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951.
952.
Marta Susana Moreno Jorge Marcelo Montagna 《Mathematical and Computer Modelling》2009,49(7-8):1372-1385
A general multiperiod model to optimize simultaneously production planning and design decisions applied to multiproduct batch plants is proposed. This model includes deterministic seasonal variations of costs, prices, demands and supplies. The overall problem is formulated as a mixed-integer linear programming model by applying appropriate linearizations of non-linear terms. The performance criterion is to maximize the net present value of the profit, which comprises sales, investment, inventories, waste disposal and resources costs, and a penalty term accounting for late deliveries. A noteworthy feature of this approach is the selection of unit dimensions from the available discrete sizes, following the usual procurement policy in this area. The model simultaneously calculates the plant structure (parallel units in every stage, and allocation of intermediate storage tanks), and unit sizes, as well as the production planning decisions in each period (stocks of both product and raw materials, production plans, policies of sales and procurement, etc.). 相似文献
953.
Marcelo R. Ubriaco 《Letters in Mathematical Physics》1991,21(4):293-300
A formulation of field quantization of bosonic and fermionic fields defined on the disconnected field of p-acid numbers Q
p is given. We introduce a canonical quantization procedure and exhibit the properties of the nonlocal operators present in the action. Its relevance to string theory on Q
p is also discussed. 相似文献
954.
Marcelo Samuel Berman 《International Journal of Theoretical Physics》1990,29(12):1419-1421
Berman and Som's solution for a Brans-Dicke cosmology with time-dependent cosmological term, Robertson-Walker metric, perfect fluid, and perfect gas law of state solves the horizon, homogeneity, and isotropy problems without requiring any unnatural fine tuning in the very early universe, thus being an alternative model to inflation. The model also does not need recourse to quantum cosmology, and solves the flatness and magnetic monopole problems. 相似文献
955.
Tomazela DM Moraes LA Pilli RA Eberlin MN D'Oca MG 《The Journal of organic chemistry》2002,67(14):4652-4658
The intrinsic gas-phase reactivity of cyclic N-acyliminium ions in Mannich-type reactions with the parent enol silane, vinyloxytrimethylsilane, has been investigated by double- and triple-stage pentaquadrupole mass spectrometric experiments. Remarkably distinct reactivities are observed for cyclic N-acyliminium ions bearing either endocyclic or exocyclic carbonyl groups. NH-Acyliminium ions with endocyclic carbonyl groups locked in s-trans forms participate in a novel tandem N-acyliminium ion reaction: the nascent adduct formed by simple addition is unstable and rearranges by intramolecular trimethylsilyl cation shift to the ring nitrogen, and an acetaldehyde enol molecule is eliminated. An NSi(CH(3))(3)-acyliminium ion is formed, and this intermediate ion reacts with a second molecule of vinyloxytrimethylsilane by simple addition to form a stable acyclic adduct. N-Acyl and N,N-diacyliminium ions with endocyclic carbonyl groups, for which the s-cis conformation is favored, react distinctively by mono polar [4(+) + 2] cycloaddition yielding stable, ressonance-stabilized cycloadducts. Product ions were isolated via mass-selection and structurally characterized by triple-stage mass spectrometric experiments. B3LYP/6-311G(d,p) calculations corroborate the proposed reaction mechanisms. 相似文献
956.
Magnasco MO 《Physical review letters》2003,90(5):058101
The tuning curve of the cochlea measures how intense an input is required to elicit a given output level as a function of the frequency. It is a fundamental object of auditory theory, for it summarizes how to identify sounds on the basis of the cochlear output. A simple model is presented showing that only two elements are sufficient for establishing the cochlear tuning curve: a broadly tuned traveling wave, moving unidirectionally from high to low frequencies, and a set of mechanosensors poised at the threshold of an oscillatory (Hopf) instability. These two components generate the various frequency-response regimes needed for a cochlear tuning curve with a high slope. 相似文献
957.
Costa L Vega M Díaz Y Marcelo JL Hernández JM Martino T 《Journal of chromatography. A》2001,907(1-2):173-179
A reversed-phase liquid chromatographic method was applied to study the stability of thimerosal in Cuban recombinant hepatitis B vaccine samples stored under different temperature conditions. Salicylic acid was used as internal standard, it allowed one to determine the thimerosal in the presence of its degradation products. Good stability of the preservative was demonstrated in vaccine samples for as long as 6 years. The same results were obtained when the vaccine samples were incubated at 37 and 45 degrees C during 30 days. The results were in compliance with the microbiological test for determining the effectiveness of antimicrobial preservative in these samples. 相似文献
958.
Marcelo B. Ribeiro 《General Relativity and Gravitation》2001,33(10):1699-1730
This paper presents an analysis of the smoothness problem in cosmology by focussing on the ambiguities originated in the simplifying hypotheses aimed at observationally verifying if the large-scale distribution of galaxies is homogeneous, and conjecturing that this distribution should follow a fractal pattern, in the sense of having a power-law type average density profile, in perturbed standard cosmologies. This is due to a geometrical effect, appearing when certain types of average densities are calculated along the past light cone. The paper starts by reviewing the argument concerning the possibility that the galaxy distribution follows such a scale invariant pattern, and the premises behind the assumption that the spatial homogeneity of standard cosmology can be observable. Next, it is argued that in order to discuss observable homogeneity one needs to make a clear distinction between local and average relativistic densities, and showing how the different distance definitions strongly affect them, leading the various average densities to display asymptotically opposite behaviours. Then the paper revisits Ribeiro's (1995) results, showing that in a fully relativistic treatment some observational average densities of the flat Friedmann model are not well defined at z 0.1, implying that at this range average densities behave in a fundamentally different manner as compared to the linearity of the Hubble law, well valid for z < 1. This conclusion brings into question the widespread assumption that relativistic corrections can always be neglected at low z. It is also shown how some key features of fractal cosmologies can be found in the Friedmann models. In view of those findings, it is suggested that the so-called contradiction between the cosmological principle, and the galaxy distribution forming an unlimited fractal structure, may not exist. 相似文献
959.
We review the construction of topological Yang–Mills theory (TYMT) from the point of view of an operator satisfying d = [, b] with b the BRST operator. We focus our attention on a situation in which [, d] 0 and show how this leads us to consider a more general derivative ~d = b + d +
k 2
k
1–k
. 相似文献
960.
We study the effects of anisotropic pressure on the properties of spherically symmetric, gravitationally bound objects. We consider the full general-relativistic treatment of this problem and obtain exact solutions for various forms of the equation of state connecting the radial and tangential pressures. It is shown that pressure anisotropy can have significant effects on the structure and properties of stellar objects. In particular, the maximum value of 2M / R can approach unity (2M / R < 8/9 for isotropic objects) and the surface redshift can be arbitrarily large. 相似文献