全文获取类型
收费全文 | 26106篇 |
免费 | 3510篇 |
国内免费 | 4207篇 |
专业分类
测绘学 | 1195篇 |
大气科学 | 4218篇 |
地球物理 | 6957篇 |
地质学 | 11411篇 |
海洋学 | 3232篇 |
天文学 | 1973篇 |
综合类 | 1762篇 |
自然地理 | 3075篇 |
出版年
2023年 | 296篇 |
2022年 | 784篇 |
2021年 | 948篇 |
2020年 | 790篇 |
2019年 | 886篇 |
2018年 | 1053篇 |
2017年 | 1012篇 |
2016年 | 1197篇 |
2015年 | 999篇 |
2014年 | 1151篇 |
2013年 | 1541篇 |
2012年 | 1199篇 |
2011年 | 1294篇 |
2010年 | 1324篇 |
2009年 | 1326篇 |
2008年 | 1149篇 |
2007年 | 1160篇 |
2006年 | 963篇 |
2005年 | 872篇 |
2004年 | 749篇 |
2003年 | 775篇 |
2002年 | 754篇 |
2001年 | 664篇 |
2000年 | 781篇 |
1999年 | 1042篇 |
1998年 | 894篇 |
1997年 | 856篇 |
1996年 | 835篇 |
1995年 | 757篇 |
1994年 | 696篇 |
1993年 | 600篇 |
1992年 | 520篇 |
1991年 | 391篇 |
1990年 | 323篇 |
1989年 | 272篇 |
1988年 | 268篇 |
1987年 | 224篇 |
1986年 | 206篇 |
1985年 | 229篇 |
1984年 | 242篇 |
1983年 | 198篇 |
1982年 | 181篇 |
1981年 | 170篇 |
1980年 | 148篇 |
1979年 | 156篇 |
1978年 | 132篇 |
1977年 | 112篇 |
1976年 | 102篇 |
1975年 | 99篇 |
1973年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
61.
位于华南褶皱带南缘的右江盆地,其发展可分为两个不同的阶段。它的轮廓和结构,与NW向及NE向同沉积断裂关系密切。盆地内的沉积物,分别由特征不同的非补偿性和补偿性沉积相组成两个双层结构。盆地内火山活动发育,也明显的分为两个阶段。海西期,古特提斯洋的发展使哀牢山洋盆开裂,导致了右江地区在拉张应力条件下出现若干NW向裂陷带,这时的盆地具有大陆边缘裂谷特点。东吴运动后开始的印支期,区域应力条件发生变化。滨大平洋构造的发生,使盆地轮廓和结构发生明显变化,与此同时开始的哀牢山洋盆向NE方向的俯冲消减作用,使盆地在新的挤压条件下再次发生张裂和拗陷。进入了弧后盆地发展阶段。印支期末,盆地封闭。 相似文献
62.
我们于1989年11月30日晚对PG0027+260进行了时间分辨率为108秒的高速CCD测光,得到了一条完整的光变曲线,从而确认其为激变食变星系统,轨道周期0.146~d 相似文献
63.
John Aitchison 《Mathematical Geology》1991,23(8):1081-1083
64.
Da-Ming Chen 《中国天文和天体物理学报》2001,1(4):287-290
1 INTRODUCTIONObservations of the most famous starburst galaxy M82 with the High-Resolution Cameraon board the Chandra X-Ray Observatory, showed that there are nine sources in the celltral11 x 11 region, but no son-roe was detected at the galactic center (Matsumoto et al. 2001).Comparing the observations on 1999 October 28 and those on 2000 January 20, the authorsfound an extremely large time variability of the source CXO M82 J095550.2 694047, which islocated gll away from the galact… 相似文献
65.
低频扩频中伪随机序列产生方法的研究 总被引:2,自引:0,他引:2
伪随机序列的产生是实现BPC低频时码发播台扩展频谱技术升级的一个重要环节。针对BPC低频时码发播台的现有系统,提出了伪随机序列的产生方案,并对其性能作了分析。 相似文献
66.
67.
Miniature gravity corer for recovering short sediment cores 总被引:12,自引:0,他引:12
John R. Glew 《Journal of Paleolimnology》1991,5(3):285-287
68.
Richard C. Preece Simon A. Parfitt G. Russell Coope Kirsty E. H. Penkman Philippe Ponel John E. Whittaker 《第四纪科学杂志》2009,24(6):557-580
Considerable debate surrounds the age of the Middle Pleistocene glacial succession in East Anglia following some recent stratigraphical reinterpretations. Resolution of the stratigraphy here is important since it not only concerns the glacial history of the region but also has a bearing on our understanding of the earliest human occupation of north‐western Europe. The orthodox consensus that all the tills were emplaced during the Anglian (Marine Isotope Stage (MIS) 12) has recently been challenged by a view assigning each major till to a different glacial stage, before, during and after MIS 12. Between Trimingham and Sidestrand on the north Norfolk coast, datable organic sediments occur immediately below and above the glacial succession. The oldest glacial deposit (Happisburgh Till) directly overlies the ‘Sidestrand Unio‐bed’, here defined as the Sidestrand Hall Member of the Cromer Forest‐bed Formation. Dating of these sediments therefore has a bearing on the maximum age of the glacial sequence. This paper reviews the palaeobotany and describes the faunal assemblages recovered from the Sidestrand Unio‐bed, which accumulated in a fluvial environment in a fully temperate climate with regional deciduous woodland. There are indications from the ostracods for weakly brackish conditions. Significant differences are apparent between the Sidestrand assemblages and those from West Runton, the type site of the Cromerian Stage. These differences do not result from contrasting facies or taphonomy but reflect warmer palaeotemperatures at Sidestrand and a much younger age. This conclusion is suggested by the higher proportion of thermophiles at Sidestrand and the occurrence of a water vole with unrooted molars (Arvicola) rather than its ancestor Mimomys savini with rooted molars. Amino acid racemisation data also indicate that Sidestrand is significantly younger than West Runton. These data further highlight the stratigraphical complexity of the ‘Cromerian Complex’ and support the conventional view that the Happisburgh Till was emplaced during the Anglian rather than the recently advanced view that it dates from MIS 16. Moreover, new evidence from the Trimingham lake bed (Sidestrand Cliff Formation) above the youngest glacial outwash sediments (Briton's Lane Formation) indicates that they also accumulated during a Middle Pleistocene interglacial – probably MIS 11. All of this evidence is consistent with a short chronology placing the glacial deposits within MIS 12, rather than invoking multiple episodes of glaciation envisaged in the ‘new glacial stratigraphy’ during MIS 16, 12, 10 and 6. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
69.
A new analysis of all 346 published 14C dated Holocene alluvial units in Britain offers a unique insight into the regional impacts of global change and shows how surprisingly sensitive British rivers have been to relatively modest but repeated changes in climate. Fourteen major but probably brief periods of flooding are identified bracketed within the periods 400–1070, 1940–3940, 7520–8100 and at ca. 10 420 cal. yr BP. There is a strong correspondence between climatic deteriorations inferred from mire wet shifts and major periods of flooding, especially at ca. 8000 cal. yr BP and since ca. 4000 cal. yr BP. The unusually long and complete British record also demonstrates that alterations in land cover have resulted in a step change in river basin sensitivity to variations in climate. This has very important implications for assessing and mitigating the impact of increasing severe flooding. In small and medium‐sized river basins land use is likely to play a key role in either moderating or amplifying the climatic signal. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
70.
地倾斜台站数字化、模拟观测数据频率特性研究 总被引:2,自引:2,他引:0
分析了四川、云南的部分地倾斜数字化观测与模拟观测资料的特性,从频率范围,周期10天以上的FFT谱特性,固体潮波振幅,相位特征值等方面,论述了地倾斜数字化资料较模拟记录资料的信息组成变化,并对资料的分析与应用进行了初步探讨。 相似文献