The short, simple answer is no.
Supporting points:
- It adds noise, not signal. The site is about photography, not about voting.
- If everyone did it, it would be horribly messy and obnoxious.
- If people got voted up for the asking rather than for their contributions, it would break the reputation system.
- It's likely to be counterproductive, and may even garner downvotes.
If you want more upvotes, work on improving your questions and answers. They'll come naturally.
Sometimes, a post doesn't get as many upvotes as you think it might deserve. You've worked on it a long time, and put some real effort into it, and it's just languishing. Sometimes it just means not very many people have looked at it, or that the people who looked at it didn't understand it. For some complicated things, that's often the case and it's just plain okay. Other times, it means your presentation could be better — maybe you can explain things more clearly, or there's some crucial part that's missing or wrong. If you have a post you're really concerned about improving — and not just asking for more votes for their own sake — you could maybe ask what's wrong here, or probably better, bring it up in the chat room.