van helan 中文意思是什麼
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Late triassic to mid jurassic strata in which owns the good coal of van ' an formation distributes widely with huge thickness in helan mountain
在賀蘭山的中生代地層中,晚三疊世-中侏羅世地層分佈廣泛、厚度巨大,中侏羅世延安組為賀蘭山的優質含煤層。
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