# SI基本单位

 SI基本单位 新修订中文定义 国际公布英文定义 秒 second 国际单位制中的时间单位，符号s。当铯频率ΔνCs，也就是铯133原子不受干扰的基态超精细跃迁频率，以单位Hz即s-1表示时，取其固定数值为9 192 631 770来定义秒。 The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency ΔνCs the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s–1. 米 metre 国际单位制中的长度单位，符号m。当真空中光速c以单位m/s表示时，取其固定数值为299 792 458来定义米，其中秒用ΔνCs定义。 The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m/s, where the second is defined in terms of ΔνCs. 千克 kilogram 国际单位制中的质量单位，符号kg。当普朗克常数h以单位J s即kg m2 s-1表示时，取其固定数值为6.626 070 15×10-34来定义千克，其中米和秒用c和ΔνCs定义。 The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10–34 when expressed in the unit J s, which is equal to kg m2 s–1, where the metre and the second are defined in terms of c and ΔνCs. 安培 ampere 国际单位制中的电流单位，符号A。当基本电荷e以单位C即A s表示时，取其固定数值为1.602 176 634×10-19来定义安培，其中秒用ΔνCs定义。 The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge e to be 1.602 176 634 ×10−19 when expressed in the unit C, which is equal to A s, where the second is defined in terms of ΔνCs. 开尔文 kelvin 国际单位制中的热力学温度单位，符号K。当玻尔兹曼常数k以单位J K-1即kg m2 s-2 K-1表示时，取其固定数值为1.380 649×10-23来定义开尔文，其中千克、米和秒用h，c和ΔνCs定义。 The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant k to be 1.380 649 ×10−23 when expressed in the unit J K−1, which is equal to kg m2 s−2 K−1, where the kilogram, metre and second are defined in terms of h, c and ΔνCs. 摩尔 mole 国际单位制中的物质的量的单位，符号mol。1摩尔精确包含6.022 140 76×1023个基本单元。该数称为阿伏伽德罗数，为以单位mol-1表示的阿伏伽德罗常数NA的固定数值。 一个系统的物质的量，符号n，是该系统包含的特定基本单元数的量度。基本单元可以是原子、分子、离子、电子、其它任意粒子或粒子的特定组合。 The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol−1 and is called the Avogadro number. The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles. 坎德拉 candela 国际单位制中的沿指定方向发光强度单位，符号cd。当频率为540×1012 Hz的单色辐射的光视效能Kcd以单位lmW-1即cd sr W-1或cd sr kg-1 m-2 s3表示时，取其固定数值为683来定义坎德拉，其中千克、米、秒分别用h, c 和ΔνCs定义。 The candela, symbol cd, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency 540 × 1012 Hz, Kcd, to be 683 when expressed in the unit lm W–1, which is equal to cd sr W–1, or cd sr kg–1 m–2 s3, where the kilogram, metre and second are defined in terms of h, c and ΔνCs.

（英文定义源自：CGPM. 26th CGPM Resolution 1: On the revision of the International System of Units (SI). 2018-11-16[2019-5-5] http://www.bipm.org/en/CGPM/db/26/1/