Plant uptake of a metal depends primarily on the free metal ion activity.

植物对金属的吸收主要取决于自由态离子活度。

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It occurs rarely as a free metal, occasionally in natural alloys (especially in meteorites), and in hundreds of minerals and ores, including hematite, magnetite, limonite, and siderite.

地壳中游离铁很少见，而通常存在于合金(特别是陨石)及数百种矿物中，包括赤铁矿、磁铁矿、褐铁矿和菱铁矿。

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When the town got free postal delivery, Miss Emily alone refused to let them fasten the metal numbers above her door and attach a mailbox to it.

全镇实行免费邮递制度之后，只有爱米丽小姐一人拒绝在她门口钉上金属门牌号，附设一个邮件箱。

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So, if we want to go from that stable state to that less stable state, we need to put in a certain amount of energy to our system, that difference between the free electron and the electron bound to the metal.

所以，如果我们想使电子,从稳态到达不够稳定的状态，我们需要引入一定数量的,能量到系统中，即自由电子和束缚于金属的,电子的能量差。

麻省理工公开课 - 化学原理课程节选

The BRABUS engine specialists also fit the engine with larger turbochargers, a more efficient intercooling system and a stainless-steel high-performance quad exhaust system with free-flow metal catalysts.

ENGADGET: Brabus iBusiness luxury sedan puts an iPad at every seat, a Magic Mouse at every hide-covered armrest

Electrons in a metal are free to oscillate when light hits them.

ECONOMIST: Optoelectronics

Although that is two to three times the cost of a metal detector, it is less than the price of the fancy explosive-sniffing equipment that is the main rival technology being developed for detecting metal-free mines.

ECONOMIST: Landmines