全文获取类型
收费全文 | 8070篇 |
免费 | 1067篇 |
国内免费 | 853篇 |
专业分类
测绘学 | 348篇 |
大气科学 | 1158篇 |
地球物理 | 2732篇 |
地质学 | 3638篇 |
海洋学 | 589篇 |
天文学 | 521篇 |
综合类 | 438篇 |
自然地理 | 566篇 |
出版年
2024年 | 20篇 |
2023年 | 70篇 |
2022年 | 123篇 |
2021年 | 164篇 |
2020年 | 116篇 |
2019年 | 141篇 |
2018年 | 580篇 |
2017年 | 490篇 |
2016年 | 392篇 |
2015年 | 298篇 |
2014年 | 271篇 |
2013年 | 273篇 |
2012年 | 805篇 |
2011年 | 579篇 |
2010年 | 241篇 |
2009年 | 304篇 |
2008年 | 267篇 |
2007年 | 235篇 |
2006年 | 250篇 |
2005年 | 940篇 |
2004年 | 950篇 |
2003年 | 726篇 |
2002年 | 234篇 |
2001年 | 155篇 |
2000年 | 151篇 |
1999年 | 173篇 |
1998年 | 127篇 |
1997年 | 159篇 |
1996年 | 125篇 |
1995年 | 81篇 |
1994年 | 105篇 |
1993年 | 81篇 |
1992年 | 57篇 |
1991年 | 44篇 |
1990年 | 60篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 13篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1965年 | 4篇 |
1958年 | 5篇 |
排序方式: 共有9990条查询结果,搜索用时 78 毫秒
31.
In this study we test Talley's hypothesis that Oyashio winter mixed-layer water (26.5–26.6σ θ) increases its density to produce the North Pacific Intermediate Water (NPIW) salinity minimum (26.7– 26.8σθ) in the Mixed Water Region, assuming a combination of cabbeling and double diffusion. The possible density change of Oyashio
winter mixed-layer water is discussed using an instantaneous ratio of the change of temperature and salinity along any particular
intrusion (R
l
). We estimate the range of R
l
DD
required to convert Oyashio winter mixed-layer water to the NPIW salinity minimum due to double diffusion, and then assume
double-diffusive intrusions as this conversion mechanism. A double-diffusive intrusion model is used to estimate R
l
DD
in a situation where salt fingering dominates vertical mixing, as well as to determine whether Oyashio winter mixed-layer
water can become the NPIW salinity minimum. Possible density changes are estimated from the model R
l
DD
by assuming the amount of density change due to cabbeling. From these results, we conclude that Oyashio winter mixed-layer
water contributes to a freshening of the lighter layer of the NPIW salinity minimum (around 26.70σθ) in the MWR. 相似文献
32.
Uwe?LangrockEmail author Ruediger?Stein Marcus?Lipinski Hans-Jürgen?Brumsack 《Geo-Marine Letters》2003,23(1):34-42
The late Volgian (early "Boreal" Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise. 相似文献
33.
九龙江河口区水体中的226Ra和228Ra 总被引:8,自引:0,他引:8
用MnO2-纤维富集大体积水样中的Ra同位素,并用直接射气法测定226Ra和228Ac的β计数法测定228Ra的方法,研究了九龙江河口区226Ra,228Ra的行为,结果表明:在该河口区226Ra,228Ra均呈非保守行为,226Ra,228Ra的最高值分别在盐度为19和9处测得。228Ra/226Ra)A.R.值在盐度小于19的区域约为3左右。与世界其他河口区相比,九龙江河口区的226Ra,22 相似文献
34.
Erkan G?ka?an Cem Gazio?lu Bedri Alpar Zeki Yücel ?ükrü Ersoy O?uz Gündo?du Cenk Yalt?rak Buser Tok 《Geo-Marine Letters》2002,21(4):183-199
Active faults aligning in NW–SE direction and forming flower structures of strike-slip faults were observed in shallow seismic data from the shelf offshore of Avcılar in the northern Marmara Sea. By following the parallel drainage pattern and scarps, these faults were traced as NW–SE-directed lineaments in the morphology of the northern onshore sector of the Marmara Sea (eastern Thrace Peninsula). Right-lateral displacements in two watersheds of drainage and on the coast of the Marmara Sea and Black Sea are associated with these lineaments. This right-lateral displacement along the course of these faults suggests a new, active strike-slip fault zone located at the NW extension of the northern boundary fault of the ?ınarcık Basin in the Marmara Sea. This new fault zone is interpreted as the NW extension of the northern branch of the North Anatolian Fault Zone (NAFZ), extending from the ?ınarcık Basin of the Marmara Sea to the Black Sea coast of the Thrace Peninsula, and passing through B üy ük ?ekmece and K ü ? ük ?ekmece lagoons. These data suggest that the rupture of the 17 August 1999 earthquake in the NAFZ may have extended through Avcılar. Indeed, Avcılar and İzmit, both located on the Marmara Sea coast along the rupture route, were strongly struck by the earthquake whereas the settlements between Avcılar and İzmit were much less affected. Therefore, this interpretation can explain the extraordinary damage in Avcılar, based on the newly discovered rupture of the NAFZ in the Marmara Sea. However, this suggestion needs to be confirmed by further seismological studies. 相似文献
35.
冰心中的气候环境记录与全球变化研究 总被引:1,自引:0,他引:1
冰心是高分辨地记录全球变化的主要信息载体之一。本文总结了冰心中提取古气候和古环境信息的系列记录,包括同位素、微量气体、阴阳离子、微粒、生物和有机质等。着重讨论了由这些记录提取的古气候和古环境变化方面的研究进展,并提出了今后的研究重点。 相似文献
36.
37.
38.
39.
台湾岛的雨量受台湾山地的雨影效应影响明显,各地各月随着风向的不同,雨量表现出很大的差异。福建沿海一线存在着一个雨量低值区,主要是由于该地带所处的地理位置及地形条件所决定,与台湾山地的雨影效应无关。 相似文献
40.
在20×10~9Pa和25×10~9Pa条件下,对石榴石橄榄岩进行的14次高温高压熔融实验研究表明,在1600℃时石榴石橄榄岩开始熔融(初熔),熔体中的SiO_2>70%,Na_2O+K_2O>8%,类似于A型花岗岩成分。本实验为地幔花岗岩的成因提供了证据。 相似文献