全文获取类型
收费全文 | 543篇 |
免费 | 168篇 |
国内免费 | 175篇 |
专业分类
地球物理 | 66篇 |
地质学 | 651篇 |
海洋学 | 88篇 |
综合类 | 35篇 |
自然地理 | 46篇 |
出版年
2024年 | 3篇 |
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 21篇 |
2020年 | 17篇 |
2019年 | 20篇 |
2018年 | 15篇 |
2017年 | 40篇 |
2016年 | 34篇 |
2015年 | 26篇 |
2014年 | 55篇 |
2013年 | 38篇 |
2012年 | 39篇 |
2011年 | 65篇 |
2010年 | 32篇 |
2009年 | 49篇 |
2008年 | 35篇 |
2007年 | 26篇 |
2006年 | 30篇 |
2005年 | 32篇 |
2004年 | 21篇 |
2003年 | 19篇 |
2002年 | 24篇 |
2001年 | 17篇 |
2000年 | 26篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 11篇 |
1993年 | 18篇 |
1992年 | 11篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有886条查询结果,搜索用时 687 毫秒
131.
Reinhard Gratzer Achim BechtelReinhard F. Sachsenhofer Hans-Gert LinzerDoris Reischenbacher Hans-Martin Schulz 《Marine and Petroleum Geology》2011,28(6):1171-1186
The Alpine Foreland Basin is a minor oil and moderate gas province in central Europe. In the Austrian part of the Alpine Foreland Basin, oil and minor thermal gas are thought to be predominantly sourced from Lower Oligocene horizons (Schöneck and Eggerding formations). The source rocks are immature where the oil fields are located and enter the oil window at ca. 4 km depth beneath the Alpine nappes indicating long-distance lateral migration. Most important reservoirs are Upper Cretaceous and Eocene basal sandstones.Stable carbon isotope and biomarker ratios of oils from different reservoirs indicate compositional trends in W-E direction which reflect differences in source, depositional environment (facies), and maturity of potential source rocks. Thermal maturity parameters from oils of different fields are only in the western part consistent with northward displacement of immature oils by subsequently generated oils. In the eastern part of the basin different migration pathways must be assumed. The trend in S/(S + R) isomerisation of ααα-C29 steranes versus the αββ (20R)/ααα (20R) C29 steranes ratio from oil samples can be explained by differences in thermal maturation without involving long-distance migration. The results argue for hydrocarbon migration through highly permeable carrier beds or open faults rather than relatively short migration distances from the source. The lateral distance of oil fields to the position of mature source rocks beneath the Alpine nappes in the south suggests minimum migration distances between less than 20 km and more than 50 km.Biomarker compositions of the oils suggest Oligocene shaly to marly successions (i.e. Schoeneck, Dynow, and Eggerding formations) as potential source rocks, taking into account their immature character. Best matches are obtained between the oils and units a/b (marly shale) and c (black shale) of the “normal” Schöneck Formation, as well as with the so-called “Oberhofen Facies”. Results from open system pyrolysis-gas chromatography of potential source rocks indicate slightly higher sulphur content of the resulting pyrolysate from unit b. The enhanced dibenzothiophene/phenanthrene ratios of oils from the western part of the basin would be consistent with a higher contribution of unit b to hydrocarbon expulsion in this area. Differences in the relative contribution of sedimentary units to oil generation are inherited from thickness variations of respective units in the overthrusted sediments. The observed trend towards lighter δ13C values of hydrocarbon fractions from oil fields in a W-E direction are consistent with lower δ13C values of organic matter in unit c. 相似文献
132.
133.
134.
Luc-Emmanuel Ricou 《Geodinamica Acta》2013,26(4-5):225-232
Abstract— Accepting that the opening or closure of seaways has consequences on the oceanic circulation which in turn influences sedimentation, major changes in Tethyan geometry are checked against major changes in sedimentation. Time relationships can be demonstrated between the two group of phenomena and causal links are discussed. As the causes for major sedimentary changes are numerous and their respective roles controversial, it is speculated if the observed change in geometry could have had a positive effect on the associated change in sediments.Ever since the birth of the Mesozoic Tethys which formed from the break-up of Pangea till its death through multiple collisions, this ocean played a major role in the world ocean circulation, being the sub-equatorial seaway which permitted a circumterrestrial circulation at low latitudes. Five successive steps, separated by four major changes, are recognized : i) during the Trias and the Jurassic, the young Tethys was a triangular cul-de-sac expanding westward through distensive tectonics and subsidence, and influenced along its southern margin by a westward current and associated upwelling; radiolarites take a growing part in its sedimentation; ii) during the Tithonian, radiolarites were abruptly replaced by pelagic limestones (Majolica) in many places and the corresponding CCD drop is tentatively correlated with the full opening of the Tethyan seaway which reached the Pacific Ocean through the Caribbean and with the corresponding reorganization of currents; iii) during the Early Cretaceous, Apulia began its collision with the precursor elements of the European margin, thus hindering deep water exchange; this pre collision favoured the mid Cretaceous anoxia with affected sedimentation in numerous basins; iv) during the Late Cretaceous, repeated distension and subsidence (since the Aptian) between Apulia and Africa gave a growing importance to the south Apulian seaway; this new opportunity of water exchange favoured the end of anoxia and the deposition of new pelagic limestones (scaglia); as a matter of fact, the location of the Late Cretaceous to Early Eocene phosphorites testify to a well-established westward current along this south-Apulian seaway; v) the late Eocene to Oligocene general collision was responsable for the death of this current and the corresponding breakdown of the Tethyan seaway into independent groups of basins. 相似文献
135.
136.
Multivariate statistical analysis of geochemical data as indicative of the hydrogeochemical evolution of groundwater in a sedimentary rock aquifer system 总被引:15,自引:0,他引:15
Vincent Cloutier Ren Lefebvre Ren Therrien Martine M. Savard 《Journal of Hydrology》2008,353(3-4):294-313
The study of groundwater hydrogeochemistry of the Paleozoic Basses-Laurentides sedimentary rock aquifer system in Québec produced a large geochemical dataset. Groundwater samples were collected at 153 sites over a 1500 km2 study area and analyzed for major and minor ions. The large number of data can lead to difficulties in the integration, interpretation and representation of the results. Two multivariate statistical methods, hierarchical cluster analysis (HCA) and principal components analysis (PCA), were applied to a subgroup of the dataset to evaluate their usefulness to classify the groundwater samples, and to identify geochemical processes controlling groundwater geochemistry. This subgroup consisted of 144 samples and 14 parameters (Ca2+, Mg2+, Na+, K+, , Cl−, , Fe2+, Mn2+, Br−, Sr2+, F−, Ba2+, HS−). Seven geochemically distinct clusters, C1–C7, resulted from the HCA. Samples from clusters C3, C4, C6 and C7 are mostly located in preferential recharge areas. The majority of these samples have Ca–Mg–HCO3 recharge groundwater (C3, C6, C7) and Na–HCO3 evolved groundwater (C4). Samples from the other three clusters (C1, C2, C5) are characteristic of an aquifer system under confined conditions. The majority of these samples have Na–HCO3 evolved groundwater (C1, C5) and Na–Cl ancient groundwater that exhibits elevated concentrations in Br− (C2). In addition to recognizing the importance of hydrogeological conditions on groundwater geochemistry, the distribution of clusters also showed the importance of the geological formations on minor and trace elements, such as Fe2+, Mn2+, Sr2+, F− and Ba2+. The first five components of the PCA account for 78.3% of the total variance in the dataset. Component 1 is defined by highly positive loadings in Na+, Cl− and Br− and is related to groundwater mixing with Champlain Sea water and solute diffusion from the marine clay aquitard. The high positive loadings in Ca2+ and Mg2+ of component 2 suggest the importance of dissolution of carbonate rocks in this aquifer system. From their characteristic loadings, the first two components are defined as the “salinity” and “hardness” components, respectively. Components 3–5 are related to more local and geological effects. The integration of the HCA and the PCA, with conventional classification of groundwater types, as well as with the hydrogeological and geological contexts, allowed the division of the region into four main geochemical areas, providing an improved regional picture of the aquifer system dynamics and hydrogeochemical evolution of groundwater. The following factors were recognized as influencing the evolution of groundwater identified in every geochemical area: (1) geological characteristics including sedimentary rock type and till mineralogy; (2) hydrogeological characteristics represented by the level of confinement and the hydraulic gradient; and (3) the geological history including the latest glaciation and the Champlain Sea invasion. With its integrated approach, this hydrogeochemical study contributes to the characterization and understanding of complex groundwater flow systems, and provides an example of the long-term geochemical evolution of hydrogeological systems after a major perturbation, in this case seawater invasion. 相似文献
137.
138.
Jessica D. Tomkins Scott F. Lamoureux Dermot Antoniades Warwick F. Vincent 《Journal of Paleolimnology》2009,41(1):225-242
Sediment aggregates (“sedimentary pellets”) within the sedimentary record of Lake A (83°00′ N, 75°30′ W), Ellesmere Island,
Canada, are used to construct a 1000 year proxy record of ice-cover extent and dynamics on this perennially ice-covered, High
Arctic lake. These pellets are interpreted to form during fall or early winter when littoral sediment adheres to ice forming
around the lake’s periphery or during summer through the development of anchor ice. The sediment likely collects in ice interstices
and is concentrated in the upper ice layers through summer surface ice melt and winter basal ice growth. The pellets remain
frozen in the ice until a summer or series of summers with reduced ice cover allows for their deposition across the lake basin.
Sedimentary pellet frequency within multiple sediment cores is used to develop a chronology of ice-cover fluctuations. This
proxy ice-cover record is largely corroborated by a record of unusual sedimentation in Lake A involving iron-rich, dark-orange
to red laminae overlying more diffuse laminae with a lighter hue. This sediment sequence is hypothesized to represent years
with reduced ice cover through increased chemocline ventilation and iron deposition. During the past millennium, the most
notable period of inferred reduced ice cover is ca. 1891 AD to present. Another period of ice cover mobility is suggested
ca. 1582–1774 AD, while persistent ice cover is inferred during the 1800s and prior to 1582 AD. The proxy ice-cover record
corresponds well with most regional melt-season proxy temperature and paleoecological records, especially during the 1800s
and 1900s.
相似文献
Jessica D. TomkinsEmail: |
139.
Providing quantitative microzonation results that can be taken into account in urban land-use plans is a challenging task that requires collaborative efforts between the seismological and engineering communities. In this study, starting from the results obtained by extensive geophysical and seismological investigations, we propose and apply an approach to the Gubbio basin (Italy) that can be easily implemented for cases of moderate-to-low ground motion and that takes into account not only simple 1D, but also more complicated 3D effects. 相似文献
140.
A case study of coseismic landslides and post-seismic sedimentary impacts of landslides due to rainfall events was conducted in the Tachia River basin, Taichung County, central Taiwan. About 3000 coseismic landslides occurred in the basin during the ML 7.3 Chi-Chi earthquake in 1999. The deposits from these landslides provided material for numerous debris flows induced by subsequent rainfall events. The estimated 4.1 × 107 m3 of landslide debris produced in the upland area caused sediment deposition in riverbeds, and flash floods inundated downstream areas with sediment during torrential rains. The landslide frequency-size distributions for the coseismic landslides and the subsequent rainfall-induced landslides were analyzed to determine the sediment budgets of the post-seismic geomorphic response in the landslide-dominated basin. Both the coseismic and the rainfall-induced landslides show a power–law frequency-size distribution with a rollover. It was found that the rainfall-induced landslide magnitude was smaller than the coseismic one, and that both have comparable negative scaling exponents in cumulative form, of about − 2.0 for larger landslides (> 10− 2 km2). This may be attributed to ongoing movement or reactivation of old landslides, and a natural stabilisation of small landslides between 10− 4 and 10− 2 km2. It is proposed that the characteristics of geological formations and rainfall as well as changes in landslide area are reflected in the power–law distribution. 相似文献