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1.
2.
We have investigated the growth of heterostructures with high lattice mismatch and the growth of quantum wires on the top of ridges and through shadowing masks. Simulations are performed within a Monte Carlo scheme using tetrahedral lattice structure of semiconductor materials. It is shown that results of different simulations present similarities that we attribute to the primary role of kinetic effects as the driving force during epitaxial growth. The formation of 3D islands showing (111) facets, or (111) side walls when depositing through a shadowing mask, has been observed. The facets are of better quality than the top (001) surface because of the higher mobility of atoms on these facets. 相似文献
3.
R. Sh. Mikhail R. I. A. Malek 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1971,21(10):277-282
Specific surface areas and pore size distribution analysis were taken as essential parameters to explore the microstructure of hardened gypsum pastes. The hydration of gypsum plaster is essentially affected by the water/plaster ratio of the mix, and by the presence of additives which might act as retarders or accelerators to the hydration process. Affecting the microstructure would mutually lead to variations of the compressive strength of the hardened pastes, and these variations are also discussed. Results are mainly expressed in terms of the solid (measured by the extent of its specific area) to the space (pore) ratios. Dual distribution of pore sizes was observed and the two groups of pores are designed as S (small) and L (large) pores. Similarities to the microstructure of hardened Portland cement pastes are indicated. Accelerators appear to function differently from retarders, and the effects of water/plaster ratios were investigated in both cases. The results obtained may carry many significant practical implications to the future use of hardened gypsum pastes. 相似文献
4.
M. Sahli C. Roques-Carmes C. Khan Malek J. C. Gelin 《Microsystem Technologies》2008,14(9-11):1545-1551
The possibility to fill cavities of finite geometry could be described using an analytical model of the hot-embossing process of viscoelastic polymers. This model is based on the volume conservation during the forming process which allows to predict data concerning the geometrical evolution of the material on one hand, and on the other hand the filling time of cavities in the mould. A particular attention was drawn on the necessary time to fill the cavities depending on their shape or a scale factor for a given cavity shape. 相似文献
5.
Moussa Yahia Pascal Acco Malek Benslama 《International Journal of Control, Automation and Systems》2011,9(6):1021-1027
This paper proposes to decompose the nonlinear dynamic of a chaotic system with Chebyshev polynomials to improve performances
of its estimator. More widely than synchronization of chaotic systems, this algorithm is compared to other nonlinear stochastic
estimator such as Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF). Chebyshev polynomials orthogonality properties
is used to fit a polynomial to a nonlinear function. This polynomial is then used in an Exact Polynomial Kalman Filter (ExPKF)
to run real time state estimation. The ExPKF offers mean square error optimality because it can estimate exact statistics
of transformed variables through the polynomial function. Analytical expressions of those statistics are derived so as to
lower ExPKF algorithm computation complexity and allow real time applications. Simulations under the Additive White Gaussian
Noise (AWGN) hypothesis, show relevant performances of this algorithm compared to classical nonlinear estimators. 相似文献
6.
M.H. Mamat Z. KhusaimiM.Z. Musa M.F. Malek M. Rusop 《Sensors and actuators. A, Physical》2011,171(2):241-247
Unique and novel thin films with aluminium (Al)-doped zinc oxide (ZnO) nanostructures consisting of nanorod-nanoflake networks were prepared for metal-semiconductor-metal (MSM)-type ultraviolet (UV) photoconductive sensor applications. These nanostructures were grown on a glass substrate coated with a seed layer using a combination of ultrasonic-assisted sol-gel and immersion methods. The synthesised ZnO nanorods had diameters varying from 10 to 40 nm. Very thin nanoflake structures were grown vertically and horizontally on top of the nanorod array. The thin film had good ZnO crystallinity with a root mean square roughness of approximately 13.59 nm. The photocurrent properties for the Al-doped ZnO nanorod-nanoflake thin films were more than 1.5 times greater than those of the seed layer when the sensor was illuminated with 365 nm UV light at a density of 5 mA/cm2. The responsivity of the device was found to be dependent on the bias voltage. We found that similar photocurrent curves were produced over eight cycles, which indicated that the UV sensing capability of the fabricated sensor was highly reproducible. Our results provide a new approach for utilising the novel structure of Al-doped ZnO thin films with a nanorod-nanoflake network for UV sensor applications. To the best of our knowledge, UV photoconductive sensors using Al-doped ZnO thin films with a nanorod-nanoflake network have not yet been reported. 相似文献
7.
Mohamed Sahli Christine Millot Claude Roques-Carmes Chantal Khan Malek 《Microsystem Technologies》2009,15(6):827-835
Numerical modelling of the deformation of a polymer using the finite elements method in axisymetrical mode was performed using the LsDyna® software to describe the filling of micro-cavities during the forming process of the material using the hot embossing. These simulations firstly allow verifying whether the chosen forming process conditions promote or not an optimized filling of the superficial cavities in order to achieve precise replicas which best reproduce the superficial topography of the mould. The simulations were carried out to evaluate the filling of the cavities taking into account the mechanical behaviour of the selected polymer into the model. Moreover, these models were developed to verify the effect of the distribution of the mould cavities on their filling. The influence of the mobility of non deformable rigid plates on the filling of the cavities represents an auxiliary variable. In the approach presented, the compression plates are assumed to be parallel and non deformable, whereas the polymer disk follows a rubbery behaviour around a temperature equal to 140°C. Globally the modelling results are satisfactory for they are rather close to the experimental observations conducted. In summary, the effect of the normal stress as also the distribution of micro-cavities at the mould surface seem to prevail in the case of the forming process by hot embossing. 相似文献
8.
High-aspect ratio microelectroforming is one of the most challenging techniques in MEMS microfabrication. This is particularly
true with plating metal into the very tall micropatterned polymer molds made by X-ray lithography for primary or secondary
metal structures or metal mold inserts within the framework of the LIGA process. Among various problems are: (1) the time
consumption in plating very tall parts or using microelectroplating as a replication technique; (2) the cost of material,
in particular in the formation of very high-aspect-ratio absorber structures for X-ray masks in the deep and ultra-deep X-ray
lithography step.
Received: 7 July 2000/Accepted: 23 August 2000 相似文献
9.
R. A. Brennen M. H. Hecht D. V. Wiberg S. J. Manion W. D. Bonivert J. M. Hruby M. L. Scholz T. D. Stowe T. W. Kenny K. H. Jackson C. K. Malek 《Microsystem Technologies》1997,3(3):91-96
We are fabricating sub-collimating X-ray grids that are to be used in an orbiting solar X-ray telescope. The telescope optics
consist of twelve rotating pairs of high aspect ratio grids. The pitch for the grids ranges from 34 μm to 317 μm. The grid
thickness-to-grid-slit ratio must be approximately 50:1, resulting in grid thicknesses of 1 to 10 millimeters. We are implementing
a design in which a 34 μm pitch, free-standing PMMA grid is fabricated with 20 μm wide slits through a 800 μm thickness. After
exposure and developing, metal is electrodeposited into the slits in the PMMA grid and the PMMA is left in place to hold the
individual metal pieces. For optimum imaging performance, the root-mean-square pitch of the two grids of each pair must match
to within 1 part in 10000 and simultaneous exposures of stacked sheets of PMMA have insured that this requirement is met.
Received: 30 October 1995 / Accepted: 25 January 1996 相似文献
10.
T. W. Tsuei R. L. Wood C. Khan Malek M. M. Donnelly R. B. Fair 《Microsystem Technologies》1998,4(4):201-204
A method for creating angled structures for use in microvalve devices applicable to control of liquid flow is presented.
This technique utilizes a modified LIGA process with successive angled and rotated exposures into free standing acrylic sheets
to form a tapered valve seat structure. These valve seats are integrated with bulk micromachined silicon diaphragms and tapered
PMMA valve bosses to complete the microvalve. The long term goal of this research effort is to develop a normally-closed,
low power, microfabricated valve for use in an implantable drug delivery system. This paper reports on the design and fabrication
of microvalves using off-axis LIGA exposures. Flow testing and fluid handling characterization results are also presented.
Received: 25 August 1997 Accepted: 22 October 1997 相似文献