全文获取类型
收费全文 | 1029篇 |
免费 | 131篇 |
国内免费 | 30篇 |
专业分类
电工技术 | 2篇 |
综合类 | 36篇 |
化学工业 | 624篇 |
金属工艺 | 2篇 |
机械仪表 | 17篇 |
建筑科学 | 3篇 |
矿业工程 | 2篇 |
能源动力 | 64篇 |
轻工业 | 300篇 |
石油天然气 | 65篇 |
武器工业 | 4篇 |
无线电 | 11篇 |
一般工业技术 | 49篇 |
冶金工业 | 5篇 |
原子能技术 | 1篇 |
自动化技术 | 5篇 |
出版年
2024年 | 9篇 |
2023年 | 21篇 |
2022年 | 33篇 |
2021年 | 27篇 |
2020年 | 34篇 |
2019年 | 55篇 |
2018年 | 45篇 |
2017年 | 52篇 |
2016年 | 38篇 |
2015年 | 49篇 |
2014年 | 65篇 |
2013年 | 74篇 |
2012年 | 93篇 |
2011年 | 64篇 |
2010年 | 53篇 |
2009年 | 67篇 |
2008年 | 48篇 |
2007年 | 57篇 |
2006年 | 55篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 25篇 |
2002年 | 22篇 |
2001年 | 27篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1982年 | 4篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有1190条查询结果,搜索用时 31 毫秒
51.
52.
产甘油假丝酵母在丙三醇发酵过程中的有机酸种类及其变化 总被引:2,自引:1,他引:2
HPLC分析研究了产甘油假丝酵母 (Candidaglycerolgenesis)发酵过程中有机酸的种类和含量变化 .C .glycerolgenesis主要在菌体生长期产生有机酸 ,使发酵液总酸增加 .确定了发酵过程形成的有机酸含有乙酸、乳酸、丙酮酸、酮戊二酸、苹果酸等 .建立了HPLC测定有机酸的方法 .分析发现 :有机酸中乙酸质量浓度最高约为 1.6 g/L .随着发酵时间的延长 ,发酵液总酸含量逐渐下降 ,而乙酸和α -酮戊二酸在发酵后期有所回升 . 相似文献
53.
Chemo-enzymatic synthesis of amino acid-based surfactants 总被引:5,自引:0,他引:5
Rao Valivety Paula Jauregi Iqbal Gill Evgeny Vulfson 《Journal of the American Oil Chemists' Society》1997,74(7):879-886
The application of lipases to the synthesis of amino acid-based surfactants was investigated. Low yields (2–9%) were obtained
in the acylation of free amino acids, such as l-serine and l-lysine, as well as their ethyl esters and amides with fatty acids, owing in part to low miscibility of the reactants. When
the N-carbobenzyloxy (Cbz)-l-amino acids were used in an effort to improve miscibility of the amino acid derivatives with the acyl donor, a dramatic improvement
was observed for N-Cbz-l-serine (92% yield) but not for N
α-Cbz- or N
ζ-Cbz-l-lysine (7 and 2% yield, respectively). As an alternative, and efficient synthesis of N
ζ-acyl-l-lysines was developed, based on the regiospecific chemical acylation of copper(II) lysinate. In pursuit of a general route
to amino acid-fatty acid surfactants, the utility of a polyol linker was investigated. Thus, the glycerol ester of N
α′
N
ζ-di-Cbz-l-lysine was prepared and evaluated as a substrate for acylation. As expected, this and other glycer-1-yl esters of N-protected amino acids were excellent substrates for lipase-catalyzed acylation. Their reaction with myristic acid in the
presence of Novozyme resulted in the regioselective acylation of the primary hydroxyl group of the glycerol moiety to afford
the corresponding 1-O-(N-Cbz-l-aminoacyl)-3-O-myris-toylglycerols with conversions of 50–90%. These were readily deprotected to give a range of 1-O-(aminoacyl)-3-O-myristoyl-glycerols with overall yields of 27–71%. 相似文献
54.
C. Borch-Jensen M. P. Magnussen J. Mollerup 《Journal of the American Oil Chemists' Society》1997,74(5):497-503
The liver oils of six different shark species have been analyzed by supercritical fluid chromatography (SFC). The liver oils
were from the species Pseudotriakis microdon (False catshark), Centroscymnus coelepsis (Portuguese dogfish), Centrophorus squanosus (Leafscalp gulper shark), Deanea calceus (Birdbeak dogfish), Etmopterus princips (Greater lantern shark), and Centroscymnus crepidater (Longnose velvet dogfish). The method was capable of direct quantitation of squalene and cholesterol, while quantitation
of triacylglycerols, cholesterol esters, and diacylglycerol ethers required thin-layer chromatographic fractionation prior
to SFC analysis. The iodine values of the liver oil samples gave a linear correlation when plotted against the squalene content
found by SFC. The variation of squalene content within one shark species is large, and there are large differences in squalene
content from species to species. The squalene contents varied between 0.22 and 82.54 wt%. The identity of the glycerol ethers
was investigated by SFC of the unsaponifiable matter. The major glycerol ethers contained chimyl, batyl, and selachyl alcohol. 相似文献
55.
56.
57.
58.
59.
建立了高效液相色谱-蒸发光散射检测器(HPLC-ELSD)测定低聚甘油组成的方法。以Econosphere Amino(250×4.6 mm,5μm)为色谱柱,乙腈-水(85∶15,V/V)为流动相,流速为1.0 mL/min,柱温为28℃,进样量为30μL,ELSD漂移管温度为32℃,载气流速为1.5 L/min。结果表明,在优化条件下,甘油、二聚甘油和三聚甘油浓度分别在100~300μg/mL、100~400μg/mL和200~600μg/mL范围内呈良好线性,相关系数分别为0.9979、0.9921和0.9969,定量下限分别为1.5、1.0和2.0μg,回收率为97%~103%,RSD<3.0%(n=6)。 相似文献
60.