Perhaps you should try some spelling variations:
sach dao » lanh dao
dao nang » cao nang, da nang, dai nang
hieu van » hieu va, thien van, lieu va
nam thuc » nam thuoc, am thuc, nam thu
thuc van » thuc vat, thuc dan, thuc va
van hanh » van thanh, ban hanh, van anh
tu sach » thu sach, su sach, te sach
mai hoi » mai khoi, dai hoi, lai hoi
doi cua » hoi cua

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: tu sach dao nang ((xa hoi) OR (mai hoi)). hieu van nam thuc van hanh ((doi cua) OR (dai cua)) vat~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach dao nang ((xa hoi) or (mai hoi)). hieu van nam thuc van hanh ((doi cua) OR (dai cua)) vat~".
• Adding a wildcard symbol may retrieve word variants: tu sach dao nang ((xa hoi) or (mai hoi)). hieu van nam thuc van hanh ((doi cua) OR (dai cua)) vat*.