全文获取类型
收费全文 | 228篇 |
免费 | 7篇 |
专业分类
化学 | 143篇 |
晶体学 | 3篇 |
力学 | 1篇 |
数学 | 4篇 |
物理学 | 72篇 |
无线电 | 12篇 |
出版年
2023年 | 7篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 6篇 |
2018年 | 10篇 |
2017年 | 13篇 |
2016年 | 12篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 16篇 |
2012年 | 20篇 |
2011年 | 19篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 14篇 |
2006年 | 19篇 |
2005年 | 5篇 |
2003年 | 1篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1994年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有235条查询结果,搜索用时 15 毫秒
191.
Abhishek Maurya Neha Kesharwani Payal Kachhap Vivek Kumar Mishra Nikita Chaudhary Chanchal Haldar 《应用有机金属化学》2019,33(9)
Liquid phase catalytic oxidation of a number of alkenes, for example, cyclohexene, cis‐cyclooctene, styrene, 1‐methyl cyclohexene and 1‐hexene, was performed using polymer‐anchored copper (II) complexes PS‐[Cu (sal‐sch)Cl] ( 5 ), PS‐[Cu (sal‐tch)Cl] ( 6 ), PS‐[CH2{Cu (sal‐sch)Cl}2] ( 7 ) and PS‐[CH2{Cu (sal‐tch)Cl}2] ( 8 ). Neat complexes [Cu (sal‐sch)Cl] ( 1 ), [Cu (sal‐tch)Cl] ( 2 ), [CH2{Cu (sal‐sch)Cl}2] ( 3 ) and [CH2{Cu (sal‐tch)Cl}2] ( 4 ) were isolated by reacting CuCl2·2H2O with [Hsal‐sch] ( I ), [Hsal‐tch] ( II ), [H2bissal‐sch] ( III ) and [H2bissal‐tch] ( IV ), respectively, in refluxing methanol. Complexes 1–4 have been covalently anchored in Merrifield resin through the amine nitrogen of the semicarbazide or thiosemicarbazide moiety. A number of analytical, spectroscopic and thermal techniques, such as CHNS analysis, Fourier transform‐infrared, UV–Vis, PMR, 13C‐NMR, electron paramagnetic resonance, scanning electron microscopy, energy‐dispersive X‐ray analysis, thermogravimetric analysis, atomic force microscopy, atomic absorption spectroscopy, and electrospray ionization‐mass spectrometry, were used to analyze and establish the molecular structure of the ligands ( I )–( IV ) and complexes ( 1 )–( 8 ) in solid state as well as in solution state. Grafted complexes 5 – 8 were employed as active catalysts for the oxidation of a series of alkenes in the presence of hydrogen peroxide. Copper hydroperoxo species ([CuIII (sal‐sch)‐O‐O‐H]), which is believed to be the active intermediate, generated during the catalytic oxidation of alkenes, are identified. It was found that supported catalysts are very economical, green and efficient in contrast to their neat complexes as well as most of the recently reported heterogeneous catalysts. 相似文献
192.
193.
194.
195.
196.
Visible‐Light/Photoredox‐Mediated sp3 CH Functionalization and Coupling of Secondary Amines with Vinyl Azides in Flow Microreactors
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Dharmendra Kumar Tiwari Dr. Ram Awatar Maurya Dr. Jagadeesh Babu Nanubolu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(2):526-530
Structurally diverse imidazole derivatives were synthesized by a visible‐light/[Ru(bpy)3][(PF6)2]‐mediated coupling of vinyl azides and secondary amines in flow microreactors. This operationally simple and atom‐economical protocol allows the formation of three new C?N bonds through the functionalization of sp3 C?H bonds adjacent to the secondary nitrogen atom. In order to get mechanistic insight of the coupling reaction, several control experiments were carried out and discussed. 相似文献
197.
R. Nageswara Rao Sravan Bompelli Pawan K. Maurya 《Biomedical chromatography : BMC》2011,25(11):1252-1259
A selective and sensitive high‐performance liquid chromatography method with fluorescence detection for simultaneous determination of irbesartan, losartan and valsartan on dried blood spots (DBS) has been developed and validated. It involves solvent extraction of a punch of DBS followed by reversed‐phase liquid chromatography on a Lichrospher® 100 RP‐18e column. Fluorescence detection was performed at 259 and 385 nm as excitation and emission wavelengths, respectively. The detection limits of irbesartan, losartan and valsartan were 1.8, 3.6 and 1.8 ng/mL respectively. The mean recoveries of irbesartan, losartan and valsartan were 98.68, 98.42 and 97.81%, respectively. The mean inter‐day and intra‐day precisions of irbesartan, losartan and valsartan were 2.07 and 1.34%, 1.42 and 1.48%, and 3.20 and 2.15% respectively. The proposed method was simple and rapid. Design of experiments was used to evaluate the robustness of the method. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
198.
Neetu Ishwar Chandra Maurya Arun Kumar Gupta Pankaj Srivastava Lal Bahadur 《Journal of Solid State Electrochemistry》2017,21(5):1229-1241
In this work, we have prepared Al-doped TiO2 nanoparticles via a hydrothermal method and used it for making photoanode in dye-sensitized solar cell (DSSC). Material characterizations were done using XRD, AFM, SEM, TEM and EDAX. XPS results reveal that Al is introduced successfully into the structure of TiO2 creating new impurity energy levels in the forbidden gap. This resulted in tuning of the conduction band of TiO2 and reduced charge recombination which led to better current conversion efficiency of DSSC. Greater dye loading and enhanced surface area was obtained for Al-doped TiO2 compared to un-doped TiO2. I-V analysis, EIS and Bode plots are employed to evaluate photovoltaic performance. The short-circuit current density (J sc) and efficiency (η) of cell employing Al-doped TiO2 photoanode were extensively enhanced compared to the cell using un-doped TiO2. The optical band gap (E g) for Al-doped and un-doped TiO2 was obtained as 2.8 and 3.2 eV, respectively. J sc and η were 13.39 mAcm?2 and 4.27%, respectively, under illumination of 100 mWcm?2 light intensity when thin films of 1% Al-doped TiO2 was employed as photoanode in DSSC using N719 as the sensitizer dye. With the use of un-doped TiO2 as photoanode under similar conditions, J sc 5.12 mAcm?2 and η 1.06% only could be obtained. The maximum IPCE% obtained with Al-doped TiO2 and un-doped TiO2 was 67 and 38% respectively at the characteristic wavelength of dye (λ max = 540 nm). The EIS analyses revealed resistive and capacitive elements that provided an insight into various interfacial processes in terms of the charge transport. It was observed that Al-doping reduced the interfacial resistance leading to better charge transport which has improved both photocurrent density and conversion efficiency. Higher electron mobility and fast diffusion resulting in greater charge collection efficiency was obtained for Al-doped TiO2 compared to the un-doped TiO2. Using the Mott–Schottky plot, the donor density was calculated for un-doped and Al-doped TiO2. The work demonstrated that the Al-doped TiO2 is potential photoanode material for low-cost and high-efficiency DSSC. 相似文献
199.
Ram Awatar Maurya Chada Narsimha Reddy Geeta Sai Mani Jeevak Sopanrao Kapure Praveen Reddy Adiyala Jagadeesh Babu Nanubolu Kiran Kumar Singarapu Ahmed Kamal 《Tetrahedron》2014
Substituted 3-methyleneindolin-2-ones were efficiently cyclopropanated with ethyl diazoacetate to yield spiro[cyclopropane-1,3′-indolin]-2′-ones in a catalyst-free and highly diastereoselective reaction in a mixture of ethanol–acetonitrile (1:1 v/v) as solvent. 相似文献
200.
Shashwati Sen DK Aswal Ajay Singh TV Chandrasekhar Rao KP Muthe JC Vyas LC Gupta SK Gupta VC Sahni 《Pramana》2002,58(5-6):867-870
The MgB2 superconductor, synthesized using solid-state and liquid-phase sintering methods, have been characterized for various properties.
The upper critical field, irreversibility line and critical current density have been determined using magnetization data.
The current-voltage characteristics recorded under an applied magnetic field revealed the existence of vortex glass transition.
The surface analysis using X-ray photoelectron spectroscopy shows that MgB2 is sensitive to atmospheric degradation. 相似文献