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排序方式: 共有93条查询结果,搜索用时 15 毫秒
1.
Type 17-4 PH martensitic precipitation-hardenable stainless steel, having a combination of high mechanical properties and
good corrosion resistance is widely used in aerospace, chemical, and petrochemical and food industries This alloy has a high
resistance to stress corrosion cracking but age hardening treatment, increases its sensitivity to stress corrosion cracking.
There are several works investigating the influence of different aging treatments on the microstructure, mechanical properties
and corrosion resistance of 17-4 PH steels, however there are little works studying the simultaneous effects of aging treatments
and molybdenum content on corrosion properties of these steels. In this research, the effect of molybdenum on stress corrosion
cracking resistance of 17-4 PH alloy using U-bend samples in chloride solutions, as well as its effect on passivity, has been
investigated. Quantometer, Scanning Electron Microscope(SEM) and potentiostat were used to determine the chemical composition,
microstructure and anodic polarization behavior of the alloys. It is found that molybdenum has a useful effect on stress corrosion
cracking resistance under the peak aged conditions, and this is because of development of delta-ferrite phase by increasing
the molybdenum content and subsequently decreasing the strength of the alloy. 相似文献
2.
Alireza Sharafi Majid Aminnayeri Amirhossein Amiri 《The International Journal of Advanced Manufacturing Technology》2012,63(1-4):209-214
Control charts are intended to aid quality practitioners in monitoring whether a change has occurred in a process. When a control chart indicates an out-of-control signal, it means that the process has changed. However, control chart signals do not indicate the real time of process changes; so estimators are applied to indicate the time when a change in the process takes place, which is referred to as the change point. This paper provides a maximum likelihood estimator to identify the real time of a step change in phase II monitoring of binary profiles, in which the quality of a process is characterized by a logistic regression between the response and predictor variables. Simulation studies are provided to evaluate the effectiveness of the change point estimator. 相似文献
3.
An engagement mode involves a subject (e.g., a user of information technology, or IT) who is engaged in an activity with an object in a certain manner (the mode). The purpose of this study is to develop a general model of engagement modes that may be used for understanding how IT-related activities are shaped by properties of the user and the IT object. A questionnaire involving items on IT engagement and the experience of flow was administered to 300 participants. The results supported an engagement mode (EM) model involving 5 different engagement modes (enjoying/acceptance, ambition/curiosity, avoidance/hesitation, frustration/ anxiety, and efficiency/productivity) characterized on 3 dimensions (evaluation of object, locus of control between subject and object, and intrinsic or extrinsic focus of motivation). The flow experience follows from a balance between enjoying/ acceptance and efficiency/productivity propelled by ambition/curiosity. The EM model could provide a platform for considering how IT users, IT applications, and IT environments should work together to yield both enjoyment and efficiency. Actual or potential applications of this research include designing IT training programs on different levels of specificity. 相似文献
4.
Vukusic J. Bryllert T. Arezoo Emadi T. Sadeghi M. Stake J. 《Electron Device Letters, IEEE》2007,28(5):340-342
We present a high-power InAlAs/InGaAs/InP heterostructure barrier varactor (HBV) frequency tripler. The HBV device topology was designed for efficient thermal dissipation and high efficiency. To verify simulations, the device was flip-chip soldered onto embedding microstrip circuitry on an aluminum nitride substrate. This hybrid circuit was then mounted in a waveguide block without any movable tuners. From the resulting RF measurements, the maximum output power was 195 mW at 113 GHz, with a conversion efficiency of 15%. The measured 3-dB bandwidth was 1.5% 相似文献
5.
Mehrorang Ghaedi Javad Tashkhourian Arezoo Amiri Pebdani Batol Sadeghian Fatemeh Nami Ana 《Korean Journal of Chemical Engineering》2011,28(12):2255-2261
The proposed research describes the synthesis and characterization of platinum nanoparticles loaded on activated carbon (Pt-NP-AC)
and its efficient application as novel adsorbent for efficient removal of reactive orange 12 (RO-12). The influences of effective
parameters following the optimization of variables on removal percentages, their value was set as 0.015 g Pt-NP-AC, pH 1,
contact time of 13 min. At optimum values of all variables at 25 and 50 mgL−1 of RO-12 enthalpy (ΔH0) and entropy (ΔS0) changes was found to be 59.89 and 225.076, respectively, which negative value of ΔG0 shows a spontaneous nature, and the positive values of ΔH0 and ΔS0 indicate the endothermic nature and adsorption organized of dye molecule on the adsorbent surface. Experimental data was
fitted to different kinetic models including first-order, pseudo-second-order, Elovich and intra-particle diffusion models,
and it was seen that the adsorption process follows pseudo-second-order model in consideration to intra-particle diffusion
mechanism. At optimum values of all variables, the adsorption process follows the second-order kinetic and Langmuir isotherm
model with adsorption capacity 285.143 mg g−1 at room temperature. 相似文献
6.
Arezoo Khosravi Hadi Baharifar Mohamad Hasan Darvishi Ali Akbar Karimi Zarchi 《IET nanobiotechnology / IET》2020,14(9):899
Tissue plasminogen activator (tPA) a thrombolytic agent is commonly used for digesting the blood clot. tPA half‐life is low (4–6 min) and its administration needs a prolonged continuous infusion. Improving tPA half‐life could reduce enzyme dosage and enhance patient compliance. Nano‐carries could be used as delivery systems for the protection of enzymes physically, enhancing half‐life and increasing the stability of them. In this study, chitosan (CS) and polyethylene glycol (PEG) were used for the preparation of CS‐g‐PEG/tPA nanoparticles (NPs) via the ion gelation method. Particles’ size and loading capacity were optimised by central composite design. Then, NPs cytotoxicity, release profile, enzyme activity and in vivo half‐life and coagulation time were investigated. The results showed that NPs does not have significant cytotoxicity. Release study revealed that a burst effect happened in the first 5 min and resulted in releasing 30% of tPA. Loading tPA in NPs could decrease 25% of its activity but the half‐life of it increases in comparison to free tPA in vivo. Also, blood coagulation time has significantly affected (p ‐value = 0.041) by encapsulated tPA in comparison to free tPA. So, CS‐g‐PEG/tPA could increase enzyme half‐life during the time and could be used as a non‐toxic candidate delivery system for tPA.Inspec keywords: drug delivery systems, nanofabrication, drugs, nanomedicine, coagulation, biomedical materials, cellular biophysics, enzymes, biochemistry, toxicology, molecular biophysics, biological tissues, blood, nanoparticles, polymersOther keywords: chitosan‐g‐PEG grafted nanoparticles, half‐life enhancer carrier, tissue plasminogen activator delivery, tPA half‐life, prolonged continuous infusion, enzyme dosage, polyethylene glycol, cytotoxicity, enzyme activity, encapsulated tPA, enzyme half‐life, blood coagulation, time 5.0 min 相似文献
7.
Seismic performance evaluation of steel moment resisting frames through incremental dynamic analysis 总被引:2,自引:0,他引:2
Earthquake hazards effect significant damage to structures and cause widespread failure throughout buildings. Moment resisting frames are widely used as lateral resisting systems when sufficient ductility is to be met. Generally three types of moment resisting frames are designed in practice namely Special, Intermediate and Ordinary Moment Frames, each of which has certain level of ductility. Comparative studies on the seismic performance of these three different types of structure are performed in this study. Analytical models of connections are employed including panel zone and beam to column joint model. Incremental dynamic analysis is then utilized to assess the structural dynamic behavior of the frames and to generate required data for performance based evaluations. Maximum annual probability of exceeding different limit states may reveal the superiority of a ductile structure in which a greater behavior factor is employed. Special moment resisting frames are expected to perform better once a certain level of ductility is to be met but the amount of superiority may be the subject of investigation especially from a performance based design standpoint. 相似文献
8.
Influence of two nano-size additives on electrical properties of suspension matrix of self-flowing low-cement high alumina refractory castable is investigated. For this purpose, castament FS 10 and FS 20 on the basis of polycarboxylate ether were considered. The self-flow value, workability and mechanical strength of the castable are evaluated and their relations with electrical conductivity are determined. Using these relations, the type and optimum amount of proper additive for these refractory castables are determined. It was shown that if the electrical conductivity of matrix suspension is less than 0.71 mS/cm, high alumina low-cement self-flowing refractory castable can be obtained. The best self-flow, sufficient working time and adequate mechanical strength in the castables are obtained with 0.08 wt.% FS 20. 相似文献
9.
A novel wideband three‐layer chessboard‐like structure is proposed to reduce the radar cross section (RCS) of the radar target. This configuration is composed of two artificial magnetic conductor (AMC) cells formed by two crossed ellipses with different sizes in two cells. A desired 180° ± 37° phase difference is achieved by combining these unit cells and the measured 10 dB RCS‐reduction bandwidth is extensively broadened to more than 96% (from 8.11 to 23.32 GHz, covering X, Ku, and K bands for different radars) in comparison with the other works. This characteristic is obtained by carefully adjusting the positions of all resonances using the proper sizes for the ellipses and the proper dielectric constants and thicknesses for the three layers. Although, the proposed design has three layers with the overall thickness of 2 mm, it is still thinner than most of the recent related works. This low‐profile structure is also cost‐effective due to the fact that 60% of the overall thickness is formed by an air substrate. The proposed cells are designed, simulated, and fabricated in a chessboard‐like configuration for both monostatic and bistatic RCSs. Simulations and measurements are in a good agreement, which shows the capabilities of the design. 相似文献
10.
Fabrication and characterization of novel nanofibers from cress seed mucilage for food applications 下载免费PDF全文
Cress seed mucilage (CSM) as a new source of biomacromolecule has gained attraction in food science due to its biodegradability and biocompatibility. In this research CSM–poly(vinyl alcohol) (PVA) nanofibers were produced under different conditions by electrospinning technique. Viscosity and electrical conductivity of the produced biopolymers were analyzed. The effect of CSM to PVA volume ratio and applied electrical field were evaluated on nanofiber morphology by scanning electron spectroscopy. The optimum nanofibers showed smooth and uniform surfaces with diameter size range of 95–278 nm. The results of Fourier transform infrared spectroscopy of CSM–PVA nanofiber with volume ratio of 60:40 showed characteristic peaks of CSM and PVA. X‐ray diffractometer data clearly revealed the amorphous structure of the electrospun nanofibers. Thermogravimetric and derivative thermogravimetric analysis indicated that thermal stability of electrospun nanofibers increased in comparison to CSM and PVA. The results of this study indicated that CSM can be applied as a new source of biopolymer for production of nanofibers that could be used for different applications such as delivery systems and packaging film fabrication. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45811. 相似文献