全文获取类型
收费全文 | 123篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 8篇 |
地球物理 | 33篇 |
地质学 | 54篇 |
海洋学 | 15篇 |
天文学 | 3篇 |
综合类 | 1篇 |
自然地理 | 11篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 2篇 |
2013年 | 8篇 |
2012年 | 8篇 |
2011年 | 18篇 |
2010年 | 10篇 |
2009年 | 11篇 |
2008年 | 3篇 |
2007年 | 5篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
排序方式: 共有131条查询结果,搜索用时 17 毫秒
61.
de Almeida EA Miyamoto S Bainy AC de Medeiros MH Di Mascio P 《Marine pollution bulletin》2004,49(5-6):386-392
Levels of antioxidant defenses and lipid peroxidation were evaluated in mussels exposed to lead (200 mg/l), iron (500 microg/l), cadmium (200 microg/l) and copper (40 microg/l), for 12, 24, 72 and 120 h. Glutathione S-transferase (GST) activity was unchanged with all treatments. Catalase (CAT) increased after 120 h of exposure to all metals. Mussels exposed to Cd for 12 h, and to Cu and Fe for 120 h had increased lipid peroxidation, which might be associated to decreased levels of reduced glutathione (GSH) and glutathione peroxidase (GPx) activity. Pb exposure caused GSH depletion after 12 h and increased GPx activity after 120 h. Negative correlations were observed between the enzyme phospholipid hydroperoxide glutathione peroxidase (PHGPx) and malonaldehyde (MDA) levels after Fe and Cu exposure, indicating a protective role of PHGPx against lipid peroxidation, and suggesting the use of this enzyme as a new potential biomarker of toxicity associated with contaminant exposure in mussels. 相似文献
62.
63.
The aim of the current work was to determine over 10 days the effects of water-borne exposure of the marine amphipod Gammarus locusta to 4 μgCu l−1 on the metallothionein (MT; measured by differential pulse polarography) protection system and lipid peroxidation (LP; thiobarbituric acid-reactive malondialdehyde equivalents) as a measure of oxidative damage. MT levels in exposed animals increased significantly at day 2 (36% > control; P<0.001) and remained high at days 6 and 10 (55 and 38%, respectively, P<0.001). The maximum level of MT at day 6 coincided with the highest Cu body-burden. LP increased within 1 day of exposure, indicative of Cu as an oxidative stressor. However, in contrast to MT, the highest LP level was seen at day 4 (68% > control, P<0.001) before returning to control values by day 6, indicating a protective role of MT against the pro-oxidant effects of Cu. 相似文献
64.
65.
Wesley R. Farnsworth Ólafur Ingólfsson Riko Noormets Lis Allaart Helena Alexanderson Mona Henriksen Anders Schomacker 《Boreas: An International Journal of Quaternary Research》2017,46(3):585-603
Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord‐system on the west coast of Spitsbergen, Svalbard. High‐resolution, remotely sensed imagery from marine and terrestrial environments was used to construct geomorphological maps that highlight an intricate glacial history of the entire fjord‐system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial–early Holocene transition. Identification and 14C dating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0±0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial‐Little Ice Age in inner St. Jonsfjorden. The present‐day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up‐fjord from its Neoglacial maximum extent. Cross‐cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break‐up of Osbornebreen. Glacial deposits, landforms and their cross‐cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene. 相似文献
66.
Jakob Heyman Arjen P. Stroeven Marc W. Caffee Clas Hättestrand Jonathan M. Harbor Yingkui Li Helena Alexanderson Liping Zhou Alun Hubbard 《Quaternary Science Reviews》2011,30(15-16):1988-2001
The Bayan Har Shan, a prominent upland area in the northeastern sector of the Tibetan Plateau, hosts an extensive glacial geological record. To reconstruct its palaeoglaciology we have determined 10Be exposure ages based on 67 samples from boulders, surface pebbles, and sediment sections in conjunction with studies of the glacial geology (remote sensing and field studies) and numerical glacier modelling. Exposure ages from moraines and glacial sediments in Bayan Har Shan range from 3 ka to 129 ka, with a large disparity in exposure ages for individual sites and within the recognised four morphostratigraphical groups. The exposure age disparity cannot be explained by differences in inheritance without using unrealistic assumptions but it can be explained by differences in post-depositional shielding which produces exposure ages younger than the deglaciation age. We present a palaeoglaciological time-slice reconstruction in which the most restricted glaciation, with glaciers less than 10 km long, occurred before 40–65 ka. More extensive glaciations occurred before 60–100 ka and 95–165 ka. Maximum glaciation is poorly constrained but probably even older. The Bayan Har Shan exposure age dataset indicates that glaciers on the northeastern Tibetan Plateau have remained surprisingly restricted for at least 40 ka, including the global last glacial maximum (LGM). This case of a missing LGM is further supported by high-resolution glacier modelling experiments. 相似文献
67.
68.
Phytoplankton seasonal and interannual variability in the Guadiana upper estuary was analyzed during 1996–2005, a period that
encompassed a climatic controlled reduction in river flow that was superimposed on the construction of a dam. Phytoplankton
seasonal patterns revealed an alternation between a persistent light limitation and episodic nutrient limitation. Phytoplankton
succession, with early spring diatom blooms and summer–early fall cyanobacterial blooms, was apparently driven by changes
in nutrients, water temperature, and turbulence, clearly demonstrating the role of river flow and climate variability. Light
intensity in the mixed layer was a prevalent driver of phytoplankton interannual variability, and the increased turbidity
caused by the Alqueva dam construction was linked to pronounced decreases in chlorophyll a concentration, particularly at the start and end of the phytoplankton growing period. Decreases in annual maximum and average
abundances of diatoms, green algae, and cyanobacteria were also detected. Furthermore, chlorophyll a decreases after dam filling and a decrease in turbidity may point to a shift from light limitation towards a more nutrient-limited
mode in the near future. 相似文献
69.
The sedimentary record from the Ugleelv Valley on central Jameson Land, East Greenland, adds new information about terrestrial palaeoenvironments and glaciations to the glacial history of the Scoresby Sund fjord area. A western extension of a coastal ice cap on Liverpool Land reached eastern Jameson Land during the early Scoresby Sund glaciation (≈the Saalian). During the following glacial maximum the Greenland Ice Sheet inundated the Jameson Land plateau from the west. The Weichselian also starts with an early phase of glacial advance from the Liverpool Land ice cap, while polar desert and ice‐free conditions characterised the subsequent part of the Weichselian on the Jameson Land plateau. The two glaciation cycles show a repeated pattern of interaction between the Greenland Ice Sheet in the west and an ice cap on Liverpool Land in the east. Each cycle starts with extensive glacier growth in the coastal mountains followed by a decline of the coastal glaciation, a change to cold and arid climate and a late stage of maximum extent of the Greenland Ice Sheet. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
70.
John Kouroutzoglou Helena A. Flocas Ian Simmonds Kevin Keay Maria Hatzaki 《Theoretical and Applied Climatology》2011,105(1-2):263-275
A comparison of two objective climatologies of explosive cyclones in the Mediterranean region is performed. The results are derived from two different mean sea-level pressure reanalysis data resolutions, but from the same assimilation model, in order to quantify the pure impact of higher resolution on the identification and characteristics of explosive cyclones, when the assimilation model is the same. The explosive cyclones were identified with the aid of the Melbourne University automatic cyclone finding and tracking scheme over a 40-year period, using the 6-hourly analyses of ERA-40 mean sea-level pressure (MSLP) on: (a) 2.5?×?2.5 and (b) 1?×?1 latitude–longitude grid. The comparison of the two datasets revealed the significant role of the increase in spatial resolution of MSLP data on the identification and tracking process, and the number of the explosive cyclones in the high-resolution dataset is almost four times greater than the respective one in the lower resolution dataset. However, the comparison of explosive cyclone characteristics, including spatial and temporal variations of explosive deepening, revealed differences in the geographical distribution of the location of the maximum explosive deepening and average explosive cyclone Laplacian of the central pressure. These differences are due to the identification in the higher resolution set of smaller scale and secondary explosives along the strongly baroclinic northern Mediterranean boundaries, south of the Alps and the Pyrenees. Explosive deepening appears a bias to the daytime period from 12 to 18 Coordinated Universal Time (UTC) for both datasets, which is more prominent in the LR dataset. Statistically significant difference of pressure tendency between the two datasets appear for the daytime period from 06 to 12 UTC, accounting for better representation of orographic forcing in the HR dataset. 相似文献