全文获取类型
收费全文 | 2363篇 |
免费 | 364篇 |
国内免费 | 461篇 |
专业分类
测绘学 | 108篇 |
大气科学 | 60篇 |
地球物理 | 743篇 |
地质学 | 1252篇 |
海洋学 | 224篇 |
天文学 | 9篇 |
综合类 | 324篇 |
自然地理 | 468篇 |
出版年
2024年 | 4篇 |
2023年 | 26篇 |
2022年 | 66篇 |
2021年 | 72篇 |
2020年 | 79篇 |
2019年 | 77篇 |
2018年 | 73篇 |
2017年 | 55篇 |
2016年 | 55篇 |
2015年 | 58篇 |
2014年 | 96篇 |
2013年 | 107篇 |
2012年 | 105篇 |
2011年 | 94篇 |
2010年 | 84篇 |
2009年 | 98篇 |
2008年 | 119篇 |
2007年 | 169篇 |
2006年 | 163篇 |
2005年 | 145篇 |
2004年 | 151篇 |
2003年 | 153篇 |
2002年 | 110篇 |
2001年 | 116篇 |
2000年 | 120篇 |
1999年 | 83篇 |
1998年 | 100篇 |
1997年 | 101篇 |
1996年 | 84篇 |
1995年 | 79篇 |
1994年 | 69篇 |
1993年 | 61篇 |
1992年 | 46篇 |
1991年 | 39篇 |
1990年 | 23篇 |
1989年 | 19篇 |
1988年 | 29篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1954年 | 4篇 |
排序方式: 共有3188条查询结果,搜索用时 406 毫秒
31.
Extensive organic-matter (OM) rich facies (black shales) occur in the Ordo-Silurian boundary successions in the Yangtze area, South China. To investigate the redox changes of the Yangtze Sea during the Ordo-Silurian transition, two OM sections (Wangjiawan in Yichang, Hubei Province, and Sanjiaguan in Zhangjiajie, Hunan Province) straddling the Ordo-Silurian boundary are studied. The measurements finished in this study include contents of the total organic carbon (TOC), pyrite sulphur, and different species of Fe, including dithionite-extractable Fe (FED), pyrite Fe (FeP), HCl-extractable Fe (FeH), and total Fe (FeT), in black shales, as well as other redox proxies, such as the SIC ratio, the ratio between highly reactive Fe (FeHR = FeD + FeP) and FeT, and the FeP/(FeP + FeH) ratio, known as the degree of pyritization (DOP). In the Wangjiawan section, the Middle Ashgill sediments have high FeHR/FeT ratios (0.20-0.77; avg. 0.45), high DOP values (0.21-0.72; avg. 0.54), and a relatively constant sulfur content independent of the organic carbon content. By the contrast, the mid-early Hirnantian deposits generally have low FeHR/FeT ratios (0.10-0.35; avg. 0.21), low DOP values (0.11- 0.40; avg. 0.28), and SIC values are clustering on the normal marine value (SIC = 0.36). The late Hirnantian and early Rhuddanian deposits, similar to those of the Middle Ashgill deposits, are characterized by high FeHR/FeT ratios (0.32-0.49; avg. 0.41), high DOP values (0.46-0.68; avg. 0.53) and fairly constant sulfur contents. These data suggest the occurrences of marine anoxia on the Yangtze Sea shelf during intervals of the Mid Ashgill, Late Hirnantian and Early Rhuddanian, and ventilated and oxygenated marine conditions during the mid-early Hirnantian time. The mid-early Hirnantian ventilated event was concomitant with the global glacial period, likely resulted from the glacio-eustatic sea-level fall and subsequent circulation of cold, dense oxygenated waters 相似文献
32.
以1999-2004年间中国西部地区近650个GPS站点的观测资料为基础,采用二维“高张力样条”函数内插算法获得了连续地壳形变场。结果表明,相对于稳定欧亚参考框架,中国西部现今地壳运动西强东弱,北向运动从西向东逐渐减弱,东向运动逐渐增强,青藏高原东缘及附近地区是东向运动的消减区带;主应变从西向东由压缩应变转变为拉伸应变;最大剪应变主要位于喜马拉雅地块及其东部地区;中国西部地区地震活动在空间分布上似乎集中发生在印度板块北东向挤压欧亚板块的两条共扼带内,与地壳形变场有一定对应关系,地壳形变的高应变率区为中强地震多发地带。 相似文献
33.
34.
Sukanta Roy Labani Ray Anurup Bhattacharya R. Srinivasan 《International Journal of Earth Sciences》2008,97(2):245-256
The Late Archaean Closepet Granite batholith in south India is exposed at different crustal levels grading from greenschist
facies in the north through amphibolite and granulite facies in the south along a ∼400 km long segment in the Dharwar craton.
Two areas, Pavagada and Magadi, located in the Main Mass of the batholith, best represent the granitoid of the greenschist
and amphibolite facies crustal levels respectively. Heat flow estimates of 38 mW m−2 from Pavagada and 25 mW m−2 from Magadi have been obtained through measurements in deep (430 and 445 m) and carefully sited boreholes. Measurements made
in four boreholes of opportunity in Pavagada area yield a mean heat flow of 39 ± 4 (s.d.) mW m−2, which is in good agreement with the estimate from deep borehole. The study, therefore, demonstrates a clear-cut heat flow
variation concomitant with the crustal levels exposed in the two areas. The mean heat production estimates for the greenschist
facies and amphibolite facies layers constituting the Main Mass of the batholith are 2.9 and 1.8 μW m−3, respectively. The enhanced heat flow in the Pavagada area is consistent with the occurrence of a radioelement-enriched 2-km-thick
greenschist facies layer granitoid overlying the granitoid of the amphibolite facies layer which is twice as thick as represented
in the Magadi area. The crustal heat production models indicate similar mantle heat flow estimates in the range 12–14 mW m−2, consistent with the other parts of the greenstone-granite-gneiss terrain of the Dharwar craton. 相似文献
35.
V. F. Uarov 《Pure and Applied Geophysics》1994,142(2):311-318
Deep seismic sounding in the region of the Mirnyi kimberlite field indicates that the boundary velocity of the uppermost mantle is elevated (v
b=8.6–8.8 km/sec) and extremely variable near the Mir kimberlite pipe. These velocity heterogeneities are probably associated with the kimberlite magmatism and may be useful in the identification of other kimberlite fields. 相似文献
36.
钻遇莫霍面是人类一直以来的梦想。深海海底是地球上离莫霍面最近的地方,目前有研究推测南海是世界上莫霍面深度最浅的海域之一,但缺乏足够的直接证据。深反射地震探测可以直接揭示岩石圈的构造形态,是莫霍面探测的重要手段。本文基于长达15000 km的深反射多道地震剖面的解释、处理、制图和分析,结合前人的研究,形成了南海海盆区莫霍面反射特征和空间分布的初步认识。① 南海东部次海盆南部早期经历了较快速扩张,岩浆供应充足,受扩张停止后岩浆活动影响较小,基底平坦,地质构造相对简单,同时洋壳地震速度结构不存在异常,且有较强的广角莫霍面反射波和可识别的地幔顶部折射波,具备莫霍面钻探的基本条件。② 南海海盆不同区域的莫霍面反射强度存在较大差异。其中东部次海盆莫霍面反射最为强烈且清晰,西北次海盆次之,西南次海盆仅有零星出现的清晰莫霍面反射且可信度不高。③ 识别南海海盆区莫霍面地震反射长度超过3500 km,首次形成了海盆区深度域莫霍面地震反射空间分布图。与重力反演的莫霍面深度相比,利用深反射多道地震计算的莫霍面深度细节更为丰富,并且可以在垂向上清晰刻画莫霍面的结构。整体上,南海海盆区莫霍面地震反射强烈和可信度高的区域中,深度较浅的区域之一是东部次海盆南部,最浅处仅约9. 5 km,其中水深4. 01 km,洋壳厚度仅5. 54 km。综合判断,东部次海盆南部是南海重要的莫霍面钻探备选区,这对南海莫霍面钻探选址具有重要意义。 相似文献
37.
中国大陆第四纪地壳运动时程 总被引:5,自引:0,他引:5
本文从中国大陆有代表性的青藏高原、黄土高原、三峡地区着手,进行了新构造运动剖析。并结合全国火山活动期次,总结出中国大陆第四纪地壳运动的时程变化。从而为进一步探讨新构造运动特点和规律,为国民经济建设及人类生存环境提供了一定的地质背景资料。 相似文献
38.
Daily measurements of atmospheric concentrations of dimethylsulfide (DMS) were carried out for two years in a marine site at remote area: the Amsterdam Island (37°50S–77°31E) located in the southern Indian Ocean. DMS concentrations were also measured in seawater. A seasonal variation is observed for both DMS in the atmosphere and in the sea-surface. The monthly averages of DMS concentrations in the surface coastal seawater and in the atmosphere ranged, respectively, from 0.3 to 2.0 nmol l-1 and from 1.4 to 11.3 nmol m-3 (34 to 274 pptv), with the highest values in summer. The monthly variation of sea-to-air flux of DMS from the southern Indian Ocean ranges from 0.7 to 4.4 mol m-2 d-1. A factor of 2.3 is observed between summer and winter with mean DMS fluxes of 3.0 and 1.3 mol m-2 d-1, respectively. 相似文献
39.
40.
The relationship between depth, age and gravity in the oceans 总被引:2,自引:0,他引:2