Perhaps you should try some spelling variations:
sampling sites » sampling designs
data sampling » a sampling, data sample
sites using » site using, states using, rates using
using soap » using social
dan china » han china, dan china's, tuan china
dong bin » dong sin, dann bin
dong di » dong sin

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: ((dong bin) OR (dong di)) ((dan china) OR (can china)) data sampling sites using soap ;~.
• Adding a wildcard symbol may retrieve word variants: ((dong bin) or (dong di)) ((dan china) or (can china)) data sampling sites using soap ;*.