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81.
We show that tapping-mode atomic force microscopy provides real-space and time-resolved observations of morphology and pattern formation resulting from crystallisation of annealed thin films of polyethelenoxide or microphase-separated low-molecular-weight hydrogenated poly(butadiene-b-ethyleneoxide) diblock copolymers. Differences in viscoelastic properties allow distinguishing crystalline and molten (amorphous) areas with a nanometer resolution. 相似文献
82.
Erhard W. Fischer Adam Patkowski Werner Steffen Harald Glser Toshiji Kanaya Lutz Reinhardt Johannes Reiter Thomas Thurn-Albrecht Franz-Josef Stickel Eva Eckstein 《Macromolecular Symposia》1997,124(1):1-2
Extended Abstract: Glass forming organic liquids and polymers exhibit long range density fluctuations with correlation length ξ in the range of 10–300 nm at temperatures above Tg (1 - 6). This follows from dynamic and static light scattering experiments revealing some unexpected features, which cannot be explained on the basis of conventional liquid state theories: (i) In static light scattering the intensity I(q → 0) is no longer proportional to the isothermal compressibility, (ii) This excess scattering Iexc shows a strong q-dependence (q = (4π/Λ.)sin(θ/2)) corresponding to a correlation length ξ in the above mentioned range, (iii) The Landau-Placzek ratio IRayleigh/2IBrillouin is much too high compared with the results of light scattering theories, (iv) In photon correlation spectroscopy a new ultraslow hydrodynamic mode (Γ ˜ q2) is detected with relaxation rates Γ about 10−6 to 10−9 lower than those of the α-process at a given temperature. In order to explain these observations, a two-state fluid model is proposed, which starts from the coexistence of “liquid-like” and “aperiodic solid-like” regions within the liquids. Such ideas have been discussed many times before, so for example A.R. Ubbelohde (7) speculates about “anticrystalline” clusters in liquids. Molecular dynamics simulations of atomic liquids showed that long range orientational fluctuations appear upon supercooling (8). A preferred icosahedral ordering is observed (9) and the number of icosahedral clusters increases with decreasing temperature (10). In connection with the interpretation of the dynamics of supercooled liquids different “two-state” models have been proposed (11 - 15). For the explanation of the light scattering results we propose that the molecules in the different dynamic states (“liquid” or “solid”) aggregate during annealing of the liquid at temperatures above Tg. Experiments showed that the equilibration times can be rather long (3 - 5), but nevertheless the liquids exhibiting long range density fluctuations are in the state of lowest free energy. We claim that our observations are the first experimental proof of the existence of such different dynamic states, which have been discussed many times before. The extended secondary clusters can also be detected by ultra small angle X-ray scattering. 相似文献
83.
Birgit Reiter Marion Lechner Eberhard Lorbeer Reiner Aichholz 《Journal of separation science》1999,22(9):514-520
A rapid method for the isolation and quantitative determination of wax esters in vegetable oils was developed. For the first time wax esters in oils were separated from the triglyceride matrix by means of solid-phase extraction, which allows rapid sample preparation in parallel and therefore a high sample throughput. The thus obtained wax ester fractions of fennel and caraway seed oils were analyzed by high temperature gas chromatography. GC-MS analyses were carried out using electron impact ionization in order to characterize the wax ester fraction. With respect to the results of the GC-MS analyses different isomers of saturated wax esters with the same carbon number were observed. Additional monounsaturated wax esters with an unsaturated fatty acid moiety were identified. 相似文献
84.
K. Jradi S. Bistac M. Schmitt A. Schmatulla G. Reiter 《The European physical journal. E, Soft matter》2009,29(4):383-389
We used the tip of an atomic force microscope (AFM) in the contact mode to scratch/rub the surface of a glassy polymer thin
film, i.e., isotactic polystyrene (i-PS) at room temperature. After subsequent isothermal crystallization, an extremely high nucleation
density of edge-on crystals within the rubbed region or at the edge of the scratched area was observed. Furthermore, a transition
from edge-on to flat-on lamellae occurred beyond a certain distance from the edge of the scratched region. Our results demonstrate
that both, soft rubbing or hard scratching, allow to lower the nucleation barrier for polymer crystallization and to control
the orientation of the resulting crystalline lamellae. The role of scratching/rubbing on chain deformation and its relation
to nucleation and crystal orientation in polymer thin films is discussed. 相似文献
85.
86.
87.
Gavin Cullen Nicolas Greiner Gudrun Heinrich Gionata Luisoni Pierpaolo Mastrolia Giovanni Ossola Thomas Reiter Francesco Tramontano 《The European Physical Journal C - Particles and Fields》2012,72(3):1-32
We present the program package GoSam which is designed for the automated calculation of one-loop amplitudes for multi-particle processes in renormalisable quantum field theories. The amplitudes, which are generated in terms of Feynman diagrams, can be reduced using either D-dimensional integrand-level decomposition or tensor reduction. GoSam can be used to calculate one-loop QCD and/or electroweak corrections to Standard Model processes and offers the flexibility to link model files for theories Beyond the Standard Model. A standard interface to programs calculating real radiation is also implemented. We demonstrate the flexibility of the program by presenting examples of processes with up to six external legs attached to the?loop. 相似文献
88.
The paper investigates a capacitated vehicle routing problem with two objectives: (1) minimization of total travel cost and
(2) minimization of the length of the longest route. We present algorithmic variants for the exact determination of the Pareto-optimal
solutions of this bi-objective problem. Our approach is based on the adaptive ε-constraint method. For solving the resulting single-objective subproblems, we apply a branch-and-cut technique, using (among
others) a novel implementation of Held-Karp-type bounds. Incumbent solutions are generated by means of a single-objective
genetic algorithm and, alternatively, by the multi-objective NSGA-II algorithm. Experimental results for a benchmark of 54
test instances from the TSPLIB are reported. 相似文献
89.
90.
The time dependence of the anisotropy of fluorescence after an impulsive excitation in the ring unit (resembling the B850 ring of the purple bacterium Rhodopseudomonas acidophila) is calculated. Fast fluctuations of the environment are simulated by dynamic disorder and slow fluctuations by static disorder. Both types of disorder are taken into account simultaneously. Without dynamic disorder modest degrees of static disorder are sufficient to cause the experimentally found initial drop of the anisotropy on a sub-100 fs time scale. Two different models of the spectral density J(ω) of phonons have been often used in the literature to describe influence of the bath. The spectral density J(ω) enters the non-Markovian dynamical equations for the one exciton density matrix (entering the time dependence of the anisotropy of fluorescence). The spectral density J(ω) with high-energy tail leads to faster anisotropy decay. 相似文献