全文获取类型
收费全文 | 19843篇 |
免费 | 2920篇 |
国内免费 | 4774篇 |
专业分类
测绘学 | 451篇 |
大气科学 | 645篇 |
地球物理 | 2690篇 |
地质学 | 14130篇 |
海洋学 | 1529篇 |
天文学 | 5120篇 |
综合类 | 774篇 |
自然地理 | 2198篇 |
出版年
2024年 | 79篇 |
2023年 | 218篇 |
2022年 | 495篇 |
2021年 | 602篇 |
2020年 | 636篇 |
2019年 | 771篇 |
2018年 | 593篇 |
2017年 | 648篇 |
2016年 | 752篇 |
2015年 | 719篇 |
2014年 | 1092篇 |
2013年 | 1231篇 |
2012年 | 1204篇 |
2011年 | 1399篇 |
2010年 | 1298篇 |
2009年 | 1729篇 |
2008年 | 1673篇 |
2007年 | 1596篇 |
2006年 | 1525篇 |
2005年 | 1277篇 |
2004年 | 1194篇 |
2003年 | 1023篇 |
2002年 | 878篇 |
2001年 | 787篇 |
2000年 | 818篇 |
1999年 | 659篇 |
1998年 | 491篇 |
1997年 | 401篇 |
1996年 | 332篇 |
1995年 | 290篇 |
1994年 | 244篇 |
1993年 | 207篇 |
1992年 | 140篇 |
1991年 | 100篇 |
1990年 | 91篇 |
1989年 | 69篇 |
1988年 | 65篇 |
1987年 | 27篇 |
1986年 | 36篇 |
1985年 | 32篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 17篇 |
1981年 | 9篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 17篇 |
1877年 | 1篇 |
1875年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
91.
R. F. Griffin 《Journal of Astrophysics and Astronomy》1990,11(4):533-540
Photoelectric radial-velocity measurements show that HD 118670 is a double-lined spectroscopic binary in an orbit which is
not quite circular and whose period is about 48 days. Spectral types of K0 V and K7 V would satisfy the photometry and the
mass ratio; the mass function would then suggest the possibility of eclipses. However, actual spectral classification indicates
a luminosity somewhat above the main sequence 相似文献
92.
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
93.
The purpose of this work was to reinvestigate the existing hydrogeological conceptual model of the basin of Madrid, Spain. A cumulative chemical isotopic diagram which enabled the distinction between different groups of water as well as calculation of the mode of their blending was used for this investigation. It was found that the groups of discharge were lighter in their isotopic composition than that of recharge. The previous explanation of this fact, backed by carbon-14 dating, was the long residence time due to flow lines going down to depths of more than 1000 m. This flow model assumes homogenous conditions to these depths. This assumption can not be supported by evidence from deep wells. Thus a modified model is suggested which maintains homogenous conditions only to about 300 m and a deep confined aquifer below containing paleowater. The higher degree of depletion of this water has been explained by a colder climate on top of an altitude effect. Another interesting observation was the correlation between the isotopic composition of the rains, the month of the rain event and the composition of the recharge group groundwater. It could be seen that the winter rains resemble the groundwater composition, which shows that practically all the spring and summer rains were evapotranspirated. 相似文献
94.
Antony J. Long Sarah A. Woodroffe Sue Dawson David H. Roberts Charlotte L. Bryant 《第四纪科学杂志》2009,24(4):345-359
In West Greenland, early and mid Holocene relative sea level (RSL) fall was replaced by late Holocene RSL rise during the Neoglacial, after 4–3 cal. ka BP (thousand calibrated years before present). Here we present the results of an isolation basin RSL study completed near to the coastal town of Sisimiut, in central West Greenland. RSL fell from 14 m above sea level at 5.7 cal. ka BP to reach a lowstand of ?4.0 m at 2.3–1.2 cal. ka BP, before rising by an equivalent amount to present. Differences in the timing and magnitude of the RSL lowstand between this and other sites in West and South Greenland record the varied interplay of local and non‐Greenland RSL processes, notably the reloading of the Earth's crust caused by a Neoglacial expansion of the Greenland Ice Sheet (GIS) and the subsidence associated with the collapse of the Laurentide Ice Sheet forebulge. This means that the timing of the sea level lowstand cannot be used to infer directly when the GIS advanced during the Neoglacial. The rise in Late Holocene RSL is contrary to recently reported bedrock uplift in the Sisimiut area, based on repeat GPS surveys. This indicates that a belt of peripheral subsidence around the current ice sheet margin was more extensive in the late Holocene, and that there has been a switch from subsidence to uplift at some point in the last thousand years or so. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
95.
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
96.
97.
98.
99.
100.