土壤侵蚀、化学退化、物理退化是全球范围内最主要的退化形式。
Globally, soil erosion, chemical deterioration and physical degradation are the important forms amongst various types of soil degradation.
土地沙漠化作为土地的一种退化形式，已成为中国北方地区一个重大的生态环境和社会经济问题。
Soil becomes desert as a sort of retrogresss form of soil has become a great problem of entironment and society economy in north area.
导出了关于混合模的耦合边界积分方程组及其退化形式，并用矩量法将之离散为齐次代数方程组，从而得波导的混合模传输常数；
The coupled boundary integral equations and their reduced forms are deduced for hybrid mode problems, and these equations are discreted into a system of linear algebraic equations by moment method.
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