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141.
We examine baryonic matter at a quark chemical potential of the order of the confinement scale μ(q)~Λ(QCD). In this regime, quarks are supposed to be confined but baryons are close to the "tightly packed limit" where they nearly overlap in configuration space. We show that this system will exhibit a percolation phase transition when varied in the number of colors N(c): at high N(c), large distance correlations at the quark level are possible even if the quarks are essentially confined. At low N(c), this does not happen. We discuss the relevance of this for dense nuclear matter, and argue that our results suggest a new "phase transition," varying N(c) at constant μ(q). 相似文献
142.
Cristiano Bocci Luca Chiantini Giorgio Ottaviani 《Annali di Matematica Pura ed Applicata》2014,193(6):1691-1702
We prove that the general tensor of size \(2^n\) and rank \(k\) has a unique decomposition as the sum of decomposable tensors if \(k\le 0.9997\frac{2^n}{n+1}\) (the constant 1 being the optimal value). Similarly, the general tensor of size \(3^n\) and rank \(k\) has a unique decomposition as the sum of decomposable tensors if \(k\le 0.998\frac{3^n}{2n+1}\) (the constant 1 being the optimal value). Some results of this flavor are obtained for tensors of any size, but the explicit bounds obtained are weaker. 相似文献
143.
Giorgio Donati Nicola Durante Alessandro Siciliano 《Designs, Codes and Cryptography》2014,72(1):135-139
The linear collineation group of a classical unital of $\mathrm{PG}(2,q^2)$ contains a group of homologies of order $q+1$ . In this paper we prove that if $\mathcal{U }$ is a unital of PG $(2,q^2)$ stabilized by a homology group of order $q+1$ and $q$ is a prime number, then $\mathcal{U }$ is classical. 相似文献
144.
Mauro Gaggero Giorgio Gnecco Marcello Sanguineti 《Computational Optimization and Applications》2014,58(1):31-85
Stochastic optimization problems with an objective function that is additive over a finite number of stages are addressed. Although Dynamic Programming allows one to formally solve such problems, closed-form solutions can be derived only in particular cases. The search for suboptimal solutions via two approaches is addressed: approximation of the value functions and approximation of the optimal decision policies. The approximations take on the form of linear combinations of basis functions containing adjustable parameters to be optimized together with the coefficients of the combinations. Two kinds of basis functions are considered: Gaussians with varying centers and widths and sigmoids with varying weights and biases. The accuracies of such suboptimal solutions are investigated via estimates of the error propagation through the stages. Upper bounds are derived on the differences between the optimal value of the objective functional and its suboptimal values corresponding to the use at each stage of approximate value functions and approximate policies. Conditions under which the number of basis functions required for a desired approximation accuracy does not grow “too fast” with respect to the dimensions of the state and random vectors are provided. As an example of application, a multidimensional problem of optimal consumption under uncertainty is investigated, where consumers aim at maximizing a social utility function. Numerical simulations are provided, emphasizing computational pros and cons of the two approaches (i.e., value-function approximation and optimal-policy approximation) using the above-mentioned two kinds of basis functions. To investigate the dependencies of the performances on dimensionality, the numerical analysis is performed for various numbers of consumers. In the simulations, discretization techniques exploiting low-discrepancy sequences are used. Both theoretical and numerical results give insights into the possibility of coping with the curse of dimensionality in stochastic optimization problems whose decision strategies depend on large numbers of variables. 相似文献
145.
146.
Starting from the Staudinger [2+2] cycloaddition between the 1-azadiene 1 and acetoxyacetylketene, generated in situ from acetoxyacetyl chloride, we developed a seven-step synthesis of the novel azeto[3′,4′:2,3]pyrano[4,5-c]pyrazole skeleton 9 in both racemic and enantiopure forms. Silver carbonate treatment of the functionalised hydrazonoyl chloride 7 promoted in situ generation of the corresponding nitrilimine 8, which underwent a clean, stereoselective cycloaddition to the target tricyclic β-lactam 9. The key step of the synthetic pathway leading to enantiopure 9 was the production of the enantiopure azetidinone (3R,4S)-3 by enzymatic resolution with Amano Lypase PS of the racemic precursor (3S1,4R1)-2. 相似文献
147.
Pier Giorgio Righetti 《Separation & Purification Reviews》2013,42(1):23-72
Electrophoretic mobility has been used for years as a basis for separation and characterization of proteins. The resolving power of conventional electrophoresis is limited, and the characterization by mobility is not unique because of the dependence of the protein mobilities on the pH and ionic strength of the buffers. 相似文献
148.
Pier Luigi Barili Maria Camilla Bergonzi Giancarlo Berti Giorgio Catelani Felicia D'Andrea Francesco De Rensis 《Journal of carbohydrate chemistry》2013,32(9):1037-1049
ABSTRACT The title compound, previously unreported in either enantioform, and its 2,6-di-O-benzyl derivative have been synthesized through a stereocontrolled epimerization at C-2 of 6-O-protected methyl 3,4-O-isopropylidene-5-C-methoxy-β-D-galactopyranosides. The epimerization, performed through a high yielding sequence of oxidation-reduction owing to the cooperative role of the equatorial C-1 aglycon and the steric hindrance of the isopropylidene group, turned out to be completely diastereoselective. Whereas the unprotected L-ribo-hexos-5-ulose exists, as proved by NMR in D2O, in five main tautomeric forms in a ratio of about 4:2:2:1:1, only two anomeric 1,4-furanosic forms are present at equilibrium in its 2,6-di-O-benzyl derivative, in ratios ranging from 10:1 to 7:3, depending on the prevalence of D2O or CD3CN in the solvent mixture. 相似文献
149.
Pier Luigi Barili Giancarlo Berti Giorgio Catelani Felicia D'Andrea Francesco De Rensis Giampaolo Goracci 《Journal of carbohydrate chemistry》2013,32(8):1167-1180
Abstract The unreported title compound and its 2,6-di-O-benzyl derivative have been prepared from methyl β-D-galactopyranoside through a sequence involving the bisglycoside methyl 2,6-di-O-benzyl-5-O-methoxv-β-D-galactopyranoside 8, the precursor of L-orabino-hexos-5-ulose, that was converted to the L-lyxo series by inversion at C-3. The inversion was achieved in acceptable yields by selective triflation, followed by displacement with benzoate, and by an oxidation/reduction sequence. Whereas 2,5-di-O-benzyl-L-lyxo-hexos-5-ulose exists entirely as a mixture of the two anomeric 1,4-furanosic forms, the unprotected hexos-5-ulose involves at equilibrium in CD3CN/D2O at least eight tautomers, one of which is predominant. 相似文献
150.
Giorgio Metafune Diego Pallara 《Journal of Mathematical Analysis and Applications》2011,377(1):170-179
Given a second-order elliptic operator on Rd, with bounded diffusion coefficients and unbounded drift, which is the generator of a strongly continuous semigroup on L2(Rd) represented by an integral, we study the time behavior of the integral kernel and prove estimates on its decay at infinity. If the diffusion coefficients are symmetric, a local lower estimate is also proved. 相似文献