全文获取类型
收费全文 | 278篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
化学 | 200篇 |
晶体学 | 1篇 |
力学 | 4篇 |
数学 | 28篇 |
物理学 | 66篇 |
出版年
2024年 | 2篇 |
2023年 | 1篇 |
2022年 | 23篇 |
2021年 | 26篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 18篇 |
2017年 | 11篇 |
2016年 | 14篇 |
2015年 | 23篇 |
2014年 | 12篇 |
2013年 | 22篇 |
2012年 | 16篇 |
2011年 | 21篇 |
2010年 | 8篇 |
2009年 | 10篇 |
2008年 | 14篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 7篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有299条查询结果,搜索用时 15 毫秒
1.
2.
Ahmad VU Zubair M Athar Abbasi M Abid Rashid M Rasool N Nahar Khan S Iqbal Choudhary M Kousar F 《Magnetic resonance in chemistry : MRC》2005,43(6):486-488
The investigation of the chemical constituents of Symplocos racemosa Roxb led to the isolation of two new glycosides, symcomoside A (1) and symcomoside B (2), together with one known glycoside, tortoside C (3), which is reported for the first time from this plant. The structures of the new compounds were determined by 1D and 2D homonuclear and heteronuclear NMR spectroscopy, from chemical evidence and by comparison with published data for closely related compounds. Symcomoside B (2) showed potent inhibitory activity against alpha-glucosidase in a concentration-dependent fashion with an IC50 value of 0.733 +/- 0.033 mM whereas symcomoside A (1) showed very weak inhibitory activity against alpha-glucosidase (9.90% in 0.70 mM). 相似文献
3.
The dependence of the diffusion parameters including slowing down area, neutron diffusion length and migration length on the voided volume fraction in water has been studied experimentally. For this purpose, the PIEAS Neutron Transport Facility (PNTF) comprised of a 10 Ci Am–Be neutron source and a water filled aluminum tank with Perspex voided tubes has been designed and fabricated. A BF3 detector was used for the neutron counting. The slowing down area was determined at the cadmium cutoff level. The diffusion parameters were determined first in the absence of voids. The experimentally measured values of the slowing down area, the diffusion length and the migration length have been found in good agreement with the corresponding values determined by other workers. By varying void volume fraction from 0% to 7.5%, the experimental measurements show a monotonic increase in the slowing down area from 58.71±2.6 to 71.28±3.2 cm2, in the diffusion length from 2.95±0.13 to 3.11±0.13 cm and in the migration length from 8.21±0.165 to 8.99±0.169 cm. Our measurements show that the diffusion parameters exhibit a quadratic dependence on the void volume fraction. 相似文献
4.
QUANTITATION OF PYRIMIDINE DIMERS BY IMMUNOSLOT BLOT FOLLOWING SUBLETHAL UV-IRRADIATION OF HUMAN CELLS 总被引:6,自引:0,他引:6
Altaf A. Wani Steven M. D'Ambrosio Nasir K. Alvi 《Photochemistry and photobiology》1987,46(4):477-482
An immunoslot blot assay was developed to detect pyrimidine dimers induced in DNA by sublethal doses of UV (254 nm) radiation. Using this assay, one dimer could be detected in 10 megabase DNA using 200 ng or 0.5 megabase DNA using 20 ng irradiated DNA. The level of detection, as measured by dimer specific antibody binding, was proportional to the dose of UV and amount of irradiated DNA used. The repair of pyrimidine dimers was measured in human skin fibroblastic cells in culture following exposure to 0.5 to 5 J m-2 of 254 nm UV radiation. The half-life of repair was approximately 24, 7 and 6 h in cells exposed to 0.5, 2 and 5 J m-2 UV radiation, respectively. This immunological approach utilizing irradiated DNA immobilized to nitrocellulose should allow the direct quantitation of dimers following very low levels of irradiation in small biological samples and isolated gene fragments. 相似文献
5.
Four new Schiff base functionalized 1,2,3-triazolylidene nickel complexes, [Ni-(L1NHC)2](PF6)2; 3, [Ni-(L2NHC)2](PF6)2; 4, [Ni-(L3NHC)](PF6)2; 7 and [Ni-(L4NHC)](PF6)2; 8, (where L1NHC = (E)-3-methyl-1-propyl-4-(2-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenyl)-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 1, L2NHC = (E)-3-methyl-4-(2-((phenethylimino)methyl)phenyl)-1-propyl-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 2, L3NHC = 4,4′-(((1E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 5, and L4NHC = 4,4′-(((1E)-(butane-1,4-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 6), were synthesised and characterised by a variety of spectroscopic methods. Square planar geometry was proposed for all the nickel complexes. The catalytic potential of the complexes was explored in the oxidation of styrene to benzaldehyde, using hydrogen peroxide as a green oxidant in the presence of acetonitrile at 80 °C. All complexes showed good catalytic activity with high selectivity to benzaldehyde. Complex 3 gave a conversion of 88% and a selectivity of 70% to benzaldehyde in 6 h. However, complexes 4 and 7–8 gave lower conversions of 48–74% but with higher (up to 90%) selectivity to benzaldehyde. Results from kinetics studies determined the activation energy for the catalytic oxidation reaction as 65 ± 3 kJ/mol, first order in catalyst and fractional order in the oxidant. Results from UV-visible and CV studies of the catalytic activity of the Ni-triazolylidene complexes on styrene oxidation did not indicate any clear possibility of generation of a Ni(II) to Ni(III) catalytic cycle. 相似文献
6.
Tarfah Al-Warhi Adil Aldhahrani Fayez Althobaiti Eman Fayad Ola A. Abu Ali Sarah Albogami Ali H. Abu Almaaty Amgad I. M. Khedr Syed Nasir Abbas Bukhari Islam Zaki 《Molecules (Basel, Switzerland)》2022,27(12)
A novel series of amides based TMP moiety was designed, synthesized and evaluated for their antiproliferative as well as enzyme inhibition activity. Compounds 6a and 6b showed remarkable cytotoxic activity against HepG2 cells with IC50 values 0.65 and 0.92 μM, respectively compared with SAHA and CA-4 as reference compounds. In addition, compound 6a demonstrated good HDAC-tubulin dual inhibition activity as it showed better HDAC activity as well as anti-tubulin activity. Moreover, compound 6a exhibited G2/M phase arrest and pre-G1 apoptosis as demonstrated by cell cycle analysis and Annexin V assays. Further apoptosis studies demonstrated that compound 6a boosted the level of caspase 3/7. Caspase 3/7 activation and apoptosis induction were evidenced by decrease in mitochondrial permeability suggesting that activation of caspase 3/7 may occur via mitochondrial apoptotic pathway. 相似文献
7.
8.
Hafiz T.Ali MRamzan M Imran Arshad Nicola A.Morley M.Hassan Abbas Mohammad Yusuf Atta Ur Rehman Khalid Mahmood Adnan Ali Nasir Amin MAjaz-un-Nabi 《中国物理 B》2022,31(2):27502-027502
We investigate the impact of Ni insertion on the structural,optical,and magnetic properties of Ba0.8La0.2Fe12-xNixO19hexaferrites(Ni substituted La-BaM hexaferrites).Samples were prepared using the conventional co-precipitation method and sintered at 1000℃for 4 hours to assist the crystallization process.An analysis of the structure of the samples was carried out using an x-ray diffraction(XRD)spectrometer.The M-type hexagonal structure of all the samples was confirmed using XRD spectra.The lattice parameters a and c were found to be in the ranges of 5.8925±0.001 nm–5.8952±0.001 nm and 23.2123±0.001 nm–23.2219±0.001 nm,respectively.The M-type hexagonal nature of the prepared samples was also indicated by the presence of corresponding FT-IR bands and Raman modes in the FT-IR and Raman spectra,respectively.EDX results confirmed the successful synthesis of the samples according to the required stoichiometric ratio.A UV-vis spectrometer was used to record the absorption spectra of the prepared samples in the wavelength range of 200 nm–1100 nm.The optical energy bandgap of the samples was found to be in the range of 1.21 eV–3.39 eV.The M–H loops of the samples were measured at room temperature at an applied magnetic field range of 0 kOe–60 kOe.A high saturation magnetization of 99.92 emu/g was recorded in the sample with x=0 at a microwave operating frequency of 22.2 GHz.This high value of saturation magnetization is due to the substitution of La3+ions at the spin-up(12k,2a,and 2b)sites.The Ni substitution is proven to be a potential candidate for the tuning of the optical and magnetic parameters of M-type hexaferrites.Therefore,we suggest that the prepared samples are suitable for use in magneto-optic applications. 相似文献
9.
Synthesis,anti‐migration and burning rate catalytic mechanism of ferrocene‐based compounds
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zain‐ul ‐Abdin Haojie Yu Li Wang Muhammad Saleem Hamad Khalid Nasir M. Abbasi Muhammad Akram 《应用有机金属化学》2014,28(8):567-575
One of the most important components of solid rocket propellant is the burning rate catalysts (BRC) which enhance burning rate of solid composite propellant. Low‐pressure exponents and stable burning rate are the key features of an excellent solid propellant. Addition of BRC to the propellant results in the increase of burning rate of the propellant and decrease in pressure exponents. Among all BRC, ferrocene‐based BRC have attracted much attention because of their better microscopic homogeneities in distribution, ignitability of the propellants and good compatibility with organic binder. However, the main barrier for the development and practical applications of ferrocene‐based BRC is their migration property. This article reviews the field and highlights recent progress. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
10.
Cover Picture: Open‐Pore Two‐Dimensional MFI Zeolite Nanosheets for the Fabrication of Hydrocarbon‐Isomer‐Selective Membranes on Porous Polymer Supports (Angew. Chem. Int. Ed. 25/2016)
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Han Zhang Prof. Qiang Xiao Prof. Xianghai Guo Prof. Najun Li Prashant Kumar Neel Rangnekar Mi Young Jeon Prof. Shaeel Al‐Thabaiti Prof. Katabathini Narasimharao Prof. Sulaiman Nasir Basahel Prof. Berna Topuz Frank J. Onorato Prof. Christopher W. Macosko Prof. K. Andre Mkhoyan Prof. Michael Tsapatsis 《Angewandte Chemie (International ed. in English)》2016,55(25):7009-7009