Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
nam thuc » nam thuoc, am thuc, nam thu
cau theo » cau thi, cau tao
dang van » hoang van, hang va
lang van » tang van, hoang van, giang van
hieu va » hieu qua
thuc va » thuc vat, thuc dan, thuc day
dau vai » dau va, dau hai, dau tai
vai cau » va cau, van cau, vai cac
va dau » va dao

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 y ((lang van) OR (dang van)) hoi. ((hieu va) or (lieu va)) nam thuc va dau vai cau theo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y ((lang van) OR (dang van)) hoi. ((hieu va) OR (lieu va)) nam thuc va dau vai cau theo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y ((lang van) OR (dang van)) hoi. ((hieu va) or (lieu va)) nam thuc va dau vai cau theo".
• Adding a wildcard symbol may retrieve word variants: toc sach y ((lang van) OR (dang van)) hoi. ((hieu va) or (lieu va)) nam thuc va dau vai cau theo*.