2022-23USACO美国计算机奥赛备赛开启，附历年真题示例
USACO 美国计算机奥林匹克学术活动 United States of America Computing Olympiad 简称USACO，USACO学术活动是美国最具认可度的计算机学术活动，用于选拔美国参加全球信息奥林匹克学术活动（IOI）的国家队，学术...
AQA A Level Chemistry复习笔记1.6.1 Bond Energy
Bond Energy During a reaction, enthalpy changes take place because bonds are being broken and formed Energy (in the form of heat) is needed to overcome attractive forces between atoms Bond breaking...
AQA A Level Chemistry复习笔记1.5.1 Shapes of Simple Molecules & Ions
Electron Pairs The valence shell electron pair repulsion theory (VSEPR) predicts the shape and bond angles of molecules Electrons are negatively charged and will repel other electrons when close to...
AQA A Level Chemistry复习笔记1.4.1 Changes in State: Energy Changes
State Changes Changes of state are physical changes that are reversible These changes do not change the chemical properties or chemical makeup of the substances involved Vaporization includes evapo...
AQA A Level Chemistry复习笔记1.3.1 The Mole & the Avogadro Constant
Mole & Avogadro Constant The Avogadro constant (NA or L) is the number of particles equivalent to the relative atomic mass or molecular mass of a substance The Avogadro constant applies to atom...
AQA A Level Chemistry复习笔记1.2.1 Relative Atomic Mass & Relative Molecular Mass
Relative Masses Atomic Mass Unit The mass of a single atom is so small that it is impossible to weigh it directly Atomic masses are therefore defined in terms of a standard atom which is called the...
AQA A Level Chemistry复习笔记1.1.1 Fundamental Particles
Structure of an Atom All matter is composed of atoms, which are the smallest parts of an element that can take place in chemical reactions Atoms are mostly made up of empty space around a very smal...
AQA A Level Biology复习笔记8.4.1 Recombinant DNA Technology
Recombinant DNA Technology Recombinant DNA The genetic code is universal, meaning that almost every organism uses the same four nitrogenous bases – A, T, C & G. There are a few exceptions The g...
AQA A Level Biology复习笔记8.3.1 Genome Sequencing Projects
Genome Sequencing Projects A genome contains all of the genes within an organism Advances in technology have allowed scientists to map and sequence the genes within an organism's genome Genome sequ...
AQA A Level Biology复习笔记8.2.1 Totipotent Cells
Totipotent Cells A stem cell is a cell that can divide (by mitosis) an unlimited number of times Each new cell that is produced when a stem cell divides has the potential to remain a stem cell or t...
AQA A Level Biology复习笔记8.1.1 Genetic Mutations
Gene Mutations A gene mutation is a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide Mutations occur continuously and spontaneously Errors in the DNA...
AQA A Level Biology复习笔记7.4.1 Communities
The Definition of a Community Species do not exist by themselves in their own isolated environment, they interact with other species forming communities A community can be defined as: Multiple popu...
