全文获取类型
收费全文 | 966篇 |
免费 | 50篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 92篇 |
地球物理 | 239篇 |
地质学 | 453篇 |
海洋学 | 61篇 |
天文学 | 103篇 |
综合类 | 4篇 |
自然地理 | 53篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 16篇 |
2020年 | 20篇 |
2019年 | 17篇 |
2018年 | 25篇 |
2017年 | 35篇 |
2016年 | 25篇 |
2015年 | 40篇 |
2014年 | 41篇 |
2013年 | 61篇 |
2012年 | 51篇 |
2011年 | 60篇 |
2010年 | 70篇 |
2009年 | 57篇 |
2008年 | 54篇 |
2007年 | 46篇 |
2006年 | 46篇 |
2005年 | 51篇 |
2004年 | 44篇 |
2003年 | 31篇 |
2002年 | 32篇 |
2001年 | 22篇 |
2000年 | 15篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 15篇 |
1994年 | 2篇 |
1993年 | 14篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 1篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1022条查询结果,搜索用时 15 毫秒
91.
Catherine Chauvel Albrecht W. Hofmann Philippe Vidal 《Earth and Planetary Science Letters》1992,110(1-4)
himu, em i andem ii are three of the main geochemical mantle components that give rise to oceanic island basalts [1]. They represent the end members that produce the extreme isotopic compositions measured on intraplate volcanics. In French Polynesia, all three mantle components are represented in volcanic rocks. The characteristichimu signature is found in Tubuai, Mangaia and Rurutu,em i is present in the source of Rarotonga and Pitcairn volcanics andem ii dominates the composition of most Society Islands. Intermediate values between the three end members are found on most islands.We suggest that the three components are not independent but are physically related in the mantle. Thehimu component is thought to be recycled oceanic crust that lost part of its Pb through hydrothermal processes prior to and during subduction.em i andem ii are believed to acquire their isotopic and trace element characteristics through entrainment of sediments that were subducted together with the oceanic crust.The trace element pattern and the isotopic composition ofhimu lavas can be quantitatively modelled using a mixture of 25% old recycledmorb crust and 75% mantle peridotite. The extreme Pb composition is modelled assuming that Pb was lost from oceanic crust when hydrothermal alteration at the ridge leached Pb from the basalt to redeposit it as sulphides on top of and throughout the crust, followed by preferential dissolution of sulphides during dehydration in the subduction zone. These processes led to a drastic increase of theU/Pb ratio of the subducted material which evolved over 2 Ga to very radiogenic Pb isotopic compositions. Pb isotopic compositions similar to those ofem i andem ii are modelled assuming that sediments with average crustal Pb isotopic compositions were subducted and recycled into the mantle together with the underlyingmorb oceanic crust. Pelagic sediments (μ 5 andκ 6) account for the Pb isotopic composition ofem i whereas terrigenous sediments (μ 10 andκ 4.5) evolve towards theem ii end member. A few percent of sediment in the recycled crust-sediment mixture will destroy the characteristic Pb isotopic signature of thehimu component. This, together with the low probability of isolating oceanic crust in the mantle for 2 Ga, explains why the extremehimu composition, as seen on Tubuai and St Helena, is sampled so rarely by oceanic volcanism. 相似文献
92.
Thierry Merceron Philippe Vieillard Anne-Marie Fouillac Alain Meunier 《Contributions to Mineralogy and Petrology》1992,112(2-3):279-292
Detailed petrographic and mineralogic investigations of an albite-lepidolite granite at Echassières (Massif Central, France; scientific deep drill program) shows the existence of hydrothermal stages which are closely related to the magmatic and structural history. According to fluid inclusion data, K-Ar datations and 18O/16O-D/H compositions of secondary minerals, two successive hydrothermal periods have been recognized. The early one (273–268 million years) produced a series of aluminous phyllosilicates: muscovite, pyrophyllite, donbassite, tosudite, kaolinite which are observed as vein deposits (<10 mm wide) and alteration products of primary minerals in wall-rocks. The vein system was sealed by monomineralic assemblages during a cooling period (400–150°C). This early hydrothermal alteration stage was controlled by interactions of rock with low salinity (1–10 wt% NaCl equivalent) fluids expelled from the granitic body during the cooling processes. The chemical properties of these fluids were the following: low pH, very low Mg and Fe and high Li, Na and K contents. Thermodynamic calculations show that the sequence pyrophyllite, Li-bearing donbassite, tosudite is mostly temperature dependent. From the chemical composition of secondary minerals and isotopic data it can be deduced that these fluids, which have a meteoric origin, have been expelled from the granite body during its cooling period and after interaction with it at high temperature. The late hydrothermal stage corresponds to deposits of fluorite and Fe-Mg rich illite (151 million years) in subvertical fractures. Temperature conditions did not exceed 250° C and fluids came through the surrounding metamorphic rocks into the granitic body. IIlite/smectite mixed-layer minerals have been identified in subvertical fractures which were opened during Tertiary periods. In the host micaschists, successive hydrothermal alterations took place during the cooling of the Beauvoir granite. Early magmatic fluids interacted with these micaschists. Locally, the metamorphic assemblage is replaced by a metasomatic one. Secondary topaz and (F, Li)-rich mica crystals were formed over a range of 450 of 150°C. Later hydrothermal fluids reacted with the country rocks to form phengite-biotite, chlorite-illite and kaolinite over a range of 300 to 150°C. Illite/smectite mixed-layer minerals crystallized in the roof micaschists and within the Beauvoir granite during the Tertiary alteration period. Meteoric water invaded open fractures producing supergene alteration mineral assemblages. 相似文献
93.
Jean-Claude Andr Jean-Yves Caneill Michel Dqu Philippe Rogel Laurent Terray Yves Tourre 《Comptes Rendus Geoscience》2002,334(16):1115
The atmosphere and the ocean are subject to many dynamical instabilities, which limit the time during which their behaviour can be deterministically forecasted. At longer timescales, the atmosphere can be predicted at best using statistical methods, as a response to external forcing linked to sea- and land-surface anomalies. Climate being defined as the mean of atmospheric states, it appears that it can be predicted up to a few months in advance, which is the characteristic time of the so-called slow components of the climate system. Forecasting can sometimes be extended to longer time ranges, especially when the coupled ocean–atmosphere system exhibits internal variability modes, with characteristic times of a few years. Seasonal climate forecasting is most often based upon Monte-Carlo simulations, where the various realisations correspond to slightly different initial conditions. The present sate-of-the-art in Europe (ECMWF) and/or in the USA (IRI) allows to forecast such major phenomena, as El Niño, up to six months in advance. Finally, some parameters may exhibit predictability at still longer time-ranges (inter-annual to decadal), but only for certain regions. The example of electricity production is used to underline the potentially large economical benefit of seasonal climate forecasting. To cite this article: J.-C. André et al., C. R. Geoscience 334 (2002) 1115–1127.
Résumé
L'atmosphère et l'océan sont le siège d'instabilités dynamiques, qui limitent la durée pendant laquelle il est possible d'en prévoir l'évolution de façon déterministe. Au-delà, l'atmosphère n'est plus prévisible, au mieux, que de façon statistique, en fonction du forçage externe qu'exerce(nt) sur elle l'océan et/ou la surface des continents. Le climat (au sens d'une moyenne des états atmosphériques) se révèle ainsi prévisible jusqu'à des échéances temporelles de quelques mois, échelle de temps caractéristique des composantes dites « lentes » du système climatique. La prévision peut s'étendre à des échéances parfois plus longues, dans le cas où le système couplé océan–atmosphère posséderait des modes de variabilité temporelle de périodes caractéristiques de quelques années. La prévision climatique saisonnière est très souvent construite à partir de simulations de type Monte-Carlo, avec des ensembles de réalisations utilisant des conditions initiales légèrement différentes. Dans l'état actuel de ces prévisions, qu'elles soient réalisées en Europe (CEPMMT) ou aux États-Unis (IRI), il est possible de prévoir environ six mois à l'avance un certain nombre de phénomènes climatiques, en particulier ceux liés aux épisodes dits « El Niño », pour lesquels l'amplitude des variations est suffisamment importante. Il existe, par ailleurs, une prévisibilité à encore plus longue échéance (inter-annuelle à décennale), mais seulement pour certains paramètres et certaines régions. L'exemple de la production d'électricité montre l'importance économique potentielle très grande de la prévision climatique saisonnière. Pour citer cet article : J.-C. André et al., C. R. Geoscience 334 (2002) 1115–1127. 相似文献94.
A calibration method to solve the groundwater inverse problem under steady- and transient-state conditions is presented. The method compares kriged and numerical head field gradients to modify hydraulic conductivity without the use of non-linear optimization techniques. The process is repeated iteratively until a close match with piezometric data is reached. The approach includes a damping factor to avoid divergence and oscillation of the solution in areas of low hydraulic gradient and a weighting factor to account for temporal head variation in transient simulations. The efficiency of the method in terms of computing time and calibration results is demonstrated with a synthetic field. It is shown that the proposed method provides parameter fields that reproduce both hydraulic conductivity and piezometric data in few forward model solutions. Stochastic numerical experiments are conducted to evaluate the sensitivity of the method to the damping function and to the head field estimation errors. 相似文献
95.
John Douglas Didier Bertil Agathe Roullé Pascal Dominique Philippe Jousset 《Journal of Seismology》2006,10(3):271-299
Strong-motion networks have been operating in the Caribbean region since the 1970s, however, until the mid-1990s only a few analogue stations were operational and the quantity of data recorded was very low. Since the mid-1990s, digital accelerometric networks have been established on islands within the region. At present there are thought to be about 160 stations operating in this region with a handful on Cuba, 65 on the French Antilles (mainly Guadeloupe and Martinique), eight on Jamaica, 78 on Puerto Rico (plus others on adjacent islands) and four on Trinidad.After briefly summarising the available data from the Caribbean islands, this article is mainly concerned with analysing the data that has been recorded by the networks operating on the French Antilles in terms of their distribution with respect to magnitude, source-to-site distance, focal depth and event type; site effects at certain stations; and also with respect to their predictability by ground motion estimation equations developed using data from different regions of the world. More than 300 good quality triaxial acceleration time-histories have been recorded on Guadeloupe and Martinique at a large number of stations from earthquakes with magnitudes larger than 4.8, however, most of the records are from considerable source-to-site distances. From the data available it is found that many of the commonly-used ground motion estimation equations for shallow crustal earthquakes poorly estimate the observed ground motions on the two islands; ground motions on Guadeloupe and Martinique have smaller amplitudes and are more variable than expected. This difference could be due to regional dependence of ground motions because of, for example, differing tectonics or crustal structures or because the ground motions so far recorded are, in general, from smaller earthquakes and greater distances than the range of applicability of the investigated equations. 相似文献
96.
André Burnol Francis Garrido Philippe Baranger Catherine Joulian Marie-Christine Dictor Françoise Bodénan Guillaume Morin Laurent Charlet 《Geochemical transactions》2007,8(1):12
High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the
release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis.
Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted.
Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The
biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and
genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing
bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase
amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant
after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant,
or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial
solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst
X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction
revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results.
The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high
Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically
more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more
weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully
applied to recent experimental results on the release of arsenic from Bengal delta sediments. 相似文献
97.
The assessment of grain size distribution and plasticity of loose geological material, during in situ geological investigations, is not obvious. Visual appreciation allows an approximative quantification of the coarse granulometric fractions, but not of the fine ones. Field soils determination methods suggested until now, are visual and tactile tests leading to a very rough estimate, which is only qualitative and not very reproducible. The new proposed field test (GEOLEP method) allows a quick quantification of the fine fraction of loose material. It allows the determination of the sand fraction (fine and medium grained sands) as well as the methylene blue value of the samples. The necessary equipment to perform this test is light and compact and the time needed to analyze one sample is approximately 15 min. Thus it is also possible to carry out numerous measurements in one day. The calibrations were carried out on a selection of 13 natural samples, chosen for their representativeness of the typical alpine quaternary deposits. The results obtained with GEOLEP method are relevant compared with standardized laboratory tests; the obtained correlation indexes are of 73% for the comparison with laboratory stain test results and of 89% with a laboratory method using a similar procedure than the field test. The correlation we performed with Atterberg's limits tests shows that a rough approximation of plasticity index can also be obtained (R2 = 75%). This method thus brings a new tool which should allow taking into account the lithological factor (by some quantitative and representative variables) in a reliable way for the evaluation of landslide hazards. 相似文献
98.
Control of wind strength and frequency in the Aral Sea basin during the late Holocene 总被引:1,自引:0,他引:1
Philippe Sorrel Hedi Oberhnsli Nikolaus Boroffka Danis Nourgaliev Peter Dulski Ursula Rhl 《Quaternary Research》2007,67(3):371-382
Changing content of detrital input in laminated sediments traced by XRF scanning and microfacies analyses reflect prominent variations in sedimentation processes in the Aral Sea. A high-resolution record of titanium from a core retrieved in the northwestern Large Aral Sea allows a continuous reconstruction of wind strength and frequency in western Central Asia for the past 1500 yr. During AD 450–700, AD 1210–1265, AD 1350–1750 and AD 1800–1975, detrital inputs (bearing titanium) are high, documenting an enhanced early spring atmospheric circulation associated with an increase in intensity of the Siberian High pressure system over Central Asia. In contrast, lower titanium content during AD 1750–1800 and AD 1980–1985 reflects a diminished influence of the Siberian High during early spring with a reduced atmospheric circulation. A moderate circulation characterizes the time period AD 700–1150. Unprecedented weakened atmospheric circulation over western Central Asia are inferred during ca. AD 1180–1210 and AD 1265–1310 with a considerable decrease in dust storm frequency, sedimentation rates, lamination thickness and detrital inputs (screened at 40-μm resolution). Our results are concurrent with changes in the intensity of the Siberian High during the past 1400 yr as reported in the GISP2 Ice Core from Greenland. 相似文献
99.
Philippe Erdmer 《Contributions to Mineralogy and Petrology》1981,76(1):109-115
The interbedding of pelite and calc-schist in part of the contact aureole of a Devonian (biotite K-Ar age 346±4 Ma) granite pluton that straddles the Quebec-Vermont border offers an opportunity to compare metamorphic conditions prevailing in both rock types, and to test for internal consistency among several different geothermometers and geobarometers.Microprobe analyses and recent thermodynamic data are used with simple activity-composition models to estimate P-T-X
fluid conditions near the sillimanite zone. Calculations yield the following results: P=2 to 3 kb, and T =400° to 600° C in the inner one kilometre of the aureole;
was around 0.8. Estimates are based on the calc-silicate isobaric invariant assemblages tremolite-K-feldspar-plagioclase-clinozoisite-phlogopite-calcite-quartz and diopside-tremolite-plagiolase-clinozoisite-calcite-quartz, and the paragonite-andalusite-sillimanite-albite-quartz equilibrium. The solid-solid reaction phlogopite+2 diopside + 4 quartz=tremolite+K-feldspar in the calc-schist (combined with the andalusite-sillimanite equilibrium), and phase relations in the granite yield apparently inconsistent results.The implied 6 to 10 km of cover at the time of intrusion may have been provided by subsequently eroded thrust sheets. 相似文献
100.
François Nicot Philippe Gotteland David Bertrand Stéphane Lambert 《国际地质力学数值与分析法杂志》2007,31(13):1477-1515
Geo‐composite cellular structures are an efficient technological solution for various applications in civil engineering. This type of structure is particularly well adapted to resisting rockfalls and can act as a defensive structure. However, the design of such structures is for the most part empirically based; this lack of research‐based design stagnates optimization and advanced development. In this paper, the mechanical behaviour of a geo‐composite cellular structure is investigated using a multi‐scale approach, from the individual cell made up of an assembly of rocky particles contained in a wire netting cage to the entire structure composed of a regular array of cells. Based on discrete modelling of both the cell and structure scales, a computational tool has been developed for design purposes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献