Hole - Similar to a positive charge, this is caused by the absence of a valence electron.

空穴-和正电荷类似，是由缺少价电子引起的。

Natural sand adsorbed viruses increasing with the presence of metal cations, their contents and valence, but this positive role was not clear to modified sand adsorption viruses.

金属阳离子可促进天然砂吸附病毒，并随其浓度和价态的增加而增加，但对修饰砂作用不明显。