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排序方式: 共有270条查询结果,搜索用时 20 毫秒
31.
Siavash Ghabezloo Jean Sulem Sylvine Guédon François Martineau 《International Journal of Rock Mechanics and Mining Sciences》2009,46(2):297-306
The effective stress law for the permeability of a limestone is studied experimentally by performing constant-head permeability tests in a triaxial cell with different conditions of confining pressure σ and pore pressure pf. Test results show that a pore pressure increase and a confining pressure decrease both result in an increase of the permeability, and that the effect of the pore pressure change on the variation of the permeability is more important than the effect of a change of the confining pressure. A power law is proposed for the variation of the permeability with the effective stress (σ′=σ–nkpf). The permeability-effective stress coefficient nk increases linearly with the differential pressure and is greater than unity as soon as the differential pressure exceeds few bars. The test results are well reproduced using the proposed permeability-effective stress law. A conceptual pore-shell model based on a detailed observation of the microstructure of the studied limestone is proposed. This model is able to explain the experimental observations on the effect of the total stress and of the pore pressure on the permeability of the limestone. Effective stress coefficients for the stress-dependent permeability which are greater than one are obtained. It is shown that the controlling factor is the ratio of the different bulk moduli of the various constituents of the rock. This ratio is studied experimentally by performing microhardness tests. 相似文献
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Seyyed Arash Azimi Siavash Ahmadi Zahra Ahmadian Javad Mohajeri Mohammad Reza Aref 《International Journal of Communication Systems》2018,31(1)
HIGHT is a lightweight block cipher introduced in CHES 2006 by Hong et al as a block cipher suitable for low‐resource applications. In this paper, we propose improved impossible differential and biclique attacks on HIGHT block cipher both exploiting the permutation‐based property of the cipher's key schedule algorithm as well as its low diffusion. For impossible differential attack, we found a new 17‐round impossible differential characteristic that enables us to propose a new 27‐round impossible differential attack. The total time complexity of the attack is 2120.4 where an amount of 259.3 chosen plaintext‐ciphertext pairs and 2107.4 memory are required. We also instantiate a new biclique cryptanalysis of HIGHT, which is based on the new idea of splitting each of the forward and backward keys into 2 parts where the computations associated to each one are performed independently. The time complexity and data complexity of this attack are 2125.7 and 242, respectively. To the best of our knowledge, this is the fastest biclique attack on full‐round HIGHT. 相似文献
34.
Siavash H. Khajavi Gege Deng Jan Holmström Pasi Puukko Jouni Partanen 《国际生产研究杂志》2018,56(14):4874-4896
The paper analyses the impact of cheaper metal powder supplies on the comparative competitiveness of additive manufacturing (AM). By utilising two case studies, we compare the economic impact of an innovative titanium extraction method on Selective Laser Melting (SLM) and conventional methods of machining and casting. A switch-over analysis identifies the production quantities above which conventional manufacturing is more cost competitive than additive manufacturing. This analysis is performed for current raw material as well as cheaper raw material supply. The results illustrate the improved comparative competitiveness of SLM as the titanium supply is commoditised and more readily available in powder form. The responsiveness of the supply chain is improved as the switch-over point between SLM and conventional methods increases. Moreover, as the raw material supply chain for titanium is transformed through the use of this novel extraction method, the manufacturing supply chain is simplified. 相似文献
35.
Farhad Heidary Ali Nemati Kharat Alireza Khodabakhshi Sayed Siavash Madaeni 《Bulletin of Materials Science》2017,40(4):631-644
Homogeneous cation-exchange membranes were prepared through evaporation and phase inversion methods using sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) and sulfonated polyvinylchloride as binders. The effect of polymers blend’s ratio and preparation method on structure and electrochemical properties of the prepared membranes were evaluated. The microstructures of the membranes were investigated by scanning electron microscopy (SEM) and the sulfonation of polyvinylchloride was confirmed by elemental analyses. Moreover, the membranes performance was evaluated by ion-exchange capacity (IEC), fixed ion concentration, membrane potential, transport number, permselectivity, areal resistance, ionic permeability, flux of ions, current efficiency, membrane oxidative stability, mechanical properties and water content tests. The results indicated that IEC and water content were affected by the SPPO content and microstructures of the membranes. The results showed increased efficiency and suitable electrochemical properties for membranes prepared by the evaporation method in comparison with others. Also, \(\hbox {Fe}_{2}\hbox {O}_{3}\) nanoparticles were synthesized at room temperature by a simple sonochemical reaction between ferric chloride and NaOH. The results revealed that the addition of different amounts of \(\hbox {Fe}_{2}\hbox {O}_{3}\) nanoparticles to the polymeric matrix could affect the hydrophilicity and transport properties of ion-exchange membranes. 相似文献
36.
Uncontrolled hemorrhage continues to be the major cause of death in trauma. In this study, the authors prepared hydrogel nanocomposites (HNCs) using three different nanoparticles, SiO2, natural clinoptilolite (nC), and Ca2+-modified clinoptilolite (mC). Fast-swelling superabsorbent hydrogel was used as a matrix of NCs. The hydrogel and HNCs were characterized by FTIR, XRD, FE-SEM, and TGA. The hemocompatibility of HNCs was evaluated by hemolysis test and blood cells function. HNC formed a physical barrier by dehydrating the injury site and concentrating clotting factors. Additionally, highly charged nanoparticles, promoted local hemostasis by activating the intrinsic pathway of the blood coagulation cascade. 相似文献
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Silver nanoparticles dispersed in polyaniline matrixes coated on titanium substrate, as a novel electrode, was easily synthesized
by electro-polymerization of aniline on titanium and then electrodeposited silver nanoparticles on PAni electrode. The electrochemical
behavior and electro-catalytic activity of silver nanoparticles/PAni/Ti electrodes were characterized by cyclic voltammetry.
The morphology of silver nanoparticles on PAni/Ti electrodes were characterized by scanning electron microscopy and energy-dispersive
X-ray techniques, respectively. Results indicated that silver nanoparticles with a diameter of about 40–70 nm were homogeneously
dispersed on the surface of polyaniline film. The silver nanoparticles/PAni/Ti electrodes were examined for electro-catalytic
activity toward oxidation of hydrazine. The results show that these modified electrodes are highly active for electro-catalytic
oxidation of hydrazine. 相似文献
40.
The coupled thermo-elasticity problem in a thick-walled sphere is solved analytically using an innovative technique in conjunction with the finite Hankel transform. Time-dependent thermal and mechanical boundary conditions are assumed to act on the boundaries of the sphere. For the thermal boundary conditions, the temperature itself is prescribed on the boundaries. For the mechanical boundary conditions, the tractions are prescribed on both the inner and the outer surfaces of the hollow sphere. The transient thermo-mechanical response of the sphere is derived and then closed-form relations are extracted for the thermo-elastic stresses. Thermal shock was observed after plotting the results. 相似文献