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61.
Leggio C Galantini L Zaccarelli E Pavel NV 《The journal of physical chemistry. B》2005,109(50):23857-23869
Small-angle X-ray scattering (SAXS) together with static (SLS) and dynamic light scattering (DLS) measurements were carried out on aqueous solutions of lysozyme (LY) and of the ionic biological detergent sodium glycocholate (NaGC). Apparent diffusion coefficients (D app), excess Rayleigh ratio, and SAXS spectra were measured for 0.1 M NaGC solutions at different ionic strengths (0.05-0.30 M NaCl). The same data were collected for LY in sodium acetate buffer 50 mM without and with 92 mM NaCl as a function of protein concentration (10-80 g L(-1)). A correlated analysis of SLS data and SAXS spectra was first tested on the LY samples and then extended to the interpretation of the NaGC data to infer information on particle structure and interaction potential. A hard-core (HC) interaction shell of uniform thickness, a screened Coulomb potential of the electric double layer (EDL) or the complete DLVO potential were alternatively used to represent the long-range tail of the interaction potential. Whenever an essentially repulsive tail is expected, all the representations give reasonable results, but the data analysis does not allow the discrimination between the oblate and the prolate symmetries of the NaGC aggregates. The DLVO model allows the interpretation of the data even when the attractive component determines the tail character. With this model an overall fit of the micelle data at all the NaCl concentrations was successfully performed by assuming a simple spherical symmetry of the micelles and invariant values of their ionization degree and Hamaker constant, thus considering just the screening effect of the added electrolyte. Whatever model is used, the results point out that the aggregates are quite hydrated (26-38 water molecules per monomer) and very slightly grow by increasing the NaCl concentration. When spherical symmetry is assumed the aggregate radii for all the samples fall in the range 15-16 A. From the SAXS and SLS, best fitting geometrical parameters, and interparticle structure factor, a D app value was calculated for each sample. An excellent consistence is achieved for LY results. On the contrary, calculated D app values systematically lower than the experimental values are always obtained for the NaGC micelles. Micelle polydispersity and internal dynamics seem to be the most probable reasons of the bad agreement. 相似文献
62.
Rusu Mihai Lucian Marutoiu Constantin Sandu Ion Tita Dumitru Gogoasa Ioan Barbu Constantin-Horia Popescu Andreea 《平面色谱法杂志一现代薄层色谱法》2007,20(2):139-140
JPC – Journal of Planar Chromatography – Modern TLC - Samples of clove, nutmeg, and cinnamon have been extracted by maceration with ethanol for 24 h and with aqueous ethanol 48 h.... 相似文献
63.
Chillemi G D'Angelo P Pavel NV Sanna N Barone V 《Journal of the American Chemical Society》2002,124(9):1968-1976
In this paper we have developed an effective computational procedure for the structural and dynamical investigation of ions in aqueous solutions. Quantum mechanical potential energy surfaces for the interaction of a transition metal ion with a water molecule have been calculated taking into account the effect of bulk solvent by the polarizable continuum model (PCM). The effective ion-water interactions have been fitted by suitable analytical potentials, and have been utilized in molecular dynamics (MD) simulations to obtain structural and dynamical properties of the ionic aqueous solutions. This procedure has been successfully applied to the Co2+-H2O open-shell system and, for the first time, Co-oxygen and Co-hydrogen pair potential functions have been determined and employed in MD simulations. The reliability of the whole procedure has been assessed by applying it also to the Zn2+ and Ni2+ aqueous solutions, and the structural and dynamical properties of the three systems have been calculated by means of MD simulations and have been found to be in very good agreement with experimental results. The structural parameters of the first solvation shells issuing from the MD simulations provide an effective complement to extended X-ray absorption fine structure (EXAFS) experiments. 相似文献
64.
Vincenza Maria Coiro Edoardo Giglio Fernando Mazza Nicolae Viorel Pavel 《Journal of inclusion phenomena and macrocyclic chemistry》1984,1(4):329-337
The 2:1 inclusion compound formed between deoxycholic acid (C24H40O4,M
r=392.58) and quadricyclane (C7H8,M
r=92.14) crystallizes in space groupP212121 witha=27.150(7),b=13.359(3),c=14.161(4) Å,Z=4. The structure was refined toR=0.086 andR
w=0.088 for 2079 observed reflections withI>2.5(I). The crystal packing is very similar to that found in the norbornadiene-deoxycholic acid inclusion compound and is characterized by an assembly of antiparallel pleated bilayers, formed by molecules of deoxycholic acid held together through hydrogen bonds. Quadricyclane occupies approximately the same position of norbornadiene and its atoms give rise to good van der Waals interactions with some methyl groups of deoxycholic acid.
Supplementary Data relating to the article are deposited with the British Library as Supplementary Publication No. SUP 82006 (14) pages. To obtain copies, see page ii of this issue. 相似文献
65.
66.
Florentina L. Chiriac Monica Ili Augustin Madalan Doina Manaila-Maximean Mihail Secu Viorel Cîrcu 《Molecules (Basel, Switzerland)》2021,26(7)
This work focuses on the investigation of the liquid crystalline behavior and luminescence properties of the lanthanide complexes of Eu(III), Sm(III) and Tb(III) with N-biphenyl-alkylated-4-pyridone ligands. The organic ligands having a biphenyl group attached via a long flexible spacer with either 9 or 10 carbon atoms were synthesized by the reaction between 4-hydroxypyridine and the corresponding bromide compounds. The chemical structures of the organic and lanthanide complexes were assigned based on elemental analysis, single-crystal X-ray diffraction, 1H, 13C NMR and IR spectroscopies, and thermogravimetric analysis (TGA). The X-ray diffraction analysis of a parent compound shows that the lanthanide ions are surrounded by three monodentate pyridone ligands and three bidentate nitrate ions, giving a 9-coordinate environment. The mesogenic behavior and the type of liquid crystalline phases exhibited by the new complexes were analyzed by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM), and powder X-ray diffraction (XRD) studies. Only the lanthanide complexes with longer spacer (10) display a monotropic SmA phase, typically on a short thermal range (less than 10 °C). The complexes with shorter flexible chains (9) show no liquid crystalline properties with melting temperatures lower than their analogs with longer spacers. The emission spectra recorded in solid state at room temperatures show typical emission bands for each lanthanide ion employed (Eu(III), Tb(III) and Sm(III)). 相似文献
67.
Marcela Stoia Mirela Barbu Mircea ?tef?nescu Paul Barvinschi Lucian Barbu-Tudoran 《Journal of Thermal Analysis and Calorimetry》2012,110(1):85-92
In this article, we present a detailed study regarding the preparation of nanosized zinc and magnesium chromites starting from a 4% poly(vinyl)alcohol (PVA) aqueous solution and metal nitrates. The controlled thermal treatment of these solutions has permitted the isolation of an intermediary solid product, used as precursor of the preferred mixed oxides: zinc and magnesium chromites. The as-obtained precursors were characterized by FT-IR spectrometry and thermal analysis. FT-IR spectrometry has evidenced the disappearance of the NO3 ? anions at 140?°C, due to the redox interaction with PVA. The thermal decompositions of the synthesized precursors were different, as resulted from both thermal analysis and FT-IR spectrometry. Thus, while ZnCrPVA precursor decomposes up to 400?°C with formation of zinc chromite, the precursor MgCrPVA decomposes up to 500?°C, with formation of MgCrO4 as intermediary amorphous phase. By thermal decomposition of MgCrO4 at 500?°C, weakly crystallized MgCr2O4 powder is obtained. The obtained chromite powders consist of fine nanoparticles with diameters ranging from 10 to 30?nm at 500?°C; on raising the annealing temperature to 1000?°C, chromite particles become octahedral, with diameter up to 500?nm, but with no sign of sintering. 相似文献
68.
Emilian Georgescu Florea Dumitrascu Florentina Georgescu Constantin Draghici Loredana Barbu 《Journal of heterocyclic chemistry》2013,50(1):78-82
New indolizine derivatives were synthesized by an efficient one‐pot three‐component procedure starting from commercially available materials such as 2,2′‐dipyridyl, substituted bromoacetophenones, and electron‐poor alkynes in 1,2‐epoxybutane as reaction solvent and acid scavenger. 相似文献
69.
We look into the operator of acoustic propagation H := -V . pV,with Dirichlet condition, in a domain R := 0' x IR, 0' being boundedin Rn-'(n > 2). The function p is assumed to be real, greater than astrictly positive constant and belongs to Lm(R). When (-1)3x, + oo itis obtained by short-range and long-range perturbations of the functionspi = p(j) @ l(j = 1,2), where E Lm(R') are real and bounded belowby a strictly positive constant. By using a variant of the conjugateoperator method of Mourre [15], and some ideas of the N-body problem in quantum mechanics, we develop the spectral analysis of operator H and obtain a limiting absorption principle. 相似文献
70.
Birthe V. Nielsen Thomas G. Nevell Eugen Barbu Gareth D. Rees John Tsibouklis 《Journal of Thermal Analysis and Calorimetry》2010,102(1):121-126
A thermogravimetric (TG) method is described for evaluating the substantivity of multi-functional polymeric materials that
may be used as protective coatings for teeth. Applied to poly(butyl methacrylate) and poly(octadecyl methacrylate) film structures
deposited onto model tooth surfaces from aqueous latex formulations, the method shows that while the latter polymer exhibits
little substantivity, the former may be a suitable candidate material for dental-care applications. 相似文献