全文获取类型
收费全文 | 122篇 |
免费 | 2篇 |
专业分类
系统科学 | 19篇 |
教育与普及 | 2篇 |
现状及发展 | 21篇 |
研究方法 | 9篇 |
综合类 | 70篇 |
自然研究 | 3篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2017年 | 1篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2012年 | 7篇 |
2011年 | 19篇 |
2010年 | 1篇 |
2009年 | 2篇 |
2008年 | 8篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 15篇 |
2004年 | 6篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1966年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有124条查询结果,搜索用时 15 毫秒
121.
Smeulders MJ Barends TR Pol A Scherer A Zandvoort MH Udvarhelyi A Khadem AF Menzel A Hermans J Shoeman RL Wessels HJ van den Heuvel LP Russ L Schlichting I Jetten MS Op den Camp HJ 《Nature》2011,478(7369):412-416
Extremophilic organisms require specialized enzymes for their exotic metabolisms. Acid-loving thermophilic Archaea that live in the mudpots of volcanic solfataras obtain their energy from reduced sulphur compounds such as hydrogen sulphide (H(2)S) and carbon disulphide (CS(2)). The oxidation of these compounds into sulphuric acid creates the extremely acidic environment that characterizes solfataras. The hyperthermophilic Acidianus strain A1-3, which was isolated from the fumarolic, ancient sauna building at the Solfatara volcano (Naples, Italy), was shown to rapidly convert CS(2) into H(2)S and carbon dioxide (CO(2)), but nothing has been known about the modes of action and the evolution of the enzyme(s) involved. Here we describe the structure, the proposed mechanism and evolution of a CS(2) hydrolase from Acidianus A1-3. The enzyme monomer displays a typical β-carbonic anhydrase fold and active site, yet CO(2) is not one of its substrates. Owing to large carboxy- and amino-terminal arms, an unusual hexadecameric catenane oligomer has evolved. This structure results in the blocking of the entrance to the active site that is found in canonical β-carbonic anhydrases and the formation of a single 15-?-long, highly hydrophobic tunnel that functions as a specificity filter. The tunnel determines the enzyme's substrate specificity for CS(2), which is hydrophobic. The transposon sequences that surround the gene encoding this CS(2) hydrolase point to horizontal gene transfer as a mechanism for its acquisition during evolution. Our results show how the ancient β-carbonic anhydrase, which is central to global carbon metabolism, was transformed by divergent evolution into a crucial enzyme in CS(2) metabolism. 相似文献
122.
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
123.
Introduction With the rapid increase of road traffic congestion in re-cent years,many intelligent transport systems(ITS)have been developed and applied throughout the world[1-3].ITS can improve road transport,driver sup-port,and mobility.Potential investm… 相似文献
124.
Raghoebarsing AA Pol A van de Pas-Schoonen KT Smolders AJ Ettwig KF Rijpstra WI Schouten S Damsté JS Op den Camp HJ Jetten MS Strous M 《Nature》2006,440(7086):918-921
Modern agriculture has accelerated biological methane and nitrogen cycling on a global scale. Freshwater sediments often receive increased downward fluxes of nitrate from agricultural runoff and upward fluxes of methane generated by anaerobic decomposition. In theory, prokaryotes should be capable of using nitrate to oxidize methane anaerobically, but such organisms have neither been observed in nature nor isolated in the laboratory. Microbial oxidation of methane is thus believed to proceed only with oxygen or sulphate. Here we show that the direct, anaerobic oxidation of methane coupled to denitrification of nitrate is possible. A microbial consortium, enriched from anoxic sediments, oxidized methane to carbon dioxide coupled to denitrification in the complete absence of oxygen. This consortium consisted of two microorganisms, a bacterium representing a phylum without any cultured species and an archaeon distantly related to marine methanotrophic Archaea. The detection of relatives of these prokaryotes in different freshwater ecosystems worldwide indicates that the reaction presented here may make a substantial contribution to biological methane and nitrogen cycles. 相似文献