Perhaps you should try some spelling variations:
tham thuc » nham thuc, tam thuc, thai thuc
pham thuc » phap thuc, pham chuc, nham thuc
va triet » va thiet, va trien, ve triet
sach thi » sach thu, sach tai, sach thieu
thi hang » thi hanh, thi nang, thi hong
hanh tai » thanh tai, hang tai, han tai
va hanh » van hanh, va thanh, va danh
tu sach » thu sach, su sach, te sach
hieu va » lieu va, hieu qua
ca hoi » cau hoi, cua hoi, co hoi
tai va » thai va, mai va, tri va

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 thi hang ((ca hoi) or (xa hoi)). hieu va ((tham thuc) OR (pham thuc)) va hanh tai va triet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: tu sach thi hang ((ca hoi) OR (xa hoi)). hieu va ((tham thuc) OR (pham thuc)) va hanh tai va triet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "tu sach thi hang ((ca hoi) or (xa hoi)). hieu va ((tham thuc) OR (pham thuc)) va hanh tai va triet".
• Adding a wildcard symbol may retrieve word variants: tu sach thi hang ((ca hoi) or (xa hoi)). hieu va ((tham thuc) OR (pham thuc)) va hanh tai va triet*.