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排序方式: 共有959条查询结果,搜索用时 15 毫秒
61.
A novel fiber tapering shape, which is based on compound parabolic geometry, is proposed to increase the acceptance angle of a compound parabolic concentrator. The proposed design is described by use of ray optics on a step-index multimode fiber. 相似文献
62.
63.
Evolving national energy supply/demand distribution systems rely, at least in part, on quantifiable factors such as local and national environmental restrictions, resource availability (type, price, and quantity) and the associated transportation infrastructure, the amount and price of capital available to consumers and suppliers of energy, total annualized system cost, including the annualized cost of end-use devices, and the demands for energy and their price/supply responsiveness. The evolution also depends on nonquantifiable factors such as personal, regionally aggregated, or even national “utility functions” and institutional or social barriers. Many models have been formulated which attempt to simulate these complex interactions.This paper describes a systematic statistical methodology for capturing, both visually and quantitatively, the trade-offs between competing quantifiable, differentiable objective functions in a model of the national energy system (Brookhaven Energy System Optimization Model). The aim is to provide decision makers with a more easily understood tool and a more easily defensible methodology on which trade-offs between certain sensitive and competing energy issues can be based. The methodology has the additional advantage of providing insights into the inherent structural relationships of the model (model simplification). 相似文献
64.
O'Driscoll NJ Beauchamp S Siciliano SD Rencz AN Lean DR 《Environmental science & technology》2003,37(10):2226-2235
Diurnal patterns for dissolved gaseous mercury (DGM) concentration, mercury flux, several water variables (pH, oxidation reduction potential (ORP), water temperature), and meteorological variables (wind speed, air temperature, % relative humidity, solar radiation) were measured in two lakes with contrasting dissolved organic carbon (DOC) concentrations in Kejimkujik Park, Nova Scotia. A continuous analysis system made it possible to measure quick changes in DGM over time. Consistently higher DGM concentrations were found in the high DOC lake as compared to the low DOC lake. An examination of current mercury flux models using this quantitative data indicated some good correlations between the date and predicted flux (r ranging from 0.27 to 0.83) but generally poor fit (standard deviation of residuals ranging from 0.97 to 3.39). Cross-correlation analysis indicated that DGM dynamics changed in response to solar radiation with lag-times of 65 and 90 min. This relationship with solar radiation was used to develop new predictive models of DGM and mercury flux dynamics for each lake. We suggest that a generalized approach using time-shifted solar radiation date to predict DGM can be incorporated into existing mercury flux models. It is clear from the work presented that DOC and wind speed may also play important roles in DGM and mercury flux dynamics, and these roles have not been adequately accounted for in current predictive models. 相似文献
65.
We present experimental measurements of the C K-ELNES of high temperature pyrolysed graphite and related crystalline materials as a function of collection angle and sample tilt. These results together with a corresponding theoretical analysis indicate that the so-called "magic angle" for EELS measurements of an anisotropic crystal such as graphite, where spectra are independent of sample orientation, is approximately two times the characteristic scattering angle. We briefly discuss the implications of this result for the experimental measurement of anisotropic structures, including interfaces, as well as for the detailed modelling of ELNES structures using advanced electronic structure calculations. 相似文献
66.
Yong-Han Kim Bo-Suk Yang Andy C. C. Tan 《Structural and Multidisciplinary Optimization》2007,33(6):493-506
A new bearing parameter identification methodology based on global optimization scheme using measured unbalance response of
rotor–bearing system is proposed. A new hybrid evolutionary algorithm which is a clustering-based hybrid evolutionary algorithm
(CHEA), is proposed for global optimization scheme to improve the convergence speed and global search ability. Clustering
of individuals by using a neural network is introduced to evaluate the degree of mature of genetic evolution. After clustering-based
genetic algorithm (GA), local search is carried out for each cluster to judge the convexity of each cluster. Finally, random
search is adapted for extrasearching to find a potential global candidate, which could be missed in GA and local search. The
proposed methodology can identify not only unknown bearing parameters but also unbalance information of disk by simply setting
them as unknown parameters. Numerical example and experimental results were used to verify the effectiveness of the proposed
methodology. 相似文献
67.
Numerical Modeling of Cemented Mine Backfill Deposition 总被引:1,自引:0,他引:1
In current underground mining practice, it is common to use tailings, without added cement, to fill mined-out voids (“stopes”). If fine-grained tailings are used, the high placement rates and low permeability can often result in undrained loading conditions and, hence, lower effective stress, when assessed in the conventional manner. Where cement is added, the cement modifies the consolidation characteristics in a number of ways, including increasing the strength and stiffness, reducing the permeability, and inducing volumetric changes associated with the hydration reactions leading to “self-desiccation.” As a result, conventional consolidation-analysis techniques are unsuitable for assessing the behavior. The one-dimensional mine-tailings-consolidation program (MinTaCo) has been modified, and renamed CeMinTaCo, to couple cement hydration with conventional consolidation analysis. The fundamental theory behind the modifications is presented. The model is used to undertake a sensitivity study, which highlights some of the important features of the behavior of cemented backfill, and shows how complex interactions between the various properties produce some outcomes that are counterintuitive. 相似文献
68.
Andy C. Yau N. K. Bose Michael K. Ng 《Multidimensional Systems and Signal Processing》2007,18(2-3):173-188
In this paper, we study the problem of reconstruction of a high-resolution (HR) image from several blurred low-resolution
(LR) image frames in medium field. The image frames consist of blurred, decimated, and noisy versions of a HR image. The HR
image is modeled as a Markov random field (MRF), and a maximum a posteriori (MAP) estimation technique is used for the restoration.
We show that with the periodic boundary condition, a HR image can be restored efficiently by using fast Fourier transforms.
We also apply the preconditioned conjugate gradient method to restore HR images in the aperiodic boundary condition. Computer
simulations are given to illustrate the effectiveness of the proposed approach.
This research was conducted with support from the Army Research Office Grant DAAD 19-03-1-0261 and the National Science Foundation
Grant CCF-0429481.
Research supported in part by RGC Grant Nos. 7130/02P, 7046/03P, 7035/04P and 7035/04P and FRG/04-05/II-51. 相似文献
69.
Sachin K. Sachdeva Prasanth B. Nair Andy J. Keane 《Probabilistic Engineering Mechanics》2006,21(2):182-192
We propose a hybrid formulation combining stochastic reduced basis methods with polynomial chaos expansions for solving linear random algebraic equations arising from discretization of stochastic partial differential equations. Our objective is to generalize stochastic reduced basis projection schemes to non-Gaussian uncertainty models and simplify the implementation of higher-order approximations. We employ basis vectors spanning the preconditioned stochastic Krylov subspace to represent the solution process. In the present formulation, the polynomial chaos decomposition technique is used to represent the stochastic basis vectors in terms of multidimensional Hermite polynomials. The Galerkin projection scheme is then employed to compute the undetermined coefficients in the reduced basis approximation. We present numerical studies on a linear structural problem where the Youngs modulus is represented using Gaussian as well as lognormal models to illustrate the performance of the hybrid stochastic reduced basis projection scheme. Comparison studies with the spectral stochastic finite element method suggest that the proposed hybrid formulation gives results of comparable accuracy at a lower computational cost. 相似文献
70.