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991.
We analyze in some detail the course that Ettore Majorana gave on theoretical physics at the University of Naples between
January and March 1938, just prior to his mysterious disappearance. We discuss, in particular, the recently discovered Moreno
Lecture Notes, in which all of Majorana’s lectures are recorded, six of which are not present in those that are preserved
in the Domus Galilaeana in Pisa, Italy.
Antonino Drago is a retired professor of history of physics at the University of Naples “Federico II.” Salvatore Esposito
is a researcher on theoretical physics and history of physics at the University of Naples “Federico II.” 相似文献
992.
T. R. Mongan 《International Journal of Theoretical Physics》2007,46(2):399-404
A closed vacuum-dominated Friedmann universe is asymptotic to a de Sitter space with a cosmological event horizon for any
observer. The holographic principle says the area of the horizon in Planck units determines the maximum number of bits of
information about the universe that will ever be available to any observer. The wavefunction describing the probability distribution
of mass quanta associated with bits of information on the horizon is the boundary condition for the wavefunction specifying
the probability distribution of mass quanta throughout the universe. Local interactions between mass quanta in the universe
cause quantum transitions in the wavefunction specifying the distribution of mass throughout the universe, with instantaneous
non-local effects throughout the universe. 相似文献
993.
K. Jin Z. C. Wang Q. Zhang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):325-332
We study the absorption spectra of a degenerate V-type
atom, where a resonant driving field and a probe field drive
different branches of transitions and a dc field is applied to
drive the transition between two excited states. The effects of
vacuum induced coherence (VIC) on the absorption spectra are
investigated. It is demonstrated that in some special cases the
VIC can lead to the depression of absorption and narrow resonance.
The origin of these features are discussed. When the pump field
and the dc field have the same intensity, it is interesting to
find that the whole absorption spectrum comes mainly from the
absorptions induced by the interferences among different
transitions between dressed states. 相似文献
994.
X. X. Yi H. Wang W. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):355-362
We present a theory to establish a relation between Hahn
spin-echo of a spin-1/2 particle and quantum phase
transitions in many-body systems. The Hahn echo is calculated and
discussed at zero as well as at finite temperatures. On the
example of XY model, we show that the critical points of the chain
are marked by the extremal values in the Hahn echo, and can
influence the Hahn echo in finite temperatures. An explanation for
the relation between the echo and criticality is also presented. 相似文献
995.
We consider a quantum system in contact with a heat bath consisting in an infinite chain of identical sub-systems at thermal
equilibrium at inverse temperature β. The time evolution is discrete and such that over each time step of duration τ, the
reference system is coupled to one new element of the chain only, by means of an interaction of strength λ. We consider three
asymptotic regimes of the parameters λ and τ for which the effective evolution of observables on the small system becomes
continuous over suitable macroscopic time scales T and whose generator can be computed: the weak coupling limit regime λ → 0, τ = 1, the regime τ → 0, λ2τ → 0 and the critical case λ2τ = 1, τ → 0. The first two regimes are perturbative in nature and the effective generators they determine is such that a
non-trivial invariant sub-algebra of observables naturally emerges. The third asymptotic regime goes beyond the perturbative
regime and provides an effective dynamics governed by a general Lindblad generator naturally constructed from the interaction
Hamiltonian. Conversely, this result shows that one can attach to any Lindblad generator a repeated quantum interactions model
whose asymptotic effective evolution is generated by this Lindblad operator. 相似文献
996.
Abhishek Verma Swati Nagpal Praveen K. Pandey P. K. Bhatnagar P. C. Mathur 《Journal of nanoparticle research》2007,9(6):1125-1131
Quantum Dots of CdS
x
Se1−x
embedded in borosilicate glass matrix have been grown using Double-Step annealing method. Optical characterization of the
quantum dots has been done through the combinative analysis of optical absorption and photoluminescence spectroscopy at room
temperature. Decreasing trend of photoluminescence intensity with aging has been observed and is attributed to trap elimination.
The changes in particle size, size distribution, number of quantum dots, volume fraction, trap related phenomenon and Gibbs
free energy of quantum dots, has been explained on the basis of the diffusion-controlled growth process, which continues with
passage of time. For a typical case, it was found that after 24 months of aging, the average radii increased from 3.05 to
3.12 nm with the increase in number of quantum dots by 190% and the size-dispersion decreased from 10.8% to 9.9%. For this
sample, the initial size range of the quantum dots was 2.85 to 3.18 nm. After that no significant change was found in these
parameters for the next 12 months. This shows that the system attains almost a stable nature after 24 months of aging. It
was also observed that the size-dispersion in quantum dots reduces with the increase in annealing duration, but at the cost
of quantum confinement effect. Therefore, a trade off optimization has to be done between the size-dispersion and the quantum
confinement. 相似文献
997.
With some reviews on the investigations on the schemes for quantum state transfer based on spin systems, we discuss the quantum
dynamics of magnetically-controlled networks for Bloch electrons. The networks are constructed by connecting several tight-binding
chains with uniform nearest-neighbor hopping integrals. The external magnetic field and the connecting hopping integrals can
be used to control the intrinsic properties of the networks. For several typical networks, rigorous results are shown for
some specific values of external magnetic field and the connecting hopping integrals: a complicated network can be reduced
into a virtual network, which is a direct sum of some independent chains with uniform nearest-neighbor hopping integrals.
These reductions are due to the fermionic statistics and the Aharonov-Bohm effects. In application, we study the quantum dynamics
of wave packet motion of Bloch electrons in such networks. For various geometrical configurations, these networks can function
as some optical devices, such as beam splitters, switches and interferometers. When the Bloch electrons as Gaussian wave packets
input these devices, various quantum coherence phenomena can be observed, e.g., the perfect quantum state transfer without
reflection in a Y-shaped beam, the multi-mode entanglers of electron wave by star-shaped network, magnetically controlled
switches, and Bloch electron interferometer with the lattice Aharonov-Bohm effects. With these quantum coherent features,
the networks are expected to be used as quantum information processors for the fermion system based on the possible engineered
solid state systems, such as the array of quantum dots that can be implemented experimentally.
相似文献
998.
Hawking radiation can be viewed as a process of quantum tunnelling near black hole horizon. When a particle with angular momentum
tunnels across the event horizon of Schwarzschild black hole, the black hole will change into a Kerr black hole. The emission
rate of the massless particles with angular momentum is calculated, and the result is consistent with an underlying unitary
theory. 相似文献
999.
A protocol of quantum secret sharing between multiparty and multiparty with four states was presented. It was shown that this
protocol can nullify the Trojan horse attack with a multi-photon signal, the fake-signal attack with Einstein-Podolsky-Rosen
pairs, the attack with single photons, and the attack with invisible photons. In addition, the upper bounds of the average
success probabilities were given for dishonest agent eavesdropping encryption using the fake-signal attack with any two-particle
entangled states.
Supported by the National Natural Science Foundation of China (Grant No. 10671054), the Key Project of Science and Technology
Research of Education Ministry of China (Grant No. 207011) and the Natural Science Foundation of Hebei Province, China (Grant
Nos. A2005000140 and 07M006) 相似文献
1000.
S. Heinemeyer 《Pramana》2007,69(5):727-733
The international linear e
+
e
− collider (ILC) could go into operation in the second half of the upcoming decade. Experimental analyses and theory calculations
for the physics at the ILC are currently performed. We review recent progress, as presented at the LCWS06 in Bangalore, India,
in the fields of Higgs boson physics and top/QCD. Also the area of loop calculations, necessary to achieve the required theory
precision, is included.
相似文献