全文获取类型
收费全文 | 13413篇 |
免费 | 2129篇 |
国内免费 | 1891篇 |
专业分类
化学 | 9886篇 |
晶体学 | 167篇 |
力学 | 811篇 |
综合类 | 137篇 |
数学 | 1760篇 |
物理学 | 4672篇 |
出版年
2024年 | 30篇 |
2023年 | 194篇 |
2022年 | 330篇 |
2021年 | 406篇 |
2020年 | 463篇 |
2019年 | 481篇 |
2018年 | 419篇 |
2017年 | 412篇 |
2016年 | 594篇 |
2015年 | 618篇 |
2014年 | 741篇 |
2013年 | 939篇 |
2012年 | 1145篇 |
2011年 | 1291篇 |
2010年 | 925篇 |
2009年 | 951篇 |
2008年 | 1073篇 |
2007年 | 923篇 |
2006年 | 852篇 |
2005年 | 654篇 |
2004年 | 490篇 |
2003年 | 396篇 |
2002年 | 431篇 |
2001年 | 371篇 |
2000年 | 340篇 |
1999年 | 299篇 |
1998年 | 229篇 |
1997年 | 196篇 |
1996年 | 234篇 |
1995年 | 196篇 |
1994年 | 118篇 |
1993年 | 114篇 |
1992年 | 96篇 |
1991年 | 94篇 |
1990年 | 74篇 |
1989年 | 68篇 |
1988年 | 40篇 |
1987年 | 40篇 |
1986年 | 37篇 |
1985年 | 25篇 |
1984年 | 20篇 |
1983年 | 23篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 5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
51.
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
52.
53.
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
54.
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
55.
半导体中多光子吸收跃迁速率的全量子理论分析 总被引:3,自引:3,他引:0
本文从非线性光学中辐射跃迁速率的表达式出发,在全量子理论下,导出了半导体中任意阶多光子吸收跃迁速率的一般表达式。理论分析结果表明,n光子吸收跃迁速率与光强的n次方和n阶光子相干度成正比。本文在多能带及二能带理论模型下,对多光子吸收跃迁速率的一般表达式进行了化简,并对非线性相互作用项对跃迁速率的贡献,作了讨论。 相似文献
56.
火焰原子吸收光谱法测定磁化杯中铅、镉和铁 总被引:1,自引:0,他引:1
本文研究了火焰原子吸收光谱法测定磁化杯陶瓷内胆中Ph、Cd和Fe含量的方法。样品经粉碎,用硝酸-高氯酸混合液进行消解后测定。本法灵敏度高,干扰少,简单,快速,具有良好的精密度和准确度,其相对标准偏差分别为Pb3.99%,Cd10.7%,Fe0.9%。回收率Pb100.61%,Cd101.18%,Fe102.4%。 相似文献
57.
惯性约束中子测温的误差研究 总被引:1,自引:0,他引:1
综合分析了ICF(惯性约束)中子测温系统的误差与其参数的关系,这些参数包括靶核温度,探测的中子数、靶到探测器的距离、探测器的响应函数以及闪烁体厚度等,考虑到中子与探测器的相互作用,探测器的响应与靶的烧蚀过程,在此基础上提出了新的统计误差计算方法,该方法对于改善中子测温的相对误差并应用于闪烁体的设计具有重要意义。 相似文献
58.
59.
60.