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81.
S. Schneider C.-J. Prenzel G. Brehm L. Gottschalk K.-H. Zhao† H. Scheer 《Photochemistry and photobiology》1996,63(2):197-206
Abstract— Resonance-enhanced coherent anti-Stokes Raman (CARS) spectra are reported for trimers of phycoerthrocyanin (PEC) dissolved in H2 O and D2 O. The CARS spectra are significantly different when recorded with pump wavelength either at 585 nm or 630 nm. By comparison of the 630 nm spectra with those of phycocyanin one can conclude that there is a change in the relative location of the lowest excited states of the β84 and β155 chromophores. Upon additional illumination with 514.5 nm laser light, only the spectra recorded with 585 nm pump wavelength change. This is in accordance with earlier observations that the phycoviolobilin chromophore of the a-subunit exhibits photochromic behavior. The changes in the CARS spectra provide evidence that it is the methine bridge between rings C and D that undergoes the geometrical changes. Furthermore, it is suggested that there are different types of photoinduced rearrangements operative and that the isomeric distribution is different in H2 O and D2 O. 相似文献
82.
Nikolay A. Pushkarevsky Sergey N. Konchenko Manfred Scheer 《Journal of Cluster Science》2007,18(3):606-617
The reaction of K2[Fe3(μ3-Q)(CO)9] (Q = Se (K2[1a]), Te (K2[1b])) with [(dppm)PtCl2] leads to the addition of a [(dppm)Pt]2+ unit to a Fe2Q face of the initial cluster. By this way new heteronuclear clusters [Fe3Pt(μ3-Q)(CO)9(dppm)] were obtained possessing a butterfly-shaped cluster core bridged by a μ4-Q unit. It has been found that the resulting Fe-Pt clusters exist as equilibrium mixtures of two isomeric forms in solution
differing by the dppm coordination mode: as a chelate ligand coordinated to Pt or as a bridging ligand coordinated to Pt and
Fe atoms. The mixtures of isomers can be separated by chromatography and the pure isomers can be isolated as stable crystalline
phases. Solutions of both isomers attain equilibrium at normal conditions in about 1 month as found by NMR.
Dedicated to Professor Dieter Fenske in the occasion of his 65th birthday. 相似文献
83.
Structure-Based Calculations of the Optical Spectra of the LH2 Bacteriochlorophyll-Protein Complex from Rhodopseudomonas acidophila 总被引:3,自引:0,他引:3
Kenneth Sauer Richard J. Cogdell Steve M. Prince y Freer Neil W. Isaacs Hugo Scheer 《Photochemistry and photobiology》1996,64(3):564-576
Abstract— The molecular structure of the light-harvesting complex 2 (LH2) bacteriochlorophyll-protein antenna complex from the purple non-sulfur photosynthetic bacterium Rhodopseudomonas acidophila , strain 10050 provides the positions and orientations of the 27 bacteriochlorophyll (BChl) molecules in the complex. Our structure-based model calculations of the distinctive optical properties (absorption, CD, polarization) of LH2 in the near-infrared region use a point-monopole approximation to represent the BChl Qy transition moment. The results of the calculations support the assignment of the ring of 18 closely coupled BChl to B850 (BChl absorbing at 850 nm) and the larger diameter, parallel ring of 9 weakly coupled BChl to B800. All of the significantly allowed transitions in the near infrared are calculated to be perpendicular to the C9 symmetry axis, in agreement with polarization studies of this membrane-associated complex. To match the absorption maxima of the B800 and B850 components using a relative permittivity (dielectric constant) of 2.1, we assign different site energies (12 500 and 12260 cm−1 , respectively) for the Qy transitions of the respective BChl in their protein binding sites. Excitonic coupling is particularly strong among the set of B850 chromophores, with pairwise interaction energies nearly 300 cm between nearest neighbors, comparable with the experimental absorption bandwidths at room temperature. These strong interactions, for the full set of 18 B850 chromophores, result in an excitonic manifold that is 1200 cm−1 wide. Some of the upper excitonic states should result in weak absorption and perhaps stronger CD features. These predictions from the calculations await experimental verification. 相似文献
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Rosie Magnall Dr. Gábor Balázs Dr. Erli Lu Michal Kern Prof. Dr. Joris van Slageren Dr. Floriana Tuna Dr. Ashley J. Wooles Prof. Dr. Manfred Scheer Prof. Dr. Stephen T. Liddle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14246-14252
Little is known about the chemistry of the 2-arsaethynolate anion, but to date it has exclusively undergone fragmentation reactions when reduced. Herein, we report the synthesis of [U(TrenTIPS)(OCAs)] ( 2 , TrenTIPS=N(CH2CH2NSiiPr3)3), which is the first isolable actinide-2-arsaethynolate linkage. UV-photolysis of 2 results in decarbonylation, but the putative [U(TrenTIPS)(As)] product was not isolated and instead only [{U(TrenTIPS)}2(μ-η2:η2-As2H2)] ( 3 ) was formed. In contrast, reduction of 2 with [U(TrenTIPS)] gave the mixed-valence arsenido [{U(TrenTIPS)}2(μ-As)] ( 4 ) in very low yield. Complex 4 is unstable which precluded full characterisation, but these photolytic and reductive reactions testify to the tendency of 2-arsaethynolate to fragment with CO release and As transfer. However, addition of 2 to an electride mixture of potassium-graphite and 2,2,2-cryptand gives [{U(TrenTIPS)}2{μ-η2(OAs):η2(CAs)-OCAs}][K(2,2,2-cryptand)] ( 5 ). The coordination mode of the trapped 2-arsaethynolate in 5 is unique, and derives from a new highly reduced and bent form of this ligand with the most acute O-C-As angle in any complex to date (O-C-As ≈128°). The trapping rather than fragmentation of this highly reduced O-C-As unit is unprecedented, and quantum chemical calculations reveal that reduction confers donor–acceptor character to the O-C-As unit. 相似文献
88.
Dr. Martin Fleischmann Dr. Fabian Dielmann Dr. Gábor Balázs Prof. Dr. Manfred Scheer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15248-15251
The oxidation of the 28 VE cyclo‐E6 triple‐decker complexes [(CpRMo)2(μ,η6:η6‐E6)] (E=P, CpR=Cp( 2 a ), Cp*( 2 b ), CpBn( 2 c )=C5(CH2Ph)5; E=As, CpR=Cp*( 3 )) by Cu+ or Ag+ leads to cationic 27 VE complexes that retain their general triple‐decker geometry in the solid state. The obtained products have been characterized by cyclic voltammetry (CV), EPR, Evans NMR, multinuclear NMR spectroscopy, MS, and structural analysis by single‐crystal X‐ray diffraction. The cyclo‐E6 middle decks of the oxidized complexes are distorted to a quinoid ( 2 a ) or bisallylic ( 2 b , 2 c , 3 ) geometry. DFT calculations of 2 a , 2 b , and 3 persistently result in the bisallylic distortion as the minimum geometry and show that the oxidation leads to a depopulation of the σ‐system of the cyclo‐E6 ligands in 2 a – 3 . Among the starting complexes, 2 c is reported for the first time including its preparation and full characterization. 相似文献
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