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21.
Bioassay-directed fractionation of an ethyl acetate extract (mycelia and broth) of the fungus Malbranchea aurantiaca led to the isolation of the novel phytotoxic alkaloid (5aS,12aS,13aS)-8,9-dichloro-12,12-dimethyl-2,3,11,12,12a,13-hexahydro-1H,6H-5a,13a (epiminomethano)indolizino[7,6b]carbazol-14-one (1) of the brevianamide series. The phytotoxin was given the trivial name of malbrancheamide (1). The structure of 1 was unequivocally established by UV, NMR, MS and X-ray studies. The absolute configuration was established by X-ray analysis according to the method of Flack. According to the conformational studies using molecular mechanics analyses, 1 exists in one preferred conformation, which was optimized by DFT calculations. Compound 1 caused moderate inhibition of radicle growth of Amaranthus hypochondriacus (IC50=0.37 μM) and inhibited the activation of the calmodulin-dependent enzyme PDE1 (IC50=3.65±0.74 μM). This effect was comparable to that of chlorpromazine (IC50=2.75±0.87 μM) a well characterized CaM antagonist. The inhibition mechanism of 1 was competitive with respect to CaM according to a kinetic analysis. 相似文献
22.
García F Moreno E Solano J Barragán M Sotomayor A Fuentes M Acevedo P 《Ultrasonics》2006,44(Z1):e307-e312
This paper describes the design of a continuous wave blood flow bi-directional Doppler system based on an open, high-resolution architecture that is portable and low cost. The system incorporates the advantages of expensive systems with dedicated hardware. The system is composed of a flow detector probe, a signal conditioning stage, a direction detection module, a signal processing stage and a graphic user interface. The direction detection of the signal is achieved using a fast digital phasing filter. The Doppler signal is processed using a short-time Fourier transform-based algorithm. This is commonly used as a reference. Nevertheless, the system allows us to incorporate alternative high-resolution spectral estimation methods that might offer more precise information to the specialist. 相似文献
23.
Sasha Alzate Acevedo lvaro Jos Díaz Carrillo Edwin Flrez-Lpez Carlos David Grande-Tovar 《Molecules (Basel, Switzerland)》2021,26(17)
Banana is a fruit grown mainly in tropical countries of the world. After harvest, almost 60% of banana biomass is left as waste. Worldwide, about 114.08 million metric tons of banana waste-loss are produced, leading to environmental problems such as the excessive emission of greenhouse gases. These wastes contain a high content of paramount industrial importance, such as cellulose, hemicellulose and natural fibers that various processes can modify, such as bacterial fermentation and anaerobic degradation, to obtain bioplastics, organic fertilizers and biofuels such as ethanol, biogas, hydrogen and biodiesel. In addition, they can be used in wastewater treatment methods by producing low-cost biofilters and obtaining activated carbon from rachis and banana peel. Furthermore, nanometric fibers commonly used in nanotechnology applications and silver nanoparticles useful in therapeutic cancer treatments, can be produced from banana pseudostems. The review aims to demonstrate the contribution of the recovery of banana production waste-loss towards a circular economy that would boost the economy of Latin America and many other countries of emerging economies. 相似文献
24.
A characterization of the iron phases precipitated from aerated solutions of iron(II) sulfate heptahydrate was made using Mössbauer spectroscopy. The experimental conditions for the preparation of the samples were varied. The results are used to the further understanding of rust formation during atmospheric corrosion. 相似文献
25.
Horacio J. Salavagione Diego F. Acevedo Maria C. Miras Artur J. Motheo Cesar A. Barbero 《Journal of polymer science. Part A, Polymer chemistry》2004,42(22):5587-5599
Polyanilines soluble in an aqueous basic medium were synthesised by copolymerization of aniline (ANI) with both 2 and 3‐aminobenzoic acids (ABA). Different composition copolymers were prepared by varying the ANI/ABA feed ratio. Poly(aniline‐co‐2‐aminobenzoic acid) (PANI2ABA) and poly(aniline‐co‐3‐aminobenzoic acid) (PANI3ABA) displayed differences in their properties, such as specific charge and fluorescence behavior because the reactivity of 2‐aminobenzoic (2ABA) and 3‐aminobenzoic (3ABA) acids are very different. The new materials were characterized by X‐ray photoelectron, Fourier transform infrared, and Raman spectroscopies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5587–5599, 2004 相似文献
26.
Metallocene ethylene homopolymer, ethylene-1-hexene and ethylene-1-octadecene copolymer films were characterized and analysed during their aging in a forced draft oven at 60 °C and compared to commercial polymers (HDPE and LDPE). Each polymer is essentially different in its structure, and the variables used in the present study are comonomer size and content in the main linear backbone polymer. The polymers were characterized initially using GPC, DSC, FTIR, and tensile tests. Later, at different time intervals, samples were removed from the oven and characterized using FTIR and GPC in order to detect changes in chemical structure, size, and molecular weight distribution due to thermo-oxidative aging. At the end of aging, films were subjected to tensile tests to quantify the effect of time on their useful life. As a qualitative reference parameter, the carbonyl index, the ratio of the infrared absorbance of the CO stretching band at 1715 cm−1 and the absorbance of a reference band at 718 cm−1, was determined. Kinetic thermo-oxidation is related to comonomer size and content in the main backbone polymer. As comonomer size decreases or comonomer content increases, degradation rate increases. The scission factor (S) and carbonyl index (CI) graphs of each material show a slope increase which is related to the autocatalytic rate of oxidation. 相似文献
27.
Summary A reexamination of the vibrational coordinates appropriate in vibronic intensity calculations in octahedral coordination compounds is presented. We derive a complete set of symmetry coordinates that is orthonormal and transforms correctly under the group generators. The vibronic hamiltonian for the crystal field and ligand polarization contributions to the intensity are calculated in the basis of these coordinates. The crystal field term is evaluated both using a truncated basis set for the intermediate electronic states and using the closure approximation. These methods have been applied to the calculation of the vibronic intensity distribution for the4
A
2g
2
E
g transition of the MnF
6
2–
ion and close agreement wtih experiment achieved. 相似文献
28.
Barrera Acevedo Santiago Ó Catháin Padraig Dietrich Heiko 《Journal of Algebraic Combinatorics》2022,55(1):201-215
Journal of Algebraic Combinatorics - The two-circulant core (TCC) construction for Hadamard matrices uses two sequences with almost perfect autocorrelation to construct a Hadamard matrix. A... 相似文献
29.
The decarboxylation of imidazolidin-2-one-1-carboxylate anion 2 has been investigated via combined quantum and statistical mechanics methodology. Monte Carlo statistical mechanics simulations utilizing free-energy perturbation theory and PDDG/PM3 for the QM method yielded free-energy profiles for the reaction in water, methanol, acetonitrile, and mixed solvents. The results for free energies of activation are uniformly in close accord with experimental data and reflect large rate accelerations in progressing from protic to dipolar aprotic media. Structural and energetic analyses confirm that the rate retardation in protic solvents comes from loss of hydrogen bonding in progressing from the carboxylate anion 2 to the more charge-delocalized transition state (TS). The structure of the TS is found to be significantly affected by the reaction medium; it occurs at a 0.2-A shorter C-N separation in protic solvents than in acetonitrile. Characterization of the hydrogen bonding for 2 and the TS also provided insights for design of decarboxylase catalysts, namely, it is desirable to have three hydrogen-bond donating groups positioned to interact with the ureido oxygen along with two hydrogen-bond donors positioned to interact with the ureido nitrogen of the breaking C-N bond. 相似文献
30.
Oscar L. Acevedo Robert S. Andrews Martin Dunkel P. Dan Cook 《Journal of heterocyclic chemistry》1994,31(4):989-995
A series of 4-(1-alkynyl)-2(1H)-pyrimidinone ribonucleosides were synthesized from the Pd-catalyzed coupling of terminal alkynes to the 4-chloropyrimidin-2-one ribonucleoside ( 2 ). These compounds were hydrated, using three different methods, to afford the 4-(2-oxoalkylidene)-2(1H)-pyrimidinones. The 4-enol-pyrimidin-2-one structure of the title compounds offers functional groups with the potential for Watson-Crick hydrogen bonding. 相似文献