全文获取类型
收费全文 | 592篇 |
免费 | 36篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 10篇 |
化学工业 | 179篇 |
金属工艺 | 10篇 |
机械仪表 | 11篇 |
建筑科学 | 17篇 |
矿业工程 | 1篇 |
能源动力 | 50篇 |
轻工业 | 55篇 |
水利工程 | 12篇 |
石油天然气 | 8篇 |
无线电 | 54篇 |
一般工业技术 | 101篇 |
冶金工业 | 28篇 |
原子能技术 | 2篇 |
自动化技术 | 94篇 |
出版年
2024年 | 5篇 |
2023年 | 15篇 |
2022年 | 30篇 |
2021年 | 36篇 |
2020年 | 38篇 |
2019年 | 27篇 |
2018年 | 44篇 |
2017年 | 40篇 |
2016年 | 36篇 |
2015年 | 22篇 |
2014年 | 21篇 |
2013年 | 48篇 |
2012年 | 37篇 |
2011年 | 39篇 |
2010年 | 27篇 |
2009年 | 37篇 |
2008年 | 29篇 |
2007年 | 19篇 |
2006年 | 11篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1996年 | 3篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有632条查询结果,搜索用时 0 毫秒
71.
Response surface methodology (RSM) based on central composite design (CCD) was used to optimize the three important reaction variables — methanol/oil molar ratio (x1), reaction time (x2) and amount of catalyst (x3) for production of biodiesel from palm oil using KF/ZnO catalyst. Based on the CCD, a quadratic model was developed to correlate the reaction variables to the biodiesel yield. From the analysis of variance (ANOVA), the most influential factor on the experimental design response was identified. The predicted yield after process optimization was found to agree satisfactory with the experimental value. The optimum conditions for biodiesel production were found as follows: methanol/oil ratio of 11.43, reaction time of 9.72 h and catalyst amount of 5.52 wt%. The optimum biodiesel yield was 89.23%. 相似文献
72.
Numerical investigations are presented for mixed convection problems in a concentric inner sinusoidal cylinder and an outer rotating circular cylinder, which were kept at constant hot and cold temperatures, respectively. The free space between the cylinders and the enclosure walls was filled with a water‐Cu nanofluid. The governing equations are formulated for velocity, pressure, and temperature formulation and are modeled in COMSOL5.2a, a partial differential equation solver based on the Galerkin finite element method. The governing parameters considered are the solid volume fraction, [0, 0.02, 0.04, and 0.06], Re (1, 25, 100, 200, and 300), and Ra (less than 104), and the inner cylinder corrugation frequencies varied from (N = 3, 6, and 9). According to the calculations, the Reynolds number, the Rayleigh number, the nanoparticle volume fraction, and the number of corrugations play an important role of forming the stream and isothermal lines, the local and the average Nusselt number inside the annulus enclosure. The average Nusselt number decreases with increasing Reynolds number and the number of corrugations, while it increases as the Rayleigh number and the volume fraction increase. 相似文献
73.
The applications of nanotechnology in oilfields have attracted the attention of researchers to nanofluid injection as a novel approach for enhanced oil recovery. To better understand the prevailing mechanisms in such new displacement scenarios, micromodel experiments provide powerful tools to visually observe the way that nanoparticles may mobilize the trapped oil. In this work, the effect of silicon oxide nanoparticles on the alteration of wettability of glass micromodels was investigated in both experimental and numerical simulation approaches. The displacement experiments were performed on the original water-wet and imposed oil-wet (after aging in stearic acid/n-heptane solution) glass micromodels. The results of injection of nanofluids into the oil-saturated micromodels were then compared with those of the water injection scenarios. The flooding scenarios in the micromodels were also simulated numerically with the computational fluid dynamics (CFD) method. A good agreement between the experimental and simulation results was observed. An increase of 9% and 13% in the oil recovery was obtained by nanofluid flooding in experimental tests and CFD calculations, respectively. 相似文献
74.
Mohsen Zolghadr Alireza Shakeri Mohammad Jalal Zohuriaan-Mehr Ali Salimi 《应用聚合物科学杂志》2019,136(40):48015
Novel self-healing Diels–Alder (DA) polymer and the corresponding semi-interpenetrated polymer networks (semi-IPNs) were synthesized and characterized. Initially, a furan-functionalized resin (FFR) was synthesized through the ring-opening reaction of a conventional epoxy resin [diglycidyl ether bisphenol A (DGEBA)] with furfuryl alcohol as a bio-based compound. Subsequently, semi-IPNs with different compositions were obtained through the blending of DGEBA, FFR, 4,4′-diaminodiphenylmethane, and 1,1′-(methylenedi-1,4-phenylene) bismaleimide in the molten state by following a predetermined time–temperature program. Fourier transform infrared and nuclear magnetic resonance analyses confirmed the successful synthesis of the materials. Thermoreversibility via retro-DA (rDA) reaction was evidenced by differential scanning calorimetry (DSC) and sol–gel transition tests. Repeated DSC cycle was successfully performed thrice on the DA polyadduct which corroborated repeatability of the DA/rDA association/dissociation. Self-healing and mechanical properties were preliminarily evaluated by scanning electronic microscopy and flexural testing analyses, respectively. The self-healing efficiencies were around 80 and 95% for semi-IPN and DA polyadduct, respectively, based on flexural strength. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48015. 相似文献
75.
76.
In this paper, the ‘guidelines for strategic environmental assessment (SEA) of nuclear power programmes’ by the International Atomic Energy Agency are introduced. This includes a reflection on their preparation process and contents as well as consultation feedback. The preparation process started with two meetings of international nuclear and SEA experts and the creation of a writing team which prepared an initial set of draft guidelines. This was followed by various consultation exercises. The guidelines are organised along an allocation of tasks within a tiered system of energy related policies, plans, programmes and projects. Whilst consultation showed that there was agreement on the approach to most issues, no consensus was present on the extent to which economic and social issues should be fully integrated with environmental considerations. Strong support was given to the way quality review is designed, going beyond focusing on the main SEA reports to cover procedural and participatory aspects next to elements of a comprehensively tiered decision making framework, the ability to influence decisions as well as the quality (expertise and experience) of those involved in conducting the SEA.
Abbreviation: SEA: Strategic Environmental Assessment; EIA: Environmental Impact Assessment; IAEA: International Atomic Energy Agency 相似文献
77.
The present work concentrates on some physical investigation of the undoped and Cr doped SnO2 thin films deposited onto precleaned glass substrates by the spray pyrolysis system. The physical properties of the undoped and Cr doped SnO2 thin films were investigated by the X-ray diffraction (XRD), atomic force electron microscope (AFM), field emission scanning electron microscope (FESEM), four-probe method and double beam spectrophotometer. The undoped and Cr doped SnO2 films display a polycrystalline nature with orthorhombic crystal structure. The linear optical constants energy gap Eg, refractive index n, absorption coefficient α, static refractive index no, oscillation energy Eo, dispersion energy Ed and the Urbach energy of the undoped and Cr doped SnO2 thin films were evaluated. The investigated films exhibit a direct energy gap and their values decrease with the increasing of Cr doping content while the Urbach energy follows a reverse behavior. On the other hand, the nonlinear optical constants (third-order nonlinear susceptibility and nonlinear refractive index n2) have been increased with increasing the Cr doping content. Finally, it has been found that the sheet resistance and conductivity of the synthesized thin films were enhanced by increasing the Cr doping content. The 5?wt% Cr doped SnO2 thin film has a high value of the figure of merit among other films. 相似文献
78.
Electrosynthesized polymers of N-methylpyrrole (NMPy) and N-methylpyrrole-2,6-dimethyl-β-cyclodextrin NMPy-β-DMCD were characterized with cyclic voltammetry and in situ conductivity measurements in aqueous and nonaqueous solutions. In situ UV–vis-spectra of PNMPy and poly(NMPy-β-DMCD) films show differences both in band absorbances and in energies of polaronic transitions. For the electrosynthesis of poly(NMPy-β-DMCD), a (1:1) (mole–mole) NMPy-β-DMCD supramolecular cyclodextrin complex of N-methylpyrrole was used as starting material, which was previously characterized with proton NMR spectroscopy. The PNMPy and poly(NMPy-β-DMCD) films were prepared from 0.05 M NMPy and 0.05 M NMPy-β-DMCD complex, respectively, in 0.1 M LiClO4 aqueous solution and 0.1 M LiClO4 nonaqueous solution (acetonitrile) by electropolymerization. A slight positive shift of the oxidation peak and further differences are observed for poly(NMPy-β-DMCD) electrosynthesized in comparison with PNMPy prepared in both aqueous and nonaqueous solutions. Different CVs and ΔEp of films were observed at various scan rates. In situ conductivity values of PNMPy and poly(NMPy-β-DMCD) films prepared in nonaqueous solution (acetonitrile) show higher values than with films prepared in aqueous solutions. 相似文献
79.
A general method for determining whether a certain design is initializable, and for generating its initialization sequence, is presented in this paper. This method is based on structural decomposition of the circuit, and can handle both logical (using X-value simulation) and functional initializability. The routines developed are then used for ATPG of sequential circuits. A pre-test sequence that initializes the good and as many of the faulty machines as possible is generated and used in conjunction with CRIS [5], a simulation based sequential ATPG program, to generate a test set for the circuit. 相似文献
80.
Jalal Yousefi Mehdi Ahmadi Najfabadi Hossein Hosseini Toudeshky Mehdi Akhlaghi 《Applied Composite Materials》2018,25(5):1021-1040
In this paper, a very promising procedure is proposed to evaluate delamination using Acoustic Emission (AE) technique in composite laminates. First, a new procedure was developed to decompose the fundamental Lamb wave modes in small size specimens. The damage mechanisms in End Notched Flexure (ENF) in woven and unidirectional specimens were then discriminated using Fuzzy Clustering Method (FCM). Afterwards, the crack-arrest phenomenon was examined in each specimen. After that, experimental and Cohesive Zone Modeling (CZM) techniques were conducted to characterize the delamination using ENF specimens. The results showed how, it is possible to successfully decrease the effect of propagating media such as attenuation of AE signals using the new proposed methodology. As a final point, the results of this study could lead to efficiently distinguishing different damages in laminated composite using AE Lamb-based technique. 相似文献