全文获取类型
收费全文 | 653篇 |
免费 | 31篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 23篇 |
地球物理 | 195篇 |
地质学 | 251篇 |
海洋学 | 58篇 |
天文学 | 122篇 |
综合类 | 3篇 |
自然地理 | 30篇 |
出版年
2023年 | 4篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 40篇 |
2017年 | 28篇 |
2016年 | 34篇 |
2015年 | 24篇 |
2014年 | 36篇 |
2013年 | 31篇 |
2012年 | 32篇 |
2011年 | 55篇 |
2010年 | 32篇 |
2009年 | 38篇 |
2008年 | 32篇 |
2007年 | 29篇 |
2006年 | 24篇 |
2005年 | 28篇 |
2004年 | 28篇 |
2003年 | 23篇 |
2002年 | 22篇 |
2001年 | 9篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1968年 | 1篇 |
1955年 | 1篇 |
1948年 | 1篇 |
1946年 | 2篇 |
1944年 | 2篇 |
1941年 | 1篇 |
1940年 | 3篇 |
排序方式: 共有688条查询结果,搜索用时 15 毫秒
61.
Giovanni MONEGATO Matteo MASSIRONI Elena MARTELLATO Giordano TEZA 《Meteoritics & planetary science》2011,46(12):1804-1813
Abstract– The Omeonga ring structure (D.R. Congo) shows a remarkable drainage pattern encircling an area up to 45 km wide and encompassing a central smoothed relief 20 km wide. This inner circular ridge is elevated about 70 m above the ring depression corresponding to the bed of the Unia River, which flows between the inner ridge and an outer irregular ridge. Landsat 7 ETM and ASTER DEM show that the structural characteristics resemble those of several wide impact structures known on Earth. Other geological modes of origin that could produce ring structures, such as magmatic activity, salt diapirism, and karst dissolution have been considered. However, after evaluating the regional stratigraphy, the distribution of volcanism, and morphometry, these processes seem to be rather unlikely. If of impact origin, the age of the Omeonga structure can be constrained to the Late Cretaceous‐Cenozoic according to the youngest units in which the ring structure was formed. 相似文献
62.
The catalog of the meteorite collection of the Italian Museum of Planetary Sciences in Prato (Italy)
Marco Morelli Annarita Franza Daniela Faggi Giovanni Pratesi 《Meteoritics & planetary science》2023,58(7):945-954
For the first time, this paper presents to the planetary scientists' community the catalog of the meteorite collection preserved at the Italian Museum of Planetary Sciences (Museo Italiano di Scienze Planetarie, henceforth MISP) in Prato (Italy). Founded in 2005, MISP is a type specimen official repository approved by the Nomenclature Committee of the Meteoritical Society. It represents one of the few museums worldwide entirely devoted to planetary sciences. The catalog of its meteorite collection encompasses 430 meteorites for a total of 1536 specimens, including 291 thin sections, 184 thick sections, and 278 specimens that MISP has classified. Furthermore, MISP is currently classifying 57 other meteorites. Some samples were found during meteorite recovery expeditions in hot deserts, promoted by MISP in collaboration with diverse Italian universities and national research institutions. MISP also keeps an impact rocks collection comprising 257 samples. In a country like Italy, where most of the collected meteorites are housed in museums whose catalogs are not available online, the publication of the MISP meteorite collection catalog, together with the catalog of the impact rocks collection, represents not only a significant scientific primary source but also a remarkable tool for disseminating meteoritics to nonresearch audiences in educational activities and citizen science projects. 相似文献
63.
In the present paper, a finite element approach is proposed to analyse the mobility of active landslides which are controlled by groundwater fluctuations within the slope. These landslides are usually characterised by low displacement rates with deformations that are essentially concentrated within a narrow shear zone above which the unstable soil mass moves with deformations of no great concern. The proposed approach utilises an elasto-viscoplastic constitutive model in conjunction with a Mohr-Coulomb yield function to describe the behaviour of the soil in the shear zone. For the other soils involved by the landslide, an elastic model is used for the sake of simplicity. A significant advantage of the present method lies in the fact that few constitutive parameters are required as input data, the most of which can be readily obtained by conventional geotechnical tests. The rest of the required parameters should be calibrated on the basis of the available monitoring data concerning the change in the piezometric levels and the associated movements of the unstable soil mass. After being calibrated and validated, the proposed approach can be used to predict future landslide movements owing to expected groundwater fluctuations or to assess the effectiveness of drainage systems which are designed to control the landslide mobility. The method is applied to back-predict the observed field behaviour of three active slow-moving landslides documented in the literature. 相似文献
64.
A numerical Round Robin on tunnels under seismic actions 总被引:3,自引:0,他引:3
Emilio Bilotta Giovanni Lanzano S. P. Gopal Madabhushi Francesco Silvestri 《Acta Geotechnica》2014,9(4):563-579
Although the seismic behaviour of shallow circular tunnels in soft ground is generally safer than aboveground structures, some tunnels were recently damaged during earthquakes. In some cases, damage was associated with strong ground shaking and site amplification, which increased the stress level in the tunnel lining. Pseudo-static and simplified dynamic analyses enable to assess transient changes in internal forces during shaking. Nevertheless, experimental evidences of permanent changes in internal loads in the tunnel lining would suggest that a full dynamic analysis including plastic soil behaviour should be performed when modelling the dynamic interaction between the tunnel and the ground. While sophisticated numerical methods can be used to predict seismic internal forces on tunnel structures during earthquakes, the accuracy of their predictions should be validated against field measurements, but the latter are seldom available. A series of centrifuge tests were therefore carried out at the University of Cambridge (UK) on tunnel models in sand, in the framework of a research project funded by the Italian Civil Protection Department. A numerical Round Robin on Tunnel Tests was later promoted among some research groups to predict the observed behaviour by means of numerical modelling. In this paper, the main results of five selected numerical predictions are summarized and compared with the experimental results. 相似文献
65.
When waves break against seawalls, vertical breakwaters, piers or jetties, they abruptly transfer their momentum into the structure. This energy transfer is always spectacular and perpetually unrepeatable but can also be very violent and affect the stability and the integrity of coastal structures. Over the last 15 years, increasing awareness of wave-impact induced structural failures of maritime structures has emphasised the need for a more complete approach to dynamic responses, including effects of impulsive loads. At the same time, movement of design standards toward probabilistic approaches requires new statistical tools able to account for uncertainties in the variability of wave loading processes. This paper presents a new approach to the definition of loads for use in performance design of vertical coastal structures subject to breaking wave impacts. 相似文献
66.
67.
Giovanni Dolif Andre Engelbrecht Alessandro Jatobá Antônio José Dias da Silva José Orlando Gomes Marcos R. S. Borges Carlos A. Nobre Paulo Victor R. de Carvalho 《Natural Hazards》2013,65(3):1831-1847
Natural disasters, particularly those triggered by heavy rainfall, may cause major damage and death. However, if an accurate early warning is issued, the damage can be mitigated. In Latin America and Brazil, characteristics of socioeconomic development often lead to a disorderly growth of cities and, consequently, occupation and irregular construction in risk areas. Therefore, forecasts of heavy rainfall, as well as preventative and mitigatory actions based on meteorological data/alerts, are essential to saving lives and minimizing material loss. An event that would have benefited from such actions is that which occurred in the mountainous region of Rio de Janeiro in January 2011, when over 800 people lost their lives. This work describes the first research initiative on resilience engineering domain in systems to forecast heavy rains in Rio de Janeiro. The results indicate important sources of brittleness in the system that supports the work of meteorologists, mainly related to the technical and organizational framework, and suggests that the main source of resilience in dealing with critical situations is the tacit knowledge of experts. 相似文献
68.
Filippo Santucci de Magistris Giovanni Lanzano Giovanni Forte Giovanni Fabbrocino 《Natural Hazards》2014,74(2):1069-1094
National and international seismic codes and recommendations provide criteria for liquefaction exclusion based on a peak ground acceleration (PGA) threshold value. In this paper, after a brief review of the procedures and the values suggested in those documents, a database of liquefaction case histories was created, exploiting the background data used in the most relevant verification charts, currently employed in research and professional practice. This dataset was used to identify, on the basis of simple statistical analyses, a PGA threshold on the free ground surface below which liquefaction is unlikely to occur, regardless of the geological site conditions. The calculated value, which is on the order of 0.07–0.1 g, based on the model employed to fit the data, was analyzed in light of information collected during the 2012 Emilia seismic sequence in Italy, which produced many liquefaction events triggered by low acceleration values. The case history of the Emilia earthquake advises setting a PGA threshold for code and recommendations at the lower probability level of occurrence, in the order of 1 %. 相似文献
69.
70.
Carbon dioxide degassing and thermal energy release in the Monte Amiata volcanic-geothermal area (Italy) 总被引:2,自引:0,他引:2
Francesco Frondini Stefano Caliro Carlo Cardellini Giovanni Chiodini Nicola Morgantini 《Applied Geochemistry》2009
The quaternary volcanic complex of Mount Amiata is located in southern Tuscany (Italy) and represents the most recent manifestation of the Tuscan Magmatic Province. The region is characterised by a large thermal anomaly and by the presence of numerous CO2-rich gas emissions and geothermal features, mainly located at the periphery of the volcanic complex. Two geothermal systems are located, at increasing depths, in the carbonate and metamorphic formations beneath the volcanic complex. The shallow volcanic aquifer is separated from the deep geothermal systems by a low permeability unit (Ligurian Unit). A measured CO2 discharge through soils of 1.8 × 109 mol a−1 shows that large amounts of CO2 move from the deep reservoir to the surface. A large range in δ13CTDIC (−21.07 to +3.65) characterises the waters circulating in the aquifers of the region and the mass and isotopic balance of TDIC allows distinguishing a discharge of 0.3 × 109 mol a−1 of deeply sourced CO2 in spring waters. The total natural CO2 discharge (2.1 × 109 mol a−1) is slightly less than minimum CO2 output estimated by an indirect method (2.8 × 109 mol a−1), but present-day release of 5.8 × 109 mol a−1 CO2 from deep geothermal wells may have reduced natural CO2 discharge. The heat transported by groundwater, computed considering the increase in temperature from the infiltration area to the discharge from springs, is of the same order of magnitude, or higher, than the regional conductive heat flow (>200 mW m−2) and reaches extremely high values (up to 2700 mW m−2) in the north-eastern part of the study area. Heat transfer occurs mainly by conductive heating in the volcanic aquifer and by uprising gas and vapor along fault zones and in those areas where low permeability cover is lacking. The comparison of CO2 flux, heat flow and geological setting shows that near surface geology and hydrogeological setting play a central role in determining CO2 degassing and heat transfer patterns. 相似文献