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101.
102.
Lucas M. Cornetta Kaline Coutinho Sylvio Canuto Márcio T. do N. Varella 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2016,70(9):176
We report free energy barriers for the ground-state dissociation of the guanosinenucleotide anion in solution, employing implicit and explicit solvation models. The latterwas based on the Free Energy Perturbation technique and Monte Carlo simulations. For thelowest-energy structure, both solvation models indicate a solvent-induced transition froma dipole-bound state in the gas phase to a π? valence state in solution. The freebarrier estimates obtained from explicit and implicit solvation are in fair agreement witheach other, although significantly overestimated in comparison to a previously reportedexplicit solvation model based on ab initio molecular dynamics simulations. Accounting forcorrections related to the different DFT functionals used in the present and previousstudies significantly improves the agreement. 相似文献
103.
104.
105.
Upadhyay SP Pissurlenkar RR Coutinho EC Karnik AV 《The Journal of organic chemistry》2007,72(15):5709-5714
A furo-fused BINOL based chiral crown was developed as an enantioselective chiral sensor for phenylethylamine and ethyl ester of valine. Fusion of furan to BINOL has resulted in a highly stereo-discriminating backbone for the chiral crown developed. This chiral crown exhibited a fluorescence enhancement difference of 2.97 times between two enantiomers of phenylethylamine and 2.55 times between two enantiomers of ethyl ester of valine. The ratio of association constants for two diastereomeric complexes of two enantiomers of phenylethylamine was found to be 11.30, and the ratio for two enantiomers of ethyl ester of valine was 7.02. 相似文献
106.
107.
Courrol LC de Oliveira Silva FR Coutinho EL Piccoli MF Mansano RD Vieira Júnior ND Schor N Bellini MH 《Journal of fluorescence》2007,17(3):289-292
Renal cell carcinoma (RCC) accounts for approximately 3% of new cancer incidence and mortality in the United States. Unfortunately
many RCC masses remain asymptomatic and nonpalpable until they are advanced. Diagnosis and localization of early carcinoma
play an important role in the prevention and curative treatment of RCC. The autofluorescence of blood porphyrin of healthy
and tumor induced in male SCID mice was analyzed using fluorescence and excitation spectroscopy. A significant contrast between
normal and tumor blood could be established. Blood porphyrin fluorophore showed enhanced fluorescence band (around 630 nm)
in function of the tumor growth. This indicates that either the autofluorescence intensity of the blood fluorescence may provide
a good parameter for the “first approximation” characterization of the tumor stage. 相似文献
108.
Controlling the Formation of Ionic‐Liquid‐based Aqueous Biphasic Systems by Changing the Hydrogen‐Bonding Ability of Polyethylene Glycol End Groups
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Prof. Dr. Jorge F. B. Pereira Dr. Kiki A. Kurnia Dr. Mara G. Freire Prof. Dr. João A. P. Coutinho Prof. Dr. Robin D. Rogers 《Chemphyschem》2015,16(10):2219-2225
The formation of aqueous biphasic systems (ABS) when mixing aqueous solutions of polyethylene glycol (PEG) and an ionic liquid (IL) can be controlled by modifying the hydrogen‐bond‐donating/‐accepting ability of the polymer end groups. It is shown that the miscibility/immiscibility in these systems stems from both the solvation of the ether groups in the oxygen chain and the ability of the PEG terminal groups to preferably hydrogen bond with water or the anion of the salt. The removal of even one hydrogen bond in PEG can noticeably affect the phase behavior, especially in the region of the phase diagram in which all the ethylene oxide (EO) units of the polymeric chain are completely solvated. In this region, removing or weakening the hydrogen‐bond‐donating ability of PEG results in greater immiscibility, and thus, in a higher ability to form ABS, as a result of the much weaker interactions between the IL anion and the PEG end groups. 相似文献
109.
Determination of polycyclic aromatic hydrocarbons in fractions in asphalt mixtures using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization
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Paulo Cicero Nascimento Luciana Assis Gobo Denise Bohrer Leandro Machado Carvalho Margareth Coutinho Cravo Leni Figueiredo Mathias Leite 《Journal of separation science》2015,38(13):2238-2244
An analytical method using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization for the determination of polycyclic aromatic hydrocarbons in asphalt fractions has been developed. The 14 compounds determined, characterized by having two or more condensed aromatic rings, are expected to be present in asphalt and are considered carcinogenic and mutagenic. The parameters of the atmospheric pressure chemical ionization interface were optimized to obtain the highest possible sensitivity for all of the compounds. The limits of detection ranged from 0.5 to 346.5 μg/L and the limits of quantification ranged from 1.7 to 1550 μg/L. The method was validated against a diesel particulate extract standard reference material (NIST SRM 1975), and the obtained concentrations agreed with the certified values. The method was applied to asphalt samples after its fractionation according to ASTM D4124 and the method of Green. The concentrations of the seven polycyclic aromatic hydrocarbons quantified in the sample ranged from 0.86 mg/kg for benzo[ghi]perylene to 98.32 mg/kg for fluorene. 相似文献
110.
Determination of oxygen and nitrogen derivatives of polycyclic aromatic hydrocarbons in fractions of asphalt mixtures using liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization
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Paulo Cicero Nascimento Luciana Assis Gobo Denise Bohrer Leandro Machado Carvalho Margareth Coutinho Cravo Leni Figueiredo Mathias Leite 《Journal of separation science》2015,38(23):4055-4062
Liquid chromatography coupled to mass spectrometry with atmospheric pressure chemical ionization was used for the determination of polycyclic aromatic hydrocarbon derivatives, the oxygenated polycyclic aromatic hydrocarbons and nitrated polycyclic aromatic hydrocarbons, formed in asphalt fractions. Two different methods have been developed for the determination of five oxygenated and seven nitrated polycyclic aromatic hydrocarbons that are characterized by having two or more condensed aromatic rings and present mutagenic and carcinogenic properties. The parameters of the atmospheric pressure chemical ionization interface were optimized to obtain the highest possible sensitivity for all compounds. The detection limits of the methods ranged from 0.1 to 57.3 μg/L for nitrated and from 0.1 to 6.6 μg/L for oxygenated derivatives. The limits of quantification were in the range of 4.6–191 μg/L for nitrated and 0.3–8.9 μg/L for oxygenated derivatives. The methods were validated against a diesel particulate extract standard reference material (National Institute of Standards and Technology SRM 1975), and the obtained concentrations (two nitrated derivatives) agreed with the certified values. The methods were applied in the analysis of asphalt samples after their fractionation into asphaltenes and maltenes, according to American Society for Testing and Material D4124, where the maltenic fraction was further separated into its basic, acidic, and neutral parts following the method of Green. Only two nitrated derivatives were found in the asphalt sample, quinoline and 2‐nitrofluorene, with concentrations of 9.26 and 2146 mg/kg, respectively, whereas no oxygenated derivatives were detected. 相似文献