全文获取类型
收费全文 | 524篇 |
免费 | 20篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 47篇 |
地球物理 | 123篇 |
地质学 | 186篇 |
海洋学 | 62篇 |
天文学 | 69篇 |
综合类 | 3篇 |
自然地理 | 36篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 15篇 |
2019年 | 9篇 |
2018年 | 23篇 |
2017年 | 19篇 |
2016年 | 27篇 |
2015年 | 30篇 |
2014年 | 26篇 |
2013年 | 46篇 |
2012年 | 31篇 |
2011年 | 47篇 |
2010年 | 28篇 |
2009年 | 39篇 |
2008年 | 28篇 |
2007年 | 20篇 |
2006年 | 22篇 |
2005年 | 13篇 |
2004年 | 17篇 |
2003年 | 11篇 |
2002年 | 21篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 7篇 |
1998年 | 13篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有550条查询结果,搜索用时 31 毫秒
151.
Numerical modeling of the transient hydrogeological response produced by tunnel construction in fractured bedrocks 总被引:10,自引:0,他引:10
Groundwater inflows into tunnels constructed in fractured bedrocks not only constitute an important factor controlling the rate of advancement in driving the tunnel but may pose potential hazards. Drawdowns caused by tunnel construction may also induce geotechnical and environmental impacts. Here we present a numerical methodology for the dynamic simulation of the hydrogeological transient conditions induced by the tunnel front advance. The methodology is based on the use of a Cauchy boundary condition at the points lying along the tunnel according to which water discharge, Q, is computed as the product of a leakage coefficient, , and the head difference, (H−h), where H is the prescribed head at the tunnel wall and h is the hydraulic head in the fractured rock in the close vicinity of the tunnel. At a given position of the tunnel, is zero until the tunnel reaches such position when it is assigned a positive value. The use of step-wise time functions for allows an efficient and accurate simulation of the transient hydrogeological conditions at and around the tunnel during the excavation process. The methodology has been implemented in TRANMEF-3, a finite element computer code for groundwater flow in 3D fractured media developed at the University of A Coruña, Spain, and has been used to simulate the impact of a tunnel on the groundwater system at the Äspö island (Sweden). This tunnel was constructed to access an underground laboratory for research on radioactive waste disposal. The large amount of available data at this site provides a unique opportunity to test the performance of the numerical model and the proposed methodology for tunnel advance. With just minor calibration, the numerical model is able to reproduce accurately the measurements of inflows into the tunnel at several reaches and hydraulic heads at surface-drilled boreholes. These results obtained at the Äspö site lead us to conclude that accurate predictions of the transient hydrogeological responses induced by tunneling works in fractured bedrocks, can be achieved provided that a sound hydrogeological characterization of large-scale fracture zones is available. 相似文献
152.
Roberto Oyarzun Alvaro Márquez Javier Lillo Ivan López Sergio Rivera 《Mineralium Deposita》2002,37(8):795-799
153.
Thierry Sempere Gabriel Carlier Pierre Soler Michel Fornari Víctor Carlotto Javier Jacay Oscar Arispe Didier Nraudeau Jos Crdenas Silvia Rosas Nstor Jimnez 《Tectonophysics》2002,345(1-4)
Integrated studies and revisions of sedimentary basins and associated magmatism in Peru and Bolivia (8–22°S) show that this part of western Gondwana underwent rifting during the Late Permian–Middle Jurassic interval. Rifting started in central Peru in the Late Permian and propagated southwards into Bolivia until the Liassic/Dogger, along an axis that coincides with the present Eastern Cordillera. Southwest of this region, lithospheric thinning developed in the Early Jurassic and culminated in the Middle Jurassic, producing considerable subsidence in the Arequipa basin of southern Peru. This 110-Ma-long interval of lithospheric thinning ended 160 Ma with the onset of Malm–earliest Cretaceous partial rift inversion in the Eastern Cordillera area.The lithospheric heterogeneities inherited from these processes are likely to have largely influenced the distribution and features of younger compressional and/or transpressional deformations. In particular, the Altiplano plateau corresponds to a paleotectonic domain of “normal” lithospheric thickness that was bounded by two elongated areas underlain by thinned lithosphere. The high Eastern Cordillera of Peru and Bolivia results from Late Oligocene–Neogene intense inversion of the easternmost thinned area. 相似文献
154.
Martha Surez Javier Avils Francisco J. Snchez-Sesma 《Soil Dynamics and Earthquake Engineering》2002,22(8)
A simplified indirect boundary element method is applied to compute the impedance functions for L-shaped rigid foundations embedded in a homogeneous viscoelastic half-space. In this method, the waves generated by the 3D vibrating foundation are constructed from radiating sources located on the actual boundary of the foundation. The impedance functions together with the free-field displacements and tractions generated along the soil–foundation interface are used to calculate the foundation input motion for incident P, S and Rayleigh waves. This is accomplished by application of Iguchi's averaging method which, in turn, is verified by comparison with results obtained rigorously using the relation between the solutions of the basic radiation (impedance functions) and scattering (input motions) problems. Numerical results are presented for both surface-supported and embedded foundations. It is shown how the seismic response of L-shaped foundations with symmetrical wings differs from that of enveloping square foundations. The effects of inclination and azimuth of the earthquake excitation are examined as well. These results should be of use in analyses of soil–structure interaction to account for the traveling wave effects usually overlooked in practice. 相似文献
155.
An evaluation of the wave passage effects on the relevant dynamic properties of structures with flexible foundation is presented. A simple soil–structure system similar to that used in practice to take into account the inertial interaction effects by the soil flexibility is studied. The kinematic interaction effects due to non‐vertically incident P, SV and Rayleigh waves are accounted for in this model. The effective period and damping of the system are obtained by establishing an equivalence between the interacting system excited by the foundation input motion and a replacement oscillator excited by the free‐field ground motion. In this way, the maximum structural response could be estimated from standard free‐field response spectra using the period and damping of the building modified by both the soil flexibility and the travelling wave effects. Also, an approximate solution for the travelling wave problem is examined over wide ranges of the main parameters involved. Numerical results are computed for a number of soil–structure systems to identify under which conditions the effects of wave passage are important. It comes out that these effects are generally negligible for the system period, but they may significantly change the system damping since the energy dissipation within the soil depends on both the wave radiation and the diffraction and scattering of the incident waves by the foundation. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
156.
We studied a large debris-avalanche deposit of Pleistocene age in the Tenteniguada Basin, Gran Canaria Island, Spain. This
deposit, which is well preserved because it is mostly covered by basanite lava flows, has distinctive matrix and block facies,
hummocky topography and internal structures typical of debris avalanches. However, neither syneruptive lavas nor some characteristic
features of volcanic debris-avalanche deposits, such as a stratovolcano edifice or a horseshoe-shaped crater, are present.
The occurrence of internal features characteristic of volcanic avalanche deposits could be attributed to the volcanic materials
involved in the movement rather than to the triggering of the avalanche during a volcanic eruption. The conditioning factors
are shown to be associated with specific structural and hydrological conditions, such as the presence of old volcanic domes,
strength reduction of the rocks, effective stress decrease, active gully erosion and water table rise during Pleistocene humid
episodes. We finally suggest that the possible triggering factor of the avalanche was a neighbouring volcanic or tectonic
earthquake. 相似文献
157.
Javier Rodriguez Jens Havskov Mathilde Bøttger Sørensen Luis Fernando Santos 《Journal of Seismology》2018,22(4):883-896
The Dominican Republic has a high level of seismic activity, and a new seismic network has been installed to improve the detection of earthquakes. The network has been operated by Instituto Politécnico Loyola since 2012. It uses six new stations of its own, as well as 17 other stations publically available. In this study, we investigate in particular the south-west of the country where no seismic stations have been operating before. We find an area, SE of the Enriquillo Plantain Garden fault (responsible for the 2010 Haiti M7.0 earthquake), with a high seismic activity (M?=?2–4) compared to the surrounding area. This shallow seismicity (except two events around 40 km depth) is not seen in any global catalogs, and it does not seem to be associated with any known faults. However, the region has been under rapid recent uplift since margins between hills and valleys are filled with massive alluvial fans. We made 24 new fault plane solutions using P-polarities and S/P amplitude ratios. The solutions show mainly reverse mechanisms and the P-axis directions are mainly NNE oriented, which is in agreement with a published strain direction from GPS measurements. We conclude that the main cause of the seismicity in our study area is the push of the Beata Ridge against Enriquillo basin and the rest of the Gonave microplate, reflected in the mainly reverse focal mechanisms. 相似文献
158.
Cordrie Louise Gailler Audrey Escartin Javier Feuillet Nathalie Heinrich Philippe 《Natural Hazards》2020,103(2):2103-2129
Natural Hazards - The arc of the Lesser Antilles is associated with a significant tectonic activity due to the subduction of the Atlantic oceanic plate under the Caribbean plate. Earthquakes in... 相似文献
159.
Javier Caraveo‐Patiño Yiqun Wang Luis A. Soto Kebreab Ghebremeskel Catherine Lehane Michael A. Crawford 《Marine Ecology》2009,30(4):437-447
The radiation of the mammalian land species that became the baleen whales happened about 27–34 Mya. Mammals require omega 6 fatty acids for reproduction. With this long exposure to the omega 3‐rich marine food chain, the Gray whale (Eschrichtius robustus) might be expected to have lost its requirement for omega 6 fatty acids. We report an unexpectedly high content of omega 6 arachidonic acid (ArA) in the Gray whale liver and muscle lipids. This whale migrates 10,000 km from the cold polar, omega 3 oil‐rich food chain to that of the breeding lagoons of the tropical waters. The food web of tropical waters is a source of omega 6 fatty acids, which are hardly present in the cold polar food web. We suggest the reason for this longest of migrations from cold to warm waters is to meet the requirement for omega 6 fatty acids for mammalian reproduction and brain growth. This extreme conservation of omega 6 fatty acids in Gray whale biology has critical implications for mammalian biology and especially for whale conservation. 相似文献
160.
In the present study we review datasets available for the Chilean margin to assess the relationship between environmental (or habitat) heterogeneity and benthic diversity. Several factors, such as the presence of different water masses, including the oxygen-deficient Equatorial Sub-surface Waters (ESSW) at the continental shelf and upper slope, and the Antarctic Intermediate Waters (AIW) at mid slope depths appear to control the bathymetric distribution of benthic communities. The presence of methane seeps and an extended oxygen minimum zone (OMZ) add complexity to the benthic distribution patterns observed. All these factors generate environmental heterogeneity, which is predicted to affect the diversity patterns both along and across the Chilean continental margin. The response to these factors differs among different faunal size groups: meio-, macro-, and megafauna. Physiological adaptations to oxygen deficiency and constraints related to body size of each group seem to explain the larger-scale patterns observed, while sediment/habitat heterogeneity ( e.g. at water mass boundaries, hardgrounds, biogeochemical patchiness, sediment organic content, grain size) may influence the local fauna diversity patterns. 相似文献