全文获取类型
收费全文 | 107篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
化学 | 81篇 |
力学 | 2篇 |
数学 | 6篇 |
物理学 | 24篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 4篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 5篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 6篇 |
2001年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有113条查询结果,搜索用时 0 毫秒
101.
Ghoneim AA 《Chemistry Central journal》2011,5(1):7
Practical procedures for production of variously blocked compounds from L-rhamnose have been developed. These compounds are
highly useful as indirect β-L-rhamnosyl donors. This approach represents a new method for the synthesis of aromatic nucleoside analogues and the synthesis
of (
3S, 4S, 5S, 6R) 3, 4, 5-triacetoxy-2-methyl-7,9-diaza-1-oxa-spiro [4,5]decane-10-one-8-thione (7). 相似文献
102.
The aim of this study was to investigate the antimycobacterial activity of the major daucane constituent, ferutinin (jaeschkeandiol p-hydroxybenzoate, 1), four of its natural analogues, its hydrolysis products, as well as methyl p-hydroxybenzoate (methylparaben) against Mycobacterium smegmatis, a rapidly growing surrogate of Mycobacterium tuberculosis. The agar dilution assay was utilised for an antimycobacterial evaluation of single compounds. A modified agar dilution assay, the checkerboard method, was utilised for evaluating the potentiating effect of 1 on different antitubercular drugs, namely isoniazid, ethionamide, rifampin and streptomycin. In the agar dilution assay, 1 exhibited higher potency (minimum inhibitory concentration [MIC] 10?μg?mL?1) than streptomycin and rifampin (MIC 20?μg?mL?1 for each). Of the natural analogues, 8,9-epoxyjaeschkeandiol p-hydroxybenzoate and 8,9-epoxyjaeschkeandiol benzoate exhibited marginal activity (MIC?≥?40 and 80?μg?mL?1, respectively). The checkerboard method showed that the combination of 1 with each antitubercular drug led to mutual enhancement of the antimycobacterial activity with isoniazid and ethionamide, while no such effect was observed with rifampin or streptomycin. Based on this study and earlier studies with Staphylococcus aureus, the major constituent 1 may be responsible for the major part of the antimicrobial activity of the root of Ferula hermonis. 相似文献
103.
Mesoporous material incorporating zinc with different Si/Zn ratios = 95, 65, and 20 have been synthesized by intercalating kanemite using cetyltrimethylammonium bromide as the intercalating agent and zinc nitrate. The resulting materials were characterized by different techniques such as: inductively coupled plasma technique, XRD, Brunauer-Emmett-Teller, and a temperature-programmed-desorption of pyridine. The catalytic performance was studied in the vapor phase tert-butylation of anisole with tert-butanol at different temperatures under atmospheric pressure. The results indicate that Zn-FSM-16 (20) was found to be more active than its relatives. The major products are found to be 4-tert-butyl anisole (4-TBA), 2-tert-butyl anisole (2-TBA) and 2,4 di-tert-butyl-anisole (2,4-DTBA). 相似文献
104.
Ground‐State Chemical Reactivity under Vibrational Coupling to the Vacuum Electromagnetic Field 下载免费PDF全文
Dr. Anoop Thomas Dr. Jino George Dr. Atef Shalabney Dr. Marian Dryzhakov Sreejith J. Varma Dr. Joseph Moran Thibault Chervy Dr. Xiaolan Zhong Dr. Eloïse Devaux Dr. Cyriaque Genet Dr. James A. Hutchison Prof. Dr. Thomas W. Ebbesen 《Angewandte Chemie (International ed. in English)》2016,55(38):11462-11466
The ground‐state deprotection of a simple alkynylsilane is studied under vibrational strong coupling to the zero‐point fluctuations, or vacuum electromagnetic field, of a resonant IR microfluidic cavity. The reaction rate decreased by a factor of up to 5.5 when the Si?C vibrational stretching modes of the reactant were strongly coupled. The relative change in the reaction rate under strong coupling depends on the Rabi splitting energy. Product analysis by GC‐MS confirmed the kinetic results. Temperature dependence shows that the activation enthalpy and entropy change significantly, suggesting that the transition state is modified from an associative to a dissociative type. These findings show that vibrational strong coupling provides a powerful approach for modifying and controlling chemical landscapes and for understanding reaction mechanisms. 相似文献
105.
Safaa Ibn Ghazala Frédéric Paul Loic Toupet Claude Lapinte 《Journal of organometallic chemistry》2007,692(4):917-920
A new cationic complex [(η2-bipy)(η5-C5Me5)Fe(η1-dppe)][BPh4] featuring a pendant free diphenylphosphine arm has been isolated in good yield after reaction of 2,2′-bipyridine with the known chloro precursor complex (η2-dppe)(η5-C5Me5)FeCl in presence of NaBPh4. This complex which can be envisioned as a new redox-active building-block has been structurally characterized. 相似文献
106.
Two new phytochemical compounds, Tetranins A and B, 1-(3,5'-dihydroxy-4'-méthoxyphenyl)-2-phenylethanol 1 and 5,2'-dihydroxy-5'-methoxy-6,7-methylenedioxy-isoflavone 2, were isolated from the EtOAc extract of Salsola tetrandra roots. They exhibited a significant antioxidant effect in 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and 2,2'-azinobis (3-ethylbenzothiazoline-6-sulphonic acid (ABTS) assays. Their structures were elucidated by extensive spectroscopic methods including 1-D-((1)H and (13)C) and 2-D-NMR experiments (CHcorr, HMBC, (1)H-(1)H COSY and NOESY) as well as high-resolution ES-MS and they were found to be quite active as antioxidants in the DPPH and ABTS assays. 相似文献
107.
Jonas Bruckhuisen Guillaume Dhont Anthony Roucou Atef Jabri Hamdi Bayoudh Thi Thanh Tran Manuel Goubet Marie-Aline Martin-Drumel Arnaud Cuisset 《Molecules (Basel, Switzerland)》2021,26(12)
Catechol is an oxygenated aromatic volatile organic compound and a biogenic precursor of secondary organic aerosols. Monitoring this compound in the gas phase is desirable due to its appreciable reactivity with tropospheric ozone. From a molecular point of view, this molecule is attractive since the two adjacent hydroxy groups can interchangeably act as donor and acceptor in an intramolecular hydrogen bonding due to the tunnelling between two symmetrically equivalent structures. Using synchrotron radiation, we recorded a rotationally-resolved Fourier Transform far-infrared (IR) spectrum of the torsional modes of the free and bonded -OH groups forming the intramolecular hydrogen bond. Additionally, the room temperature, pure rotational spectrum was measured in the 70–220 frequency range using a millimeter-wave spectrometer. The assignment of these molecular transitions was assisted by anharmonic high-level quantum-chemical calculations. In particular, pure rotational lines belonging to the ground and the four lowest energy, vibrationally excited states were assigned. Splitting due to the tunnelling was resolved for the free -OH torsional state. A global fit combining the far-IR and millimeter-wave data provided the spectroscopic parameters of the low-energy far-IR modes, in particular those characterizing the intramolecular hydrogen bond dynamics. 相似文献
108.
An optical receiver with high sensitivity and linearity specially designed for Giga-bit communications over small-bandwidth high-attenuation multimode plastic optical fiber is presented. An automatic gain control transimpedance amplifier and linear post amplifiers are used to maintain a good performance with multilevel modulation. Using multilevel signaling and large-diameter integrated photodiodes make the presented optical receiver suitable for large core plastic optical fiber. For a wavelength of 675 nm, a sensitivity of −26.3 dB m (BER = 10−9) at 500 Mb/s is presented by a binary signal. A data rate of 1 Gb/s and a sensitivity of −19.8 dB m (BER = 10−9) are achieved with four-level pulse amplitude modulation. 相似文献
109.
A large-diameter PIN photodiode (400 μm) with antireflection coating optimized for wavelength 650 nm was integrated with an automatic gain control transimpedance amplifier, linear post amplifier and 50Ω linear driver. The presented optical receiver shows a high linearity in receiving multilevel signals. A sensitivity of ?29.5dBm (BER = 10?9) at 200 Mb/s with binary signal was achieved. By using four-level pulse amplitude modulation (4-PAM) a data rate of 400 Mb/s and a sensitivity of ?21.5 dBm (SER = 10?9) was achieved. 相似文献
110.