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631.
The present paper reviews in detail the different studies now being conducted by our research team concerning the ultradeep hydrodesulfurization (HDS) of dibenzothiophene (DBT) derivatives over Mo/TiO2 and Mo/TiO2–Al2O3 catalysts. First, a detailed characterization of Mo/TiO2 (P-25 Degussa, 50 m2/g) catalysts prepared by equilibrium adsorption technique shows that Mo- species are highly and uniformly dispersed on the surface of titania up to 6.6 wt% MoO3 loading. Above this value, some aggregation of Mo occurs, leading to the formation of bulk MoO3. Below 6.6 wt% MoO3 loading, the Raman spectroscopy data of the calcined samples show that the supported Mo-species possess a highly distorted octahedral MoO6 structure. TiO2–Al2O3 composites were prepared by chemical vapor deposition (CVD) using TiCl4 as a precursor. Using several characterization techniques, we demonstrated that the support composite presents a high dispersion of TiO2 over -Al2O3 without forming precipitates up to ca. 11 wt% loading. Moreover, the textural properties of the composite support are comparable to those of alumina. Under the present sulfidation conditions (673 K, 5%H2S/95%H2), Mo-species supported on TiO2 are better sulfided than on alumina, as demonstrated using XPS. This can be attributed to the relatively lower interaction between Mo-species and titania. The state of sulfide species supported on the composite support can be considered as a transition state between TiO2 and Al2O3. However, at relatively higher TiO2 loadings (ca. 11 wt%), Mo/TiO2–Al2O3 catalysts exhibit sulfidability similar to that of Mo/TiO2. The HDS tests conducted in both the laboratory and in industry show that sulfide catalysts supported on TiO2–Al2O3 (ca. 11 wt% TiO2) are more active than those supported on TiO2 or Al2O3. 相似文献
632.
Amal Feddouli Moulay Youssef Ait Itto Aïssa Hasnaoui Didier Villemin Paul‐Alain Jaffrs Jana Sopkova‐De Oliveira Santos Abdelkhalek Riahi FranOis Huet Jean‐Claude Daran 《Journal of heterocyclic chemistry》2004,41(5):731-735
Herein we report an efficient one pot synthesis of new chiral 4,5‐dihydro‐4‐arylspiro[1,3,4‐thiadiazole]‐5,2′‐camphane‐2‐carboxylic acid ethyl esters 5–7 and 4,5‐dihydro‐3‐arylspiro[1,4,2‐oxathiazole]‐5,2′‐camphane 11–13 , using 1,3‐dipolar cycloaddition of nitrilimines 2–4 and nitrile oxides 8–10 to (1R)‐thiocamphor 1 respectively. The structure of the newly prepared 1,3,4‐thiadiazoles 5–7 (obtained as pure diastereoisomers) were fully established via spectroscopic analysis and X‐ray structural analysis which proved the absolute configuration of the C5 spiranic carbon to be (R). NMR spectral analysis were also very useful to show the new 1,4,2‐oxathiazoles 11–13 are mixtures of two (5R)/(5S) diastereoisomers with the ratio 6:4,7:3 and 6:4 respectively. 相似文献
633.
Nabil L. Youssef S. H. Abed A. Soleiman 《Rendiconti del Circolo Matematico di Palermo》1936,60(1-2):263-281
The aim of the present paper is to provide an intrinsic investigation of projective changes in Finsler geometry, following the pullback formalism. Various known local results are generalized and other new intrinsic results are obtained. Nontrivial characterizations of projective changes are given. The fundamental projectively invariant tensors, namely, the projective deviation tensor, the Weyl torsion tensor, the Weyl curvature tensor and the Douglas tensor are investigated. The properties of these tensors and their interrelationships are obtained. Projective connections and projectively flat manifolds are characterized. The present work is entirely intrinsic (free from local coordinates) (arXiv:?0904.?1602 [math.DG]). 相似文献
634.
AbstractThe elastic field generated by a semi-coherent interface formed by a succession of parallel terraces and nanoledges is investigated when the interface intersects the free surface of an isotropic half-space medium. The method uses the combination of semi-infinite Somigliana dislocations placed on each terrace and semi-infinite translation (or Volterra) dislocations placed at one or two corners of the nanoledges. Numerical examples depict the deformation fields nearby emerging regions of two semi-coherent interfaces; one is flat, while the other includes nanoledges. 相似文献
635.
Ghada M. Sami 《Czechoslovak Journal of Physics》2005,55(5):555-562
The complete time-domain fields due to a vertical magnetic dipole on the surface of two-layer earth model are reexamined when the usually neglected magnetic permeability contrast is considered using the natural-frequency concept. It is shown that for two-layered earth model, where the upper one is permeable, the electromagnetic induction response is modified with respect to the nonpermeable case. The step responses of the induced voltage in a horizontal receiving loop is found to have definite diagnostic features for the ground beneath. These features have been demonstrated by numerical results and illustrated by figures. 相似文献
636.
Krit Suknuntha Vimon Tantishaiyakul Visit Vao‐Soongnern Youssef Espidel Terrence Cosgrove 《Journal of Polymer Science.Polymer Physics》2008,46(12):1258-1264
Blends of chitosan and poly(vinyl pyrrolidone) (PVP) have a high potential for use in various biomedical applications and in advanced drug‐delivery systems. Recently, the physical and chemical properties of these blends have been extensively characterized. However, the molecular interaction between these two polymers is not fully understood. In this study, the intermolecular interaction between chitosan and PVP was experimentally investigated using 13C cross‐polarization magic angle‐spinning nuclear magnetic resonance (13C CP/MAS NMR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). According to these experimental results, the interaction between the polymers takes place through the carbonyl group of PVP and either the OH? C6, OH? C3, or NH? C2 of chitosan. In an attempt to identify the interacting groups of these polymers, molecular modeling simulation was performed. Molecular simulation was able to clarify that the hydrogen atom of OH? C6 of chitosan was the most favorable site to form hydrogen bonding with the oxygen atom of C?O of PVP, followed by that of OH? C3, whereas that of NH? C2 was the weakest proton donor group. The nitrogen atom of PVP was not involved in the intermolecular interaction between these polymers. Furthermore, the interactions between these polymers are higher when PVP concentrations are lower, and interactions decrease with increasing amounts of PVP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1258–1264, 2008 相似文献
637.
A simple and reliable liquid chromatographic method has been developed and validated for the determination of cefdinir in human urine and capsule samples. A chromatographic separation was achieved on a C18 column using a mobile phase consisting of potassium dihydrogen phosphate (10 mM, pH 4.5)–acetonitrile (90:10, v/v). Quantitation was achieved with UV detection at 285 nm, based on peak area with linear calibration curve at a concentration range of 0.7–39 µg mL−1. This method was successfully applied for the establishment of an urinary excretion pattern after oral dose.
相似文献638.
Dimensionality reduction and polynomial chaos acceleration of Bayesian inference in inverse problems
We consider a Bayesian approach to nonlinear inverse problems in which the unknown quantity is a spatial or temporal field, endowed with a hierarchical Gaussian process prior. Computational challenges in this construction arise from the need for repeated evaluations of the forward model (e.g., in the context of Markov chain Monte Carlo) and are compounded by high dimensionality of the posterior. We address these challenges by introducing truncated Karhunen–Loève expansions, based on the prior distribution, to efficiently parameterize the unknown field and to specify a stochastic forward problem whose solution captures that of the deterministic forward model over the support of the prior. We seek a solution of this problem using Galerkin projection on a polynomial chaos basis, and use the solution to construct a reduced-dimensionality surrogate posterior density that is inexpensive to evaluate. We demonstrate the formulation on a transient diffusion equation with prescribed source terms, inferring the spatially-varying diffusivity of the medium from limited and noisy data. 相似文献
639.
Stephen E. Bechtel Nivine T. Youssef M. Gregory Forest Hong Zhou Kurt W. Koelling 《Rheologica Acta》2001,40(4):373-383
A model for oscillating free surface jet flow of a fluid from an elliptical orifice, together with experimental measurements,
can be exploited to characterize the elongational viscosity of non-Newtonian inelastic fluids. The oscillating jet flow is
predominantly elongational, with a small strain that oscillates rapidly between large and zero strain rates. We find that
to reproduce the experimentally observed steady oscillating jet flow in model simulations, the assumed form of the non-Newtonian
viscosity as a function of strain rate must have zero gradient, i.e., be Newtonian, at zero strain rate (a behavior exhibited,
in general, by real inelastic fluids). We demonstrate that the Cross, Carreau, Prandtl-Eyring, and Powell-Eyring forms, although
they have finite viscosity at zero strain rate, have either nonzero or even unbounded gradient at zero, and hence are unable
to model oscillating jet behavior. We propose a new non-Newtonian viscous form which has all of the desirable features of
existing forms (high and low strain rate plateaus, with adjustable location and steepness of the transition) and the additional
feature of Newtonian behavior at low strain rates.
Received: 7 February 2000 Accepted: 31 October 2000 相似文献
640.
Mohamed Ali Ben Aissa Sabri Hassen Youssef Arfaoui 《International journal of quantum chemistry》2019,119(6):e25837
Chalcogen bonding is a noncovalent interaction, highly similar to halogen and hydrogen bonding, occurring between a chalcogen atom and a nucleophilic region. Two density functional theory (DFT) approaches B3LY-D3 and B97-D3 were performed on a series of complexes formed between CX2 (X = S, Se, Te) and diazine (pyridazine, pyrimidine and pyrazine). Chalcogen atoms prefer interacting with the lone pair of a nitrogen atom rather than with the π-cloud of an aromatic ring. CTe2 and CSe2 form a stronger chalcogen bond than CS2. The electrostatic potential of CX2 (X = S, Se and Te) reveals the presence of two equivalent σ-holes, one on each chalcogen atom. These CX2 molecules interact with diazine giving rise to supramolecular interactions. Wiberg bond index and second-order perturbation theory analysis in NBO were performed to better understand the nature of the chalcogen bond interaction. 相似文献