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991.
992.
Arturo Echeverría-Enríquez Jesús Marín-Solano Miguel C. Muñoz-Lecanda Narciso Román-Roy 《Acta Appl Math》2003,77(1):1-40
The time-evolution K-operator (or relative Hamiltonian vector field) in mechanics is a powerful tool which can be geometrically defined as a vector field along the Legendre map. It has been extensively used by several authors for studying the structure and properties of the dynamical systems (mainly the nonregular ones), such as the relation between the Lagrangian and Hamiltonian formalisms, constraints, and higher-order mechanics. This paper is devoted to defining a generalization of this operator for field theories, in a covariant formulation. In order to do this, we use sections along maps, in particular multivector fields (skew-symmetric contravariant tensor fields of order greater than 1), jet fields and connection forms along the Legendre map. As a relevant result, we use these geometrical objects to obtain the solutions of the Lagrangian and Hamiltonian field equations, and the equivalence among them (specially for nonregular field theories). 相似文献
993.
Atomistic Monte Carlo (MC) simulations have been used to study a thermally induced phase transition in poly(alpha-octadecyl-beta,L-aspartate). Simulations were performed by using the parallelized version of Configurational Bias MC algorithm adapted to study comblike polymers. A total of 1.15. 10(6) steps were carried out for a molecular system constituted by 6240 atoms/pseudoatoms. Results were consistent with available experimental observations. The limitations of atomistic simulations to study large length-scale phenomena are discussed. 相似文献
994.
Simon G. Bott Trinidad Mu?oz Michael G. Richmond 《Journal of chemical crystallography》2003,33(7):521-525
Abstract List
Index abstracts 相似文献995.
Garrido Frenich A Martínez Galera M Gil García MD Martínez Vidal JL Muñoz de la Peña A Salinas F 《Talanta》1998,46(6):1329-1340
Multi-wavelength detectors offer improved detection capabilities for liquid chromatographic methods, but require multivariate approaches to utilise all the available information. The photodiode-array detector in high-performance liquid chromatography (HPLC) generates a three-dimensional data matrix, which is conventionally presented as an isometric projection or a contour plot. In this work, a new graphical technique is described for improving the quantitative results obtained from HPLC, using the available spectrochromatographic information in both the time and wavelength domains. The technique consists of performing cross-sections through the data matrix to obtain the maximum analytical information for each of the analytes. Hence, the resolution of overlapping peaks and the sensitivity in the determination are optimised. In order to demonstrate the validity and simplicity of the approach, the method has been applied to the resolution of synthetic mixtures of iprodione, procymidone and chlorothalonil. Also, the method has been satisfactorily applied to the simultaneous determination of the pesticides in environmental groundwater samples. 相似文献
996.
997.
用改装的国产CDR-1型DSC仪研究了苯基缩水甘油醚(PGE)和环氧树脂(E-51)以双-[4-(二苯硫翁基)苯基]硫-二-六氟化磷引发的光聚合。研究了引发剂浓度,光强,温度等因素对聚合反应的影响。对于PGE,聚合速率与引发剂浓度的0.90次方,与光强的0.78次方成比例。对于E-51,聚合速率与引发剂浓度的0.87次方式成比例,而与光强的关系则比较复杂。温度分别超过70℃(对PGE)或80℃(对 相似文献
998.
Jin Deog Song Mu Shik Jhon 《Journal of polymer science. Part A, Polymer chemistry》1993,31(7):1687-1695
The interaction between Na+ and polymer was studied by 23Na-NMR for the aqueous solution of P(HEMA-co-MAANa), sodium salt of poly(2-hydroxyethyl methacrylate-co-methacrylic acid), as a function of the polymer concentration, charge density of the polymer chain, and temperature. The NMR line width of 23Na-NMR in 1% (w/v) aqueous solution of the P(HEMA-co-MAANa) narrowed with increasing temperature due to the rapid exchange of Na+ between free and polymer-bound states with a rate of exchange exceeding the quadrupolar relaxation rate in the latter state. At high concentrations of the polymer above 1.0% (w/v) at 298 K, the 23Na-NMR relaxation fits for a single Lorentzian due to the rapid exchange between two Na+ states. However, it follows a biexponential decay of magnetization in dilute solutions of polymer. The biexponential decay character of relaxation increased with the increase of the fraction of the MAANa monomer unit on the polymer chain. This feature of 23Na-NMR relaxation was used to deduce the correlation time (τc), the degree of binding (pB), and the quadrupole coupling constants (X) of the polymer-bound counterion. The χ and τc values show that the mobilities of the polymer chain are correlated with the motion of Na+ in aqueous solution of the polymer and there is a small degree of the specific binding between COO? and Na+. No evidence in support of the intramolecular conformational change by the charge density variation in P(HEMA-co-MAANa) was obtained. © 1993 John Wiley & Sons, Inc. 相似文献
999.
the ethylenediamine/pyridine-2-carbaldehyde/copper(I) system is used in a new spectrophotometric method for the determination of ethylenediamine. The batch procedure involves the formation of an orange chelate between the Schiff's base and copper(I) ions at pH 8.5 (borate buffer) and measurement of the absorbances at 475 nm against water after 10/2-15 min; Beer's law is obeyed over the range 0.5/2-11.2 μg ml?1 and the molar absorptivity is 6.21 × 103 l mol?1 cm?1. Tolerance limits for different amines [36] and other organic compounds [12] are reported. In the optimized flow-injection system, ethylenediamine (1.4/2-84.6 μg ml?1 is determined at a sample throughput of 55 h?1. The method is sensitive and selective and is satisfactory for the determination of the diamine in aminophylline and pharmaceutical preparations (ethylenediamine contents from 0.031 to 3.23%) with relative errors ranging from ?7.4 to +11.1% and relative standard deviations of about 0.65% for both procedures. 相似文献
1000.
Speciation of inorganic selenium using hydride generation method is a widespread analytical method nowadays. However, a reduction step of Se(VI) to Se(IV) is necessary as the hydride-forming species is HSeO(3)(-) (oxydation state+IV). This paper describes the development of a batch assisted microwave system allowing a rapid (<5 min) conversion of Se(VI) to Se(IV). Hydride generation is performed by a flow injection system and detection by ICP/MS. Detection limits of 6 and 8 pg for Se(IV) and for Se(VI) (by using a sample loop of 200 mul) respectively have been achieved. This method has been validated by participating in a European certification exercise for inorganic Se speciation in aqueous solutions. 相似文献