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21.
A new technique is proposed for generating a tight dark focal spot surrounded by uniform light intensity in all directions. It is based on a single focusing lens illuminated from one side, hence the alignment sensitivities associated with 4π methods are eliminated. Such a beam can be useful, e.g. as a dark atomic trap, and as the erase beam in three dimensional super-resolution fluorescence microscopy. 相似文献
22.
Nixon M Friedman M Ronen E Friesem AA Davidson N Kanter I 《Physical review letters》2011,106(22):223901
We experimentally investigate the phase dynamics of laser networks with homogenous time-delayed mutual coupling and establish the fundamental rules that govern their state of synchronization. We identified a specific substructure that imposes its synchronization state on the entire network and show that for any coupling configuration the network forms at most two synchronized clusters. Our results indicate that the synchronization state of the network is a nonlocal phenomenon and cannot be deduced by decomposing the network into smaller substructures, each with its individual synchronization state. 相似文献
23.
The relation between Coulomb displacement energies,ΔE c , andΔr=r n -r p , the difference between the rms radii of neutrons and protons in nuclei, is investigated within the energy density formalism (EDF). The variational equation, obtained by minimizing the Coulomb plus symmetry energies, is solved assuming the symmetry interaction is a simple functional of the local nuclear matter density. Varying parameters of the model, rather unique relation betweenΔE c andΔr is obtained (within ±50 keV).ΔE c isindependent ofr ex, the rms radius of the excess neutrons distribution. Using the experimental values ofr p and adjusting the model to reproduce the recent data onΔr (Δr∽~0.05 fm for48Ca and208Pb), which are significantly smaller than those obtained from current Hartree-Fock calculations, the calculatedΔE c agree with the experimental results. Using the value ofΔr~0.05 fm and the experimental values ofr ex, a small compression (<0.02 fm) of the proton core in the analogue state relative to its parent state emerges, thus contributing an additional electrostatic term to the Coulomb displacement energy. The size of this relative core-compression effect depends on the values assumed forΔr andr ex, it increases with the decreasing ofΔr and the increasing ofr ex. IfΔr~0.05 fm the effect is large enough to remove the long standing Coulomb energy anomaly. The main result of the present work is the correlation betweenΔE c andΔr, suggesting that the difficulties of current Hartree-Fock calculations in reproducing isotope shifts ofr p , the small value ofr n ?r p and the values ofΔE c may all be different manifestations of some missing residualp n effective interaction. 相似文献
24.
Michael Grouchko Alexander Kamyshny Keren Ben-Ami Shlomo Magdassi 《Journal of nanoparticle research》2009,11(3):713-716
Synthesis of well dispersed copper nanoparticles was achieved by reduction of copper nitrate in aqueous solution using hydrazine
monohydrate as a reducer in the presence of preformed silver nanoparticles as catalysts. It has been demonstrated that addition
of silver nanoparticles to the reaction mixture leads to formation of aqueous dispersion of copper nanoparticles and also
results in a drastic reduction in reaction time compared to procedures reported in the literature. The absorption spectrum
of the dispersions, HR-TEM and STEM images and XRD pattern indicate the formation of copper nanoparticles with particle size
in the range of 5–50 nm. 相似文献
25.
We explore recent contributions to research in Econophysics, switching between Macroscopic complexity and microscopic modelling, showing how each leads to the other and detailing the everyday applicability of both approaches and the tools they help develop. Over the past decades, the world underwent several major crises, leading to significant increase in interdependence and, thus, complexity. We show here that from the perspective of network science, these processes become more understandable and, to some extent, also controllable. 相似文献
26.
Oscar H Ibarra Shlomo Moran Roger Hui 《Journal of Algorithms in Cognition, Informatics and Logic》1982,3(1):45-56
We show that any m × n matrix A, over any field, can be written as a product, LSP, of three matrices, where L is a lower triangular matrix with l's on the main diagonal, S is an m × n matrix which reduces to an upper triangular matrix with nonzero diagonal elements when the zero rows are deleted, and P is an n × n permutation matrix. Moreover, L, S, and P can be found in O(mα?1n) time, where the complexity of matrix multiplication is O(mα). We use the LSP decomposition to construct fast algorithms for some important matrix problems. In particular, we develop O(mα?1n) algorithms for the following problems, where A is any m × n matrix: (1) Determine if the system of equations (where is a column vector) has a solution, and if so, find one such solution. (2) Find a generalized inverse, , of A (i.e., ). (3) Find simultaneously a maximal independent set of rows and a maximal independent set of columns of A. 相似文献
27.
What is the largest number of edges in a graph of order n and girth g? For d-regular graphs, essentially the best known answer is provided by the Moore bound. This result is extended here to cover irregular
graphs as well, yielding an affirmative answer to an old open problem ([4] p. 163, problem 10).
Received: June 27, 2000 Final version received: July 3, 2001 相似文献
28.
A rank-three condition for invariant (1, 2)-symplectic almost Hermitian structures on flag manifolds
Nir Cohen Caio J.C. Negreiros Luiz A.B. San Martin 《Bulletin of the Brazilian Mathematical Society》2002,33(1):49-73
This paper considers invariant (1, 2)-symplectic almost Hermitian structures on the maximal flag manifod associated to a
complex semi-simple Lie group G. The concept of cone-free invariant almost complex structure is introduced. It involves the rank-three subgroups of G, and generalizes the cone-free property for tournaments related to 𝕊l (n,ℂ) case. It is proved that the cone-free property is necessary for an invariant almost-complex structure to take part in
an invariant (1, 2)-symplectic almost Hermitian structure. It is also sufficient if the Lie group is not B
l , l ≥ 3, G
2 or F
4. For B
l and F
4 a close condition turns out to be sufficient.
Received: 28 October 2001 相似文献
29.
We prove that the quantum double of the quasi-Hopf algebra of dimension attached in [P. Etingof, S. Gelaki, On radically graded finite-dimensional quasi-Hopf algebras, Mosc. Math. J. 5 (2) (2005) 371–378] to a simple complex Lie algebra and a primitive root of unity q of order n2 is equivalent to Lusztig's small quantum group (under some conditions on n). We also give a conceptual construction of using the notion of de-equivariantization of tensor categories. 相似文献
30.
Michel Le Breton Juan D. Moreno-Ternero Alexei Savvateev Shlomo Weber 《International Journal of Game Theory》2013,42(3):673-694
This article studies a model of coalition formation for the joint production (and finance) of public projects, in which agents may belong to multiple coalitions. We show that, if projects are divisible, there always exists a stable (secession-proof) structure, i.e., a structure in which no coalition would reject a proposed arrangement. When projects are indivisible, stable allocations may fail to exist and, for those cases, we resort to the least core in order to estimate the degree of instability. We also examine the compatibility of stability and fairness in metric environments with indivisible projects, where we also explore the performance of well-known solutions, such as the Shapley value and the nucleolus. 相似文献