全文获取类型
收费全文 | 1181篇 |
免费 | 78篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 19篇 |
综合类 | 5篇 |
化学工业 | 259篇 |
金属工艺 | 34篇 |
机械仪表 | 68篇 |
建筑科学 | 43篇 |
矿业工程 | 1篇 |
能源动力 | 79篇 |
轻工业 | 122篇 |
水利工程 | 18篇 |
石油天然气 | 21篇 |
无线电 | 103篇 |
一般工业技术 | 233篇 |
冶金工业 | 65篇 |
原子能技术 | 5篇 |
自动化技术 | 196篇 |
出版年
2024年 | 5篇 |
2023年 | 23篇 |
2022年 | 20篇 |
2021年 | 74篇 |
2020年 | 68篇 |
2019年 | 85篇 |
2018年 | 106篇 |
2017年 | 80篇 |
2016年 | 88篇 |
2015年 | 36篇 |
2014年 | 71篇 |
2013年 | 138篇 |
2012年 | 69篇 |
2011年 | 85篇 |
2010年 | 51篇 |
2009年 | 52篇 |
2008年 | 29篇 |
2007年 | 21篇 |
2006年 | 8篇 |
2005年 | 13篇 |
2004年 | 4篇 |
2003年 | 11篇 |
2002年 | 6篇 |
2001年 | 4篇 |
1999年 | 3篇 |
1998年 | 8篇 |
1997年 | 7篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 13篇 |
1981年 | 3篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1970年 | 5篇 |
1966年 | 6篇 |
1961年 | 3篇 |
排序方式: 共有1271条查询结果,搜索用时 0 毫秒
41.
Rahmatollah Rahimi Azadeh Tadjarodi Mahboubeh Rabbani Hamed Kerdari Mina Imani 《Journal of Superconductivity and Novel Magnetism》2013,26(1):219-228
In this study, Ba-Cd-Sr-Ti doped Fe3O4 nanohollow spheres were successfully prepared via a simple solvothermal method. The crystal size, structure, morphology and elemental analysis of the as-prepared sample were investigated in detail by X-ray diffraction (XRD), FT-IR, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy, respectively. Magnetic hysteresis measurement was carried out on a vibrant sample magnetometer (VSM) showing the soft ferromagnetic property at room temperature. The synthesized nanohollow spheres were employed as a photocatalyst to study the photocatalytic degradation of dye contaminations. The UV-Vis results showed that the specimen could well catalyze the decolorizing of congo red (CR) solution and a removal efficiency of 99.5 % was obtained at pH 6. The optical characteristic of the products was studied by estimating the band-gap energy based on diffuse-reflectance spectroscopy (DRS) which represented the doped magnetite with semiconductor metals to be more prone in the visible region as compared to UV region. Some factors such as initial dye concentration, pH, and contact time influencing the decomposition of CR were evaluated. 相似文献
42.
F. Khademi A. Poorbafrani P. Kameli H. Salamati 《Journal of Superconductivity and Novel Magnetism》2012,25(2):525-531
Eu-doped M-type barium ferrite powders (Ba1−x
Eu
x
Fe12O19) with x=0.0, 0.1, 0.2 and 0.25 were prepared by sol-gel method. The synthesized samples are characterized by thermo gravimetric analysis
(TG-DTA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), vibrating
sample magnetometer (VSM) and vector network analyzer. All the synthesized samples have the nearly single-magnetoplumbite
phase. The results show that the crystallite size of doped samples is smaller than pure one. The saturation magnetization
of doped ferrites decreases by the increase in Eu doping, while the coercivity increases. Maximum coercivity achieved in this
study is 6.12 KOe for x=0.25 sample. The enhancement of coercivity by Eu doping is mainly due to the higher magnetocrystalline anisotropy, which
is attributed to the partial change of Fe+3 ion to Fe+2 ion. The maximum reflection loss (RL) of −43 dB at frequency range of 12–18 GHz for the x=0.1 sample was obtained. The increase in reflection loss at higher frequency suggests that the Eu-doped sample can be used
for the application in microwave devices. 相似文献
43.
In recent years advanced high strength steels (AHSS) received increased interest for light structures with improved performance, but they are often sensitive to edge cracking during sheet metal forming. In this study mechanically sheared edges were characterized for three dual phase steels (DP600, DP780 and DP980), sheared with three die clearances (5%t, 10%t, 15%t) and along rolling and transverse directions. Microstructures of the materials were provided first, and then the sheared edges were examined by optical microscopy and scanning electron microscopy that reveal the morphology and random feature of the sheared edges. A factorial analysis was performed to reveal the general trends of the processing parameters on four edge zones. A new strain measurement method was used for characterizing strain distribution in the sheared region, which shows the peak strain to be higher than 3. The strain quickly decreases from sheared edge to interior, leaving a shear-affected zone of about 500 μm or 31% of the thickness. The fracture processes and involved mechanisms were discussed. 相似文献
44.
Hamid Reza Shokouhfar Hamed Jooypa Daryoosh Dideban 《Analog Integrated Circuits and Signal Processing》2018,95(2):295-306
In this paper, the context of modeling of the impact of mismatch and statistical variations on analogue circuit building blocks is emphasized. The aim is to develop a new algorithm which predicts the statistical behavior of important parameters of an amplifier including output resistance, voltage gain and trans-conductance. The relative error of standard deviation of statistical parameters will remain less than 5% compared with the most accurate Monte-Carlo (MC) simulations using atomistic library model-cards. In comparison with other models which are based on the normal distribution of parameters, the proposed model does not need this limiting presumption. On the other hand, the proposed algorithm is more efficient compared with time consuming MC atomistic simulations. 相似文献
45.
Hamed Aminzadeh 《Analog Integrated Circuits and Signal Processing》2018,95(2):271-282
Hybrid cascode feedforward compensation (HCFC) is an effective technique to stabilize nano-scale three-stage amplifiers driving ultra-large load capacitors. It divides the compensation capacitance and shares it between two high-speed local feedback loops embedded within the amplifier core. In this article, a systematic approach to analyze the transfer function and to evaluate the pole expressions of nano-scale HCFC amplifiers is presented. For the first time, the equivalent output impedance is successfully modeled to approximate the complicated transfer function of the HCFC amplifier without the need for lengthy pencil-and-paper calculations. An HCFC amplifier is designed and simulated in 90-nm CMOS technology, to verify the effectiveness of the new analytic approach. The simulated transfer function of the amplifier is almost identical to a calculated transfer function derived based on the new model. 相似文献
46.
Seyed Hamed Barghi Theodore T. TsotsisMuhammad Sahimi 《International Journal of Hydrogen Energy》2014
The question of chemisorption versus physisorption during hydrogen storage in carbon nanotubes (CNTs) is addressed experimentally. We utilize a powerful measurement technique based on a magnetic suspension balance coupled with a residual gas analyzer, and report new data for hydrogen sorption at pressures of up to 100 bar at 25 °C. The measured sorption capacity is less than 0.2 wt.%, and there is hysteresis in the sorption isotherms when multi-walled CNTs are exposed to hydrogen after pretreatment at elevated temperatures. The cause of the hysteresis is then studied, and is shown to be due to a combination of weak sorption – physisorption – and strong sorption – chemisorption – in the CNTs. Analysis of the experimental data enables us to calculate separately the individual hydrogen physisorption and chemisorption isotherms in CNTs that, to our knowledge, are reported for the first time here. The maximum measured hydrogen physisorption and chemisorption are 0.13 wt.% and 0.058 wt.%, respectively. 相似文献
47.
Ahmad Jonidi Jafari Babak Kakavandi Roshanak Rezaei Kalantary Hamed Gharibi Anvar Asadi Ali Azari Ali Akbar Babaei Afshin Takdastan 《Korean Journal of Chemical Engineering》2016,33(10):2878-2890
Discharging the effluents of textile wastewaters into potable water resources can endanger the ecosystem, due to their reactivity, toxicity, and chemical stability. In this research, the application of powder activated carbon modified with magnetite nanoparticles (PAC-MNPs) as an adsorbent for removal of reactive dyes (Reactive black 5 (RB5) and reactive red 120 (RR120)) was studied in a batch system. The adsorption performance was evaluated as a function of temperature, contact time and different adsorbent and adsorbate concentrations. The levels of factors were statistically optimized using Box-Behnken Design (BBD) from the response surface methodology (RSM) to maximize the efficiency of the system. The adsorption process of both dyes was fit with the pseudo-second order kinetic and Langmuir isotherm models. The identified optimum conditions of adsorption were 38.7 °C, 46.3 min, 0.8 g/L and 102 mg/L for temperature, contact time, adsorbent dose, and initial dyes concentration, respectively. According to the Langmuir isotherm, the maximum sorption capacities of 175.4 and 172.4 mg/g were obtained for RB5 and RR120, respectively. Thermodynamics studies indicated that the adsorption process of the reactive dyes was spontaneous, feasible, and endothermic. After five cycles, the adsorption efficiency was around 84 and 83% for RB5 and RR120, respectively. A high value of desorption was achieved, suggesting that the PAC-MNPs have a good potential in regeneration and reusability, and also can be effectively utilized in industrial applications. PAC-MNPs also show a good anti-interference potential for removal of reactive dyes in dye-industry wastewaters. 相似文献
48.
Seyed Hamed Mahdaviani Matin Parvari Davood Soudbar 《Korean Journal of Chemical Engineering》2016,33(2):423-437
A hybrid approach between the Taguchi method and grey relational analysis (GRA) with entropy measurement was applied to determine a single optimum setting for reaction factors of the proposed ethylene dimerization catalyst having overall selectivity to 1-butene (S1-btn (%)) and turnover frequency (TOF (h-1)) as multiple quality characteristics. Titanium tetrabutoxide (Ti(OC4H9)4) catalyst precursor in combination with triethyl aluminum (TEA) activator, 1,4-dioxane as a suitable modifier, and ethylene dichloride (EDC) as a novel promoter were used in the catalysis. Control factors of temperature, pressure, Al/Ti, 1,4-dioxane/Ti, and EDC/Ti mol ratios were investigated on three levels and their main effects were discussed. The effect of the binary interaction between temperature, pressure, and Al/Ti mol ratio was also examined. Weight of the responses was determined using entropy. Analysis of variance (ANOVA) for data obtained from GRA indicated that EDC/Ti mol ratio with 27.64% contribution had the most profound effect on the multiple quality characteristics. Development of the weighted Grey-Taguchi method used the Taguchi method as its basic structure, adopted GRA to deal with multiple responses, and entropy to enhance the reasonability of the comprehensive index produced by GRA to make the results more objective and accurate. Overall, these combined mathematical techniques improved catalytic performance for 1-butene production. 相似文献
49.
A modified thermodynamic insight to deliquescence of a void‐containing nanocrystal confirmed by MD simulation 下载免费PDF全文
Hamed Akbarzadeh Mohsen Abbaspour Sirous Salemi Azizeh Masoumi Amir Nasser Shamkhali 《American Institute of Chemical Engineers》2016,62(11):4066-4077
Existence of voids in crystalline structures can affect their physical and chemical properties considerably. When the size of the crystal reaches to nanoscale, experimental determination of its void fraction is difficult. In this work, a molecular dynamics approach is introduced to find equilibrium void fractions of a simple cubic (CsCl) and fcc (KCl) nanocrystals by determination of their deliquescence relative humidity (DRH) for different sizes and void fractions and extrapolation of the results to the bulk limit. To confirm the simulation results, the size dependency of DRH to the nanoparticle size was studied thermodynamically by inclusion of size‐dependent density of water nanodroplet which leads to a simple homographic equation. This method proposes the equilibrium void percents of CsCl and KCl nanoparticles to be 10 and 15%, respectively, which are obtained by extrapolation of the results to the bulk limit. The success of obtained Möbius function was also confirmed by fitting it to experimental data for deliquescence of NaCl nanoparticles which implies the importance of considering density of water nanodroplet as a size dependent quantity. Also, using the mentioned thermodynamic approach, void dependency of deliquescence for the nanoparticles was found to be as a quasi‐linear trend which is compatible with the simulation results. It is noticeable that the approach used this work for determination of equilibrium void fraction is only valid if the utilized force fields are accurate. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4066–4077, 2016 相似文献
50.
Soheila Lashgari Mohammad Karrabi Ismaeil Ghasemi Hamed Azizi Massimo Messori 《Iranian Polymer Journal》2016,25(2):193-202
Poly(l-lactic acid) (PLLA)/graphene nanoplatelets (GnP) nanocomposites were prepared through solvent casting and coagulation methods. The better dispersion of graphene was achieved by ultrasounds and its effect on crystallinity, thermomechanical and electrical properties of PLLA were studied and compared in both methods. Differential scanning calorimetry (DSC) was used to investigate the crystallinity of PLLA and its composites. Field emission gun scanning electron microscope (FEG-SEM) and wide-angle X-ray scattering (WAXS) were employed to characterize the microstructure of PLLA crystallites. Dynamic mechanical thermal analysis (DMTA) was performed to study the thermomechanical properties of the nanocomposites. FEG-SEM images illustrated finer dispersion of GnP in samples obtained by coagulation method with respect to solvent casting method. Graphene imparted higher electrical conductivity to nanocomposites obtained by solvent casting under ultrasound due to better formation of graphene network. DSC thermograms and their resulting data showed positive effects of GnP on crystallization kinetics of PLLA in both methods enhanced by the nucleating effect of graphene particles. Meanwhile, the effect of GnP, as nucleating agent, was more prominent in samples produced by coagulation method without utilization of ultrasounds. WAXS patterns represented the same characteristic peaks of PLLA in nanocomposite specimens suggesting similar crystalline structure of PLLA in presence of graphene, and the intensified peaks of nanocomposites compared to neat PLLA confirmed the DSC results regarding its improved crystallinity. Graphene increased storage modulus in rubbery region and glass transition temperature of nanocomposites in the coagulation method due to restricted mobility of PLLA chains. 相似文献