全文获取类型
收费全文 | 663篇 |
免费 | 40篇 |
国内免费 | 15篇 |
专业分类
化学 | 431篇 |
力学 | 56篇 |
数学 | 92篇 |
物理学 | 139篇 |
出版年
2024年 | 3篇 |
2023年 | 1篇 |
2022年 | 14篇 |
2021年 | 35篇 |
2020年 | 30篇 |
2019年 | 31篇 |
2018年 | 35篇 |
2017年 | 36篇 |
2016年 | 44篇 |
2015年 | 25篇 |
2014年 | 49篇 |
2013年 | 84篇 |
2012年 | 69篇 |
2011年 | 58篇 |
2010年 | 45篇 |
2009年 | 29篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有718条查询结果,搜索用时 15 毫秒
101.
Ahmadi F Alizadeh AA Shahabadi N Rahimi-Nasrabadi M 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,79(5):1466-1474
In this work a complex of Al3+ with curcumin ([Al(curcumin) (EtOH)2](NO3)2) was synthesized and characterized by UV-vis, FT-IR, elemental analysis and spectrophotometric titration techniques. The mole ratio plot revealed a 1:1 complex between Al3+ and curcumin in solution. For binding studies of this complex to calf thymus-DNA various methods such as: UV-vis, fluorescence, circular dichroism (CD), FT-IR spectroscopy and cyclic voltammetry were used. The intrinsic binding constant of ACC with DNA at 25°C was calculated by UV-vis and cyclic voltammetry as 2.1×10(4) and 2.6×10(4), respectively. The thermodynamic studies showed that the reaction is enthalpy and entropy favored. The CD results showed that only the Δ-ACC interacts with DNA and the Δ-ACC form has not any tendency to interact with DNA, also the pure curcumin has not any stereoselective interaction with CT-DNA. Fluorimetric studies showed that fluorescence enhancement was initiated by a static process in the ground state. The cyclic voltammetry showed that ACC interact with DNA with a binding site size of 2. From the FT-IR we concluded that the Δ-ACC interacts with DNA via partial electrostatic and minor groove binding. In comparison with previous works it was concluded that curcumin significantly reduced the affinity of Al3+ to the DNA. 相似文献
102.
103.
Dynamics of tractor lateral overturn on slopes under the influence of position disturbances (model development) 总被引:1,自引:0,他引:1
Iman Ahmadi 《Journal of Terramechanics》2011,48(5):339-346
In order to investigate the effects of forward speed, ground slope and wheel–ground friction coefficient on lateral stability of tractor at the presence of position disturbances, a tractor dynamic model was developed. In this model two types of instability were considered: instability due to overturn and skid and for each case the stability index was determined. Different geometries and mass specifications of tractor MITSUBISHI-2501D were used to examine the model. According to the results of this model forward speed and ground slope had a reverse effect on all stability indexes. Moreover stability of this tractor was more affected by tractor skidding than overturning. Therefore to improve the overall stability of this tractor, preference should be on increasing the tractor stability index derived from skid dynamics of tractor. 相似文献
104.
Ziad Omran 《Tetrahedron letters》2009,50(20):2434-130
We report herein the synthesis and the development of homo-bifunctional photo-cleavable sulfhydryl group cross-linkers that are able to react and then to photorelease two cysteines leading to the photoregulation of cross-linkers cleavage. 相似文献
105.
The equation of Raychaudhuri is one of the key concepts in the formulation of the singularity theorems introduced by Penrose
and Hawking. In the present article, taking into account QED vacuum polarization, we study the propagation of a bundle of
rays in a background gravitational field through the perturbative deformation of Raychaudhuri’s equation. In a sense, this
could be seen as another semiclassical study in which geometry is treated classically but matter (which means the photon here)
is allowed to exhibit quantum characteristics that are encoded in its coupling to the background curvature.
相似文献
106.
107.
G. Ahmadi 《Journal of sound and vibration》1977,52(1):27-35
The stability of the null solution of a class of a system of coupled partial differential equations with stationary random coefficients is studied. Criteria for the almost sure asymptotic stability of the equilibrium state are established. Some examples of the application of the results to engineering problems are presented. A variational scheme for improvement of the stability criteria is also discussed. 相似文献
108.
F. Darabi S. K. Moayedi A. R. Ahmadi 《International Journal of Theoretical Physics》2010,49(6):1232-1235
We use a generalized scheme of supersymmetric quantum mechanics to obtain the energy spectrum and wave function for Dirac
equation in (1+1)-dimensional spacetime coupled to a static scalar field. 相似文献
109.
Although one-dimensional nonlinear photonic crystal (1D-NPC) has been widely studied, there is no comprehensive analysis on decreasing the bistability threshold power.In this paper, conditions required to create bistability have been specified for two types of structures of alternative high and low refractive index layers and defect layers with Kerr nonlinearity effect, in the order of (HL)p(D)q(LH)p and (LH)p(D)q(HL)p, where L and H denote low and high refractive index layers, respectively, D stands for the defect layers, p is the number of LH or HL layers and q is the number of defect layers.One of the essentials for the bistability is appropriate shifts of frequency of the defect mode, so the effect of the order of layer's arrangement in (1D-NPC) structures have been studied. Different structures have been introduced and the best structure for the lowest bistability threshold power has been proposed. Nonlinear finite-difference time-domain (NFDTD) in C++ has been employed for simulation. 相似文献
110.
We propose procedures to address product design and manufacturing process configurations concurrently in environments characterized by large degrees of product proliferation. Exploiting the intrinsic flexibility of product and process design, we present two approaches that synchronize production flows through the manufacturing system. These approaches integrate product and manufacturing system design decisions with operational concerns and provide powerful means for managing production in environments characterized by a proliferation of products. Experimental results show that the proposed methods can substantially reduce manufacturing lead times, work in process (WIP), and overall system complexity. 相似文献