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51.
在Lewis槽中研究了表面活性物质对三种部分互溶液液体系传质速率的影响,并与单液滴传质实验结果进行比较。结果表明,表面活性物质对Lewis糟和单液滴传质速率有类似的影响,对Lewis的影响程度高于单液滴。 相似文献
52.
Like many discussions on the pros and cons of epistemic foundationalism, the debate between C. I. Lewis and H. Reichenbach dealt with three concerns: the existence of basic beliefs, their nature, and the way in which beliefs are related. In this paper we concentrate on the third matter, especially on Lewis’s assertion that a probability relation must depend on something that is certain, and Reichenbach’s claim that certainty is never needed. We note that Lewis’s assertion is prima facie ambiguous, but argue that this ambiguity is only apparent if probability theory is viewed within a modal logic. Although there are empirical situations where Reichenbach is right, and others where Lewis’s reasoning seems to be more appropriate, it will become clear that Reichenbach’s stance is the generic one. We conclude that this constitutes a threat to epistemic foundationalism. 相似文献
53.
为制备更多新型功能高分子中间体,研究了高活性lewis酸AlCl3催化作用下,苊与硝基苯在温和条件常温常压下的反应.GC/MS分析发现生成了N-苯基氨基苊烯、N-苯基氨基苊、联苊-苊烯和联苊等产物.GC考察了不同反应条件对苊转化率和产物选择性的影响,时间对苊转化率影响不大,N-苯基氨基苊的选择性随着时间增加而增大;随着AlCl3用量的增加,苊转化率和N-苯基氨基苊的选择性随之增加;AlCl3与苊的摩尔比为1.2和2.4时,产物中联苊和N-苯基氨基苊的选择性分别达到77.6%和90.2%.对不同反应条件下的反应产物,通过重结晶获得了多环功能高分子中间体联苊和染料、医药中间体5-(N-苯基)氨基苊两种主产物的纯品,用GC/MS、FT—IR、UV和^1H NMR等分析测试手段鉴定了其结构. 相似文献
54.
C. N. Brown 《Annals of science》2013,70(4):330-360
Diffraction gratings are famously associated with Henry Rowland of Johns Hopkins University but there were precursors. Although gratings were first made and used in Europe, reliable machines for ruling gratings were developed in the USA, and two men, Lewis Rutherfurd and William Rogers, tackled the problem before Rowland. Rutherfurd, a wealthy independent astronomer, designed and built the first screw-operated engine for ruling diffraction gratings, the fore-runner of almost all subsequent ruling engines. With it he and his assistant D. C. Chapman ruled many gratings which he generously distributed to practising scientists, thereby materially advancing the science of spectroscopy. Rogers was a Harvard astronomer who developed an interest in the ruling of fine lines on glass that led him to construct a ruling engine with which he investigated the causes of the errors in the rulings he had examined. He continued to seek improvements with a second engine designed for ruling diffraction gratings. He ceased developing this engine when Rowland’s excellent gratings began to be available, concentrating instead on related problems to which he could apply the knowledge and skills he had gained, but his investigations assisted Rowland and other later ruling engine builders. This paper brings together what is known about the ruling engines of Rutherfurd and Rogers, their development, the gratings they produced, their quality and the work that was done with them, and assesses and compares their achievements and the impacts of the work of these two men. 相似文献
55.
Robert Kowalenko 《Studies in history and philosophy of science》2011,42(3):445-452
Standard objections to the notion of a hedged, or ceteris paribus, law of nature usually boil down to the claim that such laws would be either (1) irredeemably vague, (2) untestable, (3) vacuous, (4) false, or a combination thereof. Using epidemiological studies in nutrition science as an example, I show that this is not true of the hedged law-like generalizations derived from data models used to interpret large and varied sets of empirical observations. Although it may be ‘in principle impossible’ to construct models that explicitly identify all potential causal interferers with the relevant generalization, the view that our failure to do so is fatal to the very notion of a cp-law is plausible only if one illicitly infers metaphysical impossibility from epistemic impossibility. I close with the suggestion that a model-theoretic approach to cp-laws poses a problem for recent attempts to formulate a Mill–Ramsey–Lewis theory of cp-laws. 相似文献
56.
57.
研究以路易斯酸氯化锌为催化剂,乙酸和苄醇为原料合成醋酸苯甲酯的工艺条件。结果表明,反应的最佳条件是:冰醋酸¨苯甲醇=1.0¨2.0,带水剂10ml,催化剂1.5g,回流反应时间2.5h。在此条件下,酯收率达到93.2%。 相似文献
58.
目的通过观察幽门螺杆菌(Helicobacter pylori,Hp)在各血型患者中的分布情况,分析Hp感染与ABO血型、Lewis血型、分泌-非分泌表型的关系.方法收集幽门螺旋杆菌感染患者100例为感染组,100例健康的无偿献血者为对照组,分析两组患者的ABO血型系统、血型物质、Lewis血型系统的分布差异.结果 ABO血型分布比较:感染组O型血占56%(56/100),高于对照组的31%(31/100),感染组A型血占16%(16/100),低于对照组的33%(33/100).卡方检验结果显示:感染人群中O型血有较高发生率(56%),和普通人群中A型血(33%)之间具有显著性统计学意义(P0.05).ABO血型与幽门螺杆菌感染之间有相关性,O型人有较高感染倾向,而A型血则有较低感染倾向.Lewis表型分布比较:分析整个数据,感染组与对照组的表型分布基本一致,说明Lewis表型分布不受幽门螺杆菌感染的影响,感染组各表型与对照组比较差异无统计学意义.血型物质分布比较:分泌型个体分布在感染组和对照组之间比较差异无统计学意义.结论幽门螺杆菌感染与O型血有较强的关联,但与Lewis血型、分泌-非分泌表型无关. 相似文献
59.
Wang QY Guo P Duan LL Shen ZH Chen HL 《Cellular and molecular life sciences : CMLS》2005,62(2):171-178
After the transfection of -1,3-fucosyltransferase (FucT)-VII cDNA into H7721 human hepatocarcinoma cells, the protein expression of some cyclins, cyclin-dependent kinases (CDKs) and cyclin-dependent kinase inhibitors (CDIs) p16INK4 and p21waf1/Cip1 were unchanged. However, CDI p27Kip1 protein, both the total amount and the amount that bound to CDK2, but not its mRNA, was significantly reduced. The de-inhibited CDK2 stimulated the phosphorylation of retinoblastoma (Rb) protein and facilitated the G1/S transition and growth rate of the cells. The decrease of p27Kip1 protein, the increase of CDK2 activity and Rb phosphorylation, as well as the cell growth and percentage of S phase cells were correlated to the increased amount of cell surface sialyl Lewis X (SLex) antigen in cells with different -1,3-FucT-VII expression. The reduction in p27Kip1 and the difference in its expression among different transfected cells were blocked by the SLex antibody KM93 in a dose-dependent manner, indicating that p27Kip1 expression was influenced by -1,3-FucT-VII and its product SLex. The MEK/MAPK signaling pathway was more important than the PI-3K pathway in the regulation of p27Kip1 expression.Received 5 August 2004; received after revision 25 October 2004; accepted 11 November 2005 相似文献
60.
以常见易得且稳定的催化剂及膦配体为催化体系, 进一步系统优化钯催化的无铜Sonogashira偶联制备β-(2-乙炔基苯基)环丁酮类化合物的反应体系, 高产率得到一系列含有不同官能团的β-(2-乙炔基苯基)环丁酮类化合物, 并进一步实现铜催化下该类化合物的开环-复分解反应. 相似文献