全文获取类型
收费全文 | 268篇 |
免费 | 14篇 |
专业分类
化学 | 185篇 |
晶体学 | 4篇 |
力学 | 23篇 |
数学 | 21篇 |
物理学 | 49篇 |
出版年
2023年 | 6篇 |
2022年 | 14篇 |
2021年 | 20篇 |
2020年 | 10篇 |
2019年 | 13篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 14篇 |
2013年 | 19篇 |
2012年 | 27篇 |
2011年 | 15篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 6篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 9篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有282条查询结果,搜索用时 15 毫秒
151.
R. Zakaria K. Das M. Bhojak M. Radon V. Sluming C. Walker M.D. Jenkinson 《Magnetic resonance imaging》2014
Background and Purpose
Diffusion MRI characteristics have been used as biomarkers to guide prognosis in cerebral pathologies including brain metastases. The measurement of ADC is often described poorly in clinical and research studies with little detail given to the practical considerations of where to place ROIs, which post processing software package to use and how reproducible the resulting metrics will be.Method
We investigated a series of 12 patients with brain metastases and preoperative DWI. Three post processing platforms were used. ROI were placed over the tumour, peritumoural region and across the brain-tumour interface. These recordings were made by a neurosurgeon and a neuroradiologist. Inter-intra-observer variability was assessed using Bland-Altman analysis. An exploratory analysis of DWI with overall survival and tumour type was made.Results
There was excellent correlation between the software packages used for all measures including assessing the whole tumour, selective regions with lowest ADC, the change of ADC across the brain-tumour interface and the relation of the tumour ADC to peritumoural regions and the normal white matter. There was no significant inter- or intra-observer variability for repeated readings. There were significant differences in the mean values obtained using different methodologies and different metrics had differing relationships to overall survival and primary tumour of origin.Conclusion
Diffusion weighted MRI metrics offer promise as potential non-invasive biomarkers in brain metastases and a variety of metrics have been shown to be reliably measured using differing platforms and observers. 相似文献152.
K. S. Hamdan S. M. Abdullah K. Sulaiman R. Zakaria 《Applied Physics A: Materials Science & Processing》2014,115(1):63-68
We report an alternative approach to enhance the optical and electrical performance of a vanadyl 2,9,16,23-tetraphenoxy-29H,31H-phthalocyanine:poly(3hexylthiophene) (VOPcPhO:P3HT) blending system by integrating plasmonic spherical silver into an active layer of organic solar cells. Studies of the influence of the size distribution and optical properties of the silver nanoparticles were carried out using UV–Vis spectroscopy and field emission scanning electron microscopy, respectively. Electrical characteristics with and without the presence of metallic nanostructures were analyzed using J–V characteristics to observe the plasmonic effects on the performance in the VOPcPhO:P3HT organic solar cells. 相似文献
153.
M. N. Mohamad Ibrahim A. Md. Ghani N. Zakaria S. Shuib C. S. Sipaut 《Macromolecular Symposia》2008,274(1):37-42
Summary: Malaysia has over 4 million hectares of oil palm plantations that yield large amounts of empty fruit bunches (EFB) generated from palm oil milling operations. These forms of lignocellulosic residue pose an environmental hazard if their disposal is not managed in a systematic manner. One of the useful elements extracted from these EFBs is lignin. The general purpose of this study is to explore the potential uses of lignin extracted from soda black liquor (paper and pulping waste) derived from oil palm empty fruit bunches (EFB) in the formulation of a more environmentally friendly wood adhesive. In this work, the potential for replacing phenol with lignin in phenol formaldehyde resin formulation is examined. The quantity of phenol was reduced by synthesizing the resin at a lignin to phenol ratio of 1:1. The physical and chemical properties of lignin phenol formaldehyde resin (LPF) and commercial phenol formaldehyde resin (CPF) were then compared. The infrared spectrum revealed similarities in the functional groups of both LPF and CPF resins. Tensile strength comparisons between both resins revealed that the LPF resin had a higher bonding strength (11.60 MPa more in term of allowable maximum load). In addition, the kinematics viscosity test showed that the LPF resin had lower kinematic viscosity than the CPF resin after 21 days of storage. Finally, the scanning electron microscope images for both resins showed similarities in terms of penetration into wood vessels. 相似文献
154.
The present work deals with temporal stability properties of a falling liquid film down an inclined plane in the presence of a parallel subsonic gas flow. The waves are described by evolution equation previously derived as a generalization of the model for the Newtonian liquid. We confirm linear stability results of the basic flow using the Orr–Sommerfeld analysis to that obtained by long wave approximation analysis. The non-linear stability criteria of the model are discussed analytically and stability branches are obtained. Finally, the solitary wave solutions at the liquid–gas interface are discussed, using specially envelope transform and direct ansatz approach to Ginzburg–Landau equation. The influence of different parameters governing the flow on the stability behavior of the system is discussed in detail. 相似文献
155.
Elastic scattering of α + 40Ca is analyzed in the framework of the optical model. We adopted an independent α-cluster model to generate the α-cluster and matter density of 40Ca. We proposed a parametrized form for the α-cluster density and fixed its parameters according to the available experimental data about the α-particle and 40Ca nuclei. The obtained α-cluster density of 40Ca is used to generate the real part of the optical potential. The single folding procedure is used to generate this real optical potential with two different effective α–α interactions. The real calculated potential supplied with an imaginary Woods–Saxon squared potential is used to analyze 20 sets of experimental data in the energy range between 18 and 166 MeV. We found that our model is successful in reproducing the data for energies above 40 MeV and still doubtful for lower energies. 相似文献
156.
Nabati Shoghl Sina Loloei Zakaria Keshavarz Moraveji Mostafa 《Journal of Thermal Analysis and Calorimetry》2019,136(4):1831-1846
Journal of Thermal Analysis and Calorimetry - Forced convection heat transfer of two different types of water-based nanofluids (Al2O3, TiO2) was investigated numerically. In this numerical... 相似文献
157.
Zakaria?El?AllaliEmail author Mohamed?Talbi Najib?Tsouli 《Mediterranean Journal of Mathematics》2006,3(1):87-96
In this work we study the existence and regularity of solutions of the equation Δ p 2 u = λm|u| q?2 u with the boundary conditions of Navier in the case p ≠ q. 相似文献
158.
Al-Qodah Z 《Applied biochemistry and biotechnology》2000,87(1):37-55
In this study, a series of experiments was conducted to demonstrate the feasibility of continuous production of penicillin
antibiotic using a three-phase magneto airlift fermentor with immobilized Penicillium chrysogenum. The fermentation processes were carried out in a 2.4-L external loop airlift utilizing a transverse magnetic field. It was
found that the application of the magnetic field to a bed of ferromagnetic beads affects both the hydrodynamics of the reactor
and the rate of the bioconversion process occurring inside it. One hundred hours after startup, the maximum penicillin concentration
increased 48% as the magnetic field intensity increased from 0 to 35 mT, owing to the increased residence time of the substrate
in the riser and the positive effect of the magnetic field on the effective fluid-solid interfacial area. In addition, the
detached biomass concentration in the liquid phase was found to be only 5% of the immobilized biomass, owing to low shear
levels and the absence of friction among the solid-phase particles. 相似文献
159.
Christopher Simon Dr. Mohamed Barakat Zakaria Hannah Kurz David Tetzlaff Dr. André Blösser Dr. Morten Weiss Dr. Jana Timm Prof. Birgit Weber Prof. Ulf-Peter Apfel Prof. Roland Marschall 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(68):16990-17001
Phase-pure spinel-type magnetic nickel ferrite (NiFe2O4) nanocrystals in the size range of 4 to 11 nm were successfully synthesized by a fast and energy-saving microwave-assisted approach. Size and accessible surface areas can be tuned precisely by the reaction parameters. Our results highlight the correlation between size, degree of inversion, and magnetic characteristics of NiFe2O4 nanoparticles, which enables fine-tuning of these parameters for a particular application without changing the elemental composition. Moreover, the application potential of the synthesized powders for the electrocatalytic oxygen evolution reaction in alkaline media was demonstrated, showing that a low degree of inversion is beneficial for the overall performance. The most active sample reaches an overpotential of 380 mV for water oxidation at 10 mA cm−2 and 38.8 mA cm−2 at 1.7 V vs. RHE, combined with a low Tafel slope of 63 mV dec−1. 相似文献
160.
A multiscale fourth‐order model for the image inpainting and low‐dimensional sets recovery 下载免费PDF全文
Anis Theljani Zakaria Belhachmi Moez Kallel Maher Moakher 《Mathematical Methods in the Applied Sciences》2017,40(10):3637-3650
We consider a fourth‐order variational model, to solve the image inpainting problem, with the emphasis on the recovery of low‐dimensional sets (edges and corners) and the curvature of the edges. The model permits also to perform simultaneously the restoration (filtering) of the initial image where this one is available. The multiscale character of the model follows from an adaptive selection of the diffusion parameters that allows us to optimize the regularization effects in the neighborhoods of the small features that we aim to preserve. In addition, because the model is based on the high‐order derivatives, it favors naturally the accurate capture of the curvature of the edges, hence to balance the tasks of obtaining long curved edges and the obtention of short edges, tip points, and corners. We analyze the method in the framework of the calculus of variations and the Γ‐convergence to show that it leads to a convergent algorithm. In particular, we obtain a simple discrete numerical method based on a standard mixed‐finite elements with well‐established approximation properties. We compare the method to the Cahn–Hilliard model for the inpainting, and we present several numerical examples to show its performances. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献