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21.
Valerio Lombardo Maria Fabrizia Buongiorno Stefania Amici 《Bulletin of Volcanology》2006,68(7-8):641-651
The simultaneous solution of the Planck equation (involving the widely used “dual-band” technique) using two shortwave infrared (SWIR) bands allows for an estimate of the fractional area of the hottest part of an active lava flow (f
h) and the background temperature of the cooler crust (T
c). The use of a high spectral and spatial resolution imaging spectrometer with a wide dynamic range of 15 bits (DAIS 7915) in the wavelength range from 0.501 to 12.67 μm resulted in the identification of crustal temperature and fractional areas for an intra-crater hot spot at Mount Etna, Italy. This study indicates the existence of a relationship between these T
c and f
h extracted from DAIS and Landsat TM data. When the dual band equation system is performed on a lava flow, a logarithmic distribution is obtained from a plot of the fractional area of the hottest temperature vs. the temperature of the cooler crust. An entirely different distribution is obtained over active degassing vents, where increases in T
c occur without any increase in f
h. This result indicates that we can use scatter plots of T
c vs. fh to discriminate between different types of volcanic activity, in this case between degassing vents and lava flows, using satellite thermal data. 相似文献
22.
We report here, for the first time, on the new finding of extrusive calciocarbonatite (alvikite) rocks from the Pleistocene Mt. Vulture volcano (southern Italy). These volcanic rocks, which represent an outstanding occurrence in the wider scenario of the Italian potassic magmatism, form lavas, pyroclastic deposits, and feeder dikes exposed on the northern slope of the volcano. The petrography, mineralogy and whole-rock chemistry attest the genuine carbonatitic nature of these rocks, that are characterized by high to very high contents of Sr, Ba, U, LREE, Nb, P, F, Th, high Nb/Ta and LREE/HREE ratios, and low contents of Ti, Zr, K, Rb, Na and Cs. The O–C isotope compositions are close to the “primary igneous carbonatite” field and, thus, are compatible with an ultimate mantle origin for these rocks. The Sr–Nd–Pb–B isotope compositions, measured both in the alvikites and in the silicate volcanic rocks, indicate a close genetic relationship between the alvikites and the associated melilitite/nephelinite rocks. Furthermore, these latter products are geochemically distinct from the main foiditic-phonolitic association of Mt. Vulture. We propose a petrogenetic/geodynamic interpretation which has important implications for understanding the relationships between carbonatites and orogenic activity. In particular, we propose that the studied alvikites are generated through liquid unmixing at crustal levels, starting from nephelinitic or melilititic parent liquids. These latter were produced in a hybrid mantle resulting from the interaction through a vertical slab window, between a metasomatized mantle wedge, moving eastward from the Tyrrhenian/Campanian region, and the local Adriatic mantle. The occurrence of carbonatite rocks at Mt. Vulture, that lies on the leading edge of the Southern Apennines accretionary prism, is taken as an evidence for the carbonatation of the mantle sources of this volcano. We speculate that mantle carbonatation is related to the introduction of sedimentary carbon from the Adriatic lithosphere during Tertiary subduction. 相似文献
23.
淀山湖太湖形成的古生物证据 总被引:3,自引:0,他引:3
通过对湖泊周围钻孔样品的微体古生物分析,根据化石群的生态特征,结合岩性、孢粉、14C等资料探讨晚更新世中期以来淀山湖、太湖沉积环境的演变过程,并比较其异同。现代湖泊的形成于全新世晚期。 相似文献
24.
25.
本文选择大兴安岭北段诺敏大山地区早白垩世侵入岩进行了锆石U-Pb年代学和地球化学研究,探讨该区域侵入岩成因类型、岩浆来源及构造环境。该区侵入岩岩性主要为正长花岗岩、正长花岗斑岩和似斑状正长花岗岩,对其中正长花岗岩样品进行LA-ICP-MS锆石U-Pb测年表明,正长花岗岩侵位年龄为129.5±0.4 Ma,应为早白垩世岩浆活动的产物,结合区内侵入岩与地层相互接触关系,本区侵入岩形成时代为早白垩世。区内侵入岩具有富硅(SiO2= 67.36%~74.09%)、富碱(K2O+Na2O= 8.88%~9.34%)、高铝(Al2O3= 12.56%~16.15%),低MgO、TiO2、CaO的特点,属于高钾钙碱性岩石系列;铝饱和指数(A/CNK)为0.94~1.31,为准铝质—过铝质岩石。微量元素富集Rb、U、Th、K等大离子亲石元素,强烈亏损Ti、Nb、Sr、P等高场强元素,具有明显的Eu负异常,属于高分异I型花岗岩。岩石Rb/Sr为0.9~2.0,Sr/Y为4.2~7.2,显示出高Sr、低Y的特点,指示岩浆源区为地壳物质的部分熔融。结合区域研究成果,蒙古—鄂霍茨克构造域在早白垩世之前已结束碰撞,诺敏大山地区早白垩世岩浆活动可能发生在蒙古—鄂霍茨克造山后的伸展环境。 相似文献
26.
Four co-ignimbrite plumes were generated along the flow path of the pyroclastic flow of 7 August 1980 at Mount St. Helens.
Three of the plumes were generated in discrete pulses which can be linked to changes in slope along the channel. One plume
was generated at the mouth of the channel where the flow decelerated markedly as it moved onto the lower slopes of the pumice
plain. Plume generation here may be triggered by enhanced mixing due to a hydraulic jump associated with an abrupt slope change.
Measurements of plume ascent velocity and width show that the co-ignimbrite plumes increased in velocity with height. The
plumes have initial velocities of 1–2 m/s. Two of the plumes reached a velocity maximum (4.6 and 8.8 m/s, respectively, at
heights of 270 and 315 m above the flow) and thereafter decelerated. The other plumes reached velocities of 6.2 and 13 m/s.
The four plumes become systematically less energetic downstream as measured by their ascent rates, which can be interpreted
as a consequence of decreasing interaction of the pyroclastic flow front with the atmosphere. Theoretical models of both co-ignimbrite
plumes and discrete co-ignimbrite clouds assume that there is no initial momentum, and both are able to predict the observed
acceleration stage. The rising plumes mix with and heat air and sediment out particles causing their buoyancy to increase.
Theoretical models agree well with observations and suggest that the initial motion of the ascending material is best described
as a discrete thermal cloud which expands as it entrains air, whereas the subsequent motion of the head may become influenced
by material supplied from the following plume. The models agree well with observations for an initial temperature of the ash
and air mixture in the range of 500–600 K, which is in turn consistent with the measured initial ash temperature of around
920 K. Ash masses of 3.4×105 to 1.8×106 kg are estimated.
Received: 11 January 1996 / Accepted: 7 October 1996 相似文献
27.
《The Professional geographer》1986,38(3):295-316
Book Reviewed in this article: Marine Resources of Kuwait: Their Role in the Development of Non-oil Resources . Fatimah H. Y. al -Abdul -Razzak Recollections of a Revolution: Geography as Spatial Science . Mark Billinge , Derek Gregory and Ron Martin Entre l'Eden et l'Utopie . Luc Bureau Developments in Political Geography . M. A. Busteed The Elements of Graphing Data . William S. Cleveland Rural Resource Management . Paul J. Cloke and Chris C. Park Third World Atlas . Ben Crow and Alan Thomas Exploitation, Conservation, Preservation: A Geographic Perspective on Natural Resource Use . Susan L. Cutter , Hilary Lambert Renwick, and William H. Renwick . Wine Regions of the Southern Hemisphere . Harm Jan de Blij Regional Development: Problems and Policies in Eastern and Western Europe . George Demko The Geographer at Work . Peter R. Gould Change in the Amazon Basin . John Hemming Geography Since the Second World War . R. J. Johnston and P. Claval Urbanization in China: Town and Countryside in a Developing Economy 1949–2000 A.D. , R. J. R. Kirkby Transport and Communications for Pacific Microstates: Issues in Organisation and Management . Christopher C. Kissling Fluvial Forms and Processes . David Knighton The Urban Millennium . Josef W. Konvitz Technological Transition in Cartography . Mark Stephen Monmonier Field Guide to Soils and the Environment: Applications of Soil Surveys . Gerald W. Olson Northern Australia: The Arenas of Life and Ecosystems on Half a Continent . Don Parkes A Killing Rain: The Global Threat of Acid Rain . Thomas Pawlick From the Family Farm to Agribusiness: The Irrigation Crusade in California and the West, 1850–1931 . Donald J. Pisani Hybrid Maize Diffusion in Kenya . Franz -Michael Rundquist Warning and Response to the Mount St. Helens Eruption . Thomas F. Saarinen and James L. Sell Coastal Geomorphology in Australia . B. G. Thom Tropical Rain Forests of the Far East , 2nd ed . T. C. Whitmore The Dark Side of the Earth . Robert Muir Wood Categorical Data Analysis for Geographers and Environmental Scientists , Neil Wrigley 相似文献
28.
The Valhalla uranium deposit, located 40 km north of Mount Isa, Queensland, Australia, is an albitite-hosted, Mesoproterozoic
U deposit similar to albitite-hosted uranium deposits in the Ukraine, Sweden, Brazil and Guyana. Uranium mineralisation is
hosted by a thick package of interbedded fine-grained sandstones, arkoses and gritty siltstones that are bound by metabasalts
belonging to the ca. 1,780 Ma Eastern Creek Volcanics in the Western Succession of the Mount Isa basin. Alteration associated
with U mineralisation can be divided into an early, main and late stage. The early stage is dominated by laminated and intensely
altered rock comprising albite, reibeckite, calcite, (titano)magnetite ± brannerite. The main stage of mineralisation is dominated
by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite, apatite,
(uranoan)-zircon, uraninite, anatase, albite, reibeckite, calcite and hematite. The late stage of mineralisation comprises
uraninite, red hematite, dolomite, calcite, chlorite, quartz and Pb-, Fe-, Cu-sulfides. Brannerite has U–Pb and Pb–Pb ages
that indicate formation between 1,555 and 1,510 Ma, with significant Pb loss evident at ca. 1,200 Ma, coincident with the
assemblage of Rodinia. The oldest ages of the brannerite overlap with 40Ar/39Ar ages of 1,533 ± 9 Ma and 1,551 ± 7 Ma from early and main-stage reibeckite and are interpreted to represent the timing
of formation of the deposit. These ages coincide with the timing of peak metamorphism in the Mount Isa area during the Isan
Orogeny. Lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater
Mount Isa district reveals that mineralisation involved the removal of K, Ba and Si and the addition of Na, Ca, U, V, Zr,
P, Sr, F and Y. U/Th ratios indicate that the ore-forming fluid was oxidised, whereas the crystal chemistry of apatite and
reibeckite within the ore zone suggests that F− and were important ore-transporting complexes. δ18O values of co-existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380°C and involved a
fluid having δ18Ofluid values between 6.5 and 8.6‰. Reibeckite δD values reveal that the ore fluid had a δDfluid value between −98 and −54‰. The mineral assemblages associated with early and main stages of alteration, plus δ18Ofluid and δDfluid values, and timing of the U mineralisation are all very similar to those associated with Na–Ca alteration in the Eastern
Succession of the Mount Isa basin, where a magmatic fluid is favoured for this style of alteration. However, isotopic data
from Valhalla is also consistent with that from the nearby Mount Isa Cu deposit where a basinal brine is proposed for the
transport of metals to the deposit. Based on the evidence to hand, the source fluids could have been derived from either or
both the metasediments that underlie the Eastern Creek Volcanics or magmatism that is manifest in the Mount Isa area as small
pegmatite dykes that intruded during the Isan Orogeny. 相似文献
29.
表碛覆盖型冰川是中国西部较为常见的冰川类型。表碛层存在于大气—冰川冰界面,强烈影响大气圈与冰冻圈之间的热交换。表碛厚度的空间异质性可极大地改变冰川的消融率和物质平衡过程,进而影响冰川径流过程和下游水资源。基于Landsat TM/TIRS数据,运用能量平衡方程反演了贡嘎山地区冰川表碛厚度,研究了贡嘎山地区冰川在1990—2019年间表碛覆盖范围及厚度变化情况,同时对比了东西坡差异。结果表明:① 贡嘎山地区冰川表碛扩张总面积达43.824 km2。其中,海螺沟冰川扩张2.606 km2、磨子沟冰川1.959 km2、燕子沟冰川1.243 km2、大贡巴冰川0.896 km2、小贡巴冰川0.509 km2、南门关沟冰川2.264 km2,年均扩张率分别为3.2%、11.1%、1.5%、0.9%、1.0%和6.5%;② 海螺沟冰川、磨子沟冰川、燕子沟冰川、大贡巴冰川、小贡巴冰川、南门关沟冰川表碛平均增厚分别为5.2 cm、3.1 cm、3.7 cm、6.8 cm、7.3 cm和13.1 cm;③ 西坡冰川表碛覆盖度高,表碛覆盖年均扩张率低,冰川末端退缩量小;东坡冰川表碛覆盖年均扩张率高,但表碛覆盖度总体低于西坡,冰川末端退缩量大。 相似文献
30.
M. F. Grasso R. Clocchiatti F. Carrot C. Deschamps F. Vurro 《Environmental Geology》1999,37(3):207-217
The aim of this paper is to verify whether lichens have the capacity to accumulate atmospheric contaminators linked to volcanic
activity. About 100 lichens were collected in 1994 and 1995 from two active volcanic areas in Italy: Mount Etna and Vulcano
Island. Twenty-seven elements were analyzed for each individual lichen using Instrumental Neutronic Activation Analysis and
Inductively Coupled Plasma-Mass Spectrometry. Lichen composition reflects the contribution of the volcanic particulate material,
and the two areas investigated can be distinguished on the basis of the concentration of some lithophile elements. Moreover,
the distribution in lichens of the elements (As, Sb, Br, Pb) – derived from gas emissions (plume, fumaroles) – also shows
different geochemical trends on Mt. Etna and Vulcano.
Received: 20 April 1998 · Accepted: 4 July 1998 相似文献