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71.
Tom Pitts Nikitas I. Gidopoulos Nektarios N. Lathiotakis 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(6):130
In the constrained minimization method of Gidopoulos and Lathiotakis [N.I. Gidopoulos, N.N. Lathiotakis, J. Chem. Phys. 136, 224109 (2012)], the Hartree exchange and correlation Kohn-Sham potential of a finite N-electron system is replaced by the electrostatic potential of an effective charge density that is everywhere positive and integrates to a charge of N ? 1 electrons. The optimal effective charge density (electron repulsion density, ρrep) and the corresponding optimal effective potential (electron repulsion potential vrep) are obtained by minimizing the electronic total energy in any density functional approximation. The two constraints are sufficient to remove the self-interaction errors from vrep, correcting its asymptotic behavior at large distances from the system. In the present work, we describe, in complete detail, the constrained minimization method, including recent refinements. We also assess its performance in removing the self-interaction errors for three popular density functional approximations, namely LDA, PBE and B3LYP, by comparing the obtained ionization energies to their experimental values for an extended set of molecules. We show that the results of the constrained minimizations are almost independent of the specific approximation with average percentage errors 15%, 14%, 13% for the above DFAs respectively. These errors are substantially smaller than the corresponding errors of the plain (unconstrained) Kohn-Sham calculations at 38%, 39% and 27% respectively. Finally, we showed that this method correctly predicts negative values for the HOMO energies of several anions. 相似文献
72.
We derive Einstein’s equations from a linear theory in flat space-time using free-field gauge invariance and universal coupling.
The gravitational potential can be either covariant or contravariant and of almost any density weight. We adapt these results
to yield universally coupled massive variants of Einstein’s equations, yielding two one-parameter families of distinct theories
with spin 2 and spin 0. The Freund-Maheshwari-Schonberg theory is therefore not the unique universally coupled massive generalization
of Einstein’s theory, although it is privileged in some respects. The theories we derive are a subset of those found by Ogievetsky
and Polubarinov by other means. The question of positive energy, which continues to be discussed, might be addressed numerically
in spherical symmetry. We briefly comment on the issue of causality with two observable metrics and the need for gauge freedom
and address some criticisms by Padmanabhan of field derivations of Einstein-like equations along the way.
__________
Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 151, No. 2, pp. 311–336, May, 2007. 相似文献
73.
74.
R. Cornelis C. Camara L. Ebdon L. Pitts B. Welz R. Morabito O. Donard H. Crews E. H. Larsen B. Neidhart F. Ariese E. Rosenberg D. Mathé G. M. Morrison G. Cordier F. Adams P. Van Doren J. Marshall B. Stojanik A. Ekvall P. Quevauviller 《Analytical and bioanalytical chemistry》1999,363(5-6):435-438
The main objective of the EU-network is to bring together scientists with a background in analytical chemistry interested in speciation method development with potential users from industry and representatives from legislative bodies. The network started on 1/10/1997 for a duration of 2 years. A series of meetings are being organised to debate all the important questions for collecting information on environmental, food and occupational health aspects of speciation and to define possible future projects. The findings and conclusions will be summarised as a series of general papers that will be published in the open literature, recapitulating the essential information gathered to date, outlining the state of the art for each topic and recommending legislative actions. A first meeting was held in Überlingen, Germany on 5–6 December 1997. The representatives from industry explained their interest in the network and the participants from the academic and national institutes gave a state-of-the-art presentation of their research. Out of this, a program was compiled for the following meeting in Segovia from 16 to 20 March 1998. The topics dealt with were: organotin compounds in the environmental session; the speciation and bioavailability of trace element species (Cr, Fe, Se), the quality of the data and new legislation in the food session; and identification of inhaled particles and the search for bioindicators for exposure to Ni and Pt in the occupational health/hygiene session. In each session about half of the participants came from industry. The delegates agreed on a list of priorities in speciation analysis. A www-page has been created: hhtp://www. speciation 21.plymouth.ac.uk. Everybody interested in adding information to the page is requested to mail this to lpitts@plymouth.ac.uk 相似文献
75.
J. N. Pitts 《Research on Chemical Intermediates》1993,19(3):251-298
It has been four decades since the phenomenon of photochemical air pollution was first characterized and, in the same year, a tragic London smog episode caused 4,000 excess deaths. Since then, there has been a substantial increase in our understanding of the chemistry involved in both types of air pollution, and a recognition that there is a very close chemical interrelationship between them. In this overview, we provide a brief historical perspective on the atmospheric chemistry of photochemical smog and illustrate how fundamental studies on the gas-phase chemistry of uv-irradiated mixtures of volatile organic compounds (VOC) and oxides of nitrogen (NOx in polluted laboratory and ambient air masses have contributed to our understanding of three environmental problems: the atmospheric formation of ozone, nitric acid and airborne mutagens. In particular, we demonstrate the central role played by nitrogen dioxide and the hydroxyl radical in each case. We also show how certain reactive toxic and acidic species, e.g., formaldehyde and nitrous and formic acids, have been characterized in smog chambers and ambient smog by long pathlength spectroscopic techniques. It is shown that by using the same methods they now have been identified unequivocally, along with NO2, in certain common types of polluted indoor atmospheres ... and at much higher concentrations than outdoors. This has significant health implications for indoor HCHO and quite possibly the acids. We then trace the history of the direct mutagenicity of respirable particles in polluted ambient air and show how, through use of the Ames test in biologically-directed assays of products coupled with fundamental studies of gas-phase reactions of polycyclic aromatic hydrocarbons (PAH) and NOx in irradiated air, much of this activity can be accounted for in terms of the formation of nitro-PAH and oxygenated derivatives. Finally, we discuss the application of basic kinetic, mechanistic and analytical, experimental techniques and theoretical concepts to the development of a new set of “reactivity-based” regulatory controls on motor vehicle emissions of VOC’s. This novel regulatory approach applied by California’s Air Resources Board, which takes effect in 1994, illustrates the continuing need for fundamental research in the area of atmospheric chemistry and how it may be applied to “real world” environmental problems. 相似文献
76.
Andrew K. Pitts Fionn O'Hara Robert H. Snell Matthew J. Gaunt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(18):5541-5545
A sequential C H functionalization strategy for the synthesis of the marine alkaloid dictyodendrin B is reported. Our synthesis begins from commercially available 4‐bromoindole and involves six direct functionalizations around the heteroarene core as part of a gram‐scale strategy towards the natural product. 相似文献
77.
D. Lackner O.J. Pitts S. Najmi P. Sandhu K.L. Kavanagh A. Yang M. Steger M.L.W. Thewalt Y. Wang D.W. McComb C.R. Bolognesi S.P. Watkins 《Journal of Crystal Growth》2009,311(14):3563-3567
We report the OMVPE growth and characterization of InAsSb/InAs strain balanced multiple quantum wells lattice-matched to GaSb substrates for potential application as mid-infrared detectors for wavelengths beyond 4 μm. Detailed transmission electron microscopy measurements were performed to evaluate the degree of Ga and Sb intermixing at the GaSb/InAsSb and InAs/InAsSb interfaces. Photoluminescence emission up to 5 μm was observed for superlattice structures with only 15% antimony. The dependence of PL on wavelength is red shifted compared to expectations based on type I band alignment. 相似文献
78.
Vaios Dermitzakis Susan M. Pitts Konstadinos Politis 《Methodology and Computing in Applied Probability》2010,12(1):155-175
We obtain analogues of Lundberg’s inequality and the Cramér—Lundberg asymptotic relationship for the k-th moment of the time to ruin in the classical risk model. We also derive the asymptotic behaviour of the mean time to ruin
when the claim size distribution has a heavy or intermediate tail. 相似文献
79.
80.
Roger Atkinson Sara M. Aschmann Dennis R. Fitz Arthur M. Winer James N. Pitts 《国际化学动力学杂志》1982,14(1):13-18
Rate constants for the gas-phase reactions of O3 with ethene, propene, 1-hexene, 1-heptene, styrene, o-, m-, and p-cresol, o- and m-xylene, benzylchloride, acrylonitrile, and trichloroethene have been determined at 296 ± 2 K. The rate constants ranged from <5 × 10?21 cm3 molecule?1 s?1 for m-xylene to 2.16 × 10?17 cm3 molecule?1 s?1 for styrene, with those for ethene, propene, and 1-hexene being in excellent agreement with literature data. 相似文献