全文获取类型
收费全文 | 321篇 |
免费 | 14篇 |
专业分类
化学 | 229篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 45篇 |
物理学 | 54篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 20篇 |
2012年 | 22篇 |
2011年 | 20篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 15篇 |
2007年 | 24篇 |
2006年 | 23篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 16篇 |
2002年 | 15篇 |
2001年 | 3篇 |
1999年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1989年 | 4篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1963年 | 1篇 |
1962年 | 2篇 |
1960年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有335条查询结果,搜索用时 15 毫秒
1.
Marina Huber-Gedert Dr. Michał Nowakowski Dr. Ahmet Kertmen Dr. Lukas Burkhardt Dr. Natalia Lindner Dr. Roland Schoch Dr. Regine Herbst-Irmer Dr. Adam Neuba Lennart Schmitz Tae-Kyu Choi Dr. Jacek Kubicki Prof. Dr. Wojciech Gawelda Prof. Dr. Matthias Bauer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(38):9905-9918
A new base metal iron-cobalt dyad has been obtained by connection between a heteroleptic tetra-NHC iron(II) photosensitizer combining a 2,6-bis[3-(2,6-diisopropylphenyl)imidazol-2-ylidene]pyridine with 2,6-bis(3-methyl-imidazol-2-ylidene)-4,4′-bipyridine ligand, and a cobaloxime catalyst. This novel iron(II)-cobalt(III) assembly has been extensively characterized by ground- and excited-state methods like X-ray crystallography, X-ray absorption spectroscopy, (spectro-)electrochemistry, and steady-state and time-resolved optical absorption spectroscopy, with a particular focus on the stability of the molecular assembly in solution and determination of the excited-state landscape. NMR and UV/Vis spectroscopy reveal dissociation of the dyad in acetonitrile at concentrations below 1 mM and high photostability. Transient absorption spectroscopy after excitation into the metal-to-ligand charge transfer absorption band suggests a relaxation cascade originating from hot singlet and triplet MLCT states, leading to the population of the 3MLCT state that exhibits the longest lifetime. Finally, decay into the ground state involves a 3MC state. Attachment of cobaloxime to the iron photosensitizer increases the 3MLCT lifetime at the iron centre. Together with the directing effect of the linker, this potentially makes the dyad more active in photocatalytic proton reduction experiments than the analogous two-component system, consisting of the iron photosensitizer and Co(dmgH)2(py)Cl. This work thus sheds new light on the functionality of base metal dyads, which are important for more efficient and sustainable future proton reduction systems. 相似文献
2.
3.
Saulius Armalis Inga Krikŝĉiuniene Erika Kubiliene Nii-Kotey Djane Kuria Ndungu Lennart Mathiasson 《International journal of environmental analytical chemistry》2013,93(1-4):233-242
Abstract The performance of a flow-through mercury coated reticulated vitreous carbon (RVC) electrode in the potentiometric stripping analysis (PSA) of trace metals has been examined. A wall-jet glassy carbon cell was used for the comparative experiments. Experimental parameters influencing the stripping signals have been optimised in order to use the stripping analysis after the preconcentration and matrix isolation by supported liquid membrane (SLM) technique. The SLM with di-2-ethylhexyl-phosphoric acid (DEHPA) as the extractant in the membrane liquid for proton driven transport of trace metals across the membrane has been chosen. Results presented for lead determination in river water demonstrate the analytical advantages of coupled technique SLM-PSA. 相似文献
4.
Dr. Kai-Stephan Feichtner Dr. Lennart T. Scharf Dr. Thorsten Scherpf Dr. Bert Mallick Nils Boysen Prof. Dr. Viktoria H. Gessner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(69):17351-17360
The use of iminophosphoryl-tethered ruthenium carbene complexes to activate secondary phosphine P−H bonds is reported. Complexes of type [(p-cymene)-RuC(SO2Ph)(PPh2NR)] (with R = SiMe3 or 4-C6H4−NO2) were found to exhibit different reactivities depending on the electronics of the applied phosphine and the substituent at the iminophosphoryl moiety. Hence, the electron-rich silyl-substituted complex undergoes cyclometallation or shift of the imine moiety after cooperative activation of the P−H bond across the M=C linkage, depending on the electronics of the applied phosphine. Deuteration experiments and computational studies proved that cyclometallation is initiated by the activation process at the M=C bond and triggered by the high electron density at the metal in the phosphido intermediates. Consistently, replacement of the trimethylsilyl (TMS) group by the electron-withdrawing 4-nitrophenyl substituent allowed the selective cooperative P−H activation to form stable activation products. 相似文献
5.
Franz Dalitz Lennart Kreckel Michael Maiwald Gisela Guthausen 《Applied magnetic resonance》2014,45(5):411-425
Medium-resolution nuclear magnetic resonance spectroscopy is a promising tool for the monitoring of liquid reactions. For process analytical applications, the requirements of robustness and insensitivity of the spectrometer in relation to high temperatures and pressures are challenging. Within this study, a flow probe using a glass dewar is presented. Temperatures of flowing samples up to 130 °C and pressures up to 40 bar were successfully applied, and the corresponding temperature loss of the flowing sample at 2 ml min?1 was <2.4 °C at 130 °C. Furthermore, if the process requires a measurement in a non-equilibrium state of magnetization, a comprehensive data treatment is given. For this purpose, the influences of the flow and T 1 of the substances under investigation are studied in detail on the example of a homogeneously catalyzed esterification. In addition, data analysis schemes were designed such that the experiments directly revealed mole fractions from the spectra. Limited spectral resolutions and low signal-to-noise ratio still did not obstruct quantitative interpretation of the experiments. 相似文献
6.
Claudia Strobel Adriano A. Torrano Rudolf Herrmann Marcelina Malissek Christoph Bräuchle Armin Reller Lennart Treuel Ingrid Hilger 《Journal of nanoparticle research》2014,16(1):1-16
Until now, the potential effects of titanium dioxide (TiO2) nanoparticles on endothelial cells are not well understood, despite their already wide usage. Therefore, the present work characterizes six TiO2 nanoparticle samples in the size range of 19 × 17 to 87 × 13 nm, which are commonly present in sun protection agents with respect to their physicochemical properties (size, shape, ζ-potential, agglomeration, sedimentation, surface coating, and surface area), their interactions with serum proteins and biological impact on human microvascular endothelial cells (relative cellular dehydrogenase activity, adenosine triphosphate content, and monocyte chemoattractant protein-1 release). We observed no association of nanoparticle morphology with the agglomeration and sedimentation behavior and no variations of the ζ-potential (?14 to ?19 mV) in dependence on the surface coating. In general, the impact on endothelial cells was low and only detectable at concentrations of 100 μg/ml. Particles containing a rutile core and having rod-like shape had a stronger effect on cell metabolism than those with anatase core and elliptical shape (relative cellular dehydrogenase activity after 72 h: 60 vs. 90 %). Besides the morphology, the nanoparticle shell constitution was found to influence the metabolic activity of the cells. Upon cellular uptake, the nanoparticles were localized perinuclearly. Considering that in the in vivo situation endothelial cells would come in contact with considerably lower nanoparticle amounts than the lowest-observable adverse effects level (100 μg/ml), TiO2 nanoparticles can be considered as rather harmless to humans under the investigated conditions. 相似文献
7.
8.
9.
Sviatlana Viarbitskaya Linus Ryderfors Therese Mikaelsson Emad Mukhtar Lennart B.-?. Johansson 《Journal of fluorescence》2011,21(1):257-264
Multi-photon absorption induced luminescence (MAIL) from bare gold nanoparticles, silica-coated particles, as well as silica-coated agglomerated gold nanoparticles suspended in aqueous solution was studied by using time-resolved and steady-state luminescence spectroscopy. The nanoparticles were excited by femtosecond pulses of wavelengths ranging from 630 nm to 900 nm. The luminescence from the particles exhibits a broad spectrum in the UV and VIS region. The time-resolved measurements indicate a luminescence lifetime of a few ps, limited by the response of the experimental system. The studied dependence of the MAIL efficiency on the excitation wavelength showed that the luminescence from silica-coated agglomerates was enhanced over the whole range of excitation wavelengths, when compared to the luminescence from individual gold nanoparticles. The agglomerates show an almost excitation wavelength independent efficiency of the MAIL, while for individual nanoparticles a rapid decrease of the MAIL efficiency was observed with increasing excitation wavelength. The observed enhancement of the MAIL from the agglomerated nanostructures can be attributed to the presence of localized surface plasmon resonances in the spectral region corresponding to the excitation wavelengths. The high MAIL efficiency from the agglomerated nanoparticle structures in the near-infrared could be an advantage in the expanding field of luminescence-based-imaging, as well as in biosensor technology. 相似文献
10.
Christopher M. Burba Roger Frech Agneta Seidel Lennart Häggström Anton Nytén John O. Thomas 《Journal of Solid State Electrochemistry》2009,13(8):1267-1272
The first discharge of the Li+ ion anode material LiSn2(PO4)3 was investigated with Mössbauer spectroscopy and electrochemical techniques. Mössbauer spectroscopy provided insight into the structure of the tin atoms of the fully discharged anode materials. Spectra consist of overlapping peaks, which are assigned to noncrystalline β-Sn and Li–Sn alloy domains. An analysis of the relative intensities of the Mössbauer spectra shows the relative abundance of β-Sn increases at the expense of the Li–Sn alloy as the discharge rate increases. Cell polarization occurs at higher discharge rates, leading to inefficient electrode utilization and poor cycling performance. Sluggish Li+ ion diffusion through the amorphous Li3PO4 network that is formed early in the discharge process might be responsible for the poor electrochemical performance and the accumulation of unalloyed tin. 相似文献