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Development of City Transport System and Two-wheel Vehicles 总被引:1,自引:0,他引:1
Based on the study on the city transport systems of some typical cities worldwide, this paper put forward that each city transport system has its own development mode, which is influenced by the city development plan, economic development level, traveling vehicle composition etc.. When some problems occur, such as the congestions caused by contradiction between the road capacity and vehicle composition, the city transport system may come into temporary maturity period. If the improvement for road system is limited meanwhile, optimized structure of vehicle composition should be an effective solution in this case. With the development of economy-internationalization, the development speed of city transport modernization is rapid. When traveling easiness is conflicting with efficiency, the advantages of public transport system become more obvious. Correspondingly, the superiority of two-wheel vehicles will reappear. Though the important function of two-wheel vehicles for alleviating city traffic problems i 相似文献
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Gamma-ray bursts are among the most powerful events in nature. These events release most of their energy as photons with energies in the range from 30 keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical, and soft X-ray afterglows. The data are in general agreement with a relativistic shock model, where the prompt and afterglow emissions correspond to synchrotron radiation from shock-accelerated electrons. Here we report an observation of a high-energy (multi-MeV) spectral component in the burst of 17 October 1994 that is distinct from the previously observed lower-energy gamma-ray component. The flux of the high-energy component decays more slowly and its fluence is greater than the lower-energy component; it is described by a power law of differential photon number index approximately -1 up to about 200 MeV. This observation is difficult to explain with the standard synchrotron shock model, suggesting the presence of new phenomena such as a different non-thermal electron process, or the interaction of relativistic protons with photons at the source. 相似文献
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介绍了传统药物传输系统的缺陷和药物控制传输系统的特点,文中表明,控制的药物传输可以使药物通过多聚糖载体可传输到靶向位置,从而起到控制治疗的作用.多聚糖如海藻酸盐、胶质、右旋糖苷、凝胶已在制药应用中用于或正试验用于药物的靶向传输.它们稳定、无毒且可在小肠中被酶降解,利用具有特定化学和物理性质的多糖载体的微胶囊可实现蛋白质药物的靶向传输.通过几丁聚糖的化学修饰改变其性能的研究已有较多报道,包括作者提出的一种新的修饰方法. 相似文献
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This paper introduces a non-assembly manufacturing case with microstereolithography technology. The design and manufacturing process of a pneumatic thrust bearing is described, and a special tessellation method is developed to further improve the capability of the manufacturing system thus bigger products can also be easily manufactured. Implemented in a layer-by-layer fashion, stereolithography has been used for the rapid manufacturing of complex devices, and it avoids the expensive assembly process in the traditional manufacturing. This paper presents that microstereolithography can produce high-resolution products with intricate details, small openings, and smooth surfaces. The potential of the microstereolithograhy technique is explored for the rapid manufacturing of small and complex objects. 相似文献
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The earliest record of human activity in northern Europe 总被引:1,自引:0,他引:1
Parfitt SA Barendregt RW Breda M Candy I Collins MJ Coope GR Durbidge P Field MH Lee JR Lister AM Mutch R Penkman KE Preece RC Rose J Stringer CB Symmons R Whittaker JE Wymer JJ Stuart AJ 《Nature》2005,438(7070):1008-1012
The colonization of Eurasia by early humans is a key event after their spread out of Africa, but the nature, timing and ecological context of the earliest human occupation of northwest Europe is uncertain and has been the subject of intense debate. The southern Caucasus was occupied about 1.8 million years (Myr) ago, whereas human remains from Atapuerca-TD6, Spain (more than 780 kyr ago) and Ceprano, Italy (about 800 kyr ago) show that early Homo had dispersed to the Mediterranean hinterland before the Brunhes-Matuyama magnetic polarity reversal (780 kyr ago). Until now, the earliest uncontested artefacts from northern Europe were much younger, suggesting that humans were unable to colonize northern latitudes until about 500 kyr ago. Here we report flint artefacts from the Cromer Forest-bed Formation at Pakefield (52 degrees N), Suffolk, UK, from an interglacial sequence yielding a diverse range of plant and animal fossils. Event and lithostratigraphy, palaeomagnetism, amino acid geochronology and biostratigraphy indicate that the artefacts date to the early part of the Brunhes Chron (about 700 kyr ago) and thus represent the earliest unequivocal evidence for human presence north of the Alps. 相似文献
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Darwin was fascinated by the transportation of land snails across great swathes of open ocean by birds--he even immersed snails in sea water to see how long they would survive. Here we follow a molecular phylogenetic trail that reveals the incredible transequatorial dispersal of the land snail Balea from Europe to the Azores and the Tristan da Cunha islands, and back again. This long-distance dispersal is unexpected for what are proverbially considered the most pedestrian of creatures. 相似文献
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柠檬酸纳米金与丙烯酸纳米金修饰的金-海藻酸钙-几丁聚糖微胶囊渗透性比较 总被引:1,自引:1,他引:0
分别用柠檬酸钠和丙烯酸钠做还原剂制备金纳米微粒,并分别用它们对几丁聚糖微胶囊进行化学修饰,提出了新的修饰方法,制备出新的金-海藻酸钙-几丁聚糖微胶囊(GACM).运用分光光度法对2个体系下制得的GACM的渗透性进行了测定,结果表明柠檬酸体系下制得的GACM的渗透性比丙烯酸钠体系下制得的GACM的渗透性要大. 相似文献
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Penkman KE Preece RC Bridgland DR Keen DH Meijer T Parfitt SA White TS Collins MJ 《Nature》2011,476(7361):446-449
Marine and ice-core records show that the Earth has experienced a succession of glacials and interglacials during the Quaternary (last ~2.6 million years), although it is often difficult to correlate fragmentary terrestrial records with specific cycles. Aminostratigraphy is a method potentially able to link terrestrial sequences to the marine isotope stages (MIS) of the deep-sea record. We have used new methods of extraction and analysis of amino acids, preserved within the calcitic opercula of the freshwater gastropod Bithynia, to provide the most comprehensive data set for the British Pleistocene based on a single dating technique. A total of 470 opercula from 74 sites spanning the entire Quaternary are ranked in order of relative age based on the extent of protein degradation, using aspartic acid/asparagine (Asx), glutamic acid/glutamine (Glx), serine (Ser), alanine (Ala) and valine (Val). This new aminostratigraphy is consistent with the stratigraphical relationships of stratotypes, sites with independent geochronology, biostratigraphy and terrace stratigraphy. The method corroborates the existence of four interglacial stages between the Anglian (MIS 12) and the Holocene in the terrestrial succession. It establishes human occupation of Britain in most interglacial stages after MIS 15, but supports the notion of human absence during the Last Interglacial (MIS 5e). Suspicions that the treeless 'optimum of the Upton Warren interstadial' at Isleworth pre-dates MIS 3 are confirmed. This new aminostratigraphy provides a robust framework against which climatic, biostratigraphical and archaeological models can be tested. 相似文献
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