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medium frequency (MF) | 中频
| See FREQUENCY: RADIO. | 缩写“MF”。参见radio frequency（无线电频率）。 |
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medusa | 水母
| See COELENTERATE and JELLYFISH. | 参见coelenterate（腔肠动物）及jellyfish（海蜇）。 |
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megacycle | 兆周
| One million CYCLES; one thousand KILOCYCLES. The term is often used incorrectly as the equivalent of one million CYCLES PER SECOND. | 一百万周；一千千周。此术语常错误地用于替代一百万周/秒。 |
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megahertz | 兆赫
| One million HERTZ; one thousand KILOHERTZ. The term is used as the equivalent of one million CYCLES PER SECOND. | 指一百万赫；一千千赫。此术语等值于100万周/秒。 |
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melting point | 熔点
| Temperature of change from the solid to the liquid phase of a substance. It is a function of pressure. | 物质由固态变为液态的温度，是压力的函数。 |
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menu | 菜单
| A list of commands and/or options. The user selects the desired command by moving the CURSOR to the respective position on the menu or by en... more | 指令和（或）选项的清单。用户可通过移动光标到菜单上相应的位置或在显示器的指令输入行键入适当的代码来选择所需指令。 |
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Mercator: transverse | 横轴墨卡托投影 | See PROJECTION: TRANSVERSE MERCATOR. | 一种圆柱形投影，与方位转动90°的（横轴）正则墨卡托投影原则上相等。在该投影中，中央经线由一条直线表示，并与正则墨卡托投影上表示赤道的线相合。除了中央经线之外的地理经线和除了赤道（如果表示的话）之外的地理纬线均不是直线。它是一种正形投影。亦称transverse cylindri... more |
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Mercator chart | 墨卡托投影地图
| See CHART. | 采用墨卡托投影的地图，这种地图通常用于航海目的。在墨卡托投影地图中，恒向线总是直线。 |
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Mercator projection | 墨卡托投影
| See PROJECTION. | 一种圆柱型正形投影。其赤道由与实地相等的一条直线表示；其地理经线由与赤道相垂直的一系列平行直线表示；这些经线在赤道上的间距都相等。其地理纬线由与表示经线的线族相垂直的第二套直线系统表示，并且与赤道相平行。因此从数学分析可得到正形性。投影中各点处的长度比向任何方向都相等，纬线的间距... more |
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Mercator sailing | 墨卡托航法
| See SAILING. | 在墨卡托海图上标绘航线的一种数学方法。这种航行类似于平面航法，但在纬差和东西距不同的地点需分别利用对应的子午线弧长差和不同的经差。 |
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mercurial (or mercury) barometer | 水银气压表
| See BAROMETER. | 利用大气压力与水银柱施加的压力平衡测量大气压强的气压计。 |
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meridian | 子午圈
| A north-south reference line, particularly a GREAT CIRCLE through the GEOGRAPHICAL POLES of the EARTH, from which LONGITUDES (or DEPARTURES)... more | 特指通过地球地理极的大圈形成的南北基准线，由此线计算经度（或东西距）和方位角；或指垂直于大地水准面或旋转椭球的水平面所定义的这样的线。此术语通常指上半子午圈（upper branch）。 |
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meridian: astronomical | NULL | A line on the surface of the EARTH connecting points having the same ASTRONOMICAL LONGITUDE. Because the DEFLECTION OF THE VERTICAL is not t... more | NULL |
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meridian: celestial | 天球子午圈，赤经圈
| A GREAT CIRCLE of the CELESTIAL SPHERE through the CELESTIAL POLES and the ZENITH. The expression usually refers to the UPPER BRANCH. | 通过天体天极和天顶的大圆。该术语通常指上半子午圈（Upper branch）。 |
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meridian: central | 中央子午线
| See MERIDIAN: INITIAL. | 参见initial meridian（起始子午线，首子午线）。 |
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meridian: compass | 罗经子午线
| A line through the north-south points of a MAGNETIC COMPASS. The compass card axis lies in the compass meridian. | 通过磁罗经南、北两点的线。罗经刻度盘轴线位于磁子午线上。 |
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meridian: geodetic | 大地子午线
| A line on a SPHEROID which has the same GEODETIC LONGITUDE at every point. | 旋转椭球体上其各点具有相同大地经度的线。 |
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meridian: geographic(al) | 地理子午线
| A general term, applying alike to an ASTRONOMICAL or a GEODETIC MERIDIAN. | 通用术语，指天文子午线和大地子午线。 |
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meridian: Greenwich | 格林尼治子午线
| The ASTRONOMICAL MERIDIAN through the centre of the TRANSIT instrument of the observatory of Greenwich, England, serving as the reference f... more | 穿过格林尼治天文台中星仪中心的天文子午线，作为格林尼治时间的基准。与地方子午线对应。 |
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meridian: grid | 坐标网纵线
| One of the GRID lines extending in a grid north-south direction. | 指格网线中向南北方向延伸的线。 |