全文获取类型
收费全文 | 544篇 |
免费 | 27篇 |
国内免费 | 19篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 57篇 |
地球物理 | 115篇 |
地质学 | 248篇 |
海洋学 | 49篇 |
天文学 | 49篇 |
自然地理 | 63篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 12篇 |
2018年 | 9篇 |
2017年 | 14篇 |
2016年 | 19篇 |
2015年 | 20篇 |
2014年 | 24篇 |
2013年 | 40篇 |
2012年 | 25篇 |
2011年 | 27篇 |
2010年 | 22篇 |
2009年 | 32篇 |
2008年 | 23篇 |
2007年 | 28篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 29篇 |
2003年 | 16篇 |
2002年 | 20篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 14篇 |
1997年 | 8篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 5篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有590条查询结果,搜索用时 609 毫秒
61.
Arctic sea ice and Eurasian climate: A review 总被引:12,自引:0,他引:12
GAO Yongqi SUN Jianqi LI Fei HE Shengping Stein SANDVEN YAN Qing ZHANG Zhongshi Katja LOHMANN Noel KEENLYSIDE Tore FUREVIK SUO Lingling 《大气科学进展》2015,32(1):92-114
The Arctic plays a fundamental role in the climate system and has shown significant climate change in recent decades,including the Arctic warming and decline of Arctic sea-ice extent and thickness. In contrast to the Arctic warming and reduction of Arctic sea ice, Europe, East Asia and North America have experienced anomalously cold conditions, with record snowfall during recent years. In this paper, we review current understanding of the sea-ice impacts on the Eurasian climate.Paleo, observational and modelling studies are covered to summarize several major themes, including: the variability of Arctic sea ice and its controls; the likely causes and apparent impacts of the Arctic sea-ice decline during the satellite era,as well as past and projected future impacts and trends; the links and feedback mechanisms between the Arctic sea ice and the Arctic Oscillation/North Atlantic Oscillation, the recent Eurasian cooling, winter atmospheric circulation, summer precipitation in East Asia, spring snowfall over Eurasia, East Asian winter monsoon, and midlatitude extreme weather; and the remote climate response(e.g., atmospheric circulation, air temperature) to changes in Arctic sea ice. We conclude with a brief summary and suggestions for future research. 相似文献
62.
Harold Clénet Georges Ceuleneer Patrick Pinet Bénédicte Abily Yves Daydou Esther Harris Isma Amri Céline Dantas 《Lithos》2010,114(3-4):265-281
Using the HyMap instrument, we have acquired visible and near infrared hyperspectral data over the Maqsad area of the Oman ophiolite (~ 15 × 60 km). This survey allowed us to identify and map the distribution of clinopyroxene-rich cumulates (inter-layered clinopyroxenites and wehrlites) whose occurrence was previously undocumented in this area. The cumulates reach several hundred meters in thickness and crop out at distances exceeding 15 km on both sides of the Maqsad former spreading centre. They occur either in mantle harzburgites, as km-sized layered intrusions surrounded by fields of pegmatitic dykes consisting of orthopyroxene-rich pyroxenite and gabbronorites, or at the base of the crustal section where they are conformably overlain by cumulate gabbros. These ultramafic cumulates crystallized from silica- and Mg-rich melts derived from a refractory mantle source (e.g. high Cr#, low [Al2O3], low [TiO2]). These melts are close to high-Ca boninites, although, strictly speaking, not perfect equivalents of present-day, supra-subduction zone, boninites. Chemical stratigraphy reveals cycles of replenishment, mixing and fractional crystallization from primitive (high Mg#) melts, typical of open magma chambers and migration of inter-cumulus melts. The TiO2 content of clinopyroxene is always low (≤ 0.2 wt.%) but quite variable compared to the associated pegmatites that are all derived from a source ultra-depleted in high field strength elements (HFSE). This variability is not caused by fractional crystallization alone, and is best explained by hybridization between the ultra-depleted melts (parent melts of the pegmatites) and the less depleted mid-ocean ridge basalts (MORB) parent of the dunitic–troctolitic–gabbroic cumulates making up the crustal section above the Maqsad diapir.We propose that, following a period of magma-starved spreading, the Maqsad mantle diapir, impregnated with tholeiitic melts of MORB affinity, reached shallow depths beneath the ocean ridge. This diapir induced melting of the formerly accreted and hydrothermally altered lithosphere. At this stage, these boninitic-like lithospheric melts crystallized as pegmatitic dykes. As the diapir continued to rise, the amount of MORB reaching shallow depths increased, together with the surrounding temperature, leading to the formation of magma chambers where the crystallization of layered cumulates became possible. These cumulates remained rich in pyroxene and devoid of plagioclase as long as the contribution of MORB-derived melts was moderate relative to the lithospheric-derived melts. As the contribution of MORB to the refilling of the magma chamber increased, gabbroic cumulates started to crystallize. 相似文献
63.
Yves Marrocchi Emmanuel Jacquet Julia Neukampf Johan Villeneuve Michael E. Zolensky 《Meteoritics & planetary science》2023,58(2):195-206
The ungrouped carbonaceous chondrite (CC) Bells has long been considered petrographically similar to CM chondrites based on its matrix abundance and degree of aqueous alteration, but also shows significant isotopic affinities to CR chondrites. Its taxonomic status is thus important for clarifying the relationship of the CRHB (formerly “CR”) clan with other CCs. In this study, we measured the oxygen isotopic compositions of olivines in type I chondrules and isolated olivine grains in Bells. Bells olivines mostly have ∆17O > −4‰, similar to CR chondrites but unlike other CCs that are rich in refractory inclusions, in which chondrules are generally richer in 16O. Therefore, Bells is a CR chondrite (albeit an anomalous one), most similar to the rare, matrix-rich CRs like Al Rais. These chondrites (i) may not necessarily derive from the same primary parent body as mainstream CRs, (ii) bear witness to significant variations of the matrix/chondrule ratio within the CRHB clan, and (iii) may be a good analog for samples retrieved by the space mission OSIRIS-REx. 相似文献
64.
Recent studies show that mid-latitude SST variations over the Kuroshio-Oyashio Extension influence the atmospheric circulation. However, the impact of variations in SST in the Gulf Stream region on the atmosphere has been less studied. Understanding the atmospheric response to such variability can improve the climate predictability in the North Atlantic Sector. Here we use a relatively high resolution (~1°) Atmospheric General Circulation Model to investigate the mechanisms linking observed 5-year low-pass filtered SST variability in the Gulf Stream region and atmospheric variability, with focus on precipitation. Our results indicate that up to 70 % of local convective precipitation variability on these timescales can be explained by Gulf Stream SST variations. In this region, SST and convective precipitation are strongly correlated in both summer (r = 0.73) and winter (r = 0.55). A sensitivity experiment with a prescribed local warm SST anomaly in the Gulf Stream region confirms that local SST drives most of the precipitation variability over the Gulf Stream. Increased evaporation connected to the anomalous warm SST plays a crucial role in both seasons. In summer there is an enhanced local SLP minimum, a concentrated band of low level convergence, deep upward motion and enhanced precipitation. In winter we also get enhanced precipitation, but a direct connection to deep vertical upward motion is not found. Nearly all of the anomalous precipitation in winter is connected to passing atmospheric fronts. In summer the connection between precipitation and atmospheric fronts is weaker, but still important. 相似文献
65.
Daniel Paradis Laurie Tremblay René Lefebvre Erwan Gloaguen Alfonso Rivera Michel Parent Jean-Marc Ballard Yves Michaud Patrick Brunet 《Environmental Earth Sciences》2014,72(5):1325-1348
Providing a sound basis for aquifer management or remediation requires that hydrogeological investigations carried out to understand groundwater flow and contaminant transport be based on representative data that capture the heterogeneous spatial distribution of aquifer hydraulic properties. This paper describes a general workflow allowing the characterization of the heterogeneity of the hydraulic properties of granular aquifers at an intermediate scale of a few km2. The workflow involves characterization and data integration steps that were applied on a 12-km2 study area encompassing a decommissioned landfill emitting a leachate plume and its main surface water receptors. The sediments composing the aquifer were deposited in a littoral–sublittoral environment and show evidence of small-scale transitional heterogeneities. Cone penetrometer tests (CPT) combined with soil moisture and electrical resistivity (SMR) measurements were thus used to identify and characterize spatial heterogeneities in hydraulic properties over the study area. Site-specific statistical relationships were needed to infer hydrofacies units and to estimate hydraulic properties from high-resolution CPT/SMR soundings distributed all over the study area. A learning machine approach was used due to the complex statistical relationships between colocated hydraulic and CPT/SMR data covering the full range of aquifer materials. Application of this workflow allowed the identification of hydrofacies units and the estimation of horizontal hydraulic conductivity, vertical hydraulic conductivity and porosity over the study area. The paper describes and discusses data acquisition and integration methodologies that can be adapted to different field situations, while making the aquifer characterization process more time-efficient and less labor-intensive. 相似文献
66.
H. Albert Gilg Yves Krüger Heinrich Taubald Alfons M. van den Kerkhof Martin Frenz Giulio Morteani 《Mineralium Deposita》2014,49(7):861-877
Fluid inclusion studies in combination with hydrogen, oxygen and sulphur isotope data provide novel insights into the genesis of giant amethyst-bearing geodes in Early Cretaceous Paraná continental flood basalts at Amestita do Sul, Brazil. Monophase liquid inclusions in colourless quartz, amethyst, calcite, barite and gypsum were analysed by microthermometry after stimulating bubble nucleation using single femtosecond laser pulses. The salinity of the fluid inclusions was determined from ice-melting temperatures and a combination of prograde and retrograde homogenisation temperatures via the density maximum of the aqueous solutions. Four mineralisation stages are distinguished. In stage I, celadonite, chalcedony and pyrite formed under reducing conditions in a thermally stable environment. Low δ34SV-CDT values of pyrite (?25 to ?32?‰) suggest biogenic sulphate reduction by organotrophic bacteria. During the subsequent stages II (amethyst, goethite and anhydrite), III (early subhedral calcite) and IV (barite, late subhedral calcite and gypsum), the oxidation state of the fluid changed towards more oxidising conditions and microbial sulphate reduction ceased. Three distinct modes of fluid salinities around 5.3, 3.4 and 0.3 wt% NaCl-equivalent characterise the mineralisation stages II, III and IV, respectively. The salinity of the stage I fluid is unknown due to lack of fluid inclusions. Variation in homogenisation temperatures and in δ18O values of amethyst show evidence of repeated pulses of ascending hydrothermal fluids of up to 80–90 °C infiltrating a basaltic host rock of less than 45 °C. Colourless quartz and amethyst formed at temperatures between 40 and 80 °C, while the different calcite generations and late gypsum precipitated at temperatures below 45 °C. Calculated oxygen isotope composition of the amethyst-precipitating fluid in combination with δD values of amethyst-hosted fluid inclusions (?59 to ?51?‰) show a significant 18O-shift from the meteoric water line. This 18O-shift, high salinities of the fluid inclusions with chloride-sulphate composition, and high δ34S values of anhydrite and barite (7.5 to 9.9?‰) suggest that sedimentary brines from deeper parts of the Guaraní aquifer system must have been responsible for the amethyst mineralisation. 相似文献
67.
Noel P. James Margaret J. Seibel Robert W. Dalrymple David Besson Olivier Parize 《Sedimentology》2014,61(2):497-534
The Saumane‐Venasque compound palaeovalley succession accumulated in a strongly tide‐influenced embayment or estuary. Warm‐temperate normal marine to brackish conditions led to deposition of extensive cross‐bedded biofragmental calcarenites. Echinoids, bryozoans, coralline algae, barnacles and benthic foraminifera were produced in seagrass meadows, on rocky substrates colonized by macroalgae and within subaqueous dune fields. There are two sequences, S1 and S2, the first of which contains three high‐frequency sequences (S1a, S1b and S1c). Sequence 1 is largely confined to the palaeovalley with its upper part covering interfluves. Each of these has a similar upward succession of deposits that includes: (i) a basal erosional surface that is bored and glauconitized; (ii) a discontinuous lagoonal lime mudstone or wackestone; (iii) a thin conglomerate generated by tidal ravinement; (iv) a transgressive systems tract series of cross‐bedded calcarenites; (v) a maximum flooding interval of argillaceous, muddy quartzose, open‐marine limestones; and (vi) a thin highstand systems tract of fine‐grained calcarenite. Tidal currents during stages S1a, S1b and S1c were accentuated by the constricted valley topography, whereas basin‐scale factors enhanced tidal currents during the deposition of S2. The upper part of the succession in all but S1c has been removed by later erosion. There is an overall upward temporal change with quartz, barnacles, encrusting corallines and epifaunal echinoids decreasing but bryozoans, articulated corallines and infaunal echinoids increasing. This trend is interpreted to be the result of changing oceanographic conditions as the valley was filled, bathymetric relief was reduced, rocky substrates were replaced as carbonate factories by seagrass meadows and subaqueous dunes, and the setting became progressively less confined and more open marine. These limestones are characteristic of a suite of similar cool‐water calcareous sand bodies in environments with little siliciclastic or fresh water input during times of high‐amplitude sea‐level change wherein complex inboard antecedent topography was flooded by a rising ocean. 相似文献
68.
This paper presents the results of the analysis of long range propagation (~200 km) in a range-dependent environment. The propagation medium is characterized by two deep sound channels. The range dependence enables energy transfer between the channels and leads to a mismatch between real data and ray predictions. To explain this mismatch, an analysis of hybrid ray propagation is presented. This analysis is completed by an interpretation in terms of chaos. This chaos is quantified in the particular case of the Bay of Biscay environment. This paper puts forward that mesoscale perturbations, such as the Mediterranean outflow in the North Atlantic, can affect long-range propagation. However, it shows that the ray theory remains reliable for a propagation range of several hundred kilometers 相似文献
69.
Heavy rainfall events during the fall season are causing extended damages in Mediterranean catchments. A peaks‐over‐threshold model is developed for the extreme daily areal rainfall occurrence and magnitude in fall over six catchments in Southern France. The main driver of the heavy rainfall events observed in this region is the humidity flux (FHUM) from the Mediterranean Sea. Reanalysis data are used to compute the daily FHUM during the period 1958–2008, to be included as a covariate in the model parameters. Results indicate that the introduction of FHUM as a covariate can improve the modelling of extreme areal precipitation. The seasonal average of FHUM can improve the modelling of the seasonal occurrences of heavy rainfall events, whereas daily FHUM values can improve the modelling of the events magnitudes. In addition, an ensemble of simulations produced by five different general circulation models are considered to compute FHUM in future climate with the emission scenario A1B and hence to evaluate the effect of climate change on the heavy rainfall distribution in the selected catchments. This ensemble of climate models allows the evaluation of the uncertainties in climate projections. By comparison to the reference period 1960–1990, all models project an amplification of the mean seasonal FHUM from the Mediterranean Sea for the projection period 2070–2099, on average by +22%. This increase in FHUM leads to an increase in the number of heavy rainfall events, from an average of 2.55 events during the fall season in present climate to 3.57 events projected for the period 2070–2099. However, the projected changes have limited effects on the magnitude of extreme events, with only a 5% increase in the median of the 100‐year quantiles. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
70.
Studies in the past have tried to reproduce the mechanical behaviour of granular materials by proposing constitutive relations based on a common assumption that model parameters and parameters describing the properties, including gradation of individual grains are inevitably linked. However successful these models have proved to be, they cannot account for the changes in granular assembly behaviour if the grains start to break during mechanical loading. This paper proposes to analyse the relation between grading change and the mechanical behaviour of granular assembly. A way to model the influence of grain breakage is to use a critical state‐based model. The influence of the amount of grain breakage during loading, depending on the individual grain strength and size distribution, can be introduced into constitutive relations by means of a new parameter that controls the evolution of critical state with changes in grain size distribution. Experimental data from a calcareous sand, a quartz sand, and a rockfill material were compared with numerical results and good‐quality simulations were obtained. The main consequences of grain breakage are increased compressibility and a gradual dilatancy disappearance in the granular material. The critical state concept is also enriched by considering its overall relation to the evolution of the granular material. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献