全文获取类型
收费全文 | 718篇 |
免费 | 54篇 |
国内免费 | 4篇 |
专业分类
化学 | 307篇 |
力学 | 168篇 |
数学 | 151篇 |
物理学 | 150篇 |
出版年
2024年 | 4篇 |
2023年 | 13篇 |
2022年 | 38篇 |
2021年 | 37篇 |
2020年 | 35篇 |
2019年 | 29篇 |
2018年 | 46篇 |
2017年 | 32篇 |
2016年 | 58篇 |
2015年 | 25篇 |
2014年 | 26篇 |
2013年 | 37篇 |
2012年 | 59篇 |
2011年 | 72篇 |
2010年 | 42篇 |
2009年 | 41篇 |
2008年 | 50篇 |
2007年 | 28篇 |
2006年 | 14篇 |
2005年 | 16篇 |
2004年 | 22篇 |
2003年 | 17篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有776条查询结果,搜索用时 15 毫秒
761.
Ternary nanocomposites are prepared by blending hydroxyl‐terminated poly ether ether ketone having pendant methyl groups (PEEKMOH) with epoxy resin along with Nanolin DK1, followed by curing with 4,4′‐diamino diphenyl sulphone. Differential scanning calorimetry shows a two‐stage cure behavior indicating the catalytic effect of the primary amine and proton, which are generated by the dissociation of organic modifier. Tensile and flexural moduli are increased while tensile strength and glass transition temperature are decreased with increase in clay concentration. Fracture toughness and strain at break are increased by 59 and 62%, respectively, with 1 phr clay loading. Transition electron microscopy and X‐ray diffraction (XRD) analysis reveal exfoliated morphology for the nanocomposites. Scanning electron micrographs show a decrease in both, domain size as well as inter domain distance of the thermoplastic phase with the addition of clay, indicating the occurrence of gelation before phase separation. Analysis of the fracture surface reveals crack path deflection and ductile fracture behavior, confirming that toughness has been improved with the addition of clay and PEEKMOH. Coefficient of thermal expansion (CTE) of the nanocomposites is decreased up to 3 phr clay loading. Oxygen gas permeability is compared with Bharadwaj's and Neilson's models. A marginal improvement in thermal stability is observed with the addition of clay. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
762.
M. A. Gondal M. A. Dastageer A. Khalil K. Hayat Z. H. Yamani 《Journal of nanoparticle research》2011,13(8):3423-3430
Nanostructured ZnO photo catalyst was synthesized by precipitation method and was applied in conjunction with 355 nm pulsed
laser irradiation for effective disinfection of the water contaminated with Escherichia coli micro organism. The morphological studies using X-Ray Diffractometer (XRD) and Transmission Electron Microscope (TEM) were
carried out on the synthesized nano-ZnO, and these studies indicated that the catalyst has the crystallographic structure
of hexagonal wurtzite and has the grain size of around 20–40 nm. The bacteria decay rate constants were estimated for nine
different concentrations of nano-ZnO in infected water. The parametric optimization was carried out, and we could reach the
decay rate constant as high as 0.24 min,−1 which is higher than micro-structured ZnO and the familiar TiO2 photo catalysts under similar experimental condition. 相似文献
763.
D. N. Khan Marwat A. H. Kara T. Hayat 《International Journal of Theoretical Physics》2008,47(11):3075-3081
We show how one can construct conservation laws of the Liang equation which is not variational but may be regarded as Euler-Lagrange
in part. This first requires the determination of the Noether-type symmetries associated with the partial Lagrangian. The final construction
of the conservation laws resort to a formula equivalent to Noether’s theorem. A variety of subclasses are given and, for each,
a large number of conserved flows are found—the method is usable for any general choice of the variable speed of sound. 相似文献
764.
The steady two-dimensional mixed convection flow of a micropolar fluid over a non-linear stretching sheet is investigated. The governing non-linear equations and their associated boundary conditions are transformed into coupled non-linear ordinary differential equations. The series solution of the problem is obtained by utilizing the homotopy analysis method (HAM). The convergence of the obtained series solutions is carefully checked. The physical significance of interesting parameters on the flow and the thermal fields are shown through graphs and discussed in detail. The values of wall shear stress, couple wall stress and the local Nusselt number are tabulated. Comparison is also made with the corresponding results of viscous fluid with no mixed convection and an excellent agreement is noted. 相似文献
765.
numerical study is reported for two-dimensional flow of an incompressible Powell-Eyring fluid by stretching the surface with the Cattaneo-Christov model of heat diffusion. Impacts of heat generation/absorption and destructive/generative chemical reactions are considered. Use of proper variables leads to a system of non-linear dimensionless expressions. Velocity, temperature and concentration profiles are achieved through a finite difference based algorithm with a successive over-relaxation (SOR) method. Emerging dimensionless quantities are described with graphs and tables. The temperature and concentration profiles decay due to enhancement in fluid parameters and Deborah numbers. 相似文献
766.
Adel Ouannas Zaid Odibat Ahmed Alsaedi Aatef Hobiny Tasawar Hayat 《Chinese Journal of Physics (Taipei)》2018,56(5):1940-1948
Chaos and synchronization in fractional order systems have received increasing attention in recent years. In this paper, the problem of Q-S synchronization for different dimensional incommensurate fractional order chaotic systems is investigated. Based on Laplace transform and stability theory of linear integer order differential systems, some synchronization schemes are designed to achieve Q-S synchronization between n-D and m-D incommensurate fractional order chaotic systems. Test problems and numerical simulations are used to show the effectiveness of the proposed approach. 相似文献
767.
Here Darcy–Forchheimer 3D stretching flow of nanoliquid in the presence of convective condition and homogeneous–heterogeneous reactions is analyzed. Impacts of thermophoresis, Brownian diffusion and zero nanoparticles mass flux condition are considered. Adequate transformation procedure give rise to system in terms of ordinary differential equations. The governing mathematical system has been tackled by optimal homotopic technique. Graphical results have been presented for temperature and concentration dsitributions. Numerical benchmark is provided to study the values of skin friction coefficients and local Nusselt number. Skin friction coefficients are declared increasing functions of porosity and Forchheimer parameters. Furthermore the local Nusselt number is reduced for larger values of porosity and Forchheimer parameters. 相似文献
768.
Muhammad Rehan Malik Fatemah Farraj Al-Harbi Asif Nawaz Adnan Amin Arshad Farid Mohammed Al Mohaini Abdulkhaliq J. Alsalman Maitham A. Al Hawaj Yousef N. Alhashem 《Molecules (Basel, Switzerland)》2022,27(10)
In the present study, chitosan-decorated multiple nanoemulsion (MNE) was formulated using a two-step emulsification process. The formulated multiple nanoemuslion was evaluated physiochemically for its size and zeta potential, surface morphology, creaming and cracking, viscosity and pH. A Franz diffusion cell apparatus was used to carry out in vitro drug-release and permeation studies. The formulated nanoemulsion showed uniform droplet size and zeta potential. The pH and viscosity of the formulated emulsion were in the range of and suitable for topical delivery. The drug contents of the simple nanoemulsion (SNE), the chitosan-decorated nanoemulsion (CNE) and the MNE were 71 ± 2%, 82 ± 2% and 90 ± 2%, respectively. The formulated MNE showed controlled release of itraconazole as compared with that of the SNE and CNE. This was attributed to the chitosan decoration as well as to formulating multiple emulsions. The significant permeation and skin drug retention profile of the MNE were attributed to using the surfactants tween 80 and span 20 and the co-surfactant PEG 400. ATR-FTIR analysis confirmed that the MNE mainly affects the lipids and proteins of the skin, particularly the stratum corneum, which results in significantly higher permeation and retention of the drug. It was concluded that the proposed MNE formulation delivers drug to the target site of the skin and can be therapeutically used for various cutaneous fungal infections. 相似文献
769.
Image encryption based on elliptic curves (ECs) is emerging as a new trend in cryptography because it provides high security with a relatively smaller key size when compared with well-known cryptosystems. Recently, it has been shown that the cryptosystems based on ECs over finite rings may provide better security because they require the computational cost for solving the factorization problem and the discrete logarithm problem. Motivated by this fact, we proposed a novel image encryption scheme based on ECs over finite rings. There are three main steps in our scheme, where, in the first step, we mask the plain image using points of an EC over a finite ring. In step two, we create diffusion in the masked image with a mapping from the EC over the finite ring to the EC over the finite field. To create high confusion in the plain text, we generated a substitution box (S-box) based on the ordered EC, which is then used to permute the pixels of the diffused image to obtain a cipher image. With computational experiments, we showed that the proposed cryptosystem has higher security against linear, differential, and statistical attacks than the existing cryptosystems. Furthermore, the average encryption time for color images is lower than other existing schemes. 相似文献