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61.
The discovery of neutron rich isotopes of the lightest elements on the neutron drip line exhibiting a halo structure has opened
up new vistas in research activities. The novel structural features associated with the halo phenomena have been the subject
for extensive theoretical and experimental investigations in recent times. In this talk, I propose to present a broad overview
of the recent developments in this field, bringing out the striking features which show that a large number oflight nuclei
near the neutron drip line are characterized by a clear separation between a ‘normal’ core nucleus and a loosely bound low
density veil of neutrons. Specifically, the two neutron halos offer a natural premises, from a theoretical standpoint, to
employ three body techniques for studying their detailed structural properties. A considerable part of the talk will be devoted
to report and highlight the results on a number of light halo nuclei such as 11Li, 11Be, 19B and 22C on which we have been carrying out investigations employing a simple but realistic three body model. These three body systems
which have been termed as ‘Borromean’ (i.e while three body systems are bound, the corresponding binary subsystems on the
other hand are unbound) are characterized by large spacial extension and very low separation energy of the neutron. They are,
therefore, ideally suited for exploring the possibility of the existence of Efimov states in two neutron halo nuclei. We have
recently carried out the three body analyses to predict the possibility of the occurrence of such states on which experimental
work at various laboratories is underway. 相似文献
62.
Rubio-Lago L Amaral GA Arregui A González-Vázquez J Bañares L 《Physical chemistry chemical physics : PCCP》2012,14(17):6067-6078
The roaming dynamics in the photodissociation of acetaldehyde is studied through the first absorption band, in the wavelength interval ranging from 230 nm to 325 nm. Using a combination of the velocity-map imaging technique and rotational resonance enhanced multiphoton ionization (REMPI) spectroscopy of the CO fragment, the branching ratio between the canonical transition state and roaming dissociation mechanisms is obtained at each of the photolysis wavelengths studied. Upon one photon absorption, the molecule is excited to the first singlet excited S(1) state, which, depending on the excitation wavelength, either converts back to highly vibrationally excited ground S(0) state or undergoes intersystem crossing to the first excited triplet T(1) state, from where the molecule can dissociate over two main channels: the radical (CH(3) + HCO) and the molecular (CO + CH(4)) channels. Three dynamical regions are characterized: in the red edge of the absorption band, at excitation energies below the T(1) barrier, the ratio of the roaming dissociation channel increases, largely surpassing the transition state contribution. As the excitation wavelength is increased, the roaming propensity decreases reaching a minimum at wavelengths ~308 nm. Towards the blue edge, at 230 nm, an upper limit of ~50% has been estimated for the contribution of the roaming channel. The experimental results are interpreted in terms of the interaction between the different potential energy surfaces involved by means of ab initio stationary points and intrinsic reaction coordinate paths calculations. 相似文献
63.
O. Louren?o M. Dutra R. L. P. G. Amaral Antonio Delfino 《Brazilian Journal of Physics》2012,42(3-4):227-236
In this work, we show how nonlinear point-coupling models, described by a Lagrangian density containing only terms up to fourth order in the fermion condensate $(\bar{\psi}\psi)$ , are derived from a modified meson-exchange nonlinear Walecka model. We present two methods of derivation, namely the hypermassive meson limit within a functional integral approach and the mean-field approximation, in which equations of state at zero temperature of the nonlinear point-coupling models are directly obtained. 相似文献
64.
Manuel J.S. Monte Sónia P. Pinto Ana I.M.C. Lobo Ferreira Luísa M.P.F. Amaral Vera L.S. Freitas Maria D.M.C. Ribeiro da Silva 《The Journal of chemical thermodynamics》2012,45(1):53-58
This work reports new experimental thermodynamic results on fluorene. Vapor pressures of both crystalline and liquid phases were measured using a pressure gauge (capacitance diaphragm manometer) and Knudsen effusion methods over a wide temperature range (292.20 to 412.16) K yielding accurate determination of enthalpy and entropy of sublimation and of vaporization. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapor pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluorene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation. 相似文献
65.
P. Amaral et al. 《The European Physical Journal C - Particles and Fields》2001,20(3):487-495
The energy loss spectrum of 180 GeV muons has been measured with the 5.6 m long finely segmented Module 0 of the ATLAS hadron
Tile Calorimeter at the CERN SPS. The differential probability per radiation length of a fractional energy loss has been measured in the range ; it is compared with theoretical predictions for energy losses due to bremsstrahlung, production of electron–positron pairs,
and energetic knock-on electrons. The iron elastic form factor correction to muon bremsstrahlung in the region of no screening of the nucleus by atomic electrons has been measured for the first time,
and is compared with different theoretical predictions.
Received: 28 December 2000 / Revised version: 14 February 2001 / Published online: 28 May 2001 相似文献
66.
Natlia Aniceto Vanda Marques Joana D. Amaral Patrícia A. Serra Rui Moreira Cecília M. P. Rodrigues Rita C. Guedes 《Molecules (Basel, Switzerland)》2022,27(15)
Necroptosis has emerged as an exciting target in oncological, inflammatory, neurodegenerative, and autoimmune diseases, in addition to acute ischemic injuries. It is known to play a role in innate immune response, as well as in antiviral cellular response. Here we devised a concerted in silico and experimental framework to identify novel RIPK1 inhibitors, a key necroptosis factor. We propose the first in silico model for the prediction of new RIPK1 inhibitor scaffolds by combining docking and machine learning methodologies. Through the data analysis of patterns in docking results, we derived two rules, where rule #1 consisted of a four-residue signature filter, and rule #2 consisted of a six-residue similarity filter based on docking calculations. These were used in consensus with a machine learning QSAR model from data collated from ChEMBL, the literature, in patents, and from PubChem data. The models allowed for good prediction of actives of >90, 92, and 96.4% precision, respectively. As a proof-of-concept, we selected 50 compounds from the ChemBridge database, using a consensus of both molecular docking and machine learning methods, and tested them in a phenotypic necroptosis assay and a biochemical RIPK1 inhibition assay. A total of 7 of the 47 tested compounds demonstrated around 20–25% inhibition of RIPK1’s kinase activity but, more importantly, these compounds were discovered to occupy new areas of chemical space. Although no strong actives were found, they could be candidates for further optimization, particularly because they have new scaffolds. In conclusion, this screening method may prove valuable for future screening efforts as it allows for the exploration of new areas of the chemical space in a very fast and inexpensive manner, therefore providing efficient starting points amenable to further hit-optimization campaigns. 相似文献
67.
Modeling the world-wide airport network 总被引:17,自引:0,他引:17
R. Guimerá L. A. N. Amaral 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,38(2):381-385
Recently, we have presented the first exhaustive analysis of the world-wide airport network. Two important results of that study are that: (i) the world-wide airport network is a small-world network with power-law decaying degree and betweenness centrality distributions; (ii) the most connected cities (largest degree) are typically not the most central cities (largest betweenness centrality). This second finding is particularly significant because of results demonstrating that nodes with high betweenness tend to play a more important role in keeping networks connected than those with high degree. Here, we investigate if current network models can explain this finding and we show that they cannot. Thus, we propose a new model that explains this behavior in terms of the geo-political constraints that affect the growth of the airport network. We further hypothesize that in other infrastructures, affected by similar geo-political constraints, critical locations might not coincide with highly-connected hubs.Received: 14 January 2004, Published online: 14 May 2004PACS:
89.75.Fb Structures and organization in complex systems - 89.75.Da Systems obeying scaling laws - 89.40.Dd Air transporation 相似文献
68.
Fa-Nian Shi Filipe A. Almeida Paz Penka I. Girginova Luís Mafra Vítor S. Amaral Joo Rocha Anna Makal Krzysztof Wozniak Jacek Klinowski Tito Trindade 《Journal of Molecular Structure》2005,754(1-3):51-60
Two new compounds containing multidentate chelating organic residues of N-(phophonomethyl)iminodiacetic acid (H4pmida), [M(pyr)(H2O)4][M2(Hpmida)2(pyr)(H2O)2]·2(H2O) (where pyr=pyrazine and M=Co2+ or Ni2+ for I and II, respectively) have been synthesised and structurally characterised by single-crystal and powder X-ray diffraction, elemental analysis, infrared spectroscopy, thermal analysis and solid-state 31P MAS NMR. The compounds contain discrete binuclear anionic [M2(Hpmida)2(pyr)(H2O)2]2− units in which one pyrazine ligand bridges two M2+ cations which are completely trapped inside three five-membered chelate rings formed by the Hpmida3− ligands. These moieties close pack in the ac plane via a series of strong and highly directional O–HO hydrogen bonds leading to the formation of anionic layers. One-dimensional cationic coordination polymers are placed in-between and strongly hydrogen-bonded to these layers. The magnetic properties of these two materials are also reported. 相似文献
69.
Amaral A. M. S. C. Linnett J. W. Williamson C. T. 《Theoretical chemistry accounts》1970,16(4):249-262
A full configuration interaction treatment has been carried out for the four electrons of the double bond of ethylene using a minimal STO basis set. The excent to which - separability provides a good approximation for the eigenfunctions of the low-lying states and for transitions between them has been examined. Alternative formulations using various more localised orbitals as the basis are derived for a number of the states. These have been examined and discussed.
We wish to thank the Instituto de Alta Cultura of Portugal for a scholarship for A. A. and the National Science Foundation (USA) for a post-doctoral fellowship for C.T.W. 相似文献
Zusammenfassung Eine vollständige Konfigurationswechselwirkung wurde für die vier Elektronen der Doppelbindung von Äthylen durchgeführt, wobei eine minimale STO-Basis benutzt wurde. Das Maß, in dem die --Separierbarkeit eine gute Näherung für Eigenfunktionen der niedrigliegenden Zustände und für Übergänge zwischen ihnen darstellt, wurde untersucht. Alternativformulierungen, die verschiedene, lokalisierte Orbitale als Basis benutzen, werden für eine Anzahl von Zuständen angegeben und diskutiert.
Résumé Interaction de configuration complète pour les quatre électrons de la double liaison de l'éthylène dans une base STO minimale. La séparabilité - est examinée pour les plus bas états et les transitions entre ces états. D'autres formulations utilisant des orbitales plus localisées sont obtenues pour certains états. Ces formulations sont discutées.
We wish to thank the Instituto de Alta Cultura of Portugal for a scholarship for A. A. and the National Science Foundation (USA) for a post-doctoral fellowship for C.T.W. 相似文献
70.
The reaction of 5-allyl-5-isobutylbarbituric acid with several electrophilic reagents gives products resulting from the addition of the electrophile to the double bond of the allyl group and/or bicyclic products. 相似文献