全文获取类型
收费全文 | 66篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 50篇 |
数学 | 6篇 |
物理学 | 1篇 |
无线电 | 14篇 |
出版年
2023年 | 3篇 |
2022年 | 3篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 3篇 |
2012年 | 8篇 |
2011年 | 3篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 7篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
1998年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
排序方式: 共有71条查询结果,搜索用时 15 毫秒
1.
2.
Among the various Michael additions, the enantioselective reaction between cyclic ketones and nitrodienes has received little attention in comparison to the corresponding reaction with nitroolefins. A bifunctional organocatalyst consisting of the pyrrolidine moiety and a thioxotetrahydropyrimidinone ring successfully catalyzed this asymmetric transformation. The products of the reaction between various ketones and nitrodienes were obtained in high yields (up to 96%) with excellent diastereo- (up to >98:2 dr) and enantioselectivities (up to 99:1% er). 相似文献
3.
2,2,2‐Trifluoroacetophenone as an Organocatalyst for the Oxidation of Tertiary Amines and Azines to N‐Oxides 下载免费PDF全文
Dimitris Limnios Dr. Christoforos G. Kokotos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(2):559-563
A cheap, mild and environmentally friendly oxidation of tertiary amines and azines to the corresponding N‐oxides is reported by using polyfluoroalkyl ketones as efficient organocatalysts. 2,2,2‐Trifluoroacetophenone was identified as the optimum catalyst for the oxidation of aliphatic tertiary amines and azines. This oxidation is chemoselective and proceeds in high‐to‐quantitative yields utilizing 10 mol % of the catalyst and H2O2 as the oxidant. 相似文献
4.
Constantinos D. Diakoumakos John A. Mikroyannidis Christoforos A. Krontiras Michael N. Pisanias 《Journal of polymer science. Part A, Polymer chemistry》1994,32(10):1915-1921
New thermosetting resins were prepared from the reaction of 1,4-bis(2,2-dicyanovinyl)benzene with aromatic diamines in varying molar ratios. The thermal stability of these resins was correlated with their composition and the curing conditions. They were stable in N2 up to 370–448°C and afforded anaerobic char yields of 73–84% at 800°C after curing at 300°C for 20–60 h. The temperature dependence of the electrical resistivity of all resins pyrolyzed at 700°C for 15 h was studied in the temperature range from ?173–327°C (100–600 K). The results showed that at room temperature the unpyrolyzed polymers have insulating properties, whereas a dramatic decrease in the electrical resistivity is observed following pyrolysis. The temperature dependence of the electrical resistivity suggests that all of the materials studied have semiconducting properties. The observed electrical conductivity is thermally activated with activation energies ranging from 0.03–0.06 eV. © 1994 John Wiley & Sons, Inc. 相似文献
5.
Mitseva A. Prasad N. Todorova P. Fokus F. Aguero R. Garcia Armada A. Panayiotou C. Timm-Giel A. Maccari L. 《Wireless Communications, IEEE》2008,15(4):52-60
Wireless sensor networks are expected to be one of the key enabling technologies in the near future. Ubiquitous intelligent sensing environments have a promising potential to enhance the everyday life of citizens, bringing important social benefits for each person and for society as a whole. Substantial research has contributed to progress in this field. However, there are still gaps to be filled. This article presents an overview of the Creating Ubiquitous Intelligent Sensing Environments (CRUISE) project and identifies challenges in the research on WSNs. It focuses on outlining the consortium?s vision and strategy for the evolution of research. Key issues for target sensor network applications and current research orientations in CRUISE are described. Future work within the project focus areas is identified. 相似文献
6.
Kokotos CG Limnios D Triggidou D Trifonidou M Kokotos G 《Organic & biomolecular chemistry》2011,9(9):3386-3395
The synthesis of novel organocatalysts consisting of a pyrrolidine moiety and a thiohydantoin or a thioxotetrahydropyrimidinone ring is described. The compound combining the pyrrolidine with the thioxotetrahydropyrimidinone was found to be a highly effective catalyst for the Michael reaction. Low catalyst loadings (1-2.5%) can be employed leading to quantitative yields and excellent stereoselectivities in the reaction between cyclic ketones and nitroolefins. 相似文献
7.
G. S. Dritsas K. Karatasos C. Panayiotou 《Journal of Polymer Science.Polymer Physics》2008,46(20):2166-2172
Thermodynamic properties of the hyperbranched poly (ester amide) (Hybrane® 1200) were investigated by inverse gas chromatography (IGC) using 19 different solvents as the probes at infinite dilution. Retention data of probes were used for an extensive characterization of the polymer, which includes the determination of the Flory‐Huggins interaction parameter, the weight fraction activity coefficient, the total, partial, and additive solubility parameters. The analysis of the results indicated that the additive value of the solubility parameter is lower than the value obtained from a standard procedure. Furthermore, the solubility parameter decreases with increase of temperature. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2166–2172, 2008 相似文献
8.
This paper presents the design, implementation and performance evaluation of a coarse-grain dynamically reconfigurable FPGA platform for multi-service edge and access network devices. The platform consists of two MicroBlaze RISC processors and a number of hardware co-processors used for the processing of packet payloads (Data Encryption Standard (DES) and Lempel-Ziv Compression). The co-processors can be connected either directly to the processors or using a shared bus. The functionality of the co-processors is dynamically reconfigured to meet the requirements of the network workload. The system has been implemented on the Xilinx Virtex II Pro platform and the network traces from real passive measurements have been used for performance evaluation. The use of dynamically reconfigurable co-processors for network applications shows that the performance speedup versus a static version varies from 12% to 35% in the best case and from 10% to 15% on average, depending on the network traffic fluctuation. 相似文献
9.
One‐Pot Synthesis of O‐Allylhydroxylamines through the Organocatalytic Oxidation of Tertiary Allylic Amines Followed by a [2,3]‐Meisenheimer Rearrangement 下载免费PDF全文
Alexis Theodorou Dr. Dimitris Limnios Prof. Dr. Christoforos G. Kokotos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(13):5238-5241
A cheap, green, and highly efficient one‐pot method for the synthesis of O‐protected allylic alcohols is described. By utilizing 2,2,2‐trifluoroacetophenone as the organocatalyst and H2O2 as the oxidant, a variety of allylic amine N‐oxides were synthesized, which upon heating are converted to the final products through a [2,3]‐Meisenheimer rearrangement. 相似文献
10.
A series of aliphatic homopolyesters and copolyesters was prepared from 1,4 butanediol and dimethylesters of succinic and adipic acids through a two-step process of transesterification and polycondensation. The synthesized polyesters were characterized by means of nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), viscosity measurements, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and mechanical property measurements. The homopolymer poly(butylene succinate) exhibited the highest tensile strength, which decreased with increasing adipate unit content, passed through a minimum at copolyester composition close to equimolarity and then increased towards the value of poly(butylene adipate). It is interesting to note that in contrast to tensile strength, the elongation at break increased for adipate unit content of 20-40 mol%. The biodegradation of the polymers was investigated by soil burial and enzymatic hydrolysis using three enzymes, Candida cylindracea lipase, Rhizopus delemar lipase, and Pseudomonas fluorescens cholesterol esterase. It appears that the key factor affecting material degradation was its crystallinity. 相似文献