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81.
82.
Aldo?Di BiasioEmail author Elena?Agliari Adriano?Barra Raffaella?Burioni 《Theoretical chemistry accounts》2012,131(3):1104
We consider cooperative reactions and we study the effects of the interaction strength among the system components on the
reaction rate, hence realizing a connection between microscopic and macroscopic observables. Our approach is based on statistical
mechanics models and it is developed analytically via mean-field techniques. First of all, we show that, when the coupling
strength is set positive, a cooperative behavior naturally emerges from the model; in particular, by means of various cooperative
measures previously introduced, we highlight how the degree of cooperativity depends on the interaction strength among components.
Furthermore, we introduce a criterion to discriminate between weak and strong cooperativity, based on a measure of “susceptibility.”
We also properly extend the model in order to account for multiple attachments phenomena: this is realized by incorporating
within the model p-body interactions, whose non-trivial cooperative capability is investigated too. 相似文献
83.
Deraeve C Guo Z Bon RS Blankenfeldt W DiLucrezia R Wolf A Menninger S Stigter EA Wetzel S Choidas A Alexandrov K Waldmann H Goody RS Wu YW 《Journal of the American Chemical Society》2012,134(17):7384-7391
Post-translational attachment of geranylgeranyl isoprenoids to Rab GTPases, the key organizers of intracellular vesicular transport, is essential for their function. Rab geranylgeranyl transferase (RabGGTase) is responsible for prenylation of Rab proteins. Recently, RabGGTase inhibitors have been proposed to be potential therapeutics for treatment of cancer and osteoporosis. However, the development of RabGGTase selective inhibitors is complicated by its structural and functional similarity to other protein prenyltransferases. Herein we report identification of the natural product psoromic acid (PA) that potently and selectively inhibits RabGGTase with an IC(50) of 1.3 μM. Structure-activity relationship analysis suggested a minimal structure involving the depsidone core with a 3-hydroxyl and 4-aldehyde motif for binding to RabGGTase. Analysis of the crystal structure of the RabGGTase:PA complex revealed that PA forms largely hydrophobic interactions with the isoprenoid binding site of RabGGTase and that it attaches covalently to the N-terminus of the α subunit. We found that in contrast to other protein prenyltransferases, RabGGTase is autoinhibited through N-terminal (α)His2 coordination with the catalytic zinc ion. Mutation of (α)His dramatically enhances the reaction rate, indicating that the activity of RabGGTase is likely regulated in vivo. The covalent binding of PA to the N-terminus of the RabGGTase α subunit seems to potentiate its interaction with the active site and explains the selectivity of PA for RabGGTase. Therefore, psoromic acid provides a new starting point for the development of selective RabGGTase inhibitors. 相似文献
84.
Tim Hammerer Laurent Weisgerber Stefan Schenk Othmar Stelzer Ulli Englert Walter Leitner Giancarlo Franciò 《Tetrahedron: Asymmetry》2012,23(1):53-59
New diphosphinite ligands based on atropoisomeric diol backbones and (R,R)-2,5-dimethylphospholane moieties have been prepared and fully characterised. For each ligand structure, both diastereomers have been synthesised. These ligands are available through a straightforward procedure in good yields. The solid state structures of two diastereomeric ligands are reported. These ligands have been applied to Rh-catalysed asymmetric hydrogenations and hydroformylations of CC bonds as well as in Ir-catalysed asymmetric hydrogenations of CN bonds. Turnover frequencies in the range of 10,000 h?1 and enantioselectivities of up to 98% ee have been achieved. The different chirality elements within the ligands led to marked cooperative effect in catalysis. Interestingly, there is no general privileged diastereomeric structure but rather a matched diastereomer for each application. 相似文献
85.
Danijela Klemenčič Brigita Tomšič Franci Kovač Barbara Simončič 《Cellulose (London, England)》2012,19(5):1715-1729
Functional antimicrobial cotton fibres were prepared in a novel two-step procedure utilising the pad-dry-cure method to apply an inorganic–organic hybrid sol–gel precursor (reactive binder, RB) followed by the in situ synthesis of AgCl particles on the RB-treated fibres. The morphology and surface composition of the modified cotton fibres were investigated by scanning electron microscopy imaging and X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy spectral analyses. The bulk concentration of Ag on the cotton fibres was determined by inductively coupled plasma mass spectroscopy, and the antimicrobial activity against the bacteria Escherichia coli and Staphylococcus aureus was estimated according to the ISO 20645:2004 (E) and AATCC 100-1999 methods. The results showed that this application process yields the following important benefits: (1) the presence of the RB silica matrix increased the fibres’ capacity for adsorbing AgCl particles compared with the same fibres without RB; (2) the in situ synthesis enabled a simple and environmentally friendly preparation of AgCl particles from AgNO3 and their embedment into the fibres; (3) the AgCl particles were bound to the RB silica matrix by physical forces, which allowed for their controlled release from the fibres; (4) the capacity of the RB-modified cotton samples to hold embedded AgCl particles was sufficient to provide a 100 % bacterial reduction even after 10 repeated washing cycles; and (5) the chemical modification of the cotton fibres did not significantly change their whiteness, wettability or softness. 相似文献
86.
Romolo Remetti Daniele Franci 《Journal of Radioanalytical and Nuclear Chemistry》2012,292(3):1115-1122
This paper presents the alpha/beta complete deconvolution tool (ABCD-Tool), a C++ application for the analysis of spectra from liquid scintillation counting (LSC) measurements. In addition to the
basic algorithms for standard gross alpha/beta analysis and the determination of the counting efficiency, the software implements
a recent unfolding technique based on Fourier transforms, which gives precise and reliable results even in the case of complex,
strongly overlapping spectra. The application is designed to be used with alpha/beta spectra generated from Perkin Elmer Wallac
Quantulus 1220. However, future upgrades are scheduled in order to extend the compatibility to spectra from other LSC instruments
in commerce. 相似文献
87.
Signorini Raffaella Meneghetti Moreno Bozio Renato Brusatin Giovanna Innocenzi Plinio Guglielmi Massimo Negra Federico Della 《Journal of Sol-Gel Science and Technology》2001,22(3):245-253
Hybrid organic-inorganic materials are investigated as suitable materials for inclusion of fullerene derivatives and for fabrication of laser protection devices. A specific synthesis has been developed in order to optimize non-linear optical performances of fullerene derivatives. 3-glicydoxypropyltrymethoxysilane has been used as an inorganic and organic network former to obtain the host material. The sol-gel synthesis consists of the hydrolysis and condensation in acidic conditions of the inorganic network. Epoxy polymerization has been achieved by using zirconium or BF3 alkoxides precursors. Bulk and multilayer materials doped with a fullerene derivative have been fabricated. They show good optical requirements: high fullerenes concentration, high microstructural homogeneity, high laser damage threshold and high optical limiting efficiency. Optical limiting (OL) mechanisms have been investigated. The most effective in the sol-gel materials is the reverse saturable absorption (RSA) one. However, different mechanisms, like non-linear (NL) scattering and NL refraction contribute to a different extent. Open- and closed-aperture OL and z-scan measurements on sol-gel samples show the contribution of NL scattering and NL refraction at 690 nm. Laser damage threshold has been characterized as a function of the structure of the samples and of the optical configurations (f/66 and f/5). 相似文献
88.
Photosensitized hydrogen abstraction from 2-alkyl-1,3-dioxolanes by triplet benzophenone gives the corresponding 1,3-dioxolan-2-yl radicals and these are trapped by ,β-unsatured ketones yielding monoprotected 1,4-diketones. With open chain ketones (3-buten-2-one and 4-penten-3-one) the yields are low and competitive pathways in part consume the radicals. With cyclic enones however, yields are good as tested with cyclopentenone, cyclohexenone and 4-hydroxy-cyclopentenone. More generally, this is a viable alternative for the synthesis of 1,4-diketones via radicals while the thermal initiation gives only low yield. The reaction cannot be extended to strongly stabilized radicals, such as the 2-phenyl-1,3-dioxolanyl radical. 相似文献
89.
We study the behavior of a martensitic thin film with a hydrostatic pressure applied underneath the film. The problem is formulated in 3-D for a single crystal film of thickness h, and a Cosserat membrane theory is derived by Γ-convergence techniques in the limit h→0. The membrane theory is further simplified using a second Γ-convergence argument based on hard moduli. The resulting theory supports energy minimizing “tunnels”: structures having the shape of part of a cylinder cut by a plane parallel to its axis, obtained by releasing the film from the substrate along a strip with a certain orientation. As the temperature is raised (at fixed pressure) the energy minimizing shape collapses gradually to the substrate, accompanied by a martensite-to-austenite phase transformation. During this process the tunnel supports a microstructure consisting of fine bands of austenite parallel to the axis of the tunnel, alternating with bands of a single variant of martensite. Formulas for the associated volume–temperature–pressure relation are given: in these the latent heat of transformation plays an important role. 相似文献
90.
Planar bilayer lipid membranes (BLMs) are currently employed to construct many bio-inspired material systems and structures. In order to characterize the pressure effects on the equilibrium configurations of these biological membranes, a novel continuum model is proposed. The BLM is assumed to be a two-layer Smectic A liquid crystal. The mean orientation of the amphiphilic molecules comprising the membrane is postulated to be perpendicular to the layers and each layer is idealized as a two dimensional liquid. Moreover, the BLM is modeled as a simply supported plate undergoing small deformations. It is subjected to a pressure load that acts perpendicularly to the layers. The equilibrium equations and boundary conditions are derived from the bulk elastic energy for Smectic A liquid crystals as described by de Gennes and Prost (1993) by using variational methods. The resulting fourth-order linear partial differential equation is solved by employing cylindrical functions and the series solution is proved to be convergent. The solution is numerically computed for values of the model parameters that are reported in the literature. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献