全文获取类型
| 收费全文 | 342篇 |
| 免费 | 24篇 |
| 国内免费 | 5篇 |
专业分类
| 大气科学 | 32篇 |
| 地球物理 | 73篇 |
| 地质学 | 120篇 |
| 海洋学 | 30篇 |
| 天文学 | 79篇 |
| 自然地理 | 37篇 |
出版年
| 2023年 | 4篇 |
| 2022年 | 6篇 |
| 2021年 | 10篇 |
| 2020年 | 12篇 |
| 2019年 | 6篇 |
| 2018年 | 14篇 |
| 2017年 | 15篇 |
| 2016年 | 18篇 |
| 2015年 | 13篇 |
| 2014年 | 16篇 |
| 2013年 | 18篇 |
| 2012年 | 19篇 |
| 2011年 | 27篇 |
| 2010年 | 26篇 |
| 2009年 | 25篇 |
| 2008年 | 25篇 |
| 2007年 | 18篇 |
| 2006年 | 14篇 |
| 2005年 | 13篇 |
| 2004年 | 6篇 |
| 2003年 | 11篇 |
| 2002年 | 8篇 |
| 2001年 | 9篇 |
| 2000年 | 7篇 |
| 1999年 | 4篇 |
| 1998年 | 6篇 |
| 1996年 | 2篇 |
| 1995年 | 1篇 |
| 1994年 | 3篇 |
| 1993年 | 1篇 |
| 1992年 | 2篇 |
| 1991年 | 1篇 |
| 1990年 | 1篇 |
| 1988年 | 1篇 |
| 1985年 | 1篇 |
| 1984年 | 2篇 |
| 1983年 | 2篇 |
| 1982年 | 1篇 |
| 1975年 | 1篇 |
| 1973年 | 2篇 |
排序方式： 共有371条查询结果，搜索用时 15 毫秒
11.
12.
13.
14.
15.
Thomas D. Hamilton Gall M. Ashley Katherine M. Reed Charles E. Schweger 《Quaternary Research》1993,39(3)
Sediments exposed at Epiguruk, a large cutbank on the Kobuk River about 170 km inland from Kotzebue Sound, record multiple episodes of glacial-age alluviation followed by interstadial downcutting and formation of paleosols. Vertebrate remains from Epiguruk include mammoth, bison, caribou, an equid, a canid, arctic ground squirrel, lemmings, and voles. Radiocarbon ages of bone validated by concordant ages of peat and wood span the interval between about 37,000 and 14,000 yr B.P. The late Pleistocene pollen record is dominated by Cyperaceae, with Artemisia, Salix, Betula, and Gramineae also generally abundant. The fossil record from Epiguruk indicates that the Kobuk River valley supported tundra vegetation with abundant riparian willows during middle and late Wisconsin time. Large herbivores were present during the height of late Wisconsin glaciation as well as during its waning stage and the preceding interstadial interval. The Kobuk River valley would have been a favorable refugium for plants, animals, and possibly humans throughout the last glaciation. 相似文献
16.
17.
William M. Balch Patrick M. Holligan Katherine A. Kilpatrick 《Continental Shelf Research》1992,12(12)
Measurements were made of photosynthesis and calcification in a bloom of coccolithophores in the Gulf of Maine as well as in laboratory batch cultures of the Emiliania huxleyi strain 88E. The14C technique for measuring calcification was evaluated with calcifying and noncalcifying coccolithophore strains. Shipboard bloom observations showed physiological evidence of stratification between surface and deep populations within the surface mixed layer. Photosynthesis and calcification rates were enhanced within hours of addition of KNO3 or nitrate-rich deep water (to the same final concentration). Such rates were strongly temperature dependent in laboratory cultures, decreasing over a factor of two from 15 to 20°C. Calcification was considerably less light-dependent than photosynthesis and consistently had a measurable dark rate. In culture, maximum calcification rates and degree of cell plating were limited to logarithmic growth phase. This was followed by rapid increase in the coccolith shedding rate 1 day prior to the onset of stationary phase which continued several days after cell division stopped. The regional significance of these features to total organic and inorganic carbon production as well as calcite burial is discussed. 相似文献
18.
19.
Katherine L. Pering 《Geochimica et cosmochimica acta》1973,37(3):401-417
A bitumen deposit in north Derbyshire, England, is described and studied using the techniques of gas chromatography, infra-red spectrophotometry and elemental analysis. The bitumens are associated with lead-zinc-fluorite ore minerals concentrated along an unconformable contact between the Carboniferous Limestone and the overlying shales. Three varieties of bitumen are distinguished and are compared with the dispersed bitumens in both the Carboniferous Limestone and the Edale Shales, with crude oils believed to be derived from these shales, and with inclusions in the hydrothermal mineral fiuorite, associated with the limestone-shale contact. One of the varieties recognized, a brittle brown solid, contains aliphatic hydrocarbons very similar to those of the shales and to those of the crude oils likely derived from these shales. The other two are a viscous oil and a brittle, black solid, which geologic evidence suggests were originally derived from the limestone. They contain a very complex mixture of aliphatic hydrocarbons quite different from those in the limestone, however. Aliphatic hydrocarbons isolated from fluorite, which is hydrothermally formed, in nearby massive deposits are almost identical to those of the limestone and shale. This observation indicates that alteration of the aliphatic hydrocarbons in the sediment by hydrothermal fluids is an unlikely explanation for the origin of the complex mixtures of hydrocarbons in the viscous oil and brittle, black solid. On the basis of indirect evidence of high nitrogen content, presence of unsaturated hydrocarbons, and suitability of the environment for bacterial growth, it is suggested that selective bacterial alteration of the aliphatic hydrocarbons is the main process responsible for their present composition. A geologic history for the deposit is postulated that involves a two-phase introduction of bitumens. Each phase is suggested to have begun as a pulse of warm saline fluids migrating along the shale-limestone unconformity passed through the topographic high at Windy Knoll. Microbial oxidation of the bitumens may have taken place during the deposition process or, more likely, as a recent secondary oxidation process. 相似文献
20.