差频原理
difference frequency control principle
射频原理
radio frequency principle
第一性原理理论
first principles calculations
科学管理原理
principle of scientific management
热处理原理
heat treatment principles
heat treatment
principles of heating processing
热处理原理及工艺
principles & technology for heating processing
热处理原理与工艺
heat treatment principl and process
人力资源管理原理
principle of human resource administration