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461.
Preparation of polyvinylchloride membranes from solvent mixture by immersion precipitation 下载免费PDF全文
In this study, polyvinylchloride (PVC) membranes were prepared through the immersion precipitation method using a mixture of two solvents (tetrahydrofuran (THF) and dimethyl formamide (DMF)), which had different affinities with the nonsolvent (water). Membranes prepared from PVC/THF/water system showed a sponge‐like structure with isolated pores, which were impermeable to water even at a feed pressure of 20 bars, whereas those prepared from PVC/DMF/water exhibited a porous macrovoid containing morphology with a high water flux. The precipitation time and polymer concentration profiles were calculated by using a simple mathematical model and were in good agreement with the experimental findings on PVC/THF/water and PVC/DMF/water systems. By using a mixture of DMF and THF as solvent and changing the mixed solvent composition, membranes with different morphologies from sponge‐like to macrovoid containing were obtained. The membranes showed no water flux below a DMF concentration of 50 wt % and then became increasingly permeable with increasing DMF content in the casting solution. Measurement of the system cloud points showed a linear change of system thermodynamics with variation of the mixed solvent composition. The obtained results showed that although the system thermodynamics could explain the overall behavior of the system, but the local changes such as change of membrane performance from impermeable to permeable at a certain mixed solvent composition could not be explained by the thermodynamics alone. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40206. 相似文献
462.
A series of porphyrin-containing polymers with triazole rings as linkers have been successfully synthesized by click polymerization. The polycycloadditions of porphyrin-containing dialkyne 1 and 1,4-diazidobenzene 2 were initiated either by simple heating or by Cu(I)-catalyst, affording polymers P1-P8 with relatively high molecular weight. The polymerization process was monitored by gel permeation chromatography analysis. The polymer prepared by thermally initiated click polymerization has unimodal molecular weight distribution and moderate polydispersity index after prolonging reaction time to 170?h. Compared with the metal-free click polymerization, the rate of molecular weight growth in Cu(I)-catalyzed click polymerization declined, leading to relatively low molecular weight of the resulting polymer. The as-synthesized polymers are soluble in common organic solvents and stable at a temperature up to 350?°C. The photophysical properties of the porphyrin monomer and the polymer were investigated by UV?Cvis and fluorescence spectroscopy. This approach offers practical advantages over other synthetic methods used to prepare main-chain porphyrin-containing polymers with regard to the absence of byproducts generated during the polymerization reaction. 相似文献
463.
A micro-channel reactor with circular cross section was numerically studied. Inside the inner cylinder and the annulus section, steam reforming and oxidation reactions were occurred, respectively. With the variation in diameter of the annulus section along the reactor length, the effect of diameter changing was also studied. In this case, outer section is an incomplete cone. The results showed that conical annulus (right inlet) micro-reactor (when the diameter of the cone decreased along the reactor length) represents higher temperatures and conversions. Then, influences of some parameters were considered in this micro-reactor. With increasing some parameters such as inlet temperature and the steam to carbon ratio of inlet flow, methanol conversion increases, and increasing some other parameters such as flow rate, solid thickness and porosity of bed leads to the methanol conversion decreases as well. Effect of various diameters in this micro-reactor was considered. Also when oxidation reaction happened inside outer cone, the better results was represented. 相似文献
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465.
The headspace solid-phase microextraction (HS-SPME) method with two different coatings synthesized by sol-gel technology [such as poly(ethylene glycol) (PEG) and PEG reinforced with multi-walled carbon nanotubes (PEG/CNTs)] coupled with gas chromatography-flame ionization detector (GC-FID) was proposed for the determination of furan at trace levels in food samples. Under optimized conditions, the linear range for furan with PEG and PEG/CNTs fibers was 0.005-10 and 0.0005-10 ng/mL, the limit of detection (S/N = 3) was 0.001 and 0.00025 ng/mL and the limit of quantification (LOQ) was 0.005 and 0.0005 ng/mL, respectively. For PEG and PEG/CNTs fibers, repeatability (n = 5) was 6.2% and 4.9% and reproducibility (n = 3) was 6.6% and 5.3%, respectively. Relative recoveries for the spiked samples with 0.1 ng/mL of furan were ranged from 92% to 103%. The proposed HS-SPME-GC-FID method was successfully applied for the extraction of furan in two environmental food samples (baby food and fruit juice). 相似文献
466.
Raheleh Mahjoob Abdorreza Mohammadi Nafchi Elahe Omidbakhsh Amiri Jamshid Farmani 《Food science and biotechnology》2018,27(2):343-352
In this study, the effect of interesterification (using sodium methoxide) on physicochemical characteristics of fully hydrogenated palm olein (FHPO)/soybean oil blends (10 ratios) was investigated. Interesterification changed free fatty acid content, decreased oil stability index, solid fat content (SFC) and slip melting point (SMP), and does not affected the peroxide value. With the increase of FHPO ratio, oil stability index, SFC and SMP increased in both the interesterified and non-interesterified blends. Fats with higher FHPO ratio had narrower plastic range, as well. Compared to the initial blends, interesterified fats had wider plastic ranges at lower temperatures. Both the non-interesterified and interesterified blends showed monotectic behavior. The Gompertz function could describe SFC curve (as a function of temperature, saturated fatty acid (SFA) content or both) and SMP (as a function of SFA) of the interesterified fats with high R2 and low mean absolute error. 相似文献
467.
Jassiel V. H. Fontes Eliana Brandão da Silva Rodolfo Silva Mojtaba Maali Amiri Edgar Mendoza Harlysson W. S. Maia Irving D. Hernández 《Water and Environment Journal》2023,37(4):644-656
The Amazon basin is one of the largest hydrographic systems in the world, possessing a great diversity of natural resources in need of more sustainable water and environmental management. However, as much of what lies beneath the surface of Amazonian waters is still unexplored, underwater exploration technologies are seen as a means of research and monitoring. The present work therefore aims to answer two research questions: What are the current technologies that could be implemented for unmanned underwater research in the Amazon waters? What are the main limitations and existing alternatives for using unmanned underwater vehicles in the rivers of this region to provide more sustainable water and environment management? Our results demonstrate that remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) are possible options in the short and long terms, respectively. The main challenges in implementing these technologies are related to the variations in hydraulic geometry, current velocities and turbidity of the rivers, as well as the preservation of the region's biodiversity. This research can be taken as a starting point for planners and decision makers seeking more sustainable underwater and environmental exploration of the Amazon river system. 相似文献
468.
Sara Abossedgh Abbas Saghaei Amirhossein Amiri 《Quality and Reliability Engineering International》2023,39(1):99-112
The stochastic block model (SBM) is a random graph model that focuses on partitioning the nodes into blocks or communities. A degree-corrected stochastic block model (DCSBM) considers degree heterogeneity within nodes. Investigation of the type of edge label can be useful for studying networks. We have proposed a labeled degree-corrected stochastic block model (LDCSBM), added the probability of the occurrence of each edge label, and monitored the behavior of this network. The LDCSBM is a dynamic network that varies over time; thus, we applied the monitoring process to both the US Senate voting network and simulated networks by defining structural changes. We used the Shewhart control chart for detecting changes and studied the effect of Phase I parameter estimation on Phase II performance. The efficiency of the model for surveillance has been evaluated using the average run length for estimated parameters. 相似文献
469.
Silicon - Terahertz (THz) sources have attracted special attention for various applications. Compared to the standard silica-based optical fibers, silicon waveguides have more advantages such as... 相似文献