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91.
92.
M.A. Martínez-Carrillo C. Solís E. Andrade K. Isaac-Olivé M. Rocha G. Murillo Rosa Icela Beltrán-Hernández C.A. Lucho-Constantino 《Microchemical Journal》2010,96(2):386-390
In order to find out if there is a relation between atmospheric particulate matter composition and human health effects, metals and other elements measurement are performed. Analysis of atmospheric aerosols collected in filters is the usual method to achieve this task. Biological monitors provide an advantageous alternative way of sampling, since there is no need of special sampling devices, and accumulation time can be as long as desired. In this study, Tillandsia usneoides a reliable air pollution biological monitor that occurs naturally throughout Mexico was used to monitor air quality of Tula–Tepeji corridor at central Mexico. This area is considered critical zone because of atmosphere contaminants high concentration. Some biomonitors were transplanted from a clean environment to four sites at the Tula corridor. Plants samples were collected every two weeks from February to April 2008. PM10 sampling in filters was also performed simultaneously at three locations where T. usneoides was transplanted, for a comparison. Chemical composition was determined by PIXE. Results showed that T. usneoides incorporates anthropogenic elements reaching maximal levels after 6 to 10 weeks approximately. Since results obtained with biomonitors agree with those obtained with aerosol filters, T. usneoides could be employed as a first approximation to provide insights of the atmospheric pollution level previous to a detailed study using filters. 相似文献
93.
94.
Vera S. O. Farias Wilton Pereira da Silva Cleide M. D. P. S. e Silva Vicente P. T. Rocha Antonio G. B. Lima 《Heat and Mass Transfer》2013,49(5):695-709
This article proposes a numerical solution for the diffusion equation applied to solids with arbitrary geometry using non-orthogonal structured grids for the boundary condition of the first kind. A transient three-dimensional mathematical formulation written in boundary fitted coordinates and numerical formalism to discretize the diffusion equation by using the finite volume method, including numerical analysis of the computational solution are presented. To validate the proposed solution, the results obtained in this work were compared with well-known numerical solution available in literature and good agreement was observed. In order to verify the potential of the proposed numerical solution, it was applied to describe mass transfer inside ceramic roof tiles during drying. For that, it was used experimental data of the drying kinetics at the following temperatures: 55.6; 69.7; 82.7 and 98.6 °C. An optimization technique using experimental dataset has been presented to estimation of transport properties. The obtained statistical indicators enable to conclude that the numerical solution satisfactorily describes the drying processes. 相似文献
95.
Jussara de Araújo Gonçalves André Luis Dantas Ramos Layla L. L. Rocha Anderson Kurunczi Domingos Robson S. Monteiro José Sotolongo Peres Nelson C. Furtado Carlton A. Taft Donato A. G. Aranda 《Journal of Physical Organic Chemistry》2011,24(1):54-64
Biodiesel can be obtained from fatty acid raw materials through esterification. The reactivity of lauric, palmitic, stearic, oleic, and linoleic fatty acids with methanol using powdered niobic acid as a heterogeneous catalyst was investigated in this work, both experimentally (in a batch reactor) and theoretically. A 23 experimental design was used, with methanol/fatty acid molar ratio, catalyst concentration, and temperature as main factors. An empirical model demonstrated that temperature is the most important variable. Fourteen heterogeneous and 56 homogeneous‐like kinetic models were tested. A homogeneous‐like model considering zero order for all species and inhibition by water was the most adequate for experiments without catalyst. A homogeneous‐like model considering a second‐order reaction in relation to the fatty acid and no water inhibition was the most adequate for niobic acid catalyzed reaction. Molecular modeling confirmed the experimental results showing that the reactivity is directly related to the increase of unsaturated bonds and the reduction of carbon chain length. The polarity of the fatty acid is determinant in the reactivity. At the molecular level, reaction occurs between the HOMO orbital of methanol and LUMO orbitals of fatty acids and reactivity is higher when the energy difference between these orbitals is lower. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
96.
M. Manso S. Pessanha F. Figueira S. Valadas A. Guilherme M. Afonso A. C. Rocha M. J. Oliveira I. Ribeiro M. L. Carvalho 《Analytical and bioanalytical chemistry》2009,395(7):2029-2036
The reddish-brown, brown or yellowish stains of circular or irregular shape known as foxing spots have been fully described
in conservation literature but still, this phenomenon does not find any scientific agreement since many hypotheses have been
raised concerning their origin. In this work a contribution to foxing definition not only focussed on its appearance but also
reported on its chemical information. For this purpose foxing stains present in drawings from two Portuguese artists dated
from the eighteenth to nineteenth centuries were observed under ultra-violet light and optical microscope and analysed by
three non-invasive spectroscopy techniques. The observations carried out on the stains provided information on their surface
morphology. The use of energy-dispersive X-ray fluorescence revealed a variation on the elemental content between foxing and
paper region. Although the results from X-ray diffraction analysis showed no signs of cellulose degradation in foxing stains,
Fourier-transformed infrared analysis revealed the presence of oxide groups. Both the information on the chemical nature and
surface morphology of the stains achieved in this study will contribute to increase foxing formation information and develop
future protocols for conservation purposes. 相似文献
97.
We introduce a family of braided Hopf algebras that (in characteristic zero) generalizes the rank 1 Hopf algebras introduced by Krop and Radford and we study its cleft extensions. 相似文献
98.
Svedružić D Blackburn JL Tenent RC Rocha JD Vinzant TB Heben MJ King PW 《Journal of the American Chemical Society》2011,133(12):4299-4306
We studied the electrocatalytic activity of an [FeFe]-hydrogenase from Clostridium acetobutylicum (CaH2ase) immobilized on single-wall carbon nanotube (SWNT) networks. SWNT networks were prepared on carbon cloth by ultrasonic spraying of suspensions with predetermined ratios of metallic and semiconducting nanotubes. Current densities for both proton reduction and hydrogen oxidation electrocatalytic activities were at least 1 order of magnitude higher when hydrogenase was immobilized onto SWNT networks with high metallic tube (m-SWNT) content in comparison to hydrogenase supported on networks with low metallic tube content or when SWNTs were absent. We conclude that the increase in electrocatalytic activities in the presence of SWNTs was mainly due to the m-SWNT fraction and can be attributed to (i) substantial increases in the active electrode surface area, and (ii) improved electronic coupling between CaH2ase redox-active sites and the electrode surface. 相似文献
99.
Coelho S Moreno-Flores S Toca-Herrera JL Coelho MA Pereira MC Rocha S 《Journal of colloid and interface science》2011,363(2):450-455
The interaction of gum arabic (GA) with chitosan (Ch) of different degree of deacetylation was studied by turbidity measurements, dynamic light scattering and atomic force microscopy. The structure of the complexes was found to be directly related to the charge density of chitosan molecules. Gum arabic and chitosan with a degree of deacetylation of 75% form soluble complexes with a loosely globular structure of about 250 nm, at weight ratios up to 1.2, if the concentrations are kept low (total biopolymer concentration up to 0.06%). If chitosan has a higher charge density (degree of deacetylation of 93%), colloidal particles are formed, independently of the polymer concentration or ratio. At low concentrations and GA/Ch ratios of 1 or 1.2, the particles have diameters of 200-250 nm. The formation of soluble complexes is attributed to a chitosan lower charge density and the presence of non-charged monomers, which prevent the efficient self-assembly of the macromolecules. 相似文献
100.