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11.
Because of its relevance for negative hydrogen ion sources, the change in secondary electron emission with the adsorption of Cs on Cu was studied. Properly prepared disks of oxygen free high conductivity (OFHC) copper yielded a maximum secondary electron emission δmax=1.54±3%. The deposition of ≈0.5 monolayer of Cs resulted in δmax=3.40±3%. 相似文献
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Selection of reversed-phase liquid chromatographic columns with diverse selectivity towards the potential separation of impurities in drugs 总被引:1,自引:0,他引:1
Van Gyseghem E Jimidar M Sneyers R Redlich D Verhoeven E Massart DL Vander Heyden Y 《Journal of chromatography. A》2004,1042(1-2):69-80
To select appropriate stationary phases from the continuously expanding supply of potentially suitable HPLC columns, the properties of 28 frequently applied stationary phases were determined by measuring several chromatographic parameters. From these results, based on chromatographic expertise, eight stationary phases with different properties and selectivities were selected. The aim of this study is to apply chemometric tools to evaluate the initially selected set of columns, i.e. a more systematic approach for making such a selection is examined. Starting from the information obtained on the 28 stationary phases, the re-evaluation was performed independently based on the chemometric techniques Pareto-optimality, principal component analysis (PCA), and Derringer's desirability functions. The aim was to select a set of efficient columns exhibiting large selectivity differences. The chemometrically selected stationary phases were divided in groups based on hydrophobicity, a critical retention-determining property in reversed-phase chromatography. This allowed to further reducing the selection to three columns. It is demonstrated that the selection by the chemometric approaches in general is fairly comparable with the initial selection. 相似文献
14.
Ring‐Closing and Cross‐Metathesis with Artificial Metalloenzymes Created by Covalent Active Site‐Directed Hybridization of a Lipase 下载免费PDF全文
Dr. Manuel Basauri‐Molina Dide G. A. Verhoeven Arnoldus J. van Schaik Henk Kleijn Prof. Dr. Robertus J. M. Klein Gebbink 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15676-15685
A series of Grubbs‐type catalysts that contain lipase‐inhibiting phosphoester functionalities have been synthesized and reacted with the lipase cutinase, which leads to artificial metalloenzymes for olefin metathesis. The resulting hybrids comprise the organometallic fragment that is covalently bound to the active amino acid residue of the enzyme host in an orthogonal orientation. Differences in reactivity as well as accessibility of the active site by the functionalized inhibitor became evident through variation of the anchoring motif and substituents on the N‐heterocyclic carbene ligand. Such observations led to the design of a hybrid that is active in the ring‐closing metathesis and the cross‐metathesis of N,N‐diallyl‐p‐toluenesulfonamide and allylbenzene, respectively, the latter being the first example of its kind in the field of artificial metalloenzymes. 相似文献
15.
Sanders MP Verhoeven S de Graaf C Roumen L Vroling B Nabuurs SB de Vlieg J Klomp JP 《Journal of chemical information and modeling》2011,51(9):2277-2292
G-protein coupled receptors (GPCRs) are important drug targets for various diseases and of major interest to pharmaceutical companies. The function of individual members of this protein family can be modulated by the binding of small molecules at the extracellular side of the structurally conserved transmembrane (TM) domain. Here, we present Snooker, a structure-based approach to generate pharmacophore hypotheses for compounds binding to this extracellular side of the TM domain. Snooker does not require knowledge of ligands, is therefore suitable for apo-proteins, and can be applied to all receptors of the GPCR protein family. The method comprises the construction of a homology model of the TM domains and prioritization of residues on the probability of being ligand binding. Subsequently, protein properties are converted to ligand space, and pharmacophore features are generated at positions where protein ligand interactions are likely. Using this semiautomated knowledge-driven bioinformatics approach we have created pharmacophore hypotheses for 15 different GPCRs from several different subfamilies. For the beta-2-adrenergic receptor we show that ligand poses predicted by Snooker pharmacophore hypotheses reproduce literature supported binding modes for ~75% of compounds fulfilling pharmacophore constraints. All 15 pharmacophore hypotheses represent interactions with essential residues for ligand binding as observed in mutagenesis experiments and compound selections based on these hypotheses are shown to be target specific. For 8 out of 15 targets enrichment factors above 10-fold are observed in the top 0.5% ranked compounds in a virtual screen. Additionally, prospectively predicted ligand binding poses in the human dopamine D3 receptor based on Snooker pharmacophores were ranked among the best models in the community wide GPCR dock 2010. 相似文献
16.
Parallel local search 总被引:2,自引:0,他引:2
We present a survey of parallel local search algorithms in which we review the concepts that can be used to incorporate parallelism
into local search. For this purpose we distinguish between single-walk and multiple-walk parallel local search and between
asynchronous and synchronous parallelism. Within the class of single-walk algorithms we differentiate between multiple-step
and single-step parallelism. To describe parallel local search we introduce the concepts of hyper neighborhood structures
and distributed neighborhood structures. Furthermore, we present templates that capture most of the parallel local search
algorithms proposed in the literature. Finally, we discuss some complexity issues related to parallel local search. 相似文献
17.
The 13C n.m.r. spectra of complexes between o-chloranil and aromatic electron donors were studied. Complexation leads to a general diamagnetic shift of the 13C n.m.r. signals for the acceptor (o-chloranil), but for signals from the 13C nuclei in the donors both diamagnetic and paramagnetic shifts are found. These phenomena are thought to be the result of competing anisotropy and charge-migration effects. Charge migration in o-chloranil complexes appears to be more important than in corresponding 1,3,5-trinitrobenzene complexes. 相似文献
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19.
Electron Stimulated Desorption (ESD) of O+ ions from oxygen-covered Ni(100) has been investigated at 390 K and 500 eV primary energy. The ion energy distribution is found to peak at 7.5 eV and to extend to 11 eV, over our whole exposure range (0–1000 L). The 7.5 eV peak height as a function of exposure shows that desorption takes place both in the chemisorption and the oxidation region. Emission of O+ occurs preferentially along the surface normal, with a base width of ≈ 60°. No azimuthal structure is observed. Additional electron energy dependent measurements clearly show a threshold near the oxygen 2s level. 相似文献
20.