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861.
Mason D. Hart John J. Meyers Jr. Zachary A. Wood Toshinori Nakakita Jason C. Applegate Nathan R. Erickson Nikolay N. Gerasimchuk Mikhail V. Barybin 《Molecules (Basel, Switzerland)》2021,26(4)
Isocyanoazulenes (CNAz) constitute a relatively new class of isocyanoarenes that offers rich structural and electronic diversification of the organic isocyanide ligand platform. This article considers a series of 2-isocyano-1,3-X2-azulene ligands (X = H, Me, CO2Et, Br, and CN) and the corresponding zero-valent complexes thereof, [(OC)5Cr(2-isocyano-1,3-X2-azulene)]. Air- and thermally stable, X-ray structurally characterized 2-isocyano-1,3-dimethylazulene may be viewed as a non-benzenoid aromatic congener of 2,6-dimethyphenyl isocyanide (2,6-xylyl isocyanide), a longtime “workhorse” aryl isocyanide ligand in coordination chemistry. Single crystal X-ray crystallographic {Cr–CNAz bond distances}, cyclic voltametric {E1/2(Cr0/1+)}, 13C NMR {δ(13CN), δ(13CO)}, UV-vis {dπ(Cr) → pπ*(CNAz) Metal-to-Ligand Charge Transfer}, and FTIR {νN≡C, νC≡O, kC≡O} analyses of the [(OC)5Cr(2-isocyano-1,3-X2-azulene)] complexes provided a multifaceted, quantitative assessment of the π-acceptor/σ-donor characteristics of the above five 2-isocyanoazulenes. In particular, the following inverse linear relationships were documented: δ(13COtrans) vs. δ(13CN), δ(13COcis) vs. δ(13CN), and δ(13COtrans) vs. kC≡O,trans force constant. Remarkably, the net electron withdrawing capability of the 2-isocyano-1,3-dicyanoazulene ligand rivals those of perfluorinated isocyanides CNC6F5 and CNC2F3. 相似文献
862.
Angular fused tricycles were synthesized through intramolecular tandem fragmentation-cyclization reactions by photochemically induced electron transfer (PET) of tricyclic α-cyclopropyl ketones with an unsaturated side chain at the position γ to the carbonyl group. The reactions resulted in regioselective cleavage of a β-cyclopropyl bond with formation of angular fused tricyclic ring systems via ketyl radical/radical anions as reactive intermediates. In general, triethylamine (TEA) was used as a strong reducing reagent in acetonitrile. The preferred regioselectivity of the cyclization step (exo vs endo) depending on the substitution pattern at the quaternary carbon center (Cβ′) of the tricyclic α-cyclopropyl ketones was investigated. In addition, we also checked a two-step pathway for the synthesis of angular dioxa-triquinanes including photolysis of an allyloxy-substituted cyclopenta[c]furanone derivative and subsequent β-cleavage of the resulted dioxa-[4.5.5.5]fenestrane under reductive PET conditions. 相似文献
863.
Stahl M Todorov NP James T Mauser H Boehm HJ Dean PM 《Journal of computer-aided molecular design》2002,16(7):459-478
The de novo design program Skelgen has been used to design inhibitor structures for four targets of pharmaceutical interest. The designed structures are compared to modeled binding modes of known inhibitors (i) visually and (ii) by means of a novel similarity measure considering the size and spatial proximity of the maximum common substructure of two small molecules. It is shown that the Skelgen algorithm generates representatives of many inhibitor classes within a very short time and that the new similarity measure is useful for comparing and clustering designed structures. The results demonstrate the necessity of properly defining search constraints in practical applications of de novo design. 相似文献
864.
Nikolay G. Lukyanenko Alexander Yu. Lyapunov Mark M. Botoshansky Marina S. Fonari 《Tetrahedron letters》2005,46(12):2109-2112
A new crownophane containing both 2,7-dioxyfluorenone and 1,5-dioxynaphthalene moieties bridged by triethylene glycol units has been synthesized and used as a highly efficient template for the preparation of the first fluorenone-containing [2]catenane incorporating a cyclobis(paraquat-p-phenylene) tetracation as a second macrocyclic component. 相似文献
865.
The electron-stimulated luminescence (ESL) from amorphous solid water and crystalline ice films deposited on Pt(111) at 100 K is investigated as a function of the film thickness, incident electron energy (5-1000 eV), isotopic composition, and film structure. The ESL emission spectrum has a characteristic double-peaked shape that has been attributed to a transition between a superexcited state (C) and the dissociative, first excited state (A) in water: C --> A. Comparing the electron-stimulated luminescence and O2 electron-stimulated desorption (ESD) yields versus incident electron energy, we find the ESL threshold is approximately 3 eV higher than the O2 ESD threshold, which is close to the center of the emission spectrum near 400 nm and supports the C --> A assignment for the ESL. For thin films, radiative and nonradiative interactions with the substrate tend to quench the luminescence. The luminescence yield increases with coverage since the interactions with the substrate become less important. The ESL yield from D2O is approximately 4-5 times higher than that from H2O. With use of layered films of H2O and D2O, this sizable isotopic effect on the ESL is exploited to spatially profile the luminescence emission within the ASW films. These experiments show that most of the luminescence is emitted from within the penetration depth of the incident electron. However, the results depend on the order of the isotopes in the film and can be modeled by assuming some migration of the electronically excited states within the film. The ESL is very sensitive to defects and structural changes in solid water, and the emission yield is significantly higher from amorphous films than from crystalline ice. 相似文献
866.
Paata Ivanishvili Nikolay N. Osipov Dmitriy M. Stolyarov Vasily I. Vasyunin Pavel B. Zatitskiy 《Comptes Rendus Mathematique》2012,350(11-12):561-564
In this Note we describe our results on construction of the Bellman function solving an extremal problem for a large class of integral functionals on BMO. 相似文献
867.
Alexey G. Gerbst Alexey A. Grachev Dmitry V. Yashunsky Yury E. Tsvetkov Alexander S. Shashkov Nikolay E. Nifantiev 《Journal of carbohydrate chemistry》2013,32(3):205-221
The conformational behavior of linear oligo-β-(1→3)-D-glucosides was studied using NMR experiments and molecular modeling. The explicit solvent model in calculations yielded the best coincidence between experimental and theoretical values of NOE and spin-spin coupling constants to evidence the strong influence of solvation upon the conformations of the oligoglucosides. Long-range coupling constants calculated for di- and trimeric clusters of the studied glucosides fit the experimental data much better than the single-molecule approach. It was shown that conformational properties of disaccharide fragments in studied oligoglucosides depended on neither their position in the chain nor the length of the chain. 相似文献
868.
869.
Robert Johne Natalia S. Maslova Nikolay A. Gippius 《Solid State Communications》2009,149(11-12):496-500
Fluctuation-induced transitions from the lower energy state of a bistable nonlinear driven microcavity oscillator are analyzed beyond the Fluctuation–Dissipation theorem. The sources of noise are: both fluctuations of the external pumping and inevitable interaction with the exciton reservoir in the cavity. We show that finite polariton lifetime strongly modifies the phase portrait and influences the temporal parameters of the transition within the bistable regime. To investigate the transient dynamics of the driven polariton system, three different approaches are realized: numerical experiment (1), i.e. direct solution of the quasiclassical dynamic equation for polariton amplitude driven by an external pump, (2) solution of two dimensional Fokker–Planck-equation and (3) effective one dimensional Fokker–Planck-equation, obtained within a low-damping approximation. We show that the escape times obtained within the numerical experiment and the 2D-Fokker–Planck-equation coincide. In contrast, the one dimensional Fokker–Planck-approximation fails for large damping parameters due to strong deviation of the phase trajectories from those obtained within the low-damping approximation. The range of the ratio between damping and detuning for which the 1d approximation is valid, is shown to be smaller than 0.04. Finally, we determine the impact of the fluctuations on experiments illustrated by the narrowing of the hysteresis cycle. 相似文献
870.
Irina L. Odinets Oleg. I. Artyushin Nikolay E. Shevchenko Gerd-Volker Röschenthaler 《Journal of fluorine chemistry》2009,130(7):662-666
Addition of diethylphosphite to cyclic α-perfluoalkyl substituted imines in the presence of boron trifluoride etherate as a catalyst presents an efficient route for racemic saturated cyclic α-perfluoroalkyl-α-aminophosphonates. Hydrolysis of latter compounds gives the corresponding α-aminoalkanephosphonic acids existing as the corresponding zwitterions according IR and X-ray data. 相似文献