Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
phat thuc » phap thuc, pham thuc, phan thuc
hieu van » hieu va, thien van, lieu va
van phat » va phat, van chat, van phan
tu sach » thu sach, su sach, te sach
cao hoi » cau hoi, co hoi, cao hoc
thuc va » thuc vat, thuc dan, thuc day
va dan » ca dan, va dao, va dau
hai va » hai van, thai va, mai va
thiet » thieu

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

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