这四枚新邮票是为了纪念英国天文协会成立100周年而发行的。The four new stamps mark the 100th anniversary of the British Astronomical Association.在历史的年代数目和天文年代数目之间存在差别.There are differences between historical and astronomical numbering of years.数学材料是...
This seam of coal reposes on a layer of clay.这个煤层处于一层黏土岩之上.A new method for seam tracking using image centroid in gas tungsten arc welding is presented.研究一种基于图像质心识别的电弧焊焊缝跟踪新方法.The crack in the coal seam is divided into t...