全文获取类型
收费全文 | 5261篇 |
免费 | 123篇 |
国内免费 | 7篇 |
专业分类
化学 | 3127篇 |
晶体学 | 127篇 |
力学 | 174篇 |
数学 | 421篇 |
物理学 | 1542篇 |
出版年
2023年 | 41篇 |
2022年 | 119篇 |
2021年 | 113篇 |
2020年 | 117篇 |
2019年 | 127篇 |
2018年 | 124篇 |
2017年 | 163篇 |
2016年 | 202篇 |
2015年 | 140篇 |
2014年 | 196篇 |
2013年 | 410篇 |
2012年 | 321篇 |
2011年 | 339篇 |
2010年 | 222篇 |
2009年 | 197篇 |
2008年 | 268篇 |
2007年 | 230篇 |
2006年 | 165篇 |
2005年 | 154篇 |
2004年 | 125篇 |
2003年 | 103篇 |
2002年 | 111篇 |
2001年 | 60篇 |
2000年 | 54篇 |
1999年 | 35篇 |
1998年 | 32篇 |
1997年 | 38篇 |
1996年 | 43篇 |
1995年 | 30篇 |
1994年 | 32篇 |
1993年 | 41篇 |
1992年 | 51篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 49篇 |
1988年 | 44篇 |
1987年 | 42篇 |
1986年 | 32篇 |
1985年 | 61篇 |
1984年 | 57篇 |
1983年 | 40篇 |
1982年 | 44篇 |
1981年 | 51篇 |
1980年 | 45篇 |
1979年 | 46篇 |
1978年 | 43篇 |
1977年 | 51篇 |
1976年 | 54篇 |
1975年 | 44篇 |
1974年 | 38篇 |
排序方式: 共有5391条查询结果,搜索用时 15 毫秒
101.
We investigate the mean first passage time of an active Brownian particle in one dimension using numerical simulations. The activity in one dimension is modelled as a two state model; the particle moves with a constant propulsion strength but its orientation switches from one state to other as in a random telegraphic process. We study the influence of a finite resetting rate r on the mean first passage time to a fixed target of a single free active Brownian particle and map this result using an effective diffusion process. As in the case of a passive Brownian particle, we can find an optimal resetting rate r* for an active Brownian particle for which the target is found with the minimum average time. In the case of the presence of an external potential, we find good agreement between the theory and numerical simulations using an effective potential approach. 相似文献
102.
A systematic investigation of layered perovskite oxides with general formula Ln0.5Sr1.5Mn0.5Fe0.5O4 (Ln?=?La, Nd, Gd, and Dy) has been undertaken mainly to understand their structural, magnetic, as well as electrical behavior. The materials were prepared by the ceramic method. X-ray data have been analyzed by using program Checkcell and the variations of various parameters are explained. It has been concluded that not only A-site cation radius, <r A>, but also the size variance factor (σ 2) influence electrical and magnetic properties. A systematic study of electrical resistivity of all the four materials was undertaken as a function of temperature to understand the conduction mechanism. On analyzing the electrical resistivity data, it has been concluded that variable range hopping model is found to fit well. The magnetic studies suggest that the phases are antiferromagnetic and this behavior could arise from Mn4+–O–Mn4+, and Fe3+–O–Fe3+ superexchange interaction. 相似文献
103.
Aavishkar A. Patel Shraddha Sharma Amit Dutta 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(9):1-6
We study the dynamics of edge states of the two dimensional BHZ Hamiltonian in a ribbon geometry following a sudden quench to the quantum critical point separating the topological insulator phase from the trivial insulator phase. The effective edge state Hamiltonian is a collection of decoupled qubit-like two-level systems which get coupled to bulk states following the quench. We notice a pronounced collapse and revival of the Lochschmidt echo for low-energy edge states illustrating the oscillation of the state between the two edges. We also observe a similar collapse and revival in the spin Hall current carried by these edge states, leading to a persistence of its time-averaged value. 相似文献
104.
Poonam Sharma D. K. Kanchan Nirali Gondaliya Meenakshi Pant Manish S. Jayswal 《Ionics》2013,19(2):301-307
In this paper, the electrical conductivity and relaxation studies in two different temperature regions (T?<?T m and T?>?T m) on plasticized PEO–PMMA blend polymer electrolyte system with AgNO3 salt are reported. The polymer electrolyte system has been prepared by solution cast technique and characterized by X-ray diffraction and differential scanning calorimetry. The conduction and relaxation processes at various temperatures have been investigated in the framework of modulus formalism. The distribution of relaxation times is discussed using Argand plot. Variation in ionic conductivity of polymer blends is discussed with the increase of PEO as well as with temperature. 相似文献
105.
106.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献
107.
The instability of the plane interface between two viscoelastic (Oldroydian) superposed conducting fluids permeated with suspended particles in porous medium is studied when the whole system is immersed in a uniform magnetic field. The dispersion relation for the Oldroydian viscoelastic fluid is obtained which also yields dispersion relations for Maxwellian and Newtonian fluids in special cases, in the presence of suspended particles in porous medium in hydromagnelics. The system is found to be stable for potentially stable case. The presence of magnetic field stabilizes certain wave number band whereas the system was unstable for all wave numbers in the absence of magnetic field, for the potentially unstable configuration. The growth rates increase (for certain wave numbers) and decrease (for other wave numbers) with the increase in stress relaxation time, strain retardation time, suspended particles number density and medium permeability. 相似文献
108.
Sea nodules were extensively studied over a wide range of temperature ranging from 77K to 1175K using Mossbauer effect and
ESR. The Mossbauer studies of the nodules at 77K and room temperature show a quadrupole doublet whereas at higher temperatures
magnetic spectra were obtained starting at around 875K which ultimately gives a hyperfine field of around 390 KOe at 1175
K. The Mossbauer spectra recorded at 30K did not show any significant change in the room temperature spectra. The analysis
of the spectra upto 775K showed two positions of FeR+, vie., octahedral and tetrahedral which were varified by ESR of the diluted samples. 相似文献
109.
Bhanushree Gupta Rahul Sharma Namrata Singh Yevgen Karpichev Manmohan L. Satnami Kallol K. Ghosh 《Journal of Physical Organic Chemistry》2013,26(8):632-642
Kinetic studies of the reactions of tertiary oximes (monoisonitroso acetone; MINA and butane 2,3 dione monooxime; BDMO) with some carboxylate (p‐nitrophenyl acetate and p‐nitrophenyl benzoate), phosphate (p‐nitrophenyl diphenyl phosphate and bis (2,4‐dinitrophenyl) phosphate) and sulfonate (p‐nitrophenyl p‐toluene sulphonate) esters in gemini surfactants have been conducted. The observed first‐order rate constant versus surfactant profiles show micelle‐assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. Experimental results showed that MINA exhibited better nucleophilic activity towards ester cleavage than BDMO. Pseudophase model has been applied in order to determine micellar second‐order rate constants and binding constants. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
110.
The structural, electronic and magnetic properties of small gallium clusters doped with Cobalt have been studied using spin-polarised density functional theory. The binding energy per atom, second-order differences of total energies and fragmentation energies of equilibrium geometries of the host Gan+1 and doped GanCo (n = 1–12) clusters are computed. Doped clusters are found to be more stable than pure Ga clusters; Ga3Co, Ga5Co and Ga8Co clusters are exceptionally stable. Doping with Co changes the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO–LUMO) gap, and also affects the magnetic moments of clusters. 相似文献