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141.
The annealing behavior of twice-folded crystals of the long-chain alkane C294H590 is examined in situ, in real time, by atomic force microscopy (AFM). AFM is capable of following processes in real time provided that the time scale is sufficiently long for several images to be collected during the process. In this paper, we focus on the temperature dependence and the thickened morphology. We are able to investigate where the thickening starts and how this depends on temperature and how melting is influenced by morphology. By following the motion of holes within the crystal, a lower limit for the rate of diffusion of crystalline polyethylene is estimated. We also focus on the substrate effect on the crystal morphology and thickening, using mica, glass, and graphite. 相似文献
142.
143.
The conformational contribution to the entropy of fusion was calculated for poly(ethylene adipate), poly(ethylene suberate), and poly(ethylene sebacate) from consideration of rotational potentials and steric interactions in model systems. An enumeration scheme similar to that applied to polyethylene was used. Comparison of the observed and calculated conformational entropies indicated the importance of a high-energy chain twist in the crystalline polyesters in reducing their measured conformational entropies. The rigidity of the polyester chains in the melt is discussed in comparison to polyethylene. The contribution of the polar ester groups to the heats of fusion of the polyesters is evaluated semiempirically. 相似文献
144.
J. M. Hobbs 《International Journal of Theoretical Physics》1974,9(3):157-165
It is shown that the action of the usual field theory requires the inclusion of two terms in order to be equivalent, in the macroscopic case, to the action proposed by Hoyle & Narlikar (1964c). These actions correspond only to a modified form of Maxwell's equations, which, in consequence, lose their property of conformal invariance. It is also demonstrated how theC-field and electromagnetic field can be brought into unison by an appropriate re-definition of the vector potential. Both field theories can thus be described in terms of one vector Green's function. 相似文献
145.
In this paper we show that the entire graph of a bridgeless connected plane graph is hamiltonian, and that the entire graph of a plane block is hamiltonian connected and vertex pancyclic. In addition, we show that in any block G which is not a circuit, given a vertex v of G and a circuit k of G, there is a path p, suspended in G, such that p is a path in k of length at least 1 and G ? E(p) ? V0(G ? E(p)) is a block which includes v. 相似文献
146.
147.
One-pot five-component reactions of oxathiazolidine-S-oxides with mesitylmagnesium bromide, lithium bis(trimethylsilyl)amide, aldehydes and Grignard reagents afford chiral nonracemic amines or sulfinamides in good yields and high stereoselectivities. 相似文献
148.
Background
How living neural networks retain information is still incompletely understood. Two prominent ideas on this topic have developed in parallel, but have remained somewhat unconnected. The first of these, the "synaptic hypothesis," holds that information can be retained in synaptic connection strengths, or weights, between neurons. Recent work inspired by statistical mechanics has suggested that networks will retain the most information when their weights are distributed in a skewed manner, with many weak weights and only a few strong ones. The second of these ideas is that information can be represented by stable activity patterns. Multineuron recordings have shown that sequences of neural activity distributed over many neurons are repeated above chance levels when animals perform well-learned tasks. Although these two ideas are compelling, no one to our knowledge has yet linked the predicted optimum distribution of weights to stable activity patterns actually observed in living neural networks. 相似文献149.
Edward S. Briceno Katrina Stephen Christopher E. Hobbs 《Journal of polymer science. Part A, Polymer chemistry》2023,61(1):94-99
This contribution describes the ring opening metathesis polymerization of a sulfonyl fluoride decorated polynorbornene and its postsynthetic modification using the sulfur-fluoride exchange “click” reaction. 相似文献
150.
Jamie K. Hobbs Alex K. Winkel Terence J. McMaster Andrew D.L. Humphris Andrew A. Baker Stephen Blakely Meriem Aissaoui Mervyn J. Miles 《Macromolecular Symposia》2001,167(1):1-14
Some recent advances in the application of atomic force microscopy to crystalline polymers are detailed. Ultra‐high resolution imaging of crystal surfaces, combined with the analysis of computer generated Connolly surfaces, enables the unambiguous identification of features on the cellulose crystal surface at near‐atomic resolution. The electronic enhancement of the quality factor of the cantilever when tapping in liquids enables a considerable improvement in force sensitivity to be obtained, allowing the fully saturated surface of an isotactic polystyrene gel to be imaged under the solvating molecule, at nanometre resolution. A series of experiments are detailed in which processes such as crystallization, crystal thickening and crystal deformation are followed in situ, in real time, providing significant new insights into long standing problems in polymer science. 相似文献