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411.
Muniz-Miranda F Pagliai M Cardini G Righini R 《The journal of physical chemistry. A》2012,116(9):2147-2153
The hydrogen-bond dynamics of lithium nitrate trihydrate has been studied by a combined approach based on ab initio molecular dynamics simulations and wavelet analysis. The simultaneous bifurcated interaction between one hydrogen atom of water molecules and two oxygen atoms of nitrate ions is the pivotal feature of the crystal structure: this bifurcated interaction has deep effects on the O-H stretching region of the vibrational spectrum. The structural, dynamic, spectroscopic, and electronic properties of the bifurcated hydrogen bond have been investigated computationally, elucidating at the molecular level the differences with weak and strong hydrogen bonds present in the crystal. These studies corroborate the very recent IR experiments performed on the lithium nitrate trihydrate crystal, offering new perspectives to interpreting the vibrational spectra. In fact, this approach allows obtaining two-dimensional plots, which summarize the essential features of both the hydrogen-bond network and IR spectra, resulting in a peculiar "signature" of the bifurcated interaction. 相似文献
412.
Gianni Bellocchi Christian Savini Marc Van den Bulcke Marco Mazzara Guy Van den Eede 《Accreditation and quality assurance》2010,15(11):637-641
Key to sound validation studies is the formalization and harmonization of procedures for design of experiment and interpretation
of results. International guidelines (ISO 5725, ENGL) are available for the validation of GMO detection methods, and ad-hoc validation statistics (e.g. per cent bias, repeatability and reproducibility) are used for in-house and inter-laboratory
testing and decision-making. Acceptability criteria have been set but not every situation can be covered by a preset rule;
the interpretation of results in validation largely depends on expert judgement being a matter of professional judgment and
expertise. Fuzzy logic-based techniques may be used to summarize the information obtained by independent validation statistics
and are helpful in such respect. A comprehensive indicator of method performance permits direct comparison between methods
and facilitates the evaluation of multiple, yet contradictory statistics. The European Union Reference Laboratory for GM Food
and Feed has already proposed the fuzzy principle in the context of method validation. Other studies have also proved its
applicability in other areas of GMO analysis, but the application has been limited hitherto. In this article, we review the
fuzzy logic principle and its potential to support the continuous progress of GMO science and routine laboratory analyses. 相似文献
413.
Juan Aragó Pedro M. Viruela Prof. Enrique Ortí Prof. Dr. Reyes Malavé Osuna Dr. Barbara Vercelli Dr. Gianni Zotti Dr. Víctor Hernández Prof. Juan T. López Navarrete Prof. Dr. John T. Henssler Dr. Adam J. Matzger Prof. Dr. Yoshitake Suzuki Dr. Shigehiro Yamaguchi Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(18):5481-5491
This work presents an analysis of the structural, electrochemical, and optical properties of a family of triisopropylsilyl end‐capped oligothienoacenes (TIPS‐ Tn ‐TIPS, n=4–8) by combining cyclic voltammetry, spectroscopic techniques, and quantum‐chemical calculations. TIPS‐ Tn ‐TIPS compounds form stable radical cations, and dications are only obtained for the longest oligomers (n=7 and 8). Oxidation leads to the quinoidization of the conjugated backbone, from which electrons are mainly extracted. The absorption and fluorescence spectra show partially resolved vibronic structures even at room temperature, due to the rigid molecular geometry. Two well‐resolved vibronic progressions are observed at low temperatures due to the vibronic coupling, with normal modes showing wavenumbers of ≈1525 and ≈480 cm?1. Optical absorption bands display remarkable bathochromic dispersion with the oligomer length, indicative of the extent of π conjugation. The optical properties of the oxidized compounds are characterized by in situ UV/Vis/NIR spectroelectrochemistry. The radical cation species show two intense absorption bands emerging at energies lower than in the neutral compounds. The formation of the dication is only detected for the heptamer and the octamer, and shows a new band at intermediate energies. Optical data are interpreted with the help of density functional theory calculations performed at the B3LYP/6‐31G** level, both for the neutral and the oxidized compounds. 相似文献
414.
Gianni P Barghini A Bernazzani L Mollica V 《Langmuir : the ACS journal of surfaces and colloids》2006,22(19):8001-8009
The interaction of lithium perfluorononanoate (LiPFN) with poly(ethylene glycol) (PEG) molecules of different molecular weights (300 < MW < 20000 Da) has been investigated in water at 298.15 and 308.15 K by isothermal titration calorimetry (ITC). Density, viscosity, and conductivity measurements were also performed at 298.15 K. The aggregation process of this surfactant on the PEG polymeric chain was found to be very similar to that exhibited by cesium perfluorooctanoate (CsPFO) and appears to be consistent with the necklace model. ITC titrations indicated that a fully formed LiPFN micellar cluster can be wrapped by a PEG chain having a molecular weight (MW) of approximately 3200 Da, longer than that required by the shorter perfluorooctanoate (MW approximately 2600 Da), and also suggested a stepwise mechanism for the aggregation of successive micelles. Viscosity data indicate that the formation of polymer-surfactant complexes between PEG and LiPFN involves a conformational change of the polymer. The aggregation of preformed micelles of LiPFN or CsPFO or SDS on the PEG polymeric chain always gives rise to further stabilization. 相似文献
415.
Begala M Tocco G Delogu G Meli G Picciau C Podda G 《Journal of mass spectrometry : JMS》2006,41(5):577-585
The mass spectrometric behaviour of a series of 6,6-disubstituted dibenzo(d,f)(1,3)dioxepine derivatives have been studied. The fragmentation patterns were described and discussed in detail with the aid of labelled compounds, accurate mass measurements and collisionally induced dissociation experiments performed using an ion trap. 相似文献
416.
Faralli C Pagliai M Cardini G Schettino V 《The journal of physical chemistry. B》2006,110(30):14923-14928
A Car-Parrinello molecular dynamics simulation has been performed on a solution of Br- in liquid methanol analyzing with particular attention charge transfer and polarization effects. The first solvation shell has been characterized in terms of H-bonds, and it has been found that the high polarization of the bromide gives rise to a stable solvent cage. The differences in the coordination number with the chloride can be ascribed to the ionic radius and to the stronger perturbations brought by the solvent to the bromide ion. 相似文献
417.
Dense trees are undirected graphs defined as natural extensions of trees. They are already known in the realm of graph coloring under the name of k-degenerate graphs. For a given integer k1, a k-dense cycle is a connected graph, where the degree of each vertex is greater than k. A k-dense forest F=(V,E) is a graph without k-dense cycles as subgraphs. If F is connected, then is a k-dense tree. 1-dense trees are standard trees. We have |E|k|V|−k(k+1)/2. If equality holds F is connected and is called a maximal k-dense tree. k-trees (a subfamily of triangulated graphs) are special cases of maximal k-dense trees.We review the basic theory of dense trees in the family of graphs and show their relation with k-trees. Vertex and edge connectivity is thoroughly investigated, and the role of maximal k-dense trees as “reinforced” spanning trees of arbitrary graphs is presented. Then it is shown how a k-dense forest or tree can be decomposed into a set of standard spanning trees connected through a common “root” of k vertices. All sections include efficient construction algorithms. Applications of k-dense trees in the fields of distributed systems and data structures are finally indicated. 相似文献
418.
C Falavigna M Cirlini G Galaverna S Sforza A Dossena C Dall'asta 《Journal of mass spectrometry : JMS》2012,47(9):1170-1176
Fumonisins are a family of food-borne mycotoxins with a wide spectrum of toxicological activities, produced by Fusarium verticillioides. Twenty-eight fumonisin analogues have been characterised so far, which can be separated into four main groups, identified as fumonisin A, B, C and P, being fumonisin B the most widely occurring in maize and corn-based food. In this work, major and minor fumonisin analogues produced by F. verticillioides have been determined by the development of a suitable tandem mass spectrometry procedure for target compound identification and quantification. The method has been applied to the determination of the major fumonisins in culture media of F. verticillioides and in mouldy maize. In addition to the main fumonisins produced by F. verticillioides, also secondary compounds such as FB4, FB5, FAs and FCs have been detected in both fungal liquid cultures and contaminated maize samples. The use of this method for quantification of major and minor fumonisins may be useful for an exhaustive evaluation of their occurrence and toxicological relevance in food; moreover, it may be applied for a better definition of the fumonisin biosynthetic pathways in different growing media as well as in maize. Copyright ? 2012 John Wiley & Sons, Ltd. 相似文献
419.
Antonio Arcelli Alessandro Bongini Gianni Porzi Samuele Rinaldi 《Journal of Physical Organic Chemistry》2012,25(2):132-141
The ammonolysis of three morpholine‐2,5‐dione derivatives was investigated and the mechanism ascertained by kinetic studies and theoretical calculations. The kinetics, followed by high‐performance liquid chromatography analysis, evidenced the presence of two intermediates, which were isolated and characterized. The ammonolysis occurs with a complex mechanism involving two consecutive reactions followed by two parallel ones. The second step of the whole reaction involves an anchimeric assistance of the primary amide group. The pseudo‐first‐order rate constants were calculated by appropriate equations, which describe the single steps of the process. Computational density functional theory investigations of vicinal primary amide group participation were performed using a model compound, and the transition states were generated. The theoretical calculations evidenced the essential role exerted by ammonia, which acts as a proton transfer. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
420.
Elena Botta Tullio Bressani Gianni Garbarino 《The European Physical Journal A - Hadrons and Nuclei》2012,48(3):1-64
Selected topics in strangeness nuclear physics are critically reviewed. This includes production, structure and weak decay of ??-Hypernuclei, the $\bar K$ nuclear interaction and the possible existence of $\bar K$ bound states in nuclei. Perspectives for future studies on these issues are also outlined. 相似文献