全文获取类型
收费全文 | 94篇 |
免费 | 0篇 |
国内免费 | 1篇 |
专业分类
大气科学 | 5篇 |
地球物理 | 7篇 |
地质学 | 55篇 |
海洋学 | 7篇 |
天文学 | 1篇 |
自然地理 | 20篇 |
出版年
2014年 | 1篇 |
2013年 | 8篇 |
2012年 | 2篇 |
2011年 | 2篇 |
2010年 | 4篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 1篇 |
2006年 | 1篇 |
2005年 | 5篇 |
2004年 | 3篇 |
2002年 | 2篇 |
2000年 | 2篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有95条查询结果,搜索用时 15 毫秒
11.
GUILLAUME CAILLEAU ERIC P. VERRECCHIA OLIVIER BRAISSANT† LAURENT EMMANUEL‡ 《Sedimentology》2009,56(6):1858-1875
Needle fibre calcite is one of the most ubiquitous habits of calcite in vadose environments (caves deposits, soil pores, etc.). Its origin, either through inorganic, indirect or direct biological processes, has long been debated. In this study, investigations at 11 sites in Europe, Africa and Central America support arguments for its biogenic origin. The wide range of needle morphologies is the result of a gradual evolution of the simplest type, a rod. This rod is the elementary brick which, by aggregation and welding, builds more complex needles. The absence of cross‐welded needles implies that they are welded in a mould, or under a longitudinal and unidirectional constraint, before being released inside the soil pores. The difference between the lengthening of the needles and the c axis can be explained by the existence of needles observed under a scanning electron microscope in organic sleeves, which can act as a mould during rod growth. Complex morphologies with epitaxial outgrowths on straight rods cannot have grown entirely inside organic microtubes; they must result from soil diagenesis after the release of straight rods in a soil‐free medium. Whisker crystals are interpreted as the result of growth and coalescence of euhedral crystals on a rod. Rhomb chains are considered to be the consequence of successive epitaxial growth steps on a needle during variations in growth conditions. Isotopic signatures for needle fibre calcite vary from ?16·63‰ to +1·10‰ and from ?8·63‰ to ?2·25‰ for δ13C and δ18O, respectively. The absence of high δ18O values for needle fibre calcite precludes a purely physicochemical origin (evaporative) for this particular habit of calcite. As epitaxial growth cannot precipitate in the same conditions as initial needles, needle fibre calcite stable isotopic signatures should be used with caution as a proxy for palaeoenvironmental reconstructions. In addition, it is suggested that the term needle fibre calcite should be kept for the original biogenic form. The other habit should be referred to as epitaxial forms of needle fibre calcite. 相似文献
12.
GWENAëLE JAN YVES MÉNARD MATHILDE FAILLOT FLORENT LYARD ERIC JEANSOU PASCAL BONNEFOND 《Marine Geodesy》2013,36(3-4):615-629
Absolute calibration of sea level measurements collected from space-borne radar altimeters is usually performed with respect to collocated sea level in situ records from tide gauges or GPS buoys (Ménard et al. 1994; Haines et al. 1996; Bonnefond et al. 2003; Haines et al. 2003; Schum et al. 2003; Watson et al. 2003; Watson et al. 2004). Such a method allows regular and long-term control of altimetric systems with independent records. However, this approach is based on a single, geographically dependent point. In order to obtain more significant and accurate bias and drift estimates, there is a strong interest in multiplying the number of calibration opportunities. This article describes a method, called the “offshore method” that was developed to extend the single-point approach to a wider regional scale. The principle is to compare altimeter and tide gauge sea level data not only at the point of closest approach of an overflying pass, but also at distant points along adjacent satellite passes. However, connecting sea level satellite measurements with more distant in situ data requires a more accurate determination of the geoid and mean ocean dynamic topography slopes, and also of the ocean dynamical changes. In this demonstration experiment, 10 years of averaged TOPEX/Poseidon mean sea level profiles are used to precisely determine the geoid and the mean ocean circulation slope. The Mog2d barotropic ocean model (Carerre et Lyard 2003) is used to improve our estimate of the ocean dynamics term. The method is first validated with Jason-1 data, off Corsica, where the dedicated calibration site of Senetosa provides independent reference data. The method is then applied to TOPEX/Poseidon on its new orbit and to Geosat Follow On. The results demonstrate that it is feasible to make altimeter calibrations a few tens to hundreds of kilometers away from a dedicated site, as long as accurate mean sea level altimeter profiles can be used to ensure the connection with reference tide gauges. 相似文献
13.
14.
15.
16.
17.
LEE DER-CHUEN; HALLIDAY ALEX N.; DAVIES GARETH R.; ESSENE ERIC J.; FITTON J. GODFREY; TEMDJIM ROBERT 《Journal of Petrology》1996,37(2):415-441
Major element, trace element and SrNdPb isotopiccompositions of ultramafic xenoliths and megacrysts from thecontinental Cameroon line provide evidence for metasomatismof the upper most lithospheric mantle by enriched melts duringthe Mesozoic The megacrysts probably crystallized within thelower continental crust from melts similar to the host magmas.All the xenoliths originated as depleted residues after theextraction of basaltic melts, but some indicate evidence ofinteraction with enriched partial melts before entrainment.The UPb isotopic data on garnet are consistent with coolingthrough >900C at >300 Ma. The SmNd isotope systematicsin constituent phases appear to have been in equilibrium ona xenolith scale at the time of entrainment, indicating derivationfrom mantle that remained at temperatures >600C until eruption.Spinel therzolies that show simple light rare earth element(LREE) depletions are characterized by isotopic compositionsthat are comparable with, but slightly more depleted than AtlanticN-MORB, suggesting that the unmetasomatized sub-continentallithosphere of the Cameroon line may be isotopically similarto that of sub-oceanic lithosphere. The Nd-depleted mantle modelages of these xenoliths are consistent with late Proterozoicdepletion, similar in age to much of the overlying continentalcrust. In contrast, samples that have LREE-enriched clinopyr-oxenes(La/Yb =4.79.4) contain trace amounts of amphibole, areenriched in U and have more radiogenic Pb and Sr. These xenolithsyield UPb and SmNd model ages consistent withMesozoic enrichment, in agreement with the age of enrichmentof the source regions of the basalts, as deduced from Pb isotopiccompositions. Clinopyroxenes record three orders of magnitudeenrichment in U and LREE accompanied by progressive K depletionassociated with the growth of trace amphibole, with K/U ratiosthat range from 12000 to 1. The ratios of the trace elementsthought to have similar bulk D in mantle melting, Ce/Pb, Ba/Rband Nd/Sr ratios, display regional variations related to thetime integrated history of enrichments indicated by Nd isotopiccompositions. Mass balance calculations suggest that the meltsresponsible for the most recent enrichment of the lithospherehad higher La/Yb and U/Pb than Cameroon line host magmas, andwere probably the product of small degrees of partial meltingassociated with the earliest stages of the breakup of Pangea. KEY WORDS: Cameroon line; mantle xenoliths; megacrysts; REE; isotopic composition; trace element 相似文献
18.
Foreslope stromatoporoid-renalcid bioherm with evidence of early cementation, Devonian Ancient Wall reef complex, Rocky Mountains 总被引:1,自引:0,他引:1
A small mound, 4 × 23 m in size, on the fore-reef slope of the Ancient Wall reef complex at Mount Haultain, Alberta, consists of fenestral, renalcid micrite and wackestone. Stromatoporoids are the most abundant skeletal component but do not form an organic framework. Renalcids, together with early micrite cementation, performed a supporting and stabilizing role but only rarely directly encrusted skeletal material. Many of the primary shelter voids, interparticle voids and fenestrae were filled with internal sediments and submarine micrite cements. A considerable proportion of the micrite matrix appears to be cement. The location and development of the bioherm was controlled by a local hard substrate and suitable environmental conditions. The mound developed on and around a large block within an underlying megabreccia bed soon after it was deposited in a debris flow on the fore-reef slope. It formed near wave base in about 30–50 m water depth and was subject to gentle current action. Laminar stromatoporoids grew on the flanks and top of the mound, and fenestral, renalcid micrite and wackestone accumulated in the central part. Deepening water and increased rates of mud accumulation terminated further build-up of the bioherm and it was buried by basin mud. Fenestral, renalcid micrite occurs in a number of Devonian and Lower Palaeozoic organic mounds. This study suggests that early, submarine cementation was a significant factor in the development and preservation of this distinctive lithotype. 相似文献
19.
20.
Abstract A novel approach for mapping river runoff is presented. It is based on a disaggregation of the mean annual streamflow measured at the outlet of a basin to estimate water depths on elements of an exact partition of this basin. The developed technique is based on geostatistical interpolation procedures to which a global constraint of water balance has been added. The methodology is illustrated by a case study from a tributary to the Rhône River, France. The results were compared to an established method-the nested approach, and a cross-validation was performed for each mapping technique. The disaggregation approach appears to give the most consistent results. Finally, two gridded maps were derived by applying the disaggregation twice to assess water depth on an increasingly finer grid mesh. The global constraint of water balance was applied to each element of the coarser mesh to give estimates for the finer one. 相似文献