Perhaps you should try some spelling variations:
nam thuc » nam thuoc, am thuc, nam thu
hieu van » hieu va, thien van, lieu va
sach thu » sach thue, sach thieu, sach tham
lang xa » lang ha, dang xay, lang van
sach ty » sach y, sach tu, xach tay
danh va » doanh va, anh va, dan va
hanh va » hang va, hanh vi
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: toc ((sach ty) or (sach thu)) lang xa hoi. hieu van nam thuc vat ((danh va) OR (hanh va)) cua tre~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc ((sach ty) OR (sach thu)) lang xa hoi. hieu van nam thuc vat ((danh va) OR (hanh va)) cua tre.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc ((sach ty) or (sach thu)) lang xa hoi. hieu van nam thuc vat ((danh va) OR (hanh va)) cua tre".
• Adding a wildcard symbol may retrieve word variants: toc ((sach ty) or (sach thu)) lang xa hoi. hieu van nam thuc vat ((danh va) OR (hanh va)) cua tre*.