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排序方式: 共有177条查询结果,搜索用时 265 毫秒
31.
Hahn U Hirst AR Delgado JL Kaeser A Delavaux-Nicot B Nierengarten JF Smith DK 《Chemical communications (Cambridge, England)》2007,(46):4943-4945
Mixtures of an appropriate carboxylic acid and n-butylstannoic acid constitute modular gelation systems, in which the formation of a well-defined 'tin-drum' nanocluster subsequently underpins the hierarchical assembly of nanostructured fibres, which form self-supporting gel-phase networks in organic solvents. 相似文献
32.
Hirst AR Huang B Castelletto V Hamley IW Smith DK 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(8):2180-2188
This paper investigates dendritic peptides capable of assembling into nanostructured gels, and explores the effect on self-assembly of mixing different molecular building blocks. Thermal measurements, small angle X-ray scattering (SAXS) and circular dichroism (CD) spectroscopy are used to probe these materials on macroscopic, nanoscopic and molecular length scales. The results from these investigations demonstrate that in this case, systems with different "size" and "chirality" factors can self-organise, whilst systems with different "shape" factors cannot. The "size" and "chirality" factors are directly connected with the molecular information programmed into the dendritic peptides, whilst the shape factor depends on the group linking these peptides together--this is consistent with molecular recognition hydrogen bond pathways between the peptidic building blocks controlling the ability of these systems to self-recognise. These results demonstrate that mixtures of relatively complex peptides, with only subtle differences on the molecular scale, can self-organise into nanoscale structures, an important step in the spontaneous assembly of ordered systems from complex mixtures. 相似文献
33.
We show that a version of Ramsey’s theorem for trees for arbitrary exponents is equivalent to the subsystem ${{\sf ACA}^\prime_{0}}$ of reverse mathematics. 相似文献
34.
la Cour Jansen T Dijkstra AG Watson TM Hirst JD Knoester J 《The Journal of chemical physics》2006,125(4):44312
In this paper different floating oscillator models for describing the amide I band of peptides and proteins are compared with density functional theory (DFT) calculations. Models for the variation of the frequency shifts of the oscillators and the nearest-neighbor coupling between them with respect to conformation are constructed from DFT normal mode calculations on N-acetyl-glycine-N(')-methylamide. The calculated frequencies are compared with those obtained from existing electrostatic models. Furthermore, a new transition charge coupling model is presented. We suggest a model which combines the nearest-neighbor maps with long-range interactions accounted for using the new transition charge model and an existing electrostatic map for long-range interaction frequency shifts. This model and others, which account for the frequency shifts by electrostatic maps exclusively, are tested by comparing the predicted IR spectra with those from DFT calculations on the pentapeptide [Leu]-enkephalin. The new model described above gives the best agreement and, after a systematic blueshift is accounted for, reproduces the DFT frequencies to within 3.5 cm(-1). The correlation of the intensities for this model with intensities from DFT calculations is 0.94. 相似文献
35.
The aim of this tutorial review is to introduce to a broader readership the emerging technique of electrophoretic NMR (eNMR). The "electrophoretic" element of the technique refers to the fact that charged particles are induced to flow by the application of an electric field. This flow is measured using pulsed-gradient spin-echo NMR (PGSE-NMR). The great potential of this experimental approach is the fact that NMR is chemically selective and non-invasive. eNMR, especially when combined with the more established PGSE-NMR experiment, may therefore be used to quantify the structure of multi-component systems via the dynamics and charge of each species within a complex mixture. Accordingly, eNMR is likely to be of great significance for colloid scientists, biologists, technologists and formulation scientists. 相似文献
36.
Jeffry L. Hirst 《Archive for Mathematical Logic》2012,51(1-2):123-125
We show that a statement HIL, which is motivated by a lemma of Hilbert and close in formulation to Hindman’s theorem, is actually much weaker than Hindman’s theorem. In particular, HIL is finitistically reducible in the sense of Hilbert’s program, while Hindman’s theorem is not. 相似文献
37.
Andrew N. Boa Stephen Clark Paul R. Hirst Robert Westwood 《Tetrahedron letters》2003,44(52):9299-9302
6-Oxiranyl- and 3-oxiranyl-2-phenylquinoline-4-carboxylic acid diisopropylamides react with secondary amines and lithium amides to give (aminohydroxyethyl)quinolines but with opposite regioselectivities. Upon epoxidation of 3-formylquinoline 2 a 5:1 mixture of atropisomers is formed. This ratio is maintained upon epoxide ring-opening with amines in ethanol at reflux, but with lithium amides at room temperature a 1.3:1 ratio of isomers is obtained. 相似文献
38.
Jeffry L. Hirst 《Archive for Mathematical Logic》2006,45(1):1-2
This paper contains a corrected proof that the statement “every non-empty closed subset of a compact complete separable metric
space is separably closed” implies the arithmetical comprehension axiom of reverse mathematics. 相似文献
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