全文获取类型
收费全文 | 2932篇 |
免费 | 147篇 |
国内免费 | 165篇 |
专业分类
化学 | 862篇 |
晶体学 | 2篇 |
力学 | 56篇 |
综合类 | 51篇 |
数学 | 1761篇 |
物理学 | 512篇 |
出版年
2024年 | 6篇 |
2023年 | 20篇 |
2022年 | 54篇 |
2021年 | 81篇 |
2020年 | 57篇 |
2019年 | 71篇 |
2018年 | 53篇 |
2017年 | 121篇 |
2016年 | 134篇 |
2015年 | 65篇 |
2014年 | 150篇 |
2013年 | 272篇 |
2012年 | 148篇 |
2011年 | 149篇 |
2010年 | 132篇 |
2009年 | 178篇 |
2008年 | 156篇 |
2007年 | 183篇 |
2006年 | 155篇 |
2005年 | 123篇 |
2004年 | 121篇 |
2003年 | 82篇 |
2002年 | 84篇 |
2001年 | 69篇 |
2000年 | 63篇 |
1999年 | 77篇 |
1998年 | 69篇 |
1997年 | 47篇 |
1996年 | 45篇 |
1995年 | 38篇 |
1994年 | 36篇 |
1993年 | 22篇 |
1992年 | 31篇 |
1991年 | 30篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 14篇 |
1984年 | 17篇 |
1983年 | 7篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1973年 | 3篇 |
排序方式: 共有3244条查询结果,搜索用时 15 毫秒
1.
2.
Alberto Guilln Jos Martínez Juan Miguel Carceller Luis Javier Herrera 《Entropy (Basel, Switzerland)》2020,22(11)
The main goal of this work is to adapt a Physics problem to the Machine Learning (ML) domain and to compare several techniques to solve it. The problem consists of how to perform muon count from the signal registered by particle detectors which record a mix of electromagnetic and muonic signals. Finding a good solution could be a building block on future experiments. After proposing an approach to solve the problem, the experiments show a performance comparison of some popular ML models using two different hadronic models for the test data. The results show that the problem is suitable to be solved using ML as well as how critical the feature selection stage is regarding precision and model complexity. 相似文献
3.
João Marcos G. Barbosa Milenna K. Fernandes Rodrigues Lurian C. David Taynara C. e Silva Danielly A. Fortuna Lima Naiara Z. Pereira Emmanuel B. D'Alessandro Anselmo E. de Oliveira Paulo H. Jorge da Cunha Maria Clorinda S. Fioravanti Nelson R. Antoniosi Filho 《Biomedical chromatography : BMC》2020,34(11):e4935
An innovative volatolomic approach employs the detection of biomarkers present in cerumen (earwax) to identify cattle intoxication by Stryphnodendron rotundifolium Mart., Fabaceae (popularly known as barbatimão). S. rotundifolium is a poisonous plant with the toxic compound undefined and widely distributed throughout the Brazilian territory. Cerumen samples from cattle of two local Brazilian breeds (‘Curraleiro Pé-Duro’ and ‘Pantaneiro’) were collected during an experimental intoxication protocol and analyzed using headspace (HS)/GC–MS followed by multivariate analysis (genetic algorithm for a partial least squares, cluster analysis, and classification and regression trees). A total of 106 volatile organic metabolites were identified in the cerumen samples of bovines. The intoxication by S. rotundifolium influenced the cerumen volatolomic profile of the bovines throughout the intoxication protocol. In this way, it was possible to detect biomarkers for cattle intoxication. Among the biomarkers, 2-octyldecanol and 9-tetradecen-1-ol were able to discriminate all samples between intoxicated and nonintoxicated bovines. The cattle intoxication diagnosis by S. rotundifolium was accomplished by applying the cerumen analysis using HS/GC–MS, in an easy, accurate, and noninvasive way. Thus, the proposed bioanalytical chromatography protocol is a useful tool in veterinary applications to determine this kind of intoxication. 相似文献
4.
开放式、综合性量测实验的设计与应用,在巩固基础理论知识的同时,能够有效培养学生的动手实践能力、数据处理及分析能力,一定程度代表着大学物理实验课程的教学模式改革方向。以PN结物理特性的测量实验为例,基于通用型仪器与元器件的积木式组合,设计出简单、适用的实验电路;t=17.95℃时所采集的原始实验数据经三种模式回归分析,比较验证了PN结扩散电流与电压间遵循的玻尔兹曼分布律;计算出的玻尔兹曼常数与FD-PN-4测定仪的量测值相比,其结果说明了开放式测量实验方法的有效性。 相似文献
5.
《Comptes Rendus Mecanique》2019,347(11):780-792
The present work aims at proposing a new methodology for learning reduced models from a small amount of data. It is based on the fact that discrete models, or their transfer function counterparts, have a low rank and then they can be expressed very efficiently using few terms of a tensor decomposition. An efficient procedure is proposed as well as a way for extending it to nonlinear settings while keeping limited the impact of data noise. The proposed methodology is then validated by considering a nonlinear elastic problem and constructing the model relating tractions and displacements at the observation points. 相似文献
6.
7.
Smooth backfitting has been shown to have better theoretical properties than classical backfitting for fitting additive models based on local linear regression. In this article, we show that the smooth backfitting procedure in the local linear case can be alternatively performed as a classical backfitting procedure with a different type of smoother matrices. These smoother matrices are symmetric and shrinking and some established results in the literature are readily applicable. The connections allow the smooth backfitting algorithm to be implemented in a much simplified way, give new insights on the differences between the two approaches in the literature, and provide an extension to local polynomial regression. The connections also give rise to a new estimator at data points. Asymptotic properties of general local polynomial smooth backfitting estimates are investigated, allowing for different orders of local polynomials and different bandwidths. Cases of oracle efficiency are discussed. Computer-generated simulations are conducted to demonstrate finite sample behaviors of the methodology and a real data example is given for illustration. Supplementary materials for this article are available online. 相似文献
8.
选取山西省为研究对象,以美国国家极轨合作仪件-可见红外成像辐射计套件(NPP-VIIRS)夜间灯光数据、GDP统计数据等为数据源,构建GDP空间化拟合模型,建立山西省GDP密度图,据此研究山西省经济的空间差异性。通过对NPP-VIIRS夜间灯光数据的空间化处理,提取灯光指数,并将其与GDP进行回归拟合,建立最佳回归模型,得到GDP密度拟合图;利用县级GDP数据进行线性纠正,从而提高GDP的模拟精度。结果表明:(1)NPP-VIIRS夜间灯光数据与GDP的相关性较高,可用于山西省GDP模拟;(2)与GDP分区建模相比,GDP整体建模的精度更高;(3)山西省GDP的空间分布整体呈由城市中心逐渐向周边辐射的特点,构成GDP过渡带。 相似文献
9.
2000年以来,中国出境旅游高增长、高消费,影响力不断增大,成为国家外交战略的重要内容,外交效应逐渐显现。通过辨析中国出境旅游外交效应的概念、表现形式和结果,基于10个中国主要出境目的国的旅游互动数据,采用DIF-GMM计量经济模型,实证检验了中国出境旅游外交效应。结果表明,中国通过有序推进ADS协议、加强经济援助、举办“旅游年”活动、实施旅游“制裁”,并积极参与国际制度建设等旅游外交行为,促进了与世界各国的友好交往,维护了自身核心利益,提升了外交软实力和国际影响力。国际旅游反作用于国际关系,对国际关系具有显著的正向促进作用,不仅是国际关系的结果,而且是其重要动因之一。中国出境旅游与政治、经济、社会、文化等联动,多方面提升了中国的国际影响力。 相似文献
10.