This is mainly because it is a large molecule, and has difficulty passing through the blood-brain barrier which protects the brain from potentially harmful compounds in the blood.

这主要是因为它是一种大分子物质，要穿过保护大脑免受血液中可能有害化合物入侵的血脑屏障很困难。

youdao

A very large molecule, such as a polymer or protein, consisting of many smaller structural units linked together.

大分子一种很大的分子，如聚合物或蛋白质，由许多小的结构单位结合而成。

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Two types of amphiprotic high-molecular coagulants ie APAM and CGAAC were successfully synthesized by large molecule modification process.

通过大分子改性的方法，合成了两种两性高分子絮凝剂APAM和CGAAC。

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So, now you have a single molecule, very large molecule, with not just two binding sites but with ten binding sites.

所以如果你体内有一个细胞,一个体积很大的细胞,细胞表面不只有两个抗原结合位点,而有十个抗原结合位点

耶鲁公开课 - 生物医学工程探索课程节选

A polymer is just a large molecule that's made up of repeated units.

聚合物就是由,重复单位构成的大分子

耶鲁公开课 - 生物医学工程探索课程节选

This is incredibly important because if you picture having a double bond in a very large molecule, you could have all sorts of other atoms off this way and all sorts of other atoms off this way, and you can picture the shape would be very different if you have one confirmation versus another confirmation.

这是十分重要的,因为如果你想象在一个大分子里有一个双键，你可以在这里有各种各样的其它原子,在这里也有各种各样的其它原子，你可以想象一个构型,和另外一个构型之间的形状差别是非常大的。

麻省理工公开课 - 化学原理课程节选

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