指定想要获得字符串的长度，（可选，没有指定章前往从指定开端方位到原字符串完毕方位）
The number of characters in the substring. If this argument is omitted, the returned substring includes all characters from the starting position to the end of the string.
论文第四章重点介绍用非线性映射方法分析原核生物基因密码子使用情况并得到的相关结论。
In chapter IV, the codon usage preferences in prokaryotic organism are analyzed by nonlinear mapping method.
在第二章，我们提出了一种解决具有原方块角形结构正定二次规划问题的分解协调算法。
In chapter 2, we presented a method for solving positive definite quadratic programming with coupled-block structure.
昨夜，我从舟山抵达上海，与我的好兄弟、著名诗人王霆章、刘原一起喝法国红酒，每人一瓶；
Last night, I arrived at Shanghai from Zhoushan, degusting French Red Wine with my buddies, famous poets Wang Tingzhang, Liuyuan together, a bottle for each;
全文共分为三个大的章节，第一章为医疗犯罪原论；
The text is divided into three big chapters totally: chapter 1 for total say;
全文共分为三个大的章节，第一章为医疗犯罪原论；
The text is divided into three big chapters totally: chapter 1 for total say;
应用推荐