全文获取类型
收费全文 | 646篇 |
免费 | 27篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 47篇 |
地球物理 | 134篇 |
地质学 | 319篇 |
海洋学 | 49篇 |
天文学 | 76篇 |
自然地理 | 35篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 27篇 |
2017年 | 14篇 |
2016年 | 27篇 |
2015年 | 24篇 |
2014年 | 30篇 |
2013年 | 40篇 |
2012年 | 37篇 |
2011年 | 45篇 |
2010年 | 45篇 |
2009年 | 59篇 |
2008年 | 47篇 |
2007年 | 26篇 |
2006年 | 29篇 |
2005年 | 31篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 30篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1979年 | 1篇 |
排序方式: 共有677条查询结果,搜索用时 15 毫秒
161.
162.
Fission track and fault kinematics analyses for new insight into the Late Cenozoic tectonic regime changes in West-Central Sulawesi (Indonesia) 总被引:1,自引:0,他引:1
Olivier Bellier Michel Sbrier Diane Seward Thierry Beaudouin Michel Villeneuve Eka Putranto 《Tectonophysics》2006,413(3-4):201-220
A 3-D density model for the Cretan and Libyan Seas and Crete was developed by gravity modelling constrained by five 2-D seismic lines. Velocity values of these cross-sections were used to obtain the initial densities using the Nafe–Drake and Birch empirical functions for the sediments, the crust and the upper mantle. The crust outside the Cretan Arc is 18 to 24 km thick, including 10 to 14 km thick sediments. The crust below central Crete at its thickest section, has values between 32 and 34 km, consisting of continental crust of the Aegean microplate, which is thickened by the subducted oceanic plate below the Cretan Arc. The oceanic lithosphere is decoupled from the continental along a NW–SE striking front between eastern Crete and the Island of Kythera south of Peloponnese. It plunges steeply below the southern Aegean Sea and is probably associated with the present volcanic activity of the southern Aegean Sea in agreement with published seismological observations of intermediate seismicity. Low density and velocity upper mantle below the Cretan Sea with ρ 3.25 × 103 kg/m3 and Vp velocity of compressional waves around 7.7 km/s, which are also in agreement with observed high heat flow density values, point out at the mobilization of the upper mantle material here. Outside the Hellenic Arc the upper mantle density and velocity are ρ ≥ 3.32 × 103 kg/m3 and Vp = 8.0 km/s, respectively. The crust below the Cretan Sea is thin continental of 15 to 20 km thickness, including 3 to 4 km of sediments. Thick accumulations of sediments, located to the SSW and SSE of Crete, are separated by a block of continental crust extended for more than 100 km south of Central Crete. These deep sedimentary basins are located on the oceanic crust backstopped by the continental crust of the Aegean microplate. The stretched continental margin of Africa, north of Cyrenaica, and the abruptly terminated continental Aegean microplate south of Crete are separated by oceanic lithosphere of only 60 to 80 km width at their closest proximity. To the east and west, the areas are floored by oceanic lithosphere, which rapidly widens towards the Herodotus Abyssal plain and the deep Ionian Basin of the central Mediterranean Sea. Crustal shortening between the continental margins of the Aegean microplate and Cyrenaica of North Africa influence the deformation of the sediments of the Mediterranean Ridge that has been divided in an internal and external zone. The continental margin of Cyrenaica extends for more than 80 km to the north of the African coast in form of a huge ramp, while that of the Aegean microplate is abruptly truncated by very steep fractures towards the Mediterranean Ridge. Changes in the deformation style of the sediments express differences of the tectonic processes that control them. That is, subduction to the northeast and crustal subsidence to the south of Crete. Strike-slip movement between Crete and Libya is required by seismological observations. 相似文献
163.
Time-dependent response of a zonally averaged ocean–atmosphere–sea ice model to Milankovitch forcing
An ocean–atmosphere–sea ice model is developed to explore the time-dependent response of climate to Milankovitch forcing for
the time interval 5–3 Myr BP. The ocean component is a zonally averaged model of the circulation in five basins (Arctic, Atlantic,
Indian, Pacific, and Southern Oceans). The atmospheric component is a one-dimensional (latitudinal) energy balance model,
and the sea-ice component is a thermodynamic model. Two numerical experiments are conducted. The first experiment does not
include sea ice and the Arctic Ocean; the second experiment does. Results from the two experiments are used to investigate
(1) the response of annual mean surface air and ocean temperatures to Milankovitch forcing, and (2) the role of sea ice in
this response. In both experiments, the response of air temperature is dominated by obliquity cycles at most latitudes. On
the other hand, the response of ocean temperature varies with latitude and depth. Deep water formed between 45°N and 65°N
in the Atlantic Ocean mainly responds to precession. In contrast, deep water formed south of 60°S responds to obliquity when
sea ice is not included. Sea ice acts as a time-integrator of summer insolation changes such that annual mean sea-ice conditions
mainly respond to obliquity. Thus, in the presence of sea ice, air temperature changes over the sea ice are amplified, and
temperature changes in deep water of southern origin are suppressed since water below sea ice is kept near the freezing point. 相似文献
164.
Laurent Jolivet Fabien Trotet Patrick Monié Olivier Vidal Bruno Goffé Loïc Labrousse Philippe Agard Bad'r Ghorbal 《Tectonophysics》2010,480(1-4):133-148
Syn-orogenic detachments in accretionary wedges make the exhumation of high-pressure and low-temperature metamorphic rocks possible with little erosion. The velocity of exhumation within the subduction channel or the accretionary complex, and thus the shape of P–T paths, depend upon the kinematic boundary conditions. A component of slab retreat tends to open the channel and facilitates the exhumation. We document the effect of slab retreat on the shape of P–T paths using the example of the Phyllite–Quartzite Nappe that has been exhumed below the Cretan syn-orogenic detachment during the Miocene in Crete and the Peloponnese. Data show a clear tendency toward colder conditions at peak pressure and during exhumation where the intensity of slab retreat is larger. This spatial evolution of P–T gradient is accompanied with an evolution from a partly coaxial regime below the Peloponnese section of the detachment toward a clearly non-coaxial regime in Crete. 相似文献
165.
Pascal Lecroart Olivier Maire Sabine Schmidt Pierre Anschutz 《Geochimica et cosmochimica acta》2010,74(21):6049-6063
Bioturbation refers to the mixing of sediment particles resulting from benthic faunal activity. It is the dominant particle mixing process in most marine sediments and exerts an important control on diagenetic processes. In models, bioturbation is usually treated as a diffusive process where the biodiffusion coefficient (Db) characterizes the biological mixing intensity. Biodiffusion coefficients are classically computed by fitting a diffusive model to vertical profiles of particle-bound radioisotopes. One peculiar observation is tracer-dependence: Db values from short-lived tracers tend to be larger than those obtained from long-lived tracers from the same site. Recent theoretical work, based on random walk theory and Lattice Automaton Bioturbation Simulations (LABS), has suggested that this tracer-dependence is simply a model artifact and has concluded that the biodiffusion model is not applicable to the short observational time scales associated with short-lived radioisotopes. Here we have compiled a global dataset of Db values obtained from different radiotracers to assess tracer-dependence from a data perspective. Tracer-dependence is significant in low-mixing environments like slope and deep-sea sediments, but is not present in intensely mixed coastal areas. Tracer-dependence is absent when the number of mixing events is larger than 20, or the potential length scale is greater than 0.5 cm. Roughly this comes down to tracer-derived Db values greater than 2 cm2 yr−1. This condition is met for 68%, 50%, and 8% of published Db values obtained from coastal, continental slope, and abyssal environments, respectively. These results show that short-lived radioisotopes are suitable to quantify biodiffusion mixing in sedimentary environments featuring intense bioturbation. 相似文献
166.
Andrew J. Dombard Olivier S. Barnouin Louise M. Prockter Peter C. Thomas 《Icarus》2010,210(2):713-721
There are ∼300 features on the Asteroid 433 Eros that morphologically resemble ponds (flat-floored and sharply embaying the bounding depression in which they sit). Because boulders on Eros are apparently eroding in place and because ponds with associated boulders tend to be larger than ponds without blocks, we propose that ponds form from thermally disaggregated and seismically flattened boulder material, under the assumption that repeated day/night cycling causes material fatigue that leads to erosion of the boulders. Results from a simple boulder emplacement/thermal erosion model with boulders emplaced in a few discrete events (i.e., large impacts) match well the observed size distribution. Under this scenario, the subtle color differences of ponds (somewhat bluer than the rest of the surface) might be due to some combination of less space-weathered material and density stratification of silicate-rich chondrules and more metal-rich matrix from a disaggregated boulder. Volume estimates of ponds derived from NEAR Laser Rangefinder profiles are consistent with what can be supplied by boulders. Ponds are also observed to be concentrated in regions of low slope and high elevation, which suggests the presence of a less mobile regolith and thus a contrast in the resistance to seismic shaking between the pond material and the material that makes up the bounding depression. Future tests include shake-table experiments and temperature cycling (fatigue) of ordinary chondrites to test the thermal erosion mechanism. 相似文献
167.
Olivier Le Roux Stéphane Schwartz Jean François Gamond Denis Jongmans Pierre Tricart Michel Sebrier 《International Journal of Earth Sciences》2010,99(2):427-441
In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides,
from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into
a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary
fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic
and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone
(SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the
bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin
and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited
structures, the BMF and the SFZ. 相似文献
168.
169.
Bénédicte Ritt Jozée Sarrazin Jean-Claude Caprais Philippe Noël Olivier Gauthier Catherine Pierre Pierre Henry Daniel Desbruyères 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(9):1120-1136
A brackish-water cold seep on the North Anatolian Fault (NAF) in the Marmara Sea was investigated with the Nautile submersible during the MarNaut cruise in 2007. This active zone has already been surveyed and revealed evidence of active seeping on the seafloor, such as bubble emissions, patches of reduced sediments, microbial mats and authigenic carbonate crusts. MarNaut was the first opportunity to sample benthic communities in the three most common microhabitats (bioturbated and reduced sediments, carbonate crust) and to examine their relationships with environmental conditions. To do so, faunal communities were sampled and chemical measurements were taken close to the organisms. According to diversity indices, the bioturbated microhabitat exhibited the highest taxonomic diversity and evenness despite a lower number of samples. Conversely, the reduced sediment microhabitat exhibited the lowest taxonomic diversity and evenness. The carbonate crust microhabitat was intermediate although it had the highest biomass. Multivariate analyses showed that (1) fauna were relatively similar within a single microhabitat; (2) faunal community structure varied greatly between the different microhabitats; (3) there was a link between faunal distribution and the type of substratum; and (4) chemical gradients (i.e. methane, oxygen and probably sulphides) may influence faunal distribution. The estimated fluid flow velocity (0.4–0.8 m/yr) confirmed the presence of fluid emission and provided evidence of seawater convection in the two soft-sediment microhabitats. Our results suggest that the reduced sediments may represent a harsher environment with high upward fluid flow, which restrains seawater from penetrating the sediments and inhibits sulphide production, whereas bioturbated sediments can be viewed as a bio-irrigated system with sulphide production occurring at greater depths. Therefore, the environmental conditions in reduced sediments appear to prevent the colonization of symbiont-bearing fauna, such as vesicomyid bivalves, which are more often found in bioturbated sediments. Fluid flow appears to control sulphide availability, which in turn influences the horizontal and vertical distribution patterns of fauna at small spatial scales as observed at other seep sites. 相似文献
170.
Anja Eichler Willy Tinner Sabina Brütsch Susanne Olivier Tatyana Papina Margit Schwikowski 《Quaternary Science Reviews》2011,30(9-10):1027-1034
Forest fires play a key role in the global carbon cycle and thus, can affect regional and global climate. Although fires in extended areas of Russian boreal forests have a considerable influence on atmospheric greenhouse gas and soot concentrations, estimates of their impact on climate are hampered by a lack of data on the history of forest fires. Especially regions with strong continental climate are of high importance due to an intensified development of wildfires. In this study we reconstruct the fire history of Southern Siberia during the past 750 years using ice-core based nitrate, potassium, and charcoal concentration records from Belukha glacier in the continental Siberian Altai. A period of exceptionally high forest-fire activity was observed between AD 1600 and 1680, following an extremely dry period AD 1540–1600. Ice-core pollen data suggest distinct forest diebacks and the expansion of steppe in response to dry climatic conditions. Coherence with a paleoenvironmental record from the 200 km distant Siberian lake Teletskoye shows that the vegetational shift AD 1540–1680, the increase in fire activity AD 1600–1680, and the subsequent recovery of forests AD 1700 were of regional significance. Dead biomass accumulation in response to drought and high temperatures around AD 1600 probably triggered maximum forest-fire activity AD 1600–1680. The extreme dry period in the 16th century was also observed at other sites in Central Asia and is possibly associated with a persistent positive mode of the Pacific Decadal Oscillation (PDO). No significant increase in biomass burning occurred in the Altai region during the last 300 years, despite strongly increasing temperatures and human activities. Our results imply that precipitation changes controlled fire-regime and vegetation shifts in the Altai region during the past 750 years. We conclude that high sensitivity of ecosystems to occasional decadal-scale drought events may trigger unprecedented environmental reorganizations under global-warming conditions. 相似文献