全文获取类型
收费全文 | 379篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 41篇 |
地球物理 | 130篇 |
地质学 | 140篇 |
海洋学 | 18篇 |
天文学 | 56篇 |
综合类 | 2篇 |
自然地理 | 9篇 |
出版年
2024年 | 2篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 21篇 |
2016年 | 24篇 |
2015年 | 20篇 |
2014年 | 19篇 |
2013年 | 28篇 |
2012年 | 28篇 |
2011年 | 17篇 |
2010年 | 9篇 |
2009年 | 17篇 |
2008年 | 15篇 |
2007年 | 4篇 |
2006年 | 8篇 |
2005年 | 11篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 16篇 |
2001年 | 7篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 6篇 |
1992年 | 5篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1968年 | 2篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1965年 | 6篇 |
1964年 | 4篇 |
1962年 | 2篇 |
1961年 | 4篇 |
1960年 | 5篇 |
1959年 | 5篇 |
1958年 | 3篇 |
1957年 | 2篇 |
1956年 | 3篇 |
1955年 | 3篇 |
1927年 | 1篇 |
1926年 | 2篇 |
1915年 | 1篇 |
排序方式: 共有401条查询结果,搜索用时 31 毫秒
111.
Quantifying the protective function of a forest against rockfall for past,present and future scenarios using two modelling approaches 总被引:2,自引:0,他引:2
Following a major rockfall event in 1987, two types of protection measures were taken in the village Saint Martin le Vinoux
(French Alps). Firstly, technical measures using civil engineering were installed, and secondly, a forest management intervention
to increase its protection was carried out. This study aims to assess whether this intervention was successful in the sense
that it improved the protective function of the forest. We evaluated the rockfall risk for the situation of 1987 (before the
intervention), today and the future, using model simulations with past, present and future vegetation cover scenarios. To
increase the meaningfulness of our results, we used two different models, called Rockfor.NET, which is a rapid one-dimensional rockfall forest evaluation tool, using simple slope and forest characteristics and RockyFor,
a process based on three-dimensional rockfall simulation model that takes the barrier effect of individual trees explicitly
into account. Both models correctly predicted that the forest was not capable of stopping rocks from the 1987 rockfall event.
Further, both models indicate an increase of the number of rocks reaching the base of the slope from 1987 onwards. RockyFor
shows an increase from 11% in 1987 to 19% in 2086. Rockfor.NET shows an increase from 26% in 1987 to 56% in 2086. We conclude that a second attempt to increase the protective function
of the forest should aim at restoring a dense coppice stand. 相似文献
112.
Germán Zapata‐Hernández Javier Sellanes Andrew R. Thurber Lisa A. Levin Frédéric Chazalon Peter Linke 《Marine Ecology》2014,35(1):1-21
Studies of the trophic structure in methane‐seep habitats provide insight into the ecological function of deep‐sea ecosystems. Methane seep biota on the Chilean margin likely represent a novel biogeographic province; however, little is known about the ecology of the seep fauna and particularly their trophic support. The present study, using natural abundance stable isotopes, reveals a complex trophic structure among heterotrophic consumers, with four trophic levels supported by a diversity of food sources at a methane seep area off Concepción, Chile (~36° S). Although methanotrophy, thiotrophy and phototrophy are all identified as carbon fixation mechanisms fueling the food web within this area, most of the analysed species (87.5%) incorporate carbon derived from photosynthesis and a smaller number (12%) use carbon derived from chemosynthesis. Methane‐derived carbon (MDC) incorporation was documented in 22 taxa, including sipunculids, gastropods, polychaetes and echinoderms. In addition, wide trophic niches were detected in suspension‐feeding and deposit‐feeding taxa, possibly associated with the use of organic matter in different stages of degradation (e.g. from fresh to refractory). Estimates of Bayesian standard ellipses area (SEAB) reveal different isotopic niche breadth in the predator fishes, the Patagonian toothfish Dissostichus eleginoides and the combtooth dogfish Centroscyllium nigrum, suggesting generalist versus specialist feeding behaviors, respectively. Top predators in the ecosystem were the Patagonian toothfish D. eleginoides and the dusky cat shark, Bythaelurus canescens. The blue hake Antimora rostrata also provides a trophic link between the benthic and pelagic systems, with a diet based primarily on pelagic‐derived carrion. These findings can inform accurate ecosystem models, which are critical for effective management and conservation of methane seep and adjacent deep‐sea habitats in the Southeastern Pacific. 相似文献
113.
114.
Paquin Jean-Philippe Lu Youyu Taylor Stephanne Blanken Hauke Marcotte Guillaume Hu Xianmin Zhai Li Higginson Simon Nudds Shannon Chanut Jérôme Smith Gregory C. Bernier Natacha Dupont Frédéric 《Ocean Dynamics》2020,70(3):365-385
Ocean Dynamics - In the context of Canada’s Ocean Protection Plan (OPP), improved coastal and near-shore modelling is needed to enhance marine safety and emergency response capacity in the... 相似文献
115.
Since 1991, the altimeters of the ERS European Satellites allow the observation of 80% of the Antarctica ice sheet and the whole Greenland ice sheet: They thus offer for the first time a unique vision of polar ice caps. Indeed, surface topography is an essential data thanks to its capacity to highlight the physical processes which control the surface shape, or to test models. Moreover, the altimeter is also a radar which makes it possible to estimate the snow surface or subsurface characteristics, such as surface roughness induced by the strong katabatic wind or ice grain size. The polar ice caps may not be in a stationary state, they continue to respond to the climatic warming of the beginning of the Holocene, that is 18000 years ago, and possibly start to react to present climatic warming: the altimeter offers the unique means of estimating the variations of volume and thus the contribution of polar ice caps to present sea level change. 相似文献
116.
Frédéric Vitali Gérard Blanc François Gauthier-Lafaye Christian France-Lanord 《Contributions to Mineralogy and Petrology》1999,134(4):364-369
Oxygen isotopic compositions of clay minerals were determined on representative samples of the volcano-sedimentary series
from Site 841 ODP (Tonga forearc). This isotopic study has demonstrated an abnormally high crystallisation temperature of
the clay minerals with respect to temperature expected in burial diagenesis. Formation temperatures obtained using 18O reach up to 200 °C in a Fe-chlorite-corrensite paragenesis found in the vicinity of basaltic andesite sills intruded into
the Miocene tuffs. The paleothermal flux resulting from the cooling of the sills has produced very low grade contact metamorphism
in the Miocene Tonga forearc deposits. The consequence of this was the formation of a large amount of hydrous silicates characterised
near the sills by a Fe-clays-analcime mineralogical association.
Received: 26 September 1997 / Accepted: 22 September 1998 相似文献
117.
Christian Beck Pieter Van Rensbergen Marc De Batist Fernand Berthier Serge Lallier Frédéric Manalt 《Journal of Paleolimnology》2001,25(2):149-161
The sedimentary fill of Lake Annecy (northwestern Alps) - related to the last glacial/post-glacial episode - was investigated through high resolution (sparker) and very high resolution (2.5 kHz) seismic-reflection surveys. A seismostratigraphic approach led to subdivision of a 150 m-thick pile (maximum thickness in axial part) into five units. Basal units (1 and 2) represent an imbrication of subglacial and glacio-lacustrine deposits, close to the grounding line of the glaciers' fronts (respectively at the northern and southern terminations of the lake). The first acoustically well-stratified unit (3) developed during a fast retreat of the glaciers fronts far from the lake basin, and a progradational alluvial regime, with abundant underflows, in a lake larger than the present one. Unit 4 represents the progressive decrease of this clastic input mixed with the progressive development of in situ bio-induced production. As in many other alpine lakes, a topmost unit (5), relatively thin (about 8-10 m) and with a conspicuous drape configuration, is the signature of the Holocene interglacial climatic conditions with a sedimentation rate of about 1 mm/yr. On the lacustrine basin slopes, slumps and debris flow occurred mainly within Unit 3; they may be due to, either climate-induced high rate terrigenous sedimentation, or/and to a period of increased seismo-tectonic activity. 相似文献
118.
Anne-Lise Mariet Fabrice Monna Frédéric Gimbert Carole Bégeot Christophe Cloquet Simon Belle Laurent Millet Damien Rius Anne-Véronique Walter-Simonnet 《Journal of Paleolimnology》2018,60(3):399-412
A 157-cm-long sediment core from Longemer Lake in the Vosges Mountains of France spans the past two millennia and was analyzed for trace metal content and lead isotope composition. Trace metal accumulation rates highlight three main input phases: Roman Times (cal. 100 BC–AD 400), the Middle Ages (cal. AD 1000–1500), and the twentieth century. Atmospheric contamination displays a pattern that is similar to that seen in peat bogs from the region, at least until the eighteenth century. Thereafter, the lake sediment record is more precise than peat records. Some regional mining activity, such as that in archaeologically identified eighteenth-century mining districts, was detected from the lead isotope composition of sediment samples. Compositional data analysis, using six trace metals (silver, arsenic, cadmium, copper, lead and zinc), enabled us to distinguish between background conditions, periods of mining, and of other anthropogenic trace metal emissions, such as the recent use of leaded gasoline. 相似文献
119.
120.
O–H isotope ratios of high pressure ultramafic rocks: implications for fluid sources and mobility in the subducted hydrous mantle 总被引:2,自引:0,他引:2
Gretchen L. Früh-Green Marco Scambelluri Franca Vallis 《Contributions to Mineralogy and Petrology》2001,141(2):145-159
We examine the O-H isotope signatures of Alpine ultramafic rocks and eclogitic metagabbros of the Erro-Tobbio peridotite Unit (western Italian Alps), which record a subduction and exhumation cycle. Localization of subduction-related deformation along serpentinite mylonite shear zones favoured preservation of pre-subduction mantle and low temperature (oceanic) alteration assemblages within undeformed (meta)peridotite that underwent partial static recrystallization to high-pressure metamorphic parageneses. Bulk rock and mineral separate (clinopyroxene and serpentine) oxygen isotope ratios of the serpentinized mantle peridotites (5-8) are slightly enriched in 18O compared with those of the high-pressure metaperidotites and the serpentinite mylonites (4.4-7.6). The lowest values occur in high-pressure veins (3.5-5.7) and eclogitic metagabbros (3.1-5.3). These variations are comparable to variations observed in modern oceanic rocks and in non-subducted ophiolites. Preservation of pre-eclogitic '18O signatures of the Erro-Tobbio rocks and a lack of oxygen isotope re-equilibration between different shear zones imply local-scale fluid flow at low water/rock ratios and closed system behaviour during high-pressure metamorphism. Different serpentine generations show a bimodal distribution in 'D values: pre-eclogitic lizardite and chrysotile range from -102 to -77; high-pressure antigorite in the mylonites and in low strain metaperidotites range from -71 to -57 and -83 to -60, respectively. Comparable ranges occur in antigorite in the associated high-pressure veins, suggesting that the hydrogen signatures were acquired prior to veining. We propose that the isotopic variations reflect multiple events of fluid uptake in different geodynamic environments. The H- and O-isotope ratios in the eclogitic mylonites suggest that initial hydration occurred over a range of temperatures during local interaction with altered seawater along oceanic shear zones. The 18O-enriched and H-depleted compositions of chrysotile and lizardite in the mantle peridotites suggest that a second hydration event may have occurred as a result of interaction with metamorphic fluids at the early stages of burial in a forearc setting, where slabs undergo large-scale, low-temperature fluid fluxing. The oceanic mantle is thus a candidate for continuous hydration during its oceanic and early subduction history. The Erro-Tobbio unit thus represents an example of cycling of internally-derived fluids, whereby the different structural and textural domains behaved as relatively closed systems to fluid circulation during high-pressure metamorphism. 相似文献