全文获取类型
收费全文 | 724篇 |
免费 | 66篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 52篇 |
地球物理 | 143篇 |
地质学 | 298篇 |
海洋学 | 68篇 |
天文学 | 89篇 |
综合类 | 1篇 |
自然地理 | 122篇 |
出版年
2023年 | 4篇 |
2022年 | 6篇 |
2021年 | 22篇 |
2020年 | 29篇 |
2019年 | 24篇 |
2018年 | 34篇 |
2017年 | 47篇 |
2016年 | 43篇 |
2015年 | 32篇 |
2014年 | 32篇 |
2013年 | 43篇 |
2012年 | 45篇 |
2011年 | 53篇 |
2010年 | 50篇 |
2009年 | 81篇 |
2008年 | 50篇 |
2007年 | 44篇 |
2006年 | 27篇 |
2005年 | 14篇 |
2004年 | 23篇 |
2003年 | 26篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 2篇 |
1998年 | 8篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有797条查询结果,搜索用时 15 毫秒
41.
42.
43.
Julian Augley Mark Huxham Teresa F. Fernandes Alastair R. Lyndon Sarah Bury 《Estuarine, Coastal and Shelf Science》2007,72(4):648-656
The stable carbon isotope ratios (δ13C) of the organic fraction of intertidal sediments in the Forth Estuary and the Firth of Forth, Scotland, were measured to determine if terrestrially derived carbon was present in the estuarine sediments. It was hypothesised that differences in the inputs from marine vs. terrestrial sources to the organic carbon of estuarine and marine sediments, as well as differences in ambient seawater stable oxygen isotope (δ18O) ratios between the estuary and the Outer Firth, would allow the use of these two stable isotopes as habitat markers for juvenile plaice (Pleuronectes platessa), to allow determination of nursery habitats. Muddy and sandy sediments from the estuary and sandy sediments from the Outer Firth were sampled and δ13C measured. Juvenile plaice were caught at two estuarine sites and at two Outer Firth sites and otoliths were removed for δ13C and δ18O analysis. The sandy sediments in the estuary showed a strong gradient of δ13C enrichment with distance down the estuary, while the muddy sediments showed a much shallower gradient. δ13C and δ18O measured in the carbonate of juvenile plaice otoliths showed no clear difference between otoliths of fish caught at one of the estuarine sites and at the two Outer Firth sites. However, the isotope ratios of both carbon and oxygen in plaice otoliths from the other estuarine site showed the expected trend of depletion in the heavier isotopes. While the measurements recorded here did not conclusively distinguish between otoliths from juveniles caught in the estuarine site and those caught in the other three sites, they show that stable isotopes have potential to distinguish between estuarine habitats with terrestrial carbon inputs, and coastal marine habitats with predominantly marine carbon inputs. 相似文献
44.
45.
46.
Sedimentary material from coastal and nearshore areas in the Mississippi Delta region are comprised of different organic carbon sources with diverse ages that require isotopic and elemental records for resolving the various sources of plant residues. Carbon isotopic ((13)C, (14)C) values were used to differentiate contributions from plants using the C3, C4, and/or CAM (crassulacean acid metabolism) carbon fixation pathways., and iodine concentrations indicated that wetland plant residues are a significant source of organic carbon in a sediment core from the Mississippi River delta region collected at a 60 m water depth. This sediment core had been extensively described in Oktay et al. [Oktay, S.D., Santschi, P.H., Moran, J.E., Sharma, P., 2000. The (129)Iodine Bomb Pulse Recorded in Mississippi River delta Sediments: Results from Isotopes of I, Pu, Cs, Pb, and C. Geochim. Cosmochim. Acta 64 (6), 989-996.] and significantly, includes unique features that had not previously been seen in the marine environment. These special features include a plutonium isotopic close-in fallout record that indicates a purely terrestrial source for these sediment particles and the elements associated with it, and a distinct iodine isotopic peak (as well as peaks for plutonium and cesium isotopes) that indicate little bioturbation in this core. Our carbon isotopic and iodine data can thus be compared to published records of changes in drainage basin land use, river hydrology, and hydrodynamic sorting of suspended particles to elucidate if these changes are reflected in nearshore sediments. This comparison suggests a significant contribution for organic carbon (OC) from C4 plants to these sediments during the 1950's to early 1960's. Relative older carbon isotopes, and episodically high iodine concentrations (up to 34 ppm) were observed during this time period that (1) indicate sediment deposition that is coincident with the times of major hydrological changes induced from dam and levee building in both the upper and lower reaches of the Mississippi River drainage basin, and (2) suggest episodic organic carbon deposition from wetland plant residues. 相似文献
47.
Słodczyk Elżbieta Pietranik Anna Glynn Sarah Wiedenbeck Michael Breitkreuz Christoph Dhuime Bruno 《International Journal of Earth Sciences》2018,107(6):2065-2081
International Journal of Earth Sciences - The Polish Lowlands, located southwest of the Teisseyre–Tornquist Zone, within Trans-European Suture Zone, were affected by bimodal, but dominantly... 相似文献
48.
M. S. Sreekala Sarah John Sareen Sivalingam Rajathi 《Journal of the Geological Society of India》2018,91(5):621-626
Geo-environmental studies in parts of Ernakulam district (Kerala, India) were carried out. The study area comprises of sedimentary (Limestone, sandstone, Clay and Lignite) and crystalline (Charnockite and gneisses) rocks. The sedimentary terrain is characterized by confined and unconfined aquifers. In hard crystalline formations groundwater occurs under phreatic conditions in the shallow weathered portions and under semi confined to confined conditions in the deep-seated fractures. The study area is demarcated into five areas based on soil types. Climate is hot humid to hot summer with heavily raining monsoon. Two major rivers Periyar and Muvattupuzha drain through the area. Agricultural and industrial activities are prevalent in Ernakulam district. The major cause of pollution in the study area is due to the presence of coliforms. Detailed investigations carried out to identify the coliforms indicated spatial and seasonal changes in the distribution pattern. Monsoon and post monsoon showed significantly high total coliforms compared to pre-monsoon. Thermo-tolerant coliforms is high during monsoon season. This seasonal change could be due to the effect of rainfall, overland flow, nutrient load and temperature change. Wide variations in the coliform counts are observed in wells situated near rivers, canals, paddy fields and in water bodies lying close to pilgrimage center, fertilizer industry, and public places. It is noticed that the chemical characteristics of the groundwater influence the coliform survival. pH, nitrite, bicarbonate, hardness, and alkalinity play a significant role in controlling coliform count. At the outset, the study highlighted the impact of anthropogenic activities on ground water in a coastal district of Kerala state. 相似文献
49.
Hydrogeology Journal - The Illinois-Kentucky ore district hosts the largest deposits of fluorite in the USA. A long-standing hypothesis for the formation of the Illinois-Kentucky deposits is that... 相似文献
50.
Shoreline armoring is extensive in urban areas worldwide, but the ecological consequences are poorly documented. We mapped
shoreline armoring along the Duwamish River estuary (Washington State, USA) and evaluated differences in temperature, invertebrates,
and juvenile salmon (Oncorhynchus spp.) diet between armored and unarmored intertidal habitats. Mean substrate temperatures were significantly warmer at armored
sites, but water temperature similar to unarmored habitats. Epibenthic invertebrate densities were over tenfold greater on
unarmored shorelines and taxa richness double that of armored locations. Taxa richness of neuston invertebrates was also higher
at unarmored sites, but abundance similar. We did not detect differences in Chinook (O. tshawytscha) diet, but observed a higher proportion of benthic prey for chum (O. keta) from unarmored sites. Given that over 66% of the Duwamish shoreline is armored—similar to much of south and central Puget
Sound—our results underscore the need for further ecological study to address the impacts of estuary armoring. 相似文献