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81.
Amphipathic alpha-helical peptides are often ascribed an ability to induce curvature stress in lipid membranes. This may lead directly to a bending deformation of the host membrane, or it may promote the formation of defects that involve highly curved lipid layers present in membrane pores, fusion intermediates, and solubilized peptide-micelle complexes. The driving force is the same in all cases: peptides induce a spontaneous curvature in the host lipid layer, the sign of which depends sensitively on the peptide's structural properties. We provide a quantitative account for this observation on the basis of a molecular-level method. To this end, we consider a lipid membrane with peptides interfacially adsorbed onto one leaflet at high peptide-to-lipid ratio. The peptides are modeled generically as rigid cylinders that interact with the host membrane through a perturbation of the conformational properties of the lipid chains. Through the use of a molecular-level chain packing theory, we calculate the elastic properties, that is, the spontaneous curvature and bending stiffness, of the peptide-decorated lipid membrane as a function of the peptide's insertion depth. We find a positive spontaneous curvature (preferred bending of the membrane away from the peptide) for small penetration depths of the peptide. At a penetration depth roughly equal to half-insertion into the hydrocarbon core, the spontaneous curvature changes sign, implying negative spontaneous curvature (preferred bending of the membrane toward the peptide) for large penetration depths. Despite thinning of the membrane upon peptide insertion, we find an increase in the bending stiffness. We discuss these findings in terms of how the peptide induces elastic stress. 相似文献
82.
We prove that every -point metric space of negative type (and, in particular, every -point subset of ) embeds into a Euclidean space with distortion , a result which is tight up to the iterated logarithm factor. As a consequence, we obtain the best known polynomial-time approximation algorithm for the Sparsest Cut problem with general demands. If the demand is supported on a subset of size , we achieve an approximation ratio of .
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Journal of Algebraic Combinatorics - A (classical) partial Hadamard Matrix is an $$m\times n$$ matrix H with values in $$\{-1,1\}$$ such that $$HH^T=nI_m$$ . If $$m=n$$ , we say that H is a (full)... 相似文献
86.
Single‐scan 2D NMR relies on a spatial axis for encoding the indirect‐domain internal spin interactions. Various strategies have been demonstrated for fulfilling the needs underlying this procedure. All such schemes use gradient‐echoed sequences that leave at their conclusion solely the effects of the internal interactions along the indirect domain; they also include a real‐time scheme that though simple, yields in general mixed‐phase line shapes. The present paper introduces two new proposals geared up for easing the spatial encoding underlying single‐scan 2D NMR methodologies. One of these is capable of delivering dispersive‐free peaks along the indirect domain, and thereby purely‐absorptive 2D line shapes, in amplitude‐encoded experiments. The other demonstrates for the first time, the possibility to obtain single‐scan 2D spectra without echoing the effects of the encoding gradient–simply by applying a single‐pulse frequency sweep to encode the interactions. Both of these modes are compatible with homo‐ and heteronuclear correlations, and exhibit a number of complementary features vis‐à‐vis encoding alternatives that have so far been presented. The overall principles underlying these new spatially encoding protocols are derived, and their performance demonstrated with single‐scan 2D NMR TOCSY and HSQC experiments on model compounds. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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88.
Assaf Rinot 《Israel Journal of Mathematics》2014,199(2):975-1012
Assume GCH and let λ denote an uncountable cardinal. We prove that if □λ holds, then this may be witnessed by a coherent sequence 〈C α|α < λ+〉 with the following remarkable guessing property For every sequence 〈A i | i < λ〉 of unbounded subsets of λ +, and every limit θ < λ, there exists some α < λ + such that otp(C α)=θ and the (i + 1) th -element of C α is a member of A i , for all i < θ. As an application, we construct a homogeneous λ +-Souslin tree from □λ + CHλ, for every singular cardinal λ. In addition, as a by-product, a theorem of Farah and Veli?kovi?, and a theorem of Abraham, Shelah and Solovay are generalized to cover the case of successors of regulars. 相似文献
89.
M. M. Abou-Krisha F. H. Assaf S. A. El-Naby 《Journal of Solid State Electrochemistry》2009,13(6):879-885
The electrodeposition of ternary zinc–nickel–iron alloy was studied in acidic sulfate bath. The comparison between Zn, Ni,
and Fe deposition and Zn–Ni and Zn–Ni–Fe co-deposition revealed that the remarkable inhibition of Ni and Fe deposition takes
place due to the presence of Zn2+ in the plating bath. The increase in corrosion resistance of ternary deposits is not only attributed to the formation of
γ-Ni2Zn11 phase but also to iron co-deposition and formation of iron phase. It was also found that the bath temperature has a great
effect on the surface appearance and the deposit composition. The investigation was carried out using cyclic voltammetry and
galvanostatic techniques for electrodeposition, while linear polarization resistance and anodic linear sweeping voltammetry
techniques were used for corrosion study. Morphology and chemical composition of the deposits were characterized by means
of scanning electron microscopy and atomic absorption spectroscopy. 相似文献
90.
Droplet microfluidics for high-throughput biological assays 总被引:3,自引:0,他引:3
Droplet microfluidics offers significant advantages for performing high-throughput screens and sensitive assays. Droplets allow sample volumes to be significantly reduced, leading to concomitant reductions in cost. Manipulation and measurement at kilohertz speeds enable up to 10(8) samples to be screened in one day. Compartmentalization in droplets increases assay sensitivity by increasing the effective concentration of rare species and decreasing the time required to reach detection thresholds. Droplet microfluidics combines these powerful features to enable currently inaccessible high-throughput screening applications, including single-cell and single-molecule assays. 相似文献