Perhaps you should try some spelling variations:
nang doc » nang luc
dau tren » dau tien, dau tieng, dau trong
dat tren » dat trong, dua tren
sach ty » sach y, sach tu, sach thu
doc hoi » duoc hoi, hoc hoi, doc hai
sach ky » sac ky, sach y, sach kem
cac duc » cac du, cao duc, cac dac
va hanh » van hanh, va thanh, va danh
hanh ve » hanh vi, hanh va, hanh kem
hieu ve » hieu va, hieu van
ve cac » va cac, vien cac

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

• If you are trying to use Boolean operators, they must be ALL CAPS: thuoc ((sach ky) OR (sach ty)) nang doc hoi. hieu ve cac duc va hanh ve ((dau tren) OR (dat tren))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuoc ((sach ky) OR (sach ty)) nang doc hoi. hieu ve cac duc va hanh ve ((dau tren) or (dat tren))~".
• Adding a wildcard symbol may retrieve word variants: thuoc ((sach ky) OR (sach ty)) nang doc hoi. hieu ve cac duc va hanh ve ((dau tren) or (dat tren))*.