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101.
Bovi D Mezzetti A Vuilleumier R Gaigeot MP Chazallon B Spezia R Guidoni L 《Physical chemistry chemical physics : PCCP》2011,13(47):20954-20964
Carotenoids are employed in light-harvesting complexes of dinoflagellates with the two-fold aim to extend the spectral range of the antenna and to protect it from radiation damage. We have studied the effect of the environment on the vibrational properties of the carotenoid peridinin in different solvents by means of vibrational spectroscopies and QM/MM molecular dynamics simulations. Three prototypical solvents were considered: cyclohexane (an apolar/aprotic solvent), deuterated acetonitrile (a polar/aprotic solvent) and methanol (a polar/protic solvent). Thanks to effective normal mode analysis, we were able to assign the experimental Raman and IR bands and to clarify the effect of the solvent on band shifts. In the 1500-1650 cm(-1) region, seven vibrational modes of the polyene chain were identified and assigned to specific molecular vibrations. In the 1700-1800 cm(-1) region a strong progressive down-shift of the lactonic carbonyl frequency is observed passing from cyclohexane to methanol solutions. This has been rationalized here in terms of solvent polarity and solute-solvent hydrogen bond interactions. On the basis of our data we propose a classification of non-equivalent peridinins in the Peridinin-Chlorophyll-Proteins, light-harvesting complexes of dinoflagellates. 相似文献
102.
Paarmann A Lima M Chelli R Volkov VV Righini R Miller RJ 《Physical chemistry chemical physics : PCCP》2011,13(23):11351-11358
The linear and two-dimensional infrared (2DIR) responses of the amide I vibrational mode in liquid formamide are investigated experimentally and theoretically using molecular dynamics simulations. The recent method based on the numerical integration of the Schr?dinger equation is employed to calculate the 2DIR spectra. Special attention is devoted to the interplay of the structural dynamics and the excitonic nature of the amide I modes in determining the optical response of the studied system. In particular, combining experimental data, simulated spectra and analysis of the simulated atomic trajectory in terms of a transition dipole coupling model, we provide a convincing explanation of the peculiar features of the 2DIR spectra, which show a substantial increase of the antidiagonal bandwidth with increasing frequency. We point out that, at variance with liquid water, the 2DIR spectral profile of formamide is determined more by the excitonic nature of the vibrational states than by the fast structural dynamics responsible for the frequency fluctuations. 相似文献
103.
Euler’s celebrated buckling formula gives the critical load N for the buckling of a slender cylindrical column with radius B and length L as
N/(p3B2)=(E/4)(B/L)2,N/(\pi^3B^2)=(E/4)(B/L)^2, 相似文献
104.
Luigi Abis Edoardo Merlo Riccardo Po' 《Journal of Polymer Science.Polymer Physics》1995,33(4):691-697
Amorphous (1) and semicrystalline (2) samples of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) have been investigated by cross-polarization/magic angle spinning (CP/MAS) 13C NMR at 26°C (1 and 2), 100°C (1) and 120°C (2) in order to study the phase structure and the local motion of polymer chain segments at temperatures below and close to Tg (120°C). The lineshape of the ethylene unit 13C signal in sample 2 is consistent with the presence of two components which were assigned to trans and gauche conformations. The first component arises mainly from the crystalline regions and the second one from the amorphous part. Cross-polarization curves were traced by changing the contact time between carbon and proton reservoirs. TCH (cross relaxation time) and proton T1p (spin-lattice relaxation time in the rotating frame) values were obtained as best fit parameters by fitting calculated curves to the experimental data. All 13C NMR data are consistent with the presence of highly rigid ethylene units in both semicrystalline and amorphous samples within the temperature range (T) investigated. This result is in disagreement with the 1H NMR wide line spectra which showed a noticeable narrowing of the linewidth with increasing temperature in the same range, hence indicating a great mobility of the chain segments. To account for this discrepancy a qualitative model based on the existence of two distinct dynamic regions, one where motion is highly restricted and the other one where large reorientations of ethylene group torsional angles take place, is suggested. The NMR results led to the conclusion that three structural phases are present in PEN: crystalline, very rigid amorphous, and very mobile amorphous. © 1995 John Wiley & Sons, Inc. 相似文献
105.
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107.
Riccardo Salvati Manni 《Proceedings of the American Mathematical Society》2007,135(5):1241-1247
In this paper we consider varieties defined by Riemann-Mumford's relations. An irreducible component of these varieties is related to Siegel modular varieties. We prove that in most cases Riemann-Mumford varieties are not irreducible.
108.
Plasma treatments in Radio Frequency Glow Discharges fed with NH3−H2 mixtures have been performed for modifying polyethylene surfaces. Treatment kinetics and the role of species present in the
glow have been investigated. Actinometric Optical Emission Spectroscopy has been utilized as a plasma diagnostic technique.
Electron Spectroscopy for Chemical Analysis has been utilized for studying surface composition of treated substrates, which
have been examined both astreated and after derivatization of amine-functionalities with 4-trifluoromethylbenzaldehyde vapors.
It has been found that experimental plasma parameters and plasma density of active species can be controlled to achieve selective
grafting of-NH2 among all other nitrogen-containing groups. 相似文献
109.
Riccardo Zecchina 《Pramana》2005,64(6):1161-1173
The combinatorial problem of satisfying a given set of constraints that depend on N discrete variables is a fundamental one in optimization and coding theory. Even for instances of randomly generated problems, the question “does there exist an assignment to the variables that satisfies all constraints?” may become extraordinarily difficult to solve in some range of parameters where a glass phase sets in. We shall provide a brief review of the recent advances in the statistical mechanics approach to these satisfiability problems and show how the analytic results have helped to design a new class of message-passing algorithms — the survey propagation (SP) algorithms — that can efficiently solve some combinatorial problems considered intractable. As an application, we discuss how the packing properties of clusters of solutions in randomly generated satisfiability problems can be exploited in the design of simple lossy data compression algorithms. 相似文献
110.
Daniele Simoni Giuseppe GianniniPier Giovanni Baraldi Romeo RomagnoliMarinella Roberti Riccardo RondaninRiccardo Baruchello Giuseppina GrisoliaMarcello Rossi Danilo MirizziFrancesco Paolo Invidiata Stefania GrimaudoManlio Tolomeo 《Tetrahedron letters》2003,44(14):3005-3008
A double Suzuki cross-coupling protocol has been devised as a practical route to a variety of terphenyls. Good chemoselectivity was observed. Unsymmetrically substituted triphenylenes were also easily prepared. 相似文献
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