全文获取类型
收费全文 | 519篇 |
免费 | 89篇 |
国内免费 | 67篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 96篇 |
地球物理 | 178篇 |
地质学 | 192篇 |
海洋学 | 97篇 |
天文学 | 9篇 |
综合类 | 5篇 |
自然地理 | 59篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 9篇 |
2019年 | 30篇 |
2018年 | 8篇 |
2017年 | 23篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 36篇 |
2013年 | 35篇 |
2012年 | 19篇 |
2011年 | 32篇 |
2010年 | 25篇 |
2009年 | 29篇 |
2008年 | 50篇 |
2007年 | 28篇 |
2006年 | 36篇 |
2005年 | 29篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 26篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有675条查询结果,搜索用时 15 毫秒
671.
672.
末次冰期冰盛期(或称为末次盛冰期),为第四纪更新世最后一个冰期的鼎盛时期,该时期的气候与当代气候迥然不同。近年来,中国科研工作者已就末次冰期冰盛期东亚区域气候开展了一些数值模拟工作。结果表明:该时期中国大陆地表气温降低,中东部地区降水显著减少,东亚冬季风增强、夏季风显著减弱。在国际古气候模拟比较计划(PMIP)标准试验的基础上,进一步指出东亚植被的反馈作用、青藏高原可能冰川的反馈作用、以及西太平洋表面温度的作用能够引起额外的气候效应,可在一定程度上改进PMIP标准试验的模拟效果。 相似文献
673.
674.
675.
Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes. 相似文献