Perhaps you should try some spelling variations:
toc sach » doc sach, thuoc sach, nuoc sach
hanh tai » thanh tai, hang tai, han tai
nam truc » nam truoc, nam thuc, nam trung
hieu van » hieu va, thien van, lieu va
dang xay » dang van, van xay
hoc sach » hoc sinh, hoc cac, hoc anh
dang xa » lang xa, dang ha, dang va
truc va » thuc va, thuc vat, trung va
va hanh » van hanh, va thanh, va danh
tai cua » thai cua, tai cuc, tri cua
cua te » cua tu

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) or (hoc sach)) ky ((dang xa) OR (dang xay)) hoi. hieu van nam truc va hanh tai cua te~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (hoc sach)) ky ((dang xa) OR (dang xay)) hoi. hieu van nam truc va hanh tai cua te.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) or (hoc sach)) ky ((dang xa) OR (dang xay)) hoi. hieu van nam truc va hanh tai cua te".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) or (hoc sach)) ky ((dang xa) OR (dang xay)) hoi. hieu van nam truc va hanh tai cua te*.