全文获取类型
收费全文 | 279篇 |
免费 | 16篇 |
国内免费 | 5篇 |
专业分类
化学 | 168篇 |
力学 | 8篇 |
数学 | 56篇 |
物理学 | 68篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 16篇 |
2016年 | 26篇 |
2015年 | 8篇 |
2014年 | 25篇 |
2013年 | 31篇 |
2012年 | 25篇 |
2011年 | 15篇 |
2010年 | 14篇 |
2009年 | 14篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 12篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1959年 | 1篇 |
1956年 | 2篇 |
排序方式: 共有300条查询结果,搜索用时 285 毫秒
21.
Lu K Luo T Xiang Z You Z Fathi R Chen J Yang Z 《Journal of combinatorial chemistry》2005,7(6):958-967
A one-pot synthesis of diverse benzofurans and indoles from readily available starting materials was achieved via the sequential Ugi four-component reaction, intramolecular Diels-Alder reaction, and oxidative aromatization. 相似文献
22.
Matrix Heterogeneity Effects on Gas Transport and Adsorption in Coalbed and Shale Gas Reservoirs 总被引:2,自引:0,他引:2
In coalbeds and shales, gas transport and storage are important for accurate prediction of production rates and for the consideration
of subsurface greenhouse gas sequestration. They involve coupled fluid phenomena in porous medium including viscous flow,
diffusive transport, and adsorption. Standard approach to describe gas–matrix interactions is deterministic and neglects the
effects of local spatial heterogeneities in porosity and material content of the matrix. In this study, adopting weak-noise
and mean-field approximations and using a statistical approach in spectral domain, matrix heterogeneity effects are investigated
in the presence of non-equilibrium adsorption with random partition coefficient. It is found that the local heterogeneities
can generate non-trivial transport and kinetic effects which retard gas release from the matrix and influence the ultimate
gas recovery adversely. Macro-transport shows 1/[1 + N
Pe
/(1 + N
Pe
)] dependence on the Péclet number, and persists at the diffusive ultra-low permeability limit. Macro-kinetics is directly
related to Thiele modulus by the following expression: N
Th
/(1 + 2N
Pe
). It leads to trapping of gas in the adsorbed phase during its release from the matrix, and to an adsorption threshold during
the gas uptake by the matrix. Both effects are proportional to the initially available adsorbed gas amount and becomes more
pronounced with the increasing variance of the porosity field. Consequently, a new upscaled deterministic gas mass balance
is proposed for practical purposes. Numerical results are presented showing free and adsorbed gas distributions and fractional
gas sorption curves for unipore coal matrix exhibiting Gaussian porosity distribution. This study is a unique approach for
our further understanding of the coalbeds and gas shales, and it is important for the development of sound numerical gas production
and sequestration models. 相似文献
23.
New double-ring octa-aza macrocyclic complexes, synthesized by condensation of oxamide-N,N-diethanoic acid with diethylenetriamine in 1:2 ratio in the presence of CuII, NiII or CoII, have been characterized by elemental analyses, i.r., u.v., magnetic susceptibility and conductivity measurements. The complexes are non-electrolytes, in which each metal ion is in a spin-free state in a pseudo- octahedral geometry. The high magnetic moments are attributed to a ferromagnetic effect. 相似文献
24.
Fathi B. Saidp∗ 《Applicable analysis》2013,92(1-4):101-127
We study the existence, uniqueness, and asymtotic behaviour of non-negative solutions to a parabolic diffusion equation involving a nonlocal con-vective term on a bounded domain ? contained in Rn. We apply the In variance Principle of LaSalle and Hale to prove that the solution tends to zero as t → ∞ 相似文献
25.
Maroufi B. Laghmach R. EL Hadfi H. Daoud M. 《International Journal of Theoretical Physics》2021,60(8):3103-3114
The quantum Fisher information defined via the symmetric logarithmic derivative and the skew information are two different aspects describing the information contents of quantum mechanical density operators. They are considered as natural generalizations of the classical Fisher information and constitute key ingredients in the emerging field of quantum metrology. In this paper, we give the analytical expression of quantum Fisher information and skew information for two-qubit system prepared in a two-qubit state of X type.
相似文献26.
Susan Sadeghi Fatemeh Fathi 《Journal of inclusion phenomena and macrocyclic chemistry》2010,67(1-2):91-98
A new PVC membrane coated graphite electrode for cesium ion based on 4′,4″(5′)di–tert-butyl di-benzo-18-crown-6 (DTBDB18C6) as ionophore was prepared. The electrode shows a near Nernstian response of 57.0 ± 1.8 mV decade?1 over a wide activity range of 6.0 × 10?6–1.0 × 10?1 mol L?1 with a limit of detection 4.0 × 10?6 mol L?1. The proposed electrode is suitable for use in aqueous solution in the pH range of 3.0–9.5. It has a fast response time of 10 s and can be used for at least 1 month without any considerable divergence in potential. The selectivity coefficients for Cs+ ion with respect to ammonium, alkali, alkaline earth and some selected transition metal ions were determined and showed a superior selectivity over Li+, Na+ and alkaline earth metal ions. The new electrode was applied for determination of Cs+ in spiked tap water. The electrode was also used as indicator electrode in potentiometric titration of Cs+ with sodium tetraphenyl borate. 相似文献
27.
Alireza Khorsandi Saeed Ghavami Sabouri Somaieh Fathi Marzieh Asadnia-Jahromi 《Optics & Laser Technology》2011,43(5):956-959
We have reported a modified V-shaped external cavity, which is constructed around a commercial diode laser operating at a center wavelength of λ=785 nm by adding a new coated glass plate with about 50% reflectivity to the cavity. This allows simultaneous dual-wavelengths operation in the vicinity of Δνmin=0.18 THz to Δνmax=0.22 THz, which can be used as laser source for terahertz generation either for semiconductor devices or nonlinear schemes. 相似文献
28.
Although during the last years one has seen a number of systematic studies of the surface energies of metals, the aim and the scientific meaning of this research is to establish a simple and a straightforward theoretical model to calculate accurately the mechanical and the thermodynamic properties of metal surfaces due to their important application in materials processes and in the understanding of a wide range of surface phenomena. Through extensive theoretical calculations of the surface tension of most of the liquid metals, we found that the fraction of broken bonds in liquid metals (f) is constant which is equal to 0.287. Using our estimated f value, the surface tension (γm), surface energy (γSV), surface excess entropy (−dγ/dT), surface excess enthalpy (Hs), coefficient of thermal expansion (αm and αb), sound velocity (cm) and its temperature coefficient (−dc/dT) have been calculated for more than sixty metals. The results of the calculated quantities agree well with available experimental data. 相似文献
29.
A new method for modeling and analysis of deformed carbon nanotubes (CNTs) using Green’s function, is presented in this paper,
for the first time. Using the proposed method, a new circuit model is obtained for the deformation region of a deformed single-walled
CNT (SWCNT), which the values of its elements depend on the type of deformation and also the deformation parameters such as
the coupling matrices and the energy variations of deformation region. The comparison between the obtained results from the
analysis of proposed model and the literature gives a good match which approves the accuracy and correctness of the proposed
model. 相似文献
30.
Corrosion and biological behavior of nanostructured 316L stainless steel processed by severe plastic deformation
下载免费PDF全文
![点击此处可从《Surface and interface analysis : SIA》网站下载免费的PDF全文](/ch/ext_images/free.gif)
K. Hajizadeh H. Maleki‐Ghaleh A. Arabi Y. Behnamian E. Aghaie A. Farrokhi M. G. Hosseini M. H. Fathi 《Surface and interface analysis : SIA》2015,47(10):978-985
Nanostructured metals have different mechanical, chemical, and physical behaviors in comparison with the microstructured ones. Numerous research studies demonstrated that the biological behavior of nanostructured metallic implants was improved significantly. Concerning the nanostructured metals, decreasing the corrosion rate and the releasing of hazardous ions from metallic implants, and thus increasing the biocompatibility of implants are due to improving the native oxide layer. In the present study, nanostructured 316L stainless steel (biomedical grade) was manufactured via equal channel angular pressing (ECAP) method. To do so, the 316L stainless steel (SS) was exposed to the ECAP operation for eight passes. The impact of the ECAP process on corrosion behavior of SS samples was evaluated through performing the electrochemical polarization corrosion tests in Ringer's solution. Scanning electron microscopy was employed to study the surface morphology of common SS and ECAPed SS sample after the electrochemical polarization tests. Moreover, the biological behavior of the samples was evaluated via cell culture using fibroblast cells. The corrosion test results revealed a substantial decrease of corrosion rate from 3.12 (coarse‐grained sample) to 0.42 μA cm?2 (for nanostructured). Furthermore, the cell proliferation in the interface of nanostructured sample and cell culture medium enhanced dramatically compared with the coarse‐grained one. The much better biological behavior of nanostructured SS sample in comparison with the coarse‐grained one is mostly due to the significant decrease of corrosion rate on the surface of SS samples, and the presence of much more chrome oxide on the surface of SS sample. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献