全文获取类型
收费全文 | 2169篇 |
免费 | 129篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 42篇 |
综合类 | 10篇 |
化学工业 | 637篇 |
金属工艺 | 32篇 |
机械仪表 | 51篇 |
建筑科学 | 134篇 |
矿业工程 | 24篇 |
能源动力 | 58篇 |
轻工业 | 173篇 |
水利工程 | 9篇 |
石油天然气 | 12篇 |
无线电 | 182篇 |
一般工业技术 | 425篇 |
冶金工业 | 187篇 |
原子能技术 | 18篇 |
自动化技术 | 318篇 |
出版年
2023年 | 15篇 |
2022年 | 21篇 |
2021年 | 57篇 |
2020年 | 46篇 |
2019年 | 46篇 |
2018年 | 39篇 |
2017年 | 39篇 |
2016年 | 79篇 |
2015年 | 77篇 |
2014年 | 106篇 |
2013年 | 125篇 |
2012年 | 96篇 |
2011年 | 115篇 |
2010年 | 79篇 |
2009年 | 114篇 |
2008年 | 86篇 |
2007年 | 85篇 |
2006年 | 77篇 |
2005年 | 79篇 |
2004年 | 63篇 |
2003年 | 61篇 |
2002年 | 52篇 |
2001年 | 39篇 |
2000年 | 32篇 |
1999年 | 42篇 |
1998年 | 65篇 |
1997年 | 44篇 |
1996年 | 36篇 |
1995年 | 31篇 |
1994年 | 36篇 |
1993年 | 40篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 23篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 23篇 |
1985年 | 17篇 |
1984年 | 15篇 |
1983年 | 21篇 |
1982年 | 7篇 |
1981年 | 20篇 |
1980年 | 22篇 |
1979年 | 14篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1976年 | 10篇 |
1974年 | 8篇 |
1973年 | 8篇 |
排序方式: 共有2312条查询结果,搜索用时 15 毫秒
101.
Mende S Krzyzanowski L Weber J Jaros D Rohm H 《Journal of Bioscience and Bioengineering》2012,113(2):185-191
Some Lactobacillus delbrueckii ssp. bulgaricus strains are able to synthesize exopolysaccharides (EPS) and are therefore highly important for the dairy industry as starter cultures. The aim of this study was to investigate the nutritional requirements for growth and EPS production of Lactobacillus delbrueckii ssp. bulgaricus DSM 20081. A medium was developed from a semi-defined medium (SDM) in which glucose was replaced by lactose and different combinations of supplements (nucleobases, vitamins, salts, sodium formate and orotic acid) were added. Constant pH batch fermentation with the modified medium resulted in an EPS yield of approximately 210 mg glucose equivalents per liter medium. This was a 10-fold increase over flask cultivation of this strain in SDM. Although not affecting cell growth, the mixture of salts enhanced the EPS synthesis. Whereas EPS production was approximately 12 mg/g dry biomass without salt supplementation, a significantly higher yield (approximately 20 mg/g dry biomass) was observed after adding the salt mixture. In continuous fermentation, a maximal EPS concentration was obtained at a dilution rate of 0.31/h (80 mg EPS/L), which corresponded to a specific EPS production of 49 mg/g dry biomass. 相似文献
102.
Matthias Engleder Dr. Tea Pavkov‐Keller Dr. Anita Emmerstorfer Altijana Hromic Sabine Schrempf Dr. Georg Steinkellner Dr. Tamara Wriessnegger Prof. Erich Leitner Dr. Gernot A. Strohmeier Dr. Iwona Kaluzna Dr. Daniel Mink Dr. Martin Schürmann Dr. Silvia Wallner Prof. Peter Macheroux Prof. Karl Gruber Dr. Harald Pichler 《Chembiochem : a European journal of chemical biology》2015,16(12):1730-1734
Hydratases provide access to secondary and tertiary alcohols by regio‐ and/or stereospecifically adding water to carbon‐carbon double bonds. Thereby, hydroxy groups are introduced without the need for costly cofactor recycling, and that makes this approach highly interesting on an industrial scale. Here we present the first crystal structure of a recombinant oleate hydratase originating from Elizabethkingia meningoseptica in the presence of flavin adenine dinucleotide (FAD). A structure‐based mutagenesis study targeting active site residues identified E122 and Y241 as crucial for the activation of a water molecule and for protonation of the double bond, respectively. Moreover, we also observed that two‐electron reduction of FAD results in a sevenfold increase in the substrate hydration rate. We propose the first reaction mechanism for this enzyme class that explains the requirement for the flavin cofactor and the involvement of conserved amino acid residues in this regio‐ and stereoselective hydration. 相似文献
103.
Karolina Mazur Raminder Singh Ralf P. Friedrich Hatice Gen Harald Unterweger Kamila Saasiska Rafa Bogucki Stanisaw Kuciel Iwona Cicha 《大分子材料与工程》2020,305(9)
The composites based on polylactide (PLA) and poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) with the addition of antibacterial particles: silver (Ag) and copper oxide (CuO) are characterized. Basic mechanical properties and biodegradation processes, as well as biocompatibility of materials with human cells are determined. The addition of Ag or CuO to the polymers do not significantly affect their mechanical properties, flammability, or biodegradation rate. However, several differences between the base materials are observed. PLA‐based composites have higher tensile and impact strength values, while PHBV‐based ones have a higher modulus of elasticity, as well as better mechanical properties at elevated temperatures. Concerning biocompatibility, each of the tested materials support the growth of fibroblasts over time, although large differences are observed in the initial cell attachment. The analysis of hydrolytic degradation effects on the structure of materials shows that PHBV degrades much faster than PLA. The results of this study confirm the good potential of the investigated biodegradable polymer composites with antibacterial particles for future biomedical applications. 相似文献
104.
Influence of growth conditions on biofilm development and mass transfer at the bulk/biofilm interface 总被引:8,自引:0,他引:8
In a long-term study on heterotrophic biofilms in tube reactors, this investigation focused on mass transfer at the bulk/biofilm interface, biofilm density and substrate conversion rates. Several biofilms were cultivated under different substrate and hydrodynamic conditions. Oxygen concentration profiles were measured with microelectrodes in the biofilm and in the boundary layer directly in the biofilm tube reactors. The thickness of the concentration boundary layer was found to depend on the surface structure of the biofilm. The hydrodynamic conditions and the substrate load during the growth phase of the biofilm in biofilm systems are two key parameters that influence the biofilm growth, particularly the structure, density and thickness. The measured substrate conversion rates, biofilm densities and the boundary layer thickness were used to formulate an equation for the mass transfer in biofilm tube reactors. 相似文献
105.
Walter Ried Harald Knorr Gerilard Oremek 《Advanced Synthesis \u0026amp; Catalysis》1978,320(2):246-248
Reactions of Cyclobutendiones. LII. Reaction of 4-Hydroxy-3-phenyl-3-cyclobuten-1-ones with Arylhydrazines In the reaction of hydroxycyclobutenones of the typ 1 – 4 with arylhydrazines 5 an unexpected reaction behaviour is found. The major products are hydrazones of different structure, the well known hydroxy-cyclopropane-carboxylicacid hydrazines 6 [1] are byproducts. The direction of the reaction depends on the substituents X, on the different substituted arylhydrazines and the solvents. 相似文献
106.
Photovoltaics: Quantification of Nano‐ and Mesoscale Phase Separation and Relation to Donor and Acceptor Quantum Efficiency,Jsc, and FF in Polymer:Fullerene Solar Cells (Adv. Mater. 25/2014)
下载免费PDF全文
![点击此处可从《Advanced materials (Deerfield Beach, Fla.)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Wei Ma John R. Tumbleston Long Ye Cheng Wang Jianhui Hou Harald Ade 《Advanced materials (Deerfield Beach, Fla.)》2014,26(25):4399-4399
107.
Waste disposal and waste avoidance are examined from two different perspectives, from the point of view of the waste 'producing' company on the one hand, and from the point of view of the waste disposing company on the other hand. The idea of the basic model lies in the 'turning upside down' of the lot-sizing approach to inventory control theory. We derive a corresponding formula for disposal that shows that the number of waste disposals depends positively on the waste accumulation rate and negatively on the fixed costs for a pick-up. Moreover, we formally work out at which waste avoidance costs a company will enlist the services of a disposal company. Specifically, disposal tends to be preferred to avoidance when waste-avoidance is relatively expensive and three cost rates to be specified are relatively low. Finally, we take the perspective of a monopolistic disposal company that has to decide on the optimal pricing policy. In our model, we determine that the price for a pick-up should be chosen just to cover costs. The disposal company can earn a profit by the suitable choice of the price per unit waste to be disposed of. 相似文献
108.
In current cars, loops are commonly used to redirect the webbing which reels out from the retractor to the passenger's shoulder. Some types of pillar loops, also called D-rings, lead to a non-systematic instability. The webbing, which should scroll without hindrance through the D-ring, laterally shifts, bunches and produces the overturning of the ring. 相似文献
109.
110.