Perhaps you should try some spelling variations:
kho tang » cao tang
so sach » so sanh, bo sach, co sach
vai cua » dai cua, hai cua, lai cua
va hanh » van hanh, va thanh, va danh
cau duc » cao duc, cau luc, chu duc
hieu va » lieu va, hieu qua
ky tang » ky nang, ky dang, ky trong
va cau » van cau, va cac, va dau
de cua » le cua, te cua, dieu cua

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 tang) OR (kho tang)) xa hoi. hieu va cau duc va hanh ((de cua) or (vai cua)) tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: so sach ((ky tang) OR (kho tang)) xa hoi. hieu va cau duc va hanh ((de cua) OR (vai cua)) tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "so sach ((ky tang) OR (kho tang)) xa hoi. hieu va cau duc va hanh ((de cua) or (vai cua)) tre".
• Adding a wildcard symbol may retrieve word variants: so sach ((ky tang) OR (kho tang)) xa hoi. hieu va cau duc va hanh ((de cua) or (vai cua)) tre*.