全文获取类型
收费全文 | 612篇 |
免费 | 10篇 |
国内免费 | 4篇 |
专业分类
化学 | 325篇 |
晶体学 | 26篇 |
力学 | 12篇 |
数学 | 93篇 |
物理学 | 170篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 5篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 23篇 |
2012年 | 33篇 |
2011年 | 38篇 |
2010年 | 13篇 |
2009年 | 25篇 |
2008年 | 24篇 |
2007年 | 35篇 |
2006年 | 49篇 |
2005年 | 28篇 |
2004年 | 11篇 |
2003年 | 14篇 |
2002年 | 24篇 |
2001年 | 13篇 |
2000年 | 18篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 11篇 |
1995年 | 8篇 |
1994年 | 8篇 |
1993年 | 5篇 |
1992年 | 8篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 7篇 |
1974年 | 3篇 |
1971年 | 5篇 |
1960年 | 3篇 |
1947年 | 6篇 |
1946年 | 5篇 |
1944年 | 4篇 |
1943年 | 7篇 |
排序方式: 共有626条查询结果,搜索用时 15 毫秒
31.
A careful discussion is given of the definitions of “target asymmetry” and “effective neutron polarization” in the reaction with polarized deuterons. The connection between the analyzing powers, Tqk of the reaction and the target asymmetry, T is established taking into account the method of preparation of the polarized target. It is further shown that the concept of effective neutron polarization Peff is valid only in a very approximate way, even when the target deuteron is purely vector polarized. 相似文献
32.
A.?NarayananEmail author R.?Srinivasan U.?K.?Khan A.?Vudayagiri H.?Ramachandran 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,31(1):107-112
The unusually narrow features in the fluorescence from 85Rb driven by two laser fields L1 and L2, reported in [1], are explained on the basis of a four-level density matrix calculation. The L2 laser enables atom transfer to the fluorescing levels connected by the strong L1 laser. In turn the L1 laser causes the Autler-Townes splitting of the upper levels connected by L2 laser. These two effects are shown to maximise fluorescence within a narrow spectral range of the scanned L2 laser due to velocity selection of atoms from co-propagating and counter propagating L1 and L2 lasers. The analysis reveals the existence of narrow spectral features from a collection of atoms at room temperature even in the absence of induced coherences between the levels.Received: 2 July 2004, Published online: 21 September 2004PACS:
42.50.Hz Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift - 32.80.Bx Level crossing and optical pumping 相似文献
33.
Use of a graded gain random amplifier as an optical diode 总被引:1,自引:0,他引:1
The spectral characteristics of liquid amplifying media have been used to design and experimentally realize an optical device that prevents the propagation of a band of wavelengths in one direction and permits it in the opposite direction, thus acting as an optical diode. The addition of random scattering centers is shown to narrow the width of the forbidden band. A model is proposed to explain the observations and is verified by Monte Carlo simulations. 相似文献
34.
Chandran Karunakaran K.R. Justin Thomas Arunachalam Shunmugasundarama Ramachandran Murugesan 《Journal of chemical crystallography》2000,30(5):351-357
Single crystals of the helical hydrogen-bridged one-dimensional Cu(II) complex, [Cu(stpy)2(CH3COO)2(H2O)2] (1) [Cu(stpy)2(CH3COO)2(H2O)] (2), are prepared and characterized by elemental and thermal analyses, IR, electronic and X-ray crystal structure determination. The crystals are monoclinic, of space group C2/c, with unit cell parameters a = 31.842(7) Å, b = 5.9829(10) Å, c = 30.970(14) Å, = 111.78(3)°, Z = 4. The asymmetric unit contains two different types of Cu(II) polyhedra, namely, octahedron and square pyramid within the same unit cell. 1 has elongated octahedral geometry with two nitrogen atoms from stpy and two oxygen atoms from synmonodentate acetate ligands, transcoordinated to Cu(II) in the basal plane. The oxygen atoms of the two water molecules occupy the axial positions. 2 has Cu(II) coordination polyhedra similar to 1, except that only one of the apical positions is occupied by a water molecule. The structure consists of two independent linear chains, one involving octahedral (1) and the other involving square-pyramidal (2) polyhedra, held by hydrogen bridges. The Cu–Cu intra- and interchain separations in both 1 and 2 are 5.983 and 8.214 Å. The unit cell packing shows weak -stacking between adjacent coordinated stpy ligands in the chain, resulting in ladder-type structure. Further, the extended packing reveals helical arrangement of Cu(II) polyhedra in the lattice. 相似文献
35.
36.
K. Muthukkumaran P. Kuppusami R. Srinivasan K. Ramachandran E. Mohandas S. Selladurai 《Ionics》2007,13(1):47-50
Thermal properties of 15-mol% gadolinia doped ceria thin films (Ce0.85Gd0.15 O1.925) prepared by pulsed laser ablation on silicon substrates in the temperature range 473–973 K are presented. Thermal diffusivities
and thermal conductivities were evaluated using photoacoustic spectroscopy. The influence of grain size on thermal properties
of the films as a function of deposition temperature is studied. It is observed that the thermal diffusivity and the conductivity
of these films decreases up to 873 K and then increases with substrate temperatures. The thermal properties obtained in these
films are discussed on the basis of influence of grain size on phonon scattering. 相似文献
37.
The reaction of peroxomonosulfate (PMS) with glycolic acid (GLYCA), an alpha hydroxy acid, in the presence of Ni(II) ions and formaldehyde was studied in the pH range 4.05–5.89 and at 31°C and 38°C. When formaldehyde and Ni(II) ions concentrations are ~5.0 × 10?4 M to 10.0 × 10?4 M, the reaction is second order in PMS concentration. The rate is catalyzed by formaldehyde, and the observed rate equation is (?d[PMS])/dt = (k′2[HCHO][Ni(II)][PMS]2)/{[H+](1+K2[GLYCA])}. The number of PMS decomposed for each mole of formaldehyde (turnover number) is 5–10, and the major reaction product is oxygen gas. The first step of the reaction mechanism is the formation of hemiacetal by the interaction of HCHO with the hydroxyl group of nickel glycolate. The peroxomonosulfate intermediate of the Ni‐hemiacetal reacts with another molecule of PMS in the rate‐limiting step to give the product. This reaction is similar to the thermal decomposition of PMS catalyzed by Ni(II) ions. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 642–649, 2009 相似文献
38.
A high‐order element‐based Galerkin method is developed to solve the non‐divergent barotropic vorticity equation (BVE). The solution process involves solving a conservative transport equation for the vorticity fields and a Poisson equation for the stream function fields. The discontinuous Galerkin method is employed for solving the transport equation and a spectral element method (continuous Galerkin) is used for the Poisson equation. A third‐order strong stability preserving explicit Runge–Kutta scheme is used for time integration. A series of tests have been performed to validate the model, which include the evolution of an idealized tropical cyclone and interaction of dual vortices in close proximity. The numerical convergence study is performed by solving the BVE on the sphere where the analytic solution is known. The test results are consistent with physical observations, and the model exhibits exponential convergence. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
39.
40.
A theoretical study is made of the advantages to be gained in polarizing a deuteron target by applying an external electric
quadrupole field with non-zero asymmetry parameter for carrying outd(π, π)d experiments, in order to determine empirically the helicity amplitudes A, B, C, D characterizing the scattering, without
any phase ambiguities. 相似文献