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61.
Research on bond between composite and concrete on beams externally reinforced with fiber reinforced polymers (ERBs) has generated many publications, but uncertainties remain. The issue of the long term behavior of those joints, especially the effect that severe and prolonged environmental actions may induce, justifies the search for additional data and recommendations to avoid premature debonding and failures.The present paper devotes attention to the effects of environmental aging on the constitutive bond-slip curves. Aging was imposed on an accelerated manner and several actions used to degrade the behavior of the joints evaluated by mechanical testing.Prismatic blocks of reinforced concrete linked on the upper side by a stainless steel hinge and externally bonded by a continuous strip of carbon or glass fiber reinforced polymer (CFRP or GFRP) adherent to the soffit were made so as to fit in commercially available laboratory climatic chambers. After aging, they were tested till failure under four point loading.Aging conditions imposed on the CFRP beams were (i) cycles of high-low relative humidity, (ii) salt fog cycles, and, on the GFRP beams, (iii) salt fog cycles, (iv) dry/wet cycles (water with 5.0% weight of NaCl), (v) total immersion in salt water, and (vi) freeze/thaw cycles.The results of the experimental program enabled the proposal of bond-slip laws that take into account the aging of the beams. They also showed that salt fog cycles were more severe in the case of CFRP, while freeze/thaw cycles were more degrading on bond of GFRP-to-concrete. The salt water effects on the GFRP beams appeared to be beneficial, most likely by improving the tensile strength of concrete. Numerical modeling certified by the obtained experimental data is presented that allows more general estimates of the environmental effects. 相似文献
62.
《Cement and Concrete Composites》2007,29(8):637-645
This paper presents an assessment of the chemical resistance of eight different compositions of polymeric mortars using four different concentrations of filler, fly ash, and two types of unsaturated polyester resins, namely isophtalic polyester and orthophtalic polyester. The samples were exposed to seven different acid environments that represent those that often account for corrosive processes in industrial environments. None of the compositions in the study showed evidence of physical surface changes nor weight loss. There was a decrease in the flexural strength of the samples exposed to corrosive agents and this effect was more pronounced in the compositions with lower filler concentrations. However, even in those samples, the remaining flexural strength values remained far higher than those found in mortars prepared with Portland cement, an inorganic binder. Statistical analysis showed that the type of resin, the concentration of filler and the type of corrosive solution used have a significant effect on the chemical resistance of the polymeric mortars investigated in this study. SEM analyses also showed that the chemical attack occurred in the polymer matrix–aggregate interface. 相似文献
63.
Hesam Kamyab Mohd Fadhil Md Din Seyed Ehsan Hosseini Sib Krishna Ghoshal Veeramuthu Ashokkumar Ali Keyvanfar Arezou Shafaghat Chew Tin Lee Ali asghar Bavafa Muhd Zaimi Abd Majid 《Clean Technologies and Environmental Policy》2016,18(8):2513-2523
Abundant wastewater discharges from palm oil industries in tropical nations being a valuable resource of biodiesel need proper exploration. Research hinted that such wastewater as economical nutrient source or substrate can support the cultivation of microalgae. In this experiment, we have tested the growth and lipid production of five different microalgal strains in palm oil mill effluent (POME). POME as a biofuel substrate is demonstrated to be lucrative for microalgae-assisted lipids production. POME is rich in macro- and micronutrients can be used as a growth medium for algal growth in order to reduce the growth medium cost and environmental pollutions. Among the five microalgal strains tested, Chlorella sorokiniana revealed optimum biomass and lipid production. The productivity was evaluated in terms of chlorophyll content, growth rate, biomass, and lipid content, which discerned to be 0.099/day, 8.0 mg/L day and 2.68 mg/mg cell dry weight (CDW). Furthermore, in this study, an optimization study was carried out to enhance the microalgae to produce high lipid content using carbon-to-nitrogen ratio and different light/dark periods. The presence of nitrogen combined glucose (with a carbon-to-nitrogen ratio 100:7) as an alternative source to carbon displayed higher lipid production of 2.68 (mg/mg CDW) by C. sorokiniana. This study confirms that 8:16 h light/dark condition at C:TN ratio of 100:7 supported to produce high lipid content of 17 mg lipid/mg CDW. The above results revealed that POME could be a suitable growth media for the alga C. sorokiniana to improve the maximum lipid yield for biofuels production. 相似文献
64.
65.
近年来,电石渣在燃煤电厂干法脱硫工艺的应用中取得了较多进展,但在湿法脱硫的应用中仍存在消溶特性差、亚硫酸钙氧化率低、石膏脱水困难等诸多问题,导致其难以大规模推广。本文从电石渣的理化性质出发,分析了孔隙结构、反应温度、Ca/S摩尔比对脱硫效率的影响,并探讨了电石渣作为脱硫剂对循环流化床锅炉效率及运行的影响,结合电石渣的消溶特性、浆液氧化特性及石膏脱水特性,分析了电石渣在湿法脱硫工艺应用中存在的问题,提出了一种以电石渣为原料,利用燃煤机组再生水深度处理系统生产石灰石浆液的工艺路线,并在2×660MW超超临界燃煤机组再生水深度处理系统中进行了可行性试验,当Ca(OH)2纯度≥95%时,合理的污泥掺配比例区间为50%~70%,所产石膏达到了二级石膏的品质要求。 相似文献
66.
Stratified concrete poses a promising alternative for construction. Its fresh and hardened properties have been studied at the material level; however, structural behavior in steel reinforced specimens has not been studied. This paper focuses on the flexural behavior of eight stratified reinforced concrete (SRC) specimens representing slices from a slab or non-bearing wall. Specimens with two stratified concrete designs and three steel ratios were tested and compared to estimates from a fiber element numerical model and rectangular stress-block design methods from ACI 318 and Eurocode 2. The results suggest that SRC has similar damage modes as ordinary reinforced concrete (ORC). The fiber element model accurately estimated the measured behavior, while ACI 318 and Eurocode 2 differed from the experimental results by <25%. These prediction accuracies are similar to those for ORC. Therefore, the flexural design of SRC can be done using both fiber element and rectangular stress-block approaches. 相似文献
67.
68.
Zeolite-A was synthesized and converted into various ion-exchanged catalytic forms successfully. These catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer Emmett Teller (BET) surface area measurement and thermal programmed desorption (TPD). Their catalytic activity was tested on the synthesis of benzimidazole using o-phenylenediamine (OPDA) and aldehyde at room temperature. The reaction proceeds efficiently under ambient conditions. The catalysts gave a high isolated yield of benzimidazole in a shorter reaction time at room temperature and were recycled several times. 相似文献
69.
Alkali–silica reaction (ASR) is one of the most important deterioration mechanisms in concrete leading to substantial damages of structures worldwide. Synchrotron-based micro-X-ray diffraction (micro-XRD) was employed to characterize the mineral phases formed in micro-cracks of concrete aggregates as a consequence of ASR. This high spatial resolution technique enables to directly gain structural information on ASR products formed in a 40-year old motorway bridge damaged due to ASR.Micro-X-ray-fluorescence was applied on thin sections to locate the reaction products formed in veins within concrete aggregates. Micro-XRD pattern were collected at selected points of interest along a vein by rotating the sample. Rietveld refinement determined the structure of the ASR product consisting of a new layered framework similar to mountainite and rhodesite.It is conceivable that understanding the structure of the ASR product may help developing new technical treatments inhibiting ASR. 相似文献
70.
Magnesium silicate hydrate (M-S-H) gel can be formed by the reaction of MgO with amorphous silica in the presence of sodium hexametaphosphate (Na-HMP). Typical pastes contain 40% MgO and 60% SF and have a w/c ratio of 0.5, but these exhibit shrinkage cracking on drying. The shrinkage characteristics of M-S-H mortar samples containing different additions of sand have been studied using dilatometry. The drying shrinkage was found to decrease with increasing sand addition and to increase with increased water content. Mortars with 60 wt.% sand addition and a w/c ratio of 0.5 had a drying shrinkage of 0.16% and did not show shrinkage cracking. A simple geometrical model based on particle packing is presented that explains the observed changes in drying shrinkage. Based on the geometrical model, the shrinkage of M-S-H mortar system can be reduced to zero when the volume fraction of sand in the mortar is about 0.77. 相似文献