Both heat conditioning and intermittent warming enhanced PE, endo-PG and exo-PG activities, with the second intermittent warming being the most effective.

热调和间隙加温处理均能提高PE、内切PG和外切PG的活性，第二次间隙加温的效果尤为显著。

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The relationship between ethylene and Polygalacturonase(PG) was thoroughly investigated in two aspects of the effect of ethylene on PG function and the regulation of PG on ethylene synthesis.

本课题从乙烯对PG作用的影响和PG对乙烯的反馈调节两方面研究了乙烯与PG之间的关系。

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The detection rates for Pg in molars were much higher than those in incisors, and the presence of Pg and Aa in supragingival plaque was related to periodontal parameters.

两菌种检出率随年龄增长而增加，且与牙周临床指标密切相关，儿童早期采取牙周病的预防措施是非常必要的。

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But, like a lot of these films, this one has a parental guidance rating of "PG-13."

VOA: special.2011.06.20

They know a G film is harmless and a PG almost certainly is, and a PG-13 may or may not be.

WSJ: Roger Ebert on Movie Ratings

It's an open secret that some naturally PG movies have an element or two thrown in to earn a PG-13, so teenagers aren't scared off.

WSJ: Roger Ebert on Movie Ratings

Scenes of smoking have become increasingly rare in non-R-rated movies, according to the MPAA. Of the movies portraying smoking in recent years, 72% were rated R, 21% were rated PG-13, and 6% were rated PG.

CNN: Should smoking trigger an R rating?