The study centered on a substance called PM2.5.

这项研究集中在一种叫做PM2.5的物质上。

How can such a substance have an effect on the body?

这样一种物质怎么会对人体产生作用呢？

It may change the state of a substance's matter.

它可能改变物质的状态。

This is because of caffeine, a substance found in some plants.

这是因为这些植物中含有咖啡因。

There were some concerns about a substance, though, called anhydrous ammonia.

尽管称为无水氨，但有些人对这种物质表示担心。

In science, a catalyst is a substance that accelerates a chemical reaction.

在科学中，催化剂是一种加速化学反应的物质。

As a verb, " coat" also means to cover something with a substance.

作为动词，“coat”也表示用某种物质覆盖某物。

One meaning is " a substance or drug used to treat disease or pain" .

它的一个意思是" 用来治疗疾病或疼痛的物质或药物" 。

Officials say the lunch was contaminated with organo-phosphorus, a substance used in pesticides.

官员们表示，午餐被有机磷污染，这是杀虫剂中的一种成分。

They tested the chemical extracts of the plants on a substance called Brewer's yeast.

他们从一种名为“布鲁尔氏酵母”中提取了酵母进行检测。

Perhaps a substance that in just a microscopic quantity could cause unimaginable destruction.

也许一种微量的物质就能造成难以想象的破坏。

Well, we already have a substance like this that is consumed on a daily basis.

而我们已经有这种东西了，并且我们每天都吃它。

Researchers used a substance to restore normal blood sugar metabolism in diabetic laboratory mice.

研究人员试图使用一种物质来恢复患有糖尿病实验老鼠在血糖方面的正常新陈代谢。

DNA is a substance that carries genetic information in the cells of animals and plants.

DNA是指动植物细胞中携带遗传信息的物质。

The researchers found the snake's mouth open. It also contained a substance called natron.

研究人员发现蛇的嘴巴是张开的。嘴巴里还含有一种叫做泡碱的物质。

Researchers have joined the material with a substance whose cells collapse when they are hit.

研究者将一种物质加入这种材料，这种物质的细胞能在受到撞击后解体。

Sometimes a person starts using a substance or behavior to fit in.

有时，人们用某种物质或行为来融入集体。

That's because their mealy texture is tied to the breakdown of a substance called pectin.

因为与它们变面有关的是果胶这种物质的溶解。

A contaminant is something that makes a substance no longer suitable for use.

污染物是使一种物质不再适合使用的东西。

The strength of the acid or base character of a substance.

—用“p”区分被称为“q”的试液。