可以用来换取粮票的食物只有这些：代用咖啡、通心粉和小块的人造黄油。There were few provisions available in exchange for food stamps: ersatz coffee, macaroni, small cubes of margarine.这一新的代用甜味剂是用一种野生植物制成的.The new substitute sweetener is made from a wild pl...
Many groups can be added by nucleophilic substitution on a diazonium salt.许多基团可通过向得自胶的重氮盐作亲核取代而加以导入.Most direct substitution of groups bound to an aromatic nucleus is limited to diazonium salts.大多数连于芳核能被直接取代的基团仅限于重氮盐....