The rates they charge are tied to the number of readers.

VOA: special.2009.04.20

And so we have a positive charge in the nucleus which is given by the number of protons.

在原子核上,有很多质子聚集而形成的正电荷。

麻省理工公开课 - 固态化学导论课程节选

Now the last thing is that because the neutron has no net charge, we can change neutron number.

现在，最后一件事是,因为中子没有净电子，我们可以改变中子数。

麻省理工公开课 - 固态化学导论课程节选

Fyodorov was now in charge of a number of switches and the junior switchmen who operated them.

NEWYORKER: Among Animals and Plants

There are a number of other organisations which charge a percentage of the amount they eventually recover.

BBC: Finding your lost fortune

While Visa and MasterCard themselves have long levied a 1% charge, a number of issuers tack on another 2%.

FORBES: Prudent Traveler