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51.
Anchorage strength models for end-debonding predictions in RC beams strengthened with FRP composites
The increase in the flexural capacity of RC beams obtained by externally bonding FRP composites to their tension side is often
limited by the premature and brittle debonding of the external reinforcement. An in-depth understanding of this complex failure
mechanism, however, has not yet been achieved. With specific regard to end-debonding failure modes, extensive experimental
observations reported in the literature highlight the important distinction, often neglected in strength models proposed by
researchers, between the peel-off and rip-off end-debonding types of failure. The peel-off failure is generally characterized
by a failure plane located within the first few millimetres of the concrete cover, whilst the rip-off failure penetrates deeper
into the concrete cover and propagates along the tensile steel reinforcement. A new rip-off strength model is described in
this paper. The model proposed is based on the Chen and Teng peel-off model and relies upon additional theoretical considerations.
The influence of the amount of the internal tensile steel reinforcement and the effective anchorage length of FRP are considered
and discussed. The validity of the new model is analyzed further through comparisons with test results, findings of a numerical
investigation, and a parametric study. The new rip-off strength model is assessed against a database comprising results from
62 beams tested by various researchers and is shown to yield less conservative results.
Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 3, pp. 373–388, May–June, 2008. 相似文献
52.
53.
54.
We show that the complexity of a parabolic or conic spline approximating a sufficiently smooth curve with non-vanishing curvature
to within Hausdorff distance ɛ is c
1ɛ−1/4 + O(1), if the spline consists of parabolic arcs, and c
2ɛ−1/5 + O(1), if it is composed of general conic arcs of varying type. The constants c
1 and c
2 are expressed in the Euclidean and affine curvature of the curve. We also show that the Hausdorff distance between a curve
and an optimal conic arc tangent at its endpoints is increasing with its arc length, provided the affine curvature along the
arc is monotone. This property yields a simple bisection algorithm for the computation of an optimal parabolic or conic spline.
The research of SG and GV was partially supported by grant 6413 of the European Commission to the IST-2002 FET-Open project
Algorithms for Complex Shapes in the Sixth Framework Program. 相似文献
55.
For strengthening bent beams, plates of reinforced plastics are glued to their tensioned surface. As s result, the beam becomes
layered, and it is possible to control its rigidity and deflection. Based on the methods of structural mechanics of layered
media, a method is elaborated for determining the deflection of such beams on the entire range of loading up to their ultimate
failure. A comparison between the theoretical and experimental results is carried out.
__________
Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 45–60, January–February, 2006. 相似文献
56.
We present the origins and synthesis of helical polyacetylene (H‐PA) by focusing on its peculiar spiral morphology. Interfacial polymerization of acetylene was carried out in an asymmetric reaction field consisting of chiral nematic liquid crystal (N*‐LC) and Ziegler–Natta catalyst. As the N*‐LC is composed of nematic liquid crystal and a chiral compound such as a binaphthyl derivative with either the R‐ or S‐configuration, the screw directions of the polyacetylene chain and fibril bundle—and even the spiral morphology—are rigorously controlled by the chirality of the selected compound. Interestingly, the screw directions of the fibril and the bundle in H‐PA were found to be opposite to that of N*‐LC. It is worthwhile to emphasize that the hierarchical spiral morphology involving the primary to higher order structure is generated in a synthetic polymer such as polyacetylene by using N*‐LC as an asymmetric polymerization solvent. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 395–406; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20163 相似文献
57.
This paper describes an efficient method of inducing sonochemical reactions with focussed ultrasound. A sector-vortex transducer (a phased array transducer with multiple sectors and a geometric focus) is used to produce focal ultrasound fields with spiral-shaped wavefronts. Clockwise and counter-clockwise spiral focal fields, with basically the same ultrasound power distribution but having different wavefront angles, are produced by using the same array transducer. The oxidation of the iodide ions induced from the periodic switching between such a pair of spiral focal fields is investigated at an ultrasound frequency of 750 kHz. The oxidation rate at the optimum switching period (3 ms) is about ten times higher than that at switching periods of 1 s. The optimum switching period and the sonochemical reaction rate are unchanged when the viscosity was adjusted to that of human blood. 相似文献
58.
The method adopted here is based on the rigorous solution of Poisson’s equation for logarithmic disturbance density within
finite thickness galaxies. After their spiral arms are fitted directly with logarithmic spirals, the morphological parameters,
scale heights and their relative errors for 32 spiral galaxies, such as NGC4814, are obtained. 相似文献
59.
The Bridgman anvil technique offers a simple and versatile means of generating very high pressures required in solid state
studies. The opposed anvil technique is based on the principle of massive support. The practical case of a gasketted anvil
is considered, and an expression for the maximum pressure generated under massive support is derived in terms of the geometric
parameters, the strength of the anvil material and the gasket properties. In particular, for a given maximum pressure, it
is possible to calculate the taper angle, the taper height and the gasket thickness from this expression. The anvil is assumed
to be in the elastic region under load. Good agreement is obtained between the calculated and the experimental values for
the massive support factor (msf) for various taper angles. By choosing the proper geometry, it is possible to achieve a pressure as high as 130 kbar in an
alloy steel anvil. It has been clearly found that the straight portion, where the taper ends, does not really take any part
in changing the stress pattern. Thus the minimum straight portion can serve the purpose, and will result in material saving.
Anvils exhibit yielding at very high pressure. It is also pointed out that a further strengthening of the anvil can extend
the ultimate pressure. Several methods of further strengthening the anvils are discussed. 相似文献
60.
W. M. Koo 《Journal of statistical physics》1995,81(3-4):561-578
Based on transfer matrix techniques and finite-size scaling, we study the oriented polymer (self-avoiding walk) with nearest neighbor interaction. In the repulsive regime, various critical exponents are computed and compared with exact values predicted recently. The polymer is also found to undergo a spiral transition for sufficiently strong attractive interaction. The fractal dimension of the polymer is computed in the repulsive and attractive regimes and at the spiral transition point. The later is found to be different from that at the collapse transition of the ordinary self-avoiding walk. 相似文献