全文获取类型
收费全文 | 438篇 |
免费 | 30篇 |
国内免费 | 103篇 |
专业分类
测绘学 | 1篇 |
地球物理 | 22篇 |
地质学 | 501篇 |
海洋学 | 2篇 |
综合类 | 29篇 |
自然地理 | 16篇 |
出版年
2023年 | 3篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 59篇 |
2012年 | 6篇 |
2011年 | 14篇 |
2010年 | 8篇 |
2009年 | 21篇 |
2008年 | 9篇 |
2007年 | 19篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 26篇 |
2003年 | 20篇 |
2002年 | 28篇 |
2001年 | 21篇 |
2000年 | 28篇 |
1999年 | 32篇 |
1998年 | 25篇 |
1997年 | 23篇 |
1996年 | 21篇 |
1995年 | 27篇 |
1994年 | 18篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 2篇 |
排序方式: 共有571条查询结果,搜索用时 31 毫秒
171.
Rajesh K. Srivastava M. Jayananda Gulab C. Gautam V. Gireesh Amiya K. Samal 《Chemie der Erde / Geochemistry》2014
A vast tract of ENE–WSW to NE–SW trending mafic dyke swarm transects Archaean basement rocks within the eastern Dharwar craton. Petrographic data reveal their dolerite/olivine dolerite or gabbro/olivine gabbro composition. Geochemical characteristics, particularly HFSEs, indicate that not all these dykes are co-genetic but are probably derived from more than one magma batch and different crystallization trends. In most samples the LaN/LuN ratio is at ∼2, whereas others have a LaN/LuN ratio >2 and show higher concentrations of high-field strength elements (HFSEs) than the former group. As a consequence, we assume that the ENE–WSW to NE–SE trending mafic dykes of the eastern Dharwar craton do not represent one single magmatic event but were emplaced in two different episodes; one of them dated at about 2.37 Ga and another probably at about 1.89 Ga. Trace element modelling also supports this inference: older mafic dykes are derived from a melt generated through ∼25% melting of a depleted mantle, whereas the younger set of dykes shows its derivation through a lower degree of melting (∼15%) of a comparatively enriched mantle source. 相似文献
172.
173.
A lirst report on tuff beds from the Owk Shale in the Proterozoic Kurnool sub-basin in southern India is presented.The rhvolitic lo ihodacitic tuffs,overlying shclfal limestones formed at depths below storm wave base,have rheomorphic features indicative of viscoplaslic flow.and geochemical signatures of rhvolitic to rhyodacitic unwekled to welded tuffs,similar to those described from other Proterozoic intracratonie basins like Vindhvan and Chhattisgarh basins in India.Fragmentary naiure of altered glass with perlitic cracks and local admixture with intrabasinal sediments suggest phreatomagmatic reactions.The widespread and repealed occurrences of felsic luffs in these basins.possibly derived from low degree melting of continental crust.suggest intermittent(ectonothermal instability which likely intluenced hasinal topography and cyclic development of the carbonate platforms. 相似文献
174.
175.
C. R. Twidale 《Australian Journal of Earth Sciences》2013,60(1-2):195-208
Some bornhardts are of lithological origin, others are tectonic (horsts), but most are not susceptible of explanation in either of these terms. They are developed in granite or gneiss that apparently is mineralogically similar to that underlying the adjacent plains, and they are not obviously defined by fault dislocations. For these bornhardts two major hypotheses have been advanced. According to many workers bornhardts are the last residuals surviving after long distance scarp retreat. For others they are structural forms developed on massive compartments that stand in marked contrast with the well‐jointed rocks that have been weathered and worn down to form the plains. Both of these hypotheses are theoretically feasible, but the field evidence (in particular the observed contrasts in fracture density between the granite of hill and plain; the evidence of subsurface initiation of both major and minor forms; the occurrence of bornhardts in narrow valleys within upland complexes and at all levels within the landscape, not just on divides; the fracture‐delineated outlines of the residuals; the association of bornhardts and multicyclic landscapes; the evidence of phased exposure; and the antiquity of the forms) are all consistent with the two‐stage concept. On the other hand, there is no evidence of long‐distance scarp retreat, and much of the field evidence is difficult to explain in such terms. 相似文献
176.
B. P. Wade J. L. Payne M. Hand K. M. Barovich 《Australian Journal of Earth Sciences》2013,60(8):1089-1102
The Coompana Block is an essentially unknown basement province that separates the Gawler Craton of South Australia from the Yilgarn Craton of Western Australia. Previously unstudied granitic gneiss intersected by deep drilling in the Coompana Block represents an important period of within-plate magmatism during a time of relative magmatic quiescence in the Australian Proterozoic. Granitic gneiss intersected at ~1500 m depth in Mallabie 1 diamond drillhole is metaluminous and dominantly granodioritic in composition. The granodiorites have distinctive A-type chemistry characterised by high contents of Zr, Nb, Y, Ga, LREE with low Mg#, Sr, CaO and HREE. U – Pb LA-ICPMS dating of magmatic zircons provides an age of 1505 ± 7 Ma, interpreted as the crystallisation age of the granite protolith. ? Nd values are high with respect to exposed crust of the Musgrave Province and Gawler Craton, and range from +1.2 to +3.3 at 1.5 Ga. The granitic gneiss is interpreted to be a fractionated melt of a mantle-derived parental melt. The tectonic environment into which the precursor granite was emplaced is not clear. One possibility is emplacement within an extensional environment. Regardless, the granitic gneiss intersected in Mallabie 1 represents magmatic activity during the ‘Australian Mesoproterozoic magmatic gap’ of ca 1.50 – 1.35 Ga, and is a possible source for ca 1.50 detrital zircons found in sedimentary rocks of Tasmania and Antarctica, and metasedimentary rocks of the eastern Musgrave Province. 相似文献
177.
At the Sandpiper gold deposit in the Tanami region of northern Australia sericite is intimately intergrown with arsenopyrite in gold-bearing quartz veins and breccias, suggesting sericite crystallisation synchronous with gold-bearing fluid flow. This ore-stage sericite yields a 40Ar/39Ar plateau age of 1785 ± 32 Ma (2σ including both analytical and systematic uncertainties). Recalculation using revised and more precise values for the 40K decay constants and the age of the Fish Canyon Sanidine standard shifts the age to 1794 ±12 Ma (2σ including all known uncertainties). Given the possibility of post-mineralisation isotopic resetting this age can be conservatively interpreted as a minimum constraint on the timing of gold deposition although, given local geological relationships and estimates for the argon retentivity of white mica, we consider complete isotopic resetting to be unlikely. The preferred interpretation is, therefore, that the sericite 40Ar/39Ar age indicates the timing of gold mineralisation. Thesericite age accords with a limited dataset of 207Pb/206Pb xenotime ages of ca 1800 Ma from other gold deposits in the Tanami region, interpreted as mineralisation ages. The agreement between independently derived ages from several gold deposits lends support for a widespread gold-mineralising event at ca 1800 Ma in the Tanami region. 相似文献
178.
Abstract Two unconformity‐bound groups of volcanic rocks and associated sediments (El Sherana and Edith River Groups) separate the older Pine Creek Geosyncline metasediments from platform cover of the McArthur Basin. Dominated by intersecting NW and ENE rift systems, the volcanics are genetically related to an extensional tectonic system which was also active during deposition of the Pine Creek Geosyncline sequence. In contrast, the younger platform cover was deposited in a relatively stable environment. The rift valleys were filled with rhyolite flows, ignimbrite and ill‐sorted arenite and rudite, and flyschoid sediments spread onto adjacent lands. Following tight upright folding, granite intrusion and erosion, an extensive ignimbrite sheet (=6000 km2) spread from a centre probably at the intercept of the two rifts. Microgranite at this intersection was possibly emplaced in the evacuated magma chamber. The volcanic sequences were deeply eroded and weathered before platform cover deposition began. The platform sediments, represented in the area by the Kombolgie Formation, were deposited from about 1690 Ma to 1650 Ma, and their base is taken as the closest stratigraphic indicator of the boundary between the Early and Middle Proterozoic. 相似文献
179.
180.
40Ar‐39Ar age spectra on minerals from granitic, metamorphic and hydrothermal rocks confirm that the Early Proterozoic Tennant Creek Block was affected by two thermal events during its evolution. Although extensive alteration of biotite and feldspar within the granites precludes the direct determination of their cooling history, 40Ar‐39Ar analyses for hydrothermal muscovite from several nearby gold‐copper deposits indicate that regional cooling to below ~ 300°C was not prolonged. Flat, uniform muscovite age spectra were obtained from gold deposits east of the Tennant Creek town site and indicate a minimum age of 1825–1830 Ma for their formation. These ages are within error of those for the felsic volcanism of the Flynn Subgroup, and a genetic relationship between the two may exist. Samples from gold deposits elsewhere in the area indicate disturbance of the K‐Ar isotope system. The second thermal event to affect the region occurred at around 1700 Ma, and is confirmed by the 40Ar‐39Ar muscovite ages for the ‘Warrego’ granite (1677 ± 4 Ma) and for the metamorphism of the Wundirgi Formation (1696 ± 4 Ma). 相似文献