A method of sampling in a survey in which the interviewer is instructed to include certain prescribed percentages of people who come from various identifiable subpopulations, e.g. men over 60, women under 30, unemployed men.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。