全文获取类型
收费全文 | 12222篇 |
免费 | 132篇 |
国内免费 | 11篇 |
专业分类
教育 | 7977篇 |
科学研究 | 2142篇 |
各国文化 | 95篇 |
体育 | 852篇 |
综合类 | 5篇 |
文化理论 | 84篇 |
信息传播 | 1210篇 |
出版年
2021年 | 127篇 |
2020年 | 188篇 |
2019年 | 286篇 |
2018年 | 349篇 |
2017年 | 331篇 |
2016年 | 266篇 |
2015年 | 182篇 |
2014年 | 262篇 |
2013年 | 2187篇 |
2012年 | 267篇 |
2011年 | 240篇 |
2010年 | 219篇 |
2009年 | 195篇 |
2008年 | 190篇 |
2007年 | 209篇 |
2006年 | 165篇 |
2005年 | 170篇 |
2004年 | 154篇 |
2003年 | 135篇 |
2002年 | 155篇 |
2001年 | 177篇 |
2000年 | 185篇 |
1999年 | 158篇 |
1998年 | 89篇 |
1997年 | 99篇 |
1996年 | 121篇 |
1995年 | 85篇 |
1994年 | 99篇 |
1993年 | 95篇 |
1992年 | 139篇 |
1991年 | 145篇 |
1990年 | 147篇 |
1989年 | 167篇 |
1988年 | 120篇 |
1987年 | 119篇 |
1986年 | 159篇 |
1985年 | 155篇 |
1984年 | 130篇 |
1983年 | 130篇 |
1982年 | 115篇 |
1981年 | 94篇 |
1980年 | 103篇 |
1979年 | 139篇 |
1978年 | 120篇 |
1977年 | 105篇 |
1976年 | 102篇 |
1974年 | 111篇 |
1973年 | 92篇 |
1972年 | 84篇 |
1971年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
122.
123.
124.
125.
126.
127.
128.
129.
130.
Arthur H. Compton 《Journal of The Franklin Institute》1918,185(6):745-774
To sum up our argument then: It is shown, in the first place, that the arrangement of the atoms in certain crystals, as determined by the X-ray spectra, indicates definitely that in these crystals there is no molecular structure.In extending the argument to all solid matter it is pointed out, from the dependence of crystal form on chemical composition, from a consideration of the Dulong-Petit law and of the nature of cohesion, and from the evidence of X-rays as to certain crystals, that each atom in a solid oscillates about a definite position of stable equilibrium.From a further examination of the nature of cohesion and of the forces concerned in chemical combination and especially from the general relation found between the atomic heat of formation of a substance and its melting-point it is found that the forces holding the atoms in their positions of stable equilibrium are of the same nature and comparable in magnitude with the forces binding together a chemical molecule.It is seen further that the atoms in a solid are very close together so that they often come in contact. And, since an atom attracts equally all atoms of another kind which are in contact with it, an atom cannot remain combined for more than an infinitesimal interval with any other particular atom ordinary temperatures.Finally, it was shown that, since in the solid state each atom has three degrees of translational freedom and is strongly attracted by atoms other than those of its own “molecule,” it must, on the average, exert equal attractions on all the neighboring atoms.From this the conclusion is drawn that in the particular molecules cannot be definitely defined.When those properties of solid matter which have been explained by molecules are considered, nothing is found which indicates at all definitely a molecular structure.We feel justified in concluding, therefore, that the structure of solid matter is not molecular. 相似文献