全文获取类型
收费全文 | 356篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 32篇 |
地球物理 | 87篇 |
地质学 | 163篇 |
海洋学 | 22篇 |
天文学 | 53篇 |
自然地理 | 18篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 30篇 |
2012年 | 27篇 |
2011年 | 29篇 |
2010年 | 18篇 |
2009年 | 22篇 |
2008年 | 11篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1951年 | 1篇 |
1950年 | 1篇 |
1949年 | 1篇 |
排序方式: 共有385条查询结果,搜索用时 915 毫秒
331.
P. A. Polito T. K. Kyser P. Alexandre E. E. Hiatt C. R. Stanley 《Australian Journal of Earth Sciences》2013,60(5):453-474
The Alligator Rivers Uranium Field (ARUF) includes the mined and unmined Jabiluka, Ranger, Koongarra and Nabarlek unconformity-related uranium deposits and several small prospects including the newly discovered King River prospect. Uranium mineralisation is hosted by a variety of metamorphosed Nimbuwah Domain lithologies that are unconformably overlain by the Kombolgie Subgroup, a basin package of unmetamorphosed arenites and mafic volcanics. All of the uranium deposits and prospects preserve an identical alteration assemblage that is subdivided into a distal and proximal alteration zone. The distal alteration zone comprises an assemblage of sericite and chlorite that replace albite and amphibole. In some cases, this alteration can be traced >1000 m from the proximal alteration zone that is dominated by uraninite, hematite, chlorite and sericite. Uranium precipitated in the basement as uraninite at 1680 Ma at around 200°C from a fluid having δ18Ofluid values of 3.0±2.8‰ and δDfluid values of ?28±13‰ VSMOW reflecting an evolved marine source. These geochemical properties are indistinguishable from those recorded by diagenetic illite and chlorite that were collected from the Kombolgie Subgroup sandstones across the ARUF. The illite and chlorite formed in diagenetic aquifers, and where these aquifers intersected favourable basement rocks, such as those containing graphite or other reductants, U was precipitated as uraninite. Therefore, it is proposed that the Kombolgie Subgroup is the source for fluids that formed the deposits. A post-ore alteration assemblage dominated by chlorite, but also comprising quartz±dolomite±sulfide veins cut the uranium mineralisation at all deposits and has historically been recorded as part of the syn-ore mineralisation event. However, these minerals formed anywhere between 1500 to 630 Ma from fluids that have distinctly lower δ18Ofluid values around 1.5‰ and lower δDfluid values around ?45‰ reflecting a meteoric water origin. Despite unconformity-related uranium deposits having a large alteration halo, they remain difficult to find. The subtle alteration of albite to sericite several hundred metres from mineralisation occurs in isolation of any increase in trace elements such as U and radiogenic Pb and can be difficult or impossible to identify in hand specimen. Whole rock geochemical data indicate that Pearce Element Ratio (PER) analysis and General Element Ratio (GER) analysis may vector into this subtle alteration because it does not rely on an increase in trace elements to identify proximity to ore. PER and GER plots, Al/Ti vs (2Ca + Na + K)/Ti, Na/Al vs (Na + K)/Al, K/Al vs (Na + K)/Al and (Fe + Mg)/Al vs (Na + K)/Al provide a visual guide that readily distinguish unaltered from altered samples. A plot of (Na + K)/Al and (Fe + Mg)/Al on the x-axis against the concentration of trace elements on the y-axis reveals that U, Pb, Mo, Cu, B, Br, Ce, Y, Li, Ni, V and Nd are associated with the most intensely altered samples. The lithogeochemical vectors should aid explorers searching for uranium mineralisation in a prospective basin environment, but exploration must first focus on the characteristics of the basin to assess its mineralisation potential. A holistic model that describes the evolution of the Kombolgie Subgroup from deposition through diagenesis to formation of the uranium deposits in the underlying basement rocks is presented and has application to other basins that are considered prospective for unconformity-related uranium deposits. The model outlines that explorers will need to consider the thickness of the sedimentary pile, its lithological composition relative to depositional setting, the depth to which the sediments were buried during diagenesis and the degree of diagenesis achieved, which may be time dependant, before deciding on the prospectivity of the basin. 相似文献
332.
New zircon and apatite fission-track (FT) data, including apatite thermal modelling, are combined with an extensive literature survey and reconnaissance-type structural fieldwork in the Eastern Apuseni Mountains. This leads to a better understanding of the complex structural and thermal history of a key area at the boundary between two megatectonic units in the Balkan peninsula, namely the Tisza and Dacia Mega-Units. Following Late Jurassic obduction of the Transylvanian ophiolites onto a part of the Dacia Mega-Unit, that is, the Biharia nappe system, both units were buried to a minimum of 8 km during late Early Cretaceous times when these units were underthrust below the Tisza Mega-Unit consisting of the present-day Codru and Bihor nappe systems. Tisza formed the upper plate during Early Cretaceous (‘Austrian’) east-facing orogeny. Turonian to Campanian zircon FT cooling ages (95–71 Ma) from the Bihor and Codru nappe systems and the Biharia and Baia de Arie? nappes (at present the structurally lowest part of the Dacia Mega-Unit) record exhumation that immediately followed a second Cretaceous-age (i.e. Turonian) orogenic event. Thrusting during this overprinting event was NW-facing and led to the overall geometry of the present-day nappe stack in the Apuseni Mountains. Zircon FT ages, combined with thermal modelling of the apatite FT data, show relatively rapid post-tectonic cooling induced by a third shortening pulse during the latest Cretaceous (‘Laramian’ phase), followed by slower cooling across the 120°–60 °C temperature interval during latest Cretaceous to earliest Paleogene times (75–60 Ma). Cenozoic-age slow cooling (60–40 Ma) was probably related to erosional denudation postdating ‘Laramian’ large-scale updoming. 相似文献
333.
Multiple-point statistics are widely used for the simulation of categorical variables because the method allows for integrating a conceptual model via a training image and then simulating complex heterogeneous fields. The multiple-point statistics inferred from the training image can be stored in several ways. The tree structure used in classical implementations has the advantage of being efficient in terms of CPU time, but is very RAM demanding and then implies limitations on the size of the template, which serves to make a proper reproduction of complex structures difficult. Another technique consists in storing the multiple-point statistics in lists. This alternative requires much less memory and allows for a straightforward parallel algorithm. Nevertheless, the list structure does not benefit from the shortcuts given by the branches of the tree for retrieving the multiple-point statistics. Hence, a serial algorithm based on list structure is generally slower than a tree-based algorithm. In this paper, a new approach using both list and tree structures is proposed. The idea is to index the lists by trees of reduced size: the leaves of the tree correspond to distinct sublists that constitute a partition of the entire list. The size of the indexing tree can be controlled, and then the resulting algorithm keeps memory requirements low while efficiency in terms of CPU time is significantly improved. Moreover, this new method benefits from the parallelization of the list approach. 相似文献
334.
Alexandre A. Costa António Arêde Alfredo Campos Costa Andrea Penna Aníbal Costa 《地震工程与结构动力学》2013,42(14):2081-2095
The out‐of‐plane response of walls in existing stone masonry buildings is one of the major causes of vulnerability commonly observed in post‐earthquake damage surveys. In this context, a shaking table (ST) test campaign was carried out on a full‐scale masonry façade mainly focusing on the characterization of its out‐of‐plane overturning behaviour. The structure tested on the ST is a partial reproduction of an existing building from Azores, damaged during the 9 July 1998 Faial earthquake. The definition of the tested specimen as well as the selection of the input ground motion is reported in this paper. A specific emphasis is given to the definition of the time‐history to be applied during the tests because it was felt as an essential and crucial part of the work to obtain the desired overturning behaviour. The accelerogram to be imposed was selected from a large set of accelerograms (74) by means of a step‐by‐step procedure on the basis of several numerical analyses resorting to the rocking response of rigid blocks. A companion paper (Part 2) focuses on the ST test results and detailed data interpretation. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
335.
Alexandre B. Gonçalves 《International journal of geographical information science》2013,27(7):983-996
The computation of least-cost paths over a cost surface is a well-known and widely used capability of raster geographic information systems (GISs). It consists in finding the path with the lowest accumulated cost between two locations in a raster model of a cost surface, which results in a string-like, thin and long sequence of cells. In this article, a new extension of raster-based least-cost path modelling is proposed. The new modelling approach allows the computation of paths or corridors with a fixed width, larger than one cell. These swaths are called wide paths and may be useful in circumstances where the detail level of the raster cost surfaces is higher than the width of the desired path or corridor. The wide path model presented in the article is independent of the choice of least-cost algorithms, because the transformation from regular to wide paths is applied to the construction of nodes and edges of an induced graph. The article gives the foundations and discusses the particularities of such paths, regardless of the imposed width, and explores the difference from the usual least-cost path model. Test cases were included, one hypothetical and the other with real data. The results are coherent and indicative of the applicability of wide paths. 相似文献
336.
Alexandre Vazdekis 《Astrophysics and Space Science》2001,276(2-4):839-844
We explore the behaviour of the most popular spectroscopic absorption features in the optical region as a function of the initial mass function (IMF), while taking into account the spectral resolution and galaxy velocity dispersion. We conclude that the IMF produces a negligible effect on the Lick indices contained in the wavelength interval λ 3800–5500 Å, except the Mg1 index, for which the IMF could be as important as the metallicity. We also show that the IMF is irrelevant for most of the Rose (1994) indicators, except for various indices that show a non-negligible sensitivity. In contrast to the Lick indices, some of the Rose indicators vary their age–metallicity–IMF trends as a function of the spectral resolution. 相似文献
337.
338.
Analysis of individual fluid inclusions using synchrotron X-ray fluorescence microprobe: progress toward calibration for trace elements 总被引:1,自引:0,他引:1
Bénédicte Ménez Pascal PhilippotMichelle Bonnin-Mosbah Alexandre SimionoviciFrançois Gibert 《Geochimica et cosmochimica acta》2002,66(4):561-576
A critical problem for conducting quantitative analysis of individual fluid inclusions using Synchrotron X-Ray Fluorescence (SXRF) technique relates to the standardization and the calibration of the X-ray spectra. In this study, different approaches have been tested for calibration purposes: (a) the use of chlorine when Cl content can be estimated either from melting point depressions of undersaturated fluid inclusions or from saturation limits for halite-bearing fluid inclusions, (b) the use of calcium from synthetic fluid inclusions of known CaCl2 content as an external standard. SXRF analysis was performed on individual fluid inclusions from the Chivor and Guali emerald deposits, Columbia. These well-known samples contain a single fluid inclusion population for which detailed crush-leach analyses are available, thus providing a relevant compositional reference frame. Concentration estimates were also compared to Particle Induced X-ray Emission (PIXE) analysis carried out independently on the same fluid inclusions.Results of the calibration tests indicate that major (Cl, K, Ca, Fe, Mn) and trace element (Cu, Zn, As, Br, Rb, Sr, Ba, Pb) concentration estimates can be performed without precise knowledge of the analytical volume and the inclusion’s 3D geometry. Although the standard deviation of the SXRF results can be relatively high depending on the calibration mode used, mean concentration estimates for most elements are in good agreement with PIXE and crush-leach analysis. Elemental distributions within single fluid inclusions were also established. Associated correlation diagrams argue for the homogeneous distribution of most elements in the fluid inclusion. In contrast, Br shows a bimodal distribution interpreted to reflect a significant enrichment of the vapor portion of the inclusion fluid. 相似文献
339.
340.
Alexandre Canitano Ya-Ju Hsu Hsin-Ming Lee Alan T. Linde Selwyn Sacks 《Journal of Geodesy》2017,91(1):1-8
We analyze the high-resolution dilatation data for the October 2013 \(M_w\) 6.2 Ruisui, Taiwan, earthquake, which occurred at a distance of 15–20 km away from a Sacks–Evertson dilatometer network. Based on well-constrained source parameters (\(\hbox {strike}=217^\circ \), \(\hbox {dip}=48^\circ \), \(\hbox {rake}=49^\circ \)), we propose a simple rupture model that explains the permanent static deformation and the dynamic vibrations at short period (\(\sim \)3.5–4.5 s) for most of the four sites with less than 20 % of discrepancies. This study represents a first attempt of modeling simultaneously the dynamic and static crustal strain using dilatation data. The results illustrate the potential for strain recordings of high-frequency seismic waves in the near-field of an earthquake to add constraints on the properties of seismic sources. 相似文献