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2.
P. González D. Fernández J. Pou E. García J. Serra B. León M. Pérez-Amor T. Szörényi 《Applied Physics A: Materials Science & Processing》1993,57(2):181-185
A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO
x
films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase. 相似文献
3.
Patrick Pruja Sauveur Bnet Bernard Claudet Olivier Faugeroux Jean-Jacques Serra 《Superlattices and Microstructures》2004,35(3-6):409
Modeling the behavior of a protective coating during a thermal shock not only requires the knowledge of its own thermophysical characteristics, but also those of the coating–substrate discontinuity. According to its nature, this discontinuity can be modeled as a zero-thickness interface (thermal contact resistance) or a finite thickness layer (thermal third body). This paper presents an experimental device and two associated thermal transfer models developed in view of the microscale characterization of such discontinuities. 相似文献
4.
In the general case of multilevel Toeplitz matrices, we recently proved that any multilevel circulant preconditioner is not superlinear (a cluster it may provide cannot be proper). The proof was based on the concept of quasi-equimodular matrices, although this concept does not apply, for example, to the sine-transform matrices. In this paper, with a new concept of partially equimodular matrices, we cover all trigonometric matrix algebras widely used in the literature. We propose a technique for proving the non-superlinearity of certain frequently used preconditioners for some representative sample multilevel matrices. At the same time, we show that these preconditioners are, in a certain sense, the best among the sublinear preconditioners (with only a general cluster) for multilevel Toeplitz matrices.
5.
David Ribera Marta Giamberini Angels Serra Ana Mantecn 《Journal of polymer science. Part A, Polymer chemistry》2006,44(21):6270-6286
We reacted various dimeric, liquid‐crystalline epoxy–imine monomers, differing in the length of the central aliphatic spacer or the dipolar moments, with heptanedioic acid. The resulting systems showed a liquid‐crystalline phase in some cases, depending on the dimer and on the reaction conditions. The systems were characterized with respect to their mesomorphic properties and then were submitted to dynamic mechanical thermal analysis in both fixed‐frequency and frequency‐sweep modes in the shear sandwich configuration. The arrangement in the liquid‐crystalline phase seemed to be mainly affected both by the polarization of the mesogen and by the reaction temperature, which favored the liquid‐crystalline arrangement when it was lying in the range of stability of the dimer mesophase. In agreement with other recent literature data, dynamic mechanical thermal analysis results suggested that the presence of the mesogen directly incorporated into the main chain increased the lifetimes of the elastic modes both in the isotropic phase and in the liquid‐crystalline phase with respect to side‐chain liquid‐crystalline elastomers and that the time–temperature superposition principle did not hold through the liquid‐crystalline‐to‐isotropic transition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44:6270–6286, 2006 相似文献
6.
Roser Cervellera Xavier Ramis Josep Maria Salla Ana Mantecn Angels Serra 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2873-2882
N,N‐Dimethylaminopyridine (DMAP) was used as initiator to cure mixtures of diglycidylether of bisphenol A (DGEBA) and 1,3‐dioxan‐2‐one (TMC) or 5,5‐dimethyl‐1,3‐dioxan‐2‐one (DMTMC). The curing was studied by differential scanning calorimetry (DSC) and Fourier transform infrared in the attenuated‐total‐reflection mode (FTIR/ATR). FTIR/ATR was used to monitor the competitive reactive processes and to quantify the evolution of the groups involved in the curing. We observed the formation of five‐membered cyclic carbonates and anionic carbonate groups that remain unreacted at the chain ends. The formation of these groups was explained by the attack of the anionic propagation species on the methylene carbon of the carbonate group, which leads to an alkyl‐oxygen rupture. By performing the cure in the thermobalance we could evaluate the loss of CO2 produced in the samples containing carbonates. The kinetics were studied by DSC and analyzed with isoconversional procedures. The addition of carbonates slows down the curing rate. Thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA) experiments were used to evaluate the properties of the materials obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2873–2882, 2006 相似文献
7.
Visintin RF Lapasin R Vignati E D'Antona P Lockhart TP 《Langmuir : the ACS journal of surfaces and colloids》2005,21(14):6240-6249
A waxy crude oil which gels below a threshold temperature has been investigated under static and dynamic conditions, using a combination of rheological methods, optical microscopy, and DSC. Particular attention is given in this work to the influence of the mechanical history on gel strength and to describing the time-dependent rheological behavior. The gels display a strong dependence of the yield stress and moduli on the shear history, cooling rate, and stress loading rate. Of particular interest is the partial recovery of the gel structure after application of small stress or strain (much smaller than the critical values needed for flow onset) during cooling, which can be used to reduce the ultimate strength of the crude oil gel formed below the pour point. A second focus of this study is to further develop the physical interpretation of the mechanism by which wax crystallization produces gelation. Gelation of the waxy crude oil studied is suggested to be the result of the association between wax crystals, which produces an extended network structure, and it is shown that the system displays features common to attractive colloidal gels, for one of which, fumed silica (Aerosil 200) in paraffin oil, rheological data are reported. The colloidal gel model provides a simple and economical basis for explaining the response of the gelled oil to various mechanical perturbations and constitutes a fruitful basis from which to develop technologies for controlling the gelation phenomenon, as suggested by the rheological results reported. 相似文献
8.
In the present contribution, a new automated on-line hydride generation methodology was developed for dibutyltin and tributyltin speciation at the trace level, using a programmable temperature-vaporizing inlet followed by capillary gas chromatography coupled to mass spectrometry in the selected ion-monitoring mode acquisition (PTV-GC/MS(SIM)). The methodology involves a sequence defined by two running methods, the first one configured for hydride generation with sodium tetrahydroborate as derivatising agent and the second configured for speciation purposes, using a conventional autosampler and data acquisition controlled by the instrument's software. From the method-development experiments, it had been established that injector configuration has a great effect on the speciation of the actual methodology, particularly, the initial inlet temperature (-20 degrees C; He: 150 ml/min), injection volume (2 microl) and solvent characteristics using the solvent venting mode. Under optimized conditions, a remarkable instrumental performance including very good precision (RSD < 4%), excellent linear dynamic range (up to 50 microg/ml) and limits of detection of 0.12 microg/ml and 9 ng/ml, were obtained for dibutyltin and tributyltin, respectively. The feasibility of the present methodology was validated through assays upon in-house spiked water (2 ng/ml) and a certified reference sediment matrix (Community Bureau of Reference, CRM 462, Nr. 330 dibutyltin: 68+/-12 ng/g; tributyltin: 54+/-15 ng/g on dry mass basis), using liquid-liquid extraction (LLE) and solid-phase extraction (SPE) sample enrichment and multiple injections (2 x 5 microl) for sensitivity enhancement. The methodology evidenced high reproducibility, is easy to work-up, sensitive and showed to be a suitable alternative to replace the currently dedicated analytical systems for organotin speciation in environmental matrices at the trace level. 相似文献
9.
Antonino Arcoria Emanuele Maccarone Gaetano A. Tomaselli Rosario Calí Salvatore Currieri 《Journal of heterocyclic chemistry》1975,12(2):333-335
The second order rate constants k2 and the activation parameters for the reaction of 2-thiophenesulfonyl chloride with aniline together with solution enthalpies of the reactants have been measured in methanol, ethanol, 2-propanol, acetonitrile and acetone. The reaction rates are slower in dipolar aprotic solvents than in protic ones due to a remarkable activation negative entropy. The rate constants k2 are correlated with empirical solvent polarity parameters. The data seem in accord with a SAN reaction mechanism. 相似文献
10.
Behzad, Chartrand and Wall proposed the conjecture that any regular digraph of degreer and girthg has ordern r(g – 1) + 1. The conjecture was proved in [3] for vertex transitive graphs. For Loop Networks the conjecture is equivalent to a theorem of Shepherdson in additive number theory. We show that, except for graphs of a particular structure, Loop Networks, and in general Abelian Cayley graphs, verify the stronger inequalityn (r + 1)(g – 1) – 1. This bound is best possible.Supported by the Spanish Research Council (CICYT) under project TIC 90-0712 and Acción Integrada Hispanofrancesa, TIC 79B. 相似文献