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排序方式: 共有473条查询结果,搜索用时 15 毫秒
71.
Berzas Nevado JJ Rodríguez Martín-Doimeadios RC Guzmán Bernardo FJ Jiménez Moreno M 《Analytica chimica acta》2008,621(1):30-37
Laser tomography techniques were used in order to make visible the flow patterns induced by ascending bubbles in flutes poured with champagne. The stability of flow patterns was investigated in flutes showing natural (without any specific surface treatment) as well as artificial effervescence (i.e., engraved at their bottom), all along the first 15 min after pouring. Engravement conditions were found to strongly influence the kinetics and the stability with time of the mixing flow phenomena found in champagne glasses. 相似文献
72.
Kassem Mustapha Maher Nour Bernardo Cockburn 《Advances in Computational Mathematics》2016,42(2):377-393
We study the hybridizable discontinuous Galerkin (HDG) method for the spatial discretization of time fractional diffusion models with Caputo derivative of order 0 < α < 1. For each time t ∈ [0, T], when the HDG approximations are taken to be piecewise polynomials of degree k ≥ 0 on the spatial domain Ω, the approximations to the exact solution u in the L ∞(0, T; L 2(Ω))-norm and to ?u in the \(L_{\infty }(0, \textit {T}; \mathbf {L}_{2}({\Omega }))\)-norm are proven to converge with the rate h k+1 provided that u is sufficiently regular, where h is the maximum diameter of the elements of the mesh. Moreover, for k ≥ 1, we obtain a superconvergence result which allows us to compute, in an elementwise manner, a new approximation for u converging with a rate h k+2 (ignoring the logarithmic factor), for quasi-uniform spatial meshes. Numerical experiments validating the theoretical results are displayed. 相似文献
73.
A Bayesian statistical approach is introduced to assess experimental data from the analyses of radionuclide activity concentration in environmental samples (low activities). A theoretical model has been developed that allows the use of known prior information about the value of the measurand (activity), together with the experimental value determined through the measurement. The model has been applied to data of the Inter-laboratory Proficiency Test organised periodically among Spanish environmental radioactivity laboratories that are producing the radiochemical results for the Spanish radioactive monitoring network. A global improvement of laboratories performance is produced when this prior information is taken into account. The prior information used in this methodology is an interval within which the activity is known to be contained, but it could be extended to any other experimental quantity with a different type of prior information available. 相似文献
74.
Pérez Pavón JL del Nogal Sánchez M Fernández Laespada ME Moreno Cordero B 《Journal of chromatography. A》2007,1175(1):106-111
A sensitive method is presented for the fast analysis of seven fuel oxygenates (methanol, ethanol, tert-butyl alcohol (TBA), methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME) and diisopropyl ether (DIPE)) and benzene, toluene, ethylbenzene and p-xylene (BTEX) in water samples. The applicability of a headspace (HS) autosampler in combination with a GC device equipped with a programmable temperature vaporizer (PTV) and a MS detector is explored. The proposed method achieves a clear improvement in sensitivity with respect to conventional headspace methods due to the use of the PTV. Two different packed liners with materials of different trapping strengths (glass wool and Tenax-TA) were compared. The benefits of using Tenax-TA instead of glass wool as packed material for the measurement of the 11 compounds emerged as better signal-to-noise ratios and hence better detection limits. The proposed method is extremely sensitive. The limits of detection are of the order of ng/L for six of the compounds studied and of the order of microg/L for the rest, with the exception of the most polar and volatile compound: methanol. Precision (measured as the relative standard deviation for a level with an S/N ratio close to 3) was equal to or lower than 15% in all cases. The method was applied to the determination of the analytes in natural matrixes (tap, river and sea water) and the results obtained can be considered highly satisfactory. The methodology has much lower detection limits than the concentration limits proposed in drinking water by the US Environmental Protection Agency (EPA) and the European Union for compounds under regulation. 相似文献
75.
76.
77.
This article reports an efficient method to characterize constitutive responses based on multiscale modeling for fluid flow in heterogeneous media based on the concept of representative volume element (RVE). Between different scales, it is considered as the basic principles for down-scaling information the conservation of velocity and of the strain rate tensor. Within this context, we formulate (i) the problem to be solved at the micro-scale, (ii) the up-scaling procedure which involves homogenization rules, and (iii) the generalized principle of multiscale virtual power. The complete theory for constitutive modeling is revisited and shown that when employing multiscale analysis among the suitable variational arguments we are able to obtain, in a straightforward manner, new constitutive behavior between kinematic motions and actions. Some examples of application of fluid flow in heterogeneous media with obstacles are presented to show the consequences of the proposed approach. 相似文献
78.
Nicola Pizzolato Davide Valenti Dominique Persano Adorno Bernardo Spagnolo 《Central European Journal of Physics》2009,7(3):541-548
The evolutionary dynamics of a system of cancerous cells in a model of chronic myeloid leukemia (CML) is investigated by a
statistical approach. Cancer progression is explored by applying a Monte Carlo method to simulate the stochastic behavior
of cell reproduction and death in a population of blood cells which can experience genetic mutations. In CML front line therapy
is represented by the tyrosine kinase inhibitor imatinib which strongly affects the reproduction of leukemic cells only. In
this work, we analyze the effects of a targeted therapy on the evolutionary dynamics of normal, first-mutant and cancerous
cell populations. Several scenarios of the evolutionary dynamics of imatinib-treated leukemic cells are described as a consequence
of the efficacy of the different modelled therapies. We show how the patient response to the therapy changes when a high value
of the mutation rate from healthy to cancerous cells is present. Our results are in agreement with clinical observations.
Unfortunately, development of resistance to imatinib is observed in a fraction of patients, whose blood cells are characterized
by an increasing number of genetic alterations. We find that the occurrence of resistance to the therapy can be related to
a progressive increase of deleterious mutations.
相似文献
79.
José Luis Pérez Pavón Miguel del Nogal Sánchez María Esther Fernández Laespada Bernardo Moreno Cordero 《Analytical and bioanalytical chemistry》2009,394(5):1463-1470
A sensitive method for the fast analysis of filbertone in spiked olive oil samples is presented. The applicability of a headspace
(HS) autosampler in combination with a gas chromatograph (GC) equipped with a programmable temperature vaporizer (PTV) and
a mass spectrometric (MS) detector is explored. A modular accelerated column heater (MACHTM) was used to control the temperature of the capillary gas chromatography column. This module can be heated and cooled very
rapidly, shortening total analysis cycle times to a considerable extent. The proposed method does not require any previous
analyte extraction, filtration and preconcentration step, as in most methods described to date. Sample preparation is reduced
to placing the olive oil sample in the vial. This reduces the analysis time and the experimental errors associated with this
step of the analytical process. By using headspace generation, the volatiles of the sample are analysed without interference
by the non-volatile matrix, and by using injection in solvent-vent mode at the PTV inlet, most of the compounds that are more
volatile than filbertone are purged and the matrix effect is minimised. Use of a liner packed with Tenax-TA? allowed the compound
of interest to be retained during the venting process. The limits of detection and quantification were as low as 0.27 and
0.83 μg/L, respectively, and precision (measured as the relative standard deviation) was 5.7%. The method was applied to the
determination of filbertone in spiked olive oil samples and the results revealed the good accuracy obtained with the method. 相似文献
80.
Matching Points with Squares 总被引:1,自引:0,他引:1
Bernardo M. Ábrego Esther M. Arkin Silvia Fernández-Merchant Ferran Hurtado Mikio Kano Joseph S. B. Mitchell Jorge Urrutia 《Discrete and Computational Geometry》2009,41(1):77-95
Given a class
of geometric objects and a point set P, a
-matching of P is a set
of elements of
such that each C
i
contains exactly two elements of P and each element of P lies in at most one C
i
. If all of the elements of P belong to some C
i
, M is called a perfect matching. If, in addition, all of the elements of M are pairwise disjoint, we say that this matching M is strong. In this paper we study the existence and characteristics of
-matchings for point sets in the plane when
is the set of isothetic squares in the plane. A consequence of our results is a proof that the Delaunay triangulations for
the L
∞ metric and the L
1 metric always admit a Hamiltonian path. 相似文献