全文获取类型
收费全文 | 516篇 |
免费 | 33篇 |
国内免费 | 2篇 |
专业分类
化学 | 390篇 |
晶体学 | 5篇 |
力学 | 19篇 |
数学 | 42篇 |
物理学 | 95篇 |
出版年
2024年 | 6篇 |
2023年 | 11篇 |
2022年 | 32篇 |
2021年 | 46篇 |
2020年 | 33篇 |
2019年 | 29篇 |
2018年 | 29篇 |
2017年 | 21篇 |
2016年 | 34篇 |
2015年 | 17篇 |
2014年 | 23篇 |
2013年 | 46篇 |
2012年 | 42篇 |
2011年 | 43篇 |
2010年 | 35篇 |
2009年 | 21篇 |
2008年 | 10篇 |
2007年 | 17篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 3篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1987年 | 3篇 |
1984年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有551条查询结果,搜索用时 15 毫秒
181.
182.
M. Ijaz Khan Tasawar Hayat Sumaira Qayyum Muhammad Imran Khan A. Alsaedi 《Physics letters. A》2018,382(34):2343-2353
Here a novel applications of entropy generation optimization is presented for nonlinear Sisko nanomaterial flow by rotating stretchable disk. Flow is examined in the absence of magnetohydrodynamics and Joule heating. Total irreversibility rate (entropy generation rate) is investigated for different flow parameters. Heat source/sink and viscous dissipation effects are considered. Impacts of Brownian motion and thermophoresis on irreversibility have been analyzed. Governing flow equations comprise momentum, energy and nanoparticle concentration. Von Karman's similarity variables are implemented for reduction of PDEs into ODEs. Homotopy analysis technique for series solutions is implemented. Attention is given to the irreversibility. The impacts of different flow parameters on velocity, nanoparticle concentration, temperature and irreversibility rate are graphically presented. From obtained results it is examined that irreversibility rate enhances for larger estimation of Brinkman number and diffusion. Furthermore it is also examined that temperature and nanoparticle concentration show contrast behavior through Prandtl number and Brownian motion. 相似文献
183.
The enantiopure non-natural amino acids1 have been synthesized by insitu generation of iminium and iminium triflates from lactams using triflic anhydride in pyridine buffered media. These molecules with remote chiral centers may be useful in synthesis of natural product particularly Kopsia derived alkaloids. 相似文献
184.
Effect of particle size distribution on magnetic behavior of nanoparticles with uniaxial anisotropy 下载免费PDF全文
S Rizwan Ali Farah Naz Humaira Akber M Naeem S Imran Ali S Abdul Basit M Sarim Sadaf Qaseem 《中国物理 B》2018,(9)
The effect of particle size distribution on the field and temperature dependence of the hysteresis loop features like coercivity(H_C), remanence(M_R), and blocking temperature(T_B) is simulated for an ensemble of single domain ferromagnetic nanoparticles with uniaxial anisotropy. Our simulations are based on the two-state model for T T_B and the metropolis Monte-Carlo method for T T_B. It is found that the increase in the grain size significantly enhances H_C and T_B. The presence of interparticle exchange interaction in the system suppresses H_C but causes MRto significantly increase.Our results show that the parameters associated with the particle size distribution(D_(d,δ)) such as the mean particle size d and standard-deviation δ play key roles in the magnetic behavior of the system. 相似文献
185.
186.
187.
Imran Akhtar Rajat Mittal George V. Lauder Elliot Drucker 《Theoretical and Computational Fluid Dynamics》2007,21(3):155-170
Numerical simulations have been used to analyze the effect that vortices, shed from one flapping foil, have on the thrust
of another flapping foil placed directly downstream. The simulations attempt to model the dorsal–tail fin interaction observed
in a swimming bluegill sunfish. The simulations have been carried out using a Cartesian grid method that allows us to simulate
flows with complex moving boundaries on stationary Cartesian grids. The simulations indicate that vortex shedding from the
upstream (dorsal) fin is indeed capable of increasing the thrust of the downstream (tail) fin significantly. Vortex structures
shed by the upstream dorsal fin increase the effective angle-of-attack of the flow seen by the tail fin and initiate the formation
of a strong leading edge stall vortex on the downstream fin. This stall vortex convects down the surface of the tail and the
low pressure associated with this vortex increases the thrust on the downstream tail fin. However, this thrust augmentation
is found to be quite sensitive to the phase relationship between the two flapping fins. The numerical simulations allows us
to examine in detail, the underlying physical mechanism for this thrust augmentation.
相似文献
188.
In this paper, the focussing of the transmitted electromagnetic field through a quadric inhomogeneous slab of lossless uniaxial chiral medium is derived using transmission coefficient under oblique incidence. The inhomogeneity in the uniaxial chiral slab has been incorporated through permittivity parameter. Asymptotic ray theory provides valid field everywhere except at focal point where it gives infinite value. Singularity of the field at focal point is addressed using Maslov's method. The derived analytical field expressions at caustic or focal point of uniaxial quadratic inhomogeneous slab have been solved numerically using MATHEMATICA. The effects of chirality parameter, axial permittivity, transvers permittivity, angle of incidence on the refracted field are discussed and the effects of Brewster angle on the focussed field are also discussed. The results obtained using Maslov's method are compared with Huygens–Kirchhoff's integral which are in good agreement. 相似文献
189.
Ab initio study of structural,electronic and optical properties of ternary CdO1-xSex alloys using special quasi-random structures 下载免费PDF全文
The structural, electronic, and optical properties of binary CdO, CdSe, and their ternary CdO1 xSexalloys(0 ≤ x ≤ 1) in the rock salt and zinc blend phases have been studied by the special quasi-random structure(SQS) method. All the calculations are performed using full-potential linearized augmented plane wave plus local orbital’s(FP-LAPW+lo) method within the framework of density function theory(DFT). We use Wu–Cohen(WC) generalized gradient approximation(GGA) to calculate structural parameters, whereas both Wu–Cohen and Engel–Vosko(EV) GGA have been applied to calculate electronic structure of the materials. Our predicted results of lattice constant and bulk modulus show only a slight deviation from Vegard’s law for the whole concentrations. The obtained band structure indicates that for the rock-salt phase, the ternary alloys present semi-metallic behavior, while for the zinc blend phase, semiconductor behavior with direct bandgap is observed with decreasing order of x except for CdSe. Finally, by incorporating the basic optical properties, we discuss the dielectric function, refractive index, optical reflectivity, the absorption coefficient, and optical conductivity in terms of incident photon energy up to 14 eV. The calculated results of both binaries are in agreement with existing experimental and theoretical values. 相似文献
190.
Physicochemical and Rheological Properties of Novel Magnesium Salt-Polyacrylamide Composite Polymers
Khai Ern Lee Imran Khan Tjoon Tow Teng Beng Teik Poh 《Journal of Dispersion Science and Technology》2013,34(9):1284-1291
Two series of novel inorganic-organic composite polymers have been prepared through physical blending of magnesium chloride and magnesium hydroxide respectively with polyacrylamide aqueous solution. The physicochemical properties of the magnesium salt-polyacrylamide composite polymers were tuned by varying the ratio between the magnesium salt (e.g., magnesium chloride and magnesium hydroxide) and polyacrylamide. Characterizations of magnesium salt-polyacrylamide composite polymers were carried out via FTIR and TEM. Parameters such as solution conductivity and viscosity were also taken into account to characterize the physicochemical properties of the composite polymer aqueous solutions. Magnesium chloride-polyacrylamide (MCPAM) composite polymer aqueous solutions have a higher conductivity compared to magnesium hydroxide-polyacrylamide (MHPAM) composite polymer aqueous solutions. The viscosities of the MHPAM composite polymer aqueous solutions were found higher than MCPAM composite polymer aqueous solutions. The rheological properties of the composite polymer aqueous solutions were investigated using steady-state flow and oscillatory frequency sweep within the linear viscoelastic region. Shear-thinning effect was observed for both composite polymer systems when the shear rate increases. In oscillatory frequency sweep tests, both composite polymer systems show that the viscoelastic behaviors depend strongly on the magnesium salt concentrations. Viscous behavior was found to be dominant for both composite polymer systems. 相似文献