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91.
The toughness of fiber-reinforced composites largely relies on crack bridging. More specifically, intact fibers left behind the tip of a propagating crack are progressively pulled out of the matrix, dissipating energy which translates into toughness. While short fibers are traditionally straight, recent work has showed that they can be shaped to increase the pullout strength, but not necessarily the energy to pullout. In this work we have modeled, fabricated and tested short fibers with tapered ends inspired from a high-performance natural material: nacre from mollusc shells. The main idea was to duplicate a key mechanism where a slight waviness of the inclusion can generate strain hardening and energy dissipation when the inclusion is pulled out. We have incorporated a similar feature to short fibers, in the form of tapered ends with well defined opening angles. We performed pullout tests on tapered steel fibers in epoxy matrices, which showed that the pullout of tapered fiber dissipates up to 27 times more energy than straight fibers. The experimental results also indicated the existence of an optimum taper angle to maximize work of pullout while preventing the brittle fracture of the matrix. An analytical model was developed to capture the pullout mechanism and the interaction between fiber and matrix. The analytical model can guide the design of tapered fibers by providing predictions on the influence of different parameters. 相似文献
92.
Lisa J. White Sue J. Lee Kasia Stepniewska Julie A. Simpson Saw Lu Mu Dwell Ratree Arunjerdja Pratap Singhasivanon Nicholas J. White Francois Nosten Rose McGready 《Journal of the Royal Society Interface》2012,9(68):503-510
Many women in resource-poor settings lack access to reliable gestational age assessment because they do not know their last menstrual period; there is no ultrasound (US) and methods of newborn gestational age dating are not practised by birth attendants. A bespoke multiple-measures model was developed to predict the expected date of delivery determined by US. The results are compared with both a linear and a nonlinear model. Prospectively collected early US and serial symphysis-pubis fundal height (SFH) data were used in the models. The data were collected from Karen and Burmese women attending antenatal care on the Thai–Burmese border. The multiple-measures model performed best, resulting in a range of accuracy depending on the number of SFH measures recorded per mother (for example six SFH measurements resulted in a prediction accuracy of ±2 weeks). SFH remains the proxy for gestational age in much of the resource-poor world. While more accurate measures should be encouraged, we demonstrate that a formula that incorporates at least three SFH measures from an individual mother and the slopes between them provide a significant increase in the accuracy of prediction compared with the linear and nonlinear formulae also using multiple SFH measures. 相似文献
93.
This paper presents a conceptual design approach including pattern creation from designers, alternative exploration with a DOE matrix, alternative analysis via computer simulation and alternative selection by DEA analysis. Designers possessing domain knowledge create various design patterns to meet the requirements of product performance and customer expectations. Then, based on these design patterns, the alternatives, considered as decision-making units (DMUs), are extracted from various quality level combinations by following the use of the DOE matrix. The nature of the DOE matrix ensures that distinctive representatives are constructed for all design alternatives. The total alternatives (DMUs) consist of the alternatives associated with all the patterns. Computer simulation with ANSYS software is introduced to convert the quality level combination of each alternative (DMU) into simulated outputs, which are further categorised into DEA inputs and DEA outputs for DEA frontier analysis. Four DEA methods, CCR-min input, CCR-max output, BCC-min input and BCC-max output, are used for analysing typical market representatives resulting from market uncertainty. The found efficiencies are used to rank and select the explored alternatives (DMUs) for the next stage of the detailed design. A bike-frame product is chosen as an example to demonstrate the proposed approach. The results clearly show that the proposed approach enables designers to economically select appropriate design alternatives that satisfy performance expectations during the conceptual design stage. 相似文献
94.
A data‐based approach for developing robust processes is presented and illustrated with an application to an industrial membrane manufacturing process. Using historical process data, principal component analysis and partial least squares are used to extract models of the process and of the sensitivities of the process to various disturbances, including raw material variations, environmental conditions, and process equipment differences. Robustness measures are presented to quantify the robustness of the process to each of these disturbances. The process is then made robust (insensitive) to the disturbances over which one has some control (e.g., by modifying the equipment units to which the process is sensitive and imposing specification regions on sensitive raw materials). It is also made robust to disturbances over which one has little control (e.g., environmental variations) by optimizing the process operating conditions with respect to performance and robustness measures. The optimization is easily performed in the low‐dimensional space of the latent variables even though the number of process variables involved is very large. After applying the methodology to historical data from the membrane manufacturing process, results from several months of subsequent operation are used to demonstrate the large improvement achieved in the robustness of the process. © 2010 American Institute of Chemical Engineers AIChE J, 2011 相似文献
95.
The self-diffusion coefficients of different molecular weight PEGs (Polyethylene glycol) and casein particles were measured, using a pulsed-gradient nuclear magnetic resonance technique (PFG-NMR), in native phosphocaseinate (NPC) and sodium caseinate (SC) dispersions where caseins are not structured into micelles. The dependence of the PEG self-diffusion coefficient on the PEG size, casein concentration, the size and the mobility of casein obstacle particles are reported. Wide differences in the PEG diffusion coefficients were found according to the casein particle structure. The greatest reduction in diffusion coefficients was found in sodium caseinate suspensions. Moreover, sodium caseinate aggregates were found to diffuse more slowly than casein micelles for casein concentrations >9 g/100 g H2O. Experimental PEG and casein diffusion findings were analyzed using two appropriate diffusion models: the Rouse model and the Speedy model, respectively. According to the Speedy model, caseins behave as hard spheres below the close packing limit (10 g/100 g H2O for SC (Farrer & Lips, 1999) and 15 g/100 g H2O for NPC (Bouchoux et al., 2009)) and as soft particles above this limit. Our results provided a consistent picture of the effects of diffusant mass, the dynamics of the host material and of the importance of the casein structure in determining the diffusion behavior of probes in these systems. 相似文献
96.
97.
98.
Clotilde Muller Sandrine Muller Aicha Sissoko Alexandre Klein Bernadette Faller Francois Chantrel 《Hemodialysis international. International Symposium on Home Hemodialysis》2012,16(4):556-558
Lanthanum therapy is an efficient therapy of hyperphosphoremia by chelating phosphore in the digestive tract. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table. This drug is lightly absorbed and has low water solubility. It should be borne in mind that abdominal X‐rays of patients taking lanthanum carbonate may have a radio‐opaque appearance typical of imaging agents. This characteristic is suggested to confirm adherence of the patient by doing an abdominal X‐ray. We describe in our case a particular good compliant patient with slow digestive transit, which ends by pseudo‐occlusion. 相似文献
99.
David R. Archer MCIWEM Francois Leesch & Kirsty Harwood 《Water and Environment Journal》2007,21(2):133-141
Extreme floods often demonstrate unanticipated characteristics that pose problems for management and response. The floods on the Tyne and Eden in January 2005 provided numerous examples of such unexpected response. This paper describes characteristics of storm rainfall and runoff generation on the River Tyne catchment, flood effects and damage. Unusual aspects of hydrological behaviour are highlighted as a basis for assessing what lessons can be learned for flood risk management. These include problems associated with coincidence of extreme wind speeds and rainfall, the retarding influence of floodplain storage on flood wave travel time in extreme flows, the influence of critical storm duration on the severity of the resulting flood on headwaters and main river, and the variety of mechanisms of flood occurrence. The occurrence of such an extreme flood provides the opportunity to validate and enhance the review process of the Environment Agency's flood zone maps. 相似文献
100.
There is interest as to whether the electromagnetic fields used in mobile radiotelephony might affect biological processes. Other weak fields such as gravity intervene in a number of physical and biological processes. Under appropriate in vitro conditions, the macroscopic self-organization of microtubules, a major cellular component, is triggered by gravity. We wished to investigate whether self-organization might also be affected by radiotelephone electromagnetic fields. Detecting a possible effect requires removing the obscuring effects triggered by gravity. A simple manner of doing this is by rotating the sample about the horizontal. However, if the external field does not also rotate with the sample, its possible effect might also be averaged down by rotation. Here, we describe an apparatus in which both the sample and an applied radiofrequency electromagnetic field (1.8 GHz) are stationary with respect to one another while undergoing horizontal rotation. The electromagnetic field profile within the apparatus has been measured and the apparatus tested by reproducing the in vitro behavior of microtubule preparations under conditions of weightlessness. Specific adsorption rates of electromagnetic energy within a sample are measured from the initial temperature rise the incident field causes. The apparatus can be readily adapted to expose samples to various other external fields and factors under conditions of weightlessness. 相似文献