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51.
52.
The microstructural evolution of polymineralic contact metamorphic calcite marbles (Adamello contact aureole) with variable volume fractions of second-phase minerals were quantitatively analyzed in terms of changes in grain size and nearest neighbor relations, as well as the volume fractions, dispersion and occurrences of the second phases as a function of changing metamorphic conditions. In all samples, the calcite grain size is controlled by pinning of grain boundaries by second phases, which can be expressed by the Zener parameter (Z), i.e., the ratio between size and volume fraction of the second phases. With increasing peak metamorphic temperature, both the sizes of matrix grains and second phases increase in dependence on the second-phase volume fraction. Two distinct coarsening trends are revealed: trend I with coupled grain coarsening limited by the growth of the second phases is either characterized by large-sized or a large number of closely spaced-second phase particles, and results finally in a dramatic increase in the calcite grain size with Z. Trend II is manifest by matrix controlled grain growth, which is retarded by the presence of single second-phase particles that are located on calcite grain boundaries. It is supported by grain boundary pinning induced by triple junctions, and the calcite grain size increases moderately with Z. The two different grain coarsening trends manifest the transition between relatively pure polymineralic aggregates (trend II) and microstructures with considerable second-phase volume fractions of up to 0.5. The variations might be of general validity for any polymineralic rock, which undergoes grain coarsening during metamorphism. The new findings are important for a better understanding of the initiation of strain localization based on the activation of grain size dependent deformation mechanisms. 相似文献
53.
The composition and evolution of an Oligocene regolith on top of the Sesia–Lanzo Zone (Western Alps)
Notburga Kapferer Ivan Mercolli Alfons Berger 《International Journal of Earth Sciences》2011,100(5):1115-1127
An Oligocene paleosurface (regolith) lies on top of the high-pressure metamorphic rocks of the Sesia–Lanzo Zone near Biella,
NW Italy. Only the saprock, the lowermost part in a regolith profile, is preserved. No evidence for any paleosoil can be observed.
Field observations indicate that the regolith developed through in situ mechanical fracturing of the rocks of the Sesia–Lanzo
Zone in a continental environment. Density estimations of the regolith and the underlying rocks of the Sesia–Lanzo Zone confirm
the field observations and imply that a relatively small amount of alteration minerals was formed. The main detected alteration
phases are chlorite, various carbonates, quartz, clay minerals, Fe-oxides, and Fe-hydroxides. Chlorite differing in chemistry
and crystallographic ordering demonstrates different stages of alteration. Oxygen and carbon isotopic composition of carbonates
suggests temperatures higher than surface conditions. Illite and chlorite thermometry indicates temperatures related to the
anchizone (~250–300°C). These data are considered as a robust indication of the re-burial of the regolith together with its
substrate and its volcanic cover. The burial is closely related to the tilting of the preserved stratigraphic sequence formed
by the rocks of the Sesia–Lanzo Zone, the regolith, and the rocks of the Biella Volcanic Suite (Lanza, in Schweiz Miner Petrogr
MItt 57: 281–290, 1977; Lanza, in Geologishe Rundschau 68: 83–92, 1979). Furthermore, the burial is consistent with this sequence of subaerial rocks being very close to the intrusion depth of
the Valle del Cervo Pluton at the time of its emplacement (4–7 km; Zanoni et al., in Rend Online SGI Note Brevi 1: 199–202,
2008; Zanoni et al., in Int Geol Rev 52: 1244–1267, 2010 and references therein). 相似文献
54.
Raphael Schneeberger Daniel Egli Georg W. Lanyon Urs K. Mäder Alfons Berger Florian Kober Marco Herwegh 《Hydrogeology Journal》2018,26(8):2725-2738
Groundwater flow in granitic bedrock is of major interest for underground projects such as radioactive waste disposal. It is generally accepted that granitic rocks of the upper crust are characterized as faulted low-porosity rocks showing fault-related permeability. In this study, the influence of existing faults on the present-day water flow in the Grimsel Test Site (Switzerland), an underground rock laboratory situated in granitoid rocks, was investigated by mapping water discharges. As a result, the link between water flow and faults considering slip-tendency analysis and fault intersections is evaluated. Water-conducting features were combined in a structural-permeability favorability map. Faults and dykes occur as three orientation groups, NE–SW, E–W, and NW–SE trending, all steeply dipping southwards with fault intersections also steeply plunging southwards. In total, 100 water discharges were mapped in summer 2014 and 85 in winter 2016, which are located along faults or fault intersections. A comparison of water discharges with structures showed that high-slip-tendency metabasic dykes and fault or dyke intersections represent the dominant flow paths. Further, it could be demonstrated that higher slip-tendency tends to lead to enhanced average hydraulic conductivity and therefore more constant water flow. Based on water fluxes, fault intersections are inferred to represent first-order locations of water percolation followed by high-slip-tendency metabasic dykes. The combination of all water-conducting features into a structural-permeability map results in covering all water discharges. Therefore, the structural-permeability favorability map can serve as suitable representation for constraining water inflow in fractured granitoid host rocks. 相似文献
55.
Notburga Kapferer Ivan Mercolli Alfons Berger Maria Ovtcharova Bernhard Fügenschuh 《Swiss Journal of Geoscience》2012,105(1):67-84
The high-pressure metamorphic rocks of the Sesia?CLanzo zone are partly covered by a volcano-sedimentary unit, the Biella Volcanic Suite. Calc-alkaline and shoshonitic lavas extruded sub-aerially on the Oligocene surface. Uranium?CLead zircon dating yields 32.44?C32.89?Ma for the eruption of the calc-alkaline lavas and therefore fixes a minimum age for the paleosurface. The Biella Volcanic Suite consists mainly of epiclastic rocks deposited in a high-energy fluvial environment and minor lava flows. The rocks of the suite display widespread post-eruption transformations. Illite and chlorite thermometry as well as fission track dating suggest a thermal overprint related to burial of the Biella Volcanic Suite. An upper crustal rigid block tilting in the area causes this burial. Hydrothermal tourmaline and ankerite veins related to the intrusion of the nearby Valle del Cervo Pluton crosscut the already tilted Biella Volcanic Suite. The intrusion age of Valle del Cervo Pluton at 30.39?±?0.50?Ma sets therefore the lower time limit for tectonic processes responsible for the tilting and burial. After the burial, the Biella Volcanic Suite remained for around 20?million years between the zircon and the apatite partial annealing zone. The apatite fission track ages spread between 16 and 20?Ma gives the time frame for the second exhumation of these units. The Biella Volcanic Suite and the adjacent rocks of the Sesia?CLanzo zone were the second time exhumed to the surface in Messinian times, after a long residence time within the apatite partial annealing zone. 相似文献
56.
The aim of this paper is to improve understanding of the adaptive capacity of European agriculture to climate change. Extensive
data on farm characteristics of individual farms from the Farm Accountancy Data Network (FADN) have been combined with climatic
and socio-economic data to analyze the influence of climate and management on crop yields and income and to identify factors
that determine adaptive capacity. A multilevel analysis was performed to account for regional differences in the studied relationships.
Our results suggest that socio-economic conditions and farm characteristics should be considered when analyzing effects of
climate conditions on farm yields and income. Next to climate, input intensity, economic size and the type of land use were
identified as important factors influencing spatial variability in crop yields and income. Generally, crop yields and income
are increasing with farm size and farm intensity. However, effects differed among crops and high crop yields were not always
related to high incomes, suggesting that impacts of climate and management differ by impact variable. As farm characteristics
influence climate impacts on crop yields and income, they are good indicators of adaptive capacity at farm level and should
be considered in impact assessment models. Different farm types with different management strategies will adapt differently. 相似文献
57.
Fluid inclusion petrography 总被引:32,自引:0,他引:32
58.
Carbonic inclusions 总被引:17,自引:0,他引:17
The paper gives an overview of the phase relations in carbonic fluid inclusions with pure, binary and ternary mixtures of the system CO2–CH4–N2, compositions, which are frequently found in geological materials. Phase transitions involving liquid, gas and solid phases in the temperature range between −192°C and 31°C are discussed and presented in phase diagrams (PT, TX and VX projections). These diagrams can be applied for the interpretation of microthermometry data in order to determine fluid composition and molar volume (or density). 相似文献
59.
Dr. Alfons Zehnder 《Aquatic Sciences - Research Across Boundaries》1973,35(1):121-135
Ohne Zusammenfassung
Internationale Arbeitsgemeinschaft für Cyanophytenforschung IAC 相似文献
60.