Perhaps you should try some spelling variations:
chieu sach » chinh sach, chiet tach, chieu sang
song trong » cong trong, dong trong, sang trong
trong mach » trong cac, trong minh, trong anh
hieu lang » chieu sang, hieu quang, nhieu tang
quang qua » quang cua, quang tuan, quang xuan
mach toan » manh toan, hach toan, mach tuan
toan ban » van ban

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: doc ((chieu sach) OR (hieu lang)) - tinh quang qua song trong mach toan ban~.
• Adding a wildcard symbol may retrieve word variants: doc ((chieu sach) or (hieu lang)) - tinh quang qua song trong mach toan ban*.