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61.
Seafloor change detection using multibeam echosounder backscatter: case study on the Belgian part of the North Sea 总被引:1,自引:0,他引:1
Giacomo Montereale-Gavazzi Marc Roche Xavier Lurton Koen Degrendele Nathan Terseleer Vera Van Lancker 《Marine Geophysical Researches》2018,39(1-2):229-247
To characterize seafloor substrate type, seabed mapping and particularly multibeam echosounding are increasingly used. Yet, the utilisation of repetitive MBES-borne backscatter surveys to monitor the environmental status of the seafloor remains limited. Often methodological frameworks are missing, and should comprise of a suite of change detection procedures, similarly to those developed in the terrestrial sciences. In this study, pre-, ensemble and post-classification approaches were tested on an eight km2 study site within a Habitat Directive Area in the Belgian part of the North Sea. In this area, gravel beds with epifaunal assemblages were observed. Flourishing of the fauna is constrained by overtopping with sand or increased turbidity levels, which could result from anthropogenic activities. Monitoring of the gravel to sand ratio was hence put forward as an indicator of good environmental status. Seven acoustic surveys were undertaken from 2004 to 2015. The methods allowed quantifying temporal trends and patterns of change of the main substrate classes identified in the study area; namely fine to medium homogenous sand, medium sand with bioclastic detritus and medium to coarse sand with gravel. Results indicated that by considering the entire study area and the entire time series, the gravel to sand ratio fluctuated, but was overall stable. Nonetheless, when only the biodiversity hotspots were considered, net losses and a gradual trend, indicative of potential smothering, was captured by ensemble and post-classification approaches respectively. Additionally, a two-dimensional morphological analysis, based on the bathymetric data, suggested a loss of profile complexity from 2004 to 2015. Causal relationships with natural and anthropogenic stressors are yet to be established. The methodologies presented and discussed are repeatable and can be applied to broad-scale geographical extents given that broad-scale time series datasets become available. 相似文献
62.
Giacomo D’Amato Avanzi Francesco Falaschi Roberto Giannecchini Alberto Puccinelli 《Natural Hazards》2009,50(3):591-603
This study aims at contributing to the soil slip susceptibility assessment in a typical basin of the southern Apuan Alps,
Italy. On June 1996, this basin (Cardoso Torrent, 13 km2 large) was hit by an extremely heavy rainstorm (maximum intensity of about 160 mm/h), which caused many landslides (debris
slide–debris flows) and valley bottom flows (hyperconcentrated flows), destruction and deaths. Detailed surveys provided the
characterization of the main factors (geological, geomorphologic, hydrological, hydrogeological and geotechnical) which contributed
in triggering landslides. In order to evaluate the soil slip susceptibility in this area, a physically based model was applied
and a GIS analysis of digital elevation model was performed. This approach couples a mechanical model based on an infinite
slope form of the Mohr–Coulomb failure criterion, and a steady-state hydrological one (a modified version of Shalstab, which
considers the cohesion of the debris material potentially involved in landsliding). GIS techniques allowed evaluating the
effects of topographic convergence and drainage area on slope failure. In this way, based on the infiltration rate, the triggering
of the June 1996 landslides was simulated and the critical rainfall thresholds assessed at about 200–250 mm/24 h. 相似文献
63.
Duccio Tampucci Mauro Gobbi Giuseppe Marano Patrizia Boracchi Giacomo Boffa Francesco Ballarin Paolo Pantini Roberto Seppi Chiara Compostella Marco Caccianiga 《Boreas: An International Journal of Quaternary Research》2017,46(2):185-198
Active rock glaciers are periglacial landforms consisting of coarse debris with interstitial ice or ice‐core. Recent studies showed that such landforms are able to support plant and arthropod life and could act as warm‐stage refugia for cold‐adapted species due to their microclimate features and thermal inertia. However, integrated research comparing active rock glaciers with surrounding landforms to outline their ecological peculiarities is still scarce. We analysed the abiotic (ground surface temperature and humidity, soil physical and chemical parameters) and biotic (plant and arthropod communities) features of two Alpine active rock glaciers with contrasting lithology (silicate and carbonate), and compared them with the surrounding iceless landforms as reference sites (stable slopes and active scree slopes). Our data show remarkable differences between stable slopes and unstable landforms as a whole, while few differences occur between active scree slopes and active rock glaciers: such landforms show similar soil features but different ground surface temperatures (lower on active rock glaciers) and different occurrence of cold‐adapted species (more frequent/abundant on active rock glaciers). Both plant and arthropod species distributions depend mainly on the geographical context as a function of soil pH and on the contrast between stable slopes and unstable landforms as a function of the coarse debris fraction and organic matter content, while the few differences between active scree slopes and active rock glaciers can probably be attributed to microclimate. The role of active rock glaciers as potential warm‐stage refugia for cold‐adapted species is supported by our data; however, at least in the European Alps, their role in this may be less important than that of debris‐covered glaciers, which are able to host cold‐adapted species even below the climatic tree line. 相似文献
64.
65.
Cui Hua Huang Xian Xue Tao Wang Roberto De Mascellis Giacomo Mele Quan Gang You Fei Peng Anna Tedeschi 《Environmental Earth Sciences》2011,63(4):701-708
Due to the lack of freshwater, highly saline groundwater was the main irrigation source in the last few decades in the Minqin
Basin, which is in northwest China. The study evaluates the effects of salt accumulation on the soil physical–chemicals properties.
Undisturbed and disturbed soil samples were taken from the experiment site, which was irrigated with saline water at a concentration
of 0.8, 2 and 5 g L−1 (coded later as C08, C2 and C5). Undisturbed soil samples, at depths of 0–45 and 45–60 cm were taken to determine the water retention curve (WRC). Moreover,
in the same place, another set of undisturbed soil samples were taken to determine the porosity and pore-size distribution
(PoSD). From the WRC, the water-holding capacity of the soil was estimated. Disturbed soil samples at depths of 0–20, 0–45,
45–60 and 80–100 cm were taken to determine the index of aggregates stability in water (IC). The electrical conductivity of
the saturated paste (ECe) was determined at depths of 0–30, 30–60 and 60–90 cm, during the irrigation season on C08, C2 and C5 treatments. The results show that the total porosity and the index of aggregates stability in water decrease with the increasing
salinity of irrigation water, and the ECe increases with the increasing salinity of irrigation water especially in the surface soil. The water-holding capacity (WHC)
of soil also increases with the increasing salinity of irrigation water. 相似文献
66.
Antonio Hernández-Espriú J. Antonio Reyna-Gutiérrez Emilio Sánchez-León Enrique Cabral-Cano Jaime Carrera-Hernández Pedro Martínez-Santos Sergio Macías-Medrano Giacomo Falorni Davide Colombo 《Hydrogeology Journal》2014,22(6):1469-1485
Mexico City relies on groundwater for most of its domestic supply. Over the years, intensive pumping has led to significant drawdowns and, subsequently, to severe land subsidence. Tensile cracks have also developed or reactivated as a result. All such processes cause damage to urban infrastructure, increasing the risk of spills and favoring contaminant propagation into the aquifer. The effects of ground deformation are frequently ignored in groundwater vulnerability studies, but can be relevant in subsiding cities. This report presents an extension to the DRASTIC methodology, named DRASTIC-Sg, which focuses on evaluating groundwater vulnerability in urban aquifers affected by differential subsidence. A subsidence parameter is developed to represent the ground deformation gradient (Sg), and then used to depict areas where damage risk to urban infrastructure is higher due to fracture propagation. Space-geodetic SqueeSAR data and global positioning system (GPS) validation were used to evaluate subsidence rates and gradients, integrating hydrogeological and geomechanical variables into a GIS environment. Results show that classic DRASTIC approaches may underestimate groundwater vulnerability in settings such as the one at hand. Hence, it is concluded that the Sg parameter is a welcome contribution to develop reliable vulnerability assessments in subsiding basins. 相似文献
67.
Antonio Puccini Gerti Xhixha Stefano Cuccuru Giacomo Oggiano Merita Kaçeli Xhixha Fabio Mantovani Carlos Rossi Alvarez Leonardo Casini 《Environmental Earth Sciences》2014,71(1):393-405
This study focuses on the radiological characterization of granitoid outcrops and dimension stones using in situ gamma-ray spectrometry. Extensive measurements were performed on 210 granitoid outcrops of the Corsica-Sardinia Batholith. The large statistical sample allowed us to improve the analysis by considering a log-normal distribution of radioelements and propagating the uncertainties using Monte Carlo method. The activity concentrations of 40K, 226Ra (238U) and 232Th in C-SB area were 1,177 ?304 +408 , 60 ?23 +36 and 69 ?25 +38 Bq/kg (at 1σ uncertainty). The median abundance of K, U and Th on the Variscan C-SB was higher than the average values of the upper continental crust and was comparable with Variscan belt. This corresponds to an outdoor absorbed dose rate of 124 ?26 +33 nGy/h at 1σ uncertainty which is 3σ higher than the population-weighted average absorbed dose rate (60 nGy/h). Seven commercial granites (Rosa Beta, Ghiandone, Giallo San Giacomo, Rosa Cinzia, Grigio Malaga, Bianco Sardo and Grigio Perla) were investigated to characterize their radiological hazard through 147 measurements taken in 73 extractive quarries. All of the commercial granites were categorized as A2 material based on their activity concentration indices, excluding (at the 3σ level) any restriction on their utilization as superficial materials. Rosa Beta, Grigio Malaga, Grigio Perla and Bianco Sardo can also be used as bulk materials as they can be included in the A1 category. In the case of Ghiandone, Giallo San Giacomo and Rosa Cinzia, we are confident of an A1 classification only at the 1σ level. 相似文献
68.
69.
Leonardo Casini Matteo Maino Antonio Langone Giacomo Oggiano Stefania Corvò Joan Reche Estrada Montserrat Liesa 《Journal of Metamorphic Geology》2023,41(1):25-57
The Variscan high-grade metamorphic basement of northern Sardinia and southern Corsica record lower Carboniferous anatexis related to post-collisional decompression of the orogen. Migmatites exposed in the Punta Bianca locality (Italy) consist of quartz + biotite + plagioclase + K-feldspar orthogneisses, garnet and cordierite-bearing diatexite and metatexites, derived from metasediments. Field evidence, petrographic observations, ELA-ICP-MS zircon and monazite dating and pseudosection modelling suggest that anatexis was apparently episodic involving two main stages of partial melting. Using pseudosection modelling, we infer that the first stage of partial melting is in the upper amphibolite facies (~0.45 GPa at ~740°C). Cordierite overgrowths replacing sillimanite, combined with the composition of plagioclase and K-feldspar, suggest decompression followed cooling below the solidus at low pressures of ~0.3 GPa. The age of the first anatectic event is not precisely constrained because of extensive resetting of the isotopic systems during the second melting stage, yet few zircons preserve a lower Carboniferous age which is consistent with the regional dataset. This lower Carboniferous migmatitic fabric is offset by a network of pseudotachylyte-bearing faults suggestive of cooling to greenschist facies conditions. Garnet/cordierite-bearing diatexites incorporate fragments of pseudotachylite-bearing orthogneiss and metatexites. Pseudosection modelling indicates nearly isobaric re-heating up to ~750°C, followed by further cooling below the solidus. The inferred P–T path is consistent with decompression and cooling of the Variscan crust through post-collisional extension and collapse of the thickened orogenic crust, followed by nearly isobaric re-heating at low pressures (~0.3 GPa) yielding to a second melting stage under LP-HT conditions. U/Th-Pb monazite ages for diatexite migmatites indicate an upper bound of 310–316 Ma for the second melting stage, suggesting that the second melting stage is coincident with the regional phase of crustal shearing. The cause of the high geothermal gradient required for re-heating during the second melting stage is unknown but likely requires some heat source that was probably related to dissipation of mechanical work within crustal-scale shear zones. According to this interpretation, some upper Carboniferous peraluminous granite precursors of the Corsica–Sardinia Batholith could be the outcome rather than the cause of the late-Variscan high-T metamorphism. 相似文献
70.
Phylogeography of the bluespotted cornetfish,Fistularia commersonii: a predictor of bioinvasion success?
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Alexis M. Jackson Kimberly Tenggardjaja Gerardo Perez Ernesto Azzurro Daniel Golani Giacomo Bernardi 《Marine Ecology》2015,36(4):887-896
Biological invasions result in huge ecological and economic impacts; therefore, a great amount of effort is dedicated to predicting the potential success of newly established or candidate bioinvaders. Thus far, over 90 species of fish have entered the Mediterranean Sea via the Suez canal, the so‐called Lessepsian bioinvaders. The bluespotted cornetfish, Fistularia commersonii, is remarkable in its ability to disperse within the Mediterranean and has been dubbed ‘the Lessepsian sprinter’. In just a few years, starting in 2000, it expanded over the entire area, from the Suez Canal to Gibraltar. Theoretical predictions correlate the dispersal capabilities of an invader in its native range (using the population genetic metrics, Fst, as a proxy) with its dispersal capability in its invading area (continuous extent of spread, CES). Here, we estimated the population genetic characteristics of Indo‐Pacific native populations of F. commersonii in order to determine if this Lessepsian ‘sprinter’ fits the predictive model of dispersal. Indeed, we found that even in the case of such a very rapid range expansion, the predicted relationship between Fst and CES is fulfilled in F. commersonii. 相似文献