Perhaps you should try some spelling variations:
"phat trien khai hoc" » "phat trien nha hoc", "phat trien thai hoc", "phat trien khi hoc", "phat trien khai thac", "phan trien khai hoc", "phap trien khai hoc", "nhat trien khai hoc"
"pham trien khoa hoc" » "pham tren khoa hoc", "pham lien khoa hoc", "pham tieng khoa hoc", "pham trien nha hoc", "pham trien hoat hoc", "pham vien khoa hoc", "pham trien hoa hoc"
"pham tien khoa hoc" » "phan tien khoa hoc", "phap tieng khoa hoc", "phan tieng khoa hoc", "pham tien khoan hoc", "pham tien hoa hoc", "pham vien khoa hoc"

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("phat trien khai hoc") OR ((("pham trien khoa hoc") OR ("pham tien khoa hoc"))))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"phat trien khai hoc\") OR (((\"pham trien khoa hoc\") OR (\"pham tien khoa hoc\"))))".
• Removing quotes may allow a broader search: (( phat trien khai hoc ) OR ((( pham trien khoa hoc ) OR ( pham tien khoa hoc )))).
• Adding a wildcard symbol may retrieve word variants: (("phat trien khai hoc") OR ((("pham trien khoa hoc") OR ("pham tien khoa hoc"))))*.