全文获取类型
收费全文 | 128篇 |
免费 | 55篇 |
国内免费 | 20篇 |
专业分类
地球物理 | 11篇 |
地质学 | 163篇 |
海洋学 | 10篇 |
天文学 | 1篇 |
综合类 | 2篇 |
自然地理 | 16篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 10篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 4篇 |
2009年 | 4篇 |
2008年 | 10篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 6篇 |
2002年 | 12篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1992年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有203条查询结果,搜索用时 109 毫秒
31.
32.
YunFa Miao XiaoMin Fang ZhiChen Song FuLi Wu WenXia Han Shuang Dai ChunHui Song 《中国科学D辑(英文版)》2008,51(8):1089-1098
The Eocene palaeovegetation landscape and palaeoclimate reconstructed from the pollen records in the Jiuquan Basin, northwest
China provide some important information on the early uplift of the Tibetan Plateau and the origin and evolution of the aridification
in northwest China. The records show the arid-semiarid scrubs with open forest palynofloras controlled by the subtropical
high existed in northwest China during the 40.2–33.4 Ma. Four pollen assemblages are found: Nitrariadites-Cheno-podipollis-Pinaceae assemblage (40.2–37.9 Ma) is followed by Chenopodipollis-Nitrariadites assemblage (37.9–34.6 Ma), Pinuspollenites & Abietineaepollenites-Chenopodipollis assemblage (34.6–33.9 Ma), and Chenopodipollis-Nitrariadites assemblage (33.9–33.4 Ma). The percentage of thermophilic types is in anti-correlation with that of the dry types, which
means the palaeoclimate is relatively warm-wet or cold-dry during most of that time. Such aridity may be related to the water
vapor reduction and the planetary wind system movement northward in response to the cooling caused by small-ephemeral ice-sheets.
Supported by the National Key Program for Developing Basic Sciences (Grant No. 2005CB422001), the National Science Foundation
of China (Grant Nos. 40334038, 40421101) and the President Fund of Chinese Academy of Sciences 相似文献
33.
Euloma changshanense Lu采自浙江江山下奥陶统,是一个蜕壳老壳的部分及自由颊腹边缘的印痕。从这后期破损的残壳分析其蜕壳过程,认为两自由颊在头前中间连接,蜕壳时在虫体拱曲时脱落于头前,但还在新壳之上,后被新的虫体顶走,只残存自由颊腹边缘在头前的印痕。这反映了三叶虫在蜕壳过程中有一停顿休息时间,而新的虫体常常顶走或拖走老的头壳上的自由颊和唇瓣,使老壳留下缺失的背壳部件。蜕壳过程是瞬间发生的,即只有原地埋葬才能保存这一状态,说明当时三叶虫处于比较宁静的水中,又处于沉积物供给充足的环境,在蜕壳过程中或不久即被沉积物掩埋。浙江江山印渚埠组的厚度较大,上面直接覆盖着大湾阶底部的Azygograptus suecicus带;而相邻不远的江西玉山印渚埠组顶部,上覆为玉山阶的底部Tetragraptus approximatus带,证明印渚埠组是穿时的。而两个地方的印渚埠组顶部都常产有Euloma changshanense Lu,说明此三叶虫虽为下奥陶统常见化石,但延续时间较长,在特马豆克晚期到整个玉山阶都存在,也说明印渚埠组沉积厚度较大,但整个沉积环境变化不大,即使三叶虫Euloma changshanenes等种属也很少变化。这是研究三叶虫蜕壳及其生态替换、演变的好层位。 相似文献
34.
Three-dimensional modelling of a Holocene tufa system in the Lathkill Valley, north Derbyshire, using ground-penetrating radar 总被引:1,自引:0,他引:1
Unlithified and partly lithified carbonate sequences are ideally suited to the application of ground‐penetrating radar (GPR), augmented by percussion augering and shallow seismic techniques, all tied to present‐day topography using global positioning system (GPS) methods. This methodology provides the first clear information on the distribution and geometry of lithofacies within buried tufa complexes. The approach has been applied to a thick succession of Holocene tufas filling a gorge site along a 3·5‐km length of the River Lathkill, north Derbyshire. Earlier studies have demonstrated the presence of up to 16 m of tufas and sapropels associated with two transverse tufa dams (barrages). These strata have been accumulating throughout the Holocene, although tufa developments at present are of minor extent. Internal tufa morphologies are recorded by GPR as ‘bright’, laterally continuous reflections for lithified, concretionary and lithoclast‐rich horizons. The ‘brightest’ reflectors occur within well‐cemented barrages and delineate core areas and prograding buttress zones. In contrast, unlithified lime muds and sapropels produce low‐contrast reflections. Lithostratigraphic control and depth calibration of the GPR profiles was provided by percussion augering at selected sites. Six distinct lithofacies and four secondary barrages are identified in the study. Constructional and destructional events can be identified and correlated within the GPR profile network, and the internal growth morphologies of the barrages are apparent. GPR profiles also clearly define the evolution of the facies geometries. Three phases of tufa development can be recognized within the GPR data and greatly extend our understanding of Holocene tufa‐forming processes in valley sites: (a) Early Holocene barrage build‐ups but with limited paludal deposition; (b) Middle Holocene ponding and sapropel accumulation under ‘warm’ conditions; and (c) Late Holocene barrage termination and valley levelling, probably coincidental with anthropogenic activity. This type of multidisciplinary approach should be considered as an essential prerequisite to all biostratigraphic and geochemical studies of Holocene freshwater carbonate sites. 相似文献
35.
36.
37.
The organic matter-rich Toolebuc Formation of eastern Australia was deposited in a Lower Cretaceous epicontinental sea. Parameters from biological marker studies indicate that the organic matter is immature to marginally mature for hydrocarbon generation. The occurrence of abundant coccoliths and the distribution of alkane biomarkers suggest that the organic matter (Type II) is largely of planktonic origin and only in the southeastern part of the depositional area can a terrestrial influence be discerned. Variations in kerogen composition can be attributed to the extent of the oxidation of the source materials and the degree of incorporation of sulphur. The atomic H/C ratios (c. 1.1) are remarkably constant for most of the Toolebuc Formation. Atomic O/C ratios vary from 0.1 and 0.4 and can be related both to depth and paleogeographic position. Kerogen sulphur contents range up to 7%, and the highest values occur in the most carbonate-rich sediments. Total sulphur (inorganic + organic) to carbon ratios in the sediments vary from 1 to <0.2 and are a function of paleogeographic position and lithology. Most of the sulphur in the sediments is in the form of pyrite, but the proportion of sulphur in organic form increases as the total sulphur content decreases. The evidence for oxidation of the organic matter and incorporation of sulphur into it during deposition suggests that bituminite, which is the dominant organic maceral in the Toolebuc Formation, was formed from an organic gel derived by decay of predominantly algal material. These data support a modified gyttja model (Kauffman, 1981) for the deposition of organic matter in the Toolebuc Formation. 相似文献
38.
What does the occurrence of Sporormiella (Preussia) spores mean in Australian fossil sequences?
下载免费PDF全文
![点击此处可从《第四纪科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Understanding the loss of the final few species of Australian megafauna is beset by a paucity of data on human arrival, well‐provenanced megafauna, human/megafauna population range and distribution (coexistence and interaction), and the range, scale and impact of environmental changes spanning the human–megafauna period. To overcome these shortcomings, the occurrence and decline of coprophilous fungal spores of Sporormiella in sediments have been used as a proxy for extinct megaherbivores. The Sporormiella evidence is presented as the key indicator of extinction timing and these reports are often from locations where there is no known archaeological record or megafauna remains. However, interpreting fungal spore occurrence is not straightforward, as demonstrated by studies investigating taphonomy, taxonomy and the types of animal dung where Sporormiella occurs. No detailed studies on these problems exist for Australia and no evidence supporting the use of Sporormiella as a valid proxy has been reported. Here we examine the occurrence of Sporormiella spores from Cuddie Springs in south‐eastern Australia. Despite a well‐preserved suite of megafauna fossils, Sporormiella occurrence is sporadic and frequencies are low. We conclude that using Sporormiella alone as an indicator for the presence of megafauna is premature for the Australian context. 相似文献
39.
40.
羌塘盆地白垩系海相油页岩特征及其形成条件分析 总被引:2,自引:0,他引:2
近年来,在羌塘盆地胜利河、长梁山、长蛇山、托纳木等地发现的油页岩为目前我国规模最大的海相油页岩矿床,具有重要的工业开采价值。海相油页岩的主要矿物成分为碳酸盐、粘土矿物和石英,并见有黄铁矿、石膏、菱镁矿等矿物。粘土矿物以伊利石为主,少量高岭石,不含蒙脱石。有机地球化学分析表明,这些油页岩的有机质丰度较高,有机质类型较好。胜利河油页岩TOC含量在4.31%~21.37%之间,均值为8.40%;托纳木油页岩的TOC含量也较高,最大值为25.68%,平均为9.32%;长梁山剖面油页岩的TOC含量在2.96%~23.47%之间,平均值为9.56%;长蛇山油页岩的TOC含量在4.53%~9.49%之间,平均值为7.74%。长蛇山油页岩干酪根类型主要为Ⅱ1型,少数为Ⅱ2和Ⅲ型;胜利河油页岩主要为Ⅱ1和Ⅱ2型干酪根,而托纳木油页岩的干酪根类型主要为Ⅱ1型和Ⅰ型。白垩系海相油页岩的形成受多方面因素控制,包括缺氧富氧状态、古生产力、古气候、粘土矿物的混积作用、古地形条件以及海平面变化等。其中,油页岩的总有机碳含量(TOC)与古环境元素指标Mo、V存在较强的相关关系,相关系数分别为0.975和0.917,而与古生产力指标P/Ti、Ba/Al之间为弱相关或无相关关系,相关系数分别为0.481和-0.739。因此,本文认为海相油页岩的形成以"保存模式"为主,有机质沉积时的水体环境对高有机质含量的油页岩的形成起主导作用,并在此基础上建立了海相油页岩的形成演化模式。 相似文献