Perhaps you should try some spelling variations:
thanh va » thanh van, hanh va, thanh ha
cua viet » ca viet, hoa viet, cua vat
so sach » so sanh, bo sach, co sach
cao hoi » cau hoi, cao hoc, tao hoi
hieu ve » hieu va, hieu van
truc va » thuc va, trung va
y nang » ky nang, ly nang, v nang
co hoi » co hoc, co loi
ve cam » ve cham, ve cac, va cam
va cua » va chua, via cua, ca cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach y nang ((cao hoi) OR (co hoi)). hieu ve cam ((truc va) or (thuc vat)) thanh va cua viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach y nang ((cao hoi) OR (co hoi)). hieu ve cam ((truc va) OR (thuc vat)) thanh va cua viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach y nang ((cao hoi) OR (co hoi)). hieu ve cam ((truc va) or (thuc vat)) thanh va cua viet".
• Adding a wildcard symbol may retrieve word variants: so sach y nang ((cao hoi) OR (co hoi)). hieu ve cam ((truc va) or (thuc vat)) thanh va cua viet*.