全文获取类型
收费全文 | 335篇 |
免费 | 20篇 |
国内免费 | 20篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 33篇 |
地球物理 | 89篇 |
地质学 | 150篇 |
海洋学 | 20篇 |
天文学 | 37篇 |
自然地理 | 40篇 |
出版年
2024年 | 2篇 |
2022年 | 4篇 |
2021年 | 11篇 |
2020年 | 16篇 |
2019年 | 15篇 |
2018年 | 13篇 |
2017年 | 9篇 |
2016年 | 12篇 |
2015年 | 17篇 |
2014年 | 12篇 |
2013年 | 31篇 |
2012年 | 19篇 |
2011年 | 20篇 |
2010年 | 16篇 |
2009年 | 17篇 |
2008年 | 22篇 |
2007年 | 20篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 12篇 |
2003年 | 8篇 |
2002年 | 13篇 |
2001年 | 6篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有375条查询结果,搜索用时 15 毫秒
101.
102.
Vanessa Cerqueira Koppe João Felipe Coimbra Leite Costa Jair Carlos Koppe Fernando Gambin Gary Fallon Nick Davies 《Natural Resources Research》2007,16(4):293-303
Seismic reflection methods measure the time a seismic wave takes to travel through the ground, from the user defined source
to a series of signal monitoring sensors known as geophones. The measured times need to be depth converted to allow for integration
with other geological data. In order to convert from time to depth, an estimate of the rock volume velocity field must be
made. The velocity field estimate can be made by assignment of velocity estimates to a geological model independent of the
seismic processing. This article presents the results of using the acoustic geophysical log data extrapolated via sequential
Gaussian simulation to derive the velocity field. The uncertainties associated with the velocity estimates were significant
and provided the means to assess confidence limits for the actual depth determination. The technique is assessed by application
to a major coal deposit, approximately 2.1 m thick and 210 m deep. Considering only the uncertainty associated with estimating
the velocity field, half of the confidence interval values showed approximately 1 m of uncertainty in depth. The application
of sequential Gaussian simulation to model the 3D distribution of acoustic velocity can be extended to other geophysical log
parameters or derived estimates. 相似文献
103.
Calculation of magnetic anomalies caused by 2D bodies of arbitrary shape with consideration of demagnetization 总被引:1,自引:0,他引:1
Nick P. Kostrov 《Geophysical Prospecting》2007,55(1):91-115
Forward calculations of magnetic anomalies caused by two-dimensional bodies of any shape and magnetic properties may be performed either without considering demagnetization as in the equivalent source technique or taking demagnetization into account as in the volume integral equation (VIE) approach, in which, for this purpose, magnetized bodies are divided into a set of rectangular prismatic cells. Ignoring demagnetization may result in distortion of the shape and the amplitude of an anomaly, whereas rectangular cells may not be an optimal representation of the source. Moreover, an inaccurate form approximation in the VIE technique may lead to inconsistent results in the near-body region. In this paper, a method is proposed, based on the VIE approach but differing by applying triangular elementary cells. The method largely overcomes the above-mentioned limitations of the VIE technique. It allows us to delineate large and complex structures exactly and only requires the source to be divided into a few elementary cells to take demagnetization into account satisfactorily. These improvements have been attained through analytical calculation of the Green's function in the complex plane, using the theory of the Cauchy-type integral. Comparing numerical solutions with analytical solutions for homogeneous elliptic cylinders without remanence, the method is found to be consistent with the theory in the range of relative magnetic permeability of 2–20, not only far from but also at subcell distances from the body. The method is appropriate for modelling highly and inhomogeneously magnetized 2D bodies of any shape. It may be of value in interpreting underground measurements or topographic effects, as well as in modelling regional geomagnetic profiles, and it is also a convenient tool for testing questionable geological hypotheses. In the framework of the method, the gravitational anomaly for the same causative bodies can be easily calculated. However, at higher and geologically uncommon values of relative magnetic permeability, the algorithm may become unstable but may be stabilized with SVD regularization. The fact that discrepancies were found with the method employed is a basis for further research. 相似文献
104.
Thorsten Geisler Roland Vinx Nergui Martin-Gombojav Robert T. Pidgeon 《International Journal of Earth Sciences》2005,94(3):369-384
The Eckergneiss Complex (EGC) is a geologically unique medium- to high-grade metamorphic unit within the Rhenohercynian domain of the Mid-European Variscides. A previously, poorly defined conventional lower U–Pb intercept age of about 560 Ma from detrital zircons of metasedimentary rocks has led to speculations about an East Avalonian affinity of the EGC. In order to unravel the provenance and to constrain the age of the sediment protolith, we carried out sensitive high-resolution ion microprobe U–Pb analyses on detrital zircons from five different EGC quartzite occurrences. The obtained age spectrum indicates a SW Baltica provenance of the detritus. Sveconorwegian ages between 0.9–1.2 Ga are particularly well represented by analyses from metamorphic recrystallization/alteration zones penetrating into igneous zircon. Cadomian (Pan-African) ages, which might reflect a metamorphic event, could not be substantiated. Instead, zircons of igneous origin yielded concordant Lower Devonian and Silurian ages of 410±10, 419±10, and 436±6 Ma (1), implying that sedimentation of the EG protolith must have taken place after 410±10 Ma. The lower age limit of the EGC metamorphism is constrained by 295 Ma intrusion ages of the adjacent, nonmetamorphosed Harzburg Gabbronorite and Brocken Granite. Sedimentation and metamorphism must thus have taken place between about 410 Ma and 295 Ma. Given that this time span coincides with most of the sedimentation within the virtually nonmetamorphosed (lowest grade) Rhenohercynian in the Harz Mountains, including the direct vicinity of the EGC, along with the high-grade metamorphism, the EGC can hardly be seen as uplifted local basement. A possible candidate for the root region is an easterly, concealed marginal segment of the Rhenohercynian domain of the Variscides, which is tectonically overridden and suppressed by the Mid-German Crystalline Rise during continent collision. However, based on the concept of strike-slip movement of Variscan terranes with different P–T–t histories as a result of postaccretion intraplate deformation, the EGC could also represent a fault-bounded complex with an origin located far east or south east of the present location.
相似文献
Thorsten GeislerEmail: |
105.
Nick Marriner 《Quaternary Research》2006,65(1):164-171
Chrono-stratigraphic data from Tyre's ancient northern harbour delineate extensive dredging practices during the Greco-Roman and Byzantine periods. Radiocarbon dates from four cores consistently cluster between ca. 500 B.C. and 1000 A.D. and indicate rapid rates of sedimentation in the basin, namely ∼10 mm/yr during the Greco-Roman and Byzantine periods, compared to 0.5-1 mm/yr for the period 6000-4000 B.C. Absence of strata between 4000 B.C. and 500 B.C. is not consistent with a natural base-level sediment sink and cannot be interpreted as a depositional hiatus in the high-stand systems tract. Ancient dredging is further corroborated by persistent age-depth inversions within the fine-grained harbour facies. These data support removal of Middle Bronze Age to Persian period sediment strata, with deliberate overdeepening of the harbour bottom by Greco-Roman and Byzantine societies. 相似文献
106.
Research into exposure to, and experience of, environmental risk that has an explicitly spatial focus can be broadly differentiated into two strands. The first strand focuses on the responses of communities of exposure (or the threat of exposure) to some form of environmental hazard and to the policies put in place by institutional actors to manage the hazard. The second strand addresses social inequalities in exposure to environmental hazards and seeks to correlate uneven spatial distributions of risk across different social groups. It is argued that both strands are limited by their respective understandings of space - and that the way in which vulnerable communities experience environmental risk and its management will be shaped significantly by the complex interactions of different spatialisations or constructions of space. We explore this process by examining accounts of local experience of the UK’s 2001 foot and mouth disease crisis and its management in terms of the interplay of two different spatialisations: socio-cultural marginality and political-economic peripherality. We trace the relationship between these cultural and political-economic spatialisations through an analysis of the discursive mobilisation of contrasting place rhetorics. We conclude that focusing on these rhetorics can enhance our understanding of the spatial processes which are constitutive of place identity and in turn mediate the experience of environmental risk and its management. 相似文献
107.
Utility of the Hadley Centre sea ice and sea surface temperature data set (HadISST1) in two widely contrasting coral reef areas 总被引:1,自引:0,他引:1
The HadISST1 sea surface temperature data set is examined for two contrasting areas: the Chagos Archipelago, central Indian Ocean which has a small (approximately 3 degrees C) annual temperature fluctuation, and Abu Dhabi in the southern Arabian Gulf whose annual air temperature fluctuation of approximately 24 degrees C is the largest known for coral reef habitats. The HadISST1 data are shown to match air temperature records closely, both in terms of annual moving averages and residual analysis. Temperatures in 1998 caused massive mortality of corals in the Indian Ocean: sea surface temperature (SST) values causing this were 33.8 degrees C in the Arabian Gulf at a time when average daily air temperature was over 40 degrees C, while in Chagos the SST lethal to corals was 29.8-29.9 degrees C, when air temperatures peaked at about 31 degrees C. The HadISST1 record was searched back to 1870 for previous abnormal peaks: one of 29.7 degrees C was found for Chagos SST in 1972, though this did not cause coral mortality. Analysis of 12-month running means of the residuals from the annual cycle show that, between 1870 and 1999, the largest SST deviations occurred between October 1997 and May 1998 in Chagos and between August 1998 and July 1999 near Abu Dhabi. The event of 1998-1999 was the largest in these regions for at least 130 years. SSTs have risen over the last three decades at rates of about 0.22 degrees or 0.23 degrees per decade in both locations. 相似文献
108.
Zircon ages for high pressure granulites from South Bohemia, Czech Republic, and their connection to Carboniferous high temperature processes 总被引:8,自引:1,他引:7
A. Kröner P. J. O'Brien A. A. Nemchin R. T. Pidgeon 《Contributions to Mineralogy and Petrology》2000,138(2):127-142
Petrological and isotopic investigations were undertaken on high pressure granulites of granitic to mafic composition from
the Prachatice and Blansky les granulite complexes of southern Bohemia, Czech Republic. The predominant felsic granulites
are quartz + ternary feldspar (now mesoperthite)-rich rocks containing minor garnet, kyanite and rutile, and most show a characteristic
mylonitic fabric formed during retrogression along the exhumation path. Three high temperature reaction stages at distinctly
different pressures are recognized. Rare layers of intermediate to mafic composition, containing clinopyroxene, best record
a primary high pressure–high temperature stage (>15 kbar, >900 °C), and a well-defined overprint at medium pressure granulite
facies conditions (6–8 kbar, 700–800 °C) during which orthopyroxene (+plagioclase) formed from garnet and clinopyroxene. A
further high temperature overprint at lower pressure (ca. 4 kbar) is reflected in the development of cordierite- and/or andalusite-bearing
partial-melt patches in some felsic granulites.
Conventionally separated zircons from the granulites were measured on a SHRIMP II ion microprobe. Near-spherical, multifaceted
grains interpreted to be metamorphic, and short prismatic grains from the cordierite-bearing melt patch, are all concordant
and yielded indistinguishable results producing an average age, for 83 individual grain spots, of 339.8 ± 2.6 Ma (2σ). Metamorphic
grains from a meta-granodiorite associated with the granulites gave the same age (339.6 ± 3.1 Ma, mean of 9), whereas inherited
magmatic grains of the same sample yielded 367.8 ± 1.4 Ma. A mean age of 469.3 ± 3.8 Ma was obtained for two short prismatic
concordant grains in one of the granulites, whereas several of the rounded grains with ca. 340 Ma metamorphic zircon overgrowths
had much older (207Pb/206Pb minimum ages up to 1771 Ma) discordant cores. In addition to analysis of conventionally separated grains, ion-microprobe
measurements were also made on zircons extracted from thin sections (drilled-out, mounted and repolished) such that a direct
relationship between the dated zircons and petrographic position could be made. Identical results were obtained from both
preparation methods, thus showing that the considerable advantage in petrological control is not offset by any appreciable
lack of precision when compared to conventionally prepared ion-microprobe samples. All these isotopic results are identical
to those previously obtained by conventional multigrain and single-grain evaporation techniques, but rather than allowing
a greater resolution of the age of the petrographically obvious different metamorphic stages the results document, for the
first time, the apparent short time scale for high, medium and low pressure metamorphism in the granulites. The short time
period between the 340 Ma age for the high pressure granulites, as derived here and from studies of similar rocks elsewhere
in the European Variscides, and the 320–330 Ma ages for regional low pressure–high temperature metamorphism, migmatization
and granite magmatism, strongly suggests an important link between these two high temperature processes.
Received: 25 February 1999 / Accepted: 27 September 1999 相似文献
109.
Organization is recognized in the forereef–deep water slope–submarine fan system of the Burdigalian-Langhian Kaplankaya Formation. A basinwards transition from a prograding shelfal reef complex, through forereef talus, deep-water slope and laterally encroaching bypass deep-water clastic system is described, although the deep-water slope makes up the bulk of the succession. Considerable thickness variations occur between the reef and deep-water clastic complexes; these are controlled by sea-floor topography, carbonate foreslope gradient and degree of mass wasting off the platform and foreslope. The vertical and lateral heterogeneity of the Kaplankaya deep-water slope system is described from a number of localities along a 40-km-long and up to 3-km-wide exposed section of the northern margin of the Miocene Adana Basin, a foreland basin setting resulting from thrust sheet loading from the north during the Tauride Orogeny. Detailed field mapping is supplemented with vertical sedimentary logs, photomosaics, palaeontological and petrological data to investigate stratal variation, diagnostic architectural elements, controls on slope progradation, differential timing of basinward encroachment of the reefal complex and lateral onlap of the deep-water clastic system onto the slope. Three-dimensional models are presented showing the vertical and lateral facies associations in different parts of the deep-water slope system, and provide a basis for architectural prediction of geometry and relative position in such environments. 相似文献
110.
Beccy Scott Nick Ashton Kirsty E. H. Penkman Richard C. Preece Mark White 《第四纪科学杂志》2010,25(6):931-944
The late Middle Pleistocene sites in the Ebbsfleet Valley, Kent, UK, have yielded archaeological assemblages critical to understanding the early Middle Palaeolithic of northwestern Europe. Despite a long history of research, the nature and context of these assemblages are still poorly understood. This paper clarifies the stratigraphic, environmental and archaeological records at Ebbsfleet. These reflect a cold–warm–cold sequence of climatic events, preserved within part of the Taplow/Mucking Formation of the Thames (Marine Isotope Stage (MIS) 8/7/6). Levallois artefacts are shown to be restricted to the lower part of the Ebbsfleet Channel sequence (Phases I and II) and are assigned to late MIS 8/early MIS 7. This material is associated with fauna indicative of open environments during both cool and temperate conditions. Handaxe assemblages are recorded from higher up the sequence (Phases III–V), but have been redeposited from higher terrace units nearby. No primary context archaeology is apparent during these later phases of aggradation. This may indicate that humans abandoned the site once available raw material became inaccessible, and may also reflect a decline in human presence in Britain during the latter part of MIS 7. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献