全文获取类型
收费全文 | 3271篇 |
免费 | 101篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 76篇 |
综合类 | 4篇 |
化学工业 | 1047篇 |
金属工艺 | 54篇 |
机械仪表 | 30篇 |
建筑科学 | 203篇 |
矿业工程 | 31篇 |
能源动力 | 36篇 |
轻工业 | 382篇 |
水利工程 | 10篇 |
石油天然气 | 14篇 |
无线电 | 183篇 |
一般工业技术 | 474篇 |
冶金工业 | 343篇 |
原子能技术 | 36篇 |
自动化技术 | 450篇 |
出版年
2022年 | 28篇 |
2021年 | 45篇 |
2020年 | 34篇 |
2019年 | 33篇 |
2018年 | 49篇 |
2017年 | 43篇 |
2016年 | 66篇 |
2015年 | 90篇 |
2014年 | 77篇 |
2013年 | 124篇 |
2012年 | 125篇 |
2011年 | 169篇 |
2010年 | 115篇 |
2009年 | 117篇 |
2008年 | 122篇 |
2007年 | 144篇 |
2006年 | 126篇 |
2005年 | 117篇 |
2004年 | 110篇 |
2003年 | 78篇 |
2002年 | 81篇 |
2001年 | 66篇 |
2000年 | 55篇 |
1999年 | 58篇 |
1998年 | 109篇 |
1997年 | 80篇 |
1996年 | 70篇 |
1995年 | 66篇 |
1994年 | 72篇 |
1993年 | 45篇 |
1992年 | 47篇 |
1991年 | 43篇 |
1990年 | 35篇 |
1989年 | 36篇 |
1988年 | 28篇 |
1987年 | 44篇 |
1986年 | 33篇 |
1985年 | 40篇 |
1984年 | 40篇 |
1983年 | 38篇 |
1982年 | 35篇 |
1981年 | 28篇 |
1980年 | 30篇 |
1978年 | 27篇 |
1977年 | 32篇 |
1976年 | 34篇 |
1975年 | 40篇 |
1974年 | 24篇 |
1973年 | 25篇 |
1970年 | 33篇 |
排序方式: 共有3373条查询结果,搜索用时 850 毫秒
41.
42.
43.
James?A.?KenarEmail author Gerhard?Knothe Robert?O.?Dunn Thomas?W.?RyanIII Andrew?Matheaus 《Journal of the American Oil Chemists' Society》2005,82(3):201-205
Carbonates are a class of compounds that have recently found increasing interest in commercial applications owing to their
physical properties and relatively straightforward synthesis. In this work, physical and fuel properties of five straight-chain
C17–39 and three branched C17–33 oleochemical carbonates were investigated. These properties included cetane number (CN), low-temperature properties, (kinematic)
viscosity, lubricity, and surface tension. The carbonates studied had CN ranging from 47 to 107 depending on carbon chain
length and branching. For the same number of carbons, the CN of carbonates were lower than those of FA alkyl esters owing
to interruption of the CH2 chain by the carbonate moiety. Kinematic viscosities at 40°C ranged from 4.9 to 22.6 mm2/s whereas m.p. ranged from +3 to below −50°C depending on the carbonate structure. High-frequency reciprocating rig testing
showed the neat carbonates to have acceptable lubricity that improved as chain length increased. Finally, the carbonate's
ability to influence cold-flow properties in biodiesel (methyl soyate) and lubricity in low-lubricity ultra-low sulfur diesel
were examined. The carbonates studied did not significantly affect cold flow or lubricity properties at concentrations up
to 10,000 ppm (1 wt%). The properties of the carbonates resemble those of fatty alkyl esters with similar trends resulting
from compound structure. 相似文献
44.
45.
46.
47.
Studies of the microstructure of porous solids by physisorption measurements . The principal experimental methods for studying the microstructure of porous solids are based on physisorption measurements. The resulting sorption isotherms can yield data such as surface area and pore radius distribution, which are of great importance for development and characterization of porous catalysts. After a brief presentation of available measuring equipment, the main concern of this survey is the evaluation of sorption isotherms. In particular, methods for determining the micropore contribution to the total pore volume and the pore radius distribution in the micropore range are examined critically with regard to their reliability. 相似文献
48.
49.
Gerhard?KnotheEmail author Robert?O.?Dunn 《Journal of the American Oil Chemists' Society》2003,80(10):1021-1026
During storage and use, vegetable oil-derived industrial products such as biodiesel and biodegradable lubricants can be subjected
to conditions that promote oxidation of their unsaturated components. The materials arising during oxidation and subsequent
degradation can seriously impair the quality and performance of such products. Therefore, oxidative stability is a significant
issue facing these vegetable oil-derived products, and enhanced understanding of the influence of various components of vegetable
oils and storage parameters is necessary. In this work, the oil stability index (OSI) was used for assessing oxidation of
monoalkyl esters of FA by varying several parameters. Neat fatty compounds and prepared mixtures thereof were studied for
assessing the influence of compound structure and concentration. Small amounts of more highly unsaturated compounds had a
disproportionately strong effect on oxidative stability. The recently developed concept of bis-allylic equivalents correlated
more closely than the iodine value with the OSI times of mixtures of fatty esters. The OSI times of free acids were shorter
than those of the corresponding alkyl esters. The presence of copper, iron, and nickel also reduced oxidative stability, but
their effect was less than the presence of more highly unsaturated fatty compounds. Of these metals, copper had the strongest
catalytic effect on OSI time. OSI may be an alternative to long-term storage tests for determining the influence of extraneous
materials such as metals on oxidative stability. 相似文献
50.
Josa. Trujillo-Quijano Delia B. Rodriguez-Amaya W. Esteves Gerhard F. Plonis 《European Journal of Lipid Science and Technology》1990,92(6):222-226
In oils extracted from fresh and sterilized palm fruits (Elaeis guineensis, Jacq. tenera, dura dumpy and psifera and E. oleifera), cis-phytofluene, 13-cis-α-carotene, α-carotene, 13-cis-β-carotene, β-carotene, 9-cis-β-carotene, σ-carotene, zeaxanthin, --cryptoxanthin, poly-cis-lycopene, mono-lycopene and lycopene, were identified and quantified by normal phase open column chromatography (stepwise-elution), TLC, UV/Vis spectroscopy and specific chemical reactions. The sum of α- and β-carotene in all samples analysed was higher than 80% of the total carotenoid content, while the α/β-carotene ratios were W.9, 1/11.1, 1/22 and V2.6 for oils extracted from fresh fruits of dura dumpy, psifera, tenera and E. oleifera, respectively. Total carotenoid contents (pg/g) and vitamin A values (R. E./100 g) of these samples were 1 120.7 and 12 404 for dura dumpy, 283.2 and 3612 for psifera, 660.5 and 7630 for tenera and 1576.8 and 21691 for E. oleifera. The sterilization of fruits (127°C × 35 min.) resulted in isomerization of pigments and reduction of vitamin A values of approximately 45% and 25%, respectively. 相似文献