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231.
Multivariate optimization of headspace‐GC for the determination of monoaromatic compounds (benzene,toluene, ethylbenzene,and xylenes) in waters and wastewaters 下载免费PDF全文
Patrícia M. Carneiro Paulo Igor M. Firmino Mayara C. Costa Alexandre C. Lopes André B. dos Santos 《Journal of separation science》2014,37(3):265-271
The objective of this study was to optimize, by employing a central composite rotatable design, and validate an analytical method to detect and quantify monoaromatic compounds (benzene, toluene, ethylbenzene, and xylenes) in waters and wastewaters by using headspace extraction followed by GC coupled with photoionization detection. The extraction parameters optimized were: salinity, sample volume, incubation time, and extraction temperature. The results revealed that the sample volume was the most significant parameter in the extraction process, whereas the salinity effect was negligible, which extends the applicability of the analytical method to waters with different salinities. Finally, the studied method was very selective and, at the optimal extraction conditions (15 mL sample volume, 15 min incubation time, and temperature of 70°C), presented excellent repeatability (<4%), linearity (R > 0.999 for each compound), and sensitivity, since very low LODs (0.13–0.48 μg/L) and LOQs (0.43–1.61 μg/L) were achieved. 相似文献
232.
Zanichelli PG Sernaglia RL Franco DW 《Langmuir : the ACS journal of surfaces and colloids》2006,22(1):203-208
The reaction of NO and the immobilized dimer complex (edta)(2)Ru(2)(III(1/2),III(1/2)) on silica gel chemically modified with [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEATS) produces the corresponding immobilized nitrosyl complex AEATS/Ru(II)NO(+). This compound, a monomer, was obtained by reducing the immobilized ruthenium dimer either electrochemically or with Eu(II) and reacting this species with NO(2)(-) ions. The properties of [Ru(edta)NO](-) in solution and anchored (AEATS/Ru(II)NO(+)) on silica were compared using electrochemical (DPV, CV) and spectroscopic (IR, UV-vis, and ESR) techniques. The results indicate that immobilization does not alter the reactivity of the ruthenium complex and confirm that [Ru(edta)(H(2)O)](2)(-) may be used, either in solution or immobilized, as a catalyst for the conversion of NO(2)(-) to NO(+). Both the anchored nitrosyl complex AEATS/Ru(II)NO(+) and the [Ru(edta)NO](-) species in solution, upon one-electron reduction, liberate NO at comparable rates. 相似文献
233.
Dr. Patrícia B. Momo M. Sc. Alexandria N. Leveille M. Sc. Elliot H. E. Farrar Dr. Matthew N. Grayson Prof. Dr. Anita E. Mattson Prof. Dr. Antonio C. B. Burtoloso 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(36):15684-15689
The first example of enantioselective S−H insertion reactions of sulfoxonium ylides is reported. Under the influence of thiourea catalysis, excellent levels of enantiocontrol (up to 95 % ee) and yields (up to 97 %) are achieved for 31 examples in S−H insertion reactions of aryl thiols and α-carbonyl sulfoxonium ylides. 相似文献
234.
The dioxomolybdenum(VI) complexes [MoO2Cl2] (1), [MoO2(acac)2] (2), [MoO2(S2CNEt2)2] (3), [CpMoO2Cl] (4), [MoO2(mes)2] (5) and the polymeric organotin-oxomolybdates [(R3Sn)2MoO4] [R = n-Bu (6), t-Bu (7), Me (8)] were examined as catalysts for the hydrosilylation of aldehydes and ketones with dimethylphenylsilane. Of these, [MoO2Cl2] (1) was the most efficient catalyst, affording quantitative yields of the corresponding silylated ethers at room temperature in acetonitrile. Complexes 2, 4-8 also catalyzed the same reaction but required heating at 80 degrees C and longer reaction times compared with 1. Compound 3 is inactive. The wide scope of molybdenum oxide-mediated hydrosilylation was established with a variety of aldehydes and ketones. Counter intuitively, the activity of is 1 highest in NCMe. In the absence of a carbonyl substrate, [MoO2Cl2(NCBu(t))] (10) reacts with HSiMe2Ph affording [MoO(OSiMe2Ph)Cl2]2 (11) which has been fully characterized by NMR and IR spectroscopy, elemental analyses and mass spectrometry. Addition of radical scavengers strongly slows down the [MoO2Cl2]-based hydrosilylation suggesting the intermediacy of oxygen-centered radicals. 相似文献
235.
de Almeida Amanda Cosmo Ferreira Patrícia Osório Torquetti Carolina Ekawa Bruno Carvalho Ana Carina Sobral dos Santos Everton Carvalho Caires Flávio Junior 《Journal of Thermal Analysis and Calorimetry》2020,140(5):2293-2303
Journal of Thermal Analysis and Calorimetry - Novel cocrystals of ciprofloxacin with pyrazinoic acid and p-aminobenzoic acid in the 1:1 stoichiometric ratio were obtained by the mechanochemical... 相似文献
236.
Azevedo Lemos V Xavier Baliza PX Terumi Yamaki R Eça Rocha M Oliveira Alves AP 《Talanta》2003,61(5):675-682
An on-line system for preconcentration and determination of copper at μg l−1 level by flame atomic absorption spectrometry (FAAS) is proposed. Amberlite XAD-2 functionalized with 3,4-dihydroxybenzoic acid packed in a minicolumn was used as sorbent. Copper(II) ions were sorbed in the minicolumn, from which it could be eluted by hydrochloric acid solution directly to the nebulizer-burner system of the FAAS. Eluent solution was carried by water at a flow rate of 5.00 ml min−1. Signals were measured as peak height by using an instrument software. Achieved sampling rate was 27 samples per hour. Analytical parameters were evaluated and the results demonstrated that copper can be determined, with acetate buffer to adjust the sample pH at 6.0, preconcentration time of 120 s and a sample flow rate of 6.50 ml min−1. The desorption was carried out with 30 μl of a 1.0 mol l−1 hydrochloric acid solution. An enrichment factor of 33 in 13.00 ml of sample (120 s preconcentration time) was achieved by using the time-based technique. The detection limit (DL) (3 s) was 0.27 μg l−1 and the precision (assessed as the relative standard deviation) reached values of 5.7-1.1% in copper solutions of 5.00 to 50.00 μg l−1 concentration, respectively. The accuracy of procedure was confirmed by copper determination in certified reference materials. Recoveries of spike additions (1.0 or 2.0 μg g−1) to food samples were quantitative (90.0-110.0%). These results proved also that the procedure is not affected by matrix interference and can be applied satisfactorily for copper determination in rice flour and starch samples. 相似文献
237.
Neves P Gago S Balula SS Lopes AD Valente AA Cunha-Silva L Paz FA Pillinger M Rocha J Silva CM Gonçalves IS 《Inorganic chemistry》2011,50(8):3490-3500
The complex [MoO(2)Cl{HC(3,5-Me(2)pz)(3)}]BF(4) (1) (HC(3,5-Me(2)pz)(3) = tris(3,5-dimethyl-1-pyrazolyl)methane) has been prepared and examined as a catalyst for epoxidation of olefins at 55 °C using tert-butyl hydroperoxide (TBHP) as the oxidant. For reaction of cis-cyclooctene, epoxycyclooctane is obtained quantitatively within 5 h when water is rigorously excluded from the reaction mixture. Increasing amounts of water in the reaction mixture lead to lower activities (without affecting product selectivity) and transformation of 1 into the trioxidomolybdenum(VI) complex [{HC(3,5-Me(2)pz)(3)}MoO(3)] (4). Complex 4 was isolated as a microcrystalline solid by refluxing a suspension of 1 in water. The powder X-ray diffraction pattern of 4 can be indexed in the orthorhombic Pnma system, with a = 16.7349(5) ?, b = 13.6380(4) ?, and c = 7.8513(3) ?. Treatment of 1 in dichloromethane with excess TBHP led to isolation of the symmetrical [Mo(2)O(4)(μ(2)-O){HC(3,5-Me(2)pz)(3)}(2)](BF(4))(2) (2) and unsymmetrical [Mo(2)O(3)(O(2))(2)(μ(2)-O)(H(2)O){HC(3,5-Me(2)pz)(3)}] (3) oxido-bridged dimers, which were characterized by single-crystal X-ray diffraction. Complex 2 displays the well-known (Mo(2)O(5))(2+) bridging structure where each dioxidomolybdenum(VI) center is coordinated to three N atoms of the organic ligand and one μ(2)-bridging O atom. The unusual complex 3 comprises dioxido and oxidodiperoxo molybdenum(VI) centers linked by a μ(2)-bridging O atom, with the former center being coordinated to the tridentate N-ligand. The dinuclear complexes exhibit a similar catalytic performance to that found for mononuclear 1. For complexes 1 and 2 use of the ionic liquids (ILs) 1-butyl-3-methylimidazolium tetrafluoroborate and N-butyl-3-methylpyridinium tetrafluoroborate as solvents allowed the complexes to be completely dissolved, and in each case the catalyst and IL could be recycled and reused without loss of activity. 相似文献
238.
Patrícia de Almeida Rodrigo Álvaro Brandão Lopes‐Martins Shaiane Silva Tomazoni Gianna Móes Albuquerque‐Pontes Larissa Aline Santos Adriane Aver Vanin Lucio Frigo Rodolfo P Vieira Regiane Albertini Paulo de Tarso Camillo de Carvalho Ernesto Cesar Pinto Leal‐Junior 《Photochemistry and photobiology》2013,89(2):501-507
Pharmacological therapy is widely used in the treatment of muscle injuries. On the other hand, low‐level laser therapy (LLLT) arises as a promising nonpharmacological treatment. The aim of this study was to analyze the effects of sodium diclofenac (topical application) and LLLT on morphological aspects and gene expression of biochemical inflammatory markers. We performed a single trauma in tibialis anterior muscle of rats. After 1 h, animals were treated with sodium diclofenac (11.6 mg g‐1 of solution) or LLLT (810 nm; continuous mode; 100 mW; 3.57 W cm?2; 1, 3 or 9 J; 10, 30 or 90 s). Histological analysis and quantification of gene expression (real‐time polymerase chain reaction—RT‐PCR) of cyclooxygenase 1 and 2 (COX‐1 and COX‐2) and tumor necrosis factor‐alpha (TNF‐α) were performed at 6, 12 and 24 h after trauma. LLLT with all doses improved morphological aspects of muscle tissue, showing better results than injury and diclofenac groups. All LLLT doses also decreased (P < 0.05) COX‐2 compared to injury group at all time points, and to diclofenac group at 24 h after trauma. In addition, LLLT decreased (P < 0.05) TNF‐α compared both to injury and diclofenac groups at all time points. LLLT mainly with dose of 9 J is better than topical application of diclofenac in acute inflammation after muscle trauma. 相似文献
239.
Renato Sonchini Gonçalves Gabriel Batista César Patrícia Magalhães Barbosa Noboru Hioka Celso Vataru Nakamura Marcos Luciano Bruschi 《Natural product research》2019,33(8):1196-1199
Emodin reduction to emodin anthrone comprise one of three process steps involved in the hypericin synthesis, a powerful natural photosensitiser found in plants of the genus Hypericum. In this communication, an optimized protocol was established for emodin reduction enabling an efficient multigram preparation of emodin anthrone. A screening of reducing agent (SnCl2·2H2O and HClconc) under different reaction times was employed in micro-scale and monitored by electronic absorption spectroscopy technique. Data showed lower yields of emodin anthrone when some experimental conditions previously described in the literature were reproduce. However, using the optimized protocol for the emodin reduction these yields were overcoming, and a gram-scale supply experiment was reproducible for the preparation of 10 grams of emodin anthrone with excellent yield. 相似文献
240.
Műllerová Monika Mazur Jadwiga Csordás Anita Holý Karol Grządziel Dominik Kovács Tibor Kozak Krzysztof Smetanová Iveta Danyłec Karolina Kureková Patrícia Nagy Erika Neznal Matej 《Journal of Radioanalytical and Nuclear Chemistry》2019,319(2):533-666
Journal of Radioanalytical and Nuclear Chemistry - An IAEA coordinated research project that began in 2012 and ended in 2016 was primarily dedicated to the compilation, evaluation and... 相似文献