全文获取类型
收费全文 | 857篇 |
免费 | 49篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 15篇 |
大气科学 | 51篇 |
地球物理 | 257篇 |
地质学 | 197篇 |
海洋学 | 72篇 |
天文学 | 142篇 |
自然地理 | 185篇 |
出版年
2021年 | 11篇 |
2020年 | 9篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 30篇 |
2015年 | 19篇 |
2014年 | 18篇 |
2013年 | 46篇 |
2012年 | 26篇 |
2011年 | 34篇 |
2010年 | 20篇 |
2009年 | 48篇 |
2008年 | 46篇 |
2007年 | 37篇 |
2006年 | 32篇 |
2005年 | 32篇 |
2004年 | 46篇 |
2003年 | 27篇 |
2002年 | 39篇 |
2001年 | 32篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 21篇 |
1997年 | 21篇 |
1996年 | 18篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 24篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1986年 | 6篇 |
1985年 | 17篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1979年 | 6篇 |
1978年 | 4篇 |
1977年 | 9篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1973年 | 6篇 |
1970年 | 3篇 |
1965年 | 2篇 |
1924年 | 2篇 |
排序方式: 共有919条查询结果,搜索用时 640 毫秒
341.
A three-dimensional image of shallow subduction: crustal structure of the Raukumara Peninsula, New Zealand 总被引:1,自引:0,他引:1
Martin Reyners Donna Eberhart-Phillips & Graham Stuart 《Geophysical Journal International》1999,137(3):873-890
Earthquake arrival time data from a 36-station deployment of portable seismographs on the Raukumara Peninsula have been used to determine the 3-D Vp and Vp/Vs structure of this region of shallow subduction. A series of inversions have been performed, starting with an inversion for 1-D structure, then 2-D, and finally 3-D. This procedure ensures a smooth regional model in places of low resolution. The subducted plate is imaged as a northwest-dipping feature, with Vp consistently greater than 8.5 km s−1 in the uppermost mantle of the plate. Structure in the overlying plate changes significantly along strike. In the northeast, there is an extensive low-velocity zone in the lower crust underlying the most rapidly rising part of the Raukumara Range. It is bounded on its arcward side by an upwarp of high velocity. A viable explanation for the low-velocity zone is that it represents an accumulation of underplated subducted sediment, while serpentinization of the uppermost mantle may be responsible for the adjacent high-velocity region. The low-velocity zone decreases and the adjacent high-velocity region is less extensive in the southwest. This change is interpreted to be related to a change in the thickness of the crust of the overlying plate. In the northeast the crust is thinner, and subducted sediment ponds against relatively strong uppermost mantle, while in the southwest the crust is thicker, and the relatively weak lower crust allows sediment subduction to greater depths. A narrow zone of high Vp/Vs parallels the shallow part of the plate interface. This suggests elevated fluid pressures, with the distribution of earthquakes about this zone further suggesting that these pressures may be close to lithostatic. The plate interface at 20 km depth beneath the Raukumara Peninsula may thus be a closed system for fluid flow, similar to that seen at much shallower depths in other subduction décollements. 相似文献
342.
This paper provides the first radiometrically dated evidence of Holocene alluvial landform development in Upper Wharfedale, Yorkshire Dales. Four river terraces are identified. Terraces 1 and 2 are closely linked to Late Devensian and early Holocene environmental change, with gravel reworked from local glacial and periglacial sources prior to cementation by carbonate‐rich waters. U‐series dating of cement provides age estimates for cementation of between ca. 5.1–7.4 kyr BP for Terrace 1 and ca. 3.6–>8.0 kyr BP for Terrace 2. U‐series dating of tufas overlying Terraces 1 and 2 produced ages of ca. 4.2–4.5 kyr BP and ca. 2.1–2.2 kyr BP respectively, and provide upper age limits for terrace formation. Terrace 3 marks a change in sediment calibre, supply and sedimentation style, and 14C dating suggests that the principal source of fine‐grained material may be agricultural expansion in the Yorkshire Dales from ca. ad 600 (1350 cal. yr BP). Radiocarbon dates indicate that Terrace 4 was deposited from the eleventh century, with initiation of the contemporary floodplain between the fifteenth and seventeenth centuries ad. Both these lowest units contain sediments contaminated with heavy metals as a result of mining activities within the catchment. The evidence presented in this study is comparable to that of research undertaken in upland environments elsewhere in northern and western Britain, thereby adding to the corpus of information currently available for evaluating the fluvial geomorphological response to climate and vegetation change during the Holocene. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
343.
Eradication of invasive species is difficult in the marine environment, and there have only been a few successes. We report the successful eradication of the invasive seaweed Undaria pinnatifida from a sunken trawler in the Chatham Islands, New Zealand. New heat-treatment methods were developed as the most cost effective and environmentally acceptable option to kill Undaria. Monitoring of the trawler for three years after it sank found no Undaria after the vessel was treated. Key factors in the success of the eradication programme included: early detection, a rapid response, pre-existing knowledge of Undaria, an adaptive management approach, targeting of multiple life history stages, and the cooperation of the vessel's insurer. 相似文献
344.
Seismic body waves in anisotropic media: synthetic seismograms 总被引:5,自引:0,他引:5
Summary. Synthetic seismograms and particle motion diagrams are computed for simple, layered Earth models containing an anisotropic layer. The presence of anisotropy couples the P, SV and SH wave motion so that P waves incident on the anisotropic layer from below produce P, SV and small-amplitude SH waves at the surface both the P velocity and the amplitudes of the converted phases vary with azimuth. Significant SH amplitudes may be generated even when the wavelength of the P wave is much greater than the thickness of the anisotropic layer. Incident SV or SH waves may each generate large amplitudes of both SV and SH motion. This strong coupling is largely independent of the degree of velocity anisotropy of the medium. The arrivals from short-period S waves exhibit S-wave splitting, but arrivals from longer period S waves superpose into a modified waveform. This strong coupling does not allow the arrival of separate phases with pure SV and SH polarization except along directions of symmetry where the motion decouples. 相似文献
345.
Lithium (Li) isotopes are thought to provide a powerful proxy for the recycling of crustal material, affected by low temperature alteration, through the mantle. We present Li isotope compositions for basaltic volcanic rocks from Hengill, Iceland, and Jan Mayen in order to examine possible links between ocean island volcanism and recycled oceanic crust and to address recent suggestions that mantle 3He/4He is also related to recycling of ancient slabs. Basaltic glasses spanning a range of chemical enrichment from the Hengill fissure system define an inverse correlation between δ7Li (3.8-6.9‰) and 3He/4He (12-20 RA). The high-3He/4He basalts have low δ18O as well as excess Eu and high Nb/U, but carry no Li isotope evidence of being the product of recycling of altered slab or wedge material. In fact, there is no clear correlation between Li or He isotopes on the one hand and any of the other fingerprints of recycled slab components. The low-3He/4He samples do have elevated Nb/U, Sr/Nd, positive Eu anomalies and high δ7Li (∼6.9‰), providing evidence of a cumulate-enriched source that could be part of an ancient altered ocean floor slab.Basalts from Jan Mayen are characterized by large degrees of enrichment in incompatible trace elements typical of EM-like basalts but have homogeneous δ7Li typical of depleted mantle (3.9-4.7‰) providing evidence for a third mantle source in the North Atlantic. It appears that oceanic basalts can display a wide range in isotope and trace element compositions associated with recycled components whilst exhibiting no sign of modern surface-altered slab or wedge material from the Li isotope composition. 相似文献
346.
Mineralogical changes during intense chemical weathering of sedimentary rocks in Bangladesh 总被引:1,自引:0,他引:1
Md. R. Islam Rojstaczer Stuart Aario Risto Peuraniemi Vesa 《Journal of Asian Earth Sciences》2002,20(8):88
Bangladesh is situated in a subtropical to tropical climatic zone. A recently weathered crust has developed on sedimentary bedrock (sandstone, siltstone, shale and claystones) of Tertiary–Quaternary age. Weathered samples were collected from 16 sections totaling 68 samples and were analyzed mineralogically. The main primary minerals identified in the weathered crust of sedimentary rocks are quartz, plagioclase, K-feldspar, biotite, muscovite, sparse carbonate and epidote. The secondary minerals are kaolinite, illite, chlorite, gibbsite and goethite. Weathering initiated along the grain boundaries and cleavage planes of the minerals, forming small cloudy materials which were very difficult to identify. In the advanced stage of weathering, these cloudy materials have turned into secondary minerals. In region 1, high rain fall (7100 mm/yr) and monsoonic climate resulted in a kaolinite–gibbsite–goethite suite through the weathering of feldspars and biotite. The occurrence of gibbsite in the relatively elevated lands of Sylhet and Fe-kaolinite throughout the study areas is indicative of a humid–tropical climate during formation of the weathered crust. 相似文献
347.
Fluid overpressure as a control on sandstone reservoir quality in a mechanical compaction dominated setting: Magnolia Field,Gulf of Mexico
下载免费PDF全文
![点击此处可从《地学学报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The reservoir quality (porosity and permeability) of deeply buried hydrocarbon reservoir sandstones in sedimentary basins is significantly affected by burial diagenesis. Many deep reservoirs develop anomalous fluid overpressures during burial. Previous studies on the effect of fluid overpressure on reservoir quality in these deep reservoirs have been inconclusive because of the difficulty in constraining the individual contributions of various porosity preserving factors that are simultaneously active in these reservoirs. Owing to its rapid burial and low burial temperatures, the Neogene gravity‐flow sandstone reservoirs from the Magnolia Field, Gulf of Mexico, offers a unique opportunity to investigate in isolation the effect of fluid overpressure on reservoir quality. Examination of petrography, pore pressure and routine core analysis datasets showed a positive correlation between high fluid overpressure and enhanced reservoir quality. This study confirms that fluid overpressure preserves reservoir quality in deeply buried sandstone reservoirs in compaction dominated, high sedimentation basin settings. 相似文献
348.
Pirin Erdodu Ofer Lahav Saleem Zaroubi George Efstathiou Steve Moody John A. Peacock Matthew Colless Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ian Lewis Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,352(3):939-960
349.
350.