Perhaps you should try some spelling variations:
thuoc sach » hoc sach, nuoc sach, thuat sach
duoc lam » duoc pham, duoc ly, duoc li
hieu van » hieu va, thien van, lieu va
sang ma » tang ma, sang tao, mang may
sach ly » sach y, sach lo, sach ty
nang ma » tang ma, nang cao, mang may
hanh va » hang va, hanh vi
cua tre » cua te, cuu tre, cua triet
va cua » va chua, via cua, ca cua

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

• Performing a fuzzy search may retrieve terms with similar spellings: thuoc sach ly ((nang ma) OR (sang ma)) hoi. hieu van nam ((duoc ma) or (duoc lam)) hanh va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: thuoc sach ly ((nang ma) OR (sang ma)) hoi. hieu van nam ((duoc ma) OR (duoc lam)) hanh va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thuoc sach ly ((nang ma) OR (sang ma)) hoi. hieu van nam ((duoc ma) or (duoc lam)) hanh va cua tre".
• Adding a wildcard symbol may retrieve word variants: thuoc sach ly ((nang ma) OR (sang ma)) hoi. hieu van nam ((duoc ma) or (duoc lam)) hanh va cua tre*.