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41.
以γ-Al2O3为载体通过原位共沉淀法制备NiMgAl-LDHs/γ-Al2O3,经焙烧后得到NiMg(Al)O/γ-Al2O3催化剂,通过TG-DTG、XRD、SEM、BET、FT-IR、CO2-TPD等手段对催化剂进行了表征,并对其在酯交换制备生物柴油反应中的催化性能进行了研究。结果表明,NiMgAl-LDHs和NiMg(Al)O成功在γ-Al2O3内孔表面生长,并有良好的结合度。催化剂对酯交换具有很高的催化活性;在醇油物质的量比为12:1的条件下反应3 h,生物柴油产率为95%,重复使用七次后,生物柴油产率仍然在82%以上。 相似文献
42.
Dr. Rik De Clercq Prof. Michiel Dusselier Dr. Ekaterina Makshina Prof. Bert F. Sels 《Angewandte Chemie (International ed. in English)》2018,57(12):3074-3078
A new route to lactide, which is a key building block of the bioplastic polylactic acid, is proposed involving a continuous catalytic gas‐phase transesterification of renewable alkyl lactates in a scalable fixed‐bed setup. Supported TiO2/SiO2 catalysts are highly selective to lactide, with only minimal lactide racemization. The solvent‐free process allows for easy product separation and recycling of unconverted alkyl lactates and recyclable lactyl intermediates. The catalytic activity of TiO2/SiO2 catalysts was strongly correlated to their optical properties by DR UV/Vis spectroscopy. Catalysts with high band‐gap energy of the supported TiO2 phase, indicative of a high surface spreading of isolated Ti centers, show the highest turnover frequency per Ti site. 相似文献
43.
Fuming Mei Exiang Chen Guangxing Li Aiqing Zhang 《Reaction Kinetics and Catalysis Letters》2008,93(1):101-108
Mg-Al-O-t-Bu hydrotalcite was synthesized and characterized by XRD, FT-IR and TGA-DTA. It was proved to be an active heterogeneous
catalyst for the transesterification of dimethyl carbonate (DMC) with ethanol. When the reaction was carried out over Mg-Al-O-t-Bu
hydrotalcite at 80°C, 7 h, molar ratio of ethanol to DMC 5:1, 1.0 wt.% of catalyst, the conversion of DMC was 86.4%, the selectivity
to diethyl carbonate (DEC) was 61.2%. This heterogeneous catalyst could be used 5 times without loss of its activity. 相似文献
44.
Dr. Shuangyan Hu Lijun Liu Dr. Heng Li Dr. David Pahovnik Prof. Dr. Nikos Hadjichristidis Prof. Dr. Xuechang Zhou Prof. Dr. Junpeng Zhao 《化学:亚洲杂志》2023,18(1):e202201097
A series of ester-ether copolymers were obtained via the reaction between α,ω-dihydroxyl poly(ϵ-caprolactone) (PCL) and ethylene oxide (EO) or monosubstituted epoxides catalyzed by strong phosphazene bases. The two types of monomeric units were distributed in highly random manners due to the concurrence of epoxide ring-opening and fast transesterification reactions. The substituent of epoxide showed an interesting bidirectional effect on the enzymatic degradability of the copolymer. Compared with PCL, copolymers derived from EO exhibited enhanced hydrophilicity and decreased crystallinity which then resulted in higher degradability. For the copolymers derived from propylene oxide and 1,2-butylene oxide, the hydrophobic alkyl pendant groups also allowed lower crystallinity of the copolymers thus higher degradation rates. However, further enlarging the pendant groups by using styrene oxide or 2-ethylhexyl glycidyl ether caused a decrease in the degradation rate, which might be ascribed to the higher bulkiness hindering the contact of ester groups with lipase. 相似文献
45.
Regioselective Functionalization of 3‐Hydroxy‐pyridine Carboxylates by Neighboring Group Assistance
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K. Philip Wojtas Dr. Jin‐Yong Lu Daniel Krahn Prof. Dr. Hans‐Dieter Arndt 《化学:亚洲杂志》2016,11(20):2859-2862
Regioselective hydrolysis, transesterification, and aminolysis of unactivated, highly substituted pyridine esters were realized under mild conditions by employing neighboring group assisted catalysis. Excellent yields were achieved without active removal of the alcohol byproduct. Regioselective aminolysis had a considerable substrate scope ([hetero]aryl, alkyl and amino acid). A mechanism involving assistance by the deprotonated phenolic OH‐group is suggested for hydrolysis and transesterification. 相似文献
46.
监测了对-乙酰氧基苯甲酸与聚对苯二甲酸乙二醇酯(PET)共缩聚反应过程中1HNMR图谱及特性粘度的变化,对乙酰氧基酯交换反应及乙酰脂肪酯的反应活性进行了研究。并研究了以低分子量PET或对苯二甲酸二乙二醇酯为原料时反应中醚键的形成及其进入共聚酯链的规律性。 相似文献
47.
Shau-Wei Tsai Chin-Shain Tsai Chun-Sheng Chang 《Applied biochemistry and biotechnology》1999,80(3):205-219
A lipase-catalyzed enantioselective transesterification process was developed for the synthesis of (S)-naproxen 2-N-morpholinoethyl ester prodrug from racemic 2,2,2-trifluoroethyl naproxen ester in organic solvents. By selecting isooctane
and 37°C as the best solvent and temperature, the apparent fits of the initial conversion rates for transesterification and
hydrolysis side reaction suggest a ping-pong Bi-Bi enzymatic mechanism with the alcohol as a competitive enzyme inhibitor.
Improvements in the initial conversion rate and the productivity for the desired (S)-ester product were obtained after comparing with the result of an enantioselective esterification process. Studies of water
content in isooctane and alcohol containing various N,N-dialkylamino groups on the enzyme activity and enantioselectivity, as well as the recovery of (S)-ester product by using extraction, were also reported. 相似文献
48.
Fumio Sanda Taizo Fujiyama Takeshi Endo 《Journal of polymer science. Part A, Polymer chemistry》2001,39(5):732-741
α‐Methyl glutamic acid (L ‐L )‐, (L ‐D )‐, (D ‐L )‐, and (D ‐D )‐γ‐dimers were synthesized from L ‐ and D ‐glutamic acids, and the obtained dimers were subjected to polycondensation with 1‐(3‐dimethylaminopropyl)‐3‐ethylcarbodiimide hydrochloride and 1‐hydroxybenzotriazole hydrate as condensation reagents. Poly‐γ‐glutamic acid (γ‐PGA) methyl ester with the number‐average molecular weights of 5000∼20,000 were obtained by polycondensation in N,N‐dimethylformamide in 44∼91% yields. The polycondensation of (L ‐L )‐ and (D ‐D )‐dimers afforded the polymers with much larger |[α]D | compared with the corresponding dimers. The polymer could be transformed into γ‐PGA by alkaline hydrolysis or transesterification into α‐benzyl ester followed by hydrogenation. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 732–741, 2001 相似文献
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