全文获取类型
| 收费全文 | 79篇 |
| 免费 | 3篇 |
| 国内免费 | 4篇 |
专业分类
| 测绘学 | 5篇 |
| 大气科学 | 8篇 |
| 地球物理 | 23篇 |
| 地质学 | 41篇 |
| 海洋学 | 3篇 |
| 天文学 | 2篇 |
| 综合类 | 1篇 |
| 自然地理 | 3篇 |
出版年
| 2018年 | 1篇 |
| 2013年 | 1篇 |
| 2012年 | 7篇 |
| 2010年 | 1篇 |
| 2007年 | 2篇 |
| 2006年 | 5篇 |
| 2005年 | 2篇 |
| 2004年 | 6篇 |
| 2003年 | 4篇 |
| 2002年 | 1篇 |
| 2000年 | 4篇 |
| 1999年 | 4篇 |
| 1998年 | 2篇 |
| 1997年 | 3篇 |
| 1996年 | 2篇 |
| 1995年 | 4篇 |
| 1994年 | 3篇 |
| 1993年 | 3篇 |
| 1992年 | 11篇 |
| 1991年 | 1篇 |
| 1990年 | 7篇 |
| 1989年 | 9篇 |
| 1988年 | 2篇 |
| 1980年 | 1篇 |
排序方式： 共有86条查询结果，搜索用时 15 毫秒
1.
Carbon isotopic fractionation in lipids from methanotrophic bacteria: relevance for interpretation of the geochemical record of biomarkers 总被引：11，自引：0，他引：11
Experiments with cultured aerobic methane oxidising bacteria confirm that their biomarker lipids will be significantly depleted in 13C compared to the substrate. The methanotrophic bacteria Methylococcus capsulatus and Methylomonas methanica, grown on methane and using the RuMP cycle for carbon assimilation, show maximum 13C fractionation of approximately 30% in the resultant biomass. In M. capsulatus, the maximum fractionation is observed in the earliest part of the exponential growth stage and decreases to approximately 16% as cells approach stationary phase. This change may be associated with a shift from the particulate form to the soluble form of the methane monooxygenase enzyme. Less than maximum fractionation is observed when cells are grown with reduced methane availability. Biomass of M. capsulatus grown on methanol was depleted by 9% compared to the substrate. Additional strong 13C fractionation takes place during polyisoprenoid biosynthesis in methanotrophs. The delta 13C values of individual hopanoid and steroid biomarkers produced by these organisms were as much as l0% more negative than total biomass. In individual cultures, squalene was 13C-enriched by as much as 14% compared to the triterpane skeleton of bacteriohopaneaminopentol. Much of the isotopic dispersion in lipid metabolites could be attributed to shifts in their relative abundances, combined with an overall reduction in fractionation during the growth cycle. In cells grown on methanol, where there was no apparent effect of growth stage on overall fractionation there were still significant isotopic differences between closely related lipids including a 5.3% difference between the hopane and 3 beta-methylhopane skeletons. Hopane and sterane polyisoprenoids were also 13C-depleted compared to fatty acids. These observations have significant implications for the interpretation of specific compound isotopic signatures now being measured for hydrocarbons and other lipids present in sediments and petroleum. In particular, biomarker lipids produced by a single organism do not necessarily have the same carbon isotopic composition. 相似文献
2.
Seavoy RE 《Singapore journal of tropical geography》1980,1(2):61-67
The author describes the role of population pressure in the current transition from tree crops to wet rice cultivation (sawah) in Northwestern Kalimantan, Indonesia. He contends that this change is occurring "because the senescent trees no longer produce enough commodities to exchange for rice to feed an enlarged population." The historical background is described, policies of the Indonesian government are discussed, and data are presented on the rate of population growth 相似文献
3.
4.
5.
6.
7.
10.