Perhaps you should try some spelling variations:
nam thuoc » nam thuc, nam thu, nha thuoc
trinh vat » trinh van, trinh luat, sinh vat
thuoc va » thuc va, thuoc ma, thuong va
hieu van » hieu va, thien van, lieu va
sach thu » sach thue, sach thieu, sach tham
tinh va » tich va, trinh van, tinh gia
tu sach » thu sach, su sach, te sach
nang ma » tang ma, sang ma, nang cao
cua tre » cua te, cuu tre, cua triet

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

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