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21.
Eitan Altman 《Discrete Event Dynamic Systems》2009,19(1):115-136
We consider in this paper a class of vector valued processes that have the form Y
n + 1 = A
n
( Y
n
) + B
n
. B
n
is assumed to be stationary ergodic and A
n
is assumed to have a divisibility property. This class includes linear stochastic difference equations as well as multi-type
branching processes (with a discrete or with a continuous state space). We derive explicit expressions for the probability
distribution as well as for the two first moments of state vectors at the stationary regime. We then apply this approach to
derive two formalisms to describe the infinite server queue. The first is based on a branching process approach adapted to
phase type service time distributions. The second is based on a linear stochastic difference equation and is adapted to independent
and generally distributed service times with bounded support. In both cases we allow for generally distributed arrival process
(not necessarily i.i.d. nor Markovian).
Eitan Altman Since 1990, Dr. Altman has been a researcher at INRIA (National research institute in informatics and control) in Sophia-Antipolis, France. He has served on the editorial boards of several scientific journals: WINET, COMNET, JDEDS, SIAM (SICON), Stochastic Models, and Journal of Economy Dynamic and Control (JEDC). Has been plenary speaker, (co)chairman of the program committee and general chair of various international conferences. Has received the best paper award in several conferences. His main interests are application of control, game theory and bio-inspired paradigms to networking. 相似文献
Eitan AltmanEmail: |
Eitan Altman Since 1990, Dr. Altman has been a researcher at INRIA (National research institute in informatics and control) in Sophia-Antipolis, France. He has served on the editorial boards of several scientific journals: WINET, COMNET, JDEDS, SIAM (SICON), Stochastic Models, and Journal of Economy Dynamic and Control (JEDC). Has been plenary speaker, (co)chairman of the program committee and general chair of various international conferences. Has received the best paper award in several conferences. His main interests are application of control, game theory and bio-inspired paradigms to networking. 相似文献
22.
This paper reports on a method for the investigation of mechanical stress on MEMS sensor and actuator structures due to packaging
processes. A silicon test chip is developed and manufactured to validate the simulation results. Finite element analysis (FEA)
is used to optimize the geometric parameters and to find a stress sensitive sensor geometry. A diaphragm structure is used
as mechanical amplifier for bulk induced stresses during the packaging process. Piezo resistive solid state resistors are
doped into the surface of the chip to measure the stress in the diaphragms and at the contact pads being most significant
locations for analysis. A high precision ohmmeter was used to measure the resistance prior and past the packaging process.
The captured data allows for computation of the resulting stress loads in magnitude. Therefore, a stress evaluation of different
packaging technologies is conducted and the impact of the packaging process on reliability can be estimated immediately. 相似文献
23.
C Beretta-Piccoli P Weidmann R de Chatel D Hirsch FC Reubi 《Canadian Metallurgical Quarterly》1977,107(4):104-115
35 patients with benign essential hypertension were treated for 6 weeks with high doses of the mineralocorticoid-antagonist spironolactone (400 mg/day), or with the "loop-diuretic" mefruside (mean maximal dose 110 mg/day). Spironolactone caused greater reductions in blood pressure and blood volume and a more marked increase in plasma renin activity (PRA) than mefruside (p less than 0.05). It appears possible that he weaker antihypertensive effect of mefruside may relate partly to its lesser influence on circulatory volume. With both diuretics, mean decreases in blood pressure were greater in patients with low pre-therapeutic PRA than in patients with normal or high PRA. However, the diuretic-induced changes in blood pressure did not correlate with the associated variations in blood volume or PRA. Thus, the increased blood pressure sensitivity to diuretics in patients with low-renin essential hypertension did not appear to be volume or renin-dependent. Under normal conditions, the maintenance of a constant blood pressure during volume depletion may partly depend on compensatory activation of the sympathetic nervous system. Moreover, patients with low-renin essential hypertension have been found to have decreased adrenergic activity. It seems possible, therefore, that the marked blood pressure sensitivity to diuretic treatment in such patients may be the result of an impaired compensatory sympathetic response to sodium and volume depletion. Analysis of the literature suggests that the diuretic furosemide, a structural relative of mefruside, may also have less blood pressure lowering efficacy in patients with essential hypertension than the distally-acting thiazides, chlorthalidone or spironolactone. Consideration of possible differences in the blood pressure reducing potential of certain diuretics thus appears to be necessary in planning the pharmacotherapy of essential hypertension. 相似文献
24.
The U.S. Geological Survey evaluated 20 years of total phosphorus (P) and total nitrogen (N) concentration data for 18 Lake Champlain tributaries using a new statistical method based on weighted regressions to estimate daily concentration and flux histories based on discharge, season, and trend as explanatory variables. The use of all the streamflow discharge values for a given date in the record, in a process called “flow-normalization”, removed the year-to-year variation due to streamflow and generated a smooth time series from which trends were calculated. This approach to data analysis can be of great value to evaluations of the success of restoration efforts because it filters out the large random fluctuations in the flux that are due to the temporal variability in streamflow. Results for the full 20 years of record showed a mixture of upward and downward trends for concentrations and yields of P and N. When the record was broken into two 10-year periods, for many tributaries, the more recent period showed a reversal in N from upward to downward trends and a similar reversal or reduction in magnitude of upward trends for P. Some measures of P and N concentrations and yields appear to be related to intensity of agricultural activities, point-source loads of P, or population density. Total flow-normalized P flux aggregated from the monitored tributaries showed a decrease of 30 metric tons per year from 1991 to 2009, which is about 15% of the targeted reduction established by the operational management plan for the Lake Champlain Basin. 相似文献
25.
Christian Daul Pierre Graebling Ernest Hirsch 《Computer Vision and Image Understanding》1998,72(3):215-236
The edges of simple geometrical (e.g., manufactured) parts can generally be approximated sufficiently accurately by straight-line segments and elliptical arcs in order, for example, to carry out a dimensional analysis of these parts, such as required by inspection tasks. Hough transforms are robust methods for the detection of straight-line segments but are not directly suitable for the detection of elliptical arcs, for which the processing time and memory space necessary are too important. We present in this paper a new method which allows the determination of the parameters of elliptical arcs (or of ellipses) by use of a two-dimensional discretized parameter space defined similarly to the usual Hough space. This new method allows both the detection and characterization of ellipses whose major and minor axis lengths can be as small as four pixels long or of elliptical arcs with a small angular aperture. 相似文献
26.
Thomas K. Hirsch Alexandre Da S. Rocha Fabiano D. Ramos Telmo R. Strohaecker 《Metallurgical and Materials Transactions A》2004,35(11):3523-3530
Plasma nitriding of tool materials is common practice to improve the wear resistance and lifetime of tools. Machining-induced
compressive residual stresses in shallow layers of some tenths of microns are observed accompanied by other characteristic
properties of machined surfaces in these high-strength materials. After plasma nitriding of M2 high-speed steel, previously
induced compressive residual stresses remain stable and the depth of diffusion layers decreases with increasing compressive
residual stresses. This article reports investigations of plasma nitrided samples with different levels of residual stresses
induced prior to the nitriding process. For comparison, experiments with bending load stresses during plasma nitriding have
also been carried out. The plasma nitriding treatment was performed at constant temperature of 500 °C with a gas mixture of
5 vol pct N2 in hydrogen. Nitriding time was varied from 30 to 120 minutes. All samples were characterized before and after plasma nitriding
concerning microstructure, roughness, microhardness, chemical composition, and residual stress states. Experimental results
are compared with analytical calculations on (residual) stress effects in diffusion and show a clear effect of residual and
load stresses in the diffusion of nitrogen in a high-strength M2 tool steel. 相似文献
27.
The purpose of this study was to demonstrate the presence of vinculin and alpha2 integrin in chondrocytes in situ and epithelial cells. We also determined that the appropriate fixation and extraction protocols for immunohistochemistry and laser scanning confocal microscopy for an integral membrane protein and an actin-associated protein in cultured cells and whole tissue was different. Cultured epithelial cells, whole mount human cornea and avian cartilage were fixed and prepared using a number of standard procedures used for indirect fluorescence immunohistochemistry. The distribution of vinculin was cell-type and fixation-specific. Chondrocytes and cultured epithelial cells demonstrated vinculin in areas that appear to be associated with filamentous actin. Vinculin was associated with cell membranes in human cornea. The expression of alpha2 integrin observed in chondrocytes fixed with methanol, paraformaldehyde, or formaldehyde is consistent with its role in cell-substrate interaction, but may also suggest a role in dividing and differentiating cells. The localization of alpha2 integrin in human corneal epithelia supports its role as a cell-cell adhesion molecule. The cytoplasmic distribution of vinculin and alpha2 integrin in tissues fixed without detergent extraction suggests that the fixation step may be sufficient for antibody penetration and antigen extraction. These studies are the first report of vinculin and alpha2 integrin in embryonic chondrocytes. In addition we have shown that confocal laser scanning microscopy combined with proper fixation and extraction protocols may optimize the localization of antigens in cultured and whole mount cells. 相似文献
28.
Red-Light Sensitivity of Sulphur-Sensitized Silver-Bromide Dispersions and the Effect of Aurous Gold
When silver sulphide is treated with certain aurous gold complexes, silver gold sulphide (AgAuS) is formed. Since the latter has different light absorption properties in the red region of the spectrum, it follows that the spectral sensitivity of sulphur-sensitized silver bromide coatings should be changed on treatment in a gold solution. This effect has been demonstrated. 相似文献
29.
We present a user‐guided, semi‐automatic approach to completing large holes in a mesh. The reconstruction of the missing features in such holes is usually ambiguous. Thus, unsupervised methods may produce unsatisfactory results. To overcome this problem, we let the user indicate constraints by providing merely four points per important feature curve on the mesh. Our algorithm regards this input as an indication of an important broken feature curve. Our completion is formulated as a global energy minimization problem, with user‐defined spatial‐coherence constraints, allows for completion that adheres to the existing features. We demonstrate the method on example problems that are not handled satisfactorily by fully automatic methods. 相似文献
30.