全文获取类型
收费全文 | 11982篇 |
免费 | 1125篇 |
国内免费 | 106篇 |
专业分类
电工技术 | 15篇 |
综合类 | 293篇 |
化学工业 | 4976篇 |
金属工艺 | 72篇 |
机械仪表 | 113篇 |
建筑科学 | 210篇 |
矿业工程 | 32篇 |
能源动力 | 154篇 |
轻工业 | 6606篇 |
水利工程 | 35篇 |
石油天然气 | 177篇 |
武器工业 | 1篇 |
无线电 | 50篇 |
一般工业技术 | 307篇 |
冶金工业 | 64篇 |
原子能技术 | 30篇 |
自动化技术 | 78篇 |
出版年
2024年 | 84篇 |
2023年 | 228篇 |
2022年 | 451篇 |
2021年 | 550篇 |
2020年 | 460篇 |
2019年 | 449篇 |
2018年 | 422篇 |
2017年 | 479篇 |
2016年 | 529篇 |
2015年 | 521篇 |
2014年 | 600篇 |
2013年 | 781篇 |
2012年 | 776篇 |
2011年 | 738篇 |
2010年 | 535篇 |
2009年 | 533篇 |
2008年 | 522篇 |
2007年 | 622篇 |
2006年 | 507篇 |
2005年 | 402篇 |
2004年 | 360篇 |
2003年 | 318篇 |
2002年 | 289篇 |
2001年 | 219篇 |
2000年 | 276篇 |
1999年 | 192篇 |
1998年 | 207篇 |
1997年 | 122篇 |
1996年 | 152篇 |
1995年 | 131篇 |
1994年 | 108篇 |
1993年 | 106篇 |
1992年 | 120篇 |
1991年 | 100篇 |
1990年 | 60篇 |
1989年 | 43篇 |
1988年 | 30篇 |
1987年 | 37篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 24篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 14篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1974年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
KS Min AR Khan MK Kwon YJ Jung Z Yun Y Kiso 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(8):909-915
The performance of a laboratory‐scale anaerobic acidogenic fermenter fed with a mixture of blended kitchen food‐waste and primary sludge from a sewage treatment plant was investigated for the production of volatile fatty acids (VFA). The operating variables for acidogenic fermentation were kitchen food‐waste content (10 and 25 wt %), hydraulic retention time (HRT: 1, 3 and 5 days), temperature (ambient: 18 ± 2 °C, and mesophilic: 35 ± 2 °C) and pH (varied from 5.2 to 6.7). The experimental results indicated that effluent VFA concentrations and VFA production rates were higher at ambient temperature than at mesophilic conditions. The net amount of VFA with 10 wt % food‐waste increased up to 920 mg dm?3 with an increase of HRT, but contrasting results (a decrease of 2610 mg dm?3) were found due to the conversion of VFA into biogas in the case of 25 wt % food‐waste, which increased significantly at HRT of 3–5 days. In terms of biogas composition (CO2 and CH4), the organic matter was converted into CO2 through the oxidative pathway by facultative species at low temperature while mesophilic temperature and optimum pH (6.3–7.8) played a pivotal role in increasing rate of conversion of VFA into biogas by methanogenesis. Rates of VFA production and their conversion are dependent on the food‐waste content in the mixture. Yet, the higher concentration of food‐waste (25% compared with 10%) did not produce VFA proportionally due to the increased rate of conversion of VFA into gaseous products. The maximum VFA production rate (0.318 g VFAproduced g?1 VSfed day?1) was achieved in the 10 wt % food‐waste at ambient temperature and at a 5‐day HRT. Copyright © 2005 Society of Chemical Industry 相似文献
12.
Emulsification is an undesired phenomenon in the refining of highly acidic oil by alkali-washing electro-refining. In this article, a novel microwave method is applied for demulsification in the removing of naphthenic acid from diesel oil. The internal heating is attributed to molecular rotation and ionic conduction. The decrease of interface zeta-potential and the viscosity of diesel oil are responsible for the demulsification with microwave irradiation. The results exhibited that the demulsification rate is maximized when the optimum microwave irradiation power, exposure time, and irradiation pressure for Anshan and Liaohe diesel oil are deemed to be 375 W, 5/6 min and 0.05 MPa, respectively. 相似文献
13.
A series of long-chain quaternary ammonium halogen esters (UKK-chemicals), quaternary dimethyl tallow epoxypropyl ammonium
halogens (EPK1), quaternary ditallow methyl epoxypropyl ammonium halogens (EPK2), and EPK2 oligomers (EPK2P) were synthesized.
At acidic, neutral, or slightly basic conditions, EPK1-, EPK2-, EPK2P-, and UKK-chemicals operate as cationic chemicals. They
can be used, for example, as stock sizings, surface sizings, or fixatives. Stock sizing, surface sizing, and fixative experiments
indicate that EPK1-, EPK2-, EPK2P-, and UKK-chemicals function at least as well as or better than the corresponding synthetic
chemicals used in papermaking. 相似文献
14.
Two kinds of biosensors for amino acids (one with nonspecific enzyme as bioelement, the other with specific enzyme(s) as bioelement),
including their principles, applications, recent researches and future trends were discussed in detail. 61 references were
given.
A part of work for gaining Ph. D in chemical and biochemical application at FPMs (Mons, Belgique)
Synopsis of the first author Xia Jinlan, Male, born in 1963, now at Facult’e Polytechnique de Mons, Belgique 相似文献
15.
Y. C. Wu Darning Feng W. F. Koch 《Journal of research of the National Institute of Standards and Technology》1991,96(6):757-762
Ionic interactions in the two systems NaCl-HEPES (N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid) and NaCl-MOPSO (3-(N-Morpholino)-2-hydroxypropanesulfonic acid) have been studied in terms of their mutual influence on the respective activity coefficients of each component. Activity coefficients for each component of the two systems and for corresponding buffers are calculated from emf measurements of solutions containing NaCl, the aminosulfonic acid, and its conjugate base in a NalSE/solution/AgCl-Ag cell at 5, 15, 25, and 37 °C. 相似文献
16.
The present study deals with effect of the type and chemical character of incorporated polyester/polyether blocks on the hydrolytic stability of crosslinked polyurethane oligomers. Diffusion parameters of the investigated polyurethane oligomers, giving information concerning chemical changes taking place in neutral, basic and acidic aqueous environments, have also been determined. 相似文献
17.
Tatsuro Kijima Kouji Ohshima Hideo Kise 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(1):61-65
Racemic amino acid esters were optically resolved via hydrolysis in organic solvents by the catalysis of an industrial alkaline protease, “Alcalase”. The products which were composed mainly of L-amino acids were insoluble and easily separated by filtration. The activity of the enzyme and enantiomeric excess of the products were significantly dependent on the nature of solvent and the water content in the reaction media. Generally, high values of enantiomeric excess were obtained at low water contents. Many natural and unnatural amino acids were resolved by this method. 相似文献
18.
Afam I Jideani Richard K Owusu Apenten H G Muller 《Journal of the science of food and agriculture》1994,65(4):465-476
The effect of cooking on proteins from acha and durum wheat was assessed from an analysis of protein extractability, gel electrophoretic profiles, in-vitro protein digestibility (IVPD) and the amino acid compositions of wholemeal flour and residue proteins. Heating wholemeal flour samples at 100–140°C (t = 10–40 min) resulted in 0–30% and 45–55% decreases in acha and durum protein solubility, respectively. In general, high molecular weight (30–70 k Da) protein subunits were more susceptible to heat damage. For both cereals, sodium dodecyl sulphate (SDS; 10 g litre?1) and/or dithiothrcitol (DTT; 10 mM ) increased protein solubility in unheated and heated samples. The IVPD index was 90–91% and was not significantly altered by cooking (100–120°C, t = 40 min). Cooking at extreme temperatures (140°C, t = 40 min) reduced the IVPD by 8% (P = 0.05). Osborne fractionation resulted in a durum or acha residue level of 7.8% or 55.2%. Treatment with solvent containing propanol, SDS and/or DTT at room temperature followed by SDS-polyacrylamide gel electrophoresis of non-solubilised proteins showed that the glutelin fraction of acha, with the exception of a 65 kDa subunit, was insoluble owing to strong inter-subunit hydrophobic and disulphide interactions. Wholemeal acha flour and residue protein showed a significantly greater level of hydrophobic and sulphur amino acids as well as glutamine which is associated with H-bonding. The possibility that cereal protein solubility is also dependent on protein-carbohydrate links is discussed. 相似文献
19.
ALEJANDRO G. MARANGONI 《Journal of food science》1994,59(5):1096-1099
Candida rugosa lipase (CRL) and Pseudomonas fluorescein lipase (PFL) were used to hydrolyze a low-melting point butteroil fraction in the absence of orgaic solvents. CRL and PFL displayed pH activity optima of 6.7 and 7.8, and temperature-activity optima of 40–50°C and 35°C, respectively. Maximum activity for PFL was observed at 5% (v/v) water content. CRL showed higher specificity towards butyric acid relative to PFL after 3 hours of hydrolysis at 40°C (22.3 mol% vs 7.8 mol%, respectively). Both enzymes displayed, however, high specificities towards palmitic and oleic acids. CRL's inherent specificity towards butyric acid makes it an ideal choice for a biological catalyst to generate useful dairy flavor profiles. 相似文献
20.
Auguste Commeyras Hlne Collet Laurent Boiteau Jacques Taillades Odile Vandenabeele‐Trambouze Herv Cottet Jean‐Philippe Biron Raphaël Plasson Louis Mion Olivier Lagrille Herv Martin Franck Selsis Michel Dobrijevic 《Polymer International》2002,51(7):661-665
Addressing the still open question of the prebiotic origin of sequential macromolecules (peptides, nucleic acids) on the primitive Earth, we describe a molecular engine (the primary pump), which works at ambient temperature and continuously generates, elongates and complexifies sequential peptides. This new scenario is based on a cyclic reaction sequence, whose keystep is the activation of amino acids into their N‐carboxyanhydrides (NCA) through nitrosation by NOx. This process could have taken place on tidal beaches; it requires a buffered ocean, emerged land and a nitrosating atmosphere. With the help of geochemical studies and computer simulations of atmosphere photochemistry, we show that the primitive Earth during the Hadean may have satisfied all these requirements. © 2001 Society of Chemical Industry. 相似文献