Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nang tai » tang tai, sang tai, nang cao
hang tai » hang va, dung tai
hanh vai » hanh vi, hanh va, hanh tai
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
va cham » va chat, va tham
luc va » tuc va, loc va
vai va » mai va, dai va, hai 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: toc sach ky ((nang tai) OR (hang tai)) hoi. hieu va cham ((luc va) or (duc va)) hanh vai va thiet~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach ky ((nang tai) OR (hang tai)) hoi. hieu va cham ((luc va) OR (duc va)) hanh vai va thiet.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach ky ((nang tai) OR (hang tai)) hoi. hieu va cham ((luc va) or (duc va)) hanh vai va thiet".
• Adding a wildcard symbol may retrieve word variants: toc sach ky ((nang tai) OR (hang tai)) hoi. hieu va cham ((luc va) or (duc va)) hanh vai va thiet*.