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491.
492.
Scarborough CC Sproules S Doonan CJ Hagen KS Weyhermüller T Wieghardt K 《Inorganic chemistry》2012,51(12):6969-6982
The oxidation state of the chromium center in the following compounds has been probed using a combination of chromium K-edge X-ray absorption spectroscopy and density functional theory: [Cr(phen)(3)][PF(6)](2) (1), [Cr(phen)(3)][PF(6)](3) (2), [CrCl(2)((t)bpy)(2)] (3), [CrCl(2)(bpy)(2)]Cl(0.38)[PF(6)](0.62) (4), [Cr(TPP)(py)(2)] (5), [Cr((t)BuNC)(6)][PF(6)](2) (6), [CrCl(2)(dmpe)(2)] (7), and [Cr(Cp)(2)] (8), where phen is 1,10-phenanthroline, (t)bpy is 4,4'-di-tert-butyl-2,2'-bipyridine, and TPP(2-) is doubly deprotonated 5,10,15,20-tetraphenylporphyrin. The X-ray crystal structures of complexes 1, [Cr(phen)(3)][OTf](2) (1'), and 3 are reported. The X-ray absorption and computational data reveal that complexes 1-5 all contain a central Cr(III) ion (S(Cr) = (3)/(2)), whereas complexes 6-8 contain a central low-spin (S = 1) Cr(II) ion. Therefore, the electronic structures of 1-8 are best described as [Cr(III)(phen(?))(phen(0))(2)][PF(6)](2), [Cr(III)(phen(0))(3)][PF(6)](3), [Cr(III)Cl(2)((t)bpy(?))((t)bpy(0))], [Cr(III)Cl(2)(bpy(0))(2)]Cl(0.38)[PF(6)](0.62), [Cr(III)(TPP(3?-))(py)(2)], [Cr(II)((t)BuNC)(6)][PF(6)](2), [Cr(II)Cl(2)(dmpe)(2)], and [Cr(II)(Cp)(2)], respectively, where (L(0)) and (L(?))(-) (L = phen, (t)bpy, or bpy) are the diamagnetic neutral and one-electron-reduced radical monoanionic forms of L, and TPP(3?-) is the one-electron-reduced doublet form of diamagnetic TPP(2-). Following our previous results that have shown [Cr((t)bpy)(3)](2+) and [Cr(tpy)(2)](2+) (tpy = 2,2':6',2"-terpyridine) to contain a central Cr(III) ion, the current results further refine the scope of compounds that may be described as low-spin Cr(II) and reveal that this is a very rare oxidation state accessible only with ligands in the strong-field extreme of the spectrochemical series. 相似文献
493.
Dr. Hagen W. Klemm Dr. Mauricio J. Prieto Dr. Feng Xiong Ghada B. Hassine Dr. Markus Heyde Dr. Dietrich Menzel Dr. Marek Sierka Dr. Thomas Schmidt Dr. Hans-Joachim Freund 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(26):10674-10680
The crystalline-to-vitreous phase transformation of a SiO2 bilayer supported on Ru(0001) was studied by time-dependent LEED, local XPS, and DFT calculations. The silica bilayer system has parallels to 3D silica glass and can be used to understand the mechanism of the disorder transition. DFT simulations show that the formation of a Stone–Wales-type of defect follows a complex mechanism, where the two layers show decoupled behavior in terms of chemical bond rearrangements. The calculated activation energy of the rate-determining step for the formation of a Stone—Wales-type of defect (4.3 eV) agrees with the experimental value. Charge transfer between SiO2 bilayer and Ru(0001) support lowers the activation energy for breaking the Si−O bond compared to the unsupported film. Pre-exponential factors obtained in UHV and in O2 atmospheres differ significantly, suggesting that the interfacial ORu underneath the SiO2 bilayer plays a role on how the disordering propagates within the film. 相似文献
494.
Tanya Lasitza-Male Kim Bartels Jakub Jungwirth Felix Wiggers Dr. Gabriel Rosenblum Dr. Hagen Hofmann Dr. Christian Löw 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(43):19283-19290
Membrane proteins require lipid bilayers for function. While lipid compositions reach enormous complexities, high-resolution structures are usually obtained in artificial detergents. To understand whether and how lipids guide membrane protein function, we use single-molecule FRET to probe the dynamics of DtpA, a member of the proton-coupled oligopeptide transporter (POT) family, in various lipid environments. We show that detergents trap DtpA in a dynamic ensemble with cytoplasmic opening. Only reconstitutions in more native environments restore cooperativity, allowing an opening to the extracellular side and a sampling of all relevant states. Bilayer compositions tune the abundance of these states. A novel state with an extreme cytoplasmic opening is accessible in bilayers with anionic head groups. Hence, chemical diversity of membranes translates into structural diversity, with the current POT structures only sampling a portion of the full structural space. 相似文献
495.
Janis V. Musso Mathis J. Benedikter Dr. Dongren Wang Dr. Wolfgang Frey Hagen J. Altmann Prof. Dr. Michael R. Buchmeiser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(40):8709-8713
The first reversible N-heterocyclic carbene (NHC) induced α-H abstraction in tungsten(VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH2Ph)2(OtBu)2 (Ar=2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert-butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by 1H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium-labeled complex in comparison to its non-deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α-H abstraction is the rate-determining step (RDS) of the reaction. 相似文献
496.
Bruijnincx PC Lutz M Spek AL Hagen WR Weckhuysen BM van Koten G Gebbink RJ 《Journal of the American Chemical Society》2007,129(8):2275-2286
Mononuclear iron(II)- and iron(III)-catecholato complexes with three members of a new 3,3-bis(1-alkylimidazol-2-yl)propionate ligand family have been synthesized as models of the active sites of the extradiol cleaving catechol dioxygenases. These enzymes are part of the superfamily of dioxygen-activating mononuclear non-heme iron enzymes that feature the so-called 2-His-1-carboxylate facial triad. The tridentate, tripodal, and monoanionic ligands used in this study include the biologically relevant carboxylate and imidazole donor groups. The structure of the mononuclear iron(III)-tetrachlorocatecholato complex [Fe(L3)(tcc)(H2O)] was determined by single-crystal X-ray diffraction, which shows a facial N,N,O capping mode of the ligand. For the first time, a mononuclear iron complex has been synthesized, which is facially capped by a ligand offering a tridentate Nim,Nim,Ocarb donor set, identical to the endogenous ligands of the 2-His-1-carboxylate facial triad. The iron complexes are five-coordinate in noncoordinating media, and the vacant coordination site is accessible for Lewis bases, e.g., pyridine, or small molecules such as dioxygen. The iron(II)-catecholato complexes react with dioxygen in two steps. In the first reaction the iron(II)-catecholato complexes rapidly convert to the corresponding iron(III) complexes, which then, in a second slow reaction, exhibit both oxidative cleavage and auto-oxidation of the substrate. Extradiol and intradiol cleavage are observed in noncoordinating solvents. The addition of a proton donor results in an increase in extradiol cleavage. The complexes add a new example to the small group of synthetic iron complexes capable of eliciting extradiol-type cleavage and provide more insight into the factors determining the regioselectivity of the enzymes. 相似文献
497.
498.
499.
Giuseppina Orlandini Sonia Bacca Nir Barnea Gaute Hagen Mirko Miorelli Thomas Papenbrock 《Few-Body Systems》2014,55(8-10):907-911
Here we summarize how the LIT and CC methods can be coupled, in order to allow for ab initio calculations of reactions in medium mass nuclei. Results on 16O are reviewed and preliminary calculations on 40Ca are presented. 相似文献
500.
We present microscopic coupled-cluster calculations of the spectroscopic factors for proton removal from the closed-shell oxygen isotopes (14,16,22,24,28)O with a chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order. We include coupling-to-continuum degrees of freedom by using a Hartree-Fock basis built from a Woods-Saxon single-particle basis. This basis treats bound and continuum states on an equal footing. We find a significant quenching of spectroscopic factors in the neutron-rich oxygen isotopes, pointing to enhanced many-body correlations induced by strong coupling to the scattering continuum above the neutron emission thresholds. 相似文献