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51.
Atmospheric circulation associated with extreme generalized frosts persistence in central-southern South America 总被引:1,自引:1,他引:0
Generalized frosts (GF) in central-southern South America have a strong impact due to their spatial extension, and they are especially important when they become persistent. This paper aims at identifying the atmospheric circulation features that determine the extreme GF persistence, i.e. very persistent and without persistence, and the differences between them, during the 1961–1990 winters. Since the GF without persistence group outnumbers the other one, two subgroups are composed with events selected from winters with maximum and minimum frequency of GF occurrence, respectively. Additionally, the individual event of July 1988 within the very persistent GF group is analyzed due to its exceptional persistence. GF persistence is mainly conditioned by two large-scale dynamic factors. One is the Rossby wave train propagation across the Pacific Ocean, and the other one is the location with respect to the continent and the magnitude of the confluence in the jet entrance region in subtropical latitudes. A predominantly meridional Rossby wave train propagation with a confluence region to the west of the continent prior to the event favors GF with intermediate (null) persistence depending on the greater (lesser) jet acceleration. This is conditioned by the magnitude of the confluence, which, in turn, depends on the disposition of the wave train propagation pattern. Instead, an essentially zonal propagation with a confluence region to the east of the continent favors the GF persistence for several days, yet if there is no confluence the event does not persist. The greatest persistence of an event combines the confluence/diffluence of the jet entrance/exit region, which depends on the disposition with respect to the continent of the zonally propagating Rossby wave trains. 相似文献
52.
Gabriela Dan Nabil Sultan Bruno Savoye Jacques Deverchere Karim Yelles 《International Journal of Earth Sciences》2009,98(4):769-789
The Algerian margin is a seismically active region, where during the last century, several large magnitude earthquakes took
place. This study combines geotechnical and sedimentological data with numerical modelling to quantitatively assess the present-day
slope stability of the Algerian margin. Geotechnical laboratory tests, such as cyclic triaxial tests, oedometric tests and
vane shear tests were carried out on sediment cores collected on the study area. The liquefaction potential of a sediment
column located about 30 km from the Boumerdès earthquake epicentre of 21st May 2003 was evaluated theoretically for an earthquake
of M
w
= 6.8. We show that thin sand and silt beds such as those described on recovered sediment cores are the main cause of sediment
deformation and liquefaction during earthquakes. Numerical calculations showed that the slope failure may occur during an
earthquake characterised by a PGA in excess of 0.1g, and also that, under a PGA of 0.2g liquefaction could be triggered in shallow silty–sandy deposits. Moreover, comparison of the predicted slope failure with
failure geometries inferred from seafloor morphology showed that earthquakes and subsequent mass movements could explain the
present-day morphology of the study area. 相似文献
53.
Gabriela Polonic 《Tectonophysics》1985,117(1-2)
Based on geological and geophysical data, characteristics of neotectonic activity of the eastern border of the Pannonian Depression are presented.As a result of differential tectonic movements during the Neogene-Quaternary, separate morphostructural units are subjected to subsidence and uplifting, along active faults.The local seismic activity is related, mainly, to the movements along the borders of grabens, as well as at the contact between different crustal blocks. 相似文献
54.
Hans-Rudolf Wenk Erik Rybacki Georg Dresen Ivan Lonardelli Nathan Barton Hermann Franz Gabriela Gonzalez 《Physics and Chemistry of Minerals》2006,33(10):667-676
Mechanical Dauphiné twinning in quartz has been of long-standing interest, both in single crystals and polycrystalline aggregates. This study investigates texture development in fine-grained quartz rock novaculite with no initial texture using compression experiments conducted in the Paterson gas apparatus to explore the influence of stress and temperature. Texture patterns are measured with time-of-flight neutron diffraction and hard synchrotron X-rays, analyzing diffraction data with the Rietveld method. Similar texture patterns are observed as described previously but the new results establish a profound influence of temperature and document that twinning initiates at stresses less than 50 MPa. Possibilities of using Dauphiné twinning as a paleopiezometer in quartz-bearing rocks are discussed. 相似文献
55.
Modern Diatom Assemblages in Surface Sediments from Estuarine Systemsin the Southeastern Buenos Aires Province, Argentina 总被引:1,自引:0,他引:1
Paleoecological reconstructions of Holocene sea-level changes in Argentinean coastal regions were based mainly on ecological
data gathered from other regions, as there was a lack of information on modern estuarine diatom distributions. The aim of
the present work was to assess the spatial variation of diatom assemblages in two representative estuaries of Argentina in
order to gather ecological information for paleoecological reconstructions in the region. The two selected estuaries have
different geomorphologic features and salinity regimes: Mar Chiquita Lagoon is shallow, which prevents the development of
a stable salinity gradient as it occurs in the Quequén Grande River. Surface sediment samples were taken from selected stations
representative of the environmental gradient from the inlet to the inner reaches of both estuaries. Cluster analysis defined
three diatom zones at Mar Chiquita: marine/brackish assemblages dominate the inlet (zone I), where salinity, tidal range and
current speed are higher. The brackish/freshwater tychoplankton Staurosira construens var. venter and Staurosirella pinnata dominate the inner lagoon (zone II), where environmental conditions are very variable and concentrations of suspended sediments
are higher. Brackish/freshwater euryhaline diatoms dominate the headwaters (zone III). On the other hand, the Quequén Grande
River was divided into three diatom zones: coastal taxa are distributed at the inlet (zone I), while the middle estuary (zone
II) is dominated by brackish/freshwater euryhaline taxa. At the upper estuary region (zone III), freshwater diatoms dominate,
and the halophobous Nitzschia denticula increased in abundance values. Diatom distributions were most closely related to the salinity gradient at Quequén Grande
River than at Mar Chiquita Lagoon. Fossil data of a sequence from Mar Chiquita Lagoon (Las Gallinas Creek) were compared to
the modern data set in order to search for analogies between fossil and modern diatom assemblages. DCA results showed that
fossil diatom assemblages have modern counterparts. Most diatom assemblages of Las Gallinas Creek fall within Mar Chiquita
zone III, representing a shallow brackish/freshwater environment, with low salinity fluctuations
(~1–9‰) and no tidal influence. Therefore, our modern diatom data provide useful analogs to interpret paleoenvironments in
the region. 相似文献
56.
Diana Gabriela Lope-Alzina 《Singapore journal of tropical geography》2007,28(1):21-38
This paper examines the influence of gender relations and gendered domains on maize and squash varietal selection in a village in Yucatán State, southeast Mexico. Results of the exploratory study indicate that the traditional production spaces of homegardens and agricultural fields are complementary gendered domains of varietal maintenance for both crops although with different cropping patterns, while a 'new' space, of land allocated to some families for future residential construction ( terreno ) is in the meantime a jointly worked agricultural domain. Women's labour, knowledge and preferences predominate in post-harvest processes. Fieldwork revealed that neither men nor women are independent decision-makers, planning what to grow, where and in what amounts, but that in most aspects of farming the interests of both are accommodated within the household's production spaces. 相似文献
57.
Moreno Wilmer Emilio García Soares Gabriela Borges Pires Júlio César Gall Sotelo Daniela Govoni Moura Cássio Stein 《Geotechnical and Geological Engineering》2021,39(6):4593-4613
Geotechnical and Geological Engineering - A large part of the Guarani Aquifer is located in the state of Rio Grande do Sul (Brazil) and additionally possesses a recharge area located in its central... 相似文献
58.
de Azevedo Reis Gabriela de Souza Filho Francisco Assis Nelson Donald Robert Rocha Renan Vieira da Silva Samiria Maria Oliveira 《Natural Hazards》2020,104(2):1781-1799
Natural Hazards - Although climate change vulnerability research in general has increased over the last decade, Latin American countries have more directed more limited efforts toward vulnerability... 相似文献
59.
The influence of the El Niño Southern Oscillation (ENSO) phenomenon on monthly mean river flows of 12 rivers in the extreme south of South America in the 20th century is analysed. The original dataset of each river is divided into two subsets, i.e. warm ENSO events or El Niño, and cold ENSO events or La Niña. The elements of the subsets are composites of 24 consecutive months, from January of the year when the ENSO event begins to December of the following year. The ENSO signal is analysed by comparing the monthly mean value of each subset to the long-term monthly mean. The results reveal that, in general, monthly mean El Niño (La Niña) river flows are predominantly larger (smaller) than the long-term monthly mean in the rivers studied. The anomalies are more evident during the second half of the year in which the event starts and the first months of the following year. 相似文献
60.
Ricardo A. Ojeda Carlos E. Borghi Gabriela B. Diaz Stella M. Giannoni Michael A. Mares Janet K. Braun 《Journal of Arid Environments》1999,41(4):443
Octodontid rodents have a long evolutionary history in arid landscapes of South America. The red vizcacha rat, Tympanoctomys barrerae , is a monotypic, micro-endemic species that inhabits salt pan-sand dune habitats in west-central Argentina. Its natural history is almost unknown. We present an analysis of the ecology, morphology, behavior, and physiology of the red vizcacha rat and assess the overall degree of convergence of this species with rodents that inhabit similar habitats in different deserts. Our results show that Tympanoctomys barrerae is highly adapted to salt flat basin habitats. Its diet of halophytic vegetation with a high salt content, and physiological and anatomical traits related to salt consumption, are similar to those found in some members of the families Heteromyidae (Dipodomys microps) of North America, and Muridae (Psammomys obesus and Rhombomys opimus) of Africa and Asia. Similarities include feeding behavior, diet composition, kidney morphology, and urine concentration, among other traits. Tympanoctomys barrerae is more similar to these desert rodents than it is to confamilials that do not feed on halophytes. 相似文献