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71.
72.
Peroukidis SD Vanakaras AG Photinos DJ 《The journal of physical chemistry. B》2008,112(40):12761-12767
The molecular cubic-block model [ J. Chem. Phys. 2005, 123, 164904 ] is used to study a class of poly(benzyl ether) fullerodendrimers that have recently been reported to form columnar liquid crystal phases. In agreement with experiment, the model-molecules are found to self-assemble into columns which form hexagonal or rectangular lattices. The columnar cross sections are elongated in the rectangular phase. Transitions to the isotropic phase, either directly or through the intermediate formation of smectic phases, have been found. The effects of dissolving small amounts of nonbonded fullerene molecules have been explored. The results predict that the fullerene solutes restrict the range of stability of the columnar phase and may induce transitions from the columnar to the smectic or the isotropic phase. 相似文献
73.
Controlling microscopic or macroscopic alignment of liquid crystalline dendrimers (LCDrs) in a porous media is an important feature for their possible potential applications. Here, we investigate structural and alignment behaviours of model LCDr system confined in a slit pore made of two parallel impenetrable walls. Isobaric–isothermal (NPT) Monte Carlo computational simulation method is used. A coarse-grained force field for inter-/intra-dendritic and LCDr-substrate interactions has been established. The inner surfaces of confining walls are made to induce homeotropic anchoring condition. According to simulation results, a variety of stable-ordered LCDr system states have been observed and analysed depending on the temperature and pressure. 相似文献
74.
O'Malley DP Li K Maue M Zografos AL Baran PS 《Journal of the American Chemical Society》2007,129(15):4762-4775
The dimeric pyrrole imidazole natural products are a growing class of alkaloids with exotic connectivity, unique topologies, high nitrogen content, and exciting bioactivities. This full account traces the evolution of a strategy that culminated in the first total syntheses of several members of this family, including sceptrin, ageliferin, nagelamide E, nakamuric acid (and its methyl ester), and oxysceptrin. Details on the fascinating conversion of sceptrin to ageliferin, which has been used to produce gram quantities of this sensitive natural product, are provided. In addition, the first enantioselective total synthesis of sceptrin and ageliferin are reported by programming the fragmentation of an oxaquadricyclane. A hallmark of our approach to this family of alkaloids is the minimal use of protecting groups despite the presence of 10 nitrogen atoms in the target compounds. Thus, the fundamental chemistry of the 2-aminoimidazole heterocycle was explored without masking its innate reactivity. Insights gained during these explorations led to total syntheses of oxysceptrin and nakamuric acid and a successful construction of the carbon skeleton of axinellamine. 相似文献
75.
Kiriazis A Rüffer T Jäntti S Lang H Yli-Kauhaluoma J 《Journal of combinatorial chemistry》2007,9(2):263-266
As part of our continuing studies of polymer-supported pericyclic reactions for preparing biologically interesting heterocyclic compounds, we have introduced a traceless solid-phase synthesis of hexahydrocinnolines. We developed a method in which mild reaction conditions can be used for the hetero-Diels-Alder reactions on a polymeric support. The dienoic 3-vinyl-2-cyclohexenol attached to a Wang resin through an ether linkage undergoes [4 + 2] cycloaddition reaction with several azadienophiles. The highly stereoselective Diels-Alder reaction showed preferential formation of a single cycloadduct resulting from an anti attack of the dienophile on the polymer-bound diene. Trifluoroacetic acid-mediated cleavage of the polymer-bound cycloadducts yields fused nonaromatic hexahydrocinnolines in moderate yields in three steps. 相似文献
76.
A structure-based drug discovery method is described that incorporates target flexibility through the use of an ensemble of protein conformations. The approach was applied to fatty acid amide hydrolase (FAAH), a key deactivating enzyme in the endocannabinoid system. The resultant dynamic pharmacophore models are rapidly able to identify known FAAH inhibitors over drug-like decoys. Different sources of FAAH conformational ensembles were explored, with both snapshots from molecular dynamics simulations and a group of X-ray structures performing well. Results were compared to those from docking and pharmacophore models generated from a single X-ray structure. Increasing conformational sampling consistently improved the pharmacophore models, emphasizing the importance of incorporating target flexibility in structure-based drug design. 相似文献
77.
George Mavrotas José Rui Figueira Alexandros Antoniadis 《Journal of Global Optimization》2011,49(4):589-606
We propose a methodology for obtaining the exact Pareto set of Bi-Objective Multi-Dimensional Knapsack Problems, exploiting
the concept of core expansion. The core concept is effectively used in single objective multi-dimensional knapsack problems
and it is based on the “divide and conquer” principle. Namely, instead of solving one problem with n variables we solve several sub-problems with a fraction of n variables (core variables). In the multi-objective case, the
general idea is that we start from an approximation of the Pareto set (produced with the Multi-Criteria Branch and Bound algorithm,
using also the core concept) and we enrich this approximation iteratively. Every time an approximation is generated, we solve
a series of appropriate single objective Integer Programming (IP) problems exploring the criterion space for possibly undiscovered,
new Pareto Optimal Solutions (POS). If one or more new POS are found, we appropriately expand the already found cores and
solve the new core problems. This process is repeated until no new POS are found from the IP problems. The paper includes
an educational example and some experiments. 相似文献
78.
Alexandros PapafilippouMichael A. Terzidis Julia Stephanidou-Stephanatou Constantinos A. Tsoleridis 《Tetrahedron letters》2011,52(12):1306-1309
The zwitterionic intermediates generated from dialkyl azodicarboxylates and triphenylphosphine displayed excellent reactivity toward 3-formylchromones to afford chromeno[2,3-c]pyrazolines and chromeno[2,3-e]tetrazepines. 相似文献
79.
The molecular and electronic structures, stabilities, bonding features, and magnetoresponsive properties of three‐membered [c‐Ln3]+/0/? (Ln = La, Ce, Pr, Nd, Gd, Lu) and heterocyclic six‐membered [c‐Ln3E3]q (Ln = La, Ce, Pr, Nd, Gd, Lu; E = C, N; q = 0 or 1) rings have been investigated by means of electronic structure calculation methods at the DFT level. The [c‐Ln3]+/0/? clusters are predicted to be bound with respect to dissociation to their constituent atoms, the estimated binding energies ranging from 45.8 to 2056.4 kJ/mol. The [c‐Ln3] rings capture easily a planar three‐coordinated nitrogen atom at the center or above the center of the ring yielding the lanthanide nitride clusters [c‐Ln3(μ3‐N)] adopting a planar geometry, except [c‐La3(μ3‐N)] which exhibits pyramidal geometry. The [c‐Ln3(μ3‐N)] clusters are predicted to be bound, with respect to dissociation to N (4S) atom and [c‐Ln3] clusters in their ground states, the binding energies ranging from 53.9 to 257.9 kcal/mol. The six‐membered [c‐Ln3E3]q rings are predicted to be bound with respect to dissociation to LnEq monomers in their ground states with dissociation energies in the range of 173.8 to 318.0 kcal/mol. Calculation of the NICSzz‐scan curves of the clusters predicted a “hermaphrodic” magnetic response of the [c‐Ln3]+/0/? and heterocyclic six‐membered [c‐Ln3E3]q rings, manifested by the coexistence of successive diatropic (aromatic) and paratropic (antiaromatic) zones. The [c‐La3]+/0/? and [c‐Lu3]? are predicted to be weakly antiaromatic, the [c‐Lu3]0/+, [c‐Lu3C3]+, and [c‐Lu3N3] double (σ+π) aromatic, and the [c‐Gd3C3] and [c‐Gd3N3]+ rings (σ+δ)‐aromatic systems. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011 相似文献
80.
Coarse-grained models of poly(ethylene oxide) oligomer-grafted nanoparticles are established by matching their structural distribution functions to atomistic simulation data. Coarse-grained force fields for bulk oligomer chains show excellent transferability with respect to chain lengths and temperature, but structure and dynamics of grafted nanoparticle systems exhibit a strong dependence on the core-core interactions. This leads to poor transferability of the core potential to conditions different from the state point at which the potential was optimized. Remarkably, coarse graining of grafted nanoparticles can either accelerate or slowdown the core motions, depending on the length of the grafted chains. This stands in sharp contrast to linear polymer systems, for which coarse graining always accelerates the dynamics. Diffusivity data suggest that the grafting topology is one cause of slower motions of the cores for short-chain oligomer-grafted nanoparticles; an estimation based on transition-state theory shows the coarse-grained core-core potential also has a slowing-down effect on the nanoparticle organic hybrid materials motions; both effects diminish as grafted chains become longer. 相似文献