全文获取类型
收费全文 | 872篇 |
免费 | 113篇 |
国内免费 | 60篇 |
专业分类
化学 | 1015篇 |
晶体学 | 2篇 |
综合类 | 4篇 |
物理学 | 24篇 |
出版年
2024年 | 1篇 |
2023年 | 25篇 |
2022年 | 25篇 |
2021年 | 158篇 |
2020年 | 97篇 |
2019年 | 101篇 |
2018年 | 89篇 |
2017年 | 44篇 |
2016年 | 107篇 |
2015年 | 60篇 |
2014年 | 36篇 |
2013年 | 50篇 |
2012年 | 40篇 |
2011年 | 28篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 21篇 |
2005年 | 11篇 |
2004年 | 11篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 1篇 |
2000年 | 14篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1983年 | 1篇 |
排序方式: 共有1045条查询结果,搜索用时 46 毫秒
41.
A novel flavone, penimethavone A (1), possessing a rare unique methyl group at ring-B, was isolated from the fungus Penicillium chrysogenum cultured from a gorgonian Carijoa sp. collected from the South China Sea. The structure was elucidated by extensive spectroscopic analysis and by comparison with related known compound. Compound 1 showed selective and moderate cytotoxicity against cervical cancer (HeLa) and rhabdomyosarcoma cell lines with IC50 values of 8.41 and 8.18 μM, respectively. 相似文献
42.
Dual Chemical Modification of a Polytheonamide Mimic: Rational Design and Synthesis of Ion‐Channel‐Forming 48‐mer Peptides with Potent Cytotoxicity 下载免费PDF全文
Atsushi Hayata Dr. Hiroaki Itoh Shoko Matsutaka Prof.Dr. Masayuki Inoue 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3370-3377
Polytheonamide B ( 1 ) is a natural peptide that displays potent cytotoxicity against P388 mouse leukemia cells (IC50=0.098 nm ). Linear 48‐mer 1 is known to form monovalent cation channels on binding to lipid bilayers. We previously developed a fully synthetic route to 1 , and then achieved the design and synthesis of a structurally simplified analogue of 1 , namely, dansylated polytheonamide mimic 2 . Although the synthetically more accessible 2 was found to emulate the channel function of 1 , its cytotoxicity was decreased 120‐fold. Herein, the chemical preparation and biological evaluation of seven analogues 3 – 9 of 2 are reported. Compounds 3 – 9 were modified at their N terminus and/or the side chain of residue 44 of 2 to alter their physicochemical properties. The total synthesis of 3 – 9 was accomplished in a unified fashion by a combination of solid‐phase and solution‐phase chemistry. Systematic evaluation of the hydrophobicities, single‐channel currents, ion‐exchange activities, and cytotoxicities of 3 – 9 revealed that their hydrophobicities are correlated with the total magnitude of ion exchange and determine their cytotoxic potency. Consequently, the most hydrophobic analogue 9 exhibited the lowest IC50 value, which is comparable to that of 1 . Therefore, these results clarified that the bioactivity of the polytheonamide‐based peptides can be rationally controlled by changing their hydrophobicity at the N and C termini of the 48‐amino‐acid sequence. 相似文献
43.
Dominic Thibeault Jean Legault Charles Gauthier Serge Lavoie Jimmy Bouchard 《合成通讯》2013,43(2):213-221
22(17 → 28)abeo-Lupene derivatives 5a and 6a were obtained after the acid-catalyzed E-ring expansion of 3-acetylbetulin (1a). Glycosylation of these dehydrated triterpenoids using Schmidt's trichloroacetimidate sugar donors in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) provided the new anhydrobetulin saponins 7b–7e in which the terminal olefin C-20(29) isomerizes to form a C-19 tetrasubstituted alkene. The preliminary cytotoxic evaluation revealed that saponins 7b–7d exhibited a moderate cytotoxic activity against A549, DLD-1, and WS1 human cell lines with IC50 ranging from 22 to 49 μM. 相似文献
44.
《应用有机金属化学》2017,31(9)
The synthesis of monomeric pentacoordinated diorganotin(IV) complexes derived from pyridoxal hydrochloride and 4‐ or 5‐R ‐substituted ortho ‐aminophenols is described. The complexes were characterized using UV–visible, infrared, mass, 1H NMR, 13C NMR and 119Sn NMR spectral techniques. The molecular structure of three complexes was established using X‐ray diffraction: 3b and 3d show a distorted trigonal bipyramidal geometry, in which the basal plane is defined by the butyl groups and the iminic nitrogen atom, whereas the oxygen atoms from the aromatic ring occupy axial positions; in contrast, complex 3e exhibits a square pyramidal geometry. The cytotoxic activity of all complexes against human cell lines U‐251 (glioblastoma), K‐562 (chronic myelogenous leukemia), HCT‐15 (human colorectal cancer), MCF‐7 (human breast cancer) and SKLU‐1 (non‐small‐cell lung cancer) was evaluated, and the inhibitory percentage values indicated higher activity than the reference standard, cisplatin. Acute toxicity studies were performed in vivo for the prepared complexes to determine the lethal medium dose (LD50) after intraperitoneal administration to mice. 相似文献
45.
46.
Pavel Arsenyan Irina Shestakova 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):2427-2430
The cytotoxic activity of a series of methylammonium tellurates on human fibrosarcoma HT-1080, mouse hepatoma MG-22A, and mouse fibroblasts 3T3 cell lines is described. The role of tellurates as free radical regulators is discussed. 相似文献
47.
Samuel O. Grim Anthony W. Yankowsky 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):191-195
Abstract The 31P chemical shifts of eleven (4-ZC6H4)3P compounds show a slight correlation with the Hammet [sgrave]para constant of Z. The unusually large upfield chemical shifts of (2-ZC6H4)3P compounds are attributed to an extreme “gamma” effect caused by the restricted conformations due to the steric influence of the ortho substituents. Chemical shifts are given for about thirty triarylphosphines, and group contributions to phosphine chemical shifts are listed for twenty-one aryl groups. 相似文献
48.
49.
Superparamagnetic iron oxide nanoparticles with narrow size distributions were successfully prepared in large scale by a facile one‐pot synthetic method in the presence of hydrophilic polymers, such as polyethylene glycol diacid (HOOC‐PEG‐COOH) and poly(acrylic acid) (PAA). The as‐prepared products were investigated in detail by powder X‐ray diffraction (XRD), thermogravimetric analyses (TGA), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), and vibrating sample magnetometer (VSM). The interaction between polymers and iron oxide nanoparticles was investigated using Fourier transform infrared spectrometry (FT‐IR). The results show that polymers can be attached onto the surface of iron oxide nanoparticle by bridging coordination and monodentate fashion, respectively. The interaction affects iron oxide nanoparticle properties significantly, such as XRD diffraction intensity, hydrodynamic diameter, isoelectric point, and saturation magnetization. Furthermore, the results of in vitro experiments indicated that iron oxide‐PEG‐COOH nanoparticle is more cytotoxic than iron oxide‐PAA nanoparticle due to different coordinating modes. 相似文献
50.
A six‐step general and very efficient synthesis of 4‐(arylmethyl)‐5,5‐dialkyldihydrofuranones starting from corresponding aryl aldehyde has been developed. Solafuranone, a novel furanone isolated from the Chinese folk medicine Solanum indicum, has been accomplished starting from 2,6‐dimethylbenzaldehyde in six steps in an overall yield of 70%. Contrary to expectations, solafuranone and its analogue failed to exhibit any significant cytotoxicity against A549 (lung adenocarcinoma) and HL60 (leukemia cells) cell lines. 相似文献