Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
thuc van » thuc vat, thuc dan, thuc va
tuc van » truc van, tuc va, duc van
hieu ve » hieu va, hieu van
lang ha » long ha
lang xa » dang xay, lang van
ve cam » ve cham, ve cac, va cam
vi cua » vai cua, di cua
cua tu » cua tuc, cua su, cua cu

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 xa) OR (lang ha)) hoi. hieu ve cam ((tuc van) or (thuc van)) hanh vi cua tu~.
• If you are trying to use Boolean operators, they must be ALL CAPS: toc sach y ((lang xa) OR (lang ha)) hoi. hieu ve cam ((tuc van) OR (thuc van)) hanh vi cua tu.
• The words AND, OR and NOT may confuse the search; try adding quotes: "toc sach y ((lang xa) OR (lang ha)) hoi. hieu ve cam ((tuc van) or (thuc van)) hanh vi cua tu".
• Adding a wildcard symbol may retrieve word variants: toc sach y ((lang xa) OR (lang ha)) hoi. hieu ve cam ((tuc van) or (thuc van)) hanh vi cua tu*.