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排序方式: 共有416条查询结果,搜索用时 15 毫秒
411.
Biogas is considered as a valuable source of renewable energy. Indeed, it can be turned into useful energy (heat, electricity, fuel) and can contribute to reduce greenhouse gas emissions. Knowledge of its safety characteristics is a very important practical issue. Experimental investigation of synthesised biogas explosion characteristics was conducted in a 20-L sphere at various temperatures (30-70 degrees C) and at atmospheric pressure. The studied biogas was made of 50% methane (CH(4)) and 50% carbon dioxide (CO(2)). It was also saturated with humidity: this composition is frequently met in digesters during waste methanisation. There are two inert gases in biogas: water vapour and carbon dioxide. Its vapour water content rises along with temperature. The presence of these inert gases modifies considerably biogas characteristics compared to the ones of pure methane: explosion limits are lowered and beyond 70 degrees C, water vapour content is sufficient to inert the mixture. Furthermore, explosion violence (estimated with the maximum rate of pressure rise values, (dp/dt)(max)) is three times lower for biogas than for pure methane at ambient temperature. 相似文献
412.
D. Buttin M. Dupont M. Straumann R. Gille J-C. Dubois R. Ornelas G.P. Fleba E. Ramunni V. Antonucci A.S. Aricò P. Cretì E. Modica M. Pham-Thi J-P. Ganne 《Journal of Applied Electrochemistry》2001,31(3):275-279
A five-cell 150 W air-feed direct methanol fuel cell (DMFC) stack was demonstrated. The DMFC cells employed Nafion 117® as a solid polymer electrolyte membrane and high surface area carbon supported Pt-Ru and Pt catalysts for methanol electrooxidation and oxygen reduction, respectively. Stainless steel-based stack housing and bipolar plates were utilized. Electrodes with a 225 cm2 geometrical area were manufactured by a doctor-blade technique. An average power density of about 140 mW cm–2 was obtained at 110 °C in the presence of 1 M methanol and 3 atm air feed. A small area graphite single cell (5 cm2) based on the same membrane electrode assembly (MEA) gave a power density of 180 mW cm–2 under similar operating conditions. This difference is ascribed to the larger internal resistance of the stack and to non-homogeneous reactant distribution. A small loss of performance was observed at high current densities after one month of discontinuous stack operation. 相似文献
413.
Site-directed mutagenesis study of a conserved residue in family 10 glycanases: histidine 86 of xylanase A from Streptomyces lividans 总被引:1,自引:0,他引:1
Roberge M; Shareck F; Morosoli R; Kluepfel D; Dupont C 《Protein engineering, design & selection : PEDS》1998,11(5):399-404
Xylanases from family 10 glycanases contain three conserved histidine
residues in their active site. The role of H86 in the structure- function
of xylanase A from Streptomyces lividans (XlnA) was studied by
site-directed mutagenesis. Six mutant proteins (H86A/E/F/K/Q/W) were
produced, purified and characterized. The six mutations reduced the
affinity of XlnA towards xylan without having any major effect on the
catalytic constant. All these mutations also lowered the pKa of the
acid-base catalyst by 0.46-1.94 pH units. The mutations decreased the
enzyme stability at 60 degrees C by up to 95% and the transition
temperature by 2.2-5.8 degrees C. Unfolding of the protein with guanidine
hydrochloride (GdnxHCl) showed that five out of six mutations decreased the
concentration required to denature 50% of the XlnA, confirming the
importance of H86 for the stability of the enzyme. The increase in m value
m=d(deltaG)/d[GdnxHCl] also suggested the involvement of residue H86 in the
structure of the denatured state of XlnA. It can be concluded from this
study that this active site residue was conserved in family 10 glycanases
for its function in maintaining the elevated pKa of the acid-base catalyst
and in the stability of the protein, while being of little importance for
the activity.
相似文献
414.
Simultaneous maximum a posteriori reconstruction of attenuation andactivity distributions from emission sinograms 总被引:1,自引:0,他引:1
Nuyts J. Dupont P. Stroobants S. Benninck R. Mortelmans L. Suetens P. 《IEEE transactions on medical imaging》1999,18(5):393-403
In order to perform attenuation correction in emission tomography an attenuation map is required. We propose a new method to compute this map directly from the emission sinogram, eliminating the transmission scan from the acquisition protocol. The problem is formulated as an optimization task where the objective function is a combination of the likelihood and an a priori probability. The latter uses a Gibbs prior distribution to encourage local smoothness and a multimodal distribution for the attenuation coefficients. Since the attenuation process is different in positron emission tomography (PET) and single photon emission tomography (SPECT), a separate algorithm for each case is derived. The method has been tested on mathematical phantoms and on a few clinical studies. For PET, good agreement was found between the images obtained with transmission measurements and those produced by the new algorithm in an abdominal study. For SPECT, promising simulation results have been obtained for nonhomogeneous attenuation due to the presence of the lungs. 相似文献
415.
Mnica Carcuchinski Haag Joo Henrique Zimnoch Dos Santos Jairton Dupont Argimiro Resende Secchi 《应用聚合物科学杂志》2000,76(3):425-438
A mathematical model for the homogeneous terpolymerization of ethylene–propylene–diene (EPDM) in a semibatch reactor using Et(Ind)2ZrCl2/MAO as a catalyst system was developed and reported herein. In this study, we developed a kinetic model in order to explain the catalyst and EPDM properties such as catalyst activity, weight‐average molecular weight, and terpolymer composition, which were experimentally and theoretically obtained. For this system, a lower E/P feed ratio leads to a lower molecular weight and a broader initial molecular weight distribution, while the increase in diene concentration leads to a decrease in the catalyst activity without broadening the MWD of the resulting polymers. The proposed model accounts for these experimental trends and for some data in the literature. 相似文献
416.
Meng Zhang Asher E. Vokoun Boyuan Chen Weichen Deng Robert L. Dupont Yang Xu Xiaoguang Wang 《加拿大化工杂志》2023,101(9):5189-5207
Traditional chemical reactors, such as batch reactors, continuous reactors, and semi-batch reactors, have been extensively studied and frequently act as central components of modern chemical plants. Recently, various advances in reaction times, surface-to-volume ratios, required amounts of reagents, and throughput have led to new directions in the design of miniaturized chemical reactors. In this Perspective, we provide an overview of the progress from traditional to miniaturized chemical reactors by summarizing the characteristics and applications of different types of reactors. Furthermore, we compare classical chemical reactors and miniaturized droplet reactors to highlight advancements in the design of droplet reactor systems based on open functional surfaces. Finally, we provide an outlook on the research directions of miniaturized droplet reactors. 相似文献