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91.
Shi L Traaseth NJ Verardi R Gustavsson M Gao J Veglia G 《Journal of the American Chemical Society》2011,133(7):2232-2241
Residual dipolar couplings (RDCs) are widely used as orientation-dependent NMR restraints to improve the resolution of the NMR conformational ensemble of biomacromolecules and define the relative orientation of multidomain proteins and protein complexes. However, the interpretation of RDCs is complicated by the intrinsic degeneracy of analytical solutions and protein dynamics that lead to ill-defined orientations of the structural domains (ghost orientations). Here, we illustrate how restraints from paramagnetic relaxation enhancement (PRE) experiments lift the orientational ambiguity of multidomain membrane proteins solubilized in detergent micelles. We tested this approach on monomeric phospholamban (PLN), a 52-residue membrane protein, which is composed of two helical domains connected by a flexible loop. We show that the combination of classical solution NMR restraints (NOEs and dihedral angles) with RDC and PRE constraints resolves topological ambiguities, improving the convergence of the PLN structural ensemble and giving the depth of insertion of the protein within the micelle. The combination of RDCs with PREs will be necessary for improving the accuracy and precision of membrane protein conformational ensembles, where three-dimensional structures are dictated by interactions with the membrane-mimicking environment rather than compact tertiary folds common in globular proteins. 相似文献
92.
It has recently become possible to focus a beam of high-energy electrons to a spot smaller than an atom, with vast potential for the study of condensed matter. We devise an experiment that can image, with subangstrom resolution, the distribution of such an electron beam as it scatters within an atomic lattice. Our experiments reveal the acute sensitivity of the scattered electron distribution to 0.1 ? shifts of the impact point. Scattering due to plasmon excitations is also examined. Implications for the study of the atomic and electronic structure of condensed matter are discussed. 相似文献
93.
M.S. Baptista F. Moukam Kakmeni Gianluigi Del Magno M.S. Hussein 《Physics letters. A》2011,375(10):1309-1318
Positive Lyapunov exponents measure the asymptotic exponential divergence of nearby trajectories of a dynamical system. Not only they quantify how chaotic a dynamical system is, but since their sum is an upper bound for the rate of information production, they also provide a convenient way to quantify the complexity of a dynamical network. We conjecture based on numerical evidences that for a large class of dynamical networks composed by equal nodes, the sum of the positive Lyapunov exponents is bounded by the sum of all the positive Lyapunov exponents of both the synchronization manifold and its transversal directions, the last quantity being in principle easier to compute than the latter. As applications of our conjecture we: (i) show that a dynamical network composed of equal nodes and whose nodes are fully linearly connected produces more information than similar networks but whose nodes are connected with any other possible connecting topology; (ii) show how one can calculate upper bounds for the information production of realistic networks whose nodes have parameter mismatches, randomly chosen; (iii) discuss how to predict the behavior of a large dynamical network by knowing the information provided by a system composed of only two coupled nodes. 相似文献
94.
We present a new method that combines carbonyl-selective labeling with frequency-selective heteronuclear recoupling to resolve the spectral overlap of magic angle spinning (MAS) NMR spectra of membrane proteins in fluid lipid membranes with broad lines and high redundancy in the primary sequence. We implemented this approach in both heteronuclear (15)N-(13)C(α) and homonuclear (13)C-(13)C dipolar assisted rotational resonance (DARR) correlation experiments. We demonstrate its efficacy for the membrane protein phospholamban reconstituted in fluid PC/PE/PA lipid bilayers. The main advantage of this method is to discriminate overlapped (13)C(α) resonances by strategically labeling the preceding residue. This method is highly complementary to (13)C(i-1)(')-(15)N(i)-(13)C(i)(α) and (13)C(i-1)(α)-(15)N(i-1)-(13)C(i)(') experiments to distinguish inter-residue spin systems at a minimal cost to signal-to-noise. 相似文献
95.
96.
Sabrina Giofr Roberto Sala Egle Maria Beccalli Leonardo Lo Presti Gianluigi Broggini 《Helvetica chimica acta》2019,102(7)
A procedure for the iodoamination of unfunctionalized olefins tethered to a tosyl‐protected NH‐group has been developed. The combined use of KI and H2O2 in aqueous medium was effective for the preparation of iodomethyl‐substituted nitrogen‐containing heterocycles. The selective exo‐trig iodocyclization provided 1,2‐bifunctional 5‐, 6‐, and 7‐membered cyclic skeletons. 相似文献
97.
Dr. Marcin Górecki Dr. Filippo Lipparini Dr. Gianluigi Albano Dr. Tamás Jávorfi Dr. Rohanah Hussain Dr. Giuliano Siligardi Prof. Gennaro Pescitelli Prof. Lorenzo Di Bari 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(4):e202103632
Solid-state ECD (ss-ECD) spectra of a model microcrystalline solid, finasteride, dispersed into a KCl pellet were recorded by using the synchrotron radiation source at the Diamond B23 beamline. Scanning a surface of 36 mm2 with a step of 0.5 mm, we measured a set of ECD imaging (ECDi) spectra very different from each other and from the ss-ECD recorded with a bench-top instrument (1 cm2 area). This is due to the anisotropic part of the ECD (ACD), which averages to zero in solution or on a large number of randomly oriented crystallites, but can otherwise be extremely large. Two-way singular value decomposition (SVD) analysis, through experimental and simulated TDDFT spectra, disclosed that the measured and theoretical principal components are in line with each other. This finding demonstrates that the observed isotropic ss-ECD spectrum is governed by the anisotropy of locally oriented crystals. It also introduces a new quality for ss-ECD measurements and opens a new future for probing and mapping chiral materials in the solid state such as active pharmaceutical ingredients (APIs). 相似文献
98.
99.
Olivier Gautreau Lina Gunawan M.P. Singh Gianluigi A. Botton 《Journal of magnetism and magnetic materials》2009,321(11):1799-1802
The multiferroic behavior of epitaxial γ-Fe2O3-BiFeO3 (composite)/Bi3.25La0.75Ti3O12 bi-layered heterostructures grown on SrRuO3/SrTiO3 (1 1 1) substrates has been studied using piezoresponse force microscopy, magnetic force microscopy and magnetometry. The ferroelectric domain structure is ascribed to the BiFeO3 phase while the magnetism originates in the γ-Fe2O3 phase of the composite layer. Our studies demonstrate the presence and switching of magnetic and ferroelectric domains within the same area of the sample. This confirms the presence of multiferroic behavior at the nanoscale in our γ-Fe2O3-BiFeO3 nanocomposite thin films. 相似文献
100.
Leonid A. Bunimovich Gianluigi Del Magno 《Communications in Mathematical Physics》2009,288(2):699-713
We study a class of planar billiards having the remarkable property that their phase space consists up to a set of zero measure
of two invariant sets formed by orbits moving in opposite directions. The tables of these billiards are tubular neighborhoods
of differentiable Jordan curves that are unions of finitely many segments and arcs of circles. We prove that under proper
conditions on the segments and the arcs, the billiards considered have non-zero Lyapunov exponents almost everywhere. These
results are then extended to a similar class of 3-dimensional billiards. Interestingly, we find that for some track billiards,
the mechanism generating hyperbolicity is not the defocusing one, which requires every infinitesimal beam of parallel rays
to defocus after every reflection off of the focusing boundary. 相似文献