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141.
In this study, we have calculated the linear, nonlinear and total refractive index changes and absorption coefficients for the transitions 1s–1p, 1p–1d and 1d–1f in a spherical quantum dot with parabolic potential. Quantum Genetic Algorithm (QGA) and Hartree–Fock–Roothaan (HFR) method have been employed to calculate the wavefuctions and energy eigenvalues. The results show that impurity, dot radius, stoichiometric ratio, incident optical intensity and carrier density of the system have important effects on the optical refractive index changes and absorption coefficients. Also, we find that as the transitions between orbitals with big l value move to lower energy region in case with parabolic potential, in case without parabolic potential these transitions move to higher energy region. 相似文献
142.
We show that the sum of the series formed by the so-called hyperharmonic numbers can be expressed in terms of the Riemann zeta function. These results enable us to reformulate Euler's formula involving the Hurwitz zeta function. In additon, we improve Conway and Guy's formula for hyperharmonic numbers. 相似文献
143.
In this study, urease was immobilized in a polymer network obtained by complexation of poly(1-vinyl imidazole) (PVI) with
poly(acrylic acid) (PAA). Preparation of the polymer network was monitored by FT-IR spectroscopy. Scanning electron microscopy
(SEM) revealed that enzyme immobilization had a strong effect on film morphology. Proton conductivity of the PVI/PAA network
was measured via impedance spectroscopy under humidified conditions. Values of the Michaelis-Menten constant (K
M) for immobilized urease were higher than for the free enzyme, indicating a decreased affinity of the enzyme to its substrate.
The basic characteristics (pHopt, pHstability, T
opt, T
stability, reusability, and storage stability) of immobilized urease were determined. The results show that the PAA/PVI polymer network
is suitable for enzyme immobilization. 相似文献
144.
We study the dynamic assignment of flexible servers to stations in the presence of setup costs that are incurred when servers
move between stations. The goal is to maximize the long-run average profit. We provide a general problem formulation and some
structural results, and then concentrate on tandem lines with two stations, two servers, and a finite buffer between the stations.
We investigate how the optimal server assignment policy for such systems depends on the magnitude of the setup costs, as well
as on the homogeneity of servers and tasks. More specifically, for systems with either homogeneous servers or homogeneous
tasks, small buffer sizes, and constant setup cost, we prove the optimality of “multiple threshold” policies (where servers’
movement between stations depends on both the number of jobs in the system and the locations of the servers) and determine
the values of the thresholds. For systems with heterogeneous servers and tasks, small buffers, and constant setup cost, we
provide results that partially characterize the optimal server assignment policy. Finally, for systems with larger buffer
sizes and various service rate and setup cost configurations, we present structural results for the optimal policy and provide
numerical results that strongly support the optimality of multiple threshold policies. 相似文献
145.
Reaction of trichloronitromethane with secondary amine leads to the formation of corresponding carcinogeneous N-nitrosamines under mild conditions. 相似文献
146.
Synthesis of Novel Alkyl‐Sulfanyl 1,3,4‐Oxadiazolyl‐1,3,5,7‐Tetraazatricyclic Ammonium Chloride Type Cationic Surfactants
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Ayhan Yıldırım 《Journal of heterocyclic chemistry》2015,52(2):522-526
A series of novel cationic surfactants bearing 1,3,4‐oxadiazole and tetraazatricyclic ring structures were synthesized by alkyl chain elongation of 5‐{10‐[4‐(hydroxymethyl)phenoxy]decyl}‐2,3‐dihydro‐1,3,4‐oxadiazole‐2‐thione with homologous series of alkyl bromides, followed by chlorination of the corresponding benzyl alcohols with thionyl chloride and quaternization of the obtained intermediates with hexamethylenetetramine. 相似文献
147.
We have prepared glycosyl type phosphonates via hetero Diels-Alder (HDA) reactions of acyl phosphonates with electron rich dienes. HDA reactions of acyl phosphonates with Danishefsky’s diene required thermal activation to yield the desired dihydropyranones in good yield (70-91%). The reactions with Brassard’s diene involved Lewis acid promotion to yield the corresponding lactones, though in moderate yield (33-69%). 相似文献
148.
Walcarius A Nasraoui R Wang Z Qu F Urbanova V Etienne M Göllü M Demir AS Gajdzik J Hempelmann R 《Bioelectrochemistry (Amsterdam, Netherlands)》2011,82(1):46-54
Complexes of the (2,2'-bipyridyl) (pentamethylcyclopentadienyl)-rhodium family ([Cp*Rh(bpy)Cl](+), which is actually hydrolyzed in the form of [Cp*Rh(bpy)H(2)O](2+) in aqueous medium) are suitable solution-phase mediators likely to regenerate nicotinamide cofactors associated to dehydrogenases involved in many biocatalytic applications. Their practical application as bioelectrocatalysts, e.g., in fine chemicals synthesis or biosensors, remains however restricted to their durable immobilization in an active form onto solid electrode surfaces. This paper reports some new observations on the electrocatalytic properties of this mediator towards NAD(+) reduction, notably the critical effect of pH and cofactor-to-mediator concentration ratio, and investigates the behavior of a series of ([Cp*Rh(bpy)Cl](+)) derivatives bearing various substituents on the bipyridine ligand in view of their subsequent integration in electrochemical bioreactors. It will be shown that such compounds containing S- or N- moieties (i.e., often used as precursors to functionalize electrode surfaces) lead to inactivation of the electrocatalyst because their interaction with the Rh center prevents the formation of the active rhodium hydride complex. It was thus necessary to find another strategy of immobilization, and we found that adsorption of [Cp*Rh(bpy)Cl](+) by π-stacking on single-walled carbon nanotubes is an effective mean to reach this goal, leading to efficient and stable catalytic responses for NAD(+) reduction. Preliminary electroenzymatic experiments in the presence of d-sorbitol dehydrogenase further point out the interest of this approach for bioelectrocatalysis purposes and provide the proof-of-concept for this immobilization strategy. 相似文献
149.
Ali O. Ayhan 《International Journal of Solids and Structures》2011,48(3-4):492-505
In the absence of automated and customized methods and tools, some of today’s existing methods for solving three-dimensional fracture problems require comprehensive finite element meshing, labor-intensive analysis and post-processing efforts. In this study, a tetrahedral enriched element method and related applications are presented that demonstrate employment of fully unstructured tetrahedral meshes for general mixed-mode three-dimensional fracture problems. As in the case of hexahedral enriched elements, the tetrahedral enriched elements also alleviate the needs of pre- and post-processing the finite element model, allowing direct computation of stress intensity factors in the solution phase. In addition, when tetrahedral enriched elements are used, the crack front region can also be meshed using unstructured elements allowing direct use of automatic free-meshing programs. The applications presented are plane-strain central crack problem, mode-I surface crack in a plate, inclined penny-shaped crack, edge-cracked bar under constant heat flux and lens-shaped crack embedded in a large elastic body. The results obtained are in good comparative agreement with those available in the literature. Thus, it is concluded that the enriched tetrahedral elements can be applied efficiently and accurately on a general three-dimensional fracture problem allowing usage of fully unstructured finite element meshes. 相似文献
150.
Dr. M. Menaf Ayhan Ceyda Bayraktar Kai Bin Yu Dr. Gabriel Hanna Dr. A. Ozgur Yazaydin Dr. Yunus Zorlu Dr. Gündoğ Yücesan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):14813-14816
A one-dimensional nanotubular metal–organic framework (MOF) [Ni(Cu-H4TPPA)]⋅2 (CH3)2NH2+ (H8TPPA=5,10,15,20-tetrakis[p-phenylphosphonic acid] porphyrin) constructed by using the arylphosphonic acid H8TPPA is reported. The structure of this MOF, known as GTUB-4 , was solved by using single-crystal X-ray diffraction and its geometric accessible surface area was calculated to be 1102 m2 g−1, making it the phosphonate MOF with the highest reported surface area. Due to the extended conjugation of its porphyrin core, GTUB-4 possesses narrow indirect and direct bandgaps (1.9 eV and 2.16 eV, respectively) in the semiconductor regime. Thermogravimetric analysis suggests that GTUB-4 is thermally stable up to 400 °C. Owing to its high surface area, low bandgap, and high thermal stability, GTUB-4 could find applications as electrodes in supercapacitors. 相似文献