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931.
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
932.
The effect of light noise on a Neurospora circadian clock system in the steady states is investigated. It is found that the circadian oscillations could be induced
by light noise, leading to various resonance phenomena including internal signal stochastic resonance (ISSR) and ISSR without
tuning in the system. The strength of ISSR could be significantly reinforced with the decrease of the distance of the control
parameter to the Hopf bifurcation point of the system. The fundamental frequency of noise-induced circadian oscillations almost
does not change with the increment of light noise intensity, which implies that the Neurospora system could sustain intrinsic circadian rhythms. In addition, the ISSR and ISSR without tuning could be both amplified,
suppressed or destroyed by tuning the frequency or amplitude of external signal. 相似文献
933.
We consider the question of the existence of stationary solutions for the Navier Stokes equations describing the flow of a
incompressible fluid past a semi-infinite flat plate at zero incidence angle. By using ideas from the theory of dynamical
systems we analyze the vorticity equation for this problem and show that a symmetry-breaking term fits naturally into the
downstream asymptotic expansion of a solution. Finally, in order to check that our asymptotic expressions can be completed
to a symmetry-breaking solution of the Navier–Stokes equations we solve the problem numerically by using our asymptotic results
to prescribe artificial boundary conditions for a sequence of truncated domains. The results of these numerical computations
a clearly compatible with the existence of such a solution.
Mathematics Subject Classification (2000). 76D05, 76D25, 76M10, 41A60, 35Q35
Supported in part by the Fonds National Suisse. 相似文献
934.
Cédric Boutillier 《Communications in Mathematical Physics》2007,271(1):55-91
In this paper, we introduce a family of observables for the dimer model on a bi-periodic bipartite planar graph, called pattern density fields. We study the scaling limit of these objects for non-frozen Gibbs measures of the dimer model, and prove that they converge
to a linear combination of a derivative of the Gaussian massless free field and an independent white noise. 相似文献
935.
Anita Topkar S. Praveenkumar Bharti Aggarwal S. K. Kataria M. D. Ghodgaonkar 《Pramana》2007,69(6):1085-1088
A specific research and development program has been carried out by BARC in India to develop the technology for large area
silicon strip detectors for application in nuclear and high energy physics experiments. These strip detectors will be used
as pre-shower detector in the CMS experiment at LHC, CERN for π
0/λ rejection. The fabrication technology to produce silicon strip detectors with very good uniformity over a large area of ∼40
cm2, low leakage currents of the order of 10 nA/cm2 per strip and high breakdown voltage of >500 V has been developed by BARC. The production of detectors is already under way
to deliver 1000 detector modules for the CMS and 90% production is completed. In this paper, research and development work
carried out to develop the detector fabrication technology is briefly described. The performance of the silicon strip detectors
produced in India is presented. The present status of the detector technology is discussed.
相似文献
936.
Hakim Boumaza 《Mathematical Physics, Analysis and Geometry》2007,10(2):97-122
We study a continuous matrix-valued Anderson-type model. Both leading Lyapunov exponents of this model are proved to be positive
and distinct for all energies in (2, +∞) except those in a discrete set, which leads to absence of absolutely continuous spectrum
in (2, +∞). This result is an improvement of a previous result with Stolz. The methods, based upon a result by Breuillard
and Gelander on dense subgroups in semisimple Lie groups, and a criterion by Goldsheid and Margulis, allow for singular Bernoulli
distributions.
相似文献
937.
Acrylic acid modified magnesium hydroxide nano-needles (AA–Mg(OH)2) had been synthesized by alkaline injected into magnesium chloride solution at about 0°C in the presence of acrylic acid
(AA). Then the polystyrene/magnesium hydroxide nano-needles composite (PS/Mg(OH)2) had been prepared by the radical copolymerization with styrene in toluene system using AA–Mg(OH)2 as a macro-monomer. The elemental analysis (EA) and Fourier transform infrared (FTIR) analyses show that the polystyrene
had been grafted onto the surfaces of the nano-needles (AA–Mg(OH)2). The nano-needles (AA–Mg(OH)2) had better dispersibility in polystyrene matrix as observed by transmission electron microscope (TEM) analysis. The thermal
behavior analysis results from the differential scanning calorimetry (DSC) indicated that the magnesium hydroxide nano-needles
had lower thermal decomposition temperature than that of the polymer matrix and it is expected that the nano-needles prepared
by the proposed method could be used as an environmental-friendly flame retardant. 相似文献
938.
Stanislav V. Averin Petr I. Kuznetzov Victor A. Zhitov Nikolai V. Alkeev 《Optical and Quantum Electronics》2007,39(3):181-192
Solar-blind MSM photodetectors based on the AlGaN heterostructures have been fabricated and investigated. The influence of
material properties on device parameters is discussed. Effect of different buffer layers on the detector performances has
been examined. Detectors exhibit low dark currents and high sensitivity within the range of 250–290 nm. Effect of optical
excitation energy on GaN-based MSM-detector performance is analyzed and discussed. At high excitation level the detector speed
of response is limited by the field screening caused by the space-charge of the holes. The impulse response of GaN-based MSM-detector
is compared favorably with GaAs MSM-device. 相似文献
939.
N. Sankara Subramanian R. Vivek Sabaapathy P. Vickraman G. Vimal Kumar R. Sriram B. Santhi 《Ionics》2007,13(5):323-328
P-type porous silicon (PS) structure has been prepared by anodic electrochemical etching process under optimized conditions.
Photoluminescence studies of the PS structure show emission at longer wavelengths (red) for the excitation at 365 nm. Scanning
electron microscope investigations of the PS surface confirm the formation of uniform porous structure, and the pore diameter
have been estimated as 25 μm. Pd:SnO2/PS/p-Si heterojunction with top gold ohmic contact developed by conventional methods has been used as the sensor device.
Sensing properties of the device towards liquefied petroleum gas (LPG) and NO2 gas have been investigated in an indigenously developed sensor test rig. The response and recovery characteristics of the
sensor device at different operating temperatures show short response time for LPG. From the studies, maximum sensitivity
and optimum operating temperature of the device towards LPG and NO2 gas sensing has been estimated as 69% at 180 °C and 52% at 220 °C, respectively. The developed sensor device shows a short
response time of 25 and 57 s for sensing LPG and NO2 gases, respectively.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
940.
Dominique Fellah 《Letters in Mathematical Physics》2007,80(2):101-113