2 questions:
1.If my government have war weariness 0,but in conquered cities citizens say:'Stop the aggresion against our mother country',police stations will decrease unhappiness in these cities ?
No, because the 'Stop the aggression' message does not (AFAIK) indicate the same unHappiness-cause as the 'All we are sayin'...' (WW) message.
To counter Aggression-unHappiness in conquered towns, you need to either end the war, or kill off the parent-civ, or (in the shorter term), produce Happy- and Content-faces from military police (if your gov-type allows it, but IIRC, all the zero-WW govs allow use of Mil-Pol), Luxes + Markets, LUX%-slider spending, and e.g. Temples/ Cathedrals/ Colosseums). Police stations reduce WW and Corruption, but do not provide Happy-faces -- or at least, not directly.
Under Republic/Democracy, if those conquered towns are close enough to your core to be halfway useful, then the reduced corruption from Courthouses and Police Stations
might result in more base-commerce being converted via the LUX%-slider (depending on settings), and hence more Happy-faces available to the town. But under Republic, by the time Police Stations become available, chances are that your unhappy conquests are a long way from your core, so Police Stations likely won't help you in that respect.
Communism is a different story. Since corruption/waste are flattened across your entire Empire, decorrupting base-commerce (and hence boosting any LUX%-output) in outlying, late-game conquests can make a
much bigger difference to (un)Happiness in those cities.
2.What is the percent of research penalty in communism,is fluctuating or stabile,I don't find a thread about this? If will increase science(more libraries,universities) matter,or can use just a maximal value ?
I'm not sure what your question is. In the epic game, there are no 'Rate-Caps' (on the SCI%-, LUX%-, and TAX%-sliders) for any of the governments.
Building Libs and Unis will do exactly the same thing for Communist civs as for Rep/Dem civs -- it will add +50% to the SCI%-slider 'commerce -> beaker' output (allowing for rounding) per improvement per city. But since Communism doesn't get the +1 commerce-bonus on commerce-producing tiles, which is enjoyed by Republic and Democracy, each 'core' city (i.e. those in the 1st couple of rings round the Palace) will produce less commerce (and hence fewer beakers for any given SCI%-setting) under Communism than it would under the representative governments.
OTOH, Communist civs by definition don't have a 'core', and don't suffer any tile-penalties either (unlike Despotism and Anarchy), so outlying cities (relative to the Palace) can be hugely more productive in terms of using the shields/commerce from their surrounding tiles, than they would be under Rep/Dem. But in order to reap that benefit, you'd be aiming to get every one of those outlying Cities fully developed into Metros, so you'd want them spaced fairly widely (Cxx(x)xC) to give each of them access to 16-20 exclusive tiles. Or just take the towns from the AI-Civs, because that's how they always space their cities anyway...