全文获取类型
收费全文 | 87199篇 |
免费 | 1375篇 |
国内免费 | 656篇 |
专业分类
测绘学 | 2472篇 |
大气科学 | 6713篇 |
地球物理 | 17624篇 |
地质学 | 29603篇 |
海洋学 | 7299篇 |
天文学 | 20097篇 |
综合类 | 214篇 |
自然地理 | 5208篇 |
出版年
2021年 | 695篇 |
2020年 | 766篇 |
2019年 | 834篇 |
2018年 | 1927篇 |
2017年 | 1847篇 |
2016年 | 2356篇 |
2015年 | 1490篇 |
2014年 | 2330篇 |
2013年 | 4489篇 |
2012年 | 2435篇 |
2011年 | 3127篇 |
2010年 | 2913篇 |
2009年 | 3814篇 |
2008年 | 3358篇 |
2007年 | 3325篇 |
2006年 | 3123篇 |
2005年 | 2611篇 |
2004年 | 2593篇 |
2003年 | 2414篇 |
2002年 | 2387篇 |
2001年 | 2116篇 |
2000年 | 1978篇 |
1999年 | 1794篇 |
1998年 | 1728篇 |
1997年 | 1746篇 |
1996年 | 1431篇 |
1995年 | 1397篇 |
1994年 | 1322篇 |
1993年 | 1184篇 |
1992年 | 1093篇 |
1991年 | 1081篇 |
1990年 | 1165篇 |
1989年 | 1070篇 |
1988年 | 987篇 |
1987年 | 1160篇 |
1986年 | 983篇 |
1985年 | 1257篇 |
1984年 | 1484篇 |
1983年 | 1360篇 |
1982年 | 1316篇 |
1981年 | 1238篇 |
1980年 | 1073篇 |
1979年 | 1045篇 |
1978年 | 1048篇 |
1977年 | 947篇 |
1976年 | 872篇 |
1975年 | 825篇 |
1974年 | 863篇 |
1973年 | 895篇 |
1972年 | 566篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
R. A. Heath 《Marine Geodesy》2013,36(4):337-350
Tide gauge records from several New Zealand east coast ports show persistent oscillations in sea level with a period of 2.4–2.7 h. These are superimposed on local resonant oscillations, and appear to be associated with edge wave excitation on the continental shelf, possibly by meteorological disturbances. A shelf response is also excited by tsunamis. 相似文献
912.
A 35 mm camera system has been developed to operate to depths of 4,000 m. The system takes up to 24 pictures at one lowering, and uses standard torch batteries which last more than 10 lowerings. 相似文献
913.
914.
915.
916.
917.
918.
The present experimental investigation focuses on the characteristics of near bed turbulence in a fully rough, uniform open-channel
flow over a gravel-type bed. Due to bed topography small scale heterogeneity, the flow is not uniform locally in the near
bed region and a double averaging methodology is applied over a length scale much larger than the gravel size. The double-averaged
Turbulent Kinetic Energy (TKE) budget derived in the context of the present flow over a gravel bed differs from the TKE budget
written for flow over a vegetation canopy. The non-constant shape of the roughness function measured in our gravel bed leads
to an additional bed-induced production term which is null for vertical roughness elements, such as simplified vegetation
elements.
The experimental estimation of the terms of the TKE budget reveals that the maximum turbulent activity takes place away from
the reference plane, near the roughness crests. However, within the interface sublayer the work of the bed induced velocity
fluctuations against the Reynolds stress is of the same magnitude as the main turbulence production term. Consequently, the
characteristics of the TKE budget have similarities with uniform flows over canopies and strongly differ from uniform flows
over smooth and transitionally rough flows over sedimentlike beds. 相似文献
919.
B. Wagner R. Sulpizio G. Zanchetta S. Wulf M. Wessels G. Daut N. Nowaczyk 《Journal of Volcanology and Geothermal Research》2008
A 1075 cm long core (Lz1120) was recovered in the south-eastern part of the Lake Ohrid (Republics of Macedonia and Albania) and sampled for identification of tephra layers. Magnetic susceptibility investigations show rather high magnetic values throughout the core, with peaks unrelated to the occurrence of tephra layers but instead to the relative abundance of detrital magnetic minerals in the sediment. Naked-eye inspection of the core allowed us to identify of two tephra layers, at 896–897 cm and 1070–1075 cm. Laboratory inspection of the grain-size fraction > 125 μm allowed for the identification of a third cryptotephra at 310–315 cm. Major element analyses on glass shards of the tephra layers at 896–897 cm and 1070–1075 cm show a trachytic composition, and indicate a correlation with the regionally dispersed Y-3 and Y-5 tephra layers, dated at ca 30 and 39 cal ka BP. The cryptotephra at 310–315 cm has a mugearitic–benmoreitic composition, and was correlated with the FL eruption of Mt. Etna, dated at 3370 ± 70 cal yr BP. These ages are in agreement with five 14C AMS measurements carried out on plant remains and macrofossils from the lake sediments at different depths along the core. 相似文献
920.
J.T. Caulfield S.P. Turner A. Dosseto N.J. Pearson C. Beier 《Earth and Planetary Science Letters》2008,273(3-4):279-288
The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism.We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab. 相似文献