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Our experimental results clearly show that the slow breakdown of ascorbic acid during its separation on a paper partition chromatogram is mainly due to the presence of oxygen and such destruction may be completely prevented upon removal of the latter. A quantitative procedure employing filter paper-partition chromatography is described for the determination of ascorbic acid in plant and animal tissues, using a mixture of n-butanol and 4% aqueous trichloroacetic acid solution as solvent (4:6, v/v)....

Our experimental results clearly show that the slow breakdown of ascorbic acid during its separation on a paper partition chromatogram is mainly due to the presence of oxygen and such destruction may be completely prevented upon removal of the latter. A quantitative procedure employing filter paper-partition chromatography is described for the determination of ascorbic acid in plant and animal tissues, using a mixture of n-butanol and 4% aqueous trichloroacetic acid solution as solvent (4:6, v/v). The chromatogram is developed in an atmosphere of carbon dioxide with a few per cent of hydrogen sulfide. The average recovery of added ascorbic acid is about 98%. Due to the irregularity in the percentage reduction of dehydroascorbic acid in the chromatographic chamber in the presence of H_2S, the procedure can only be used to determine the total content of ascorbic acid after preliminary reduction of the dehydro-compound.

(一)利用濾紙層析法分離維生素丙時,氧氣是破壞維生素丙的主要因素,防上這種破壞作用的最有效方法是用CO_2把層析室及溶媒中的O_2排出,並加一定量的H_2S。 (二)以正丁醇、三氯醋酸和水(混合四體積的正丁醇和六體積的4%三氯醋酸水溶液)為溶媒,用CO_2把溶媒及層析室中O_2盡量完全排出,並置飽和H_2S水溶液50—100毫升於層析室內,可以完全防止層析分離時維生素丙的破壞。用這種方法測定動植物組織中維生素丙的總合量時,回收率茌98%以上。 (三)層析室中的H_2S對脫氫維生素丙的還原能力不規律,因此不能用這種方法測定樣品中脫氫維生素丙的含量,只能用以測定還原維生素丙的總合量(浸取液先經H_2S處理然後層析)。

The effect of aqueous ethanol (50% v/v) on the activity of purified mushroom polyphenol oxidase has been found to be as follows: (1)The oxidation of catechol or pyrogallol is greatly stimulated,an increase in the rate of oxygen uptake of over 100% having been invariably observed with catechol as the substrate,whereas the oxidation of other substituted o-dihydric phenols is inhibited in 50% ethanol. (2)When excess ascorbic acid is added to the reaction mixture to reduce o-quinone back to catechol...

The effect of aqueous ethanol (50% v/v) on the activity of purified mushroom polyphenol oxidase has been found to be as follows: (1)The oxidation of catechol or pyrogallol is greatly stimulated,an increase in the rate of oxygen uptake of over 100% having been invariably observed with catechol as the substrate,whereas the oxidation of other substituted o-dihydric phenols is inhibited in 50% ethanol. (2)When excess ascorbic acid is added to the reaction mixture to reduce o-quinone back to catechol as soon as the former is formed,the same stimulatory effect of ethanol on the rate of oxygen uptake has also been observed,indicating that ethanol stimulates only in the early stages of catechol oxidation.Treatment of the experimental results obtained in the presence of excess ascorbic acid and of different catechol concentrations according to Lineweaver and Burk shows that ethanol doubles the maximal velocity and raises the Michaelis constant 7-fold from 0.072 mM to 0.49 mM. Similar results have been obtained with pyrogallol as the substrate.This seems to suggest that the enzyme has a lower affinity for its substrates in 50% ethanol than in aqueous solution. (3)From simultaneous determinations of the amount of oxygen con- sumed and the amount of ascorbic acid oxidized the value of 1 is obtained for the ratio of oxygen consumed:ascorbic acid oxidized,both in the absence and in the presence of ethanol.This seems to indicate that the presence of ethanol does not affect the complete reduction of oxygen to water by the action of polyphenol oxidase. The effect of a number of other organic solvents on catechol oxidation has also been examined.Methanol,iso-propanol,tert-butanol and acetone are all stimulatory whereas dioxane,ethylene glycol and glycerol are in- hibitory.In 50% acetone,the rate of oxygen uptake is 3 times that of the control in aqueous solution.

(一)乙醇能够使多酚氧化酶接触儿茶酚及焦性没食子酸氧化的活力提高,在50%乙醇溶液中,以儿茶酚为底料时,多酚氧化酶的活力比没有乙醇存在时的活力高出一倍以上。(二)50%的乙醇不能使多酚氧化酶接触其他双酚衍生物氧化的活力提高,相反地却有抑制作用。(三)无论有无抗坏血酸的存在,50%乙醇对多酚氧化酶活力的提高程度是一样的,在有一定量的抗坏血酸的存在下,多酚氧化酶对儿茶酚的 Michaelis 常数(25℃)在水溶液及50%乙醇溶液中各为0.072×10~(-3)M 及0.49×10~(-3)M。(四)乙醇的存在,并不影响多酚氧化酶氧化儿茶酚作用时氧气被完全还原为水的作用。无论乙醇存在与否,每一分子底料的氧化,都消耗一个氧原子。(五)其他水溶性有机溶剂对多酚氧化酶氧化儿茶酚活力的影响不同,如甲醇、异丙醇、叔丁醇、丙酮等能使酶活力提高;但1,4-二氧己圜、乙二醇、甘油等则有抑制作用。50%丙酮能使酶活力提高约3倍。

Platforming reactions of n-heptane have been studied. The liquid products of platforming reactions of n-heptane were analyzed by methods of chromatography, fractional distillation, and Raman spectroscopy. A scheme of various reactions taking place under platforming conditions has been proposed. The effect of temperature, pressure, space velocity and catalyst life upon the degree of hydrocracking, isomerization and total conversion of n-heptane were investigated. Isomerization of n-heptane initially increased...

Platforming reactions of n-heptane have been studied. The liquid products of platforming reactions of n-heptane were analyzed by methods of chromatography, fractional distillation, and Raman spectroscopy. A scheme of various reactions taking place under platforming conditions has been proposed. The effect of temperature, pressure, space velocity and catalyst life upon the degree of hydrocracking, isomerization and total conversion of n-heptane were investigated. Isomerization of n-heptane initially increased with increase of contact time, passed through maximum, then decreased. This suggests that isomerization is an intermediate step of hydrocracking reaction. The results of hydrocracking and total conversion were analyzed kinetically under the following conditions: temperature, 455—515°, pressure, 20—40 atm., space velocity, 2.0—6.0 v/v/hr., catalyst life, 1—70 to 160—240 hrs. It was found that the hydrocracking reaction can be described by first order equation, and total conversion of n-heptane can be described by equation of first order reaction with retardation of products.

對正庚烷在鉑重整條件下的各種反應進行了考察。詳細分析了反應產品,並根據產品分析結果,提出了可能進行的一些反應的图式,考察了反應變數如温度、壓力、空速、催化劑使用時間等對於加氫裂化、異構化及總轉化程度的影響。並求得在溫度455—515°、壓力20—40大氣壓、空速2.0—6.0(體積/體積/小時)等試驗條件範圍內,催化劑使用初期與晚期的加氫裂化及總轉化反應的速率常數,動力學方程式及视活化能,加氫裂化反應服從一次反應式。正庚烷的總轉化服從反應產品有阻抑作用的一次反應式。並提出正庚烷的加氫裂化可能經過異構化階段的假設。

 
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