全文获取类型
收费全文 | 17377篇 |
免费 | 2928篇 |
国内免费 | 2465篇 |
学科分类
数理化 | 22770篇 |
出版年
2024年 | 39篇 |
2023年 | 276篇 |
2022年 | 442篇 |
2021年 | 576篇 |
2020年 | 688篇 |
2019年 | 666篇 |
2018年 | 581篇 |
2017年 | 579篇 |
2016年 | 791篇 |
2015年 | 832篇 |
2014年 | 1048篇 |
2013年 | 1281篇 |
2012年 | 1535篇 |
2011年 | 1703篇 |
2010年 | 1203篇 |
2009年 | 1220篇 |
2008年 | 1314篇 |
2007年 | 1119篇 |
2006年 | 1011篇 |
2005年 | 808篇 |
2004年 | 646篇 |
2003年 | 524篇 |
2002年 | 578篇 |
2001年 | 509篇 |
2000年 | 414篇 |
1999年 | 373篇 |
1998年 | 285篇 |
1997年 | 232篇 |
1996年 | 285篇 |
1995年 | 219篇 |
1994年 | 169篇 |
1993年 | 139篇 |
1992年 | 110篇 |
1991年 | 108篇 |
1990年 | 85篇 |
1989年 | 78篇 |
1988年 | 53篇 |
1987年 | 48篇 |
1986年 | 49篇 |
1985年 | 32篇 |
1984年 | 21篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1981年 | 12篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
考虑到量子相干效应和界面散射效应 ,利用 L ambert理论模型 ,计算正常金属 /绝缘层 /超导 /绝缘层 /正常金属双垒隧道结中的准粒子输运系数和隧道谱。研究表明 :( 1)所有的准粒子输运系数和电导谱在超导能隙之上都随能量作周期性振荡 ,其振荡周期依赖于超导层的厚度 ;( 2 )在超导能隙之上 Andreev反射系数随能量呈现周期性消失现象 ;( 3)在绝缘层势垒强度取很大的隧道极限下 ,超导层中会形成一系列的准粒子束缚态 ,其位置由量子化条件决定 ;( 4)界面散射效应不仅能压低各子能隙电导峰 ,还能使子能隙电导峰劈裂为两个峰。 相似文献
62.
The influence of hydrogen bonds on the physical and chemical properties of hydrogen bonding fluid system of A a D d type is investigated from two viewpoints by the principle of statistical mechanics. In detail, we proposed two new ways that can be used to obtain the equilibrium size distribution of the hydrogen bonding clusters, and derived the analytical expression of a relationship between the hydrogen bonding free energy and hydrogen bonding degree. For the nonlinear hydrogen bonding systems, it is shown that the sol-gel phase transition can take place under proper conditions, which is further proven to be a kind of geometrical phase transition rather than a thermodynamic one. Moreover, several problems associated with the geometrical phase transition and liquid-solid phase transition in nonlinear hydrogen bonding systems are discussed. 相似文献
63.
In this paper we consider a class of nonlinear delay partial difference equations and a class of linear delay partial difference equations with variable coefficients, which may change sign. We obtain oscillation criteria for these equations. There are no results for the oscillation of these equations up to now. 相似文献
64.
65.
Fang Yao 《Journal of multivariate analysis》2007,98(1):40-56
The estimation of a regression function by kernel method for longitudinal or functional data is considered. In the context of longitudinal data analysis, a random function typically represents a subject that is often observed at a small number of time points, while in the studies of functional data the random realization is usually measured on a dense grid. However, essentially the same methods can be applied to both sampling plans, as well as in a number of settings lying between them. In this paper general results are derived for the asymptotic distributions of real-valued functions with arguments which are functionals formed by weighted averages of longitudinal or functional data. Asymptotic distributions for the estimators of the mean and covariance functions obtained from noisy observations with the presence of within-subject correlation are studied. These asymptotic normality results are comparable to those standard rates obtained from independent data, which is illustrated in a simulation study. Besides, this paper discusses the conditions associated with sampling plans, which are required for the validity of local properties of kernel-based estimators for longitudinal or functional data. 相似文献
66.
Charge density fluctuation of low frequency in a dusty plasma 总被引:2,自引:0,他引:2
The charge density fluctuation of low frequency in a dusty plasma, which is derived from the longitudinal dielectric permittivity
of the dusty plasma, has been studied by kinetic theory. The results show that theP value, which describes the relative charge density on the dust in the plasma, and the charging frequency of a dust particle
Ω
c
, which describes the ratio of charge changing of the dust particles, determine the character of the charge density fluctuation
of low frequency. For a dusty plasma ofP≪1, when the charging frequency Ω
c
, is much smaller than the dusty plasma frequency ωd, there is a strong charge density fluctuation which is of character of dust acoustic eigenwave. For a dusty plasma ofP≫1, when the frequency Ω
c
, is much larger than ω
d
there are weaker fluctuations with a wide spectrum. The results have been applied to the ionosphere and the range of radius
and density of dust particles is found, where a strong charge density fluctuation of low frequency should exist. 相似文献
67.
68.
69.
70.
教师课堂教学质量的多元统计分析 总被引:3,自引:0,他引:3
应用多元统计分析中的聚类分析法和主成分分析法对教师高等数学的课堂教学质量进行了统计分析,通过对数据的聚类分析结果提出教师应注重启发性教学并善于引导学生解决实际问题.同时利用主成分分析将原先众多的评价指标用三个指标代替,为进一步提高教学质量提供科学的依据. 相似文献