全文获取类型
收费全文 | 510篇 |
免费 | 31篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 25篇 |
地球物理 | 183篇 |
地质学 | 200篇 |
海洋学 | 23篇 |
天文学 | 86篇 |
综合类 | 2篇 |
自然地理 | 20篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 14篇 |
2020年 | 21篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 35篇 |
2016年 | 50篇 |
2015年 | 34篇 |
2014年 | 39篇 |
2013年 | 37篇 |
2012年 | 21篇 |
2011年 | 33篇 |
2010年 | 26篇 |
2009年 | 34篇 |
2008年 | 36篇 |
2007年 | 30篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 8篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有548条查询结果,搜索用时 15 毫秒
461.
462.
463.
Luca Cozzolino Renata Della Morte Carmine Covelli Giuseppe Del Giudice Domenico Pianese 《Advances in water resources》2011,34(11):1413-1426
Free-surface flows are usually modelled by means of the Shallow-water Equations: this system of hyperbolic equations exhibits a source term which is proportional to the product of the water depth by the bed slope, and which takes into account the effect of gravity onto fluid mass. Recently, much attention has been paid to the case in which bottom discontinuities are present in the physical domain to be represented: in this case, it is difficult to define the non-conservative product in the distributional sense. Here, the discontinuous-bottom Shallow-water Equations with hydrostatic pressure distribution at the bed step (Bernetti et al., 2006) are discussed in the context of the theory of Dal Maso et al. (1995) [9]; finally, a first-order numerical scheme is presented, which is consistent for regular solutions, and which is able to capture contact discontinuities at bottom steps. Numerous tests are presented to show the feasibility of the scheme and its ability to converge to the exact solution in the cases of smooth as well as discontinuous bed profiles. 相似文献
464.
Paolo Ricci Flavia De Luca Gerardo Mario Verderame 《Bulletin of Earthquake Engineering》2011,9(1):285-305
On 6th April 2009 an earthquake of magnitude M
w
= 6.3 occurred in the Abruzzo region; the epicentre was very close to the city of L’Aquila (about 6 km away). The event
produced casualties and damage to buildings, lifelines and other infrastructures. An analysis of the main damage that reinforced
concrete (RC) structures showed after the event is presented in this study. In order to isolate the main causes of structural
and non-structural damage, the seismological characteristics of the event are examined, followed by an analysis of the existing
RC building stock in the area. The latter issue came under scrutiny after the release of official data about structural types
and times of construction, combined with a detailed review of the most important seismic codes in force in the last 100 years
in Italy. Comparison of the current design provisions of the Italian and European codes with previous standards allows the
main weaknesses of the existing building stock to be determined. Damage to structural and non-structural elements is finally
analyzed thanks to photographic material collected in the first week after the event; the main causes of damage are then inferred. 相似文献
465.
Observation of damage caused by the recent Abruzzo earthquake on April 6th 2009 showed how local interaction between infills and RC structures can lead to soft‐storey mechanisms and brittle collapses. Results of the present case study are based on observed damage caused by the earthquake in the zone of Pettino. Analytical model based on simulated design procedure was built up and time history analyses were employed to verify the causes of the structural collapse, as highlighted by observed damage. This failure mechanism was investigated taking into consideration all components of the ground motion. Nonlinear behavior of brick masonry infills was taken into account and two parametric hypotheses for infill mechanical properties were considered, given the uncertainties that typically characterize these nonstructural elements. Nonlinear modeling of infills was made by a three‐strut macro‐model aimed at considering both local and global interaction between RC frame and infills. Seismic input was characterized by the real signal registered during the mainshock near the case‐study structure. Different shear capacity models were considered in the assessment. Analytical results seem to confirm with good approximation the likely collapse scenario that damage observation highlighted; the lack of proper detailing in the columns made the local interaction between infills and RC columns and the strong vertical component of the ground motion to be the main causes of the brittle failure. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
466.
467.
A series of laboratory flume experiments under conditions of sediment starvation (zero sediment feeding) and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers. The experiments were carried out in an 8 m long flume using a bimodal grain‐size mixture (D50 = 6·2 mm) and a range of shear stresses ranging from 4·0 to 8·6 N m–2. The results confirm that a static armour layer is coarser than a mobile one, and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength. An analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer. Under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges. The topography of mobile armour layers created by rising discharges differed. They exhibited a greater roughness length scale and were less organized, despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation. Also, the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges. These differences were mainly due to the transport of the coarser fraction of bed sediments, which diminished to zero over the static armour because of being hidden within the bed, whereas in the mobile armour the coarser particles protruded into the flow and were actively transported, increasing the vertical roughness length scale. Overall, the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness. Detailed elevation models of exposed surfaces of gravel‐bed rivers are required to provide critical insight on the sediment availability and sedimentation processes. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
468.
The dynamics and the surface evolution of a post‐LGM debris‐flow‐dominated alluvial fan (Tartano alluvial fan), which lies on the floor of an alpine valley (Valtellina, Northern Italy), have been investigated by means of an integrated study comprising geomorphological field work, a sedimentological study, photointerpretation, quantitative geomorphology, analysis of ancient to modern cartography and consultation of historical documents and records. The fan catchment meteoclimatic, geological and geomorphological characteristics result in fast rates of geomorphic reorganization of the fan surface (2 km2). The dynamics of the fan are determined by the alternation of low‐return period catastrophic alluvial events dominated by non‐cohesive debris flows triggered by extreme rainstorms which caused aggradation and steepening of the fan and avulsion of its main channel, with periods of low to moderate streamflow discharge punctuated by low‐ to intermediate‐magnitude flood events, causing slower but steady topographic reworking. The most ancient parts of the fan surface date back at least to the first half of the 19th century, but most of the fan surface has been restructured after 1911, mainly during the debris‐flow‐dominated events of 1911 and 1987. Phases of rapid fan toe incision and fan degradation have been recognized; since the 1930s or 1940s, the Tartano fan has been subjected to a state of deep entrenchment and narrowing of the main trunk channel and distributary area. Post‐Little Ice Age climate change and present‐day surface uplift rates have been considered as possible explanations for the observed geomorphic evolution, but tectonic or climatic controls cannot account for the order of magnitude of the erosional pace. Anthropogenic controls plausibly override the natural ones: in particular, the building of a dam in the late 1920s, about 2 km upstream of the fan, seems to have triggered fan dissection, having altered the sediment discharge through sediment retention. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
469.
Mario Boccaletti Giacomo Corti Luca Martelli 《International Journal of Earth Sciences》2011,100(6):1331-1348
We present a comprehensive study of the recent and active tectonics of the external part of the Northern Apennines (Italy)
by using morphotectonic, geological–structural, and stratigraphic analysis, compared with the current seismicity of the region.
This analysis suggests that the external part of the Northern Apennines is characterised by presence of three major systems
of Quaternary compressive structures corresponding to (1) the Apenninic watershed, (2) the Apennines–Po Plain margin (pede-Apenninic
thrust front), and (3) the Emilia, Ferrara, and Adriatic Fold systems buried below the Po Plain. Geological data and interpreted
seismic sections indicate a roughly N–S Quaternary deformation direction, with rates <2.5 mm/year. The shortening decreased
since the Pliocene, when our data indicate compression in a NNW–SSE direction and rates up to 7 mm/year. The trend and kinematics
of the structures affecting the Apennines–Po Plain margin and the Po Plain subsoil fit well the pattern of the current seismicity
of the area, as well as recent GPS and geodetic levelling data, pointing to a current activity of these thrust systems controlled
by an overall compressive stress field. Close to the Apenninic watershed, earthquake focal mechanisms indicate that shallow
extension is associated to deep compression. The extensional events may be related to a secondary extensional stress field
developing on the hangingwall of the thrust system affecting the Apenninic watershed; alternatively, this thrust system may
have been recently deactivated and overprinted by active normal faulting. Deeper compressive events are related to the activity
of both a major basement thrust that connects at surface with the pede-Apenninic thrust front and a major Moho structure. 相似文献
470.
Carlo Bertok Luca Martire Elena Perotti Anna d’Atri Fabrizio Piana 《Swiss Journal of Geoscience》2011,104(2):237-255
The Middle–Upper Jurassic succession of the Marguareis–Mongioie area (Ligurian Briançonnais Domain), developed in a protected shelf environment evolving into a pelagic plateau, bears clear evidence of synsedimentary tectonics such as: growth fault-related structures; neptunian dykes; marked lateral variations in stratigraphic thicknesses testifying to the juxtaposition of sectors characterized by different sedimentation and subsidence rates; discordant, anomalous stratigraphic contacts corresponding to paleoescarpments; nodular beds showing evidence of fluidification interpreted as seismites; and the occurrence of sand-sized quartz grains pointing to denudation of Permo-Triassic quartz-rich rocks. Such evidence documents an important Middle-Late Jurassic post-breakup tectonic activity, which was more effective in controlling the basin topography than the Early Jurassic syn-rift tectonic phase. Two main tectono-sedimentary stages, one occurring during the Bathonian, the other falling within the Callovian–Kimmeridgian interval, were reconstructed. The first stage can be referred to a fault-related activity occurring shortly after the initial stages of oceanic spreading of the Ligurian Tethys; the second can be genetically related to the far effects of the first rifting stage of the Bay of Biscay and the Valais basin. 相似文献