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21.
Grard Delahay Stphane Kieger Nathalie Tanchoux Philippe Trens Bernard Coq 《Applied catalysis. B, Environmental》2004,52(4):251-257
The kinetics of the selective catalytic reduction (SCR) of NO by NH3 in the presence of O2 has been studied on a 5.5% Cu-faujasite (Cu-FAU) catalyst. Cu-FAU was composed of cationic and oxocationic Cu species. The SCR was studied in a gas phase-flowing reactor operating at atmospheric pressure. The reaction conditions explored were: 458<TR<513 K, 2503 (ppm) < 4000, 12 (%) < 4. The kinetic orders were 0.8–1 with respect to NO, 0.5–1 with respect to O2, and essentially 0 with respect to NH3. Based on these kinetic partial orders of reactions and elementary chemistry, a wide variety of mechanisms were explored, and different rate laws were derived. The best fit between the measured and calculated rates for the SCR of NO by NH3 was obtained with a rate law derived from a redox Mars and van Krevelen mechanism. The catalytic cycle is described by a sequence of three reactions: (i) CuI is oxidized by O2 to “CuII-oxo”, (ii) “CuII-oxo” reacts with NO to yield “CuII-NxOy”, and (iii) finally “CuII-NxOy” is reduced by NH3 to give N2, H2O, and the regeneration of CuI (closing of the catalytic cycle). The rate constants of the three steps have been determined at 458, 483, and 513 K. It is shown that CuI or “CuII-oxo” species constitute the rate-determining active center. 相似文献
22.
StudyonAdsorptionandDiffusioninZeoliteXiao-guangRenandYong-jiSong(DepartmentofChemicalEngineeringLiaoyangPetrochenicalEnginee... 相似文献
23.
Mansoor Kazemimoghadam Afshin Pak Toraj Mohammadi 《Microporous and mesoporous materials》2004,70(1-3):127-134
In this research, dehydration of water/1-1-dimethylhydrazine (UDMH) mixtures by zeolite NaA and hydroxy sodalite membranes has been investigated. Support of these membranes has been tubular mullites that have been made by extruding a mixture of about 67–75% kaolin clay and 33–25% distilled water using an extruder. Zeolite NaA and hydroxy sodalite membranes have been coated on the external surface of the porous supports by the hydrothermal synthesis.
UDMH/water mixtures have been separated at ambient temperature and pressure by pervaporation (PV) using these zeolite membranes. These membranes showed very high selectivity of water for all UDMH mixtures. For the UDMH/water mixtures, separation factor as high as 10 000 has been obtained for UDMH feed concentration of 2%. Total mass fluxes of 1.05–0.2 kg/(m2 h) have been also obtained. 相似文献
24.
Silica gel or zeolites AlPO-5 and SAPO-34 are recommended as adsorbents in water-driven heat pumps because of their selective water uptake. Secondary energy, like solar energy, can be used for regeneration of loaded adsorbers. In case of the availability of only low energy levels, the use of dealuminated Y zeolite (DAY) is the better choice because of the infinitely variation of its hydrophilic properties by tailoring of the framework Si/Al ratio. Actual data on the hydrothermal stability of DAY are lacking. Thus, we report on the long-term behavior of DAY zeolites with different Si/Al ratios. 相似文献
25.
26.
Zeolite based trace humidity sensor for high temperature applications in hydrogen atmosphere 总被引:1,自引:0,他引:1
We present a humidity sensor based on H-ZSM-5 type zeolite that is suitable to detect traces of humidity (10–110 ppmV) under harsh conditions, e.g. reducing atmosphere (H2) and high temperature (up to 600 °C). By means of complex impedance spectroscopy (IS) we show that the zeolite sensor responds linearly towards minimal changes in humidity. Therefore this result indicates that the zeolite sensor is capable to detect traces of humidity in processes where high temperatures in a hydrogen environment are required. 相似文献
27.
28.
在改性β分子筛液相催化异丁烯与甲醇合成MTBE反应动力学的基础上,考察了内扩散阻力和催化剂失活对醚化反应的影响。假设符合平行失活机理,建立了带内扩散阻力的失活动力学方程,通过实验数据拟合确定了失活动力学参数。计算结果表明,醚化失活机理符合平行失活机理,异丁烯与甲醇合成MTBE的同时,发生副反应生成积碳是失活的原因。该失活动力学方程能很好地拟合试验数据,统计检验表明在置信度为99%以下是适合的。用所建失活模型预测了反应温度、催化剂颗粒度及进料时间对催化剂相对活性、有效因子和异丁烯转化率的影响。 相似文献
29.
The long term radiation and thermal effects on porous and layer structured materials that may function as getters for radionuclides have been evaluated using accelerated laboratory experiments including energetic electron, ion or neutron irradiation, as well as high-temperature thermal annealing. The materials studied include: zeolites, layered silicates (mica and smectite clays), open framework structured apatite and crystalline silicotitanate (CST) which is an important synthetic ion-exchange material for the chemical separation of high-level liquid radioactive wastes.In situ transmission electron microscopy during irradiation by energetic electrons and ions has shown that all the studied materials are susceptible to irradiation-induced amorphization. Amorphization can be induced by ionization and/or direct displacement processes. Amorphization may be preceded or accompanied with dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layer silicates, radiation effects are significantly enhanced at higher temperatures. In fact, thermal annealing at high temperatures alone can cause complete amorphization of zeolites. Our experiments have shown that amorphization or even partial amorphization will cause a dramatic reduction (up to 95%) in ion-exchange and sorption/desorption capacities of zeolite for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g., zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release rate of sorbed or ion-exchanged radionuclides. 相似文献
30.
Zhaohui Li 《Canadian Metallurgical Quarterly》2004,130(2):205-208
In this study, the influence of solution pH and ionic strength on sorption of chromate by surfactant-modified zeolite was tested. The sorption of chromate followed a Langmuir isotherm under different pH and ionic strength conditions. However, as the solution pH and ionic strength increased, the Langmuir sorption coefficient of chromate decreased systematically, reflecting an increased competition of background electrolyte anions against chromate for sorption sites. The chromate sorption maximum also decreased slightly as the solution pH and ionic strength increased. The stoichiometric relationship between chromate sorption and counterion desorption further indicated that chromate sorption on surfactant-modified zeolite surfaces was mainly due to surface anion exchange. In addition, increases in background electrolyte reduced counterion desorption and resulted in a better surfactant bilayer formation. 相似文献