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81.
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83.
《International Journal of Hydrogen Energy》2022,47(3):1752-1764
Subsurface hydrogen (H2) storage in geological formations is of growing interest for decarbonization. However, there is a knowledge gap in understanding the multiphase flow involved in this process, which can have a significant impact on the recovery performance of H2. Therefore, a full-compositional modeling study was conducted to analyze potential issues and to understand the fundamental hydrodynamic mechanisms of H2 storage. We performed a range of 2D vertical simulations at the decametre scale with a very fine cell size (0.1 m) to observe the detailed flow behaviour of H2 with carbon dioxide (CO2) as cushion gas in various flow regimes. Issues such as viscous instability, capillary bypassing, gas trapping and gravity segregation are analysed here. To generalize our calculations, we have validated and applied the scaling theory in the context of subsurface H2 storage. Since this study is focused on the hydrodynamic behaviour, three dimensionless groups, including aspect factor, capillary/viscous ratio and gravity/viscous ratio were identified to correlate recovery performance between various scales in a fixed heterogeneous system. It was found that H2 could infiltrate the cushion gas in the proximity of the injectors, meaning that CO2 is not displaced away from the injectors in a piston-like fashion. As a result, the purity of the back produced H2 is much degraded, particularly in a viscous-dominated scenario. On the other hand, the injected H2 mostly accumulates at the top forming a highly restricted mixing zone with CO2 in the gravity-dominated case. The recovery performance is therefore much improved in this case. Although the gas distribution can be significantly altered by capillary forces leading to bypassed zones, the recovery performance of H2 is hardly influenced. This is because the back-produced H2 recovery is not dependent on the sweep efficiency of the gas. H2 can be back produced following the same paths which were formed during injection. 相似文献
84.
Some optimization problems in the field of nuclear engineering, as for example the incore nuclear fuel management and a nuclear reactor core design, are highly multimodal, requiring techniques that overcome local optima, exploring the search space and promoting the exploitation of its most promising areas. The differential evolution algorithm (DE) relies mainly on the mechanism of mutation, where an individual is perturbed using the weighted difference (with the so-called “scaling factor” F) between two randomly chosen individuals. DE's canonical version employs a constant value of F. However, this parameter should be variable in order to balance the exploration and exploitation of the search space. In this work, we test some variable scaling factors from the literature and present the novel exponential scaling factor. These methods are applied to two problems: the aforementioned core design and the turbine balancing problem, which is an NP-hard (i.e. intrinsically harder than those that can be solved in nondeterministic polynomial time) combinatorial optimization problem that can be used to assess the potential of an algorithm to be applied to fuel management optimization. DE with variable scaling factors perform well in both problems, showing potential to be used in other nuclear science and engineering optimization problems. 相似文献
85.
An experimental investigation into in-plane scaled Over-height Compact Tension (OCT) [45/90/−45/0]4s carbon/epoxy laminates was carried out to study the scaling of fracture response. The dimensions of the baseline specimens were scaled up and down by a factor of 2. Interrupted tests were carried out for specimens of each size in which the tests were stopped after certain load drops in order to study the failure mechanisms. X-ray Computed Tomography (CT) scanning was applied after the interrupted tests to examine the damage development and its effect on the fracture response. The test results showed that the scaling of the initial propagation of fracture follows Linear Elastic Fracture Mechanics (LEFM), but the development of the damage process zone differs with specimen sizes. The OCT specimens were found to be not large enough to generate a self-similar damage zone during propagation, and so no conclusions could be drawn regarding the R-curve effect. 相似文献
86.
87.
微波自动测量线系统与阻抗参数的CAT 总被引:10,自引:0,他引:10
根据手动测量的原理,将传统的微波测量线系统进行智能化、自动化和数字化改造,成为由PC机控制,自动测量,数据采集和处理、结果显示的微波CAT(Computer Aided Test)系统,并在此基础上实现了阻抗参数的CAT。 相似文献
88.
An input time delay always exists in practical systems. Analysis of the delay phenomenon in a continuous-time domain is sophisticated.
It is appropriate to obtain its corresponding discrete-time model for implementation via digital computers. In this paper
a new scheme for the discretization of nonlinear systems using Taylor series expansion and the zero-order hold assumption
is proposed. The mathematical structure of the new discretization method is analyzed. On the basis of this structure the sampled-data
representation of nonlinear systems with time-delayed multi-input is presented. The delayed multi-input general equation has
been derived. In particular, the effect of the time-discretization method on key properties of nonlinear control systems,
such as equilibrium properties and asymptotic stability, is examined. Additionally, hybrid discretization schemes that result
from a combination of the scaling and squaring technique (SST) with the Taylor series expansion are also proposed, especially
under conditions of very low sampling rates. Practical issues associated with the selection of the method’s parameters to
meet CPU time and accuracy requirements, are examined as well. A performance of the proposed method is evaluated using a nonlinear
system with time delay: maneuvering an automobile. 相似文献
89.
T. Zhao 《Electrochimica acta》2006,51(11):2255-2260
Atomic force microscopy (AFM) was used to study the morphology of electrodeposited Cu at current densities from 183 to 253 A m−2. Digital image analysis was employed to parameterize the morphological information encoded in AFM images and to extract information concerning the mechanism of the electrodeposition reaction. It has been shown how the limiting roughness, δ, the critical scaling length, Lc and the aspect ratio, 4δ/Lc, vary as a function of the deposition time and electrodeposition conditions, such as temperature, current density and the amount of organic additives. It has been demonstrated how laboratory experiments of short duration and the scaling analysis of AFM images can be used to predict roughness of the metal sample after 2 weeks of industrial electrorefining. 相似文献