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排序方式: 共有197条查询结果,搜索用时 15 毫秒
121.
Jorge Armando Ardila Frederico Luis Felipe Soares Marco Antônio dos Santos Farias 《Analytical letters》2017,50(7):1126-1138
A rapid Raman spectroscopy protocol is reported to classify gasoline according to its distributor and to identify and quantify common adulterants. Gasoline from three distributors was collected from 19 stations in São Paulo, Brazil. Principal component analysis (PCA) showed specific clusters for each distributor, and partial least squares discriminant analysis (PLS-DA) correctly identified the origin of the samples. To evaluate the technique for the identification and quantification of the adulterants, authentic samples from each distributor were fortified at levels from 2.5 up to 25.0% (v/v) using ethanol, methanol, toluene, and turpentine to obtain 120 altered samples. PCA showed clear separation among the samples with the adulterants and PLS-DA precisely identified the adulterants (478 in 480 predictions by cross-validation), irrespective of the distributor and the concentration. One classification model was used to characterize all distributors. To quantify the adulterants, 36 multivariate calibration models were constructed using partial least squares (PLS), interval PLS, and PLS genetic algorithm for each distributor and for each adulterant. Cross-validation errors of less than 5.0% were obtained for all adulterants regardless of the distributor. Raman spectroscopy and multivariate analysis were shown to be powerful for rapid and inexpensive for the characterization of gasoline origin and the identification and quantification of common adulterants. 相似文献
122.
Rafael Cao Lucas Cortez Ismael de Farias Ernee Kozyreff Jalil Khatibi Moqadam Renato Portugal 《Entropy (Basel, Switzerland)》2021,23(10)
We study discrete-time quantum walks on generalized Birkhoff polytope graphs (GBPGs), which arise in the solution-set to certain transportation linear programming problems (TLPs). It is known that quantum walks mix at most quadratically faster than random walks on cycles, two-dimensional lattices, hypercubes, and bounded-degree graphs. In contrast, our numerical results show that it is possible to achieve a greater than quadratic quantum speedup for the mixing time on a subclass of GBPG (TLP with two consumers and m suppliers). We analyze two types of initial states. If the walker starts on a single node, the quantum mixing time does not depend on m, even though the graph diameter increases with it. To the best of our knowledge, this is the first example of its kind. If the walker is initially spread over a maximal clique, the quantum mixing time is , where ϵ is the threshold used in the mixing times. This result is better than the classical mixing time, which is . 相似文献
123.
Farias Jan-Michel C. Stainier Laurent Fancello Eduardo Alberto 《Continuum Mechanics and Thermodynamics》2020,32(4):1037-1055
Continuum Mechanics and Thermodynamics - In this paper, a viscoelastic model able to capture important mechanical features of a wide class of glassy polymers is presented. Among them, the ability... 相似文献
124.
125.
Glacio S. Araujo Leonardo J.B.L. Matos Jader O. Fernandes Samuel J.M. Cartaxo Luciana R.B. Gonçalves Fabiano A.N. Fernandes Wladimir R.L. Farias 《Ultrasonics sonochemistry》2013,20(1):95-98
Microalgae have the ability to grow rapidly, synthesize and accumulate large amounts (approximately 20–50% of dry weight) of lipids. A successful and economically viable algae based oil industry will depend on the selection of appropriate microalgal strains and the selection of the most suitable lipid extraction method. In this paper, five extraction methods were evaluated regarding the extraction of lipids from Chlorella vulgaris: Bligh and Dyer, Chen, Folch, Hara and Radin, and Soxhlet. Furthermore, the addition of silica powder was studied to evaluate the introduction of more shear stress to the system as to increase the disruption of cell walls. Among the studied methods, the Bligh and Dyer method assisted by ultrasound resulted in the highest extraction of oil from C. vulgaris (52.5% w/w). Addition of powder silica did not improve the extraction of oil. 相似文献
126.
We calculate the susceptibility amplitude ratio near a generic higher character Lifshitz point up to one-loop order. We employ a renormalization group treatment with L independent scaling transformations associated to the various inequivalent subspaces in the anisotropic case in order to compute the ratio above and below the critical temperature and demonstrate its universality. Furthermore, the isotropic results with only one type of competition axes have also been shown to be universal. We describe how the simpler situations of m-axial Lifshitz points as well as ordinary (noncompeting) systems can be retrieved from the present framework. 相似文献
127.
Rosiane M. C. Farias Marta M. Conceição Roberlúcia A. Candeia Marta C. D. Silva Valter J. FernandesJr. Antonio G. Souza 《Journal of Thermal Analysis and Calorimetry》2011,106(3):651-655
The diversity of raw materials and technological routes employed in the biodiesel production has resulted in products with
different chemical properties. This non-uniformity in the biodiesel composition may influence to the fuel quality. The aim
of this study was to evaluate biodiesel blends of passion fruit and castor oil in different proportions and their thermal
stability. Biodiesel blends of passion fruit and castor oil presented parameters in the standards of the Petroleum, Natural
Gas and Biofuels National Agency. The TG curves indicated that castor oil biodiesel was more stable. Passion fruit biodiesel
has a high content of oleic and linoleic acids, which are more susceptible to oxidation. Biodiesel blend of passion fruit
and castor oil 1:1 increased the thermal stability in relation to passion fruit biodiesel. Biodiesel blend of passion fruit
and castor oil 1:2 presented higher thermal stability, because castor oil has a high content of ricinoleic acid. 相似文献
128.
Maria J. F. Costa Antonio S. Araujo Edjane F. B. Silva Mirna F. Farias Valter J. FernandesJr. Petrus d’Amorim Santa-Cruz José G. A. Pacheco 《Journal of Thermal Analysis and Calorimetry》2011,106(3):767-771
The nanostructured hybrid AlMCM-41/ZSM-5 composite was synthesized starting from a hydrogel with molar composition SiO2:0.32Na2O:0.03Al2O3:0.20TPABr:0.16CTMABr:55H2O. The cetyltrimethylammonium bromide (CTMABr) and tetrapropylammonium bromide (TPABr) were used as templates. The above mentioned
material presents morphological properties with specific characteristics, such as the surface area of the composite which
is approximately half of the surface area of the conventional MCM-41. Another interesting feature is the formation of walls
with the double of the density of the MCM-41 structure, which characterizes the hybrid material, resulting in a high stability
material for catalytic application. The aim of this study is obtain optimized structures of the hybrid material and for this
purpose variations in the synthesis time were carried out. A comparative analysis was performed including X-ray diffraction,
Fourier transform infrared spectroscopy, and Thermogravimetry measurements. The model-free kinetic algorithms were applied
in order to determinate conversion and apparent activation energy of the decomposition of the CTMA+ and TPA+ species from the hybrid AlMCM-41/ZSM-5. 相似文献
129.
Prof. André A. Vieira Giliandro Farias Wallison C. Costa Prof. Juliana Eccher Prof. Ivan H. Bechtold Dr. Fabien Durola Dr. Harald Bock 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(35):9003-9010
Whereas their para homologs are not mesogenic, the disk-shaped triphenyltriazine meta-trialkylesters obtained via trimerization of 3-cyanobenzoic alkylester, which are configurationally more flexible, exhibit a monotropic nematic mesophase. Introduction of fluorine atoms into the alkyl chains or into the phenyl moieties leads to the appearance of an enantiotropic columnar mesophase. If fluorine is introduced both in the chains and in the phenyl moieties, only a monotropic mesophase remains. Fluorination of either the alkyl chains or the aromatic core, but not both, appears thus as a simple means of inducing or stabilizing columnar self-assembly in disk-shaped systems. As the homeotropically alignable columnar mesophase can thus be made to persist at room temperature, as energies higher than 3 eV of the first excited triplet state are computed in agreement with the value reported for the parent arene, and as they are not fluorescent themselves, these compounds are of promise as aligning host matrices for blue-emitting TADF devices with improved light outcoupling. Dilution of a columnar with a nonmesogenic homolog induces the nematic state, indicating that the nanoscopic make-up of both mesophases is closely related. 相似文献
130.
T. F. A. Alves A. C. A. Ramos G. A. Farias R. N. Costa Filho N. S. Almeida 《The European Physical Journal B - Condensed Matter and Complex Systems》2012,85(3):92-9
The effect of Dresselhauss spin-orbit coupling on transport and thermodynamic properties
of a non-interacting two-dimensional electron gas (2DEG) is investigated. The Hamiltonian
used also includes a tilted magnetic field and a Rashba spin-orbit interaction. The
Dresselhauss spin-orbit interaction, likewise the Rashba spin-orbit interaction,
introduces a beating pattern in the conductivity tensor and in the magnetization along the
field direction. A method to estimate the contribution of the Rashba and Dresselhauss
interactions to the beating pattern is given using the periodicity of the beating
patterns. 相似文献