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61.
62.
Curtis L. Card Myron B. Allen 《Numerical Methods for Partial Differential Equations》1995,11(2):147-163
Difference-like schemes for the wave equation arise naturally from a Galerkin finite-element formulation, if we adopt certain quadrature rules in evaluating the mass and stiffness matrices. One can extend these schemes to problems involving sharp interfaces by applying the quadrature on a refinement of the finite-element grid that includes the interfaces. We develop error estimates for this modified scheme that corroborate numerical results for acoustic and elastic wave equations, presented in a companion article. © 1995 John Wiley & Sons, Inc. 相似文献
63.
Electronically induced lattice instabilities in metals are discussed by means of an accurate determination of the generalized susceptibility function, χ(q), from a KKR band structure and Fermi surface determined for b.c.c. Zr. We describe how the detailed behavior of χ(q) for b.c.c. Zr may be related to the omega phase upon alloying with Nb or upon application of pressure to the b.c.c. lattice. 相似文献
64.
65.
Ambroz Almássy Andrej Bohá? Marta Sališová Myron Rosenblum 《Journal of organometallic chemistry》2004,689(7):1131-1138
The kinetic and thermodynamic parameters for regioisomerisation of 2-methyl- and 2,6-dimethyl-derivatives of tricarbonyl[η4-tropone]iron complexes have been studied by 1H NMR spectrometry over a range of 40 °C. Regioisomerisation of these complexes proceeds by an intramolecular first-order process and results in the almost complete conversion of the less stable complexes (4, 8) to more stable regioisomers (1, 5). The activation energies and half lifes for the conversion (4 → 1) and (8 → 5) were found to be ΔG#=92 kJ mol−1; τ1/2=12.8 h, and ΔG#=107 kJ mol−1; τ1/2=26.8 h, respectively, at 23 °C. Complex 1 reacts with (1R,2S,5R)-menthol in sulphuric acid solution, followed by neutralisation with sodium carbonate to give a separable mixture of diastereomeric tricarbonyl[(2,3,4,5-η)-(1R′,2S′,5R′)-6-menthyloxy-2-methyltropone]iron complexes, 9 and 10. The corresponding dimethylated complex 5 fails to react under these conditions. 相似文献
66.
Myron J. Holm Ferdinand B. Zienty 《Journal of polymer science. Part A, Polymer chemistry》1972,10(5):1311-1318
One crystalline form of α,α′-bis(4-acetoxy-3-methoxybenzylidene)-p-benzenediacetonitrile is photopolymerized by a four-center reaction to give a polymer containing alternating benzene and cyclobutane rings. The polymer is highly crystalline and insoluble in most solvents. Location of groups around the cyclobutane ring is deduced from the products obtained on thermal decomposition. Chain contained benzene rings are located in positions 1 and 3; aromatic groups alternate sides of the cyclobutane ring. Special characterization and quantum yield of the polymerization are reported, as well as polymer solution viscosity and alkaline depolymerization of the polymer. 相似文献
67.
Consider the boundary value problem where β ? 0, τ ? 0. We are concerned with a mathematically rigorous numerical study of the number of solutions in any bounded portion of the positive quadrant (τ ? 0, β ? 0) of the τ, β plane. These correct computational results may then be matched with asymptotic (β→∞, τ ? 0) results developed earlier. These numerical results are based on the development of a posteriori error estimates for the numerical solution of an associated initial-value problem and a priori bounds on . 相似文献
68.
Bassam M. Tashtoush Amjad M. Qandil Elaine L. Jacobson Myron K. Jacobson 《Chromatographia》2008,68(1-2):135-138
Octyl nicotinate is an ester prodrug which is under development for delivery of nicotinic acid to skin for treatment and prevention of dermatological conditions that involve skin barrier impairment such as chronic photodamage and atopic dermatitis or for mitigating skin barrier impairment that results from therapy such as retinoids or steroids. We report here an isocratic RF-LC method with water/acetonitrile (10:90, v/v) as a mobile phase, for the rapid analysis of octyl nicotinate in aqueous solutions. The method was validated in terms of linearity, precision, accuracy and mean recovery of octyl nicotinate from skin homogenate ranging from 98.8 to 102.6%. Separation and quantification of amounts as low as 0.25 μg mL?1 octyl nicotinate was accomplished. The kinetic of degradation of octyl nicotinate in aqueous solution at 310, 333, 343, and 353 K was studied. The hydrolysis rate constants for degradation of octyl nicotinate in phosphate buffer and skin homogenate were reported. This method will be effective for routine analysis of octyl nicotinate stability in different formulations in future studies. 相似文献
69.
Myron M. Johnson Kennedy J. Ngwira Amanda L. Rousseau Andreas Lemmerer Charles B. de Koning 《Tetrahedron》2018,74(1):12-18
The synthesis of the benz[a]anthracene skeleton of the angucyclines is described. Key steps involve the Suzuki-Miyaura reaction, isomerization of an aromatic allyl substituent to the corresponding styrene, and the use of the ring closing metathesis reaction to construct a benzene ring. For example, exposure of 3-allyl-2-bromo-1,4,5-trimethoxynaphthalene to (2-formyl-4-methoxyphenyl)boronic acid under palladium catalysis conditions resulted in the formation of 2-(3-allyl-1,4,5-trimethoxynaphthalen-2-yl)-5-methoxybenzaldehyde. This 2-naphthyl benzaldehyde then underwent a Wittig reaction to furnish 3-allyl-1,4,5-trimethoxy-2-(4-methoxy-2-vinylphenyl)naphthalene. Isomerization of the allyl group of this compound afforded the diene, (E)-1,4,5-trimethoxy-2-(4-methoxy-2-vinylphenyl)-3-(prop-1-en-1yl)naphthalene. Exposure of the formed diene to the Grubbs II catalyst resulted in the formation of the benzanthracene, 3,7,8,12-tetramethoxytetraphene, which was easily oxidized to the corresponding quinone. 相似文献
70.
Human habitation is dependent on the chemical and physical processes that shape Earth's surface environment and control the transport, cycling, and chemical form of elements. The challenges facing society concerning water, energy, climate change, and health require a molecular-scale understanding of these processes. It is not surprising therefore that synchrotron radiation (SR) techniques have become essential research tools for the molecular environmental science (MES) and low-temperature geochemistry (LTG) communities as they address critical needs for society. 相似文献