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131.
Bijay Kumar Pokhrel Pierre Chevallier Vazken Andréassian Adnan Ahmad Tahir Yves Arnaud Luc Neppel 《水文科学杂志》2013,58(8):1507-1518
AbstractThe glaciers in the Nepalese Himalayas are retreating due to rising temperatures. Lack of data and information on Nepal’s cryosphere has impeded scientific studies and field investigations in the Nepalese Himalayas. Therefore, IRD France and Ev-K2 CNR Italy have conducted the PAPRIKA (CryosPheric responses to Anthropogenic PRessures in the HIndu Kush-Himalaya regions: impacts on water resources and society adaptation in Nepal) project in Nepal with the financial support of the French and Italian scientific agencies. This project aims to address the current and future evolution of the cryosphere in response to overall environmental changes in South Asia, and its consequences for water resources in Nepal. Thus, two hydrological models, the GR4J lumped precipitation–runoff model and the snowmelt runoff model (SRM), were used in the Dudh Koshi basin. The GR4J model has been successfully applied in different parts of Europe. To obtain better results in such a harsh and rugged topography, modifications needed to be made, particularly in the snow module. The runoff pattern is analysed herein both for past years and, in a sensitivity analysis, for possible future climatic conditions (i.e. precipitation and temperature) using the SRM and GR4J modelling approaches. The results reveal a significant contribution of snow- and glacier-melt to runoff, and the SRM model shows better performance in Nepalese catchments than the GR4J model.
Editor D. Koutsoyiannis; Associate editor D. Gerten 相似文献
132.
Valérie Wilquet Rachel Drummond Arnaud Mahieux Séverine Robert Ann Carine Vandaele Jean-Loup Bertaux 《Icarus》2012,217(2):875-881
The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (~200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (~80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well. 相似文献
133.
Filippo Pantellini Soraya Belheouane Nicole Meyer-Vernet Arnaud Zaslavsky 《Astrophysics and Space Science》2012,341(2):309-314
High rate sampling detectors measuring the potential difference between the main body and boom antennas of interplanetary spacecraft have been shown to be efficient means to measure the voltage pulses induced by nano dust impacts on the spacecraft body itself (see Meyer-Vernet et al. in Sol. Phys. 256:463, 2009). However, rough estimates of the free charge liberated in post impact expanding plasma cloud indicate that the cloud’s own internal electrostatic field is too weak to account for measured pulses as the ones from the TDS instrument on the STEREO spacecraft frequently exceeding 0.1 V/m. In this paper we argue that the detected pulses are not a direct measure of the potential structure of the plasma cloud, but are rather the consequence of a transitional interruption of the photoelectron return current towards the portion of the antenna located within the expanding cloud. 相似文献
134.
In this study, we report the elastic properties of three ultrahigh-pressure phases of SiO2: pyrite, cotunnite and Fe2P types between 300 and 1,500 GPa calculated by means of the density functional ab initio method. It is generally thought
that materials tend to be more compact and isotropic with increasing pressure. These three ultrahigh-pressure phases of silica
are mechanically stable in the investigated pressure range according to the Born criteria, while the cotunnite and Fe2P types are unstable at lower pressure. The elastic azimuthal anisotropy of these ultrahigh-pressure phases of silica shows
that all the structures counterintuitively have considerable anisotropies even at multimegabar pressures. Among the three
investigated structures, the cotunnite type of SiO2 is the most elastically anisotropic phase due to a soft compression along the b axis combined with a large distortion of the polyhedrons that make the structure. This might also be related to its thermodynamic
unfavorability compared to the Fe2P type under extreme pressure condition. The bond property analyses clearly show that the Si–O bond remains an ionic-covalent
mixed bond even at multimegabar pressures with an invariable ionicity with pressure. This argument can explain the monotonously
pressure dependence of the elastic anisotropy in the case of pyrite, while the changes in the velocity distribution patterns
out of the thermodynamic instability range largely contribute to those of the cotunnite and Fe2P types. 相似文献
135.
Michael Wiedenbeck Roxana Bugoi M. John M. Duke Tibor Dunai Jacinta Enzweiler Mary Horan Klaus Peter Jochum Kathryn Linge Jan Košler Silke Merchel Luiz F.G. Morales Lutz Nasdala Roland Stalder Paul Sylvester Ulrike Weis Arnaud Zoubir 《Geostandards and Geoanalytical Research》2012,36(4):337-398
Advances in the chemical and isotopic characterisation of geological and environmental materials can often be ascribed to technological improvements in analytical hardware. Equally, the creation of novel methods of data acquisition and interpretation, including access to better reference materials, can also be crucial components enabling important breakthroughs. This biennial review highlights key advances in either instrumentation or data acquisition and treatment, which have appeared since January 2010. This review is based on the assessments by scientists prominent in each of the given analytical fields; it is not intended as an exhaustive summary, but rather provides insight from experts of the most significant advances and trends in their given field of expertise. In contrast to earlier reviews, this presentation has been formulated into a unified work, providing a single source covering a broad spectrum of geoanalytical techniques. Additionally, some themes that were not previously emphasised, in particular thermal ionisation mass spectrometry, accelerator‐based methods and vibrational spectroscopy, are also presented in detail. 相似文献
136.
Tectonic evolution of the Dabieshan orogen: In the view from polyphase deformation of the Beihuaiyang metamorphic zone 总被引:1,自引:0,他引:1
LIN Wei Faure Michel WANG Qingchen & Arnaud Nicolas . LTE Institute of Geology Geophysics Chinese Academy of Sciences Beijing China . Department of Earth Planetary Sciences Graduate School of Science Nagoya University Japan . ISTO UMR CNRS Batiment Géosciences Orléans Université d’Orléans Orléans Cedex France . UMR "Magmas et Volcans" Rue Kessler Clermont-Ferrand France 《中国科学D辑(英文版)》2005,48(7)
The Dabieshan and its geological counterpart in the Sulu area represent the eastern part of the Qinling-Dabie orogenic belt in Eastern China. This Orogen corresponds to the collision zone between the North and South China blocks (denoted as NCB and SCB, respectively) during the Early Mesozoic. Since the discovery of ultra-high-pressure (UHP) metamor- phism[1?3], research of the Dabieshan has made great progress from petrological work (e.g. Cong and Wang, 1999 and enclosed references)[… 相似文献
137.
Influence of rainfall spatial variability on flood prediction 总被引:9,自引:0,他引:9
Patrick Arnaud Christophe Bouvier Leonardo Cisneros Ramon Dominguez 《Journal of Hydrology》2002,260(1-4):216-230
This paper deals with the sensitivity of distributed hydrological models to different patterns that account for the spatial distribution of rainfall: spatially averaged rainfall or rainfall field. The rainfall data come from a dense network of recording rain gauges that cover approximately 2000 km2 around Mexico City. The reference rain sample accounts for the 50 most significant events, whose mean duration is about 10 h and maximal point depth 170 mm. Three models were tested using different runoff production models: storm-runoff coefficient, complete or partial interception. These models were then applied to four fictitious homogeneous basins, whose sizes range from 20 to 1500 km2. For each test, the sensitivity of the model is expressed as the relative differences between the empirical distribution of the peak flows (and runoff volumes), calculated according to the two patterns of rainfall input: uniform or non-uniform. Differences in flows range from 10 to 80%, depending on the type of runoff production model used, the size of the basin and the return period of the event. The differences are generally moderate for extreme events. In the local context, this means that uniform design rainfall combining point rainfall distribution and the probabilistic concept of the areal reduction factor could be sufficient to estimate major flood probability. Differences are more significant for more frequent events. This can generate problems in calibrating the hydrological model when spatial rainfall localization is not taken into account: a bias in the estimation of parameters makes their physical interpretation difficult and leads to overestimation of extreme flows. 相似文献
138.
Virginie Garnier Gaston Giuliani Daniel Ohnenstetter Anthony E. Fallick Jean Dubessy David Banks Hong Quang Vinh Thrse Lhomme Henri Maluski Arnaud Pêcher Kausar Allah Bakhsh Pham Van Long Phan Trong Trinh Dietmar Schwarz 《Ore Geology Reviews》2008,34(1-2):169
Marble-hosted ruby deposits represent the most important source of colored gemstones from Central and South East Asia. These deposits are located in the Himalayan mountain belt which developed during Tertiary collision of the Indian plate northward into the Eurasian plate. They are spatially related to granitoid intrusions and are contained in platform carbonates series that underwent high-grade metamorphism. All occurrences are located close to major tectonic features formed during Himalayan orogenesis, directly in suture zones in the Himalayas, or in shear zones that guided extrusion of the Indochina block after the collision in South East Asia. Ar–Ar dating of micas syngenetic with ruby and U–Pb dating of zircon included in ruby gives evidence that these deposits formed during Himalayan orogenesis, and the ages document the extensional tectonics that were active, from Afghanistan to Vietnam, between the Oligocene and the Pliocene.The petrography shows that ruby-bearing marbles formed in the amphibolite facies (T = 610 to 790 °C and P ~ 6 kbar). A fluid inclusion study defines the conditions of gem ruby formation during the retrograde metamorphic path (620 < T < 670 °C and 2.6 < P < 3.3 kbar) for the deposits of Jegdalek, Hunza and northern Vietnam.Whole rock analyses of non-ruby-bearing marbles indicate that they contain enough aluminum and chromiferous elements to produce all the ruby crystals that they contain. In addition, (C, O)-isotopic analyses of carbonates from the marbles lead to the conclusion that the marbles acted as a metamorphic closed fluid system that were not infiltrated by externally-derived fluids. The carbon isotopic composition of graphite in marbles reveals that it is of organic origin and that it exchanged C-isotopes with the carbonates during metamorphism. Moreover, the O-isotopic composition of ruby was buffered by metamorphic CO2 released during devolatilisation of marble and the H-isotopic composition of mica is consistent with a metamorphic origin for water in equilibrium with the micas. The (C, O, H)-isotopic compositions of minerals associated with marble-hosted ruby are all in agreement with the hypothesis, drawn from the unusual chemistry of CO2–H2S–COS–S8–AlO(OH)-bearing fluids contained in fluid inclusions, that gem ruby formed at P ~ 3 kbar and 620 < T < 670 °C, during thermal reduction of evaporite by organic matter, at high temperature-medium pressure metamorphism of platform carbonates during the Tertiary India–Asia collision. The carbonates were enriched in Al- and chromiferous-bearing detrital minerals, such as clay minerals that were deposited on the platform with the carbonates, and in organic matter. Ruby formed during the retrograde metamorphic path, mainly by destabilization of muscovite or spinel. The metamorphic fluid system was rich in CO2 released from devolatilisation of carbonates, and in fluorine, chlorine and boron released by molten salts (NaCl, KCl, CaSO4). Evaporites are key to explaining the formation of these deposits. Molten salts mobilized in situ Al and metal transition elements contained in marbles, leading to crystallization of ruby. 相似文献
139.
Ultra-high pressure eclogite/amphibolite grade metamorphism of the Dora Maira Massif in the western Alps is a well established
and intensively studied event. However, the age of peak metamorphism and early cooling remains controversial. The 40Ar-39Ar step-heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 Ma which have been interpreted
as the time of early cooling after the high pressure event. Recent U/Pb and Sm/Nd results challenge this assertion, indicating
a much younger age for the event, around 45 Ma, and hence a radically different timing for the tectonic evolution of the western
Alps. In a new approach to the problem, samples from the undeformed Hercynian metagranite, Brossasco, were studied using an
ultra-violet laser ablation microprobe technique for 40Ar-39Ar dating. The new technique allowed selective in situ analysis, at a spatial resolution of 50 μm, of quartz, phengite, biotite
and K-feldspar. The results demonstrate the frequent occurrence of excess argon with high 40Ar-36Ar ratios (1000–10000) and a strong relationship between apparent ages and metamorphic textures. The highest excess argon
ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases.
The best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high
pressure event, then mixed with an atmospheric component during rapid cooling and retrogression, producing a wide range of
argon concentrations and 40Ar/36Ar ratios. Step-heating analysis of minerals with this mixture would produce linear arrays on a 36Ar/40Ar versus 39Ar/40Ar correlation diagram, leading to geologically meaningless plateau ages, older than the true closure age. In the present
case, some ages in the range 60–110 Ma could be explained by the presence of excess argon incorporated around 40–50 Ma ago.
Similar results found in other high pressure terrains in the Alps may reconcile the argon geochronometer with other systems
such as Rb/Sr, U/Pb or Sm/Nd. This study therefore calls for an increasing use of high resolution in situ sampling techniques
to clarify the meaning of 40Ar/39Ar ages in many high pressure terrains.
Received: 6 January 1994/Accepted: 4 April 1995 相似文献
140.
Olivier Maurel Jean-Patrick Respaut Patrick Monié Nicolas Arnaud Maurice Brunel 《Comptes Rendus Geoscience》2004,336(12):1091-1098
Zircon UPb dating by SIMS of the Mont-Louis granite yields an age of 305±5 Ma, intrepreted to reflect the igneous emplacement age of the massif. It is in agreement with the Hercynian syntectonic character of Pyrenees granite. 40Ar/39Ar on hornblende, biotite and K-feldspar permit, to estimate the massif cooling. A rapid temperature decrease (≈30 °C/Ma) is revealed from Westphalian to Late Stephanian, coeval with the emplacement of a laccolithe in the upper crust. Then, the cooling rate decreases to ≈1 °C/Ma. This would be consistent with a long time residence for the pluton from the Late Palaeozoic to the Early Cainozoic at 6–8 km depth. To cite this article: O. Maurel et al., C. R. Geoscience 336 (2004). 相似文献