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