全文获取类型
收费全文 | 961篇 |
免费 | 63篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 50篇 |
大气科学 | 154篇 |
地球物理 | 217篇 |
地质学 | 404篇 |
海洋学 | 47篇 |
天文学 | 91篇 |
综合类 | 2篇 |
自然地理 | 72篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 23篇 |
2020年 | 29篇 |
2019年 | 24篇 |
2018年 | 53篇 |
2017年 | 29篇 |
2016年 | 52篇 |
2015年 | 35篇 |
2014年 | 50篇 |
2013年 | 63篇 |
2012年 | 53篇 |
2011年 | 64篇 |
2010年 | 54篇 |
2009年 | 78篇 |
2008年 | 58篇 |
2007年 | 41篇 |
2006年 | 49篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 31篇 |
2002年 | 14篇 |
2001年 | 18篇 |
2000年 | 14篇 |
1999年 | 11篇 |
1998年 | 16篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1987年 | 5篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 5篇 |
1968年 | 3篇 |
1967年 | 4篇 |
1964年 | 1篇 |
排序方式: 共有1037条查询结果,搜索用时 28 毫秒
1.
Thomas Smith David L. Cook Silke Merchel Stefan Pavetich Georg Rugel Andreas Scharf Ingo Leya 《Meteoritics & planetary science》2019,54(12):2951-2976
We measured the He, Ne, and Ar isotopic concentrations and the 10Be, 26Al, 36Cl, and 41Ca concentrations in 56 iron meteorites of groups IIIAB, IIAB, IVA, IC, IIA, IIB, and one ungrouped. From 41Ca and 36Cl data, we calculated terrestrial ages indistinguishable from zero for six samples, indicating recent falls, up to 562 ± 86 ka. Three of the studied meteorites are falls. The data for the other 47 irons confirm that terrestrial ages for iron meteorites can be as long as a few hundred thousand years even in relatively humid conditions. The 36Cl‐36Ar cosmic ray exposure (CRE) ages range from 4.3 ± 0.4 Ma to 652 ± 99 Ma. By including literature data, we established a consistent and reliable CRE age database for 67 iron meteorites. The high quality of the CRE ages enables us to study structures in the CRE age histogram more reliably. At first sight, the CRE age histogram shows peaks at about 400 and 630 Ma. After correction for pairing, the updated CRE age histogram comprises 41 individual samples and shows no indications of temporal periodicity, especially not if one considers each iron meteorite group separately. Our study contradicts the hypothesis of periodic GCR intensity variations (Shaviv 2002, 2003), confirming other studies indicating that there are no periodic structures in the CRE age histogram (e.g., Rahmstorf et al. 2004; Jahnke 2005). The data contradict the hypothesis that periodic GCR intensity variations might have triggered periodic Earth climate changes. The 36Cl‐36Ar CRE ages are on average 40% lower than the 41K‐K CRE ages (e.g., Voshage 1967). This offset can either be due to an offset in the 41K‐K dating system or due to a significantly lower GCR intensity in the time interval 195–656 Ma compared to the recent past. A 40% lower GCR intensity, however, would have increased the Earth temperature by up to 2 °C, which seems unrealistic and leaves an ill‐defined 41K‐K CRE age system the most likely explanation. Finally, we present new 26Al/21Ne and 10Be/21Ne production rate ratios of 0.32 ± 0.01 and 0.44 ± 0.03, respectively. 相似文献
2.
Stefan Wenau Tiago M. Alves 《Boreas: An International Journal of Quaternary Research》2020,49(4):799-812
Tunnel valleys are major features of glaciated margins and they enable meltwater expulsion from underneath a thick ice cover. Their formation is related to the erosion of subglacial sediments by overpressured meltwater and direct glacial erosion. Yet, the impact of pre-existing structures on their formation and morphology remains poorly known. High-quality 3D seismic data allowed the mapping of a large tunnel valley that eroded underlying preglacial delta deposits in the southern North Sea. The valley follows the N–S strike of crestal faults related to a Zechstein salt wall. A change in downstream tunnel valley orientation towards the SE accompanies a change in the strike direction of salt-induced faults. Fault offsets indicate important activity of crestal faults during the deposition of preglacial deltaic sediments. We propose that crestal faults facilitated tunnel valley erosion by acting as high-permeability pathways and allowing subglacial meltwater to reach low-permeability sediments in the underlying Neogene deltaic sequences, ultimately resulting in meltwater overpressure build-up and tunnel valley excavation. Active faults probably also weakened the near-surface sediment to allow a more efficient erosion of the glacial substrate. This control of substrate structures on tunnel valley morphology is considered as a primary factor in subglacial drainage pattern development in the study area. 相似文献
3.
4.
Prímula Viana Campos Pedro Manuel Villa Jaquelina Alves Nunes Carlos E.G.R. Schaefer Stefan Porembski Andreza Viana Neri 《山地科学学报》2018,15(6):1186-1198
In Eastern South America, high altitude grasslands represent a mountain system that has a high number of endemic species. However, studies on the ecology of plant communities in these environments remain scarce. We aimed to evaluate the patterns of biodiversity and structure of plant communities from rocky outcrops in high altitude grasslands of three areas at the Caparaó National Park, southeastern Brazil, by sampling 300 randomly distributed plots. Then, we compared the floristic composition, relative abundance, and biological and vegetation spectra among areas. We classified species as endemic and non-endemic and verified the occurrence of endangered species. Species richness was evaluated by rarefaction analysis on the sampling units. The importance value and species abundance distribution (SAD) models were assessed. We also performed an indicator species analysis. We sampled 58 species belonging to 49 genera and 32 families. The number of species decreased with increasing altitude, with significant differences being observed among areas regarding richness, abundance, and cover. Of the total number of species, 10 are endemic to the Caparaó National Park and 17 are listed on the Brazilian Red List of endangered species. The dominant families on all peaks were Asteraceae and Poaceae. The SAD models showed lognormal and geometric distributions, corroborating the fact that 10 species that were common to all three areas were also the most dominant ones in the communities and showed the highest importance values, which ranged between 35% and 60%. Indicator species analysis revealed that 28 species (48.27%) were indicators. Of these, 42.85% had maximum specificity, meaning that they occurred only in one area. Thus, the number of species per life form ratio was similar among areas, yet vegetation spectra differed, especially for hemicryptophytes. The altimetric difference among the areas showed to be a very important driver in the community assembly, influencing the evaluated variables, however, other drivers as soil depth, slope and water could also influence the community structure on a smaller and local spatial scale. 相似文献
5.
Ype van der Velde Nikki Vercauteren Fernando Jaramillo Stefan C. Dekker Georgia Destouni Steve W. Lyon 《水文研究》2014,28(13):4110-4118
The Budyko framework characterizes landscape water cycles as a function of climate. We used this framework to identify regions with contrasting hydroclimatic change during the past 50 years in Sweden. This analysis revealed three distinct regions: the mountains, the forests, and the areas with agriculture. Each region responded markedly different to recent climate and anthropogenic changes, and within each region, we identified the most sensitive subregions. These results highlight the need for regional differentiation in climate change adaptation strategies to protect vulnerable ecosystems and freshwater resources. Further, the Budyko curve moved systematically towards its water and energy limits, indicating augmentation of the water cycle driven by changing vegetation, climate and human interactions. This finding challenges the steady state assumption of the Budyko curve and therefore its ability to predict future water cycles. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
6.
The Azores Archipelago is one of the most active volcanic areas in the North Atlantic region. Approximately 30 eruptions have been reported over the last 600 years with some major VEI 5 (Volcanic Explosivity Index) eruptions further back in time. The geochemical composition of associated tephra-derived glass, however, is not well characterized. An Azorean origin of cryptotephras found in distal areas such as North Africa, the British Isles and Greenland has been suggested, but proximal data from the Azores are scarce and the correlations have only been tentative. These tephras have a traychtic composition, which excludes an Icelandic origin. In a previous study, we presented major element analyses of proximal tephra-derived glass from five Holocene eruptions on the Azores Islands. There is a striking geochemical similarity between tephras from volcanoes on São Miguel and Irish cryptotephras, and especially with eruptives from the Furnas volcano. Here we present new analyses of proximal tephras that confirm and strengthen a link between Furnas and cryptotephras found in south-west Ireland. We also suggest a correlation between a previously unsourced tephra found in a Swedish bog with an eruption of the Sete Cidades volcano c. 3880 a cal BP. 相似文献
7.
Mesocosm experiments identifying hotspots of groundwater upwelling in a water column by fibre optic distributed temperature sensing 下载免费PDF全文
Amaya Irene Marruedo Arricibita Stefan Krause Jesus Gomez‐Velez David M. Hannah Jörg Lewandowski 《水文研究》2018,32(2):185-199
Lacustrine groundwater discharge (LGD) can substantially impact ecosystem characteristics and functions. Fibre optic distributed temperature sensing (FO‐DTS) has been successfully used to locate groundwater discharge into lakes and rivers at the sediment–water interface, but locating groundwater discharge would be easier if it could be detected from the more accessible water surface. So far, it is not clear if how and under which conditions the LGD signal propagates through the water column to the water surface–atmosphere interface, and what perturbations and signal losses occur along this pathway. In the present study, LGD was simulated in a mesocosm experiment. Under winter conditions, water with temperatures of 14 to 16 °C was discharged at the bottom of a 10 × 2.8‐m mesocosm. Water within this mesocosm ranged from 4.0 to 7.4 °C. Four layers (20, 40, 60, and 80 cm above the sediment) of the 82 cm deep mesocosm were equipped with FO‐DTS for tracing thermal patterns in the mesocosm. Aims are (a) to test whether the positive buoyancy of relatively warm groundwater imported by LGD into shallow water bodies allows detection of LGD at the lake's water surface–atmosphere interface by FO‐DTS, (b) to analyse the propagation of the temperature signal from the sediment‐water interface through the water column, and (c) to learn more about detectability of the signal under different discharge rates and weather conditions. The experiments supported the benchmarking of scale dependencies and robustness of FO‐DTS applications for measuring upwelling into aquatic environments and revealed that weather conditions can have important impacts on the detection of upwelling at water surface–atmosphere interfaces at larger scales. 相似文献
8.
Jonathan D Mackay Nicholas E Barrand David M Hannah Stefan Krause Christopher R Jackson Jez Everest Alan M MacDonald Brighid É Ó Dochartaigh 《水文研究》2020,34(26):5456-5473
Proglacial aquifers are an important water store in glacierised mountain catchments that supplement meltwater-fed river flows and support freshwater ecosystems. Climate change and glacier retreat will perturb water storage in these aquifers, yet the climate-glacier-groundwater response cascade has rarely been studied and remains poorly understood. This study implements an integrated modelling approach that combines distributed glacio-hydrological and groundwater models with climate change projections to evaluate the evolution of groundwater storage dynamics and surface-groundwater exchanges in a temperate, glacierised catchment in Iceland. Focused infiltration along the meltwater-fed Virkisá River channel is found to be an important source of groundwater recharge and is projected to provide 14%–20% of total groundwater recharge by the 2080s. The simulations highlight a mechanism by which glacier retreat could inhibit river recharge in the future due to the loss of diurnal melt cycling in the runoff hydrograph. However, the evolution of proglacial groundwater level dynamics show considerable resilience to changes in river recharge and, instead, are driven by changes in the magnitude and seasonal timing of diffuse recharge from year-round rainfall. The majority of scenarios simulate an overall reduction in groundwater levels with a maximum 30-day average groundwater level reduction of 1 m. The simulations replicate observational studies of baseflow to the river, where up to 15% of the 30-day average river flow comes from groundwater outside of the melt season. This is forecast to reduce to 3%–8% by the 2080s due to increased contributions from rainfall and meltwater runoff. During the melt season, groundwater will continue to contribute 1%–3% of river flow despite significant reductions in meltwater runoff inputs. Therefore it is concluded that, in the proglacial region, groundwater will continue to provide only limited buffering of river flows as the glacier retreats. 相似文献
9.
Martin Sudmanns Dirk Tiede Stefan Lang Andrea Baraldi 《International Journal of Digital Earth》2018,11(1):95-112
ABSTRACTThe challenge of enabling syntactic and semantic interoperability for comprehensive and reproducible online processing of big Earth observation (EO) data is still unsolved. Supporting both types of interoperability is one of the requirements to efficiently extract valuable information from the large amount of available multi-temporal gridded data sets. The proposed system wraps world models, (semantic interoperability) into OGC Web Processing Services (syntactic interoperability) for semantic online analyses. World models describe spatio-temporal entities and their relationships in a formal way. The proposed system serves as enabler for (1) technical interoperability using a standardised interface to be used by all types of clients and (2) allowing experts from different domains to develop complex analyses together as collaborative effort. Users are connecting the world models online to the data, which are maintained in a centralised storage as 3D spatio-temporal data cubes. It allows also non-experts to extract valuable information from EO data because data management, low-level interactions or specific software issues can be ignored. We discuss the concept of the proposed system, provide a technical implementation example and describe three use cases for extracting changes from EO images and demonstrate the usability also for non-EO, gridded, multi-temporal data sets (CORINE land cover). 相似文献
10.
Maviza Auther Grab Stefan Engelbrecht Francois 《Theoretical and Applied Climatology》2022,149(1-2):309-325
Theoretical and Applied Climatology - This study evaluates precipitation trends in the upper Mzingwane sub-catchment (UMS) of Zimbabwe using ten World Meteorological Organization (WMO)’s... 相似文献