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  valence
Studies on exposure status of inhabitants to water-arsenic valence states in areas with endemic arsenism in the Datong basin in
      
This study aimed to describe the distribution of water-arsenic (As) valence states and its relationship to areas with endemic arsenism in the Datong basin.
      
The most common type of drinking water arsenic valence state was As(III) in the endemic disease-areas.
      
This led us to conclude that the fraction of each water-arsenic valence state should be studied when determining the arsenic content of drinking water.
      
The valence of atoms was determined by X-ray photoelectron spectroscopy.
      
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When ceric iodate is precipitated from acid solution by the addition of asoluble iodate,a gelatinous precipitate is obtained,which is difficult to filterand wash.The precipitate must be redissolved and reprecipitated as oxalatefor final ignition to ceric oxide.A method has been deviced to improve the form of the ceric iodateprecipitate by slow precipitation in homogeneous solution.Advantage is takenof the fact that cerium exists in two distinct valence states,the cerous and theceric.Cerous iodate is soluble...

When ceric iodate is precipitated from acid solution by the addition of asoluble iodate,a gelatinous precipitate is obtained,which is difficult to filterand wash.The precipitate must be redissolved and reprecipitated as oxalatefor final ignition to ceric oxide.A method has been deviced to improve the form of the ceric iodateprecipitate by slow precipitation in homogeneous solution.Advantage is takenof the fact that cerium exists in two distinct valence states,the cerous and theceric.Cerous iodate is soluble in dilute acid solution,while ceric iodate isinsoluble.Cerium is first reduced to the cerous state by hydrogen peroxide innitric acid solution.Ammonium iodate is added and no precipitation occurs atthis moment.The precipitation is brought about by the slow formation ofceric ion in the iodate solution by ammonium persulfate.Thus a denseprecipitate is formed slowly.This compact volume of the precipitate facilitatesfiltration and washing.The precipitate is ignited directly to ceric oxide,part of which is always stained with a brown color.This is remedied by evapora-tion of the ignited precipitate to dryness with a few drops of concentratedsulfuric acid and ignition to ceric oxide for final weighing.For samples containing 10-50 mg of ceric oxide,a total volume of 300-400 ml gives best results.The optimum concentration of the nitric acid presentis 0.4-0.5 N.A starting temperature of 40-60℃ favors the denseness of theprecipitate.Precipitation is continued at an elevated temperature(70-80℃ )on a hot plate.Stirring not only improves the crystallinity of the precipitateand may decrease the occlusion of impurities,but also shortens the time forcomplete precipitation.Dilute iodic acid solution(1-2%)is used as washsolution.This method is good for samples containing 2.5-250 mg of cericoxide.The composition of the precipitate is not reproducible.The precipitate is abasic iodate and the ratio of IO_3~-found/IO_3~- theoretical for Ce(IO_3)_4 increaseswith the concentration of the nitric acid present(up to 0.5 N)to a maximumvalue of about 0.92.The ratio never reaches unity.An analysis of the pre-cipitate dried at 40-45℃ for 2-3 days shows a fairly constant ratio of IO_3~- found/IO_3 theoretical for Ce(IO_3)_4 From the ratio of Ce:IO_3,an approximate formulaCe_2(IO_3)_7(OH)·XH_2O has been proposed for the precipitate obtained under theconditions described.The number of water molecules in the formula is in-definite,varying from 3 to 5.

1.在均匀溶液中沉淀的碘酸铈,性质紧密,便利于过滤和洗涤。烧灼成为氧化铈后,适合于作为铈的定量分析。2.利用碘酸亚铈能溶解于稀酸溶液而碘酸铈则不溶的区别,先用过氧化氢把全部铈离子还原,再加入碘酸铵,然后进行氧化,使碘酸铈在均匀溶液中沉淀出来。3.本方法适用于含氧化铈2.5—250毫克的样品。4.所得沉淀的分子式经初步测定为 C_(e2)(IO_3)_7(OH)·x H_2O,其中 x 的数值不定,涨落在3与5之间。

Slater and Krutter have attempted to solve the problem of cohesive energy of metals by using the Fermi-Thomas method. They treated the valence electrons and the electrons in the ion core on the same footing. In a way similar to Seitz's cellular method, a sphere with a volume equal to that of a unit cell was drawn and periodic boundary conditions were applied on the surface. Furthermore another boundary condition was imposed in their calculation, namely, on the ground that the sphere as a whole is electrically...

Slater and Krutter have attempted to solve the problem of cohesive energy of metals by using the Fermi-Thomas method. They treated the valence electrons and the electrons in the ion core on the same footing. In a way similar to Seitz's cellular method, a sphere with a volume equal to that of a unit cell was drawn and periodic boundary conditions were applied on the surface. Furthermore another boundary condition was imposed in their calculation, namely, on the ground that the sphere as a whole is electrically neutral, the potential energy of an electron on the surface should be equal to zero. Then it was expected that there existed a minimum of the total energy versus the interatomic distance. However, actual computation gave no such a minimum at all. This discrepancy was ascribed to the neglect of the correlation energy of the electrons.

本文用Fermi-Thomas方法计算了金属的结合能。得到初步结果:金属的能量舆晶格常数的关系中,有一极小值。此极小值所对应的原子间距对重金属舆实验值相近,而对单价碱金属则理论值太小。所得结合能的数值较实验值大很多。作者认为这是由於F.T.方法应用到原子上所存在的误差所引起的,而不是在金属内应用的误差所引起的。

The nature of the chemical bond in conjugate triatomic molecules such as ClO2, O3, SO2, NO2, CO2, N3-, NO2+, N2O, HgCl2, etc. has been discussed from the point of view of the molecular orbital theory. It has been demonstrated quantum mechanically that the conditions of forming a conjugate π bond are: (1) Each atom of the AB2 molecule has a p orbital of approximately equal energy and parallel to one another; (2) the total number of p electrons must be less than two times the number of p orbitala. Triatomic molecules...

The nature of the chemical bond in conjugate triatomic molecules such as ClO2, O3, SO2, NO2, CO2, N3-, NO2+, N2O, HgCl2, etc. has been discussed from the point of view of the molecular orbital theory. It has been demonstrated quantum mechanically that the conditions of forming a conjugate π bond are: (1) Each atom of the AB2 molecule has a p orbital of approximately equal energy and parallel to one another; (2) the total number of p electrons must be less than two times the number of p orbitala. Triatomic molecules with 16 to 19 valence electrons fulfil these conditions, hence they are conjugate molecules. Two styles of writing the structural formulas of such molecules are proposed as shown in the following table:where the dotted lines in type (Ⅰ) formulas represent the conjugate π bonds, while the symbol Ⅱnm means that the π bond involves m electrons and n atoms. The m electrons will fill the bonding, nonbonding and anti-bonding molecular orbitals successively, so that the bond orders of Ⅱ35,Ⅱ34 and Ⅱ33 are 1/2, 1 and 1 respectively. Intype (Ⅱ) formulas, the dots in each rectangular block represent electrons forming a conjugate π bond, while those outside are non-bonding electrons, and the valence electrons of each atom may be clearly counted. The observed bond angles, bond distances, dipole moments and magnetic susceptibilities of AB2 molecules are listed and compared with those expected from their structural formulas.

本文用分子轨道法处理了AB_2型无机共轭分子的结构,讨论了形成大π键的条件,具体分析了具有16至20个价电子的AB_2型分子的结构和性质,提出结构式的两种写法。

 
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