Perhaps you should try some spelling variations:
"kon mach tinh son - toan giao" » "kon mach tich son - toan giao", "kon manh tinh son - toan giao", "kon trach tinh son - toan giao", "kon mach tinh son - ton giao", "kon mach tinh son - toan cao", "kon mach tinh son - hoa giao", "ke mach tinh son - toan giao", "ban mach tinh son - toan giao", "kon mach tinh toan - toan giao", "kon mach dinh so - toan giao", "kon mach tinh hoc - toan giao"
"vu bac dinh su - don gian" » "vu xac dinh su - don gian", "vu bac ninh su - don gian", "vu ba dinh su - don gian", "vu bac dinh su - dan gian", "vu bac dinh so - don gian", "vu bac hinh su - don gian", "vu bac dinh cu - don gian", "vu bach dinh su - don gian", "vu ban dinh su - don gian", "xu bac dinh su - don gian"

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("kon mach tinh son - toan giao") or ("vu bac dinh su - don gian"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("kon mach tinh son - toan giao") OR ("vu bac dinh su - don gian")).
• Removing quotes may allow a broader search: (( kon mach tinh son - toan giao ) or ( vu bac dinh su - don gian )).
• Adding a wildcard symbol may retrieve word variants: (("kon mach tinh son - toan giao") or ("vu bac dinh su - don gian"))*.