| 释义 |
quadrivalent, a. and n.
(see below)
[f. quadri- + L. valēnt-em, pres. pple. of valēre to be worth.]
A. adj.
1. Chem. |kwɒdrɪˈveɪlənt|. Having a valency of four; capable of combining with four univalent atoms.
1865A. W. Hofmann in Chem. News 13 Oct. 176/1 The nitrogen and carbon atoms, respectively trivalent and quadrivalent, are provided with three and four arms, indicating the three and four combining units respectively distinguishing these atoms. 1869Eng. Mech. 12 Nov. 198/3 The elements are classified as..tetratomic or quadrivalent, having four attractions. 1880E. Cleminshaw Wurtz' Atom. The. 283 Carbon is quadrivalent and oxygen bivalent. 1922A. D. Udden tr. Bohr's Theory of Spectra III. iii. 109 While an element like titanium in the fourth period already shows a marked tendency to occur with various valencies, on the other hand an element like zirconium is still quadri-valent like carbon in the second period and silicon in the third. 1964J. W. Linnett Electronic Struct. Molecules ii. 30 The carbon atom..is, of course, quadrivalent. 1978Sci. Amer. Feb. 58/2 Cerium, alone among the trivalent rare earths, can be oxidized to the relatively insoluble quadrivalent state.
2. Cytology. |kwɒˈdrɪvələnt|. Applied to a meiotic structure composed of four wholly or partly homologous chromosomes joined together.
Less common than the corresp. n. (see B. 2).
1898Zool. Jahrb. (Abt. für Anat.) XII. 44 Frequently also in the loose spirem are found quadrivalent chromosomes with a constriction about the middle. 1929Jrnl. Genetics XXI. 18 The hyacinths offered an opportunity for the comparative study in the same cell of the structure and behaviour of bivalent, trivalent and quadrivalent chromosomes of distinct types.
B. n.
1. Chem. A quadrivalent element. rare—1.
1880E. Cleminshaw Wurtz' Atom. The. 211 Carbon is therefore a quadrivalent.
2. Cytology. |kwɒˈdrɪvələnt|. A quadrivalent group of chromosomes.
1923Proc. Nat. Acad. Sci. IX. 109 In one quarter and more of the pollen-mother-cells this regular distribution does not occur with regard to all of the 12 quadrivalents. 1946[see microsporogenesis]. 1952[see bivalent a. 2]. 1975Nature 17 Apr. 595/2 A sister plant which was a monosomic (2n = 41)..formed some trivalents, quadrivalents.., pentavalents and hexavalents, in addition to bivalents. |