全文获取类型
收费全文 | 355篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 32篇 |
地球物理 | 87篇 |
地质学 | 162篇 |
海洋学 | 22篇 |
天文学 | 53篇 |
自然地理 | 18篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 5篇 |
2021年 | 12篇 |
2020年 | 5篇 |
2019年 | 8篇 |
2018年 | 22篇 |
2017年 | 20篇 |
2016年 | 26篇 |
2015年 | 15篇 |
2014年 | 20篇 |
2013年 | 30篇 |
2012年 | 26篇 |
2011年 | 29篇 |
2010年 | 18篇 |
2009年 | 22篇 |
2008年 | 11篇 |
2007年 | 17篇 |
2006年 | 15篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1951年 | 1篇 |
1950年 | 1篇 |
1949年 | 1篇 |
排序方式: 共有384条查询结果,搜索用时 312 毫秒
311.
Axial and Radial Permeability Evolutions of Compressed Sandstones: End Effects and Shear-band Induced Permeability Anisotropy 总被引:2,自引:0,他引:2
Jeremie Dautriat Nicolas Gland Jean Guelard Alexandre Dimanov Jean L. Raphanel 《Pure and Applied Geophysics》2009,166(5-7):1037-1061
The influence of hydrostatic and uniaxial stress states on the porosity and permeability of sandstones has been investigated. The experimental procedure uses a special triaxial cell which allows permeability measurements in the axial and radial directions. The core sleeve is equipped with two pressure samplers placed distant from the ends. They provide mid-length axial permeability measure as opposed to the overall permeability measure, which is based on the flow imposed through the pistons of the triaxial cell. The core sleeve is also equipped to perform flows in two directions transverse to the axis of the sample. Two independent measures of axial and complementary radial permeability are thus obtained. Both Fontainebleau sandstone specimens with a porosity of about 5.8% to 8% and low permeability ranging from 2.5 mD to 30 mD and Bentheimer sandstone with a porosity of 24% and a high permeability of 3D have been tested. The initial axial permeability values obtained by each method are in good agreement for the Fontainebleau sandstone. The Bentheimer sandstone samples present an axial mid-length permeability 1.6 times higher than the overall permeability. A similar discrepancy is also observed in the radial direction, also it relates essentially to the shape of flow lines induced by the radial flow. All the tested samples have shown a higher stress dependency of overall and radial permeability than mid-length permeability. The effect of compaction damage at the pistons/sample and radial ports/sample interfaces is discussed. The relevance of directional permeability measurements during continuous uniaxial compression loadings has been shown on the Bentheimer sandstone until the failure of the sample. We can efficiently measure the influence of brittle failure associated to dilatant regime on the permeability: It tends to increase in the failure propagation direction and to decrease strongly in the transverse direction. 相似文献
312.
313.
Marengo Jose A. Cunha Ana Paula M. A. Nobre Carlos A. Ribeiro Neto Germano G. Magalhaes Antonio R. Torres Roger R. Sampaio Gilvan Alexandre Felipe Alves Lincoln M. Cuartas Luz A. Deusdará Karinne R. L. Álvala Regina C. S. 《Natural Hazards》2020,103(2):2589-2611
Natural Hazards - Historically, during periods of extreme drought, food security in the drylands of the semiarid region of Northeast Brazil (NEB) is under severe risk due to agricultural collapse.... 相似文献
314.
315.
Alexandre Loye Andrea Pedrazzini Joshua I. Theule Michel Jaboyedoff Frédéric Liébault Richard Metzger 《地球表面变化过程与地形》2012,37(13):1407-1423
Structural settings and lithological characteristics are traditionally assumed to influence the development of erosional landforms, such as gully networks and rock couloirs, in steep mountain rock basins. The structural control of erosion of two small alpine catchments of distinctive rock types is evaluated by comparing the correspondences between the orientations of their gullies and rock couloirs with (1) the sliding orientations of potential slope failures mechanisms, and (2) the orientation of the maximum joint frequency, this latter being considered as the direction exploited primarily by erosion and mass wasting processes. These characteristic orientations can be interpreted as structural weaknesses contributing to the initiation and propagation of erosion. The morphostructural analysis was performed using digital elevation models and field observations. The catchment comprised of magmatic intrusive rocks shows a clear structural control, mostly expressed through potential wedges failure. Such joint configurations have a particular geometry that encourages the development of gullies in hard rock, e.g. through enhanced gravitational and hydrological erosional processes. In the catchment underlain by sedimentary rocks, penetrative joints that act as structural weaknesses seem to be exploited by gullies and rock couloirs. However, the lithological setting and bedding configuration prominently control the development of erosional landforms, and influence not only the local pattern of geomorphic features, but the general morphology of the catchment. The orientations of the maximum joint frequency are clearly associated with the gully network, suggesting that its development is governed by anisotropy in rock strength. These two catchments are typical of bedrock‐dominated basins prone to intense processes of debris supply. This study suggests a quantitative approach for describing the relationship between bedrock jointing and geomorphic features geometry. Incorporation of bedrock structure can be relevant when studying processes governing the transfer of clastic material, for the assessment of sediment yields and in landforms evolution models. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
316.
Sustained slow slip, which is a distinctive feature of slow slip events (SSEs), is investigated theoretically, assuming a fault embedded within a fluid-saturated 1D thermo-poro-elastic medium. The object of study is specifically SSEs occurring at the down-dip edge of seismogenic zone in hot subduction zones, where mineral dehydrations (antigorite, lawsonite, chlorite, and glaucophane) are expected to occur near locations where deep slow slip events are observed. In the modeling, we introduce dehydration reactions, coupled with slip-induced dilatancy and thermal pressurization, and slip evolution is assumed to interact with fluid pressure change through Coulomb’s frictional stress. Our calculations show that sustained slow slip events occur when the dehydration reaction is coupled with slip-induced dilatancy. Specifically, slow slip is favored by a low initial stress drop, an initial temperature of the medium close to that of the dehydration reaction equilibrium temperature, a low permeability, and overall negative volume change associated with the reaction (i.e., void space created by the reaction larger than the space occupied by the fluid released). Importantly, if we do not assume slip-induced dilatancy, slip is accelerated with time soon after the slip onset even if the dehydration reaction is assumed. This suggests that slow slip is sustained for a long time at hot subduction zones because dehydration reaction is coupled with slip-induced dilatancy. Such slip-induced dilatancy may occur at the down-dip edge of seismogenic zone at hot subduction zones because of repetitive occurrence of dehydration reaction there. 相似文献
317.
The black shale-hosted selenide vein-type deposit at Tilkerode, eastern Harz, Germany, has specular hematite enclosed in clausthalite (PbSe). The specular hematite has Ti and V in amounts of up to ~1 wt.% TiO2 and ~3 wt.% V2O5, and subordinate, but important, contents of Mo (22–372 ppm) and B (up to 68 ppm). The Tilkerode hematite serves as a reference for hydrothermal hematite formed at relatively low temperatures (<150 °C). The composition of the Tilkerode hematite is compared with that of two generations of specular hematite from itabirite-hosted iron-ore deposits in the Quadrilátero Ferrífero of Minas Gerais, Brazil. The first generation of specular hematite represents an early tectonic hematitisation of dolomitic itabirite at Águas Claras and occurs as fine-grained crystals. Reconnaissance data indicate that the Águas Claras hematite is poorer in Ti and V, relative to the Tilkerode hematite, but has ~5–10 ppm B and ~7–11 ppm Li. The second generation of specular hematite defines the pervasive tectonic foliation of the Gongo Soco iron ore. This hematite has Ti contents of up to ~2 wt.% TiO2 and subordinate amounts of V (62–367 ppm); its B and Li concentrations are mostly below <2 ppm B and <1 ppm Li. The presence of Ti and B in the Tilkerode hematite can be explained by highly saline, B-bearing fluids that were capable of mobilising otherwise immobile Ti. The Mo signature of the Tilkerode hematite suggests that Mo was derived from the host black shale. In Minas Gerais, B and Li were incorporated into the early tectonic hematite from saline fluids at relatively low temperatures (Águas Claras) and then released during metamorphic hematite growth at higher temperatures, as suggested by the foliation-defining hematite without B–Li signature (Gongo Soco). 相似文献
318.
The importance of geochronology in the study of mineral deposits in general, and of unconformity-type uranium deposits in
particular, resides in the possibility to situate the critical ore-related processes in the context of the evolution of the
physical and chemical conditions in the studied area. The present paper gives the results of laser step heating 40Ar/39Ar dating of metamorphic host-rock minerals, pre-ore and syn-ore alteration clay minerals, and laser ablation inductively
coupled plasma mass spectrometer (LA-ICP-MS) U/Pb dating of uraninite from a number of basement- and sediment-hosted unconformity-related
deposits in the Athabasca Basin, Canada. Post-peak metamorphic cooling during the Trans-Hudson Orogen of rocks from the basement
occurred at ca 1,750 Ma and gives a maximum age for the formation of the overlying Athabasca Basin. Pre-ore alteration occurred
simultaneously in both basement- and sandstone-hosted mineralizations at ca 1,675 Ma, as indicated by the 40Ar/39Ar dating of pre-ore alteration illite and chlorite. The uranium mineralization age is ca 1,590 Ma, given by LA-ICP-MS U/Pb
dating of uraninite and 40Ar/39Ar dating of syn-ore illite, and is the same throughout the basin and in both basement- and sandstone-hosted deposits. The
mineralization event, older than previously proposed, as well as several fluid circulation events that subsequently affected
all minerals studied probably correspond to far-field, continent-wide tectonic events such as the metamorphic events in Wyoming
and the Mazatzal Orogeny (ca 1.6 to 1.5 Ga), the Berthoud Orogeny (ca 1.4 Ga), the emplacement of the McKenzie mafic dyke
swarms (ca 1.27 Ga), the Grenville Orogeny (ca 1.15 to 1 Ga), and the assemblage and break-up of Rodinia (ca 1 to 0.85 Ga).
The results of the present work underline the importance of basin evolution between ca 1.75 Ga (basin formation) and ca 1.59 Ga
(ore deposition) for understanding the conditions necessary for the formation of unconformity-type uranium deposits.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
319.
Sung Hi Choi Samuel B. Mukasa Alexandre V. Andronikov Maria C. Marcano 《Contributions to Mineralogy and Petrology》2007,153(4):443-463
An origin of the Tinaquillo Peridotite Complex in northern Venezuela, and a model for the tectonic framework of the boundary
zone between the southern Caribbean Plate margin and the South American Plate (SAP) during Late Jurassic to Mid-Cretaceous
time are developed using newly measured Sr, Nd, Pb and Hf isotopic compositions as well as major and trace element geochemistry
for some hornblendite veins and their spinel peridotite host rocks. Depleted geochemical characteristics, principally major
element concentrations, and Nd and Hf isotopes (e.g., εNd = + 27; εHf = +50; ca. 3.4 Ga-Nd model age) of the Tinaquillo peridotites suggest a genetic link between this complex and the Guiana
Shield farther to the south within Venezuela. Scattered zones within the Tinaquillo peridotite were overprinted by what we
interpret as channelized hydrous fluids (<∼3%) derived from the eastward-dipping subduction of the Farallon Plate beneath
the SAP in the Late Jurassic, leading to modification of the original Sr, Nd and Hf isotopic compositions as well as the incompatible
element concentrations. The hornblendite veins have Sr, Nd, Pb and Hf isotopic compositions, falling within the range of present-day
Pacific/Atlantic MORB, but trace element abundance patterns with combinations of arc- and MORB-like characteristics. These
results rule out the possibility of local melting of the host peridotites to produce magmas from which the hornblendite veins
formed. We suggest that during inception of the westward-dipping subduction of the Protocaribbean Plate immediately following
polarity reversal in the Mid-Cretaceous, melts infiltrated the mantle lithosphere and produced the veins. 相似文献
320.
Alessandro Mondanaro Mirko Di Febbraro Marina Melchionna Francesco Carotenuto Silvia Castiglione Carmela Serio Simone Danisi Lorenzo Rook Jose Alexandre F. Diniz‐Filho Pasquale Raia 《Boreas: An International Journal of Quaternary Research》2019,48(3):605-615
Cave bears (Ursus spelaeus) are an iconic component of the European late Quaternary Ice Age megafauna. Recent demographic analyses based on cave bear mtDNA sequences and refined radiocarbon dating indicate that cave bear population size and genetic diversity started to decline some 50 kilo years ago (kya). Hence, neither the coldest phase of the last glaciation (started some 24 kya), nor the colonization of Europe by Palaeolithic hunters (started some 45 kya) coincides with the beginning of population decline. Here, we reconstructed cave bear climatic niche evolution through time. Then, we performed spatially explicit population viability analyses to assess cave bear demographics through time in response to climatic changes, human effects on bear survival and their combination. We found that climate change was responsible for a 10‐fold decrease in cave bear population size after 40 kya. However, climate change on its own could not explain U. spelaeus extinction at 24 kya. Additional negative effects consistent with human population expansion are required to explain both U. spelaeus' retreat from eastern Europe since 40 kya and its final extinction. 相似文献