全文获取类型
收费全文 | 247篇 |
免费 | 1篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 5篇 |
教育与普及 | 1篇 |
现状及发展 | 60篇 |
研究方法 | 19篇 |
综合类 | 153篇 |
自然研究 | 11篇 |
出版年
2014年 | 1篇 |
2013年 | 2篇 |
2012年 | 9篇 |
2011年 | 18篇 |
2010年 | 5篇 |
2008年 | 12篇 |
2007年 | 4篇 |
2006年 | 8篇 |
2005年 | 4篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 11篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1992年 | 4篇 |
1991年 | 7篇 |
1990年 | 2篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 2篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 16篇 |
1969年 | 3篇 |
1968年 | 10篇 |
1967年 | 6篇 |
1966年 | 2篇 |
1965年 | 3篇 |
1962年 | 1篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有249条查询结果,搜索用时 281 毫秒
241.
242.
243.
244.
245.
246.
247.
248.
Dinsdale EA Edwards RA Hall D Angly F Breitbart M Brulc JM Furlan M Desnues C Haynes M Li L McDaniel L Moran MA Nelson KE Nilsson C Olson R Paul J Brito BR Ruan Y Swan BK Stevens R Valentine DL Thurber RV Wegley L White BA Rohwer F 《Nature》2008,452(7187):629-632
Microbial activities shape the biogeochemistry of the planet and macroorganism health. Determining the metabolic processes performed by microbes is important both for understanding and for manipulating ecosystems (for example, disruption of key processes that lead to disease, conservation of environmental services, and so on). Describing microbial function is hampered by the inability to culture most microbes and by high levels of genomic plasticity. Metagenomic approaches analyse microbial communities to determine the metabolic processes that are important for growth and survival in any given environment. Here we conduct a metagenomic comparison of almost 15 million sequences from 45 distinct microbiomes and, for the first time, 42 distinct viromes and show that there are strongly discriminatory metabolic profiles across environments. Most of the functional diversity was maintained in all of the communities, but the relative occurrence of metabolisms varied, and the differences between metagenomes predicted the biogeochemical conditions of each environment. The magnitude of the microbial metabolic capabilities encoded by the viromes was extensive, suggesting that they serve as a repository for storing and sharing genes among their microbial hosts and influence global evolutionary and metabolic processes. 相似文献
249.
Stream denitrification across biomes and its response to anthropogenic nitrate loading 总被引:11,自引:0,他引:11
Mulholland PJ Helton AM Poole GC Hall RO Hamilton SK Peterson BJ Tank JL Ashkenas LR Cooper LW Dahm CN Dodds WK Findlay SE Gregory SV Grimm NB Johnson SL McDowell WH Meyer JL Valett HM Webster JR Arango CP Beaulieu JJ Bernot MJ Burgin AJ Crenshaw CL Johnson LT Niederlehner BR O'Brien JM Potter JD Sheibley RW Sobota DJ Thomas SM 《Nature》2008,452(7184):202-205
Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating that substantial sinks for nitrogen must exist in the landscape. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification. Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes. We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of in-stream nitrate that is removed from transport. Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration. In addition, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks. 相似文献