全文获取类型
收费全文 | 583篇 |
免费 | 15篇 |
专业分类
化学 | 318篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 33篇 |
物理学 | 220篇 |
出版年
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 16篇 |
2015年 | 8篇 |
2014年 | 10篇 |
2013年 | 29篇 |
2012年 | 22篇 |
2011年 | 37篇 |
2010年 | 20篇 |
2009年 | 34篇 |
2008年 | 40篇 |
2007年 | 34篇 |
2006年 | 29篇 |
2005年 | 34篇 |
2004年 | 31篇 |
2003年 | 23篇 |
2002年 | 16篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 11篇 |
1998年 | 8篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1978年 | 4篇 |
1976年 | 2篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有598条查询结果,搜索用时 78 毫秒
1.
Marisa C. Oliveira Renan A. P. Ribeiro Elson Longo Mauricio R. D. Bomio Sergio R. de Lázaro 《International journal of quantum chemistry》2020,120(22):e26368
The structural, electronic, and vibrational properties of two leading representatives of the Zn-based spinel oxides class, normal ZnX2O4 (X = Al, Ga, In) and inverse Zn2MO4 (M = Si, Ge, Sn) crystals, were investigated. In particular, density functional theory (DFT) was combined with different exchange-correlation functionals: B3LYP, HSE06, PBE0, and PBESol. Our calculations showed good agreement with the available experimental data, showing a mean percentage error close to 3% for structural parameters. For the electronic structure, the obtained HSE06 band-gap values overcome previous theoretical results, exhibiting a mean percentage error smaller than 10.0%. In particular, the vibrational properties identify the significant differences between normal and inverse spinel configurations, offering compelling evidence of a structure-property relationship for the investigated materials. Therefore, the combined results confirm that the range-separated HSE06 hybrid functional performs the best in spinel oxides. Despite some points that cannot be directly compared to experimental results, we expect that future experimental work can confirm our predictions, thus opening a new avenue for understanding the structural, electronic, and vibrational properties in spinel oxides. 相似文献
2.
Non‐Invasive Salivary Electrochemical Quantification of Paraquat Poisoning Using Boron Doped Diamond Electrode 下载免费PDF全文
Thiago Matheus Guimarães Selva William Reis de Araujo Thiago Regis Longo Cesar da Paixão 《Electroanalysis》2015,27(7):1642-1648
The present work describes the first electrochemical method for quantifying paraquat herbicide poisoning in human saliva samples. Paraquat shows two couples of well‐defined peaks in aqueous solution using a boron doped diamond (BDD) electrode. By using square wave voltammetry (SWV) technique under optimum experimental conditions, a linear analytical curve was obtained for paraquat concentrations ranging from 0.800 to 167 µmol L?1, with a detection limit of 70 nmol L?1. This method was applied to quantify paraquat spikes in human saliva samples and in two different water samples (tap and river). The recovery values obtained ranged from 83.0 to 104 % and 99.1 to 105 %, respectively, which highlight the accuracy of the proposed method. 相似文献
3.
4.
Grain shear flow in a rotating drum 总被引:2,自引:0,他引:2
In the present paper we report on the experimental activities carried out on a rotating drum partially filled with grains
or glass beads. The experiments give information about rheology through velocity profiles and through the velocity covariance
tensor structure. We used a LDV system to measure the velocity of the grains at several points along three vertical sections.
The data were also used to obtain the grain volume concentration, with encouraging results. Instantaneous velocity data were
elaborated in order to obtain velocity and pseudotemperature profiles for all the experiments; for a subset of the experiments
a large set of data were elaborated to obtain the velocity covariance. The velocity covariance is not collinear with the rate
of deformation tensor. An attempt to justify the rotation of the tensor axes as a consequence of the kinetically induced anisotropy
and of some free surface perturbations slowly moving upstream was partially successful.
Received: 23 April 1999 / Accepted: 15 July 2001 相似文献
5.
A Combined Experimental and Theoretical Study on the Formation of Ag Filaments on β‐Ag2MoO4 Induced by Electron Irradiation 下载免费PDF全文
Juan Andrés Mateus M. Ferrer Lourdes Gracia Armando Beltran Valeria M. Longo Guilherme H. Cruvinel Ricardo L. Tranquilin Elson Longo 《Particle & Particle Systems Characterization》2015,32(6):646-651
A combined experimental and theoretical study is presented to understand the novel observed nucleation and early evolution of Ag filaments on β‐Ag2MoO4 crystals, driven by an accelerated electron beam from an electronic microscope under high vacuum. The growth process, chemical composition, and the element distribution in these filaments are analyzed in depth at the nanoscale level using field‐emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) with energy‐dispersive spectroscopy (EDS) characterization. To complement experimental results, chemical stability, structural and electronic aspects have been studied systematically using first‐principles electronic structure theory within a quantum theory of atoms in molecules (QTAIM) framework. The Ag nucleation and formation on β‐Ag2MoO4 are a result of structural and electronic changes of the AgO4 tetrahedral cluster as a constituent building block of β‐Ag2MoO4, consistent with Ag metallic formation. The formation of Ag filament transforms the β‐Ag2MoO4 semiconductor from n‐ to p‐type concomitant with the appearance of Ag defects. 相似文献
6.
The Reynolds-averaged flow for a solid/free-surface juncture boundary layer and wake is documented. The three mean-velocity
components and five of the Reynolds stresses are measured for a surface-piercing flat plate in a towing tank using a laser-Doppler
velocimeter system for both boundary-layer and wake planes in regions close to the free surface. The experimental method is
described, including the foil-plate model, laser-Doppler velocimeter system, conditions, and uncertainty analysis. The underlying
flow data is in excellent agreement with benchmark data. Inner (near the plate and wake centerplane and below the free surface)
and outer (near the free surface) regions of high streamwise vorticity of opposite sign are observed, which transport, respectively,
high mean velocity and low turbulence from the outer to the inner and low mean velocity and high turbulence from the inner
to the outer portions of the boundary layer and wake. For the wake, the inner region of vorticity is relatively weak. The
physical mechanism for the streamwise vorticity is analyzed with regard to the Reynolds-averaged streamwise vorticity equation.
The anisotropy of the crossplane normal Reynolds stresses closely correlates with the vorticity and, additionally, indicates
similarity, i.e., its nature is such that it only depends on the proximity to the plate and free surface boundaries or wake
centerplane symmetry plane. Free-surface effects on the Reynolds stresses are analyzed with regard to the behavior close to
the free surface of the turbulent kinetic energy and the normal components of the anisotropy tensor and the anisotropy invariants.
Close to the free surface, the turbulent kinetic energy is nearly constant and increases for the inner and outer portions,
respectively, of the boundary layer and wake and the normal components of the anisotropy tensor and the anisotropy invariants
roughly correspond to the limiting values for two-component turbulence. The similarities and differences between the present
results and analysis with those from related studies are discussed. The data and analysis should have practical application
with regard to the development of turbulence models for computational fluid dynamics methods for the Reynolds-averaged Navier–Stokes
equations.
Received: 27 May 1997/Accepted: 1 August 1997 相似文献
7.
Sandro Longo 《Experiments in fluids》2006,41(4):593-602
We report on experiments on the effects of air bubbles on ultrasound velocity measurements in fluids. We used an acoustic Doppler velocimeter system for measuring the three velocity components in a single point and an acoustic Doppler velocimetry profiler system for measuring axial velocity in several points along the beam. The results suggest that both systems essentially measure the velocity of the bubbles, independent of the low air-volume concentration and of bubble radii in the flow field. 相似文献
8.
Edoardo Longo Ksenia Morozova Sine Yener Emanuele Boselli Franco Biasioli Matteo Scampicchio 《Journal of mass spectrometry : JMS》2019,54(5):412-421
This work proposes a novel method for the direct flow injection profiling of acylglycerols in edible oils and fats without preliminary extraction and consequent reconstitution in the injection solvent. The work exploits the outstanding performance of high‐resolution mass spectrometry to target unique elemental compositions even in the most complex matrices. The performance of isopropanol as the unique solvent for both the solubilization and analysis of acylglycerols was investigated in comparison with other classical methods involving preliminary extractions, sample recovery, and analysis. The calibrations of two triglyceride standards (triolein and trilinolenin) were successfully performed in presence and absence of oil matrix. As final application, the effects on the acylglycerol fraction of a heat treatment on three different fat samples (extra virgin olive oil, lard oil, and fat from dry cured ham—speck) were monitored. The proposed method is therefore suitable for a rapid evaluation of acylglycerol fractions in food lipid samples. 相似文献
9.
10.
Pharmacokinetics (PK) is a branch of pharmacology dedicated to the study of the time course of drug concentrations, from absorption to excretion from the body. PK dynamic models are often based on homogeneous, multi-compartment assumptions, which allow to identify the PK parameters and further predict the time evolution of drug concentration for a given subject. One key characteristic of these time series is their high variability among patients, which may hamper their correct stratification. In the present work, we address this variability by estimating the PK parameters and simultaneously clustering the corresponding subjects using the time series. We propose an expectation maximization algorithm that clusters subjects based on their PK drug responses, in an unsupervised way, collapsing clusters that are closer than a given threshold. Experimental results show that the proposed algorithm converges fast and leads to meaningful results in synthetic and real scenarios. 相似文献