Perhaps you should try some spelling variations:
thuoc sach » nuoc sach, thuat sach, thuoc sinh
hieu van » hieu va, thien van, lieu va
hoc sach » hoc sinh, hoc cac, hoc anh
nam thuc » nam thuoc, am thuc, nam thu
hanh va » hang va, hanh vi
va hanh » van hanh, va thanh, va danh
thuc va » thuc vat, thuc dan, thuc day
cua tre » cua te, cuu tre, cua triet
hieu ve » hieu va
nang o » nang co, nang ho, nang ro
va cua » va chua, via cua, ca cua
o hoi » co hoi, o hoc, o hai

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

• Performing a fuzzy search may retrieve terms with similar spellings: ((thuoc sach) OR (hoc sach)) ky nang o hoi. ((hieu ve) or (hieu van)) nam thuc va hanh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((thuoc sach) OR (hoc sach)) ky nang o hoi. ((hieu ve) OR (hieu van)) nam thuc va hanh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((thuoc sach) OR (hoc sach)) ky nang o hoi. ((hieu ve) or (hieu van)) nam thuc va hanh va cua tre".
• Adding a wildcard symbol may retrieve word variants: ((thuoc sach) OR (hoc sach)) ky nang o hoi. ((hieu ve) or (hieu van)) nam thuc va hanh va cua tre*.