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排序方式: 共有238条查询结果,搜索用时 15 毫秒
1.
Federica Valentini Giulia Brufani Benedetta Di Erasmo Luigi Vaccaro 《Current Opinion in Green and Sustainable Chemistry》2022
The great challenge for modern research is to define the most efficient tools to make more sustainable the industrial production and manufacturing. Among the different aspects that require attention the replacement of toxic and/or non-renewable solvents it is certainly playing a crucial role. Dealing with widely used dipolar aprotic solvents, among the different alternatives proposed in the literature γ-valerolactone (GVL) plays a pivotal role covering different application area. In this contribution, the benefits derived from the use of GVL as a circular, safe, biomass-derived reaction medium are highlighted covering most recent publications (2021). The presentation has been divided into three major sections: (i) biomass valorization, (ii) materials synthesis, manufacturing and recycle and (iii) new synthetic methodologies. 相似文献
2.
Effect of the π Bridge and Acceptor on Intramolecular Charge Transfer in Push–Pull Cationic Chromophores: An Ultrafast Spectroscopic and TD‐DFT Computational Study 下载免费PDF全文
Dr. Benedetta Carlotti Dr. Enrico Benassi Prof. Vincenzo Barone Dr. Giuseppe Consiglio Prof. Fausto Elisei Dr. Alessandra Mazzoli Prof. Anna Spalletti 《Chemphyschem》2015,16(7):1440-1450
Three (donor–π–acceptor)+ systems with a methyl pyridinium or quinolinium as the electron‐deficient group, a dimethyl amino as the electron‐donor group, and an ethylene or butadiene group as the spacer have been investigated in a joint spectroscopic and TD‐DFT computational study. A negative solvatochromism has been revealed in the absorption spectra, which implies a solution color change, and interpreted by considering the variation in the permanent dipole moment modulus and orientation upon photoexcitation. The fluorescence efficiency decreases upon increasing solvent polarity, in agreement with the excited‐state optimized geometries (planar in low‐polarity media and twisted in high‐polarity media). Femtosecond transient absorption has revealed the occurrence of a fast photoinduced intramolecular charge transfer (ICT) and the molecular factors that determine an efficient ICT. Considering the crucial role of the ICT in tuning the nonlinear optical (NLO) properties, these compounds can be considered promising NLO materials. 相似文献
3.
Davide L. Ferrario 《Archive for Rational Mechanics and Analysis》2006,179(3):389-412
Periodic and quasi-periodic solutions of the n-body problem can be found as minimizers of the Lagrangian action functional restricted to suitable spaces of symmetric paths.
The main purpose of this paper is to develop a systematic approach to the equivariant minimization for the three-body problem
in three-dimensional space. First we give a finite complete list of symmetry groups fitting to the minimization of the action,
with the property that any other symmetry group can be reduced to be isomorphic to one of these representatives. A second
step is to prove that the resulting (local and global) symmetric action-minimizers are always collisionless (when they are
not already bound to collisions). Furthermore, we prove some results which address the question of whether minimizers are
planar or non-planar; as a consequence of our theory we will give general criteria for a symmetry group to yield planar or
homographic minimizers (either homographic or not, as in the Chenciner-Montgomery eight solution). On the other hand we will
provide a rigorous proof of the existence of some interesting one-parameter families of periodic and quasi-periodic non-planar
orbits. These include the choreographic Marchal's P12 family with equal masses – together with a less-symmetric choreographic family (which anyway probably coincides with the
P12 family). 相似文献
4.
Tuning the phase transition of ZnO thin films through lithography: an integrated bottom‐up and top‐down processing 下载免费PDF全文
Luca Malfatti Alessandra Pinna Stefano Enzo Paolo Falcaro Benedetta Marmiroli Plinio Innocenzi 《Journal of synchrotron radiation》2015,22(1):165-171
An innovative approach towards the physico‐chemical tailoring of zinc oxide thin films is reported. The films have been deposited by liquid phase using the sol–gel method and then exposed to hard X‐rays, provided by a synchrotron storage ring, for lithography. The use of surfactant and chelating agents in the sol allows easy‐to‐pattern films made by an organic–inorganic matrix to be deposited. The exposure to hard X‐rays strongly affects the nucleation and growth of crystalline ZnO, triggering the formation of two intermediate phases before obtaining a wurtzite‐like structure. At the same time, X‐ray lithography allows for a fast patterning of the coatings enabling microfabrication for sensing and arrays technology. 相似文献
5.
6.
Benedetta Lisena 《Nonlinear Analysis: Real World Applications》2009,10(4):2256-2263
A delayed competition system of Lotka–Volterra type, with periodic coefficients, is considered. The topics of existence and global asymptotic stability of a periodic solution are investigated. The novelty of our results consists in the fact that they require only average conditions. In the study of global attractivity an unusual Lyapunov function is introduced. Our method takes advantage of the fact that there is no deviating argument in the negative feedback terms. 相似文献
7.
P. Español J. A. de la Torre M. Ferrario G. Ciccotti 《The European physical journal. Special topics》2011,200(1):107-129
The method of constraints in molecular dynamics is useful because it avoids the resolution of high frequency motions with
very small time steps. However, the price to pay is that both the dynamics and the statistics of a constrained system differ
from those of the unconstrained one. Instead of using constraints, we propose to dispose of high frequency motions by a coarse-graining
procedure in which fast variables are eliminated. These fast variables are thus modeled as friction and thermal fluctuations.
We illustrate the methodology with a simple model case, a diatomic molecule in a monoatomic solvent, in which the bond between
the atoms of a diatomic molecule is stiff. Although the example is very simple and does not display the interesting effects
of “wrong” statistics of the constrained system (i.e. the well-known issue connected to the Fixman potential), it is well
suited to give the proof of concept of the whole procedure. 相似文献
8.
Dr. Benedetta Carlotti Dr. Ilijana Kikaš Prof. Irena Škorić Prof. Anna Spalletti Prof. Fausto Elisei 《Chemphyschem》2013,14(5):970-981
Time‐resolved transient absorption and fluorescence spectroscopy with nano‐ and femtosecond time resolution were used to investigate the deactivation pathways of the excited states of distyrylfuran, thiophene and pyridine derivatives in several organic solvents of different polarity in detail. The rate constant of the main decay processes (fluorescence, singlet–triplet intersystem crossing, isomerisation and internal conversion) are strongly affected by the nature [locally excited (LE) or charge transfer (CT)] and selective position of the lowest excited singlet states. In particular, the heteroaromatic central ring significantly enhances the intramolecular charge‐transfer process, which is operative even in a non‐polar solvent. Both the thiophene and pyridine moieties enhance the S1→T1 rate with respect to the furan one. This is due to the heavy‐atom effect (thiophene compounds) and to the 1(π,π)*→3(n,π)* transition (pyridine compounds), which enhance the spin‐orbit coupling. Moreover, the solvent polarity also plays a significant role in the photophysical properties of these push–pull compounds: in fact, a particularly fast 1LE*→1CT* process was found for dimethylamino derivatives in the most polar solvents (time constant, τ≤400 fs), while it takes place in tens of picoseconds in non‐polar solvents. It was also shown that the CT character of the lowest excited singlet state decreased by replacing the dimethylamino side group with a methoxy one. The latter causes a decrease in the emissive decay and an enhancement of triplet‐state formation. The photoisomerisation mechanism (singlet/triplet) is also discussed. 相似文献
9.
Benedetta Marmiroli Fernando Cacho‐Nerin Barbara Sartori Javier Pérez Heinz Amenitsch 《Journal of synchrotron radiation》2014,21(1):193-202
Liquid jets are of interest, both for their industrial relevance and for scientific applications (more important, in particular for X‐rays, after the advent of free‐electron lasers that require liquid jets as sample carrier). Instability mechanisms have been described theoretically and by numerical simulation, but confirmed by few experimental techniques. In fact, these are mainly based on cameras, which is limited by the imaging resolution, and on light scattering, which is hindered by absorption, reflection, Mie scattering and multiple scattering due to complex air/liquid interfaces during jet break‐up. In this communication it is demonstrated that synchrotron small‐angle X‐ray scattering (SAXS) can give quantitative information on liquid jet dynamics at the nanoscale, by detecting time‐dependent morphology and break‐up length. Jets ejected from circular tubes of different diameters (100–450 µm) and speeds (0.7–21 m s?1) have been explored to cover the Rayleigh and first wind‐induced regimes. Various solvents (water, ethanol, 2‐propanol) and their mixtures have been examined. The determination of the liquid jet behaviour becomes essential, as it provides background data in subsequent studies of chemical and biological reactions using SAXS or X‐ray diffraction based on synchrotron radiation and free‐electron lasers. 相似文献
10.
Giovanni Ricci Giuseppe Leone Giorgia Zanchin Benedetta Palucci Alessandra Forni Anna Sommazzi Francesco Masi Stefano Zacchini Massimo Guelfi Guido Pampaloni 《Molecules (Basel, Switzerland)》2021,26(13)
Some novel cobalt diphenylphosphine complexes were synthesized by reacting cobalt(II) chloride with (2-methoxyethyl)diphenylphosphine, (2-methoxyphenyl)diphenylphosphine, and 2-(1,1-dimethylpropyl)-6-(diphenylphosphino)pyridine. Single crystals suitable for X-ray diffraction studies were obtained for the first two complexes, and their crystal structure was determined. The novel compounds were then used in association with methylaluminoxane (MAO) for the polymerization of 1,3-butadiene, and their behavior was compared with that exhibited in the polymerization of the same monomer by the systems CoCl2(PnPrPh2)2/MAO and CoCl2(PPh3)2/MAO. Some significant differences were observed depending on the MAO/Co ratio used, and a plausible interpretation for such a different behavior is proposed. 相似文献