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排序方式: 共有236条查询结果,搜索用时 15 毫秒
81.
Andresen GB Bertsche W Bowe PD Bray CC Butler E Cesar CL Chapman S Charlton M Fajans J Fujiwara MC Funakoshi R Gill DR Hangst JS Hardy WN Hayano RS Hayden ME Hydomako R Jenkins MJ Jørgensen LV Kurchaninov L Lambo R Madsen N Nolan P Olchanski K Olin A Povilus A Pusa P Robicheaux F Sarid E El Nasr SS Silveira DM Storey JW Thompson RI van der Werf DP Wurtele JS Yamazaki Y;ALPHA Collaboration 《Physical review letters》2008,100(20):203401
Control of the radial profile of trapped antiproton clouds is critical to trapping antihydrogen. We report the first detailed measurements of the radial manipulation of antiproton clouds, including areal density compressions by factors as large as ten, by manipulating spatially overlapped electron plasmas. We show detailed measurements of the near-axis antiproton radial profile and its relation to that of the electron plasma. 相似文献
82.
Riadh Kefi Erwann Jeanneau Frederic Lefebvre Cherif Ben Nasr 《Structural chemistry》2007,18(6):923-929
Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) Å3, Z = 1, and Dx = 1.565 g cm?3. The crystal structure has been determined and refined to R = 0.030 and R w(F 2) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H2PO4] n n? chains with (C6H16N2)2+ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, 13C and 31P MAS NMR spectroscopies and Ab initio calculations. 相似文献
83.
In this study, an efficient and green procedure is explained for the preparation of 1‐amidoalkyl‐2‐naphthols applying one‐pot condensation reaction of 2‐naphthol, amide and aromatic nanoparticles (Fe3O4@SiO2@IL‐PVP) as a novel solid acid catalyst under solvent‐free conditions. The remarkable features of this method are short reaction time, high conversions, and high yield of product, easy workup procedures and solvent‐free conditions. The Fe3O4@SiO2@IL‐PVP catalyst was characterized via Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction patterns (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), vibrating sample magnetometer (VSM), and energy‐dispersive X‐ray spectroscopy (EDS). Also, nanocatalysts could be easily recovered by a simple magnet and reused for the next reactions without significant loss of its catalytic activity. 相似文献
84.
The catalyst (N,N‐bis(2,6‐dibenzhydryl‐4‐ethoxyphenyl)butane‐2,3‐diimine)nickel dibromide, a late transition metal catalyst, was prepared and used in ethylene polymerization. The effects of reaction parameters such as polymerization temperature, co‐catalyst to catalyst molar ratio and monomer pressure on the polymerization were investigated. The α‐diimine nickel‐based catalyst was demonstrated to be thermally robust at a temperature as high as 90 °C. The highest activity of the catalyst (494 kg polyethylene (mol cat)?1 h?1) was obtained at [Al]/[Ni] = 600:1, temperature of 90 °C and pressure of 5 bar. In addition, the performance of a binary catalyst using nickel‐ and palladium‐based complexes was compared with that of the corresponding individual catalytic systems in ethylene polymerization. In a study of the catalyst systems, the average molecular weight and molecular weight distribution for the binary polymerization were between those for the individual catalytic polymerizations; however, the binary catalyst activity was lower than that of the two individual ones. The obtained polyethylenes had high molecular weights in the region of 105 g mol?1. Gel permeation chromatography analysis showed a narrow molecular weight distribution of 1.44 for the nickel‐based catalyst and 1.61 for the binary catalyst system. The branching density of the polyethylenes generated using the binary catalytic system (30 branches/1000 C) was lower than that generated using the nickel‐based catalyst (51/1000 C). X‐ray diffraction study of the polymer chains showed higher crystallinity with lower branching of the polymer obtained. Also Fourier transform infrared spectra confirmed that all obtained polymers were low‐density polyethylene. 相似文献
85.
Jaafar A. El-Awady Ming Wen Nasr M. Ghoniem 《Journal of the mechanics and physics of solids》2009,57(1):32-50
We present a computational study on the effects of sample size on the strength and plastic flow characteristics of micropillars under compression loading. We conduct three-dimensional simulations using the parametric dislocation dynamics coupled with the boundary element method. Two different loading techniques are performed. The plastic flow characteristics as well as the stress-strain behavior of simulated micropillars are shown to be in general agreement with experimental observations. The flow strength versus the diameter of the micropillar follows a power law with an exponent equal to -0.69. A stronger correlation is observed between the flow strength and the average length of activated dislocation sources. This relationship is again a power law, with an exponent -0.85. Simulation results with and without the activation of cross-slip are compared. Discontinuous hardening is observed when cross-slip is included. Experimentally observed size effects on plastic flow and work-hardening are consistent with a “weakest-link activation mechanism”. 相似文献
86.
87.
A.M. Kabiel A.M. Shoaeb F.I. Nasr Y.M. Ali 《Spectrochimica Acta Part B: Atomic Spectroscopy》1981,36(2):129-137
A satisfactory and accurate spectrographic analysis is obtained through the use of line width measurements. The precautions necessary to permit reasonably accurate application of the method are described. 相似文献
88.
Mannich reaction upon 4-hydroxy-2-methyl-7,8,9,10-tetrahydrobenzo[h]quinoline ( 1 ) as well as its nitration were studied. Condensation of the chloroquinoline 6b with sodium azide, benzylamine and ethanolamine gave the quinoline derivatives 6c, 6f and 6g , respectively. Phenylhydrazine and sodium borohydride effected reduction of the azidoquinoline 6c to the corresponding amino- and hydroxyamino derivatives 6d and 6e , respectively. Also, Turpin's reaction gave the benzoquinobenzoxazines 7a-d when applied to 6b . Treatment of 6f, 6g with alkali and the condensation of 6b with glycine in alcoholic sodium carbonate solution afforded the imidazo[4,5-c]quinoline derivatives 9a-c , respectively. 相似文献
89.
Mohamed Lahbib Mrad Souhir Belhajsalah Mohammed Said M. Abdelbaky Sergio García-Granda Khaled Essalah C. Ben Nasr 《Journal of Coordination Chemistry》2019,72(2):358-371
An investigation of the solid-state X-ray structure of the new organic–inorganic compound [C5H14N2]2PbCl6·3H2O shows a layered organization of the (PbCl6)4– anions, with (R2NH2)+ groups and water molecules developed in the [001] plane at x = (2n?+?1)/4. The crystal structure is stabilized by N???H···Cl, N???H···O, O???H···Cl, O???H···O, and C???H···Cl hydrogen bonds. The powder X-ray diffraction and X-ray photoelectron spectroscopic (XPS) analyses confirm the phase purity of the crystal sample. The intermolecular contacts are quantified using the Hirshfeld surfaces computational method. The major inter-contacts contributing to the Hirshfeld surfaces are H…Cl, H…H, and O…H. The vibrational modes were identified and assigned by IR and Raman spectroscopies. The optical properties were investigated by UV–visible and photoluminescence spectroscopic studies. The compound was characterized by thermal analysis to determine its thermal behavior with respect to the temperature. Finally, X-ray photoelectron spectroscopy analysis is reported for analyzing the surface chemistry of [C5H14N2]2PbCl6·3H2O. 相似文献
90.
Ahmed A. Abd El-Raady Nasr E. Fouad Mohamed A. Mohamed Samih A. Halawy 《Monatshefte für Chemie / Chemical Monthly》2002,133(10):1351-1361
Summary. Selective decomposition of ethanol was used as a test reaction at 350°C to evaluate the catalytic activity of two Al–Mg–O
mixed oxides prepared by two different methods (wet impregnation and coprecipitation). The catalyst precursors were examined
by TG and DTA and were calcined between 500–900°C for 5 h in air. The surface area of all catalysts was measured by N2 sorption using the BET method. The total acidity and basicity were determined by TPD using pyridine and formic acid. The
catalysts were characterized by XRD analysis. It was found that the preparation method of Al–Mg–O catalyst has a great effect
on the selective decomposition of ethanol. Al–Mg–O (I) catalysts, prepared by wet impregnation, were more selective towards
ethene formation during dehydration of ethanol. This is ascribed to their high total surface acidity. On the other hand, Al–Mg–O
(II) catalysts, prepared by coprecipitation, were highly selective in the oxidative dehydrogenation of ethanol to yield acetaldehyde.
This could be attributed to their high concentration of basic sites. In addition, the production of traces of diethyl ether
was also observed (three times more for Al–Mg–O (II) than for Al–Mg–O (I)).
Corresponding author. E-mail: shalawy99@yahoo.com
Received October 12, 2001. Accepted (revised) January 7, 2002 相似文献