全文获取类型
收费全文 | 2177篇 |
免费 | 169篇 |
国内免费 | 53篇 |
专业分类
电工技术 | 14篇 |
综合类 | 75篇 |
化学工业 | 932篇 |
金属工艺 | 14篇 |
机械仪表 | 24篇 |
建筑科学 | 33篇 |
矿业工程 | 41篇 |
能源动力 | 37篇 |
轻工业 | 648篇 |
水利工程 | 10篇 |
石油天然气 | 417篇 |
武器工业 | 3篇 |
无线电 | 20篇 |
一般工业技术 | 72篇 |
冶金工业 | 37篇 |
原子能技术 | 5篇 |
自动化技术 | 17篇 |
出版年
2024年 | 7篇 |
2023年 | 17篇 |
2022年 | 38篇 |
2021年 | 64篇 |
2020年 | 60篇 |
2019年 | 66篇 |
2018年 | 58篇 |
2017年 | 61篇 |
2016年 | 71篇 |
2015年 | 86篇 |
2014年 | 114篇 |
2013年 | 223篇 |
2012年 | 166篇 |
2011年 | 184篇 |
2010年 | 125篇 |
2009年 | 101篇 |
2008年 | 105篇 |
2007年 | 122篇 |
2006年 | 95篇 |
2005年 | 82篇 |
2004年 | 80篇 |
2003年 | 48篇 |
2002年 | 56篇 |
2001年 | 62篇 |
2000年 | 65篇 |
1999年 | 31篇 |
1998年 | 39篇 |
1997年 | 35篇 |
1996年 | 23篇 |
1995年 | 28篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 16篇 |
1991年 | 13篇 |
1990年 | 9篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有2399条查询结果,搜索用时 0 毫秒
1.
2.
Yu‐Qing Cao Zhan Zhang Yan‐Xin Guo 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(10):1441-1444
A new efficient method for synthesising nitriles, important organic reagents, is reported in this paper. In an environmentally benign solvent‐free system, aryl carboxylic acids were converted into the corresponding nitriles via one‐pot reactions, by amidation with ethyl carbamate followed by dehydration with thionyl chloride, in excellent yields. The results showed that the method has the advantages of lower cost, higher yield, less pollution and greater ease of work‐up. Copyright © 2008 Society of Chemical Industry 相似文献
3.
以硫酸、磷钨酸、ZRP-5分子筛为催化剂,研究了二甘醇(DEG)脱水环化的反应规律。结果表明,DEG发生分子内脱水环化反应,生成1,4-二氧六环(DOX),DEG分子间脱水不仅可以生成四甘醇、六甘醇等,同时可生成三甘醇、五甘醇等一系列的多甘醇(PEG)。不仅DEG可以脱水环化生成DOX,在反应中生成的PEG也同样可以进行生成DOX的反应。对于二甘醇(DEG)脱水环化反应,硫酸是性能优良的催化剂,反应可以在较低的温度下进行,馏出产物中DOX选择性大于95%。 相似文献
4.
The effects of glycol methacrylate as a dehydrating agent on the dimensional changes of liver tissue
The dimensional changes of liver sections during the course of processing with glycol methacrylate (GMA) or with ethanol are described. Tissue processing with ethanol served as a control. During prolonged processing steps (24 h each), linear shrinkage of tissue specimens dehydrated with GMA at room temperature was 13.2%. Subsequent infiltration with GMA resulted in trivial swelling, and polymerization in slight shrinkage (2.3%). In comparison, processing with cold GMA resulted in shrinkage during dehydration (about 10.8%), a slight swelling in pure GMA, followed by shrinkage during polymerization (2.2%). Short routine processing schedules resulted in similar shrinkage/swelling patterns, although precise values differed slightly. In all experiments, ethanolic dehydration resulted in smaller dimensional tissue changes than did GMA dehydration. The dimensional changes of tissue sections during stretching on water, mounting and drying compensated for the major part of the shrinkage manifested during processing. 相似文献
5.
以偏苯三甲酸酐和氯化亚砜为原料 ,其摩尔比为 1:1 2 ,在回流状态下首先合成中间体 4 -氯甲酰基苯甲酸酐Ⅱ ,产率可达 98%。Ⅱ经过胺化、减压脱水制得 4 -氰基苯甲酸酐 ,其沸点为 175~ 180 C/ 0 2 6KPa ,各反应物摩尔比为n (Ⅱ ) :n (NH3 ) :n (P2 O5) =1 0 :4 7:2 1。通过红外分析、1H -NMR分析及元素分析证明 ,所得到的化合物即为目标物。 相似文献
6.
Diced green bell peppers were soaked in a solution of hydrochloric acid or calcium chloride, air-dried to 50% moisture, held in CO2 at 5.8 MPa for 1, 3 or 5 min, and puffed by abruptly releasing the CO2 pressure. Treatment with 1% CaCl2 increased the size of puffed-dried products as compared to a control; however, HCl treatments did not. The treatment with 1 or 2% CaCl2 reduced shrinkage as compared to the control. The 1% CaCl2 treatment may have increased the CO2 saturation rate. 相似文献
7.
《Drying Technology》2007,25(1):85-95
Artificial neural network (ANN) models were developed for the prediction of transient moisture loss (ML) and solid gain (SG) in osmotic dehydration of fruits using process kinetics data from the literature. ANN models for ML and SG were developed based on data over a broad range of operating conditions and ten common processing variables: temperature and concentration of osmotic solution, immersion time, initial water and solid content of the fruit, porosity, surface area, characteristic length, solution-to-fruit mass ratio, and agitation level. The trained models were able to accurately predict the outputs with associated regression coefficients (r) of 0.96 and 0.93, respectively, for ML and SG. These ANN models performed much better than those obtained from linear multivariate regression analysis. The large number of process variables and their wide ranges considered along with their easy implementation in a spreadsheet make them very useful and practical for process design and control. 相似文献
8.
A set of Co promoted 10% Mo/Al2O3 samples have been characterized by means of Raman spectroscopy under ambient as well as in situ dehydrated conditions. Under ambient conditions, the degree of the polymerization of surface molybdenum oxide species decreases with increasing Co loading. Under dehydrated conditions, the polymeric molybdenum oxide species is absent with the addition of only 0.2% Co. At low Co loadings (2%), before the formation of CoMoO4 compound, the spectral features are very similar under ambient conditions. Dehydration causes the upward shift of the Mo=O symmetric stretching mode. A broad band around 920–930 cm–1 was thus observed. This band has been suggested to be associated with the Co-Mo interaction species. In contrast to crystalline CoMoO4, this species shows a reversibility on H2 reduction-O2 reoxidation treatments. From the results obtained, it is proposed that cobalt oxide interacts with the most polymerized molybdenum oxide species to form Co-Mo interaction species and/or crystalline CoMoO4; therefore, the amount of the surface molybdenum oxide species decreases with a change in the molecular structure as a function of the Co concentration. 相似文献
9.
10.
Yoshitsugu Kosugi Tsutomu Kunieda Naoki Azuma 《Journal of the American Oil Chemists' Society》1994,71(4):445-448
Rice bran oil containing 30–50% free fatty acid was continually converted to an oil containing more than 75% of triacylglycerol
(TG) by means of immobilized lipase. The reaction was carried out at 60°C for 24 h with dehydration and reactant mixing by
dry nitrogen flow under a positive nitrogen atmosphere. Enzymatic TG synthesis with evaporation by heating was not suitable
because of the increasing peroxide value of the oil.
Part of this article was presented at the annual meeting of the Japan Oil Chemists' Society at Sendai, Japan, October, 16,
1990. 相似文献