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91.
Steven J. Teertstra Wai Yau Lin Mario Gauthier Mark Ingratta Jean Duhamel 《Polymer》2009,50(23):5456-5466
The ability of the Fluorescence Blob Model (FBM) to probe the chain dynamics of a polymer backbone was verified for the first time by investigating whether it responds to known differences in backbone flexibility for flexible cis-polyisoprene (PIP) and more sterically hindered polystyrene (PS), both randomly labeled with pyrene. For comparable pyrene contents, the steady-state fluorescence spectra indicated that Py-PIP formed considerably more excimer than the Py-PS samples. Analysis of the fluorescence decays with the FBM provided the rate constant for intramolecular excimer formation. This rate constant was much larger for Py-PIP than for Py-PS, in agreement with the enhanced excimer formation observed for Py-PIP. The enhanced ability of Py-PIP to form excimer is attributed to the PIP backbone being less sterically hindered than the PS backbone. This study is the first example of a comparison of the long range polymer chain dynamics for two different polymeric backbones randomly labeled with pyrene. 相似文献
92.
93.
Valentin H. Prevost Olivier M. Girard Gopal Varma David C. Alsop Guillaume Duhamel 《Magma (New York, N.Y.)》2016,29(4):699-709
Objectives
The recently reported inhomogeneous magnetization transfer technique (ihMT) has been proposed for specific imaging of inhomogeneously broadened lines, and has shown great promise for characterizing myelinated tissues. The ihMT contrast is obtained by subtracting magnetization transfer images obtained with simultaneous saturation at positive and negative frequency offsets (dual frequency saturation experiment, MT +/?) from those obtained with single frequency saturation (MT +) at the same total power. Hence, ihMT may be biased by MT-asymmetry, especially at ultra-high magnetic field. Use of the average of single positive and negative frequency offset saturation MT images, i.e., (MT ++MT ?) has been proposed to correct the ihMT signal from MT-asymmetry signal.Materials and methods
The efficiency of this correction method was experimentally assessed in this study, performed at 11.75 T on mice. Quantitative corrected ihMT and MT-asymmetry ratios (ihMTR and MTRasym) were measured in mouse brain structures for several MT-asymmetry magnitudes and different saturation parameter sets.Results
Our results indicated a “safe” range of magnitudes (/MTRasym/<4 %) for which MT-asymmetry signal did not bias the corrected ihMT signal. Moreover, experimental evidence of the different natures of both MT-asymmetry and inhomogeneous MT contrasts were provided. In particular, non-zero ihMT ratios were obtained at zero MTRasym values.Conclusion
MTRasym is not a confounding factor for ihMT quantification, even at ultra-high field, as long as MTRasym is restricted to ±4 %.94.
Satoshi Gunji Kotaro Tonoike Jean-Baptiste Clavel Isabelle Duhamel 《Journal of Nuclear Science and Technology》2021,58(1):51-61
ABSTRACT The new critical assembly STACY will be able to contribute to the validation of criticality calculations related to the fuel debris. The experimental core designs are in progress in the frame of JAEA/IRSN collaboration. This paper presents the method applied to optimize the design of the new STACY core to measure the criticality characteristics of pseudo fuel debris that simulated Molten Core Concrete Interaction (MCCI) of the fuel debris. To ensure that a core configuration is relevant for code validation, it is important to evaluate the reactivity worth of the main isotopes of interest and their keff sensitivity to their cross sections. In the case of the fuel debris described in this study, especially for the concrete composition, silicon is the nucleus with the highest keff sensitivity to the cross section. For this purpose, some parameters of the core configuration, were adjusted using optimization algorithm to find efficiently the optimal core configurations to obtain high sensitivity of silicon capture cross section. Based on these results, realistic series of experiments for fuel debris in the new STACY could be defined to obtain an interesting feedback for the MCCI. This methodology is useful to design other experimental conditions of the new STACY. 相似文献
95.
This paper proposes a new blind channel estimation method for orthogonal frequency division multiplexing (OFDM) systems. The algorithm makes use of the redundancy introduced by the cyclic prefix to identify the channel based on a subspace approach. Thus, the proposed method does not require any modification of the transmitter and applies to most existing OFDM systems. Semi-blind procedures taking advantage of training data are also proposed. These can be training symbols or pilot tones, the latter being used for solving the intrinsic indetermination of blind channel estimation. Identifiability results are provided, showing that in the (theoretical) situation where channel zeros are located on subcarriers, the algorithm does not ensure uniqueness of the channel estimation, unless the full noise subspace is considered. Simulations comparing the proposed method with a decision-directed channel estimator finally illustrates the performance of the proposed algorithm 相似文献
96.
I.F. Kozhevnikov D. Duhamel Z.-Q. Feng 《International Journal of Mechanical Sciences》2010,52(3):399-78
In this paper the contact problem between rigid indenters of arbitrary shapes and a viscoelastic half-space is considered. Under the action of a normal force the penetration of the indenters changes and a few contact areas appeared. We wish to find the relations which link the pressure distribution, the resultant forces on the indenters and the penetration on the assumption that the surfaces are frictionless. For indenters of arbitrary shapes the problem may be solved numerically by using the matrix inversion method, extended to viscoelastic cases [1]. But when the problem involves a large number of points the matrix inversion method can become very time-consuming. Here the problem is solved using an alternative scheme, called the two-scale iterative method. In this method the local matrix inversion method is used at the micro-scale for each contact area to compute the pressure distribution taking into account interacting effect (the forces on the other contact areas which can be calculated at the macro-scale) between indenters. Two algorithms were proposed. The first algorithm takes into account the distribution of forces on the other contact areas and the second is the approximation of the first algorithm and takes into account the resultant forces on the other contact areas. The method was implemented for a simple configuration of seven spherical indenters, seven spherical-ended cylindrical indenters and seven flat-ended cylindrical indenters as well as for a more complex configuration of 12 randomly positioned indenters of arbitrary shapes: spherical-ended cylindrical, flat-ended cylindrical, conical and cylindrical indenters (finite cylindrical shape with its curved face). This last case is more difficult as the indenting geometry does not have an axisymmetric profile. For all these cases the two-scale iterative method permits to find the pressure distribution and the contact forces versus the penetration. It can be validated by comparing the numerical results to the numerical results obtained with the matrix inversion method. 相似文献
97.
98.
Denis Duhamel Tien-Minh Nguyen 《Computer Methods in Applied Mechanics and Engineering》2009,198(37-40):3006-3019
This paper proposes a new method, in the frequency domain, to define absorbing boundary conditions for general two-dimensional problems. The main feature of the method is that it can obtain boundary conditions from the discretized equations without much knowledge of the analytical behavior of the solutions and is thus very general. It is based on the computation of waves in periodic structures and needs the dynamic stiffness matrix of only one period in the medium which can be obtained by standard finite element software. Boundary conditions at various orders of accuracy can be obtained in a simple way. This is then applied to study some examples for which analytical or numerical results are available. Good agreements between the present results and analytical solutions allow to check the efficiency and the accuracy of the proposed method. 相似文献
99.
The population dynamics of a mixed microbial culture dechlorinating trichloroethene (TCE), cis-1,2-dichloroethene (cDCE), 1,2-dichloroethane (1,2-DCA), and vinyl chloride (VC) to ethene were studied. Quantitative PCR revealed that Dehalococcoides, Geobacter, Sporomusa, Spirochaetes, and Methanomicrobiales phylotypes grew in short-term experiments. Both Geobacter and Dehalococcoides populations grew during TCE dechlorination to cDCE, but only Dehalococcoides populations grew during further dechlorination to ethene. The cell yields for Dehalococcoides determined in this study were similar on an electron equivalent basis regardless of the chlorinated compound transformed: (0.9+/-0.3) x 10(8)16S rRNA gene copies/microelectron equivalent (microeeq) ethene produced during cDCE dechlorination, (1.5 +/-0.3) x 10(8) copies/microeeq ethene produced during VC dechlorination, and (1.6+/-0.8) x 10(8) copies/ u,eeq ethene produced during 1,2-DCA dihaloelimination. The yield for the Geobacter population on TCE was estimated to be (1+/-0.5) x 10(8) copies/microeeq cDCE produced. Calculations showed that the Geobacter population was likely responsible for approximately 80% of the TCE dechlorinated to cDCE in this experiment. Acetogenesis by a Sporomusa population was the main competition to dechlorination for reducing equivalents. Sporomusa did not transform any chlorinated substrates tested, but was capable of converting methanol to acetate and hydrogen for dechlorination. Understanding the functions of various populations in mixed communities may explain why Dehalococcoides spp. are active at some sites and not others, and may also assist in optimizing the growth of bioaugmentation cultures, both in the laboratory and in the field. 相似文献
100.
A Sirigu L Cohen JR Duhamel B Pillon B Dubois Y Agid C Pierrot-Deseilligny 《Canadian Metallurgical Quarterly》1995,6(7):997-1001
The chronometry of imagined and actual movements was investigated in a patient with a unilateral lesion of the motor cortex. Motor imagery generated highly accurate estimates of motor performance in a variety of situations, reflecting the hypokinesia of the contralesional hand. There were parallel increases in mental and actual movement times from proximal to distal limb segments. Bimanual movements adopted the slower speed of the impaired hand in both conditions. Imagined motor sequences to the beat of a metronome predicted the maximum speed reached in actual performance. Finally, visually guided pointing showed the same target-size effects in the imagery and movement conditions. The results are in agreement with the hypothesis that common cerebral motor representations are activated when imaging and planning voluntary movements. 相似文献