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321.
In this paper, polyethylene glycol (PEG) molecules have been grafted onto the surface of nanometer silica in toluene by using 1,4‐phenylene diisocyanate (PPDI) as a coupling agent, and dibutyltion dilaurate (DBTDL) as a catalyst. This process was executed by using a one‐step procedure involving a first reaction of PPDI with silica and a subsequent reaction of isocyanate‐bound silica with PEG. The PEG‐grafted silica has been characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and SEM analyses. The effects of reaction time, temperature and molar ratio of reactant on the effectiveness of the surface grafting were also investigated. Optimum grafting conditions of PEG were obtained at the temperature of 80 °C for 8 h. Maximum grafting of PEG molecules ratio was 22.6%, and maximum overall grafting ratio was 35%, as determined by TGA. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
322.
In a quantitative single particle analysis, named the low-Z particle EPMA, number concentration data for chemical species encountered in aerosol sample are provided. However, it will be more useful if mass concentration data can be obtained from single particle analysis; i.e., the single particle analysis data for weight fractions of chemical species can be complementarily used in combination with the bulk analysis data, for more clearly understanding the behavior of airborne aerosols. In order to investigate how reliably mass concentration data can be obtained from the low-Z particle EPMA technique, a potassium feldspar powdered standard reference material (SRM), of which elemental weight fractions are well defined by various bulk analytical techniques, was analyzed using the low-Z particle EPMA technique. In this work, it is demonstrated that weight fractions of major elements in the powdered SRM sample obtained by the low-Z particle EPMA are within 8% to the certified values obtained by bulk analytical techniques, although the single particle and bulk analyses employ different approaches. Further, it is shown that the quantitative single particle analysis, i.e., low-Z particle EPMA, can provide molecular mass concentration data for chemical species, which is not easy to obtain using bulk analysis. 相似文献
323.
Strontium
isolation from natural samples with Sr resin and subsequent determination of 90Sr</p>
</p>
Ž. Grahek K. Košutić M. Rožmarić-Mačefat 《Journal of Radioanalytical and Nuclear Chemistry》2006,268(2):179-190
The
reliability of an 90Sr determination method was tested using an Sr
extraction chromatographic resin for strontium isolation. The 90Sr-content
in samples of vegetables, soil and water (obtained from Environmental
Measurement Laboratory, USA) were determined and the results were controlled by
classical methods and by using an anion-exchanger and an alcohol solution of
nitric acid for the strontium isolation. These methods were previously tested
by determining 90Sr in IAEA 326 and 327 samples of soil. It is shown
that the isolation process with Sr resin is simpler and faster than the
classical and mixed solvent anion-exchange methods. The efficiency of isolation
on a Sr column depends on the resin quantity and separation conditions; and is
the highest with a Sr column, compared to the classical and anion-exchange
methods. Experimental data and theoretical models were used to calculate the
parameters that enable the estimation of optimum dimensions of the column for
isolation. A simple relation is proposed for the calculation of breakthrough
volume, which defines the sample and eluent volumes for an optimal strontium
isolation.</p>
</p> 相似文献
324.
Highly Fluorinated Tris(indazolyl)borate Silylamido Complexes of the Heavier Alkaline Earth Metals: Synthesis,Characterization, and Efficient Catalytic Intramolecular Hydroamination 下载免费PDF全文
Nuria Romero Sorin‐Claudiu Roşca Dr. Yann Sarazin Prof. Jean‐François Carpentier Dr. Laure Vendier Sonia Mallet‐Ladeira Dr. Chiara Dinoi Prof. Michel Etienne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(10):4115-4125
Heteroleptic silylamido complexes of the heavier alkaline earth elements calcium and strontium containing the highly fluorinated 3‐phenyl hydrotris(indazolyl)borate {F12‐Tp4Bo, 3Ph}? ligand have been synthesized by using salt metathesis reactions. The homoleptic precursors [Ae{N(SiMe3)2}2] (Ae=Ca, Sr) were treated with [Tl(F12‐Tp4Bo, 3Ph)] in pentane to form the corresponding heteroleptic complexes [(F12‐Tp4Bo, 3Ph)Ae{N(SiMe3)2}] (Ae=Ca ( 1 ); Sr ( 3 )). Compounds 1 and 3 are inert towards intermolecular redistribution. The molecular structures of 1 and 3 have been determined by using X‐ray diffraction. Compound 3 exhibits a Sr ??? MeSi agostic distortion. The synthesis of the homoleptic THF‐free compound [Ca{N(SiMe2H)2}2] ( 4 ) by transamination reaction between [Ca{N(SiMe3)2}2] and HN(SiMe2H)2 is also reported. This precursor constitutes a convenient starting material for the subsequent preparation of the THF‐free complex [(F12‐Tp4Bo, 3Ph)Ca{N(SiMe2H)2}] ( 5 ). Compound 5 is stabilized in the solid state by a Ca???β‐Si?H agostic interaction. Complexes 1 and 3 have been used as precatalysts for the intramolecular hydroamination of 2,2‐dimethylpent‐4‐en‐1‐amine. Compound 1 is highly active, converting completely 200 equivalents of aminoalkene in 16 min with 0.50 mol % catalyst loading at 25 °C. 相似文献
325.
Lee MK Hwang BY Lee SA Oh GJ Choi WH Hong SS Lee KS Ro JS 《Chemical & pharmaceutical bulletin》2003,51(4):409-411
The inhibitory compound of monoamine oxidase (MAO) activity was isolated from the CH(2)Cl(2) fraction of the fructus of Evodia rutaecarpa and identified as 1-methyl-2-undecyl-4(1H)-quinolone (1). Compound 1 showed a selective inhibition of type B MAO (MAO-B) activity with the IC(50) value of 15.3 microM using a substrate kynuramine, but did not inhibit type A MAO (MAO-A) activity. The kinetic analysis using Lineweaver-Burk plots indicated that compound 1 competitively inhibited MAO-B activity with the K(i) value of 9.91 microM. The inhibition of MAO-B by compound 1 was found to be irreversible by dialysis of the incubation mixture. These results suggest that compound 1 is a potent irreversible inhibitor of MAO-B, and may regulate catecholamine content in the neurons. 相似文献
326.
George Cordoyiannis Sašo Gyergyek Brigita Rožič Samo Kralj Zdravko Kutnjak George Nounesis 《Liquid crystals》2016,43(3):314-319
We report on wide-angle X-ray scattering measurements along the smectic-A to chiral ferroelectric smectic-C* phase transition of the liquid crystal SCE9 and its mixture with maghemite magnetic nanoparticles of typical dimension 20 nm. The temperature profiles of the tilt angle are fitted by an extended mean-field model. Neither pre-transitional order effects nor variations in the SmA layer thickness are observed, indicating a rather negligible influence of these nanoparticles upon the molecular orientation at the smectic-A to smectic-C* phase transition of SCE9. These results are very different from what was observed for smaller CdSe nanoparticles (3.5 nm) where both a dilation of the smectic layers in the SmA phase and a crossover behaviour for the smectic-A to smectic-C* transition away from tricriticality have been observed for analogous concentrations. 相似文献
327.
Nicolas I. Regenauer Prof. Dr. Hubert Wadepohl Dr. Dragoş-Adrian Roşca 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(58):e202202172
Nitrogen fixation at iron centres is a fundamental catalytic step for N2 utilisation, relevant to biological (nitrogenase) and industrial (Haber-Bosch) processes. This step is coupled with important electronic structure changes which are currently poorly understood. We show here for the first time that terminal dinitrogen dissociation from iron complexes that coordinate N2 in a terminal and bridging fashion leaves the Fe-N2-Fe unit intact but significantly enhances the degree of N2 activation (Δν≈180 cm−1, Raman spectroscopy) through charge redistribution. The transformation proceeds with local spin state change at the iron centre (S= →S=3/2). Further dissociation of the bridging N2 can be induced under thermolytic conditions, triggering a disproportionation reaction, from which the tetrahedral (PNN)2Fe could be isolated. This work shows that dinitrogen activation can be induced in the absence of external chemical stimuli such as reducing agents or Lewis acids. 相似文献
328.
The endocrine disruptors bisphenol A (BPA) and benzophenone (BFN) could be important ingredients in thermochromic printing inks in significant amounts. Due to patent protection and use of the inks, manufacturers are not obliged to state their precise chemical composition. These substances in increasingly used thermochromic printing inks present a hazard for human health and environment in the case of inappropriate application and waste disposal. In this work we enabled identification of the inks that contain these hazardous substances by developing a new method for the analysis of BPA and BFN in thermochromic printing inks. The method is based on the reversed-phase liquid chromatography (LC) with UV detection at 226 and 254?nm. Ultrasound-assisted sample extraction in methanol was proven to be the most suitable and effective among several other solvents. The method was completely validated with satisfactory results. The specificity of the method was proven by the additional LC–tandem mass spectrometry analysis. A representative group of 15 ink samples from various manufacturers, curing and printing modes was analyzed. BPA was found in three samples with mass fractions of about 2% while BFN was found in two samples with mass fractions of 0.34 and 0.66%. 相似文献