全文获取类型
收费全文 | 553篇 |
免费 | 27篇 |
国内免费 | 2篇 |
专业分类
化学 | 382篇 |
晶体学 | 12篇 |
力学 | 16篇 |
数学 | 55篇 |
物理学 | 117篇 |
出版年
2024年 | 1篇 |
2022年 | 17篇 |
2021年 | 25篇 |
2020年 | 14篇 |
2019年 | 14篇 |
2018年 | 18篇 |
2017年 | 21篇 |
2016年 | 18篇 |
2015年 | 18篇 |
2014年 | 22篇 |
2013年 | 38篇 |
2012年 | 22篇 |
2011年 | 47篇 |
2010年 | 24篇 |
2009年 | 22篇 |
2008年 | 23篇 |
2007年 | 36篇 |
2006年 | 24篇 |
2005年 | 36篇 |
2004年 | 16篇 |
2003年 | 23篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 7篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1975年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有582条查询结果,搜索用时 15 毫秒
51.
We have theoretically investigated two-dimensional atom localization using the absorption spectra of birefringence beams of light in a single wavelength domain.The atom localization is controlled and modified through tunneling effect in a conductive chiral atomic medium with absorption spectra of birefringent beams.The significant localization peaks are investigated in the left and right circularly polarized beam.Single and double localized peaks are observed in different quadrants with minimum uncertainty and significant probability.The localized probability is modified by controlling birefringence and tunneling conditions.These results may be useful for the capability of optical microscopy and atom imaging. 相似文献
52.
Sibel Irmak Kemal Solakyildirim Arif Hesenov Oktay Erbatur 《Journal of Analytical Chemistry》2010,65(9):899-906
The aim of this study was to examine the influence of storage conditions and duration on composition and antioxidant activity
of supercritical fluid (SCF) extracted essential oil of rosemary (Rosmarinus officinalis L.). Supercritical extraction was carried out sequentially by using SCF carbondioxide in the first two steps and with 5%
ethanol as entrainer in the third step. The compositions of the extracts were determined by gas chromatography/mass spectrometry.
The total phenolics were analyzed using Folin-Ciocalteau assay. Antioxidant activities of the extracts were tested by β-carotene-linoleic
acid bleaching method. 相似文献
53.
In laser cutting of sheet metals, thermal stresses are developed in the region of the cutting section. Depending on the cutting conditions and substrate material properties, the thermal stress levels can attain high values. In the present study, thermal stress developed in the region of the laser cut edges is modeled and temperature as well as stress fields are predicted. Temperature predictions are validated through the experimental results. It was found that the temporal variation of the maximum temperature along y-axis follows the laser heating source. However, temporal variation of von-Mises stress deviates slightly from the temporal variation of temperature along the cutting direction. Increase in scanning speed enhances the von-Mises stress levels due to the attainment of high temperature gradients in the substrate material. 相似文献
54.
We provide a simple physical proof of the reciprocity theorem of classical electrodynamics in the general case of material media that contain linearly polarizable as well as linearly magnetizable substances. The excitation source is taken to be a point-dipole, either electric or magnetic, and the monitored field at the observation point can be electric or magnetic, regardless of the nature of the source dipole. The electric and magnetic susceptibility tensors of the material system may vary from point to point in space, but they cannot be functions of time. In the case of spatially non-dispersive media, the only other constraint on the local susceptibility tensors is that they be symmetric at each and every point. The proof is readily extended to media that exhibit spatial dispersion: For reciprocity to hold, the electric susceptibility tensor χE_mn that relates the complex-valued magnitude of the electric dipole at location rm to the strength of the electric field at rn must be the transpose of χE_nm. Similarly, the necessary and sufficient condition for the magnetic susceptibility tensor is χM_mn = χTM_nm. 相似文献
55.
We study the coupling of a tetraquark system to an exchanged meson-meson channel, using a pure gluonic theory based four-quark
potential matrix model which is known to fit well a large number of data points for lattice simulations of different geometries of a four-quark
system. We find that if this minimal-area-based potential matrix replaces the earlier used simple Gaussian form for the gluon
field overlap factor f in its off-diagonal terms, the resulting T -matrix and phase shifts develop an angle dependence whose partial-wave analysis reveals D wave and higher angular-momentum components in it. In addition to the obvious implications of this result for the meson-meson
scattering, this new feature indicates the possibility of orbital excitations influencing properties of meson-meson molecules
through a polarization potential. We have used a formalism of the resonating group method, treated kinetic energy and overlap
matrices on model of the potential matrix, but decoupled the resulting complicated integral equations through the Born approximation.
In this exploratory study we have used a quadratic confinement and not included the spin dependence; we also used the approximation
of equal constituent quark masses. 相似文献
56.
Nosheen Akbar Bilal Masud Saba Noor 《The European Physical Journal A - Hadrons and Nuclei》2011,47(10):124
We propose some extensions of the quark potential model to hybrids, fit them to the lattice data and use them for the purpose of calculating the masses, root mean square radii and wave functions at the origin of the conventional and hybrid charmonium mesons. We treat the ground and excited gluonic field between a quark and an antiquark as in the Born-Oppenheimer expansion, and use the shooting method to numerically solve the required Schrödinger equation for the radial wave functions; from these wave functions we calculate the mesonic properties. For masses we also check through a Crank Nichelson discretization. For hybrid charmonium mesons, we consider the exotic quantum number states with J PC = 0+?, 1?+ and 2+?. We also compare our results with the experimentally observed masses and theoretically predicted results of the other models. Our results have implications for scalar form factors, energy shifts, magnetic polarizabilities, decay constants, decay widths and differential cross-sections of conventional and hybrid mesons. 相似文献
57.
Arif D. SheikhAbdulsamee Fawzi V.L. Mathe 《Journal of magnetism and magnetic materials》2011,323(6):740-747
We present systematic studies that comprise phase connectivity and dielectric, multiferroic (MF) and magnetoelectric (ME) properties of (x) Ni0.8Co0.2Fe2O4+(1−x) Pb(Mg1/3Nb2/3)0.67Ti0.33O3 [where x=0.15, 0.30 and 0.45] ME composites prepared by conventional solid-state reaction method. Scanning electron microscopic images of the composites predict different types of connectivity schemes viz 3-0, 3-1 and 3-3. The phase transition temperature of PMN-PT is independent of Ni0.8Co0.2Fe2O4 content. Room temperature P-E and M-H loops indicate the simultaneous existence of ferroelectric/magnetic ordering. In order to study the possibility of monitoring electrical ordering by means of a magnetic field, ME measurements were carried out. The composition-dependent phase connectivity was well co-related to formation of percolation path and inturn magnetoelectric output. 相似文献
58.
We present a class of interacting nonlocal quantum field theories, in which the CPT invariance is violated while the Lorentz invariance is present. This result rules out a previous claim in the literature that the CPT violation implies the violation of Lorentz invariance. Furthermore, there exists the reciprocal of this theorem, namely that the violation of Lorentz invariance does not lead to the CPT violation, provided that the residual symmetry of Lorentz invariance admits the proper representation theory for the particles. The latter occurs in the case of quantum field theories on a noncommutative space–time, which in place of the broken Lorentz symmetry possesses the twisted Poincaré invariance. With such a CPT-violating interaction and the addition of a C-violating (e.g., electroweak) interaction, the quantum corrections due to the combined interactions could lead to different properties for the particle and antiparticle, including their masses. 相似文献
59.
Ljubomir iri Arif Rafiq Nenad Caki 《Nonlinear Analysis: Theory, Methods & Applications》2009,70(12):4332-4337
In this note, we speed up the convergence of the Picard sequence of iterations for strongly accretive and strongly pseudo-contractive mappings. Our results improve the results of Chidume [C.E. Chidume, Picard iteration for strongly accretive and strongly pseudo-contractive Lipschitz maps, ICTP Preprint no. IC2000098; C.E. Chidume, Iterative Algorithms for Non-expansive Mappings and Some of Their Generalizations, in: Nonlinear Analysis and Applications: To V. Lakshmikantham on his 80th Birthday, vol. 1, 2, Kluwer Acad. Publ, Dordrecht, 2003, pp. 383–429], and Liu [L. Liu, Approximation of fixed points of a strictly pseudo-contractive mapping, Proc. Amer. Math. Soc. 125 (2) (1997) 1363–1366], and some other known results. The technique of the proof, presented in this paper, is different from the technique used by Chidume. 相似文献
60.