Perhaps you should try some spelling variations:
hieu van » hieu va, thien van, hieu ve
so sanh » do sanh
co sach » bo sach, cuon sach, hoc sach
tang ma » mang may, tang van
cac tac » cac toc, cac bac, cac dac
va hanh » van hanh, va thanh, va danh
ma hoi » mai hoi, xa hoi, ma hoa
tac va » tac da, tac xa, tuc va
vi va » vi van, vai va, vu 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: ((so sanh) or (co sach)) 6 tang ma hoi. ((hieu van) OR (lieu va)) cac tac va hanh vi va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((so sanh) OR (co sach)) 6 tang ma hoi. ((hieu van) OR (lieu va)) cac tac va hanh vi va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((so sanh) or (co sach)) 6 tang ma hoi. ((hieu van) OR (lieu va)) cac tac va hanh vi va thiet".
• Adding a wildcard symbol may retrieve word variants: ((so sanh) or (co sach)) 6 tang ma hoi. ((hieu van) OR (lieu va)) cac tac va hanh vi va thiet*.