结果,搜索用时 406 毫秒
61.
Inputs of dissolved and particulate 226Ra to lakes and implications for 210Pb dating recent sediments 总被引:8,自引:6,他引:2
Gamma spectroscopy was used to measure radioisotope (210Pb, 226Ra, 137Cs) activities in sediment cores from 20 lakes and a wetland in Florida, USA. Nine profiles display relatively low (<5 dpm g–1) and constant 226Ra activities, whereas 12 show high (>5 dpm g–1) and variable 226Ra activities. In the latter group, most display up-core increases in activity. Upper sediments from two lakes (Round and Rowell) possess very high (>20 dpm g–1) 226Ra activities that exceed total 210Pb activities, clearly illustrating disequlibrium between 226Ra and supported 210Pb. Supported 210Pb activity is generally thought to come from in situ, 226Ra-containing detrital mineral particles, and is typically assumed to be in secular equilibrium with 226Ra activity. Since 1966, Round Lake has been augmented hydrologically with 226Ra-rich (6.2 dpm L–1) groundwater pumped from the local deep aquifer. Adsorption of dissolved 226Ra to recent Round Lake sediments probably accounts for the high measured 226Ra activities and the pronounced disequilibrium between 226Ra and supported 210Pb in topmost deposits. We suspect that many Florida waterbodies receive some 226Ra-rich runoff and seepage from groundwater pumped for irrigation, residential use, industrial applications, and mining. This may account for up-core increases in 226Ra activity measured in sediment cores from some Florida lakes. Significant groundwater pumping began within the last century, and there has been insufficient time for supported 210Pb to come into equilibrium with adsorbed 226Ra in uppermost deposits. Input of 226Ra-rich groundwater to lakes may occur in any geographic region where local bedrock contains 238U and its daughters. When dissolved 226Ra adsorbs to recent sediments, it complicates accurate estimation of supported 210Pb activity, and confounds calculation of unsupported 210Pb activity that is used in dating models. 相似文献
62.
Prior to have long-term sunshine-duration series, data rescue effort has to be engaged. Eighteen series have been homogenized over the period 1931–2000. These series complete the set of diagnoses on climate change at a regional scale, confirm part of the diagnosis established for the temperatures, and offer new tracks for the mechanisms of climate change. To cite this article: J.-M. Moisselin, C. Canellas, C. R. Geoscience 337 (2005). 相似文献
63.
Claire Buchanan Richard V. Lacouture Harold G. Marshall Marcia Olson Jacqueline M. Johnson 《Estuaries and Coasts》2005,28(1):138-159
Phytoplankton reference communities for Chesapeake Bay were quantified from least-impaired water quality conditions using
commonly measured parameters and indicators derived from measured parameters. A binning approach was developed to classify
water quality. Least-impaired conditions had relatively high water column transparency and low concentrations of dissolved
inorganic nitrogen and orthophosphate. Reference communities in all seasons and salinity zones are characterized by consistently
low values of chlorophylla and pheophytin coupled with relative stable proportions of the phytoplankton taxonomic groups and low biomasses of key bloom-forming
species. Chlorophyll cell content was lower and less variable and average cell size and seasonal picophytoplankton biomass
tended to be greater in the mesohaline and polyhaline reference communities as compared to the impaired communities. Biomass
concentrations of the nano-micro phytoplankton size fractions (2–200 μm) in 12 of the 16 season-specific and salinity-specific
reference communities were the same or higher than those in impaired habitat conditions, suggesting that nutrient reductions
will not decrease the quantity of edible phytoplankton food available to large consumers. High (bloom) and low (bust) biomass
events within the impaired phytoplankton communities showed strikingly different chlorophyll cell content and turnover rates.
Freshwater flow had little effect on phytoplankton responses to water quality condition in most of the estuary. Improved water
column transparency, or clarity, through the reduction of suspended sediments will be particularly important in attaining
the reference communities. Significant nitrogen load reductions are also required. 相似文献
64.
Postcolonial geographies of development: Introduction 总被引:1,自引:0,他引:1
65.
66.
Variations in production rates of warm North Atlantic Deep Water (NADW) have been proposed as a mechanism for linking climate fluctuations in the northern and southern hemispheres during the Pleistocene. We have tested this hypothesis by examining the sensitivity of a thermodynamic/dynamic model for Antarctic sea ice to changes in vertical ocean heat flux and comparing the simulations with modified CLIMAP sea-ice maps for 18 000 B.P. Results suggest that changes in NADW production rates, and the consequent changes in the vertical ocean heat flux in the Antarctic, can only account for about 20%–30% of the overall variance in Antarctic sea-ice extent. This conclusion has been validated against an independent geological data set involving a time series of sea-surface temperatures from the subantarctic. The latter comparison suggests that, although the overall influence of NADW is relatively minor, the linkage may be much more significant at the 41 000-year obliquity period. Despite some limitations in the models and geological data, we conclude that NADW variations may have played only a modest role in causing late Pleistocene climate change in the high latitudes of the southern hemisphere. Our conclusion is consistent with calculations by Manabe and Broccoli (1985) suggesting that atmospheric CO2 changes may be more important for linking the two hemispheres. 相似文献
67.
Jean-Philippe Clment Christelle Legendre Martial Caroff Herv Guillou Joseph Cotten Claire Bollinger Grard Guille 《Journal of Volcanology and Geothermal Research》2003,120(1-2):87-101
Occurrences of debris avalanche deposits newly identified in Tahiti (Society Islands) and Ua Huka (Marquesas Archipelago) are described and interpreted here. In both islands, the breccias are located within horseshoe-shaped residual calderas. In Tahiti, the epiclastic formations, up to 500 m thick, lie on the floor of the central depression and in the valley of the northwards running Papenoo River. In Ua Huka, the breccias crop out within a depression limited by a semicircular crest in four bays along the southern coast. Their thickness is ca. 100 m. A few clasts collected in the Tahitian breccias and some rocks forming their substratum have been dated (K–Ar datings) and analysed (major and trace elements, Sr–Nd isotopes) for this study. Using these data, we show that the debris avalanche(s) occurred in Tahiti Nui at the end of the growth of the shield volcano (between 570 000 and 390 000 years ago), maybe in consequence of the emplacement of the plutonic body which occupies the central part of the caldera. In Ua Huka, the collapse took place nearly 3 Ma ago, between the construction of the shield volcano and that of the inner one. The southwards orientation of the caldera, like that of the neighbouring island Nuku Hiva, might reflect a preferential direction of weakness in the substratum of the central Marquesas. 相似文献
68.
Claire L. Beaney 《Quaternary International》2002,90(1)
Tunnel channels in southeast Alberta are attributed to erosion by channelized, subglacial meltwater flows. An anabranching tunnel channel network dissects the preglacial drainage divide of the ancestral Milk River. Channel morphology and landform associations are used to evaluate competing hypotheses of tunnel channel formation. Mechanisms that invoke subaerial channel incision, direct glacial erosion or steady state, time-transgressive erosion at the ice margin cannot explain convex-up longitudinal channel profiles, anabranching channel networks or confinement to the preglacial drainage divide. Results conclude that the tunnel channel network in southeast Alberta represents late-stage erosion by a channelised subglacial flow of catastrophic dimensions. Interpretations for this tunnel channel network are in agreement with conclusions obtained for the regional subglacial landform assemblage. 相似文献
69.
Jacq Kévin Ployon Estelle Rapuc William Blanchet Claire Pignol Cécile Coquin Didier Fanget Bernard 《Journal of Paleolimnology》2021,66(3):249-260
Journal of Paleolimnology - Images of sediment cores are often acquired to preserve primary color information, before such profiles are altered by subsequent sampling and destructive analyses. In... 相似文献
70.
Catherine O. de Burgh-Day Claire M. Spillman Craig Stevens Oscar Alves Graham Rickard 《新西兰海洋与淡水研究杂志》2019,53(2):201-221
We present a first assessment of the Sea Surface Temperature (SST) and 300m Heat Content (HC) ensemble mean skill of the Australian Community Climate and Earth-System Simulator-Seasonal v1.0 (ACCESS-S1) around New Zealand on seasonal timescales, using a set of retrospective ensemble forecasts for 1990-2012. This was verified against Reynolds AVHRR analysis and Bluelink ReANalysis 3.5 (BRAN3.5). For inshore areas with depth <300m, the model shows skill forecasting for summer at a lead time of 0 months, with 66% and 65% of model grid cells having correlation coefficients exceeding 0.6 for SST and 300m HC respectively. Regions of lower skill seem to be associated with the model representation of the complex and variable frontal systems around New Zealand, and an overly-strong response to the El Niño Southern-Oscillation (ENSO). Nevertheless, the skill of ACCESS-S1 around New Zealand suggests there is potential for the development of useful seasonal forecast products for the region. 相似文献