全文获取类型
收费全文 | 176篇 |
免费 | 21篇 |
国内免费 | 10篇 |
专业分类
大气科学 | 3篇 |
地球物理 | 40篇 |
地质学 | 116篇 |
海洋学 | 13篇 |
天文学 | 5篇 |
综合类 | 1篇 |
自然地理 | 29篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 4篇 |
2017年 | 9篇 |
2016年 | 2篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 13篇 |
2012年 | 3篇 |
2011年 | 7篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 15篇 |
2006年 | 8篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 9篇 |
1997年 | 8篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有207条查询结果,搜索用时 15 毫秒
141.
Marine reservoir age is reported for Foxe Basin, Canada, during deglaciation of the Laurentide Ice Sheet. Radiocarbon (14C) measurements were made on pairs of contemporaneous molluscs and Salix (willow) macrofossils, yielding a mean marine reservoir age of 985 ± 10 14C a. Mean regional ΔR is calculated to be 615 ± 20 14C a relative to a mean global reservoir age of ca. 400 14C a. Previous studies in the Canadian Arctic that have been conducted on modern pre‐bomb molluscs give ΔR values of ca. 100–300 14C a. The difference between modern and deglacial reservoir ages indicates that ΔR in Foxe Basin has changed over time, which has implications for the reconstruction of past events based on marine 14C dates. We recalculate the timing of deglaciation of Hudson Strait with this new reservoir age and relate this to the 8.2 cal. ka event. We recommend that local ΔR be determined for the time period being examined whenever possible, and that in cases where this is impossible a ΔR value of 615 14C a be applied when calibrating marine samples from Foxe Basin and vicinity during deglaciation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
142.
143.
This is one of the first applications of geochemical proxies to define changes in vegetation, hydrology and atmospheric dust influence on a peat deposit in the southern hemisphere. A 6.6 m deep peat record from Lynch's Crater in NE-Queensland, Australia, provides a sensitive 5000 to 30,000 cal years BP archive of environmental change. The deposit consists of 1.5 m of ombrotrophic peat underlain by a minerotrophic peat. Within the minerotrophic section, sponge spicules and diatom fragments offer evidence of prolonged flooding of the peat environment resulting in several layers containing (up to 50%) high inorganic material. The Ca and Mg data display episodes of enhanced dust influx and nutrient recycling and support previous palynological studies that show a Pleistocene to Holocene switch from sclerophyll woodlands to rainforest vegetation. 相似文献
144.
S.G. Arzhannikov A.V. Ivanov A.V. Arzhannikova E.I. Demonterova M. Jolivet V.I. Voronin V.A. Buyantuev V.A. Oskolkov 《Russian Geology and Geophysics》2017,58(1):20-36
Dendrochronology and radiocarbon dating, with reference to remote sensing, digital elevation modeling, geological, and geomorphological data, provide new age constraints for the Jombolok lava field in the East Sayan Mountains (Siberia). The Jombolok lava field originated in the latest Late Pleistocene and underwent at least four phases of volcanic activity recorded in lava flows. Two earliest phases followed shortly one after another more than 13 kyr ago. The third phase corresponding to eruptions of Kropotkin volcano can be timed only relatively. The fourth phase has been dated by dendrochronology and AMS 14C of well-preserved wood buried under the youngest lava which occurs among older lavas near the Jombolok River mouth. The age of this activity is bracketed between the death of trees caused by eruptions 1268-928 years ago and the beginning of new tree growth on the surface of the most recent lavas 900 years ago. 相似文献
145.
The Holocene and pre-Holocene sediments and stratigraphy of the Yarra Delta have been examined using nearly 600 geotechnical bores. The oldest Holocene unit is the Coode Island Silt that has two depocentres, each up to 20.0–25.0 m thick, separated by a NW–SE belt of older pre-Holocene units. The northern depocentre represents estuarine infill to the Yarra and Maribyrnong, a river system, whereas the southern depocentre appears to be an offshore bay facies. The youngest unit is the Port Melbourne Sand, which is largely restricted to the area south of the present Yarra River. It is between 5.0 and 28.0 m thick, and is diachronous with the underlying Coode Island Silt. New 14C shell dates from the Coode Island Silt and Port Melbourne Sand have shown an age range between 8341 and 2760 yrs BP. These sediments infill former swamplands covering low-stand river valleys of the Yarra and Maribyrnong rivers across West Melbourne, Fishermans Bend and South Melbourne. After ca 2760 yrs BP active sedimentation in the delta ceased as base-levels fell, and Yarra and Maribyrnong river sediments bypassed the delta because of falling bay levels. The Yarra and Maribyrnong river courses also shifted progressively westwards behind growing beach barriers of the Port Melbourne Sand. A comparable stratigraphy exists between the Yarra Delta and the adjacent Port Phillip Bay, i.e. marine and lagoonal shelly sediments of the Coode Island Silt and barrier sands of the Port Melbourne Sand infill last-glacial channels cut into the middle Pleistocene Fishermans Bend Silt. 相似文献
146.
147.
Else Kolstrup 《第四纪科学杂志》1992,7(2):163-172
Radiocarbon-dated pollen diagrams from four Danish sequences are presented in their sedimentological context. The pollen diagrams indicate the former presence of stands of Betula and Pinus and of Ericales, Poaceae, Cyperaceae and other herbs. From a straightforward comparison with other diagrams, one of the present series is tentatively correlated with part of the Early Weichselian Brørup Interstadial and two with parts of the Odderade Interstadial, which has not been demonstrated previously in Denmark. One diagram and part of another do not seem to match previously published records in northwest Europe. Yet, the possibility that the sediments date to hitherto unrecorded periods with environmental conditions similar to those reflected in known Weichselian deposits is not excluded. In two of the sequences high percentages of charcoal particles suggest the former occurrence of fires, which influenced the palaeovegetation and soil surface stability. It is suggested that counting of charcoal particles is included in future investigations in order to establish whether periods with fires can be identified in the sedimentary sequences. 相似文献
148.
149.
Geoffrey D. Corner Vasili V. Kolka Vladimir Y. Yevzerov Jakob J. Mller 《Global and Planetary Change》2001,31(1-4)
A relative sea-level curve for the Holocene is constructed for Polyarny on the Kola Peninsula, northwest Russia. The curve is based on 18 radiocarbon dates of isolation contacts, identified from lithological and diatomological criteria, in nine lake basins situated between 12 and 57 m a.s.l. Most of the lakes show a conformable, regressive I–II–III (marine–transitional–freshwater) facies succession, indicating a postglacial history comprising an early (10,000–9000 radiocarbon years BP) phase of rapid, glacio-isostatically induced emergence (5 cm year−1) and a later phase (after 7000 years BP,) having a moderate rate of emergence (<0.5 cm year−1). Three lakes together record a phase of very low rate of emergence or slight sea-level rise at a level of 27 m a.s.l., between 8500 and 7000 years BP, which correlates with the regional Tapes transgression. Pollen stratigraphy in the highest lake shows that the area was deglaciated before the Younger Dryas and that previously reconstructed Younger Dryas glacier margins along the north Kola coast lie too far north. 相似文献
150.
Weston Blake Jr. 《Journal of Paleolimnology》1989,2(1):41-54
A small lake on top of Rundfjeld, central Ellesmere Island, at an elevation of approximately 830 m, is frozen to the bottom, and the thickness of lake ice present is at least 5.45 m. Under present climatic conditions the lake does not thaw to the bottom, even during the warmest summers; i.e., 3 to 4 m of ice still floored the deepest part of the lake in mid-August 1987. A radiocarbon age determination via accelerator mass spectrometry (AMS) on a sample of the filamentous green alga Mougeotia sp., recovered from the lake ice at a depth below 4 m, gave 5730±70 BP (TO-530). The date indicates that the lake was probably completely open for an unspecified period of time during the warmest part of the Hypsithermal Interval. This situation is in agreement with data derived from a variety of other sources in Ellesmere Island and adjacent Greenland. 相似文献