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51.
Microstructure evolution during the homogenization heat treatment of Al–Mn–Fe–Si, or AA3xxx, alloys has been investigated using a combination of modeling and experimental studies. The model is fully coupled to CALculation PHAse Diagram (CALPHAD) software and has explicitly taken into account the two different length scales for diffusion encountered in modeling the homogenization process. The model is able to predict the evolution of all the important microstructural features during homogenization, including the inhomogeneous spatial distribution of dispersoids and alloying elements in solution, the dispersoid number density and the size distribution, and the type and fraction of intergranular constituent particles. Experiments were conducted using four direct chill (DC) cast AA3xxx alloys subjected to various homogenization treatments. The resulting microstructures were then characterized using a range of characterization techniques, including optical and electron microscopy, electron micro probe analysis, field emission gun scanning electron microscopy, and electrical resistivity measurements. The model predictions have been compared with the experimental measurements to validate the model. Further, it has been demonstrated that the validated model is able to predict the effects of alloying elements (e.g. Si and Mn) on microstructure evolution. It is concluded that the model provides a time and cost effective tool in optimizing and designing industrial AA3xxx alloy chemistries and homogenization heat treatments. 相似文献
52.
In this paper, a two-step scale-up procedure based on asymptotic homogenization theory is proposed for hierarchical structures consisting of multigrains and multidomains in piezoelectric materials. Intragranular domains are modeled as a microstructure during the first-step homogenization. Then, in the second-step homogenization, an aggregate of randomly oriented grains is modeled by applying the first-step homogenized material properties of multidomains to every grain. A dual-domain structure consisting of positive and negative directional domains with a 180° orientation gap is computed for case study analysis. The three-dimensional electron backscatter diffraction-measured microstructure is employed for the multigrain structure. The effect of the domain configuration on the macroscopic homogenized material properties of polycrystalline piezoelectric materials is investigated through the two-step homogenization process. In particular, the material property changes caused by the piezoelectric effect, which cannot be estimated by the mixture law, are discussed for multigrain and multidomain structures. 相似文献
53.
After fabrication the carbon-carbon (C/C) plain weave textile composites often show a certain degree of geometrical or material disorder including yarn waviness and misalignment or nesting of individual fiber tows together with intrinsic material porosity observed at all relevant scales. A brief survey of recently developed approaches for estimating overall elastic stiffnesses or thermal conductivities of such composite systems is presented in this paper. Depending on the source and type of available geometrical data the homogenization scheme usually relies either on finite element (FEM) simulations performed for a suitable Periodic Unit Cell (PUC) or employs one of the popular averaging techniques such as the Mori-Tanaka (MT) method. While existing applications of both methodologies are encouraging, there still exists a number of steps to be completed in the course of the future research. 相似文献
54.
受限于乡村的技术与经济能力,各地村镇普遍处于一个快速低技术的建设模式之下,造成各地的新兴村镇景观风貌状况日益堪忧。本文立足于解决实际问题,探索在当前村镇建设模式下,如何通过可操作手段来改善村镇空间环境。 相似文献
55.
Whey protein isolate (WPI) nanoparticles were prepared by diluting an alkaline solution of protein in ethanol at concentrations varying between 50 and 80%. The nanoparticles were then immediately diluted in buffer. While the nanoparticles were not stable at pH 7, they showed no changes in size when diluted at pH 3. When 75–80% ethanol was added during preparation, the size of the WPI nanoparticles ranged between 10 and 100 nm, with no change in size after dilution and storage at pH 3 for 96 h at 22 °C. When heating was applied, particle aggregation occurred, and large aggregates (>1 μm) were observed at temperatures > 60 °C. The particle size of the heat-induced aggregates could be reduced by homogenization. The nanoparticles prepared by desolvation showed interfacial pressure values similar to those of the corresponding protein solutions, indicating similar interfacial properties and the potential to be used to stabilize emulsions but as supramolecular aggregates of WPI. 相似文献
56.
Carbon nanotubes (CNTs) are an excellent candidate for the reinforcement of composite materials owing to their distinctive mechanical and electrical properties. Reticulate carbon nanotubes (R-CNTs) with a 2D or 3D configuration have been manufactured in which nonwoven connected CNTs are homogeneously distributed and connected with each other. A composite reinforced by R-CNTs can be fabricated by infiltrating a polymer into the R-CNT structure, which overcomes the inherent disadvantages of the lack of weaving of the CNTs and the low strength of the interface between CNTs and the polymer. In this paper, a 2D plane strain model of a R-CNT composite is presented to investigate its micro-deformation and effective stiffness. Using the two-scale expansion method, the effective stiffness coefficients and Young’s modulus are determined. The influences of microstructural parameters on the micro-deformation and effective stiffness of the R-CNT composite are studied to aid the design of new composites with optimal properties. It is shown that R-CNT composites have a strong microstructure-dependence and better effective mechanical properties than other CNT composites. 相似文献
57.
Two organic molecular crystalline species, ibuprophen (IB) and indomethacine (IM) were subjected to methanol absorption in the presence of hydrophilic organic matrix, hydroxypropyl methylcellulose (HPMC). While spraying of 8–10% methanol or water on the drug–matrix mixture decreased the subsequent milling time for amorphization, absorption of methanol in a closed container caused spontaneous amorphization of IB was observed to give a nanocomposites with macroscopic agglomerates up to 250 μm after methanol absorption for overnight. Gentle mechanical homogenization under saturated methanol vapor with a newly developed apparatus, a tandem rotation mill (TRM), brought about homogeneous grains of IB-HPMC nanocomposites with the average particle size, 30 μm. We observed amorphous particles of IB in 60 nm regime dispersed in HPMC matrix under a transmission electron microscope (TEM). In the case of IM, mechanical homogenization with TRM was indispensable to obtain similar nanocomposites with HPMC. 相似文献
58.
利用金相组织观察、差示扫描量热法、扫描电镜、X射线衍射等手段对7050铝合金铸态组织、不同条件下的均匀化效果和均匀化前后的组织转变进行了分析。结果表明,7050合金半连续铸锭中存在大量具有η-MgZn2型晶体结构的非平衡第二相Mg(AlZnCu)2,其熔化温度为477℃,在均匀化处理过程中,该非平衡凝固共晶相在477℃向合金基体溶解并转变成Al2CuMg(S相),S相在该合金中的熔化温度为490℃;在460℃均匀化处理时,结晶相η全部消失,晶间和晶内均出现球状S相。在随后的冷却过程中η相和S相先后在晶内析出,但在260℃时S相再一次消失。 相似文献
59.
60.