全文获取类型
收费全文 | 1789篇 |
免费 | 400篇 |
国内免费 | 57篇 |
专业分类
化学 | 2030篇 |
晶体学 | 4篇 |
综合类 | 7篇 |
数学 | 27篇 |
物理学 | 178篇 |
出版年
2023年 | 20篇 |
2022年 | 26篇 |
2021年 | 69篇 |
2020年 | 158篇 |
2019年 | 100篇 |
2018年 | 86篇 |
2017年 | 63篇 |
2016年 | 122篇 |
2015年 | 122篇 |
2014年 | 120篇 |
2013年 | 139篇 |
2012年 | 101篇 |
2011年 | 93篇 |
2010年 | 81篇 |
2009年 | 75篇 |
2008年 | 84篇 |
2007年 | 106篇 |
2006年 | 101篇 |
2005年 | 79篇 |
2004年 | 76篇 |
2003年 | 79篇 |
2002年 | 38篇 |
2001年 | 26篇 |
2000年 | 24篇 |
1999年 | 33篇 |
1998年 | 26篇 |
1997年 | 38篇 |
1996年 | 29篇 |
1995年 | 26篇 |
1994年 | 17篇 |
1993年 | 17篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1970年 | 3篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有2246条查询结果,搜索用时 78 毫秒
1.
Yuying Qu Yingchun Li Xiaoli Tan Weixiang Zhai Dr. Guifang Han Dr. Jingli Hou Prof. Guoquan Liu Prof. Yuguang Song Prof. Yangping Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(33):7888-7895
Tetrathiatriarylmethyl (TAM, trityl) radicals have found wide applications as spin probes/labels for EPR spectroscopy and imaging, and as polarizing agents for dynamic nuclear polarization. The high hydrophilicity of TAM radicals is essential for their biomedical applications. However, the synthesis of hydrophilic TAM radicals (e.g., OX063) is extremely challenging and has only been reported in the patent literature, to date. Herein, an efficient synthesis of a highly water-soluble TAM radical bis(8-carboxyl-2,2,6,6-tetramethylbenzo[1,2-d:4,5-d′]bis([1,3]dithiol-4-yl)-mono-(8-carboxyl-2,2,6,6-tetrakis(2-hydroxyethyl)benzo[1,2-d:4,5-d′]bis([1,3]dithiol-4-yl)methyl (TFO), which contains four additional hydroxylethyl groups, relative to the Finland trityl radical CT-03, is reported. Similar to OX063, TFO exhibits excellent properties, including high water solubility in phosphate buffer, low log P, low pKa, long relaxation times, and negligible binding with bovine serum albumin. On the other hand, TFO has a sharper EPR line and higher O2 sensitivity than those of OX063. Therefore, in combination with its facile synthesis, TFO should find wide applications in magnetic resonance related fields and this synthetic approach would shed new light on the synthesis of other hydrophilic TAM radicals. 相似文献
2.
Xiaopei Li Tasuku Ogihara Prof. Dr. Manabu Abe Dr. Yasuyuki Nakamura Prof. Dr. Shigeru Yamago 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(42):9846-9850
The effect of viscosity on the diffusion efficiency (Fdif) of an organic radical pair in a solvent cage and the termination mechanism, that is, the selectivity of disproportionation (Disp) and combination (Comb) of the geminated caged radical pair and the diffused radicals encountered, were investigated quantitatively by following the photolysis of dimethyl 2,2′-azobis(2-methylpropionate) (V-601) in the absence and presence of PhSD. Fdif and Disp/Comb selectivity outside the cage [Disp(dif)/Comb(dif)] are highly sensitive to the viscosity. In contrast, the Disp/Comb selectivity inside the cage [Disp(cage)/Comb(cage)] is rather insensitive. The difference in viscosity dependence between Disp(cage)/Comb(cage) and Disp(dif)/Comb(dif) is explained by the spin state of the radical pair inside and outside the cage and the spin state dependent configurational changes of the radical pair upon their collision. Given that the configurational change of the radicals associates the displacement and reorganization of solvents around the radicals, the termination outside the cage, which requires larger change than that inside the cage, is highly viscosity dependent. Furthermore, while the bulk viscosity of each solvent shows good correlation with Fdif and Disp/Comb selectivity, microviscosity is the better parameter predicting Fdif and Disp(dif)/Comb(dif) selectivity regardless of the solvents. 相似文献
3.
Visible‐Light‐Induced Trifluoromethylation of Isonitrile‐Substituted Methylenecyclopropanes: Facile Access to 6‐(Trifluoromethyl)‐7,8‐Dihydrobenzo[k]phenanthridine Derivatives 下载免费PDF全文
Yu‐Chao Yuan Hou‐Lu Liu Xu‐Bo Hu Prof. Dr. Yin Wei Prof. Dr. Min Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(37):13059-13063
A new visible‐light‐induced trifluoromethylation of isonitrile‐substituted methylenecyclopropanes is developed. A range of substituted 6‐(trifluoromethyl)‐7,8‐dihydrobenzo[k]phenanthridine derivatives are readily furnished by this newly developed tandem reaction with moderate to good yields. This reaction allows the direct formation of two six‐membered rings and three new C?C bonds, including the C?CF3 bond, under visible light irradiation. 相似文献
4.
Hydroxyl Radical Generation and DNA Nuclease Activity: A Mechanistic Study Based on a Surface‐Immobilized Copper Thioether Clip‐Phen Derivative 下载免费PDF全文
Adolfo I. B. Romo Dieric S. Abreu Dr. Tércio de F. Paulo Dr. Marta S. P. Carepo Prof. Eduardo H. S. Sousa Prof. Luis Lemus Prof. Carolina Aliaga Prof. Alzir A. Batista Prof. Otaciro R. Nascimento Prof. Héctor D. Abruña Prof. Izaura C. N. Diógenes 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(29):10081-10089
Coordination compounds of copper have been invoked as major actors in processes involving the reduction of molecular oxygen, mostly with the generation of radical species the assignment for which has, so far, not been fully addressed. In the present work, we have carried out studies in solution and on surfaces to gain insights into the nature of the radical oxygen species (ROS) generated by a copper(II) coordination compound containing a thioether clip‐phen derivative, 1,3‐bis(1,10‐phenanthrolin‐2‐yloxy)‐N‐(4‐(methylthio)benzylidene)propan‐2‐amine (2CP‐Bz‐SMe), enabling its adsorption/immobilization to gold surfaces. Whereas surface plasmon resonance (SPR) and electrochemistry of the adsorbed complex indicated the formation of a dimeric CuI intermediate containing molecular oxygen as a bridging ligand, scanning electrochemical microscopy (SECM) and nuclease assays pointed to the generation of a ROS species. Electron paramagnetic resonance (EPR) data reinforced such conclusions, indicating that radical production was dependent on the amount of oxygen and H2O2, thus pointing to a mechanism involving a Fenton‐like reaction that results in the production of OH.. 相似文献
5.
Redox Communication within Multinuclear Iron–Sulfur Complexes Related to Electronic Interplay in the Active Site of [FeFe]Hydrogenase 下载免费PDF全文
Kai‐Ti Chu Dr. Yu‐Chiao Liu Yi‐Lan Huang Dr. Gene‐Hsiang Lee Dr. Mei‐Chun Tseng Prof. Ming‐Hsi Chiang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(18):6852-6861
The one‐electron oxidations of a Fe2 complex lead to the formation of a persistent metal‐stabilized thiyl radical Fe2 species, mixed‐valent Fe4, and Fe8 complexes. The unpaired spin in the Fe2 radical species delocalizes over the Fe2 and the aromatic dithiolate, mostly on the terminal sulfur. The subsequent dimerization of the singly oxidized Fe2 to the Fe4 retains the partial thiyl radical character. For an analogue with less steric hindrance, the π–π stacking interaction between the dithiolato aromatic rings induces generation of the Fe8, in which process electronic structures of the species are modulated through reducing the thiyl radical to the thiolate. Electronic reorganization repeats when the Fe8 is converted to Fe4. Electronic interplay in the complexes decreases the energy gap of frontier MOs and buffers electronic impacts upon redox events. Easier accessible redox potentials and increased stability of the species are facilitated. The results demonstrate that electronic versatility of the benzenedithiolate exerts pronounced influences on electronic and coordination structure of the metal complexes. 相似文献
6.
Nickel(II) meso‐Hydroxyporphyrin Complexes Revisited: Palladium‐Catalysed Synthesis,Electronic Structures of Derived Oxy Radicals,and Oxidative Coupling to a Dioxoporphodimethene Dyad 下载免费PDF全文
Dr. Louisa J. Esdaile Dr. Llew Rintoul Mean See Goh Khalissa Merahi Dr. Nathalie Parizel Dr. R. Mark Wellard Dr. Sylvie Choua Prof. Dennis P. Arnold 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3430-3446
We report the synthesis and characterisation of new examples of meso‐hydroxynickel(II) porphyrins with 5,15‐diphenyl and 10‐phenyl‐5,15‐diphenyl/diaryl substitution. The OH group was introduced by using carbonate or hydroxide as nucleophile by using palladium/phosphine catalysis. The NiPor?OHs exist in solution in equilibrium with the corresponding oxy radicals NiPor?O.. The 15‐phenyl group stabilises the radicals, so that the 1H NMR spectra of {NiPor?OH} are extremely broad due to chemical exchange with the paramagnetic species. The radical concentration for the diphenylporphyrin analogue is only 1 %, and its NMR line‐broadening was able to be studied by variable‐temperature NMR spectroscopy. The EPR signals of NiPor?O. are consistent with somewhat delocalised porphyrinyloxy radicals, and the spin distributions calculated by using density functional theory match the EPR and NMR spectroscopic observations. Nickel(II) meso‐hydroxy‐10,20‐diphenylporphyrin was oxidatively coupled to a dioxo‐terminated porphodimethene dyad, the strongly red‐shifted electronic spectrum of which was successfully modelled by using time‐dependent DFT calculations. 相似文献
7.
Degradation of rhodamine B photocatalyzed by Eu-doped CdS nanowires illuminated by visible radiation
Anukorn Phuruangrat Siwat Thungprasert Thawatchai Sakhon Budsabong Kuntalue Titipun Thongtem Somchai Thongtem 《印度化学会志》2022,99(2):100349
CdS nanowires doped with different contents of Eu dopant were synthesized by solvothermal method. XRD, SEM, TEM and Raman analyses certified that the as-synthesized samples were hexagonal CdS uniform nanowires. The pure CdS nanowires were 1–3 ?μm long and 80 ?nm diameter with the 1st and 2nd order longitudinal phonon modes at 298 and 594 ?cm?1. The 3% Eu-doped CdS wires were 800 ?nm–2.5 ?μm long and 75 ?nm diameter with the 1st and 2nd order longitudinal phonon modes at 296 and 593 ?cm?1. CdS nanowires grew along the [001] direction due to the surface energy effect. The photocatalytic properties of CdS and Eu-doped CdS nanowires were investigated for the degradation of rhodamine B (RhB) illuminated by visible radiation. In this research, Eu dopant played the role in promoting the photocatalytic kinetics because Eu3+ ions act as an electron acceptor to promote charge separation and photocatalytic activity. Both ●OH and ●O2? were the main active radicals used to transform RhB molecules into CO2, H2O and other intermediates. 相似文献
8.
AbstractReactive oxygen species including free radicals are responsible for noxious changes in living organisms which can be associated with many diseases for e.g. cardiovascular, neurodegenerative, and inflammatory diseases or cancer. In the struggle against free radicals the organism is supported by antioxidants. As they are often provided by nature, they can be considered safe. 5-Caffeoylquinic acid is one of main chlorogenic acids found in vegetables and fruits. The main objective of the presented article was monitoring the changes of 5-caffeoylquinic acid during the reaction with colorful radicals. The experiments were conducted at different molar ratios of radicals to antioxidant using liquid chromatography–mass spectrometry. Irrespective of the applied molar ratios, the obtained results proved that the antioxidant takes part in the reaction for three days. Additionally, during the radical neutralization the formation of semiquinones and/or quinones, methoxy adduct of caffeoylquinic acid, and quinones adduct with methanol was observed. 相似文献
9.
Elaine Tsui Anthony J. Metrano Yuto Tsuchiya Prof. Robert R. Knowles 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(29):11943-11947
We report a catalytic, light-driven method for the intramolecular hydroetherification of unactivated alkenols to furnish cyclic ether products. These reactions occur under visible-light irradiation in the presence of an IrIII-based photoredox catalyst, a Brønsted base catalyst, and a hydrogen-atom transfer (HAT) co-catalyst. Reactive alkoxy radicals are proposed as key intermediates, generated by direct homolytic activation of alcohol O−H bonds through a proton-coupled electron-transfer mechanism. This method exhibits a broad substrate scope and high functional-group tolerance, and it accommodates a diverse range of alkene substitution patterns. Results demonstrating the extension of this catalytic system to carboetherification reactions are also presented. 相似文献
10.
Radical-Cation Cascade to Aryltetralin Cyclic Ether Lignans Under Visible-Light Photoredox Catalysis
Dr. Jia-Chen Xiang Dr. Qian Wang Prof. Dr. Jieping Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):21381-21388
The development of concise, sustainable, and cost-effective synthesis of aryltetralin lignans, bearing either a fused lactone or cyclic ether, is of significant medicinal importance. Reported is that in the presence of Fukuzumi's acridinium salt under blue LED irradiation, functionalized dicinnamyl ether derivatives are converted into aryltetralin cyclic ether lignans with concurrent generation of three stereocenters in good to high yields with up to 20:1 diastereoselectivity. Oxidation of an alkene to the radical cation is key to the success of this formal Diels–Alder reaction of electronically mismatched diene and dienophile. Applying this methodology, six natural products, aglacin B, aglacin C, sulabiroin A, sulabiroin B, gaultherin C, and isoshonanin, are synthesized in only two to three steps from readily available biomass-derived monolignols. A revised structure is proposed for gaultherin C. 相似文献