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排序方式: 共有76条查询结果,搜索用时 0 毫秒
1.
In this paper, we examine a class of convex problems of Bolza type, involving a time delay in the state. It encompasses a variety of time-delay problems arising in the calculus of variations and optimal control. A duality analysis is carried out which, among other things, leads to a characterization of minimizers in terms of the Euler-Lagrange inclusion. The results obtained improve in significant respects on what is achievable by techniques previously employed, based on elimination of the time delay by introduction of an infinite-dimensional state space or on the method of steps. 相似文献
2.
S. David Morley Raymond J. Abraham Ian S. Haworth David E. Jackson Martin R. Saunders Jeremy G. Vinter 《Journal of computer-aided molecular design》1991,5(5):475-496
Summary Four modifications to the COSMIC molecular mechanics force field are described, which greatly increase both its versatility and the accuracy of calculated conformational energies. The Hill non-bonded van der Waals potential function has been replaced by a two-parameter Morse curve and a new H-H potential, similar to that in MM3, incorporated. Hydrocarbon energies in particular are much improved.A simple iterative Hückel pi-electron molecular orbital calculation allows modelling of conjugated systems. Calculated bond lengths and rotational barriers for a series of conjugated hydrocarbons and nitrogen heterocycles are shown to be as accurate as those determined by the MM2 SCF method.Explicit hydrogen-bonding potentials for H-bond acceptor-donor atom pairs have been included to give better hydrogen bond energies and lengths. The van der Waals radii of protonic hydrogens are reduced to 0.5 Å and the energy well depth is increased to 1.0 kcal mol-1.Two new general atom types, N+
sp
2
and O-
sp
3
, have been introduced which allow a wide variety of charged conjugated systems to be studied. A minimum of parameterisation is required, as the new types are easily included in the Hückel scheme which automatically adjusts bond and torsional parameters according to the defined bond-order relationships. 相似文献
3.
Arikainen EO Boden N Bushby RJ Lozman OR Vinter JG Wood A 《Angewandte Chemie (International ed. in English)》2000,39(13):2333-2336
4.
S.D. Morley D.E. Jackson M.R. Saunders J.G. Vinter 《Journal of computational chemistry》1992,13(6):693-703
A hybrid conformational search algorithm (DMC) is described that combines a modified form of molecular dynamics with Metropolis Monte Carlo sampling, using the COSMIC(90) force field. Trial configurations are generated by short bursts of high-temperature dynamics in which the initial kinetic energy is focused into single bond rotations or alternatively into “corner-flapping” motions in ring systems. Constant temperature and simulated annealing search protocols have been applied to the conformational analysis of several model hydrocarbons (cyclopentane, cyclohexane, cycloheptane, cyclooctane, cycloheptadecane, decane, and tetradecane), and the performance compared with conventional molecular dynamics and Monte Carlo sampling methods. Optimum Metropolis sampling temperatures have been determined and range from 1000–2000 K for acyclic molecules to 3000 K for cyclic systems. Simulated annealing runs are most successful at locating the global minimum when cooling slowing from these optimum temperatures. 相似文献
5.
J. P. Waltho J. G. Vinter A. Davis D. H. Williams 《Journal of computer-aided molecular design》1988,2(1):31-41
Summary NMR studies of the rotation barrier of the disaccharide of the glycopeptide antibiotic vancomycin have been used to test the performance of computer simulation techniques using molecular mechanics. In the absence of any solvated water, no correlation could be found between experiment and calculation. By introducing solvent water molecules into the binding region of the antibiotic, the NMR results could be simulated both qualitatively and quantitatively within experimental error without using massive computational resources. 相似文献
6.
Robert P. Apaya Baldo Lucchese Sarah L. Price J.G. Vinter 《Journal of computer-aided molecular design》1995,9(1):33-43
Summary Ligands which bind to a specific protein binding site are often expected to have a similar electrostatic environment which complements that of the binding site. One method of assessing molecular electrostatic similarity is to examine the possible overlay of the maxima and minima in the electrostatic potential outside the molecules and thereby match the regions where strong electrostatic interactions, including hydrogen bonds, with the residues of the binding site may be possible. This approach is validated with accurate calculations of the electrostatic potential, derived from a distributed multipole analysis of an ab initio charge density of the molecule, so that the effects of lone pair and -electron density are correctly included. We have applied this method to the phosphodiesterase (PDE) III substrate adenosine-3,5-cyclic monophosphate (cAMP) and a range of nonspecific and specific PDE III inhibitors. Despite the structural variation between cAMP and the inhibitors, it is possible to match three or four extrema to produce relative orientations in which the inhibitors are sufficiently sterically and electrostatically similar to the natural substrate to account for their affinity for PDE III. This matching of extrema is more apparent using the accurate electrostatic models than it was when this approach was first applied, using semiempirical point charge models. These results reinforce the hypothesis of electrostatic similarity and give weight to the technique of extrema matching as a useful tool in drug design. 相似文献
7.
8.
Relaxed controls induce convexity of the velocity sets in optimal control problems, permitting a general existence theory. Here we obtain complete convexity, of the set of control-trajectory pairs, by relaxing the problem constraints to admit certain measures on the product of the control and trajectory spaces. It is proved that these measures are just unit mixtures of control-trajectory pairs and that admitting them does not alter the minimum value of the control problems. This can be used to derive necessary and sufficient conditions for optimality of dynamic programming type. 相似文献
9.
Hunter CA Low CM Rotger C Vinter JG Zonta C 《Chemical communications (Cambridge, England)》2003,(7):834-835
Chemical double mutant cycles have been used to quantify cation-pi interactions in chloroform as a function of the nature of the counteranion. The cation-pi interaction is -2.5 +/- 0.4 kJ mol(-1) and independent of the anion, even though the overall stability of the complexes varies by an order of magnitude due to competition of the anion for alternative binding sites. 相似文献
10.
J.-M. Chauveau C. Morhain B. Lo B. Vinter P. Vennéguès M. Laügt D. Buell M. Tesseire-Doninelli G. Neu 《Applied Physics A: Materials Science & Processing》2007,88(1):65-69
Non polar ZnO and (Zn, Co)O layers were successfully grown on (11̄02) sapphire (R-plane sapphire). The growth process was
shown to directly influence the surface morphology as well as the strain state in (112̄0) ZnO (A-plane ZnO). The dominant
defect lines seen in photoluminescence were due to basal stacking faults as demonstrated by means of selective photoluminescence
and transmission electron microscopy. We present a novel method for growing high quality A-plane ZnO by inserting a (Zn, Co)O
thin buffer layer, which strongly reduced the surface roughness. Finally (Zn, Mg)O/ZnO quantum well structures were grown
on such a buffer layer. These quantum wells exhibited no intrinsic quantum confined Stark effect.
PACS 81.05.Dz; 81.15.Hi; 78.67.Hc; 68.65.Fg 相似文献