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71.
Magne?Lygren Helge I.?AnderssonEmail author 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》2004,55(2):268-281
Large eddy simulations of the flow between a rotating
and a stationary disk have been performed using a dynamic and a
mixed dynamic subgrid-scale model. The simulations were compared
to direct numerical simulation results. The mixed dynamic model
gave better overall predictions than the dynamic model.
Modifications of the near-wall structures caused by the mean flow
three-dimensionality were also investigated. Conditional
averages near strong stress-producing events led to the same
conclusions regarding these modifications as studies of the flow
generated by direct numerical simulation, namely a distinct
asymmetry of the vortices producing sweeps and ejections. 相似文献
72.
Sigve Sporst⊘l Kjell Urdal Hilde Drangsholt Nina Gj⊘s 《International journal of environmental analytical chemistry》2013,93(1-2):129-138
Abstract A method for automated determination of 73 organic pollutants in water is described. The compounds, which are key representatives for different types of pollutants are determined in two chromatographic runs. 11 halogenated aliphatic hydrocarbons are determined using capillary GC equipped with electron capture detector. The remaining pollutants, representing both basic/neutral and acidic compounds are determined by using GC/MS combined with an automated search computer program. The majority of the compounds have a limit of quantitation at 1 ig/1 or lower. The precision of the GC method is in the range of 1.8% to 4.3%, with an average of 3.2%. The precision for compounds determined by GC/MS is in the range of 1% to 38%, with an average of 14%. So far 30 water samples representing both polluted fjord areas as well as effluents from municipal treatment plants, refineries, petrochemical industries and metallurgic industries have been analysed. The method has been found to be an interesting alternative to traditional methods for monitoring water quality, and has demonstrated its potential both as a screening method for detecting “hot spots” as well as for routine monitoring of specific hazardous compounds. 相似文献
73.
Kjell?HauskenEmail author Gregory?Levitin 《Central European Journal of Operations Research》2011,19(4):589-603
The paper considers optimal resource distribution between offense and defense in a duel. In each round of the duel two actors
exchange attacks distributing the offense resources equally across K rounds. The offense resources are expendable (e.g. missiles), whereas the defense resources are not expendable (e.g. bunkers).
The outcomes of each round are determined by a contest success functions which depend on the offensive and defensive resources.
The game ends when at least one target is destroyed or after K rounds. We show that when each actor maximizes its own survivability, then both actors allocate all their resources defensively.
Conversely, when each actor minimizes the survivability of the other actor, then both actors allocate all their resources
offensively. We then consider two cases of battle for a single target in which one of the actors minimizes the survivability
of its counterpart whereas the counterpart maximizes its own survivability. It is shown that in these two cases the minmax
survivabilities of the two actors are the same, and the sum of their resource fractions allocated to offense is equal to 1.
However, their resource distributions are different. In the symmetric situation when the actors are equally resourceful and
the two contest intensities are equal, then the actor that fights for the destruction of its counterpart allocates more resources
to offense. We demonstrate a methodology of game analysis by illustrating how the resources, contest intensities and number
of rounds in the duels impact the survivabilities and resource distributions. 相似文献
74.
The novel title compound, a linear isomer of the food mutagen IQ, has been prepared in 67 % yield by Friedländer synthesis from creatinine and 2-aminobenzaldehyde. 相似文献
75.
The use of Lax pair tensors as a unifying framework for Killing tensors of arbitrary rank is discussed. Some properties of the tensorial Lax pair formulation are stated. A mechanical system with a well-known Lax representation—the three-particle open Toda lattice—is geometrized by a suitable canonical transformation. In this way the Toda lattice is realized as the geodesic system of a certain Riemannian geometry. By using different canonical transformations we obtain two inequivalent geometries which both represent the original system. Adding a timelike dimension gives four-dimensional spacetimes which admit two Killing vector fields and are completely integrable. 相似文献
76.
Fredrik Carlsson Anders Forsgren Henrik Rehbinder Kjell Eriksson 《Annals of Operations Research》2006,148(1):81-94
Optimization is of vital importance when performing intensity modulated radiation therapy to treat cancer tumors. The optimization
problem is typically large-scale with a nonlinear objective function and bounds on the variables, and we solve it using a
quasi-Newton sequential quadratic programming method. This study investigates the effect on the optimal solution, and hence
treatment outcome, when solving an approximate optimization problem of lower dimension. Through a spectral decompostion, eigenvectors
and eigenvalues of an approximation to the Hessian are computed. An approximate optimization problem of reduced dimension
is formulated by introducing eigenvector weights as optimization parameters, where only eigenvectors corresponding to large
eigenvalues are included.
The approach is evaluated on a clinical prostate case. Compared to bixel weight optimization, eigenvector weight optimization
with few parameters results in faster initial decline in the objective function, but with inferior final solution. Another
approach, which combines eigenvector weights and bixel weights as variables, gives lower final objective values than what
bixel weight optimization does. However, this advantage comes at the expense of the pre-computational time for the spectral
decomposition.
A preliminary version of this paper was presented at the AAPM 46th annual meeting, held July 25–29, 2004 in Pittsburgh, PA. 相似文献
77.
Given a pattern string P=p1p2pm and K parallel text strings over an integer alphabet Σ, our task is to find the smallest integer κ>0 such that P can be split into κ pieces P=P1…Pκ, where each Pi has an occurrence in some text track Tki and these partial occurrences retain the order. We study some variations of this minimum splitting problem, such as splittings with limited gaps and transposition invariance, and show how to use sparse dynamic programming to solve the variations efficiently. In particular, we show that the minimum splitting problem can be interpreted as a shortest path problem on line segments. 相似文献
78.
Kjell Rosquist 《Communications in Mathematical Physics》1983,88(3):339-355
Caustics formed by timelike and null geodesics in a space-timeM are investigated. Care is taken to distinguish the conjugate points in the tangent space (T-conjugate points) from conjugate points in the manifold (M-conjugate points). It is shown that most nonspacelike conjugate points are regular, i.e. with all neighbouring conjugate points having the same degree of degeneracy. The regular timelikeT-conjugate locus is shown to be a smooth 3-dimensional submanifold of the tangent space. Analogously, the regular nullT-conjugate locus is shown to be a smooth 2-dimensional submanifold of the light cone in the tangent space. The smoothness properties of the null caustic are used to show that if an observer sees focusing in all directions, then there will necessarily be a cusp in the caustic. If, in addition, all the null conjugate points have maximal degree of degeneracy (as in the closed Friedmann-Robertson-Walker universes), then the space-time is closed. 相似文献
79.
The 5-methyldihydrothiazolo (3,2-c) pyrimidinium cation is evaporated as the corresponding anhydro base. In competition with anhydro base formation the 8-ethoxy derivative eliminates ethyl bromide to give the corresponding betaine. The latter appears to be electronically rearranged and evaporated as a covalent valence isomer. The 3-carboxy derivative investigated suffered decarboxylation and ring opening to a vinyl thione. In the absence of a pyrimidyl methyl group the thiazolo ring was attacked by the anion. The electronically induced fragmentations are discussed and used to deduce the structures of the pyrolytic products. 相似文献
80.
From ionisation potential measurements it is shown that 2,4,6-triphenylpyrylium and thiopyrylium cations are thermally reduced in the mass spectrometer to the corresponding free radicals during evaporation of the bromides, iodides and fluoroborates. For the fluoroborates minor amounts of a fluoride adduct were also present. Perchlorate salts led to oxidation. The gaseous species from 2,6-diphenyl-4-methylpyrylium iodide consists of the anhydro base and hydrogen iodide. 相似文献