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排序方式: 共有83条查询结果,搜索用时 281 毫秒
71.
72.
研究了2羟基4仲辛基二苯甲酮肟(N530)与2乙基已基2乙基已基膦酸(HEHEHP)的氯仿溶液,从高氯酸介质中对钯的协同萃取。采用斜率法确定萃合物的组成为:L·Pd·A。协萃反应平衡常数为g K12= 1658,协同萃取配合物的生成常数为β12= 174。计算了协同萃取反应的热力学函数值  相似文献   
73.
In cases of animal mimicry, the receiver of the signal learns the truth that he is either dealing with the real thing or with a mimic. Thus, despite being a prototypical example of animal deception, mimicry does not seem to qualify as deception on the traditional definition, since the receiver is not actually misled. We offer a new account of propositional content in sender-receiver games that explains how the receiver is misled (and deceived) by mimicry. We show that previous accounts of deception, and of propositional content, give incorrect results about whether certain signals are deceptive.  相似文献   
74.
论述了如何利用PowerBuilder开发一个比较通用的技术咨询子系统,对数据的插入、修改、删除、存储、查询及打印功能的技术问题进行了研究,在面向对象的开发方式下,充分考虑数据共享、数据的可移植性,以优化系统性能。  相似文献   
75.
The phenomenological tradition has had a long interest in embodiment, and bodily experience beyond the confines of the “skinbag” body. Here I respond to Helena De Preester’s analysis of different types of protheses: limb, perceptual, cognitive. In her paper “Technology and the body: the (im)possibilities of re-embodiment”, she wants to make finer distinctions between extensions and incorporations. Today’s hi-tech developments make this refinement necessary and possible. I respond to the three levels or types of prostheses taking note of the increasing difficulty at each level and express certain worries about cognitively framed notions of bodily experience.  相似文献   
76.
Chen B  Vogan EM  Gong H  Skehel JJ  Wiley DC  Harrison SC 《Nature》2005,433(7028):834-841
Envelope glycoproteins of human and simian immunodeficiency virus (HIV and SIV) undergo a series of conformational changes when they interact with receptor (CD4) and co-receptor on the surface of a potential host cell, leading ultimately to fusion of viral and cellular membranes. Structures of fragments of gp120 and gp41 from the envelope protein are known, in conformations corresponding to their post-attachment and postfusion states, respectively. We report the crystal structure, at 4 A resolution, of a fully glycosylated SIV gp120 core, in a conformation representing its prefusion state, before interaction with CD4. Parts of the protein have a markedly different organization than they do in the CD4-bound state. Comparison of the unliganded and CD4-bound structures leads to a model for events that accompany receptor engagement of an envelope glycoprotein trimer. The two conformations of gp120 also present distinct antigenic surfaces. We identify the binding site for a compound that inhibits viral entry.  相似文献   
77.
78.
Apoptosis is an evolutionarily conserved cell suicide process executed by cysteine proteases (caspases) and regulated by the opposing factions of the Bcl-2 protein family. Mammalian caspase-9 and its activator Apaf-1 were thought to be essential, because mice lacking either of them display neuronal hyperplasia and their lymphocytes and fibroblasts seem resistant to certain apoptotic stimuli. Because Apaf-1 requires cytochrome c to activate caspase-9, and Bcl-2 prevents mitochondrial cytochrome c release, Bcl-2 is widely believed to inhibit apoptosis by safeguarding mitochondrial membrane integrity. Our results suggest a different, broader role, because Bcl-2 overexpression increased lymphocyte numbers in mice and inhibited many apoptotic stimuli, but the absence of Apaf-1 or caspase-9 did not. Caspase activity was still discernible in cells lacking Apaf-1 or caspase-9, and a potent caspase antagonist both inhibited apoptosis and retarded cytochrome c release. We conclude that Bcl-2 regulates a caspase activation programme independently of the cytochrome c/Apaf-1/caspase-9 'apoptosome', which seems to amplify rather than initiate the caspase cascade.  相似文献   
79.
Seismology: energy radiation from the Sumatra earthquake   总被引:1,自引:0,他引:1  
Ni S  Kanamori H  Helmberger D 《Nature》2005,434(7033):582
We determined the duration of high-frequency energy radiation from Indonesia's great Sumatra-Andaman earthquake (26 December 2004) to be about 500 seconds. This duration can be translated into a rupture length of about 1,200 km, which is more than twice as long as that inferred from body-wave analyses performed soon after the event. Our analysis was able rapidly to define the extent of rupture, thereby aiding the assessment of seismic hazard in the immediate future.  相似文献   
80.
Fusion of biological membranes is mediated by specific lipid-interacting proteins that induce the formation and expansion of an initial fusion pore. Here we report the crystal structure of the ectodomain of the Semliki Forest virus fusion glycoprotein E1 in its low-pH-induced trimeric form. E1 adopts a folded-back conformation that, in the final post-fusion form of the full-length protein, would bring the fusion peptide loop and the transmembrane anchor to the same end of a stable protein rod. The observed conformation of the fusion peptide loop is compatible with interactions only with the outer leaflet of the lipid bilayer. Crystal contacts between fusion peptide loops of adjacent E1 trimers, together with electron microscopy observations, suggest that in an early step of membrane fusion, an intermediate assembly of five trimers creates two opposing nipple-like deformations in the viral and target membranes, leading to formation of the fusion pore.  相似文献   
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