Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
gia hanh » gia thanh, giao hanh, gia anh
phan duc » pham duc, phan tu, phan dau
duc gia » quoc gia
hieu va » lieu va, hieu qua
lang xa » lang ha, dang xay, lang van
ty lang » tay lang, ty xang, ty hang
va phan » van phan, va phat, va phap
ve cau » ke cau, ve cac, le cau
va cau » van cau, va cac, va dau

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: ((te sach) or (toc sach)) ty lang xa hoi. hieu va phan duc gia hanh ((ve cau) OR (va cau)) treo~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((te sach) OR (toc sach)) ty lang xa hoi. hieu va phan duc gia hanh ((ve cau) OR (va cau)) treo.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((te sach) or (toc sach)) ty lang xa hoi. hieu va phan duc gia hanh ((ve cau) OR (va cau)) treo".
• Adding a wildcard symbol may retrieve word variants: ((te sach) or (toc sach)) ty lang xa hoi. hieu va phan duc gia hanh ((ve cau) OR (va cau)) treo*.