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71.
André Eliezer Polloni Viviane Chiaradia Eduardo Moresco Figura João Pedro De Paoli Débora de Oliveira J. Vladimir de Oliveira Pedro Henrique Hermes de Araujo Claudia Sayer 《Applied biochemistry and biotechnology》2018,184(2):659-672
The demand for environmentally friendly products allied with the depletion of natural resources has increased the search for sustainable materials in chemical and pharmaceutical industries. Polyesters are among the most widely used biodegradable polymers in biomedical applications. In this work, aliphatic polyesters (from globalide and ω-pentadecalactone) were synthesized using a new commercial biocatalyst, the low-cost immobilized NS 88011 lipase (lipase B from Candida antarctica immobilized on a hydrophobic support). Results were compared with those obtained under the same conditions using a traditional, but more expensive, commercial biocatalyst, Novozym 435 (lipase B from C. antarctica immobilized on Lewatit VP OC). When NS 88011 was used in the polymerization of globalide, longer reaction times (240 min)—when compared to Novozym 435—were required to obtain high yields (80–90 wt%). However, higher molecular weights were achieved. When poly(ω-pentadecalactone) was synthesized, high yields and molecular weights (130,000 g mol?1) were obtained and the enzyme concentration showed strong influence on the polyester properties. This is the first report describing NS 88011 in polymer synthesis. The use of this cheaper enzymatic preparation can provide an alternative for polyester synthesis via enzymatic ring-opening polymerization. 相似文献
72.
María S. Di Nezio Marcelo F. Pistonesi Wallace D. Fragoso Mrcio J.C. Pontes Hctor C. Goicoechea Mrio C.U. Araujo e Beatriz S. Fernndez Band 《Microchemical Journal》2007,85(2):194-200
This paper proposes an analytical method to determine directly and simultaneously five phenolic compounds (4-nitrophenol, 2-nitrophenol, phenol, 2,4,6-trichlorophenol and 4-chlorophenol) in sea water (Ria de Bahía Blanca, Argentine). The advantages of this method is that only requires spectrophotometric measurements (separation steps and derivatization reagents are avoided) and chemometric modelling (PLS and MLR–SPA).The statistical comparison between PLS — a well established multivariate method — and MLR–SPA — a recently presented chemometric modelling — demonstrated better analytical performance for the later one. This fact is indicative of the potentiality of MLR–SPA for solving complex analytical problems. 相似文献
73.
Araujo E Rodríguez-Malave AJ González AM Rojas OJ Peñaloza N Bullón J Lara MA Dmitrieva N 《Applied biochemistry and biotechnology》2002,97(2):91-103
In this work, the effect of Fento’s reagent on the degradation of residual Kraft black liquor was investigated. The effect
of Fenton’s reagent on the black liquor degradation was dependent on the concentration of H2O2. At low concentrations (5 and 15 mM) of H2O2, Fenton’s reagent caused the degradation of phenolic groups (6.8 and 44.8%, respectively), the reduction of reaction medium
pH (18.2%), and the polymerization of black liquor lignin. At a high concentration (60 mM) of H2O2, Fenton’s reagent induced an extensive degradation of lignin (95–100%) and discoloration of the black liquor. In the presence
of traces of iron, the addition of H2O2 alone induced mainly lignin fragmentation. In conclusion, Fenton’s reagent and H2O2 alone can degrade residual Kraft black liquor under acidic conditions at room temperature. 相似文献
74.
M.A. Pimenta A.P. Gomes C. Fantini L.G. Canado P.T. Araujo I.O. Maciel A.P. Santos C.A. Furtado V.S.T. Peressinotto F. Plentz A. Jorio 《Physica E: Low-dimensional Systems and Nanostructures》2007,37(1-2):88
Resonance Raman and photoluminescence excitation (PLE) spectroscopies are used to study the optical properties of different types of carbon nanostructures such as carbon nanotube, nanoribbons, nanographites and graphite edges. In the resonance Raman experiments of carbon nanotubes, the (n,m) assignment is obtained by comparing the experimental and theoretical diameter and chirality dependence of the optical transitions. The influence of the environment on the optical transitions of the nanotubes is also obtained in the Raman experiments. The PLE measurements in different samples of carbon nanotubes show both direct and phonon-assisted optical transitions, and the results give new evidences that the optical transitions in nanotubes have an excitonic character, which is very strong for the low energy transitions. We also analyze the Raman spectra of nanoribbons and nanographites, showing that this technique is an important tool for defect characterization in graphitic materials, and can be used to distinguish the atomic structure of the graphite edges. 相似文献
75.
Oliveira BG Araujo RC Carvalho AB Ramos MN 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(3):626-631
B3LYP/6-311+G(d,p) calculations were used to explore the geometry, intermolecular energy and the vibrational harmonic spectrum of heterocyclic complexes formed between 2,5-dihydrofuran and thiophene cyclic ethers and the HCl and HF acids. The simulated structures of these hydrogen complexes are discussed in terms of the linearity deviation of the n...HX hydrogen bond. Theoretical results are satisfactory as compared to the experimental equilibrium structure. The energies of the hydrogen bonds were determinate through the difference between the complex and its correspondent isolated monomers. Moreover, to obtain the correct energies of the hydrogen bonds, it was included the values of the zero point vibrational energy and the basis set superposition error. The infrared spectra reveal the direct relationship between the distance of the hydrogen bond and its stretching frequencies, as well as a good interpretation of the bathochromic effect of the HCl and HF stretching modes from intermolecular charge transfer. 相似文献
76.
Sulene A. Araújo Antonio S. Araujo Nedja S. Fernandes Valter J. Fernandes Jr. Massao Ionashiro 《Journal of Thermal Analysis and Calorimetry》2010,99(2):465-469
The aim of this work is to determine the activation energy for the thermal decomposition of poly(ethylene terephthalate)—PET, in the presence of a MCM-41 mesoporous catalyst. This material was synthesized by the hydrothermal method, using cetyltrimethylammonium as template. The PET sample has been submitted to thermal degradation alone and in presence of MCM-41 catalyst at a concentration of 25% in mass (MCM-41/PET). The degradation process was evaluated by thermogravimetry, at temperature range from 350 to 500 °C, under nitrogen atmosphere, with heating rates of 5, 10 and 25 °C min?1. From TG, the activation energy, determined using the Flynn–Wall kinetic method, decreased from 231 kJ mol?1, for the pure polymer (PET), to 195 kJ mol?1, in the presence of the material (MCM-41/PET), showing the catalyst efficiency for the polymer decomposition process. 相似文献
77.
Fábio G. Lepri Rennan G.O. Araujo Bernhard Welz Frank Wendler Marcus Krieg Helmut Becker-Ross 《Talanta》2010,81(3):980-987
Reactivity and concentration of additives, especially activated charcoal, employed for the Lyocell process, enhance the complexity of reactions in cellulose/N-methylmorpholine-N-oxide monohydrate solutions. Analytical control of the starting materials is a basic requirement to know the concentration of heavy metals, which are potential initiators of autocatalytic reactions. Seven activated charcoal and two carbon black samples have been analyzed regarding their content of seven elements, Cr, Cu, Fe, Mn, Mo, Ni and V using direct solid sampling high-resolution continuum source graphite furnace AAS (SS-HR-CS GF AAS) and inductively coupled plasma optical emission spectrometry (ICP OES) after microwave-assisted acidic digestion as a reference method. The limits of detection of the former technique are 1-2 orders of magnitude lower than those of ICP OES and comparable to those of more sophisticated techniques. For iron the working range of HR-CS GF AAS has been expanded by simultaneous measurement at two secondary absorption lines (344,099 nm and 344,399 nm). Partial least-squares regression between measured and calculated temperatures for beginning exothermicity (Ton) has been used to investigate the prediction capability of the investigated techniques. Whereas the ICP OES measurements for seven elements resulted in an error of prediction of 3.67%, the results obtained by SS-HR-CS GF AAS exhibited a correlation coefficient of 0.99 and an error of prediction of only 0.68%. Acceptable correlation has been obtained with the latter technique measuring only three to four elements. 相似文献
78.
Rinaldo A. M. Vieira Leticia S. V. S. Su?é Carlos A. M. Pires Antonio O. S. Silva Marcelo J. B. Souza Antonio S. Araujo 《Reaction Kinetics and Catalysis Letters》2006,88(1):119-126
Summary The catalytic oxidation of phenol over CuZSM-12 (SAR = 200) has been studied using a semi-batch slurry reactor at temperatures
of 110; 120 and 130oC, and acidic neutral and basic pH. At 130oC, the phenol undergoes total conversion to carbon dioxide and water in 1.5 h. The kinetic parameters were evaluated using
a modified homogeneous-heterogeneous model for the experimental data. Using this modified model, the activation energy for
the catalytic oxidation process was ca. 90 kJ mol-1. 相似文献
79.
Araujo M. Lucia G. C. Giordano Roberto C. Hokka Carlos O. 《Applied biochemistry and biotechnology》1998,(1):493-504
Cells ofCephalosporium acretnonium ATCC 48272 immobilized in calcium alginate beads were utilized for cephalosporin C production and the results were compared
with those obtained with free cells. The experiments were performed with synthetic medium containing glucose and sucrose as
carbon and energy sources. Experimental effectiveness factor values were obtained at various cell and dissolved-oxygen concentrations,
considering Monod kinetics for the respiration rate, and were compared with the values calculated with zero-order kinetics
in spherical bioparticle. The results showed that the assumption of oxygen limitation by diffusion in the bioparticle was
correct, and that cephalosporin C production with immobilized cells is perfectly viable, although a slightly lower rate than
that obtained in the free cell process was observed. 相似文献
80.
Determination of pyrimethanil and kresoxim-methyl in soils by headspace solid-phase microextraction and gas chromatography-mass spectrometry 总被引:1,自引:0,他引:1
Navalón A Prieto A Araujo L Vílchez JL 《Analytical and bioanalytical chemistry》2004,379(7-8):1100-1105
A method using headspace solid-phase microextraction (HS-SPME) then gas chromatography–mass spectrometry with selected ion monitoring (GC–MS, SIM) has been developed for determination of trace amounts of the fungicides pyrimethanil and kresoxim-methyl in soil and humic materials. Both fungicides were extracted on to a fused-silica fibre coated with 85 m polyacrylate (PA). Response-surface methodology was used to optimise the experimental conditions. For soil samples the linear dynamic range of application was 0.004–1.000 g g–1 for pyrimethanil and 0.013–1.000 g g–1 for kresoxim-methyl. The detection limits were 0.001 g g–1 and 0.004 g g–1 for pyrimethanil and kresoxim-methyl, respectively. HP-SPME–GC–MS analysis was highly reproducible—relative standard deviations (RSD) were between 6.7 and 12.2%. The method was validated by analysis of spiked matrix samples and used to investigate the presence of pyrimethanil and kresoxim-methyl above the detection limits in soil and humic materials. 相似文献