全文获取类型
收费全文 | 930篇 |
免费 | 53篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 73篇 |
地球物理 | 198篇 |
地质学 | 373篇 |
海洋学 | 89篇 |
天文学 | 171篇 |
综合类 | 4篇 |
自然地理 | 65篇 |
出版年
2023年 | 5篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 20篇 |
2019年 | 14篇 |
2018年 | 33篇 |
2017年 | 30篇 |
2016年 | 41篇 |
2015年 | 30篇 |
2014年 | 42篇 |
2013年 | 56篇 |
2012年 | 52篇 |
2011年 | 60篇 |
2010年 | 41篇 |
2009年 | 64篇 |
2008年 | 54篇 |
2007年 | 52篇 |
2006年 | 51篇 |
2005年 | 42篇 |
2004年 | 24篇 |
2003年 | 34篇 |
2002年 | 36篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 15篇 |
1998年 | 14篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 4篇 |
1993年 | 9篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1967年 | 1篇 |
排序方式: 共有991条查询结果,搜索用时 46 毫秒
901.
High performance computing has undergone a radical transformation during the past decade. Though monolithic supercomputers continue to be built with significantly increased computing power, geographically distributed computing resources are now routinely linked using high‐speed networks to address a broad range of computationally complex problems. These confederated resources are referred to collectively as a computational Grid. Many geographical problems exhibit characteristics that make them candidates for this new model of computing. As an illustration, we describe a spatial statistics problem and demonstrate how it can be addressed using Grid computing strategies. A key element of this application is the development of middleware that handles domain decomposition and coordinates computational functions. We also discuss the development of Grid portals that are designed to help researchers and decision makers access and use geographic information analysis tools. 相似文献
902.
Michael Emch James W. Quinn Marc Peterson Mark Alexander 《The Professional geographer》2005,57(2):256-267
Measuring land‐cover change is an essential part of sustainable conservation planning. This project uses Landsat MSS and ETM+ data to document forest cover change in the Toledo District, Belize, from 1975 to 1999 and provides an initial assessment of why these changes took place. Supervised and subpixel classification methods were employed. The results showed an aggregate forest loss of almost 10 percent, which is approximately 36,000 ha. Deforestation expanded significantly in the most populous Mayan areas of central Toledo District and along the Guatemalan border. Subpixel classification results showed that in 1999 the most densely forested areas were in northern Toledo District in the Maya Mountains. 相似文献
903.
Mobile, location‐aware computing technology is widely available. In this article we sketch out a manifesto on mobile computing in geographic education (MoGeo) for consideration and debate within the geographic community. At the core of our argument is the idea that emerging mobile computing technologies will allow teachers to bring the classroom and pedagogic materials into the field, and that the resulting in situ educational experience will enhance learning by contextualizing the complex and abstract concepts that we teach. We provide a set of key principles that can guide the development of field experiences for students using these new technologies. 相似文献
904.
Ingrid Berrodier François Farges Marc Benedetti Gordon E. Brown Jr Michel Deveughèle 《Geochimica et cosmochimica acta》2004,68(14):3019-3042
Gold adsorption products on powdered ferrihydrite, goethite, and boehmite samples, prepared by reacting Au(III)-Cl solutions ([Au] = 4.2 × 10−5-9.0 × 10−3 M; [Cl] = 0.017-0.6 M) with these adsorbents at pH values of 4 to 9 and Au adsorption densities ranging from 0.046 to 1.53 μmol/m2 were characterized using Au-LIII XAFS spectroscopy. The solutions (before and after uptake) were investigated by Raman scattering to determine speciation and by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) to determine solution composition. We present an analysis of several effects that are observed in the Au LIII-edge XAFS spectra, including X-ray beam-induced photo-reduction, multi-electronic excitations, disorder effects, and multiple scattering, that would complicate interpretation of the spectra if not accounted for. A combination of methods (spectral deconvolution, principal component analysis, spectral inversion, and wavelet analysis) was used to identify and quantify these effects, to characterize the nature of mixed ligands around gold, and to distinguish between multiple-scattering features and features due to next-nearest neighbors in the XAFS spectra.Analysis of the Au-LIII XAFS spectra showed that Au(III) is present as square-planar Au(III)(O,Cl)4 complexes in the aqueous solutions and on the surfaces of the Al/Fe-(oxy)hydroxide adsorption samples with dominantly O ligands at pH > 6 and mixed O/Cl ligands at lower pH values. The EXAFS-derived Au-O and Au-Cl distances are 2.00(2) and 2.28(2) Å, respectively, and the magnitudes of the Debye-Waller factors and third cumulants from anharmonic analyses indicate very little thermal or positional disorder around Au(III) in the adsorption samples. Iron second neighbors are present around Au in the Au(III)/ferrihydrite and Au(III)/goethite adsorption samples, with Au-Fe distances of 3.1(1) and 3.3(1) Å. In boehmite, two sets of Au-Al distances were detected at 3.0(1) and 3.2(1) Å. A reverse Monte Carlo study of the XAFS spectroscopic data suggests the presence of a continuum of edge-shared AuO4-FeO6 distances, which cannot be described correctly by a classical model of these data in which only a mean distance (although severely under-estimated) is derived. 相似文献
905.
From rifting to spreading in the eastern Gulf of Aden: a geophysical survey of a young oceanic basin from margin to margin 总被引:1,自引:0,他引:1
Sylvie Leroy Pascal Gente Marc Fournier Elia d'Acremont Philippe Patriat Marie-Odile Beslier Nicolas Bellahsen Marcia Maia Angelina Blais Julie Perrot Ali Al-Kathiri Serge Merkouriev Jean-Marc Fleury Pierre-Yves Ruellan Claude Lepvrier Philippe Huchon 《地学学报》2004,16(4):185-192
A geophysical survey in the eastern Gulf of Aden, between the Alula–Fartak (52°E) and the Socotra (55°E) transform faults, was carried out during the Encens–Sheba cruise. The conjugate margins of the Gulf are steep, narrow and asymmetric. Asymmetry of the rifting process is highlighted by the conjugate margins (horst and graben in the north and deep basin in the south). Two transfer fault zones separate the margins into three segments, whereas the present‐day Sheba Ridge is divided into two segments by a transform discontinuity. Therefore segmentation of the Sheba Ridge and that of the conjugate margins did coincide during the early stages of oceanic spreading. Extensive magma production is evidenced in the central part of the western segment. Anomaly 5d was identified in the northern and southern parts of the oceanic basin, thus confirming that seafloor spreading in this part of Gulf of Aden started at least 17.6 Ma ago. 相似文献
906.
Catherine M. Cress & Marc Kamionkowski 《Monthly notices of the Royal Astronomical Society》1998,297(2):486-492
We develop the formalism required to interpret, within a CDM framework, the angular clustering of sources in a deep radio survey. The effect of non-linear evolution of density perturbations is discussed, as is the effect of the assumed redshift distribution of sources. We also investigate what redshift ranges contribute to the clustering signal at different angular scales. Application of the formalism is focused on the clustering detected in the FIRST survey, but measurements made for other radio surveys are also investigated. We comment on the implications for the evolution of clustering. 相似文献
907.
Highly Robust Variogram Estimation 总被引:5,自引:0,他引:5
Marc G. Genton 《Mathematical Geology》1998,30(2):213-221
The classical variogram estimator proposed by Matheron is not robust against outliers in the data, nor is it enough to make simple modifications such as the ones proposed by Cressie and Hawkins in order to achieve robustness. This paper proposes and studies a variogram estimator based on a highly robust estimator of scale. The robustness properties of these three estimators are analyzed and compared. Simulations with various amounts of outliers in the data are carried out. The results show that the highly robust variogram estimator improves the estimation significantly. 相似文献
908.
Melting and metasomatism in the continental lithosphere: laser ablation ICPMS analysis of minerals in spinel lherzolites from eastern Australia 总被引:28,自引:0,他引:28
Marc D. Norman 《Contributions to Mineralogy and Petrology》1998,130(3-4):240-255
Olivine, low-Ca pyroxene, diopside, and spinel from a suite of protogranular lherzolite xenoliths from southeastern Australia
have been analysed for their major and trace element compositions using electron microprobe and laser ablation ICPMS. Bulk
compositions of the lherzolites range from fertile (12–13% modal diopside) to depleted (2–3% modal diopside), with equilibration
temperatures of 850–900 °C indicating entrainment of these lherzolites from relatively shallow depths (probably ≤ 35 km) within
the lithosphere. Mineral compositions and abundances indicate a primary control by partial melting, with decreasing abundance
of modal diopside accompanied by increasing Mg# of olivine and pyroxene, decreasing Al and Ti contents of diopside, increasing
Ni contents of olivine, and increasing Cr/Al of spinel. HREE, Y, and Ga in diopside also follow melting trends, decreasing
in concentration with increasing Mg#. In contrast, highly incompatible elements such as LREE, Nb, and Th reveal divergent
behaviour that cannot be ascribed entirely to partial melting. Diopsides from the fertile lherzolites have mantle-normalized
patterns that are depleted in Th, Nb, and the LREE relative to Y and the HREE, whereas, diopsides from the cpx-poor samples
are strongly enriched in Th, Nb and the LREE, and have elevated Sm/Hf and Zr/Hf, and low Ti/Nb. All diopsides have strongly
negative Nb anomalies relative to Th and the LREE. Trace element patterns of diopside in the fertile lherzolites can be reproduced
by ≤ 5% batch melting of a primitive source. The negative Nb anomalies are a consequence of this melting, and do not require
special conditions or tectonic environments. The low concentrations of Y and HREE in diopside from the cpx-poor lherzolites
cannot be produced by realistic degrees of batch melting, but can be accomplished by up to ∼20% fractional melting, suggesting
multiple episodes of melt depletion. Os isotopic compositions of these lherzolites show that the melt depletion events occurred
in the middle and late Proterozoic, demonstrating the long-term stability of lithospheric mantle beneath regions of eastern
Australia. The LREE-enriched diopsides are well equilibrated and record metasomatic enrichment events that pre-date the magmatism
that entrained these xenoliths. Trace element patterns of these pyroxenes suggest a carbonatitic melt as the metasomatic agent.
Received: 24 September 1996 / Accepted: 12 August 1997 相似文献
909.
Based on airborne observations during the Baltex Bridge Cloud (BBC) campaign in September 2001, the impact of two layer cloud systems, gas absorption and surface albedo on cloud radiative smoothing is investigated. Multispectral nadir radiance measurements have been conducted which cover the visible and near infrared wavelength range. The observed radiances are transformed into Fourier space where ranges of scale-invariance are identified. Associated slopes and scale breaks are determined and used to characterize the impacts on cloud radiative smoothing. The results reveal that an increase of gas absorption reduces the small scale slope and the scale break due to a decreasing likelihood of horizontal photon transport. Another impact is that the increasing gas absorption reduces the cloud surface interaction, which is indicated by an increase of the large scale slope. An increasing surface albedo results in large scale cloud radiative smoothing and is associated with a decrease of the large scale slope. This effect depends on the cloud height and the cloud morphology. Two layer cloud systems exhibit a similar behaviour in Fourier space as large surface albedos beneath a single cloud deck. It is argued that the impact of two layer cloud systems on large scale cloud radiative smoothing may not be typical for two layer clouds. 相似文献
910.
Abdelilah Dekayir Marc Amouric Juan Olives Claude Parron Abdelilah Nadiri Abdelkader Chergui M.Abdeljalil El Hajraoui 《Comptes Rendus Geoscience》2004,336(12):1061-1070
In Volubilis, Roman mosaics are very beautiful and reveal, from the bottom to the surface, three layers: (i) ‘hedgehog’ layer, (ii) coarse grain mortar layer (rudus + nucleus) and (iii) tesselatum. Mineralogical analysis of coarse grain mortar sampled in Flavius Germanus mosaic shows that it consisted of quartz and calcite, with some feldspar and probably mica and dolomite. Fine-grained mortar in tesselatum is made from a mixture of calcite and quartz only. Limestone tesserae (white, pink and brown) show petrographic facies that change from micritic to oolithic limestone. Conversely, black and brick red tesserae are respectively made of marble, red sandstone and from fire clay. Other colours as yellow, blue, green and grey are obtained from artificial glass with different chemical compositions. To cite this article: A. Dekayir et al., C. R. Geoscience 336 (2004). 相似文献