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71.
Petrogenesis of Permian alkaline lamprophyres and diabases from the Spanish Central System and their geodynamic context within western Europe 总被引:1,自引:1,他引:0
D. Orejana C. Villaseca K. Billström B. A. Paterson 《Contributions to Mineralogy and Petrology》2008,156(4):477-500
Basic to ultrabasic alkaline lamprophyres and diabases intruded within the Spanish Central System (SCS) during Upper Permian.
Their high LREE, LILE and HFSE contents, together with positive Nb–Ta anomalies, link their origin with the infiltration of
sublithospheric K-rich fluids. These alkaline dykes may be classified in two distinct groups according to the Sr–Nd isotope
ratios: (1) a depleted PREMA-like asthenospheric component, and (2) a BSE-like lithospheric component. A slight enrichment
in radiogenic 207Pb and 208Pb allows the contribution of a recycled crustal or lithospheric component in the mantle sources. The intrusion of this alkaline
magmatism is likely to have occurred due to adiabatic decompression and mantle upwelling in the context of the widespread
rifting developed from Carboniferous to Permian in western Europe. The clear differences in the geochemical affinity of Lower
Permian basic magmas from north-western and south-western Europe might be interpreted in terms of a more extensive separation
of both regions during that period, until they were assembled during Upper Permian.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
72.
Sources and biological fractionation of Silicon isotopes in the Eastern Equatorial Pacific 总被引:1,自引:0,他引:1
Charlotte P. Beucher Mark A. Brzezinski Janice L. Jones 《Geochimica et cosmochimica acta》2008,72(13):3063-3073
Silicon isotopes in dissolved silicic acid were measured in the upper four kilometers between 4°N and 3°S latitude at 110°W longitude in the eastern Equatorial Pacific. Silicon isotopes became progressively heavier with silicic acid depletion of surface water as expected from biological fractionation. The value of ε estimated by applying a steady-state isotope fractionation model to data from all stations between 4°N and 3°S was −0.77 ± 0.12‰ (std. err.). When the analysis was restricted to those stations whose temperature and salinity profiles indicated that they were directly influenced by upwelling of the Equatorial Undercurrent (EUC), the resulting value of ε was −1.08 ± 0.27‰ (std. err.) similar to the value established in culture studies (−1.1‰). When the non steady state Rayleigh model was applied to the same restricted data set the resulting value of ε was significantly more positive, −0.61 ± 0.16‰ (std. err.). To the extent that the equatorial system approximates a steady state these results support a value of −1.1‰ for the fractionation factor for isotopes of Si in the sea. Without the assumption of steady state the value of ε can only be constrained to be between −0.6 and −1.1‰. Silicic acid in Equatorial Pacific Deep Water below 2000 m had a near constant δ30Si of +1.32 ± 0.05‰. That value is significantly more positive than obtained for North Pacific Deep Water at similar depths at stations to the northwest of our study area (0.9-1.0‰) and it is slightly less positive than new measures of the δ30Si of silicic acid from the silicic acid plume centered over the Cascadia basin in the Northeast Pacific (Si(OH)4 > 180 μM, δ30Si = +1.46 ± 0.12‰ (SD, n = 4). We show that the data from the equator and Cascadia basin fit a general trend of increasing δ30Si(OH)4 with increasing silicic acid concentration in the deep sea, but that the isotope values from the Northeast Pacific are anomalously light. The observed level of variation in the silicon isotope composition of deep waters from this single ocean basin is considerably larger than that predicted by current models based on fractionation during opal formation with no isotope effect during dissolution. Confirmation of such high variability in deep water δ30Si(OH)4 within individual ocean basins will require reassessment of the mechanisms controlling the distribution of isotopes of silicon in the sea. 相似文献
73.
C. R. L. Friend P. D. Kinny G. Rogers R. A. Strachan B. A. Paterson 《Contributions to Mineralogy and Petrology》1997,128(2-3):101-113
The age and Precambrian history of the Moine Supergroup within the Caledonide belt of north-west Scotland have long been contentious
issues. The Ardgour granite gneiss is essentially an in situ anatectic granite formed during deformation and regional high-grade
metamorphism from Moine metasediments. High-precision TIMS and SHRIMP U-Pb zircon dating shows that the age of the anatectic
Ardgour granite gneiss and its enclosed segregation pegmatites is 873 ± 7 Ma. This demonstrates the reality of a Neoproterozoic
episode of high-grade metamorphism in the Glenfinnan Group Moine and, contrary to previous evidence, the absence of Grenvillian-aged
metamorphism. This conclusion places constraints on Neoproterozoic palaeogeographic reconstructions of the North Atlantic
region, indicating that the Moine rocks cannot be used as a link between the Grenvillian belt of North America and the Sveconorwegian
orogen in Scandinavia. SHRIMP ages of between c. 1100 and 1900 Ma were obtained from detrital, inherited zircons and reflect
the provenance of the Glenfinnan Group Moine sediments which must, therefore, have been deposited between c. 1100 and 870 Ma.
Potential sources are found as relatively minor, tectonically bounded basement inliers within the British Caledonides, although
more widespread source areas occur outside Britain in both Laurentia and Baltica. The most important feature of the provenance
is the absence of detrital Archaean grains. This suggests that the Archaean Lewisian gneiss complex, which forms the basement
component of the western foreland to the Caledonides in Britain, was not a major contributor to the Glenfinnan Group basin.
Received: 16 June 1996 / Accepted: 29 January 1997 相似文献
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76.
Ethnic neighborhoods and ethnic economies do not always involve a single nationality or ethnic group. Quite often several groups operate side by side in the neighborhood and within the establishments themselves. This can give rise to a modification of the ethnic economy concept. We discuss an example of such a multiethnic residential and business district in Paris, the Goutte d’Or, with particular attention to three shopping streets. Although somewhat distinct from one another, each of these streets is multiethnic in regard to the proprietors, employees, and customers, and this multiethnicity extends within the establishments themselves. The primary questions we ask in this article are, first, what the nature of this ethnic economy is and how it fits within the different types of ethnic economy. Beyond this, we demonstrate how the activities taking place here reflect separate circuits of activity at separate spatial scales and what this ethnic business activity suggests for immigrant incorporation in Paris and the nature of cross-ethnic relations. To answer these questions, we rely on observation, interviews with several merchants in defined commercial corridors, and some official statistical and political information gleaned from various government sources. This Parisian neighborhood exemplifies strategies of immigrant incorporation into French society. As such, it provides a possible new model of a multiethnic economy, one that might become a common fixture in increasingly diverse cities in the world. 相似文献
77.
The Politics of Slums in the Global South: Urban informality in Brazil,India, South Africa and Peru Véronique Dupont,David Jordhus‐Lier,Catherine Sutherland and Einar Braathen (eds). Routledge,Oxon, 2016, pp. xvii + 230 (ISBN 978‐1‐138‐83981‐6). 下载免费PDF全文
Charlotte Lemanski 《Singapore journal of tropical geography》2016,37(2):272-273
78.
It's not all about wealth and beauty: Changing perceptions of fatness among Makola market women of Accra,Ghana 下载免费PDF全文
Charlotte Wrigley‐Asante Samuel Agyei‐Mensah Faustina Adomaa Obeng 《Singapore journal of tropical geography》2017,38(3):414-428
Within the African context, body shape preferences may be influenced by culture without necessarily taking into consideration health implications. Thus, fatness is culturally associated with beauty, prosperity, and prestige while thinness is perceived as a sign of ill‐health or poverty. Using a cross section of Makola market women, who traditionally are perceived as fat and affluent, our findings revealed that the perception of fatness as a sign of richness and beauty is changing due to women's access to knowledge and information on the health implications of fatness. The challenge for these women however, is adhering to healthy lifestyles despite living sedentary lives in the market place which is a conducive environment for one to become fat. We recommend that qualified professionals should encourage these women through continuous programmes on regenerative health and nutrition aimed at healthy lifestyle behaviour at the market places. The social groups that women belong to should be targeted, trained and equipped with the right information on healthy living so that they can disseminate this information to other members of their networks. 相似文献
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