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21.
We provide a result of non-analytic integrability of the so-called J
2-problem. Precisely by using the Lerman theorem we are able to prove the existence of a region of the phase space, where the dynamical system exhibits chaotic motions. 相似文献
22.
Ettore Perozzi 《Celestial Mechanics and Dynamical Astronomy》1983,30(3):249-261
A detailed investigation about Discrete Mechanics (a numerical method developed by D. Greenspan and R. A. LaBudde) in Celestial Mechanics applications has been carried out. The method shows a remarkable precession of the argument of pericentre, whose value depends mainly on the time step scaling used and on the length of the integration step. It has been found that this behaviour is due to the structure of Discrete Mechanics and that the precession, taken as a function of the length of the integration step, follows with good agreement an inverse square law. The existence of this relationship allowed the development of a modified version of the method: its consistence with respect to the original one is discussed both from an analytical and a computational point of view. Furthermore the Modified Discrete Mechanics allowed the extension of the method to the case of the potential due to an oblate spheroid. 相似文献
23.
A global perspective on African climate 总被引:4,自引:1,他引:3
Alessandra Giannini Michela Biasutti Isaac M. Held Adam H. Sobel 《Climatic change》2008,90(4):359-383
We describe the global climate system context in which to interpret African environmental change to support planning and implementation of policymaking action at national, regional and continental scales, and to inform the debate between proponents of mitigation v. adaptation strategies in the face of climate change. We review recent advances and current challenges in African climate research and exploit our physical understanding of variability and trends to shape our outlook on future climate change. We classify the various mechanisms that have been proposed as relevant for understanding variations in African rainfall, emphasizing a “tropospheric stabilization” mechanism that is of importance on interannual time scales as well as for the future response to warming oceans. Two patterns stand out in our analysis of twentieth century rainfall variability: a drying of the monsoon regions, related to warming of the tropical oceans, and variability related to the El Niño–Southern Oscillation. The latest generation of climate models partly captures this recent continent-wide drying trend, attributing it to the combination of anthropogenic emissions of aerosols and greenhouse gases, the relative contribution of which is difficult to quantify with the existing model archive. The same climate models fail to reach a robust agreement regarding the twenty-first century outlook for African rainfall, in a future with increasing greenhouse gases and decreasing aerosol loadings. Such uncertainty underscores current limitations in our understanding of the global climate system that it is necessary to overcome if science is to support Africa in meeting its development goals. 相似文献
24.
The renewed interest of the major space agencies for the exploration of the Moon has made a review of the present/near future scenario and the related accessible mission profiles desirable. In particular the application of the dynamical systems approach to spaceflight dynamics could bring a significant contribution. A simple method for evaluating the efficiency of these novel spaceways for reaching the Moon if compared to more traditional mission profiles is presented and some general considerations on their utilization for automatic precursor missions as well as for the setting up and the maintenance of a Moon Base are discussed. 相似文献
25.
26.
Lorenzo Alfieri Peter Salamon Alessandra Bianchi Jeffrey Neal Paul Bates Luc Feyen 《水文研究》2014,28(13):4067-4077
Flood hazard maps at trans‐national scale have potential for a large number of applications ranging from climate change studies, reinsurance products, aid to emergency operations for major flood crisis, among others. However, at continental scales, only few products are available, due to the difficulty of retrieving large consistent data sets. Moreover, these are produced at relatively coarse grid resolution, which limits their applications to qualitative assessments. At finer resolution, maps are often limited to country boundaries, due to limited data sharing at trans‐national level. The creation of a European flood hazard map would currently imply a collection of scattered regional maps, often lacking mutual consistency due to the variety of adopted approaches and quality of the underlying input data. In this work, we derive a pan‐European flood hazard map at 100 m resolution. The proposed approach is based on expanding a literature cascade model through a physically based approach. A combination of distributed hydrological and hydraulic models was set up for the European domain. Then, an observed meteorological data set is used to derive a long‐term streamflow simulation and subsequently coherent design flood hydrographs for a return period of 100 years along the pan‐European river network. Flood hydrographs are used to simulate areas at risk of flooding and output maps are merged into a pan‐European flood hazard map. The quality of this map is evaluated for selected areas in Germany and United Kingdom against national/regional hazard maps. Despite inherent limitations and model resolution issues, simulated maps are in good agreement with reference maps (hit rate between 59% and 78%, critical success index between 43% and 65%), suggesting strong potential for a number of applications at the European scale. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
27.
Alessandra Musso Michael E. Ketterer Konrad Greinwald Clemens Geitner Markus Egli 《地球表面变化过程与地形》2020,45(12):2824-2839
High mountainous areas are geomorphologically active environments which are strongly shaped by redistribution of sediments and soils. With the projected climate warming in the twenty-first century and the continued retreat of glaciers, the area of newly exposed, highly erodible sediments and soils will increase. This presents a need to better understand and quantify erosion processes in young mountainous soils, as an increase in erodibility could threaten human infrastructure (i.e. hydroelectric power, tourist installations and settlements). While soil development is increasingly well understood and quantified, a coupling to soil erosion rates is still missing. The aim of this study was, therefore, to assess how soil erosion rates change with surface age. We investigated two moraine chronosequences in the Swiss Alps: one in the siliceous periglacial area of Steingletscher (Sustenpass), with soils ranging from 30 a to 10 ka, and the other in the calcareous periglacial area of Griessgletscher (Klausenpass) with surfaces ranging from age of 110 a to 13.5 ka. We quantified the erosion rates using the 239+240Pu fallout radionuclides and compared them to physical and chemical soil properties and the vegetation coverage. We found no significant differences between the two parent materials. At both chronosequences, the erosion rates were highest in the young soils (on average 5−10 t ha-1 a-1 soil loss). Erosion rates decreased markedly after 3−5 ka of soil development (on average 1−2.5 t ha-1 a-1 soil loss) to reach a more or less stable situation after 10−14 ka (on average 0.3–2 t ha-1 a-1). Climate change not only causes glacier retreat, but also increased sediment dynamics. Depending on the relief and vegetational development, it takes up to at least 10 ka to reach soil stability. The establishment of a closed vegetation cover with dense root networks seems to be the controlling factor in the reduction of soil erodibility. © 2020 John Wiley & Sons, Ltd. 相似文献
28.
29.
Modeling ground deformations of Panarea volcano hydrothermal/geothermal system (Aeolian Islands, Italy) from GPS data 总被引:1,自引:0,他引:1
Alessandra Esposito Marco Anzidei Simone Atzori Roberto Devoti Guido Giordano Grazia Pietrantonio 《Bulletin of Volcanology》2010,72(5):609-621
Panarea volcano (Aeolian Islands, Italy) was considered extinct until November 3, 2002, when a submarine gas eruption began
in the area of the islets of Lisca Bianca, Bottaro, Lisca Nera, Dattilo, and Panarelli, about 2.5 km east of Panarea Island.
The gas eruption decreased to a state of low degassing by July 2003. Before 2002, the activity of Panarea volcano was characterized
by mild degassing of hydrothermal fluid. The compositions of the 2002 gases and their isotopic signatures suggested that the
emissions originated from a hydrothermal/geothermal reservoir fed by magmatic fluids. We investigate crustal deformation of
Panarea volcano using the global positioning system (GPS) velocity field obtained by the combination of continuous and episodic
site observations of the Panarea GPS network in the time span 1995–2007. We present a combined model of Okada sources, which
explains the GPS results acquired in the area from December 2002. The kinematics of Panarea volcano show two distinct active
crustal domains characterized by different styles of horizontal deformation, supported also by volcanological and structural
evidence. Subsidence on order of several millimeters/year is affecting the entire Panarea volcano, and a shortening of 10−6 year−1 has been estimated in the Islets area. Our model reveals that the degassing intensity and distribution are strongly influenced
by geophysical-geochemical changes within the hydrothermal/geothermal system. These variations may be triggered by changes
in the regional stress field as suggested by the geophysical and volcanological events which occurred in 2002 in the Southern
Tyrrhenian area. 相似文献
30.
Combined analyses of pollen, seeds, woods, micro-charcoal and non-pollen palynomorphs from Stagno di Maccarese, an artificially
dried out coastal basin north of the Tiber delta now occupied by the Fiumicino Airport (Rome, Italy), document marked vegetation
and environmental changes during the last 8300 years. Between 8300 and 5400 cal. a BP dense mixed deciduous and evergreen
forests surrounded a eutrophic freshwater basin. An abrupt change around 5400 cal. a BP marks the transition to a marshy environment,
due to a lowering of the water table. An increase of cereals and micro-charcoals matches the presence of a nearby Eneolithic
settlement. Between 5100 and 2900 cal. a BP there is a remarkable expansion of riparian trees, indicating an increase of the
water level. Between 2900 and 2000 cal. a BP, a new development of marshlands points to a progressive lowering of the lake.
After 2000 cal. a BP, during the Roman exploitation of the area, an expansion of arboreal vegetation is recorded, characterized
by evergreen and deciduous oak-dominated forests, while an extensive chenopods marshland matches the presence of saltworks.
On the whole, the Stagno di Maccarese area appears very unstable, due to changes in lake level, introgression of marine water,
eutrophic phases, flood events, desiccations and openings of the forest vegetation. 相似文献