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21.
Brain activation has been used to understand brain-level events associated with cognitive tasks or physical tasks. As a quantitative measure for brain activation, we propose entropy in place of signal amplitude and beta value, which are widely used, but sometimes criticized for their limitations and shortcomings as such measures. To investigate the relevance of our proposition, we provided 22 subjects with physical stimuli through elbow extension-flexion motions by using our exoskeleton robot, measured brain activation in terms of entropy, signal amplitude, and beta value; and compared entropy with the other two. The results show that entropy is superior, in that its change appeared in limited, well established, motor areas, while signal amplitude and beta value changes appeared in a widespread fashion, contradicting the modularity theory. Entropy can predict increase in brain activation with task duration, while the other two cannot. When stimuli shifted from the rest state to the task state, entropy exhibited a similar increase as the other two did. Although entropy showed only a part of the phenomenon induced by task strength, it showed superiority by showing a decrease in brain activation that the other two did not show. Moreover, entropy was capable of identifying the physiologically important location. 相似文献
22.
Park BK Jeong S Kim D Moon J Lim S Kim JS 《Journal of colloid and interface science》2007,311(2):417-424
We describe herein the synthesis of metallic copper nanoparticles in the presence of poly(vinylpyrrolidone), employed as a protecting agent, via a polyol method in ambient atmosphere. The obtained copper particles were confirmed by XRD to be crystalline copper with a face-centered cubic (fcc) structure. We observed monodisperse spherical copper nanoparticles with a diameter range 45+/-8 nm. The particle size and its distribution are controlled by varying the synthesis parameters such as the reducing agent concentration, reaction temperature, and precursor injection rate. The precursor injection rate plays an important role in controlling the size of the copper nanoparticles. On the basis of XPS and HRTEM results, we demonstrate that the surface of the copper is surrounded by amorphous CuO and that poly(vinylpyrrolidone) is chemisorbed on the copper surface. 相似文献
23.
Studies of the relationship between interfacial structure and mechanical properties in multicomponent materials are reviewed in this article. The following categories are considered for role of the interface in multicomponent systems: Interpenetrating polymer network(IPN), catalytic effect of silane coupling agent, morphological differences of filler surface, particle-particle interaction and particle size of the filler. The interfacial role in terms of the reinforcement mechanism of the composite and the behavior in the melt state is also discussed in the multicomponent system. 相似文献
24.
Three kinds of europium β-diketonates Eu(DBM)3, Eu(BA)3 and Eu(TTA)3 (DBM: Dibenzoylmethane; BA: 1-Benzoylacetone; TTA: Thenoyltrifluoroacetone) were doped in poly(methyl methacrylate) (PMMA) matrix. The doped systems were studied by using photoluminescent (PL) spectroscopy, emission decay experiments and X-ray diffractometry. Eu(III) ions in the doped Eu(DBM)3/PMMA systems have two distinct symmetric sites and the emission band changes greatly with the compositions. Eu(III) in the Eu(BA)3/PMMA systems gives only one symmetric site in the doped systems and the emission band changes slightly with the compositions. Although two distinct symmetric sites of Eu(III) can be distinguished in the doped systems of Eu(TTA)3/PMMA, the two sites have similar 5D0 lifetimes and the luminescent spectra almost do not change with the compositions. XRD reveals that crystallites were formed in the doped Eu(DBM)3/PMMA systems that have different crystalline structure from that of the chelate, and Eu(BA)3 and Eu(TTA)3 exist in amorphous state in the doped systems. The difference between the PL properties and structures of the doped systems for the three kinds of chelates should be attributed to different interactions between the chelate molecules and between the chelate and PMMA. 相似文献
25.
O-Kab Kwon Dongmin Jang Yoonbai Kim D. D. Tolla 《The European Physical Journal C - Particles and Fields》2018,78(10):856
We investigate the gauge/gravity duality between the \(\mathcal{N} = 6\) mass-deformed ABJM theory with \(\hbox {U}_k(N)\times \hbox {U}_{-k}(N)\) gauge symmetry and the 11-dimensional supergravity on LLM geometries with SO(2,1)\(\times \)SO(4)/\({\mathbb {Z}}_k\) \(\times \)SO(4)/\({\mathbb {Z}}_k\) isometry, in terms of a KK holography, which involves quadratic order field redefinitions. We establish the quadratic order KK mappings for various gauge invariant fields in order to obtain the canonical 4-dimensional gravity equations of motion and to reduce the LLM solutions to an asymptotically AdS\(_4\) gravity solutions. The non-linearity of the KK maps indicates that we can observe the true purpose of the non-linear KK holography of the LLM solutions. We read the vacuum expectation value of conformal dimension two operator from the asymptotically AdS\(_4\) gravity solutions. For the LLM solutions which are represented by square-shaped Young diagrams, we compare the vacuum expectation value obtained from the holographic procedure with the result obtained from the field theory, which is given by \(\langle \mathcal{O}^{(\Delta =2)}\rangle =\sqrt{k}N^{\frac{3}{2}}f_{(\Delta =2)}+\mathcal{O}(N)\), where \(f_{\Delta }\) is independent of N. Based on this result, we examine the gauge/gravity duality in the large N limit and finite k. We also show that the vacuum expectation values of the massive KK graviton modes are vanishing as expected by the supersymmetry. 相似文献
26.
We investigated the transverse beam dynamics in a thermal wave model by using a functional method. It can describe the beam optical elements separately with a kernel for a component. The method can be applied to general quadrupole magnets beyond a thin lens approximation as well as drift spaces. We found that the model can successfully describe the PARMILA simulation result through an FODO lattice structure for the Gaussian input beam without space charge effects. 相似文献
27.
针对广义Birkhoff系统动力学,提出广义Birkhoff系统动力学的一类逆问题,研究由已知积分流形来建立广义Birkhoff方程. 这类逆问题的解通常不是唯一的,需给出必要的补充要求. 最后举例说明结果的应用.
关键词:
广义Birkhoff系统
动力学逆问题
积分流形 相似文献
28.
A pressed CuCl pellet is optically excited at 2 K using an excitation energy in the range from 1892 to 2843 meV, which is far below the bandgap. The steady-state population dynamics unambiguously indicates an unusual two-photon generation of ground-state excitons. At high-excitation levels, the observed spectra exhibit rich spectral features arising from electron-hole plasma and electron-hole droplets formation. This nonresonant two-photon excitation is presumably assisted by impurity bands due to grain boundaries and surfaces in this random semiconductor. 相似文献
29.
Jongho Shin Kyungsik Jang Ki-Soo Lim Ik-Bu Sohn Young-Chul Noh Jongmin Lee 《Applied Physics A: Materials Science & Processing》2008,93(4):1015-927
We report the spectroscopic properties of femtosecond laser-irradiated sodium-alumino-borate glass doped with silver and gold
ions. We precipitated gold and silver nanoparticles by laser irradiation and annealing at 400°C for 30 min. The irradiation
and annealing treatment produced different absorption and emission characteristics in Au3+ doped and Au3+, Ag+ codoped glasses, and the possible mechanisms of the observed results are discussed. The size of the nanoparticles was estimated
by TEM and absorption band analysis. 相似文献
30.
The perturbation function of a Cd probe atom bound in a hydrogen-decorated vacancy complex in Pt is found to exhibit dynamical
relaxation at 294 K, as measured by the technique of perturbed γ-γ angular correlations. Based on other characteristics of
the complex, a model is proposed for the structure of the complex. In the undecorated state, it consists of a probe atom at
the center of a tetrahedron of vacancies in the fcc structure. In the decorated state at low temperature, the probe atom returns
to one of the four vacant lattice sites. The relaxation at room temperature is attributed to motion of the probe atom in a
cage formed by the four vacant sites. 相似文献