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排序方式: 共有108条查询结果,搜索用时 31 毫秒
21.
Guimaraes Giulia A. A. Lacerda Janiny N. Xing Yutao Ponzio Eduardo A. Pacheco Wagner F. Semaan Felipe S. Dornellas Rafael M. 《Journal of Solid State Electrochemistry》2020,24(8):1769-1779
Journal of Solid State Electrochemistry - This work presents the development and characterization of an electrochemical sensor of tin hexacyanoferrate (SnHCF), produced from the modification by... 相似文献
22.
Roy MD Herzing AA De Paoli Lacerda SH Becker ML 《Chemical communications (Cambridge, England)》2008,(18):2106-2108
Water soluble CdSe/ZnS nanoparticles with emission maxima from 511 nm to 596 nm and quantum efficiencies ranging from 11% to 28% are synthesized in a facile two-step method in ambient atmospheric conditions using a commercially available microwave reactor. 相似文献
23.
M.B. Lacerda Santos M.A. Amato 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,7(3):393-400
Using a light-beating technique we have measured the damping time of thermal fluctuations of the nematic director for the
so called cylindrical or calamitic nematic (NC) phase of the lyotropic system K-laurate/decanol/. By varying the scattering angle in suitable geometries, we have been able to estimate the orientational diffusivities associated
to the three pure deformations of splay, twist and bend. A former measurement made in the disk-like ND phase of the same system yielded a large deviation between the splay and twist diffusivities. The effect was then attributed
to induced flows, or backflow, which could be responsible for the reduction of the splay viscosity. In fact, this is the analogous
effect, for disks, to the one recognized since long time ago arriving for rod-like molecules in a classical nematic, though
in this case it is associated with bend deformations. The analogy comes about thanks to the interchange of the role played
by disks and cylinders for, respectively, splay and bend fluctuations.The measurements reported here provide a new test on
the applicability of the backflow model to a nematic system composed of micelles, that is, aggregates made of amphiphilic
(surfactant) molecules, in its cylindrical-like variant, i.e. the NC phase. In addition, the comparative study made here with the previous results existing in the literature for the ND phase, allows us to conjecture on structural issues concerning lyotropic nematics.
Received: 29 April 1998 / Revised: 19 August 1998 / Accepted: 31 August 1998 相似文献
24.
This paper proposes a three-dimensional system for modelling stress in thin films deposited on plane substrates much thicker than the film itself. The approach is the minimization of the deformation energy of the sample (substrate + film), considering the deformed substrate as a small spherical surface with large curvature radius. Results of the model show the validity limits of the well-established Stoney equation that satisfy the upper theoretical limit of Poisson ratio (ν) for isotropic materials. Our main result is that the stress values obtained in general literature using Stoney equation are underestimated when considering a typical Poisson ratio for substrates in the range of 0.25 ≤ νs ≤ 0.4. 相似文献
25.
Ana Luiza Coeli Cruz Ramos Laiza Andrade Nogueira Mauro Ramalho Silva Ana Carolina do Carmo Mazzinghy Ana Paula Xavier Mariano Tssia Nunes de Albuquerque Rodrigues Ana Cardoso Clemente Filha Ferreira de Paula Angelita Cristine de Melo Rodinei Augusti Raquel Linhares Bello de Araújo Inayara Cristina Alves Lacerda Júlio Onsio Ferreira Melo 《Molecules (Basel, Switzerland)》2022,27(15)
Grumixama (Eugenia brasiliensis Lam.) is a native fruit of the Brazilian Atlantic Forest, belonging to the Myrtaceae family, which designatesthe most significant number of species with food potential. It stands out due to its phytochemical characteristics because of the presence of polyphenols and volatile organic compounds. Volatile compounds are substances released by foods that give off an aroma and influence flavor. Solid-phase microextraction is a technique that allows for low-cost, fast, and solvent-free extraction, has an affinity for numerous analytes, and is easily coupled to gas chromatography. The objectives of this work were to evaluate the efficiency of different fibers of SPME (solid-phase microextraction) in the extraction of volatile organic compounds from grumixama pulp; optimize a method for extraction time, temperature, and sample weight; and to determine the characteristic volatile profile of this fruit. For the extraction of volatile compounds, three fibers of different polarities were used: polar polyacrylate (PA) fibers, divinylbenzene/carboxyne/polydimethylsiloxane (DVB/CAR/PDMS) semipolar fibers, and polydimethylsiloxane/divinylbenzene (PDMS/DVB). Fourteen volatile organic compounds (VOCs) were identified by DVB/CAR/PDMS, six by PA, and seven by PDMS/DVB through solid-phase microextraction in the headspace mode (SPME-HS). Considering the total number of compounds identified, regardless of the fiber used, and the optimization of the method, Eugenia brasiliensis presented sesquiterpene fractions (85.7%, 83.3%, and 85.7% of total VOCs) higher than the monoterpene fractions (14.3%, 16.7%, and 14.3%) for DVB/CAR/PDMS, PA, and PDMS/DVB, respectively in its composition. In addition, it was possible to verify that the fiber DVB/CAR/PDMS presented a better efficiency due to the larger chromatographic area observed when the grumixama pulp was subjected to conditions of 75 °C, 2.0 g, and an adsorption time of 20 min. 相似文献
26.
Luís J. de Lacerda Neto A. G. B. Ramos M. R. Kerntopf L. J. Quintans-Junior J. R. G. S. Almeida 《Natural product research》2018,32(4):477-480
The aim of this study was to identify the presence of tannins, phenols and flavonoids on the hydroalcoholic extract of Caryocar coriaceum leaves (HECCL) and to determine the antioxidant and antibacterial activity of this extract. The extract was tested alone (1024–1 μg/mL) or associated (MIC/8) with several antibiotics in order to identify any antibacterial activity against multiresistant bacterial strains (Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa). The existence of tannins, total phenols (901.31 mg/g) and flavonoids (89.68 mg/g) was confirmed in the HECCL. The presence of rutin and quercetin were confirmed by Thin-layer chromatography (TLC). Using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method, the antioxidant activity of the extract (9 μg/mL) was determined. Moreover, the Minimum Inhibitory Concentration (MIC) value found for HECCL was 1024 μg/mL and the association between HECCL (MIC/8) with benzylpenicillin significantly changed its minimum inhibitory concentration from 2500 to 625 μg/mL against E. coli. 相似文献
27.
28.
The conceptual basis for the development of mitochondrial targeting as a novel therapeutic strategy for both chemotherapy and photochemotherapy of neoplastic diseases rests on the observation that enhanced mitochondrial membrane potential is a common tumor cell phenotype. The potential of this strategy is highlighted by the fact that the toxic effects associated with a number of cationic dyes known to localize in energized cell mitochondria are much more pronounced in tumor cells than in normal cells. Here we evaluate the phototoxic properties of four bromine derivatives of rhodamine-123 toward human uterine sarcoma (MES-SA) and green monkey kidney (CV-1) cells and compare the degrees of tumor cell selectivity associated with these dyes with those associated with two model mitochondrial triarylmethanes (crystal violet and ethyl violet). Selective phototoxicity toward tumor cells was found to be highly dependent upon the lipophilic/hydrophilic character of the cationic photosensitizer. Our experimental data have indicated that the probability of success of mitochondrial targeting in (photo)chemotherapy of neoplastic diseases is higher when the octan-1-ol/water partition coefficient of the drug candidate falls within approximately two orders of magnitude from that of the prototypical mitochondria-specific dye rhodamine-123. 相似文献
29.
Roberta C. Salles Valdemar Lacerda Jr Adilson Beatriz Felicia M. Ito Reginaldo B. dos Santos Sandro J. Greco Eustáquio V. R. de Castro Dênis P. de Lima 《Magnetic resonance in chemistry : MRC》2010,48(5):409-415
Bioactive cage‐like polycyclic compounds have attracted the attention of several research groups because of their unique appearance and their biological activities. Their structures were established on the basis of 1H NMR and 13C NMR spectroscopic data. The 1H and 13C signal assignments and most homonuclear hydrogen coupling constants were assigned by use of techniques such as 1D 1H and 13C NMR and 2D gCOSY, non‐edited gHSQC and gHMBC. The gNOESY experiments proved the endo‐stereochemistry. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
30.
M. Paula C. Campello Dr. Sara Lacerda Dr. Isabel C. Santos Dr. Giovannia A. Pereira Dr. Carlos F. G. C. Geraldes Prof. Dr. Jan Kotek Dr. Petr Hermann Dr. Jakub Vaněk Přemysl Lubal Vojtěch Kubíček Dr. Éva Tóth Isabel Santos Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(28):8446-8465
Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p, H6 L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H4dota and H8dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several LnIII–H6 L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H2O)]3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the 1H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H2O)]2? and [Yb(H L )]2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between 31P/1H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N4 and O4 planes. 相似文献