全文获取类型
收费全文 | 429篇 |
免费 | 27篇 |
专业分类
化学 | 380篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 17篇 |
物理学 | 56篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 4篇 |
2020年 | 8篇 |
2019年 | 16篇 |
2018年 | 7篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 20篇 |
2012年 | 48篇 |
2011年 | 54篇 |
2010年 | 24篇 |
2009年 | 13篇 |
2008年 | 40篇 |
2007年 | 28篇 |
2006年 | 32篇 |
2005年 | 30篇 |
2004年 | 27篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1995年 | 1篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1930年 | 2篇 |
排序方式: 共有456条查询结果,搜索用时 15 毫秒
91.
Mohammad A. Halim Marion Girod Luke MacAleese Jérôme Lemoine Rodolphe Antoine Philippe Dugourd 《Journal of the American Society for Mass Spectrometry》2016,27(9):1435-1442
Herein we report the successful implementation of the consecutive and simultaneous photodissociation with high (213 nm) and low (10.6 μm) energy photons (HiLoPD, high-low photodissociation) on ubiquitin in a quadrupole-Orbitrap mass spectrometer. Absorption of high-energy UV photon is dispersed over the whole protein and stimulates extensive C–Cα backbone fragmentation, whereas low-energy IR photon gradually increases the internal energy and thus preferentially dissociates the most labile amide (C–N) bonds. We noticed that simultaneous irradiation of UV and IR lasers on intact ubiquitin in a single MS/MS experiment provides a rich and well-balanced fragmentation array of a/x, b/y, and z ions. Moreover, secondary fragmentation from a/x and z ions leads to the formation of satellite side-chain ions (d, v, and w) and can help to distinguish isomeric residues in a protein. Implementation of high-low photodissociation in a high-resolution mass spectrometer may offer considerable benefits to promote a comprehensive portrait of protein characterization. 相似文献
92.
Pollet BG Lorimer JP Hihn JY Phull SS Mason TJ Walton DJ 《Ultrasonics sonochemistry》2002,9(5):267-274
Ultrasound was found to increase the oxidation peak current and hence the decomposition rate of thiosulphate 50-fold compared to silent conditions. The effects of the ultrasonic frequency (20 and 38 kHz) and power upon the electrochemical oxidation of thiosulphate in aqueous KCl (1 mol dm-3) at stationary stainless steel and platinum electrodes were studied chronoamperometrically and potentiostatically (at various scan rates). No sigmoidal-shaped voltammograms were observed for the redox couple S4O6(2-)/S2O3(2-) in the presence of ultrasound. However, application of ultrasound to this redox couple provided an increase in the oxidation peak current at the frequencies employed, the magnitude of which varied with concentration, scan rate and ultrasonic power. Under sonication at 20 and 38 kHz, the oxidation peak potential shifted anodically with increasing ultrasonic power. This anodic shift in potential may be due to the formation of hydroxyl radicals, changes in electrode surface composition and complex adsorption phenomena. The large increase in oxidation peak currents and the rates of decomposition of thiosulphate, in the presence of ultrasound, are explained in terms of enhanced mass transfer at the electrode due to cavitation and acoustic streaming together with microstreaming coupled with adsorption phenomena. It is also shown that changes in macroscopic temperature throughout the experiment are insufficient to cause the observed enhanced diffusion. 相似文献
93.
94.
All-silica nanofluidic devices for DNA-analysis fabricated by imprint of sol-gel silica with silicon stamp 总被引:1,自引:0,他引:1
Mikkelsen MB Letailleur AA Søndergård E Barthel E Teisseire J Marie R Kristensen A 《Lab on a chip》2012,12(2):262-267
We present a simple and cheap method for fabrication of silica nanofluidic devices for single-molecule studies. By imprinting sol-gel materials with a multi-level stamp comprising micro- and nanofeatures, channels of different depth are produced in a single process step. Calcination of the imprinted hybrid sol-gel material produces purely inorganic silica, which has very low autofluorescence and can be fusion bonded to a glass lid. Compared to top-down processing of fused silica or silicon substrates, imprint of sol-gel silica enables fabrication of high-quality nanofluidic devices without expensive high-vacuum lithography and etching techniques. The applicability of the fabricated device for single-molecule studies is demonstrated by measuring the extension of DNA molecules of different lengths confined in the nanochannels. 相似文献
95.
96.
Lips F Hołyńska M Clérac R Linne U Schellenberg I Pöttgen R Weigend F Dehnen S 《Journal of the American Chemical Society》2012,134(2):1181-1191
Two K([2.2.2]crypt) salts of lanthanide-doped semimetal clusters were prepared, both of which contain at the same time two types of ternary intermetalloid anions, [Ln@Sn(7)Bi(7)](4-) and [Ln@Sn(4)Bi(9)](4-), in 0.70:0.30 (Ln = La) or 0.39:0.61 (Ln = Ce) ratios. The cluster shells represent nondeltahedral, fullerane-type arrangements of 14 or 13 main group metal atoms that embed the Ln(3+) cations. The assignment of formal +III oxidation states for the Ln sites was confirmed by means of magnetic measurements that reveal a diamagnetic La(III) compound and a paramagnetic Ce(III) analogue. Whereas the cluster anions with a 14-atomic main-group metal cage represent the second examples in addition to a related Eu(II) cluster published just recently, the 13-atomic cages exhibit a yet unprecedented enneahedral topology. In contrast to the larger cages, which accord to the Zintl-Klemm-Busmann electron number-structure correlation, the smaller clusters require a more profound interpretation of the bonding situation. Quantum chemical investigations served to shed light on these unusual complexes and showed significant narrowing of the HOMO-LUMO gap upon incorporation of Ce(3+) within the semimetal cages. 相似文献
97.
I Bhowmick EA Hillard P Dechambenoit C Coulon TD Harris R Clérac 《Chemical communications (Cambridge, England)》2012,48(78):9717-9719
A new cyanido-bridged Re(IV)-Mn(III) heterometallic 1D system, [Mn(III)(5-Me-saltmen)](2)[Re(IV)Cl(4)(CN)(2)]·3CH(3)CN (), was designed and structurally characterized. Interchain interactions stabilize a canted antiferromagnetic ordered state below 6.2 K that does not prevent slow relaxation of the magnetization reminiscent of the single-chain magnet properties of the individual chains. 相似文献
98.
Larini P Kefalidis CE Jazzar R Renaudat A Clot E Baudoin O 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(7):1932-1944
The palladium‐catalyzed β‐arylation of ester enolates with aryl bromides was studied both experimentally and computationally. First, the effect of the ligand on the selectivity of the α/β‐arylation reactions of ortho‐ and meta‐fluorobromobenzene was described. Selective β‐arylation was observed for the reaction of o‐fluorobromobenzene with a range of biarylphosphine ligands, whereas α‐arylation was predominantly observed with m‐fluorobromobenzene for all ligands except DavePhos, which gave an approximate 1:1 mixture of α‐/β‐arylated products. Next, the effect of the substitution pattern of the aryl bromide reactant was studied with DavePhos as the ligand. We showed that electronic factors played a major role in the α/β‐arylation selectivity, with electron‐withdrawing substituents favoring β‐arylation. Kinetic and deuterium‐labeling experiments suggested that the rate‐limiting step of β‐arylation with DavePhos as the ligand was the palladium–enolate‐to‐homoenolate isomerization, which occurs by a β? H‐elimination, olefin‐rotation, and olefin‐insertion sequence. A dimeric oxidative‐addition complex, which was shown to be catalytically competent, was isolated and structurally characterized. A common mechanism for α‐ and β‐arylation was described by DFT calculations. With DavePhos as the ligand, the pathway leading to β‐arylation was kinetically favored over the pathway leading to α‐arylation, with the palladium–enolate‐to‐homoenolate isomerization being the rate‐limiting step of the β‐arylation pathway and the transition state for olefin insertion its highest point. The nature of the rate‐limiting step changed with PCy3 and PtBu3 ligands, and with the latter, α‐arylation became kinetically favored. The trend in selectivity observed experimentally with differently substituted aryl bromides agreed well with that observed from the calculations. The presence of electron‐withdrawing groups on these bromides mainly affected the α‐arylation pathway by disfavoring C? C reductive elimination. The higher activity of the ligands of the biaryldialkylphosphine ligands compared to their corresponding trialkylphosphines could be attributed to stabilizing interactions between the biaryl backbone of the ligands and the metal center, thereby preventing deactivation of the β‐arylation pathway. 相似文献
99.
Prof. Dr. Hitoshi Miyasaka Tomokura Madanbashi Ayumi Saitoh Dr. Natsuko Motokawa Ryuta Ishikawa Prof. Dr. Masahiro Yamashita Dr. Stefan Bahr Prof. Dr. Wolfgang Wernsdorfer Dr. Rodolphe Clérac 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):3942-3954
A series of isostructural cyano‐bridged MnIII(h.s.)–MIII(l.s.) alternating chains, [MnIII(5‐TMAMsalen)MIII(CN)6] ? 4H2O (5‐TMAMsalen2?=N,N′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), MnIII(h.s.)=high‐spin MnIII, MIII(l.s.)=low‐spin CoIII, Mn? Co ; FeIII, Mn? Fe ; MnIII, Mn? Mn ; CrIII, Mn? Cr ) was synthesized by assembling [MnIII(5‐TMAMsalen)]3+ and [MIII(CN)6]3?. The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [‐MnIII‐NC‐MIII‐CN‐] repeating motif, for which the ‐NC‐MIII‐CN‐ motif is provided by the [MIII(CN)6]3? moiety adopting a trans bridging mode between [MnIII(5‐TMAMsalen)]3+ cations. The MnIII and MIII ions occupy special crystallographic positions: a C2 axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the MnIII(h.s.) ion is perpendicular to the N2O2 plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐Naxis‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M???M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn? Fe and Mn? Mn display intra‐chain ferromagnetic interactions, whereas Mn? Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas Mn? Co is merely paramagnetic with SMn=2 and D/kB=?5.3 K (D being a zero‐field splitting parameter). At low temperatures, the Mn? M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits. 相似文献
100.
Feng X Zhou W Li Y Ke H Tang J Clérac R Wang Y Su Z Wang E 《Inorganic chemistry》2012,51(5):2722-2724
The reactions of [CuTbL(Schiff)(H(2)O)(3)Cl(2)]Cl complexes with A- or B-type Anderson polyoxoanions lead to new polyoxometalate-supported 3d-4f heterometallic systems with single-molecule-magnet behavior. 相似文献