全文获取类型
收费全文 | 11261篇 |
免费 | 1453篇 |
国内免费 | 942篇 |
专业分类
化学 | 3008篇 |
晶体学 | 69篇 |
力学 | 799篇 |
综合类 | 242篇 |
数学 | 4598篇 |
物理学 | 4940篇 |
出版年
2023年 | 79篇 |
2022年 | 268篇 |
2021年 | 298篇 |
2020年 | 246篇 |
2019年 | 226篇 |
2018年 | 243篇 |
2017年 | 322篇 |
2016年 | 360篇 |
2015年 | 306篇 |
2014年 | 584篇 |
2013年 | 798篇 |
2012年 | 586篇 |
2011年 | 680篇 |
2010年 | 578篇 |
2009年 | 679篇 |
2008年 | 776篇 |
2007年 | 756篇 |
2006年 | 643篇 |
2005年 | 615篇 |
2004年 | 495篇 |
2003年 | 479篇 |
2002年 | 457篇 |
2001年 | 328篇 |
2000年 | 341篇 |
1999年 | 322篇 |
1998年 | 314篇 |
1997年 | 243篇 |
1996年 | 203篇 |
1995年 | 181篇 |
1994年 | 185篇 |
1993年 | 118篇 |
1992年 | 116篇 |
1991年 | 90篇 |
1990年 | 71篇 |
1989年 | 80篇 |
1988年 | 72篇 |
1987年 | 65篇 |
1986年 | 47篇 |
1985年 | 73篇 |
1984年 | 47篇 |
1983年 | 34篇 |
1982年 | 47篇 |
1981年 | 23篇 |
1980年 | 22篇 |
1979年 | 28篇 |
1978年 | 33篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 10篇 |
1973年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
We study the large-sample properties of a class of parametric mixture models with covariates for competing risks. The models allow general distributions for the survival times and incorporate the idea of long-term survivors. Asymptotic results are obtained under a commonly assumed independent censoring mechanism and some modest regularity conditions on the survival distributions. The existence, consistency, and asymptotic normality of maximum likelihood estimators for the parameters of the model are rigorously derived under general sufficient conditions. Specific conditions for particular models can be derived from the general conditions for ready check. In addition, a likelihood-ratio statistic is proposed to test various hypotheses of practical interest, and its asymptotic distribution is provided. 相似文献
73.
分形维数与城市规模分布评析 总被引:3,自引:1,他引:2
本在分形概念的基础上,指出城市规模分布是基于统计意义上的一种分形分布,并计算了安徽省1978~1998年城市规模分布的分维值,评析了安徽省城市规模分布变化的特征。 相似文献
74.
A method has been developed to determine the boiling point distribution of sulfur compounds in light cycle oils (LCO'S). The method chosen for this analysis was GC with a flame photometric detector (FPD) and pyrolyzer. Tests were carried out to evaluate the recovery efficiency, repeatability, and accuracy of the method. Repeatabilities within 2% were obtained. The recovery of benzothiophenes and dibenzothiophenes was close to 100%; this was important because these are the major sulfur components in LCO's. No hydrocarbon or solvent interferences were observed with the use of the pyrolyzer, even for a 95% solvent level. Comparison with results from other techniques showed that the method accurately determined the levels of sulfur compounds in the LCO boiling point range. 相似文献
75.
76.
M. C. Jones 《Annals of the Institute of Statistical Mathematics》2004,56(4):733-742
A simple new family of distributions is proposed which has support the unit disc in two dimensions. The density functions
of the family are unimodal, monotonic or uniantimodal. The bivariate symmetric beta distributions, which include the uniform
distribution, are special cases, but many members of the family are skew. The distributions have three parameters, one controlling
orientation, one controlling degree of concentration and the third controlling skewness, or more precisely off-centredness.
Importantly, these parameters are globally orthogonal. An illustrative example of fitting the model to data is given. Conditional
and marginal distributions are considered. The new distributions are compared favourably with an earlier suggestion of the
same author. 相似文献
77.
饮食中微量元素砷的分布规律与人体健康关系 总被引:3,自引:1,他引:2
采用催化动力学光度法测定了六大类(共三十种)样品中的总砷含量,探讨了砷在食品中的分布规律,建立了砷在人体中的安全系效和积累系效的效学评价公式,用于评价砷与人体健康的关系,这对人们选择食物有一定的指导意义。 相似文献
78.
The symplectic, optical, and photon-number tomographic symbols of binomial states of the radiation field are studied. Explicit relations for all tomograms of the binomial states are obtained. Two measures for nonclassical properties of these states are discussed. 相似文献
79.
The paper is devoted to the research of large deviation probabilities in the approximation by compound Poisson law. 相似文献
80.
The existing model for multivariate skew normal data does not cohere with the joint distribution of a random sample from a
univariate skew normal distribution. This incoherence causes awkward interpretation for data analysis in practice, especially
in the development of the sampling distribution theory. In this paper, we propose a refined model that is coherent with the
joint distribution of the univariate skew normal random sample, for multivariate skew normal data. The proposed model extends
and strengthens the multivariate skew model described in Azzalini (1985,Scandinavian Journal of Statistics,12, 171–178). We present a stochastic representation for the newly proposed model, and discuss a bivariate setting, which confirms
that the newly proposed model is more plausible than the one given by Azzalini and Dalla Valle (1996,Biometrika,83, 715–726). 相似文献