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Internet information services replicate their servers to improve availability, response time, and fault tolerance. Traditional replication algorithms do not address the scale and administrative decentralization of today's internetworks. We have proposed and implemented a scalable and efficient tool to replicate wide-area, autonomously managed services. We target replication degrees of thousands of weakly consistent replicas. The main goal of our replication tool is to make traditional replication services scale in today's exponentially growing, autonomously managed internetworks. Our tool, which we call flood-d, allows servers to be organized in multiple replication groups. For each replication group, flood-d builds a logical update topology that is resilient to server failure, and tries to minimize the communication cost and propagation time needed to transmit updates. Flood-d's logical topologies are computed based on communication latency and available network bandwidth. This paper describes flood-d, and presents simulation results obtained when using flood-d to extend existing replication algorithms. Our results show the gains of organizing service replicas into multiple, smaller replication groups, and using network-cognizant logical topologies to propagate updates. We argue that existing as well as emerging Internet information services can benefit from flood-d's services 相似文献
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Noppe H De Wasch K Poelmans S Van Hoof N Verslycke T Janssen CR De Brabander HF 《Analytical and bioanalytical chemistry》2005,382(1):91-98
An analytical procedure enabling routine analysis of four environmental estrogens at concentrations below 1 ng L–1 in estuarine water samples has been developed and validated. The method includes extraction of water samples using solid-phase extraction discs and detection by gas chromatography (GC) with tandem mass spectrometry (MS–MS) in electron-impact (EI) mode. The targeted estrogens included 17- and 17-estradiol (aE2, bE2), estrone (E1), and 17-ethinylestradiol (EE2), all known environmental endocrine disruptors. Method performance characteristics, for example trueness, recovery, calibration, precision, accuracy, limit of quantification (LOQ), and the stability of the compounds are presented for each of the selected estrogens. Application of the procedure to water samples from the Scheldt estuary (Belgium – The Netherlands), a polluted estuary with reported incidences of environmental endocrine disruption, revealed that E1 was detected most frequently at concentrations up to 7 ng L–1. aE2 was detected once only and concentrations of bE2 and EE2 were below the LOQ.Presented at the 9th FECS Conference on Chemistry and the Environment, Bordeaux, France, 29 August–1 September 2004 相似文献
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Naringenin is a natural widespread flavanone occurring in different foodstuffs that presents several important biological activities. Although its properties are well documented, its mechanisms of action are still controversial. The present article reports a conformational analysis of naringenin, using the semiempirical AM1 and ab initio methods, at the Hartree–Fock level of theory. The 3-21G, 3-21G*, 6-31G, and 6-31G** basis sets were used. The electron correlation effects were included through the Møller–Plesset second-order perturbation theory. The solvation of naringenin has been investigated through the standard SCRF, the supermolecule (SM), and the combined SM/SCRF models. The results have shown that there are two degenerate forms of naringenin, differing mainly by the orientation of a hydroxyl group (C4—OH). The energy barrier for the interconversion between them is ca. 6 kcal.mol–1, suggesting some conjugation between the -system of the aromatic B ring and the hydroxyl group (C4—OH). 相似文献
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Valérie Chevalier-Billosta Jean-Paul Joseleau Alain Cochaux Katia Ruel 《Cellulose (London, England)》2007,14(2):141-152
The composition and ultrastructural arrangement of cell wall polymers in wood fibres have determining influence on the properties
of wood derived materials. It is therefore important to improve our understanding of the relationship between fibres organisation,
the modifications induced by pulping treatments, and the resulting paper sheet mechanical properties. The different treatments
to which fibres are subjected during the manufacturing of pulps and papers induce morphological and micro-structural alterations
due to the removal of wall constituents and of microfibrillar elements. The impact of pulping processes on fibres was investigated
at the ultrastructural scale of transmission electron microscopy. Particular attention was given to the effects of beating
in refiners at various intensities on the ultrastructure of fibres. The most characteristic effects consisted of delaminations,
microfibril disorganisation, and even fractures, of varying importance depending on the intensity of the mechanical refining.
The consequences of internal alterations and surface modifications of the fibres were examined in relation to the paper sheet
mechanical properties. Correlations between the type of alteration observed in the fibres and its possible impact on a given
paper mechanical property are suggested. With similar approaches, the effects of drying and recycling were studied. 相似文献
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We consider a one-dimensional peridynamical medium and show the existence of solitary waves with small amplitudes and long wavelength. Our proof uses nonlinear Bochner integral operators and characterizes their asymptotic properties in a singular scaling limit. 相似文献
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Katia Wehbe Jacob Filik Mark D. Frogley Gianfelice Cinque 《Analytical and bioanalytical chemistry》2013,405(4):1311-1324
The study of individual cells with infrared (IR) microspectroscopy often requires living cells to be cultured directly onto a suitable substrate. The surface effect of the specific substrates on the cell growth—viability and associated biochemistry—as well as on the IR analysis—spectral interference and optical artifacts—is all too often ignored. Using the IR beamline, MIRIAM (Diamond Light Source, UK), we show the importance of the substrate used for IR absorption spectroscopy by analyzing two different cell lines cultured on a range of seven optical substrates in both transmission and reflection modes. First, cell viability measurements are made to determine the preferable substrates for normal cell growth. Successively, synchrotron radiation IR microspectroscopy is performed on the two cell lines to determine any genuine biochemically induced changes or optical effect in the spectra due to the different substrates. Multivariate analysis of spectral data is applied on each cell line to visualize the spectral changes. The results confirm the advantage of transmission measurements over reflection due to the absence of a strong optical standing wave artifact which amplifies the absorbance spectrum in the high wavenumber regions with respect to low wavenumbers in the mid-IR range. The transmission spectra reveal interference from a more subtle but significant optical artifact related to the reflection losses of the different substrate materials. This means that, for comparative studies of cell biochemistry by IR microspectroscopy, it is crucial that all samples are measured on the same substrate type. Figure
Cell separation by PCA due to the refractive index of the substrate used, revealing transmission artifact. 相似文献