全文获取类型
收费全文 | 27448篇 |
免费 | 3886篇 |
国内免费 | 2018篇 |
专业分类
化学 | 5015篇 |
晶体学 | 102篇 |
力学 | 4936篇 |
综合类 | 485篇 |
数学 | 10544篇 |
物理学 | 12270篇 |
出版年
2024年 | 63篇 |
2023年 | 289篇 |
2022年 | 787篇 |
2021年 | 772篇 |
2020年 | 909篇 |
2019年 | 803篇 |
2018年 | 740篇 |
2017年 | 1027篇 |
2016年 | 1197篇 |
2015年 | 875篇 |
2014年 | 1468篇 |
2013年 | 2139篇 |
2012年 | 1527篇 |
2011年 | 1815篇 |
2010年 | 1560篇 |
2009年 | 1837篇 |
2008年 | 1697篇 |
2007年 | 1709篇 |
2006年 | 1438篇 |
2005年 | 1285篇 |
2004年 | 1191篇 |
2003年 | 1007篇 |
2002年 | 964篇 |
2001年 | 766篇 |
2000年 | 736篇 |
1999年 | 643篇 |
1998年 | 579篇 |
1997年 | 429篇 |
1996年 | 369篇 |
1995年 | 354篇 |
1994年 | 325篇 |
1993年 | 271篇 |
1992年 | 244篇 |
1991年 | 186篇 |
1990年 | 165篇 |
1989年 | 124篇 |
1988年 | 123篇 |
1987年 | 132篇 |
1986年 | 109篇 |
1985年 | 128篇 |
1984年 | 131篇 |
1983年 | 72篇 |
1982年 | 96篇 |
1981年 | 61篇 |
1980年 | 29篇 |
1979年 | 37篇 |
1978年 | 29篇 |
1977年 | 28篇 |
1976年 | 15篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
91.
Mass distributions of fragments in the low-energy fission of nuclei from 187Ir to 213At have been analysed. This analysis has shown that shell effects in symmetric-mode fragment mass yields from the fission of pre-actinide nuclei could be described if one assumes the existence of two strongly deformed neutron shells in the arising fragments with neutron numbers N1 ≈ 52 and N2 ≈ 68. A new method has been proposed for quantitatively describing the mass distributions of the symmetric fission mode for pre-actinides with A ≈ 180–220. 相似文献
92.
随机化交通灯的二维元胞自动机交通模型 总被引:8,自引:0,他引:8
元胞自动机交通模型以简单的规则反映交通系统中的多种因素,可以分析各种交通现象,且可在计算机上方便、高效地运作·Biham-Middleton-Levine模型(BML模型)实现了二维交通问题的元胞自动机模型的模拟研究·本文对BML模型作了改进,解除了该模型中关于交通灯同步变化的限制·在新模型中,每个路口的交通灯可以自由选定起始工作时间和变化节奏,于是可以更全面、准确地反映交通灯对交通系统性能的影响·本文还对新模型中出现的若干新效应作了解释· 相似文献
93.
In this paper we show that the Boltzmann weights of the three-dimensional Baxter-Bazhanov model give representations of the braid group if some suitable spectral limits are taken. In the trigonometric case we classify all possible spectral limits which produce braid group representations. Furthermore, we prove that for some of them we get cyclotomic invariants of links and for others we obtain tangle invariants generalizing the cyclotomic ones. 相似文献
94.
A theoretical model of Dewangan, in which the total scattering wave function is approximated by a distorted wave containing
two Coulomb wave functions, is discussed and its relation with the Brauner-Briggs-Klar model for ionization is examined. An
important feature of the theory is that it includes a second Born amplitude naturally and in addition, contains, albeit approximately,
both real and imaginary parts of all higher order Born terms. The theory is applied to study the 1s→2s excitation of hydrogen by electrons in the energy range 54.4 to 400eV. The differential and integral cross sections predicted
by the theory are compared with the results of other theories and experimental data at 54.4eV and a good agreement is found. 相似文献
95.
The Modeling of Velocity Enhancement in Polymer Flooding 总被引:1,自引:0,他引:1
In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur. 相似文献
96.
In [5] Phillips proved that one can obtain the additive group of any nonstandard model *? of the ring ? of integers by using a linear mod 1 function h : F ?, where F is the α-dimensional vector space over ? when α is the cardinality of *?. In this connection it arises the question whether there are linear mod 1 functions which are neither addition nor quasi-linear. We prove that this is the case. 相似文献
97.
Yoshikazu Takada 《Annals of the Institute of Statistical Mathematics》1998,50(2):325-335
This paper gives a condition which implies the nonexistence of parametric statistical procedures with bounded risk or error performance characteristics. Many examples for which such a condition is satisfied are considered. 相似文献
98.
Recently, Fishbum and Lavalle (1995) and Lefèvre and Utev (1996) have considered some stochastic order relations specific for arithmetic random variables. The present work is concerned with these orderings, together with two other classes of stochastic order relations closely related. First, attention is paid to characterizations and various properties of all these orderings. Then, sufficient conditions of crossing-type for the two new classes of orderings are derived and extrema among discrete random variables are deduced. This is applied in actuarial sciences to obtain new bounds for the classical single life premiums as well as for the probability of ruin in the compound binomial risk model. 相似文献
99.
在工农业产品评定级别中,专家组的水平是至关重要的。文中给出一个挑选专家组成员的数学模型,可以检验专家对参评产品的决策水平,为评价所评结论的可信度提供参考依据。 相似文献
100.
T. Ishii M. Asai A. Makishima I. Hossain P. Kleinheinz M. Ogawa M. Matsuda S. Ichikawa 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):15-19
Nuclei in the neutron-rich Ni region have been studied by γ-ray spectroscopy. Gamma-rays emitted from isomers, with T
1/2 > 1 ns, produced in heavy-ion deep-inelastic collisions were measured with an isomer-scope. The nuclear structure of the
doubly magic 68Ni and its neighbor 69,71Cu is discussed on the basis of the shell model. Future experiments for more neutron-rich Ni nuclei are also viewed.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献