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排序方式: 共有96条查询结果,搜索用时 15 毫秒
41.
Fabio Simonelli F.A. Marques Alberto Wisniewski Jr. Edison P. Wendler 《Tetrahedron letters》2004,45(43):8099-8101
The oxazoline cyanocuprates addition to conjugated cyanoalkenes, was shown to be an efficient method for the synthesis of a variety of γ-cyanooxazolines, interesting intermediates with different, but convertible, functions in a symmetrical position. 相似文献
42.
We present an application of a recently developed dynamic mean field theory to the study of relaxation dynamics in adsorption
and desorption from pore networks. The theory predicts the evolution of density distribution in the system, based on an underlying
free energy functional from static mean field theory and the system evolves to equilibrium or metastable equilibrium states
consistent with the static theory. The theory makes it possible to follow the evolution of the density distribution with time
in response to a change in the bulk pressure or chemical potential. We compare uptake dynamics for a 2D slit pore network
with that in a single slit pore. We see more rapid uptake dynamics in the pore network in some cases, due to the greater access
of the pore space to the bulk. We also observe that the formation of liquid bridges can slow down the mass transfer in the
pore network in certain situations. 相似文献
43.
A design of polarization-maintaining retro-reflectors(PMRRs) for folded-path applications is proposed and analyzed.The prism-based scheme enables the output light,which is parallel to the input,to have an identical state of polarization.The principle of the design is theoretically verified,and the related error is analyzed due to possible manufacturing imperfection.The maximum spatial angle error is ±2.75°.The effect on the extinction ratio and insertion loss is also discussed,which further proves the design’s feasibility in practical applications. 相似文献
44.
Omar. D. Gutierrez Edison Osorio Carlos. G. Paucar C.Z. Hadad 《Journal of luminescence》2009,129(8):836-1528
Vitroceramic powders of Li2O-Al2O3-SiO2 systems (LAS), doped with 1% (LAS:1Ce) and 10% (LAS:10Ce) molar of cerianite (CeO2) were synthesized by means of the gelification technique of metal formates of aluminum and lithium, in the presence of tetraethoxy silane and CeO2. The gels obtained were dried (120 °C, 2.5 h), calcined (480 °C, 5 h) and sinterized (1250 °C, 30 min). The sinterized samples were characterized by X-ray difraction (XRD), scanning electron microscopy (SEM) and microchemical analysis (EDS). There is evidence for a mixture of two phases of 64% β-spodumene (Li2O-Al2O3-4SiO2) and 36% β-eucryptite (Li2O-Al2O3-2SiO2). The LAS:1Ce system was enriched in aluminum, the LAS:10Ce system showed areas of heterogeneous composition; some regions with a shortage of CeO2, while others zones with cerium cumulus. From the microscopy images it was found that CeO2 acts as a densificant agent in LAS system, favoring the sintering in the host. The chemical route and the sintering processes utilized allow the production of samples exhibiting an acceptable linear correlation between total thermoluminescent emission intensity and the irradiation dose when the CeO2 concentration is low (less than 1%), opening the possibility of using this kind of glass-ceramic in dosimetry. 相似文献
45.
We present an extension of Karmarkar's linear programming algorithm for solving a more general group of optimization problems: convex quadratic programs. This extension is based on the iterated application of the objective augmentation and the projective transformation, followed by optimization over an inscribing ellipsoid centered at the current solution. It creates a sequence of interior feasible points that converge to the optimal feasible solution in O(Ln) iterations; each iteration can be computed in O(Ln
3) arithmetic operations, wheren is the number of variables andL is the number of bits in the input. In this paper, we emphasize its convergence property, practical efficiency, and relation to the ellipsoid method. 相似文献
46.
Lei Liu Diego Moreno Edison Osorio Abril C. Castro Sudip Pan Pratim K. Chattaraj Thomas Heine Gabriel Merino 《ChemInform》2016,47(22):no-no
DFT‐based calculations reveal that the global minimum of IrB12‐ is a C3v symmetric bowl‐like structure in which the Ir atom is located on the concave side of the bowl similar to its lighter congeners, CoB12‐ and RhB12‐. 相似文献
47.
Karina Sierra Laura Naranjo Luis Carrillo-Hormaza German Franco Edison Osorio 《Molecules (Basel, Switzerland)》2022,27(7)
The purpose of this study was to chemically compare samples of Mentha spicata (marketing byproducts, production byproducts, and export material), cultivated in the open field and under greenhouse, using an integrated approach by HPLC/DAD and GC/MS analysis. The presence of phenolic compounds was higher in the marketing byproducts cultivated in the open field. Marketing byproducts also had the highest amount of carvone. For this reason, this byproduct was selected as a candidate for the development of natural ingredients. With the best selected material, the optimization of simultaneous high-intensity ultrasound-assisted extraction processes was proposed for the recovery of the compounds of interest. This extraction was defined by Peleg’s equation and polynomial regression analysis. Modeling showed that the factors amplitude, time, and solvent were found to be significant in the recovery process (p < 0.005). The maximum amount of compounds was obtained using 90% amplitude for 5 min and ethanol/water mixture (80:20) for extraction to simultaneously obtain phenolic and terpenoid compounds. This system obtained the highest amount of monoterpenoid and sesquiterpenoid compounds from the essential oil of M. spicata (64.93% vs. 84.55%). Thus, with an efficient and eco-friendly method, it was possible to optimize the extraction of compounds in M. spicata as a starting point for the use of its byproducts. 相似文献
48.
Juan Camilo Henao-Rojas Edison Osorio Stephanie Isaza Ins Amelia Madronero-Solarte Karina Sierra Isabel Cristina Zapata-Vahos Jhon Fredy Betancur-Prez Jorge W. Arboleda-Valencia Adriana M. Gallego 《Molecules (Basel, Switzerland)》2022,27(11)
Spearmint (Mentha spicata L.) has been widely studied for its diversity of compounds for product generation. However, studies describing the chemical and biological characteristics of commercial spearmint materials from different origins are scarce. For this reason, this research aimed to bioprospecting spearmint from three origins: Colombia (Col), Mexico (Mex), and Egypt (Eg). We performed a biological activity analysis, such as FRAP, DPPH, and ABTS, inhibition potential of S. pyogenes, K. pneumoniae, E. coli, P. aeuroginosa, S. aureus, S aureus Methicillin-Resistant, and E. faecalis. Furthermore, we performed chemical assays, such as total polyphenol and rosmarinic acid, and untargeted metabolomics via HPLC-MS/MS. Finally, we developed a causality analysis to integrate biological activities with chemical analyses. We found significant differences between the samples for the total polyphenol and rosmarinic acid contents, FRAP, and inhibition analyses for Methicillin-Resistant S. aureus and E. faecalis. Also, clear metabolic differentiation was observed among the three commercial materials evaluated. These results allow us to propose data-driven uses for the three spearmint materials available in current markets. 相似文献
49.
Osorio E Olson JK Tiznado W Boldyrev AI 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(31):9677-9681
We performed global minimum searches for the B(n) H(n+2) (n=2-5) series and found that classical structures composed of 2c-2e B-H and B-B bonds become progressively less stable along the series. Relative energies increase from 2.9?kcal?mol(-1) in B(2) H(4) to 62.3?kcal?mol(-1) in B(5) H(7). We believe this occurs because boron atoms in the studied molecules are trying to avoid sp(2) hybridization and trigonal structure at the boron atoms, as in that case one 2p-AO is empty, which is highly unfavorable. This affinity of boron to have some electron density on all 2p-AOs and avoiding having one 2p-AO empty is a main reason why classical structures are not the most stable configurations and why multicenter bonding is so important for the studied boron-hydride clusters as well as for pure boron clusters and boron compounds in general. 相似文献
50.
Gliseida Z. Melgar Edison P. Wendler Alcindo A. dos Santos André L.M. Porto 《Tetrahedron: Asymmetry》2010,21(18):2271-2274
Hydroxypropargylpiperidones rac-1–3 were efficiently obtained by a one-pot three-component coupling reaction; enantioenriched propargylpiperidones were then obtained by a kinetic resolution process using the lipase from Candida antarctica. Lipase CALB has been shown to efficiently catalyse the stereocontrolled acetylation of hydroxypropargylpiperidones rac-3 by promoting stereodiscrimination at the carbinolic centre. The enzymatic catalytic processes allow the separation of the (S,R)- and (S,S)-3 diastereoisomers into the corresponding acetates produced as a (R,S)- and (R,R)-6 diastereoisomeric pair. The CALB was able to discriminate the stereogenic centre of the secondary (R)-enantiomer of rac-3 according to the Kaslauzkas rule. The remote stereogenic centre was not discriminated by the lipase. The functionalised enantioenriched diastereoisomers obtained are important building blocks in organic synthesis. 相似文献