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排序方式: 共有73条查询结果,搜索用时 15 毫秒
1.
Piccioni G Drossart P Sanchez-Lavega A Hueso R Taylor FW Wilson CF Grassi D Zasova L Moriconi M Adriani A Lebonnois S Coradini A Bézard B Angrilli F Arnold G Baines KH Bellucci G Benkhoff J Bibring JP Blanco A Blecka MI Carlson RW Di Lellis A Encrenaz T Erard S Fonti S Formisano V Fouchet T Garcia R Haus R Helbert J Ignatiev NI Irwin PG Langevin Y Lopez-Valverde MA Luz D Marinangeli L Orofino V Rodin AV Roos-Serote MC Saggin B Stam DM Titov D Visconti G 《Nature》2007,450(7170):637-640
Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition. 相似文献
2.
Stark A Lin MF Kheradpour P Pedersen JS Parts L Carlson JW Crosby MA Rasmussen MD Roy S Deoras AN Ruby JG Brennecke J;Harvard FlyBase curators;Berkeley Drosophila Genome Project Hodges E Hinrichs AS Caspi A Paten B Park SW Han MV Maeder ML Polansky BJ Robson BE Aerts S van Helden J Hassan B Gilbert DG Eastman DA Rice M Weir M Hahn MW Park Y Dewey CN Pachter L Kent WJ Haussler D Lai EC Bartel DP Hannon GJ Kaufman TC Eisen MB Clark AG Smith D Celniker SE Gelbart WM Kellis M 《Nature》2007,450(7167):219-232
3.
A system for the continuous directed evolution of biomolecules 总被引:1,自引:0,他引:1
4.
Schreiner PR Chernish LV Gunchenko PA Tikhonchuk EY Hausmann H Serafin M Schlecht S Dahl JE Carlson RM Fokin AA 《Nature》2011,477(7364):308-311
Steric effects in chemistry are a consequence of the space required to accommodate the atoms and groups within a molecule, and are often thought to be dominated by repulsive forces arising from overlapping electron densities (Pauli repulsion). An appreciation of attractive interactions such as van der Waals forces (which include London dispersion forces) is necessary to understand chemical bonding and reactivity fully. This is evident from, for example, the strongly debated origin of the higher stability of branched alkanes relative to linear alkanes and the possibility of constructing hydrocarbons with extraordinarily long C-C single bonds through steric crowding. Although empirical bond distance/bond strength relationships have been established for C-C bonds (longer C-C bonds have smaller bond dissociation energies), these have no present theoretical basis. Nevertheless, these empirical considerations are fundamental to structural and energetic evaluations in chemistry, as summarized by Pauling as early as 1960 and confirmed more recently. Here we report the preparation of hydrocarbons with extremely long C-C bonds (up to 1.704??), the longest such bonds observed so far in alkanes. The prepared compounds are unexpectedly stable--noticeable decomposition occurs only above 200?°C. We prepared the alkanes by coupling nanometre-sized, diamond-like, highly rigid structures known as diamondoids. The extraordinary stability of the coupling products is due to overall attractive dispersion interactions between the intramolecular H???H contact surfaces, as is evident from density functional theory computations with and without inclusion of dispersion corrections. 相似文献
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作为一部经典的中国独立电影,<苏州河>不仅描绘了魅力上海的底层生活世界,而且生动地表明中国新生代导演如何在全球类型电影创作的互文文本中确定自身的独特位置.作者从类型分析、叙事结构和视觉风格等方面,细致地探讨了怂<苏州河>与好莱坞以及法国新浪潮电影之间吊诡的互文关系. 相似文献
7.
Presynaptic neurones may contribute a unique glycoprotein to the extracellular matrix at the synapse 总被引:4,自引:0,他引:4
As the extracellular matrix at the original site of a neuromuscular junction seems to play a major part in the specificity of synaptic regeneration, considerable attention has been paid to unique molecules localized to this region. Here we describe an extracellular matrix glycoprotein of the elasmobranch electric organ that is localized near the nerve endings. By immunological criteria, it is synthesized in the cell bodies, transported down the axons and is related to a glycoprotein in the synaptic vesicles of the neurones that innervate the electric organ. It is apparently specific for these neurones, as it cannot be detected elsewhere in the nervous system of the fish. Therefore, neurones seem to contribute unique extracellular matrix glycoproteins to the synaptic region. Synaptic vesicles could be involved in transporting these glycoproteins to or from the nerve terminal surface. 相似文献
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G. P. Carlson 《Cellular and molecular life sciences : CMLS》1979,35(4):513-514
Summary Unlike the highly porphyrinogenic fungicide hexachlorobenzene, hexabromobenzene was a poor inducer of porphyria. Similarly, 1,2-dibromobenzene and 1,2,4-tribromobenzene, while causing small increases in hepatic porphyrins, did not increase ALA synthetase or the urinary excretion of porphobilinogen (PBG), aminolevulinic acid (ALA) or porphyrins.Supported by grant R805070 from the US Environmental Protection Agency. 相似文献
10.
KANG Ning ZHANG Jun Eric S Carlson 《上海大学学报(自然科学版)》2004,10(Z1):13-17
A new approach for noninvasively tracing brain white matter fiber tracts is presented using diffusion tensor magnetic resonance imaging (DT-MRI) data. This technique is based on successive anisotropic diffusion simulations over the human brain, which are utilized to construct three dimensional diffusion fronts. The fiber pathways are determined by evaluating the distance and orientation from fronts to their corresponding diffusion seeds. Real DT-MRI data are used to demonstrate the tracking scheme. It is shown that several major white matter fiber pathways can be reproduced noninvasively, with the tract branching being allowed. Since the diffusion simulation,which is a truly physical phenomenon reflecting the underlying architecture of cerebral tissues, makes full use of the entire diffusion tensor data, the proposed approach is expected to enhance robustness and reliability of the DT-MRI based fiber tracking techniques in white matter fiber reconstruction. 相似文献