Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
va tinh » may tinh
va dinh » van dinh, va kinh, vu dinh
sach ky » sac ky, sach y, sach ty
qua dam » cua dam, qua da, dua dam
tang ma » mang may, tang van
nang ma » sang ma, nang cao, mang may
su viet » so viet
dam tu » nam tu, cam tu, tam tu
ve su » va su

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