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571.
Yuanxin ZHANG Abdol CHINI R. Edward MINCHIN Jr. Lourdes PTSCHELINZEW Dev SHAH 《工程管理前沿(英文版)》2018,5(2):240
The conventional Design-Bid-Build (DBB) construction contracting method has had various drawbacks exposed in highway construction practice, including lack of communication, inefficient design, antagonizing relationships, and increased disputes. To mitigate the negative aspects of DBB, several alternative contracting methods and alternative project delivery systems have been devised and introduced to the industry over the past 30 years. Five such innovations were tested by a research team from the University of Florida under the sponsorship of the Florida Department of Transportation (FDOT). To perform a realistic assessment, this study categorized FDOT projects built between 2006 and 2015 into groups according to current contract amounts. Both absolute and relative metrics were defined and employed. For comparison purposes, a collective analysis on all gathered data was performed. Additionally, the influence of outliers on the results was examined. The results showed that analyses based on individual cost categories are more convincing because large projects tend to impose stronger influence on the analyses. In addition, outliers must be identified and screened to reach realistic and reliable conclusions. With regard to the actual performance of the contracting methods, each performs differently within different cost categories. 相似文献
572.
In this paper, 2D and 3D Multiphysics Voronoi Cells (MVCs) are developed, for the Direct Mesoscale Numerical Simulation (DMNS) of the switching phenomena in ferroelectric polycrystalline materials. These arbitrarily shaped MVCs (arbitrary polygons in 2D, and arbitrary polyhedrons in 3D with each face being an arbitrary polygon) are developed, based on assuming radial basis functions to represent the internal primal variables (mechanical displacements and electric potential), and assuming linear functions to represent the primal variables on the element boundaries. For the 3D case, the linear functions used to represent the primal variables on each of the polygonal surfaces of the polyhedral VCs are the Barycentric Washspress functions. The present 2D MVC is denoted as MVC-RBF, while the 3D MVC is denoted as MVC-RBF-W. Each MVC can represent a single grain or crystallite, with an irregular polygonal shape for the 2D case, and an irregular polyhedral shape for the 3D case. In this work, a nonlinear constitutive model is used to describe the evolution of volume fractions of the constitutive-variants in each grain, as the electric or mechanical loading changes. This constitutive model is based on satisfying a local dissipation inequality in each grain in the polycrystalline that yields the minimum Gibbs free energy in this grain. This requirement should always hold in order to be consistent with the second law of thermodynamics and is used to govern the switching process in each grain in each simulation step. Since the interaction between the grains during the loading cycles has a profound influence on the switching phenomena, it is important to simulate the grains with geometrical shapes that are similar to the real shapes of the grains as seen in the lab experiments. Hence the use of 3D MVCs, which allow for the presence of all the six variants of the constitutive relations, together with the randomly generated crystallographic axes in each grain (or MVC), as done in the present paper, is considered to be the most realistic analytical model that can be used for the direct mesoscale numerical simulation of polycrystalline ferroelectric materials. 相似文献
573.
In this paper, a multiple-source-point boundary-collocation Trefftz method, with characteristic lengths being introduced in the basis functions, is proposed to solve the direct, as well as inverse Cauchy problems of the Laplace equation for a multiply connected domain. When a multiply connected domain with genus p (p>1) is considered, the conventional Trefftz method (T-Trefftz method) will fail since it allows only one source point, but the representation of solution using only one source point is impossible. We propose to relax this constraint by allowing many source points in the formulation. To set up a complete set of basis functions, we use the addition theorem of Bird and Steele (1992), to discuss how to correctly set up linearly-independent basis functions for each source point. In addition, we clearly explain the reason why using only one source point will fail, from a theoretical point of view, along with a numerical example. Several direct problems and inverse Cauchy problems are solved to check the validity of the proposed method. It is found that the present method can deal with both direct and inverse problems successfully. For inverse problems, the present method does not need to use any regularization technique, or the truncated singular value decomposition at all, since the use of a characteristic length can significantly reduce the ill-posed behavior. Here, the proposed method can be viewed as a general Trefftz method, since the conventional Trefftz method (T-Trefftz method) and the method of fundamental solutions (F-Trefftz method) can be considered as special cases of the presently proposed method. 相似文献
574.
Naif H. Alsharif Christine E. M. Berger Satya S. Varanasi Yimin Chao Benjamin R. Horrocks Harish K. Datta 《Small (Weinheim an der Bergstrasse, Germany)》2009,5(2):221-228
Nanocrystals of various inorganic materials are being considered for application in the life sciences as fluorescent labels and for such therapeutic applications as drug delivery or targeted cell destruction. The potential applications of the nanoparticles are critically compromised due to the well‐documented toxicity and lack of understanding about the mechanisms involved in the intracellular internalization. Here intracellular internalization and toxicity of alkyl‐capped silicon nanocrystals in human neoplastic and normal primary cells is reported. The capped nanocrystals lack cytotoxicity, and there is a marked difference in the rate and extent of intracellular accumulation of the nanoparticles between human cancerous and non‐cancerous primary cells, the rate and extent being higher in the malignant cells compared to normal human primary cells. The exposure of the cells to the alkyl‐capped nanocrystals demonstrates no evidence of in vitro cytotoxicity when assessed by cell morphology, apoptosis, and cell viability assays. The internalization of the nanocrystals by Hela and SW1353 cells is almost completely blocked by the pinocytosis inhibitors filipin, cytochalasin B, and actinomycin D. The internalization process is not associated with any surface change in the nanoparticles, as their luminescence spectrum is unaltered upon transport into the cytosol. The observed dramatic difference in the rate and extent of internalization of the nanocrystals between malignant and non‐malignant cells therefore offers potential application in the management of human neoplastic conditions. 相似文献
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578.
Coding theorems are an important area of study in information theory. Currently there is interest in studies using side information, and there is continued interest in problems of information under a fidelity criterion, i.e., rate distortion theory. We combine rate distortion theory and communication under side information. The paper proves the source coding theorem under a fidelity criterion when side information is provided at the encoder and the decoder. A converse of the source coding theorem has also been proved. 相似文献
579.
580.
The sulphidation behaviour of Fe—15Cr—4Al alloy has been investigated under low sulphur vapour pressure of 10?9 to 10?3 atm in the temperature range of 700–1000°C. Distinct changes in sulphide scale morphology were observed with the increase of partial vapour pressure of sulphur (ps2). Triplex and duplex sulphide layers were observed at higher and lower ps2 respectively. Parabolic rate constants of sulphidation of this alloy are strongly dependent on ps2 and activation energies of the order of 83,6 kJ/mole suggesting diffusion of iron as a rate controlling step. 相似文献