| 释义 |
nu·cle·us
\ˈn(y)üklēəs\ noun
(plural nu·clei \-ēˌī\ ; also nucleuses)
Etymology: New Latin, from Latin, kernel, diminutive of nuc-, nux nut — more at nut
1.
a. : the relatively small, brighter, and denser portion of a galaxy, of the head of a comet, or of another celestial body
b. : the hot faint central star of a planetary nebula
2. : a central point, part, group, or mass about which gathering, concentration, or accretion takes place : a center for subsequent increase or growth
< the nucleus of masters and students that should grow into a university — H.O.Taylor >
< a nucleus of fact beneath the incrustation of fable over famous names — Edward Clodd >
< enough patients … to form the nucleus of a new practice — O.S.J.Gogarty >
< not primarily boarding schools but rather day schools with a nucleus of boarders — J.B.Conant >
< frontiers of pioneer settlement have appeared around the margins of the original nucleuses — P.E.James >
as
a. : an element of the protoplasm of most plant and animal cells that is regarded as an essential agent in their metabolism, growth, and reproduction and in the transmission of hereditary characters and that typically consists of a more or less rounded mass of nucleoplasm made up of a hyaline ground substance in which is suspended a network rich in nucleoproteins from which the mitotic chromosomes and one or more nucleoli condense, the whole being enclosed by a nuclear membrane — see macronucleus, micronucleus; compare coenocyte, energid, protoplast; karyolymph, linin; meiosis, mitosis; see cell illustration
b. : the earliest formed part of a shell, operculum, or other similar structure
c. : a visceral mass containing the stomach and other organs of some tunicates
d. : madreporite
e. : focus 8
f. : the hilum of a starch granule
g. : core 1 k
h. : a mass of gray matter or group of nerve cells in the central nervous system
i. : a small mass of bees and combs of brood used in forming a new colony or in rearing queens
j. : a characteristic and stable complex of atoms or groups in a molecule; especially : a ring system : ring
< the naphthalene nucleus >
— compare benzene ring
k. : a particle on which metal forms and grows (as in solidification, condensation, recrystallization, or transformation from one solid crystalline form to another)
l. : a particle upon which water vapor condenses in free air — called also kern
m. : the positively charged central portion of an atom that comprises nearly all of the atomic mass and that consists of protons and neutrons except in hydrogen in which it consists of one proton only — see atomic number, mass number
n.
(1) : the peak of energy in the utterance of a syllable
(2) : the syllable that is the seat of maximum stress in a stress group
o. : head 25
Synonyms: see center |