全文获取类型
收费全文 | 7106篇 |
免费 | 404篇 |
国内免费 | 24篇 |
专业分类
化学 | 4295篇 |
晶体学 | 67篇 |
力学 | 117篇 |
数学 | 1015篇 |
物理学 | 1495篇 |
无线电 | 545篇 |
出版年
2023年 | 79篇 |
2022年 | 96篇 |
2021年 | 168篇 |
2020年 | 219篇 |
2019年 | 251篇 |
2018年 | 130篇 |
2017年 | 112篇 |
2016年 | 296篇 |
2015年 | 227篇 |
2014年 | 250篇 |
2013年 | 353篇 |
2012年 | 423篇 |
2011年 | 421篇 |
2010年 | 270篇 |
2009年 | 225篇 |
2008年 | 341篇 |
2007年 | 272篇 |
2006年 | 272篇 |
2005年 | 227篇 |
2004年 | 176篇 |
2003年 | 119篇 |
2002年 | 137篇 |
2001年 | 107篇 |
2000年 | 128篇 |
1999年 | 100篇 |
1998年 | 78篇 |
1997年 | 81篇 |
1996年 | 83篇 |
1995年 | 84篇 |
1994年 | 102篇 |
1993年 | 93篇 |
1992年 | 83篇 |
1991年 | 74篇 |
1990年 | 65篇 |
1988年 | 49篇 |
1987年 | 55篇 |
1986年 | 67篇 |
1985年 | 64篇 |
1984年 | 54篇 |
1983年 | 58篇 |
1982年 | 51篇 |
1981年 | 50篇 |
1980年 | 70篇 |
1979年 | 48篇 |
1978年 | 64篇 |
1977年 | 60篇 |
1976年 | 54篇 |
1975年 | 59篇 |
1974年 | 47篇 |
1973年 | 54篇 |
排序方式: 共有7534条查询结果,搜索用时 15 毫秒
171.
172.
The shadow of a black hole is usually calculated, either analytically or numerically, on the assumption that the black hole is eternal, i.e., that it has existed for all time. Here we ask the question of how this shadow comes about in the course of time when a black hole is formed by gravitational collapse. To that end we consider a star that is spherically symmetric, dark and non-transparent and we assume that it begins, at some instant of time, to collapse in free fall like a ball of dust. We analytically calculate the dependence on time of the angular radius of the shadow, first for a static observer who is watching the collapse from a certain distance and then for an observer who is falling towards the centre following the collapsing star. 相似文献
173.
Crime is the result of a rational distinctive balance between the benefits and costs of an illegal act. This idea was proposed by Becker more than forty years ago (Becker (1968) [1]). In this paper, we simulate a simple artificial society, in which agents earn fixed wages and can augment (or lose) wealth as a result of a successful (or not) act of crime. The probability of apprehension depends on the gravity of the crime, and the punishment takes the form of imprisonment and fines. We study the costs of the law enforcement system required for keeping crime within acceptable limits, and compare it with the harm produced by crime. A sharp phase transition is observed as a function of the probability of punishment, and this transition exhibits a clear hysteresis effect, suggesting that the cost of reversing a deteriorated situation might be much higher than that of maintaining a relatively low level of delinquency. Besides, we analyze economic consequences that arise from crimes under different scenarios of criminal activity and probabilities of apprehension. 相似文献
174.
175.
176.
177.
Patrick Achenbach Sebastian Bleser Josef Pochodzalla Alicia Sanchez Lorente Marcel Steinen 《Hyperfine Interactions》2012,208(1-3):99-104
Samples obtained as a result of the valleriite synthesis process under different conditions (temperature and proportion Cu:Fe:Mg in the initial mixture) were investigated by 57Fe M?ssbauer spectroscopy with attraction data of X-ray diffraction. Parameters of hyperfine interactions for valleriite were determined and crystal chemical identification of 57Fe subspectra was carried out. It was found that valleriite was formed in samples synthesized at 150°C and 180°C and not formed in samples synthesized at 250°C. 相似文献
178.
179.
180.