Perhaps you should try some spelling variations:
toc sach » hoc sach, thuoc sach, nuoc sach
doc sach » hoc sach, nuoc sach, dac sac
thanh do » thanh de, thanh pho, thanh hoa
dau tren » dau tien, dat tren, dau tieng
hieu ve » hieu va, hieu van
cau luc » cau truc, cau phuc
luc gia » luoc gia, duc gia, quoc gia
y hang » ly hang, ty hang, yu hang
ve cau » ke cau, va cau, ve cac
do dau » doi dau, do dai, mo dau

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 (doc sach)) y hang ((van hoc) or (van hoa)). hieu ve cau luc gia thanh do dau tren~.
• If you are trying to use Boolean operators, they must be ALL CAPS: ((toc sach) OR (doc sach)) y hang ((van hoc) OR (van hoa)). hieu ve cau luc gia thanh do dau tren.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((toc sach) OR (doc sach)) y hang ((van hoc) or (van hoa)). hieu ve cau luc gia thanh do dau tren".
• Adding a wildcard symbol may retrieve word variants: ((toc sach) OR (doc sach)) y hang ((van hoc) or (van hoa)). hieu ve cau luc gia thanh do dau tren*.