Perhaps you should try some spelling variations:
nang cai » nang tai, nang cap, nang can
so sach » so sanh, bo sach, co sach
sach ky » sac ky, sach y, sach ty
hieu va » lieu va, hieu qua
cac luc » cau luc, coc luc, cac nuoc
va hanh » van hanh, va thanh, va danh
vai cua » hai cua, lai cua, bai cua
luc va » duc va, tuc va, loc va

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

• Performing a fuzzy search may retrieve terms with similar spellings: so sach ky ((nang cai) or (nang cao)) hoi. hieu va cac luc va hanh ((vai cua) OR (dai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ky ((nang cai) OR (nang cao)) hoi. hieu va cac luc va hanh ((vai cua) OR (dai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ky ((nang cai) or (nang cao)) hoi. hieu va cac luc va hanh ((vai cua) OR (dai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: so sach ky ((nang cai) or (nang cao)) hoi. hieu va cac luc va hanh ((vai cua) OR (dai cua)) tre*.