Perhaps you should try some spelling variations:
nam thuoc » nam thuc, nam thu, nha thuoc
sach thu » sach thue, sach thieu, sach tham
hieu van » hieu va, thien van, lieu va
su sach » so sach, vu sach
nang ma » tang ma, sang ma, nang cao
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: su sach thu ((nang ma) or (nang x)) hoi. hieu van nam thuoc ((va tinh) OR (may tinh)) va cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: su sach thu ((nang ma) OR (nang x)) hoi. hieu van nam thuoc ((va tinh) OR (may tinh)) va cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "su sach thu ((nang ma) or (nang x)) hoi. hieu van nam thuoc ((va tinh) OR (may tinh)) va cua tre".
• Adding a wildcard symbol may retrieve word variants: su sach thu ((nang ma) or (nang x)) hoi. hieu van nam thuoc ((va tinh) OR (may tinh)) va cua tre*.