Perhaps you should try some spelling variations:
su sach » so sach, vu sach
co sach » bo sach, cuon sach, hoc sach
nang ma » tang ma, sang ma, nang cao
van bac » van ban, van bao, dan bac
van hac » van hoc, van ha, van hai
va hanh » van hanh, va thanh, va danh
v nang » va nang, vu nang, van nang
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: ((su sach) or (co sach)) v nang ma hoa. hieu ((van bac) OR (van hac)) tac va hanh vi va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((su sach) OR (co sach)) v nang ma hoa. hieu ((van bac) OR (van hac)) tac va hanh vi va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((su sach) or (co sach)) v nang ma hoa. hieu ((van bac) OR (van hac)) tac va hanh vi va thiet".
• Adding a wildcard symbol may retrieve word variants: ((su sach) or (co sach)) v nang ma hoa. hieu ((van bac) OR (van hac)) tac va hanh vi va thiet*.