全文获取类型
收费全文 | 1763篇 |
免费 | 89篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 15篇 |
综合类 | 1篇 |
化学工业 | 423篇 |
金属工艺 | 25篇 |
机械仪表 | 37篇 |
建筑科学 | 52篇 |
矿业工程 | 1篇 |
能源动力 | 63篇 |
轻工业 | 300篇 |
水利工程 | 14篇 |
石油天然气 | 8篇 |
无线电 | 167篇 |
一般工业技术 | 272篇 |
冶金工业 | 203篇 |
原子能技术 | 15篇 |
自动化技术 | 258篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 101篇 |
2021年 | 97篇 |
2020年 | 52篇 |
2019年 | 59篇 |
2018年 | 54篇 |
2017年 | 46篇 |
2016年 | 63篇 |
2015年 | 49篇 |
2014年 | 77篇 |
2013年 | 118篇 |
2012年 | 105篇 |
2011年 | 126篇 |
2010年 | 82篇 |
2009年 | 65篇 |
2008年 | 84篇 |
2007年 | 66篇 |
2006年 | 42篇 |
2005年 | 42篇 |
2004年 | 40篇 |
2003年 | 36篇 |
2002年 | 30篇 |
2001年 | 21篇 |
2000年 | 22篇 |
1999年 | 25篇 |
1998年 | 78篇 |
1997年 | 54篇 |
1996年 | 43篇 |
1995年 | 24篇 |
1994年 | 17篇 |
1993年 | 21篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1975年 | 3篇 |
1971年 | 1篇 |
1965年 | 2篇 |
1964年 | 1篇 |
排序方式: 共有1854条查询结果,搜索用时 15 毫秒
71.
72.
Marco Baldi Franco Chiaraluce Nicola Maturo Giacomo Ricciutelli Alessandro Ardito Francesco Barbaglio Stefano Finocchiaro Lorenzo Simone Ricard Abell Javier De Vicente Mattia Mercolino 《International Journal of Satellite Communications and Networking》2019,37(6):571-587
A thorough analysis of the behavior of error‐correcting codes over space links affected by solar scintillation is presented. The relevant channel parameters are fixed through the development of a model based on real missions' data. Both telecommand and telemetry links are considered in fast and slow fading conditions. Besides classical coherent modulation schemes, the possibility to use noncoherent modulation schemes is considered, to eliminate the problem of phase tracking. For the case of channels with very slow fading, the use of external interleavers or erasure coding is proposed to cope with error bursts. 相似文献
73.
Use of homogenisation pressure to improve quality and functionality of probiotic fermented milks containing Lactobacillus rhamnosus BFE 5264 下载免费PDF全文
Francesca Patrignani Diana I. Serrazanetti Julius Maina Mathara Lorenzo Siroli Fausto Gardini Wilhelm H. Holzapfel Rosalba Lanciotti 《International Journal of Dairy Technology》2016,69(2):262-271
The effects of 60‐MPa milk homogenisation treatment were investigated on the viability of the probiotic strain Lactobacillus rhamnosus BFE5264, when used as yoghurt co‐starter, as well as on the aroma profile, texture and microstructure of the resulting set‐type fermented milks. The results demonstrated that the combined use of homogenisation pressure and co‐inoculation of the probiotic strain with the traditional yoghurt starters allowed the reduction in the product coagulation time, the increase of the probiotic strain viability and the improvement of the product volatile molecule profiles. The rheological indices and the microstructure results indicated the positive effects of the milk homogenisation treatment on the product viscosity index and exopolysaccharide production. 相似文献
74.
Daniele Naviglio Fabiana Pizzolongo Lydia Ferrara Alejandro Aragòn Antonello Santini 《Journal of the science of food and agriculture》2008,88(14):2414-2420
BACKGROUND: Lycopene, a precursor of β‐carotene with a well‐known antioxidant activity, contained in many natural products such as tomato (Lycopersicon esculentum Mill.), watermelon, red pepper and papaya, is usually recovered from natural vegetal sources using organic solvents and a purification step. In this paper an innovative process for the extraction of pure lycopene from tomato waste in water that uses the Naviglio® extractor and water as extracting phase is presented. RESULTS: Lycopene was obtained in the all‐trans form at a very high grade of purity, not less than 98% (w/w), with an average recovery of 14% (w/w). The availability of high‐purity trans‐lycopene allowed measurement of the molar absorption coefficient. An alternative procedure for high‐performance liquid chromatographic analysis using a phenyl‐hexyl silicone phase as inverse phase and a linear gradient in water and acetonitrile is also described. CONCLUSIONS: The use of water as extracting phase considerably reduces the cost of the entire process when compared with the commonly used solvent‐based procedure or with the newer supercritical extraction process of lycopene from tomato waste. Lycopene, not soluble in water, was recovered in a quasi‐crystalline solid form and purified by solid‐phase extraction using a small amount of organic solvent. Copyright © 2008 Society of Chemical Industry This article was published online on September 15, 2008. Errors in Figures 2 ‐ 4 were subsequently identified. The publishers wish to apologise for these errors. This notice is included in the online and print versions to indicate that both have been corrected [September 19, 2008] 相似文献
75.
Phosphate depletion is associated with neuromuscular dysfunction due to changes in mitochondrial respiration that result in a defect of intracellular oxidative metabolism. Phosphate diabetes causes phosphate depletion due to abnormal renal re-absorption of phosphate be the proximal renal tubule. Most of the symptoms presented by patients with phosphate diabetes such as myalgia, fatigue and mild depression, are also common in patients with chronic fatigue syndrome, but this differential diagnosis has not been considered. We investigated the possible association between chronic fatigue syndrome and phosphate diabetes in 87 patients who fulfilled the criteria for chronic fatigue syndrome. Control subjects were 37 volunteers, who explicitly denied fatigue and chronic illness on a screening questionnaire. Re-absorption of phosphate by the proximal renal tubule, phosphate clearance and renal threshold phosphate concentration were the main outcome measures in both groups. Of the 87 patients with chronic fatigue syndrome, nine also fulfilled the diagnostic criteria for phosphate diabetes. In conclusion, we report a previously undefined relationship between chronic fatigue syndrome and phosphate diabetes. Phosphate diabetes should be considered in differential diagnosis with chronic fatigue syndrome; further studies are needed to investigate the incidence of phosphate diabetes in patients with chronic fatigue syndrome and the possible beneficial effect of vitamin D and oral phosphate supplements. 相似文献
76.
77.
J Buc CL Santini F Blasco R Giordani ML Cárdenas M Chippaux A Cornish-Bowden G Giordano 《Canadian Metallurgical Quarterly》1995,234(3):766-772
A soluble alpha beta complex of nitrate reductase can be obtained from a strain of Escherichia coli that lacks the narI gene and expresses only the alpha and beta subunits. The beta subunit contains four Fe-S centres and the alpha subunit contains the molybdenum cofactor, which is the site at which nitrate is reduced. Despite the lack of the gamma subunit of the complete enzyme, this complex can still catalyse the reduction of nitrate with artificial electron donors such as benzyl viologen, so that it is suitable for studying the transfer of electrons between these two types of redox centre. To examine whether the electrons from reduced benzyl viologen are initially delivered to the Fe-S centres, or directly to the molybdenum cofactor, or both, we have studied the steady-state kinetics and the binding of benzyl viologen to the alpha beta complex and mutants alpha beta* with altered beta subunits. Reduction of the enzyme by reduced benzyl viologen in the absence of nitrate showed that all four Fe-S centres and the molybdenum cofactor could be reduced. Two classes of site with different equilibrium constants could be distinguished. The kinetic results suggest that benzyl viologen supplies its electrons directly to the molybdenum cofactor, at a rate showing a hyperbolic dependence on the square of the concentration of the electron donor. A reaction mechanism is proposed for the reduction of nitrate catalysed by the alpha beta complex of nitrate reductase with artificial electron donors. 相似文献
78.
The ATP-binding site of protein kinase CK2 holds a positive electrostatic area and conserved water molecules 总被引:1,自引:0,他引:1
Battistutta R Mazzorana M Cendron L Bortolato A Sarno S Kazimierczuk Z Zanotti G Moro S Pinna LA 《Chembiochem : a European journal of chemical biology》2007,8(15):1804-1809
CK2 is a highly pleiotropic Ser/Thr protein kinase that is able to promote cell survival and enhance the tumour phenotype under specific circumstances. We have determined the crystal structure of three new complexes with tetrabromobenzimidazole derivatives that display K(i) values between 0.15 and 0.30 microM. A comparative analysis of these data with those of four other inhibitors of the same family revealed the presence of some highly conserved water molecules in the ATP-binding site. These waters reside near Lys68, in an area with a positive electrostatic potential that is able to attract and orient negatively charged ligands. The presence of this positive region and two unique bulky residues that are typical of CK2, Ile66 and Ile174, play a critical role in determining the ligand orientation and binding selectivity. 相似文献
79.
Mauro Epifani Marco Alvisi Luciana Mirenghi Gabriella Leo Pietro Siciliano Lorenzo Vasanelli 《Journal of the American Ceramic Society》2001,84(1):48-54
A chloride-based inorganic sol–gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO2 sol. SnCl4 was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO2 lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO2 grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO2 grain size very close to that of pure SnO2 . 相似文献
80.
Analysis of samples taken at the Gentilly 2 (Québec) CANDU-PHW (CANadian Deuterium Uranium - Pressurized Heavy Water) plant after chlorination and demineralization revealed the presence of all four trihalomethanes (THMs) (CHCl3, CHBrCl2, CHBr2Cl and CHBr3) and other unidentified halogenated volatile compounds. Among the THMs, chloroform was the major contaminant. A study of its thermal stability in water at different temperatures confirmed the degradation of the CHCl3 molecule according to the equation CHCl3 + H2O → CO + 3 HCl. The reaction follow a first order kinetics and has an activation energy of 100 kJ/mol. The estimated half-life is six seconds at 260°C, the maximum temperature of the steam-condensate cycle. 相似文献