Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nang ma » tang ma, sang ma, nang cao
hieu va » lieu va, hieu qua
va dinh » van dinh, vu dinh, va sinh
va kinh » qua kinh
va tinh » may tinh
su viet » so viet
y nang » ky nang, ly nang, v nang
ma hoi » mai hoi, xa hoi, ma hoa
va dam » van dam, va dao, va dau
dam tu » nam tu, cam tu, tam tu

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

• Performing a fuzzy search may retrieve terms with similar spellings: toc sach y nang ma hoi. hieu va dam tu ((va dinh) or (((va kinh) OR (va tinh)))) va su viet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y nang ma hoi. hieu va dam tu ((va dinh) OR (((va kinh) OR (va tinh)))) va su viet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y nang ma hoi. hieu va dam tu ((va dinh) or (((va kinh) OR (va tinh)))) va su viet".
• Adding a wildcard symbol may retrieve word variants: toc sach y nang ma hoi. hieu va dam tu ((va dinh) or (((va kinh) OR (va tinh)))) va su viet*.