occurrencen.发生;事件;出现
occurrence of disease包涵体
occurrence and damage发生危害
occurrence regularity发生规律
occurrence characters病虫发生特点
occurrence determinant重发成因
occurrence probability发生概率
Occurrence of chromium铬赋存状态
occurrence development发生演变
occurrence environment赋存环境
Occurrence's mechanism逐步缩小