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111.
Luis?Alberto?B.?Moraes Ad?o?A.?Sabino Eduardo?C.?Meurer Marcos?N.?EberlinEmail author 《Journal of the American Society for Mass Spectrometry》2005,16(4):431-436
A general method based solely on mass spectrometric techniques for the absolute configuration assignment of ortho, meta, or para isomers of acyl nitrobenzenes and derivatives is described. Instead of comparing the mass spectra of the three intact molecules
of each positional isomer and investigating each one of the many sets of positional isomers, the method generalizes the effort
by performing structural analysis on configurationally diagnostic fragment ions that are common for a given class of compounds.
These ions must therefore retain the positional information of the parent molecules and be unequivocally distinguished. Nitrobenzoyl
cations are common and stable fragment ions of most acyl nitrobenzenes and derivatives retaining the respective ortho, meta, or para configuration of the precursor molecules. The different NO2 and CO+ ring alignments profoundly influence their collision-induced dissociation and bimolecular reactivity, and the isomeric 2-,
3-, and 4-nitrobenzoyl cations are found to be unequivocally distinguished using both approaches. Absolute ortho, meta, or para positional assignment by tandem MS of every isomeric molecule of the acyl nitrobenzene class and derivatives forming detectable
amounts of any of those diagnostic nitrobenzoyl cations is, therefore, possible. The ability to perform absolute (non-comparative)
configuration assignment using such diagnostic ions is exemplified for a single test molecule of (2R)-(−)-2-methylglycidyl
4-nitrobenzoate. The general application of this absolute MS-only method for other classes of positional isomers is discussed. 相似文献
112.
A simple procedure was developed for the direct determination of As(III) and As(V) in water samples by flow injection hydride generation atomic absorption spectrometry (FI–HG–AAS), without pre-reduction of As(V). The flow injection system was operated in the merging zones configuration, where sample and NaBH4 are simultaneously injected into two carrier streams, HCl and H2O, respectively. Sample and reagent injected volumes were of 250 μl and flow rate of 3.6 ml min−1 for hydrochloric acid and de-ionised water. The NaBH4 concentration was maintained at 0.1% (w/v), it would be possible to perform arsine selective generation from As(III) and on-line arsine generation with 3.0% (w/v) NaBH4 to obtain total arsenic concentration. As(V) was calculated as the difference between total As and As(III). Both procedures were tolerant to potential interference. So, interference such as Fe(III), Cu(II), Ni(II), Sb(III), Sn(II) and Se(IV) could, at an As(III) level of 0.1 mg l−1, be tolerated at a weight excess of 5000, 5000, 500, 100, 10 and 5 times, respectively. With the proposed procedure, detection limits of 0.3 ng ml−1 for As(III) and 0.5 ng ml−1 for As(V) were achieved. The relative standard deviations were of 2.3% for 0.1 mg l−1 As(III) and 2.0% for 0.1 mg l−1 As(V). A sampling rate of about 120 determinations per hour was achieved, requiring 30 ml of NaBH4 and waste generation in order of 450 ml. The method was shown to be satisfactory for determination of traces arsenic in water samples. The assay of a certified drinking water sample was 81.7±1.7 μg l−1 (certified value 80.0±0.5 μg l−1). 相似文献
113.
Paredes-Gamero EJ França JP Moraes AA Aguilar MO Oshiro ME Ferreira AT 《Journal of fluorescence》2004,14(6):711-722
Fura-2 is one of the most used fluorophore for measuring intracellular calcium concentration ([Ca2+]i). In mouse bone marrow cell suspensions ATP produces a biphasic effect: till 1 mM, ATP produces increases in [Ca2+]i; from 1 mM on an increase is observed, that is followed by the decrease in the 340/380 nm ratio (R340/380). At high ATP (4 mM) concentration fura-2 leaked from loaded bone marrow cell suspensions. We observed that ATP decreases fluorescence in the absorption and excitation spectra of fura-2, consequently the emitted one is decreased including the isobestic point (360 nm). ATP analogs: BzATP, ATPyS and UTP, but not alphabetaATP, ADP or AMP, promote decrease of fluorescence in the isobestic point of fura-2. The physical/chemical process that reduces the absorption and excitation of fura-2 by ATP is unknown. The P2X7 inhibitors, Mg2+ (5 mM), OxATP (300 microM) and Brilliant Blue (100 nM), blocked the efflux of fura-2 and ATP-induced R340/380 decrease. The J774 cell line and mononuclear cells with a higher expression of P2X7 receptors show the same decrease in R340/380 as that induced by ATP. In the HL-60 cell line, myeloid cells and erythroblasts extracted from bone marrow, such effect does not occur. It is concluded that the use of the fluorescent Ca2+ indicator fura-2 does not allow the correct measurement of [Ca2+]i in these cells in the presence of a higher concentration of ATP which activated the P2X7 receptor. 相似文献
114.
Alechia Crown Ines R. Moraes Andrzej Wieckowski 《Journal of Electroanalytical Chemistry》2001,500(1-2)
Ruthenium and osmium were deposited in submonolayer amounts on Pt(111) single crystal surfaces using the previously reported ‘spontaneous deposition’ procedure [Chrzanowski et al., Langmuir, 13 (1997) 5974]. Such surfaces were first explored using ex situ scanning tunneling microscopy (STM) to image the deposition characteristics of ruthenium and osmium islands on Pt(111). It was found that, using the spontaneous deposition procedure, a maximum coverage of 0.20 ML ruthenium is formed on the surface after 120 s of exposure to a RuCl3 solution in 0.1 M HClO4. A homogeneous deposition on the Pt(111) surface was found, with no observed preferential deposition on step edges or surface defect sites. In contrast, in the spontaneous deposition of osmium, osmium clusters form preferentially at, though not limited to, surface defect sites and step edges. Osmium island deposition occurs at a greater rate than ruthenium on Pt(111), and possible explanations are presented. Methanol activity on the Pt(111)/Ru and Pt(111)/Os surfaces is also studied, using the coverage values determined to yield the highest activity for methanol electro-oxidation (0.20 ML coverage for Ru and 0.15 ML for Os). At potentials more negative than 0.40 V vs. RHE, the Pt(111)/Ru surface yields a higher surface activity than Pt(111)/Os. However, at potentials more positive than 0.04 V, Pt(111)/Os exhibits demonstrably higher surface activity. The relevance of this data is discussed and future avenues of interest are indicated. 相似文献
115.
Matioli Graciette Zanin Gisella M. De Moraes Flávio F. 《Applied biochemistry and biotechnology》2001,91(1-9):643-654
The enzyme cyclod extringly cosyltransferase (CGTase), EC2.4.1.19, which produces cyclodextrins (CDs) from starch, was obtained
from Bacillus firmus strain no. 37 isolated from Brazilian soil and characterized in the soluble form using as substrate 100 g/L of maltodextrin
in 0.05 M Tris-HCl buffer, 5 mM CaCl2, and appropriate buffers. Enzymatic activity and its activation energy were determined as a function of temperature and pH.
The activation energy for the production of β- and γ-CD was 7.5 and 9.9 kcal/mol, respectively. The energy of deactivation
was 39 kcal/mol. The enzyme showed little thermal deactivation in the temperature range of 35–60°C, and Arrhenius-type equations
were obtained for calculating the activity, deactivation, and half-life as a function of temperature. The molecular weight
of the enzyme was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, giving 77.6k Da. Results for CGTase
activity as a function of temperature gave maximal activity for the production of β-CD at 65°C, pH 6.0, and 7 1.5 mmol of
β-CD/(min·mg of protein), whereas for γ-CD it was 9.1 m mol of γ-CD/(min·mg of protein) at 70°C and pH 8.0. For long contact
times, the bestuse of the enzymatic activity occurs at 60°C oratalower temperature, and the reaction pH may be selected to
increase the vield of a desired CD. 相似文献
116.
Pereira Ernandes B. De Castro Heizir F. De Moraes Flávio F. Zanin Gisella M. 《Applied biochemistry and biotechnology》2001,91(1-9):739-752
The search for an in expensive support has motivated our group to undertake this work dealing with the use of chitosan as
matrix for immobilizing lipase. In addition to its low cost, chitosan has several advantages for use as a support, including
its lack of toxicity and chemical reactivity, allowing easy fixation of enzymes. In this article, we describe the immobilization
of Canada rugosa lipase onto porous chitosan beads for the enzymatic hydrolysis of oliveoil. The binding of the lipase onto the support was
performed by physicalad sorption using hexane as the dispersion medium. A comparativestudy between free and immobilized lipase
was conducted in terms of pH, temperature, and thermal stability. A slightly lower value for optimum pH (6.0) was found for
the immobilized form in comparison with that attained for the soluble lipase (7.0). The optimum reaction temperature shifted
from 37°C for the free lipase to 50°C for the chitosan lipase. The patterns of heat stability indicated that the immobilization
process tends to stabilize the enzyme. The half-life of the soluble free lipase at 55°C was equal to 0.71 h (K
d=0.98 h−1), whereas for the immobilized lipase it was 1.10 h (K
d=0.63 h−1). Kinetics was tested at 37°C following the hydrolysis of olive oil and obeys the Michaelis-Menten type of rate equation.
The K
m was 0.15 mM and the V
max was 51 μmol/(min·mg), which were lower than for free lipase, suggesting that the apparent affinity toward the substrate changes
and that the activity of the immobilized lipase decreases during the course of immobilization. 相似文献
117.
Natalia Canhete de Moraes Eiva Natiele Tiago da Silva Jacqueline Marques Petroni Valdir Souza Ferreira Bruno Gabriel Lucca 《Electrophoresis》2020,41(5-6):278-286
This paper describes the development of a novel, simple, and inexpensive electrochemical device containing an integrated and disposable three-electrode system for detection. The base of this platform consists on a PDMS structure containing microchannels which were prototyped using 3D-printed molds. Pencil graphite leads were inserted into these microchannels and utilized as working, counter and reference electrodes in a novel design. Morphological analysis and electrochemical experiments with benchmark redox probes were carried out in order to evaluate the performance and characterize the miniaturized device proposed. Even using inexpensive materials and a simple fabrication protocol, the electrochemical platform developed provided good repeatability and reproducibility over a low cost (ca. $2 per device), acceptable lifetime (ca. 250 voltammetric runs) and extremely reduced consumption of samples and reagents (order of µL). As proof of concept, the analytical feasibility of the platform was investigated through the simultaneous determination of dopamine (DOPA) and acetaminophen (AC). The two analytes showed linear dependence on the concentration range from 1 to 15 µM and the LODs achieved were 0.21 µM for DOPA and 0.29 µM for AC. Moreover, the platform was successfully applied on the determination of DOPA and AC in spiked blood serum and urine samples. The results obtained with the device described here were better than some reports in literature that use more costly electrodic materials and complex modification steps for the detection of the same analytes. 相似文献
118.
Sébastien Fumeron Bertrand Berche Fernando Moraes Fernando A. N. Santos Erms Pereira 《The European Physical Journal B - Condensed Matter and Complex Systems》2017,90(5):95
The presence of topological defects in a material can modify its electrical, acoustic or thermal properties. However, when a group of defects is present, the calculations can become quite cumbersome due to the differential equations that can emerge from the modeling. In this work, we express phonons as geodesics of a 2 + 1 spacetime in the presence of a channel of dislocation dipoles in a crystalline environment described analytically in the continuum limit with differential geometry methods. We show that such a simple model of 1D array of topological defects is able to guide phonon waves. The presence of defects indeed distorts the effective metric of the material, leading to an anisotropic landscape of refraction index which curves the path followed by phonons, with focusing/defocusing properties depending on the angle of the incident wave. As a consequence, using Boltzmann transfer equation, we show that the defects may induce an enhancement or a depletion of the elastic energy transport. We comment on the possibility of designing artificial materials through the presence of topological defects. 相似文献
119.
120.
Alex Neves Junior Romildo Dias Toledo Filho Eduardo de Moraes Rego Fairbairn Jo Dweck 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1577-1584
During the formation of pastes, mortar and concretes have been used to capture CO2. This work presents a methodology to estimate the carbon dioxide (CO2) sequestered by high strength and sulfate-resistant Portland cement pastes during their early stages of hydration, by Thermogravimetry and Derivative Thermogravimetry. Water to cement ratio equal to 0.50 and 0.70 were evaluated and the captured CO2 amount was determined through TG/DTG curve data on initial cement mass basis, obtained during accelerated carbonation from the fluid state and accelerated carbonation after a first hydration process. The experiments were performed in a controlled chamber, maintaining the CO2 content at 20 vol % and the temperature at 25 °C, at different relative humidity (RH) (60 and 80 %) ambient. The procedure allows one to estimate the amount of CO2 sequestered by the initial cement mass of a given volume of paste, as well as to evaluate the RH and W/C ratio influence on the amount of hydrated formed products, mainly on the Ca(OH)2, important for CO2 fixation. 相似文献