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1.
We address the problem of computing fundamental performance bounds for estimation of object boundaries from noisy measurements in inverse problems, when the boundaries are parameterized by a finite number of unknown variables. Our model applies to multiple unknown objects, each with its own unknown gray level, or color, and boundary parameterization, on an arbitrary known background. While such fundamental bounds on the performance of shape estimation algorithms can in principle be derived from the Cramer-Rao lower bounds, very few results have been reported due to the difficulty of computing the derivatives of a functional with respect to shape deformation. We provide a general formula for computing Cramer-Rao lower bounds in inverse problems where the observations are related to the object by a general linear transform, followed by a possibly nonlinear and noisy measurement system. As an illustration, we derive explicit formulas for computed tomography, Fourier imaging, and deconvolution problems. The bounds reveal that highly accurate parametric reconstructions are possible in these examples, using severely limited and noisy data. 相似文献
2.
3.
G. Moulin 《Journal of Materials Science》1991,26(3):756-762
During the laser surface treatment, oxidation can take place even with the protection of helium gas. The CW-CO2 laser melting of the surface does not induce a large distortion of the crystallographic orientation which remains (1 0 0). A misorientation of 3–4 degrees between the melted zone and the unaffected base alloy was measured by Laue diffraction and ion channelling studies. Surface chemical analysis was carried out by X-ray photoelectron and Auger electron spectroscopies in order to obtain information on surface segregation during either the laser cooling, or after annealing up to 850 °C, in PO2=5 × 10–9 Torr. The latter causes segregation of sulphur and/or nitrogen to the surface. This segregation of sulphur and nitrogen is modified between the untreated zone and the treated surfaces (thermal affected zone and melted zone). For instance, on the contrary of nitrogen, the diffusion of sulphur is increased on the melted surface and the activation energy for this diffusion is very dependent upon the defect nature. A difference of nearly 65–70 kJ mol–1 is calculated for the enthalpy for the surface segregation of sulphur H
seg, between the treated and untreated surface. This difference is only 37 kJ mol–1 for nitrogen. In both cases the absolute H
seg values are smaller for the treated zone than for the base alloy. A structural study by low electron diffraction (LEED) which gives information on the structure of the surface when clean and in the presence of sulphur and/or nitrogen, shows also the formation of edges, terraces and steps on the treated surfaces. These results are mainly associated with the difference in the content and nature of the defects between the different zones, as observed by scanning electron microscopy analysis or channelling study. Finally a comparison between the mechanical properties of the different zones is made on account of the observation of a linear change of the microhardness on the thermally affected surface. In the thin outer surface zone which is treated by the laser, the stresses associated with the cooling or the isothermal annealing are calculated using formula which associate the stress and the radius of curvature of the sample (from the misorientation which was analysed by ion channelling between the different surface domains). The influence of such an isothermal stress is believed to increase the percentage of vacancies in the melted zone and therefore to modify the activation energy for the diffusion of a substitutional element, such as sulphur. The influence of the elastic energy which is kept during cooling, for example according to the analysis of Evans and Lobb [12], is also discussed.Part of this work was done in the Laboratoire de Physicochimie des Surfaces, associe au CNRS, ENSCP, Université P et M Curie, 11 rue P et M Curie, 75005 Paris, France. 相似文献
4.
G. Moulin C. Mons C. Severac C. Haut G. Rautureau E. Beauprez 《Oxidation of Metals》1993,40(1-2):85-108
Nickel-base alloys, such as Astroloy, used for aeronautical turbine disks, are sensitive to time-dependent cracking in environments containing oxygen. The mosaic structure of the alloy consisting islands (200 nm average size) surrounded by the -phase (100 nm thick) induces complex oxidation phenomena. Various analytical approaches allow the delineation of all the steps from segregation to oxidation occurring on the surface of such a duplex structure. The protection of Astroloy by its outer oxide layer against oxygen penetration was studied also, using alternative
16O2
then
18O2
oxidation. In association with STEM studies, it is shown that the outer oxide scale is not a real barrier against oxygen penetration and that inner precipitation of chronium (+ aluminium and titanium)-enriched oxides, takes place especially in the structure. 相似文献
5.
The oxidation of presulphidized Ni-Cr alloys has been studied by taking into account the influence of the two distinct oxidation mechanisms described in part I of this article. Sulphur enters the Cr2O3 scale (in Ni-34Cr alloys) mainly as S2– species, which at high temperatures increases the VCr content, and hence the oxidation kinetics. Sulphur is randomly distributed in the scale, except at the inner oxide-alloy interface, where intergranular microsulphides are analyzed in the oxide-scale zone. In the case of NiO, NiCr2O4, Cr2O3 oxide multilayers (in a Ni-20Cr alloy), sulphur in the S2– state is distributed in the oxide layers or at Si-precipitate interfaces. Such a distribution leads to crack formation, especially during cooling. 相似文献
6.
Marion Woytasik Johan Moulin Emile Martincic Anne-Lise Coutrot Elisabeth Dufour-Gergam 《Microsystem Technologies》2008,14(7):951-956
Recent advances in microtechnology allow realization of planar microcoils. These components are integrated in MEMS as magnetic sensor or actuator. In the latter case, it is necessary to maximize the effective magnetic field which is proportional to the current passing through the copper track and depends on the distance to the generation microcoil. The aim of this work was to determine the optimal microcoil design configuration for magnetic field generation. The results were applied to magnetic actuation, taking into account technological constraints. In particular, we have considered different realistic configurations that involve a magnetically actuated device coupled to a microcoil. Calculations by a semi-analytical method using Matlab software were validated by experimental measurements. The copper planar microcoils are fabricated by UV micromoulding on different substrates: flexible polymer (Kapton®) and silicate on silicon. They are constituted by a spiral-like continuous track. Their total surface is about 1 mm2. 相似文献
7.
P.-Y. Le Gal A. Merot C.-H. Moulin M. Navarrete J. Wery 《Environmental Modelling & Software》2010,25(2):258-268
Given the new challenges confronting world agriculture, innovative production systems need to be designed at the farm level. As experiments are not easy to conduct at this level, modelling is required to evaluate ex-ante the multiple impacts of proposed innovations. A conceptual framework based on three sub-systems (biophysical, technical, and decisional) interacting within the farm is proposed to guide this process. The advantages and limitations of the framework are illustrated with three examples. The first describes a conceptual, rule-based model representing management decisions for the cultivation of salad in southern France. The second uses a computerized model of the three sub-systems to study irrigation management strategies on farms producing hay in southern France. The third presents a spreadsheet model designed to assist dairy farms in Morocco to define new livestock and forage system strategies. The lessons learned concern the modelling process, the fit between the type of model and its use, and the advantage of involving stakeholders in the design process of tools and innovations. 相似文献
8.
9.
Towards a continuous microfluidic rheometer 总被引:1,自引:1,他引:0
Pierre Guillot Thomas Moulin Roman Kötitz Matthieu Guirardel Arash Dodge Mathieu Joanicot Annie Colin Charles-Henri Bruneau Thierry Colin 《Microfluidics and nanofluidics》2008,5(5):619-630
In a previous paper we presented a way to measure the rheological properties of complex fluids on a microfluidic chip (Guillot
et al., Langmuir 22:6438, 2006). The principle of our method is to use parallel flows between two immiscible fluids as a pressure
sensor. In fact, in a such flow, both fluids flow side by side and the size occupied by each fluid stream depends only on
both flow rates and on both viscosities. We use this property to measure the viscosity of one fluid knowing the viscosity
of the other one, both flow rates and the relative size of both streams in a cross-section. We showed that using a less viscous
fluid as a reference fluid allows to define a mean shear rate with a low standard deviation in the other fluid. This method
allows us to measure the flow curve of a fluid with less than 250 μL of fluid. In this paper we implement this principle in
a fully automated set up which controls the flow rate, analyzes the picture and calculates the mean shear rate and the viscosity
of the studied fluid. We present results obtained for Newtonian fluids and complex fluids using this set up and we compare
our data with cone and plate rheometer measurements. By adding a mixing stage in the fluidic network we show how this set
up can be used to characterize in a continuous way the evolution of the rheological properties as a function of the formulation
composition. We illustrate this by measuring the rheological curve of four formulations of polyethylene oxide solution with
only 1.3 mL of concentrated polyethylene oxide solution. This method could be very useful in screening processes where the
viscosity range and the behavior of the fluid to an applied stress must be evaluated. 相似文献
10.
The paper provides a survey of the creep-fatigue design rules for the LMFBR in France. These rules are the ones currently implemented in French component manufacturing. The background of each item is discussed and the trends for improvements currently investigated are described. The cree-fatigue rules apply to elastic analysis only. 相似文献