全文获取类型
收费全文 | 2421篇 |
免费 | 170篇 |
专业分类
电工技术 | 21篇 |
综合类 | 29篇 |
化学工业 | 962篇 |
金属工艺 | 26篇 |
机械仪表 | 42篇 |
建筑科学 | 99篇 |
矿业工程 | 6篇 |
能源动力 | 61篇 |
轻工业 | 380篇 |
水利工程 | 41篇 |
石油天然气 | 4篇 |
无线电 | 84篇 |
一般工业技术 | 379篇 |
冶金工业 | 137篇 |
原子能技术 | 7篇 |
自动化技术 | 313篇 |
出版年
2024年 | 16篇 |
2023年 | 28篇 |
2022年 | 174篇 |
2021年 | 177篇 |
2020年 | 96篇 |
2019年 | 85篇 |
2018年 | 90篇 |
2017年 | 94篇 |
2016年 | 109篇 |
2015年 | 93篇 |
2014年 | 125篇 |
2013年 | 172篇 |
2012年 | 143篇 |
2011年 | 208篇 |
2010年 | 120篇 |
2009年 | 118篇 |
2008年 | 129篇 |
2007年 | 96篇 |
2006年 | 72篇 |
2005年 | 50篇 |
2004年 | 48篇 |
2003年 | 49篇 |
2002年 | 41篇 |
2001年 | 27篇 |
2000年 | 28篇 |
1999年 | 29篇 |
1998年 | 31篇 |
1997年 | 15篇 |
1996年 | 12篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 15篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 1篇 |
1971年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2591条查询结果,搜索用时 15 毫秒
61.
Claudia Nurra Luizildo Pitol‐Filho Raphaelle Carraud Said Pertuz Domènec Puig Miguel A. García Joan Salvadó Carles Torras 《Polymer Engineering and Science》2016,56(1):118-124
One of the challenges in membrane technology is predicting permeability in porous membranes for liquid applications in an easy and inexpensive way. This is the aim of this work. To achieve this objective, several techniques can be considered. In this study, a morphological approach from two‐dimensional scanning electron micrographs is proposed. First, numerical membrane morphological parameters have been determined from micrographs by using the QUANTS tool, which applies a texture recognition process. Second, the obtained data have been fit to the Darcy's and Hagen–Poiseuille models to calculate permeations. The QUANTS results have also been compared with the ones obtained through a mercury porosimeter, which is a classic and well‐known methodology. Each parameter of the Hagen–Poiseuille model has been analyzed. A comparison between experimentally measured permeations and calculated ones has been performed. An even easier approach is proposed to predict flow rate with the only knowledge of membrane surface mean pore size. This method is based on cross‐section pore size interpolation by using function fits from surface mean pore sizes. The obtained results show a reasonable agreement between measured and computed results, making this technique a valid approach for predicting membrane permeability. POLYM. ENG. SCI., 56:118–124, 2016. © 2015 Society of Plastics Engineers 相似文献
62.
Claudia Holec Katharina Neufeld Jrg Pietruszka 《Advanced Synthesis \u0026amp; Catalysis》2016,358(11):1810-1819
Enzymatic oxidations of primary and secondary alcohols catalysed by nicotinamide dependent alcohol dehydrogenases on the preparative scale require cofactor regeneration systems. Of critical value from an economic and ecological perspective is the application of NAD(P)H‐oxidases, which utilise molecular oxygen as a cost‐effective, atom‐efficient and environmentally benign oxidant to regenerate the cofactor NAD(P)+. Herein, the P450 BM3 monooxygenase from Bacillus megaterium is presented as an NAD(P)H‐oxidase for the successful regeneration of both NADP+ and NAD+ on the preparative scale. This enzyme was exemplarily applied for ADH‐catalysed oxidative kinetic resolutions of racemic secondary alcohols and the desymmetrisation of a meso‐diol leading to enantiomerically enriched secondary alcohols in both cases. Furthermore, the ADH‐catalysed oxidation of a primary alcohol targeting the corresponding aldehyde was performed. The obtained results significantly broaden the scope of feasible oxidative biotransformations, thereby increasing the number of synthetic reactions complying with key challenges of a modern and sustainable chemistry such as mild reaction conditions, environmentally benign solvents, and biodegradable non‐toxic catalysts.
63.
Claudia M. TrentinAna P. Lima Isabela P. AlkimimCamila da Silva Fernanda de CastilhosMarcio A. Mazutti J. Vladimir Oliveira 《Fuel Processing Technology》2011,92(5):952-958
This work investigates the production of fatty acid ethyl esters (FAEE) from the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process using carbon dioxide as co-solvent. The experiments were performed in a microtube reactor in the temperature range of 523 K to 598 K, from 10 MPa to 20 MPa, oil to ethanol molar ratio from 1:20 to 1:40, and co-solvent to substrates mass ratio from 0.05:1 to 0.2:1. Results showed that ethyl esters yield obtained increased with increasing addition of carbon dioxide to the system. Considerable reaction yields were achieved at 598 K, 20 MPa, oil to ethanol molar ratio of 1:20 and using a CO2 to substrate mass ratio of 0.2:1. 相似文献
64.
Gámbaro A Raggio L Dauber C Claudia Ellis A Toribio Z 《Archivos latinoamericanos de nutrición》2011,61(3):308-315
The relationship between nutritional knowledge and the consumption frequency of preferred food-types was studied among one sample of Uruguayan consumers. A locally-adapted version of Parmenter & Wardle's General Nutrition Knowledge Questionnaire and a food consumption survey based on 39 food groups were completed by a total of 270 participants. Cluster Analysis enabled the identification of two clusters showing different levels of nutritional knowledge--cluster 1 (n = 177) and cluster 2 (n = 93), providing an average of 73.6% and 52.9% of correct answers, respectively. These clusters differed significantly (p < or = 0.05) in age and educational distribution--cluster 1 was composed mainly by older adults and persons with a higher educational level. A number of areas were identified where nutritional knowledge was extremely poor, as was the case with the recommended daily fruit and vegetable intake and the caloric content of the nutrients. Overall, nutritional knowledge was found to have a positive influence on food preferences and consumption frequency, those participants with a higher nutritional knowledge reporting a higher consumption of fruits, vegetables and low-fat products, in addition to a lower consumption of high-fat and high-sugar foods. 相似文献
65.
Kelly D Singh A Barrett CA O'Sullivan C Coughlan C Laffir FR O'Dwyer C Ryan KM 《Nanoscale》2011,3(11):4580-4583
A facile spin cast route was developed to convert perpendicularly aligned nanorod assemblies of cadmium chalcogenides into their silver and copper analogues. The assemblies are rapidly cation exchanged without affecting either the individual rod dimensions or collective superlattice order extending over several multilayers. 相似文献
66.
Walter F Schroeder Silvana L Asmussen Wayne D Cook Claudia I Vallo 《Polymer International》2011,60(9):1362-1369
The efficiency of 4,4′‐bis(N,N‐diethylamino)benzophenone (DEABP) for the polymerization of dimethacrylate monomers in thick sections ( 1 – 2 mm) was studied. DEABP (λmax = 365 nm) represents a complete initiating system as it contains both ketone and amine functional groups. During irradiation, DEABP photobleaches at a fast rate causing deeper penetration of light through the underlying layers, but the photoinitiation efficiency (rate of polymerization per photon absorption rate) is relatively poor. As a result, irradiation of methacrylate monomers at 365 nm results in a slow average polymerization rate and a reduced monomer conversion for thick sections due to the light attenuation caused by the high absorptivity of DEABP and photolysis products. These results highlight the inherent interlinking of light attenuation and photobleaching rate in polymerization of thick sections. Copyright © 2011 Society of Chemical Industry 相似文献
67.
Claudia F. Galinha Gilda Carvalho Carla A. M. Portugal Giuseppe Guglielmi Maria A. M. Reis João G. Crespo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2011,86(7):985-992
BACKGROUND: The use of two‐dimensional (2D) fluorescence for monitoring complex biological systems requires careful assessment of the effect of chemical species present, which may be fluorescent and/or may interfere with the fluorescence response of target fluorophores. Given the complexity of fluorescence data (excitation emission matrices—EEMs), the challenge is how to recover the information embedded into those EEMs that can be related quantitatively with the observed performance of the biological processes under study. RESULTS: This work shows clearly that interference effects (such as quenching and inner filter effects) occur due to the presence of multiple species in complex biological media, such as natural water matrices, wastewaters and activated sludge. A statistical multivariate analysis is proposed to recover quantitative information from 2D fluorescence data, correlating EEMs with the observed performance. A selected case study is discussed, where 2D fluorescence spectra obtained from the effluent of a membrane bioreactor were compressed using PARAFAC and successfully correlated with the effluent chemical oxygen demand, using projection to latent structures modelling. CONCLUSION: This study demonstrates the potential of using 2D fluorescence spectroscopy as a status fingerprint. Additionally, it is shown how statistical multivariate data analysis can be used to correlate EEMs with selected performance parameters for monitoring of biological systems. Copyright © 2011 Society of Chemical Industry 相似文献
68.
Polymer/clay nanocomposites were prepared from dimethacrylate monomers, commonly used in dental restorative resins, and an organically modified silicate (montmorillonite). The photopolymerization process was hardly affected by the presence of the silicate filler, and thus 2 mm thick samples containing 3 wt% clay were extensively cured. Transmission electron microscopy revealed that the montmorillonite platelets were either intercalated or exfoliated. Nevertheless, for all formulations, intermediate‐sized aggregates of about 1 µm were present and their fraction increased as the amount of filler increased. The presence of the clay was found to have no major effect on the flexural modulus and compressive yield strength of the nanocomposites. Moreover, the water uptake of nanocomposites containing 3 wt% clay was about 10–15% higher than that of unfilled monomers. Modification of the clay surface with alternative organic cations is certainly necessary in order to achieve an optimal dispersion of the clay in the polymer matrix. Copyright © 2010 Society of Chemical Industry 相似文献
69.
Volker Schusdziarra Margit Hausmann Claudia Wittke Johanna Mittermeier Marietta Kellner Aline Naumann Stefan Wagenpfeil Johannes Erdmann 《Nutrition journal》2011,10(1):5
Objective
The role of breakfast energy in total daily energy intake is a matter of debate. Acute feeding experiments demonstrated that high breakfast energy leads to greater overall intake supported by cross-sectional data of a free-living population. On the other hand, a large intraindividual analysis has indicated that a high proportion of breakfast to overall intake is associated with lower daily energy intake. To evaluate these apparently contradictory results in greater detail both ways of analysis were applied to the same data set of dietary records. 相似文献70.
A method for coating membranes with polypyrrole (PPy) has been developed. Different membranes, such as microfiltration as well as ion exchanger membranes have been coated with PPy to yield electrical conductivity of the membranes.The coated membranes have been investigated by cyclic voltammetry and scanning electron microscopy and their permeability and permselectivity have been tested. The results show that PPy can be tailored as cation or anion exchanger and its porosity can be controlled to avoid any impairment of the membrane by the polymer layer. These PPy coated membranes can be applied as electrochemically switchable, functionalised membranes with controllabel and variable separation properties. 相似文献