Perhaps you should try some spelling variations:
toc sach » hoc sach, doc sach, thuoc sach
sach han » sach tham, sach danh, sach nang
dung ky » mung ky, vung ky, dung may
tu sach » thu sach, su sach, tu cach
han day » phan day, han dau, dan day
day khi » dau khi, day thi, nhay khi
ky khi » ky thi, ly khi

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (( ((te sach) OR (toc sach)) dung ky khi đong luc ) OR ( tu sach han day khi đong luc ))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( ((te sach) OR (toc sach)) dung ky khi đong luc ) or ( tu sach han day khi đong luc ))~".
• Adding a wildcard symbol may retrieve word variants: (( ((te sach) OR (toc sach)) dung ky khi đong luc ) or ( tu sach han day khi đong luc ))*.