全文获取类型
收费全文 | 748篇 |
免费 | 19篇 |
国内免费 | 14篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 51篇 |
地球物理 | 148篇 |
地质学 | 350篇 |
海洋学 | 40篇 |
天文学 | 141篇 |
自然地理 | 40篇 |
出版年
2021年 | 5篇 |
2019年 | 7篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 15篇 |
2015年 | 13篇 |
2014年 | 20篇 |
2013年 | 46篇 |
2012年 | 16篇 |
2011年 | 24篇 |
2010年 | 18篇 |
2009年 | 37篇 |
2008年 | 31篇 |
2007年 | 23篇 |
2006年 | 36篇 |
2005年 | 37篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 41篇 |
2001年 | 27篇 |
2000年 | 17篇 |
1999年 | 10篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 13篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 16篇 |
1989年 | 16篇 |
1988年 | 5篇 |
1987年 | 23篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 12篇 |
1981年 | 9篇 |
1980年 | 8篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1975年 | 8篇 |
1974年 | 13篇 |
1971年 | 4篇 |
1970年 | 5篇 |
1966年 | 3篇 |
排序方式: 共有781条查询结果,搜索用时 15 毫秒
621.
Geochemistry of an oceanite-ankaramite-basalt suite from East Island,Crozet Archipelago 总被引:1,自引:0,他引:1
Bernard M. Gunn Ramon Coy-Yll Norman D. Watkins Christian E. Abranson Jacques Nougier 《Contributions to Mineralogy and Petrology》1970,28(4):319-339
The petrology and geochemistry of East Island have been investigated for the first time. The island is a deeply dissected remnant of a Pleistocene shield volcano, one of several emerging from an oceanic rise forming part of the southwest branch of the Indian Ocean ridge system. The lavas form a flat-lying sequence of oceanites, ankaramites, olivine basalts and feldsparphyric basalts, the ankaramites containing 1 cm phenocrysts of diopsidic clinopyroxene. X-Ray fluorescence analyses were made of 43 lavas for the major elements plus Cr, Ni, Rb, Sr, Ba, Pb, and Th and the minerals were analysed by electron microprobe. The elements Mg, Cr, and Ni are strongly concentrated in spinel, olivine and clinopyroxene phases and in the ankaramites and oceanite lavas with maximum concentrations of 18% MgO, 1,000 ppm Cr, 380 ppm Ni, while Al, Ti, K, Rb, Ba, Th, Na, P, Sr concentrate in the groundmass and in the feldspathic and aphyric basalts. The elements Si, Ca, Fe and Mn remain virtually constant throughout the series.Correlations of +0.95 or better exist between the concentrations of elements within the two groups given above, and negative correlations between elements in different groups. The fractionation trends are unique with respect to the constant Al/Ti ratio and K/Sr ratio, but all trends may be reproduced by calculating the effect of subtraction of suitable amounts of chromite, olivine and low Ti clinopyroxene from an alkaline olivine basalt parent. Either fractionation has taken place involving these three phases under low pressure conditions or it is the result of different degrees of partial melting of mantle material.A complex magnesian chrome spinel is found in the ankaramites and is often jacketed by a chromian titanomagnetite. A complete series of intermediate compositions appears to exist between the two end members. 相似文献
622.
Jacques Touret 《Lithos》1971,4(3):239-249
The basement of Southern Norway is a genetically homogeneous migmatite complex in which old supracrustals produced granitic and granodioritic ‘neosome’ during a late Precambrian (109 years ago) regional metamorphism. Observed isograds of critical minerals: muscovite, cordierite, orthopyroxene indicate that the Telemark amphibolite facies in the North passes into the coastal Bamble granulite facies in the South. The data of expeimental petrology suggest that the transition, which took place at temperatures of 700–800°C, is essentially due to a decrease of the partial water pressure. PH2O was equal to total pressure Ps in the amphibolite facies and lower than 2 kb in the granulite facies. 相似文献
623.
Prof. Georges Millot Prof. Jacques Lucas Hélène Paquet 《International Journal of Earth Sciences》1966,55(1):1-20
Résumé Les dégradations des minéraux argileux sont fréquentes dans les altérations. Elles comportent une évolution des réseaux cristallins depuis les micas et chlorites jusqu'aux minéraux ouverts comme les vermiculites et les montmorillonites par l'intermédiaire d'édifices interstratifiés. Les agradations constituent le mécanisme réciproque et sont fréquentes dans la sédimentation et la diagenèse. Elles régénèrent par cicatrisation, construction et croissance, les phyllites caractéristiques du prémétamorphisme: illite et chlorite. Ces transformations minérales dépendant des milieux naturels sont un chapitre important de la Géochimie des silicates de l'Hydrosphère.
The clay mineral degradations are frequent during weathering. They involve an evolution of the crystal lattices, from the micas and the chlorites to the open-minerals, through the mixed-layers. The aggradations constitute the reciprocal mechanism and they are frequent during sedimentation and diagenesis. Through cicatrization, construction and growth, they regenerate the phyllites typical of premetamorphism: illite and chlorite. These mineral transformations, subject to the natural environments, are an important chapter of the Geochemistry of Hydrosphere silicates.
Zusammenfassung Während der Verwitterungen kommt oft ein Abbau der Tonminerale vor, der sich durch die Entwicklung des Gitters von Glimmer und Chlorit, über ein Zwischenstadium von Wechsellagertonen, zu offenen Mineralen wie Vermiculit und Montmorillonit kennzeichnet. Der entgegengesetzte Vorgang spielt sich in dem, in Ablagerung und Diagenese häufigen Aufbau ab. So werden die charakteristischen Phyllosilikate der Vormetamorphose: Illit und Chlorit, durch Vernarbung, Aufbau und Anwachsen der Gitter wieder hergestellt. Diese Veränderungen, die von den Bedingungen der natürlichen Milieus abhängen, stellen ein wichtiges Kapitel der Geochemie der Hydrosphärensilikate dar.
. .相似文献
624.
The level fluctuations of Lake Ilay, Jura (France) during the last three millennia are reconstructed from sedimentological and malacological analyses of a core that is well-dated by tree-ring, radiocarbon and pollen datings. Changes in sediment facies, in carbonate concretion assemblages and in mollusc assemblages highlight a major lowering phase atc. 1550 BP and minor lowering phases atc. 2800 BP and shortly before AD 1394. Rises in lake level developed during the early Subatlantic and betweenc. 1500 and 1000 BP. These data are in good agreement with other proxy data from higher European and American latitudes. These correlations support the climatic origin of the level fluctuations of the Lake Ilay during the late Holocene. They suggest that the mediaeval climatic optimum is centred rather in the early than the late Middle Age. 相似文献
625.
626.
The Dog Creek archaeological site (NcVi‐3), located in the northern Yukon, provides evidence of complex site transformational processes related to microclimatic conditions occurring since the mid‐Holocene. Geoarchaeological research at Dog Creek sought to interpret site formation processes in order to understand the relationship between surficial artifacts, buried artifacts, and stratified sediments. It also attempted to reconstruct the periglacial processes that were active in transforming the site and their relationships to microclimatic conditions. Sedimentology and fabric analysis show that artifacts were buried by solifluction and disturbed by frost heave and cryoturbation. Radiocarbon dating and pollen analysis demonstrated that solifluction took place approximately 5200–2000 years ago when a spruce forest existed at the site. This evidence suggests an onset of cooling conditions that continues to the present. After the mid‐Holocene, the spruce treeline began to move south toward its present position. © 2001 John Wiley & Sons, Inc. 相似文献
627.
628.
A 1.5-dimensional, 1.5-layer shallow water model and an ensemble Kalman filter are used to evaluate the feasibility of estimating friction parameters and determining friction laws of oceanic gravity currents. The two friction laws implemented are a linear Rayleigh friction and a quadratic drag law. We demonstrate that the assimilation procedure rapidly estimates the total frictional force, whereas the distinction between the two laws is evolving on a slower time scale. We also demonstrate that parameter estimation can, in this way, choose between different parametrisations and help to discriminate between physical laws of nature by estimating the coefficients presented in such parametrisations. 相似文献
629.
In 2007, the Government of Ecuador announced the Yasuní-ITT Initiative: a proposal to forego exploiting 20% of its oil reserves located in the Yasuní National Park – home to one of the earth’s most biodiverse places and several indigenous groups living in voluntary isolation. In exchange, Ecuador asked the international community for $3.6 billion, roughly half the projected revenues of conventional oil extraction. Five years later, Ecuador received less than 10% of the required pledges and the initiative was canceled. Many accounts emphasized the then President Rafael Correa’s perceived untrustworthiness as key in explaining the initiative’s failure. This article instead examines the role of entrenched institutions of the petrostate, emphasizing how the initiative defied expectations by offering a post-extractivist path for Ecuador. Despite its failure, this horizon continues to orient debates on development and extractivism, forming “afterlives” of a call to mitigate climate change by leaving oil in the ground. 相似文献
630.
E. Jacques J. C. Ruegg J. C. Lépine P. Tapponnier G. C. P. King & A. Omar 《Geophysical Journal International》1999,138(2):447-469
The Ethiopian side of central Afar was struck in August 1989 by the largest seismic sequence (three 6.1 ≤ M s ≤ 6.3 events, 15 with M s or m b ≥ 5.0) since that of Serdo in 1969. Using the Djibouti seismological network, we relocated 297 of the events of that sequence. As most of the large events took place outside the network, we assessed the accuracy and stability of earthquake relocations by using three different velocity models and two relocation codes to try to relate individual shocks to distinct faults and surface breaks. A majority of the events apparently occurred underneath the floor of the Dôbi graben, an area about 45 km long and 15 km wide, rupturing boundary and inner floor faults, in agreement with the surface cracks and scarps that we mapped in the area. The relocation shows that the principal events propagated about 50 km northwestwards along the graben in the first 40 hr. A day and a half after the beginning of the sequence, smaller events ( M ≤ 4) started to propagate more than 55 km eastwards, towards Asal Lake. Using two three-component stations installed near the Ethiopian border, we could determine reliable depths for 21 events. The depths are compatible with a seismogenic crust about 14 km thick in the Dôbi and Hanle graben area. Although the Dôbi sequence ruptured about 50 km of the fault array extending from Serdo to Asal, where the regional stress was released by earthquakes in 1969 and 1978, respectively, a seismic gap about 50 km long still subsists along the northern part of the Gaggade region (Der'êla half-graben). 相似文献