英语语法分析

At 7 days, in the tubules spermatogonia appeared.

生后7天出现精原细胞。

Objective to obtain a simple method to isolate and purify spermatogonia stem cells.

目的寻求一种获取小鼠的生精干细胞的简单方法。

Methods: the sister chromatid exchange (SCE) test in mice spermatogonia was used in the study.

方法：采用小鼠精原细胞姐妹染色单体交换实验。