全文获取类型
收费全文 | 3255篇 |
免费 | 153篇 |
国内免费 | 187篇 |
专业分类
化学 | 940篇 |
晶体学 | 2篇 |
力学 | 88篇 |
综合类 | 51篇 |
数学 | 1900篇 |
物理学 | 614篇 |
出版年
2024年 | 8篇 |
2023年 | 23篇 |
2022年 | 90篇 |
2021年 | 104篇 |
2020年 | 65篇 |
2019年 | 80篇 |
2018年 | 59篇 |
2017年 | 126篇 |
2016年 | 145篇 |
2015年 | 69篇 |
2014年 | 165篇 |
2013年 | 296篇 |
2012年 | 174篇 |
2011年 | 161篇 |
2010年 | 142篇 |
2009年 | 190篇 |
2008年 | 172篇 |
2007年 | 200篇 |
2006年 | 166篇 |
2005年 | 138篇 |
2004年 | 126篇 |
2003年 | 93篇 |
2002年 | 95篇 |
2001年 | 71篇 |
2000年 | 67篇 |
1999年 | 83篇 |
1998年 | 75篇 |
1997年 | 56篇 |
1996年 | 48篇 |
1995年 | 43篇 |
1994年 | 42篇 |
1993年 | 24篇 |
1992年 | 33篇 |
1991年 | 33篇 |
1990年 | 14篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有3595条查询结果,搜索用时 15 毫秒
171.
Panel‐based stratified cluster sampling and analysis for photovoltaic outdoor measurements
下载免费PDF全文
![点击此处可从《商业与工业应用随机模型》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We study a stratified multisite cluster‐sampling panel time series approach in order to analyse and evaluate the quality and reliability of produced items, motivated by the problem to sample and analyse multisite outdoor measurements from photovoltaic systems. The specific stratified sampling in spatial clusters reduces sampling costs and allows for heterogeneity as well as for the analysis of spatial correlations due to defects and damages that tend to occur in clusters. The analysis is based on weighted least squares using data‐dependent weights. We show that this does not affect consistency and asymptotic normality of the least squares estimator under the proposed sampling design under general conditions. The estimation of the relevant variance–covariance matrices is discussed in detail for various models including nested designs and random effects. The strata corresponding to damages or manufacturers are modelled via a quality feature by means of a threshold approach. The analysis of outdoor electroluminescence images shows that spatial correlations and local clusters may arise in such photovoltaic data. Further, relevant statistics such as the mean pixel intensity cannot be assumed to follow a Gaussian law. We investigate the proposed inferential tools in detail by simulations in order to assess the influence of spatial cluster correlations and serial correlations on the test's size and power. ©2016 The Authors. Applied Stochastic Models in Business and Industry published by John Wiley & Sons, Ltd. 相似文献
172.
Oleg Burdakov Anders Grimvall Oleg Sysoev 《计算数学(英文版)》2006,24(6):771-790
Monotonic regression (MR) is a least distance problem with monotonicity constraints induced by a partiaily ordered data set of observations. In our recent publication [In Ser. Nonconvex Optimization and Its Applications, Springer-Verlag, (2006) 83, pp. 25-33], the Pool-Adjazent-Violators algorithm (PAV) was generalized from completely to partially ordered data sets (posets). The new algorithm, called CPAV, is characterized by the very low computational complexity, which is of second order in the number of observations. It treats the observations in a consecutive order, and it can follow any arbitrarily chosen topological order of the poset of observations. The CPAV algorithm produces a sufficiently accurate solution to the MR problem, but the accuracy depends on the chosen topological order. Here we prove that there exists a topological order for which the resulted CPAV solution is optimal. Furthermore, we present results of extensive numerical experiments, from which we draw conclusions about the most and the least preferable topological orders. 相似文献
173.
木材密度可以反映木材的干缩性、抗压抗拉强度等多种物理性质,是重要的木材物理特性。采用近红外光谱技术能够实现木材密度的快速预测,可克服传统检测方法耗费人力、物力、时间的弊端,但建模结果往往受异常样本的影响。为准确识别并剔除样本集中的异常样本,提出一种孤立森林结合学生化残差方法(IFSR),在利用孤立森林集成特征的优点基础上考虑样本对模型的影响度,可同时检测异常样本与强影响样本。该研究对181个落叶松木材样本的近红外光谱及其在常温下的气干密度进行了测定。通过对比多种方法预处理和特征选择方法,确定采用标准正态变量变化(SNV)+去趋势处理(DT)+均值中心化(MC)+标准化(Auto)方法进行预处理,采用竞争性自适应重加权算法(CARS)进行特征波段选择,消除噪声及无关信息对算法的影响,简化数据集,提高算法剔除异常样本的准确性。为验证IFSR方法剔除异常样本的能力,将其与蒙特卡洛交互验证(MCCV)、马氏距离(MD)等其他六种异常检测方法对比分析,建立偏最小二乘(PLS)模型对其进行异常检测性能评价。同时在上述基础上采用粒子群寻优-支持向量机回归(PSO-SVR), BP神经网络(BPNN)... 相似文献
174.
175.
Correlation functions of a driven two‐level system embedded in a photonic crystal are analyzed. The spectral density of the photonic bands near a gap makes this system non‐Markovian. The equations of motion for two‐time correlations are derived by two different methods, the quantum regression theorem and the fluctuation dissipation theorem, and found to be the same. 相似文献
176.
利用回归分析拟合Duncan-Chang双曲线E-γ模型的材料参数 总被引:1,自引:0,他引:1
介绍了回归分析的基本概念及求解回归系数的方法,并分析了利用回归分析Duncan-Chang双曲线E-γ土力学模型时所建立起的方程组的特点.而基于方程组的这些特点及材料参数的数值限制,提出了在求解之前需先设定其中一个材料参数R_f的值.最后,通过一个例子的分析,总结了回归分析计算结果的特点,并对R_f值之设定作出了说明及探讨. 相似文献
177.
178.
Z. Xiancheng N. Zhaodong X. Yan Z. Yuanqin Z. Honglin 《Journal of Thermal Analysis and Calorimetry》1999,58(2):279-285
The power-time curves of two species of bacteria, Vibro metschnikovii, Vibro bollisae were determined calorimetrically by using a 2277 bioactivity monitor. The power-time curve equation of bacterial growth in the log phase can be expressed as
. A self-function recursion equation, fi=b1fi+1+b2fi+2, was obtained through the perfect non-linear function
. A linear equation, i/i+1=b1+b2i+2/i+1, was obtained by using the self-function recursion equation. The rate constants of bacterial growth k1, the time constant of the calorimeter k, the generation times G, and the pre-exponential factors A were obtained from the power—time curve equations.Power—time curve equations of bacterial growth in the log phase are expressed for V.metschnikovii as =1.05(e0.0228t–e–0.0175t), and for V. bollisae as =1.58(e0.0278t–e–0.0170t).This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
179.
Regression relations between the first main component, slope of the SBC curve towards the wavelength axis, and the degree
of mineralization of peat soils are established from experimental data. Errors in determination of peat soil productivity
are estimated using different spectral indices. For practical use it is recommended to measure the spectral brightness coefficients
of peat soils in the 0.50–0.75 μm range.
B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 1, pp. 102–106, January–February, 1998. 相似文献
180.
To analyze the isotonic regression problem for normal means, it is usual to assume that all variances are known or unknown but equal. This paper then studies this problem in the case that there are no conditions imposed on the variances. Suppose that we have data drawn fromkindependent normal populations with unknown meansμi's and unknown variancesσ2i's, in which the means are restricted by a given partial ordering. This paper discusses some properties of the maximum likelihood estimates ofμi's andσ2i's under the restriction and proposes an algorithm for obtaining the estimates. 相似文献