全文获取类型
收费全文 | 4942篇 |
免费 | 257篇 |
国内免费 | 32篇 |
专业分类
化学 | 3387篇 |
晶体学 | 57篇 |
力学 | 175篇 |
数学 | 766篇 |
物理学 | 846篇 |
出版年
2023年 | 34篇 |
2022年 | 141篇 |
2021年 | 150篇 |
2020年 | 101篇 |
2019年 | 197篇 |
2018年 | 155篇 |
2017年 | 111篇 |
2016年 | 245篇 |
2015年 | 155篇 |
2014年 | 248篇 |
2013年 | 487篇 |
2012年 | 283篇 |
2011年 | 293篇 |
2010年 | 209篇 |
2009年 | 203篇 |
2008年 | 218篇 |
2007年 | 207篇 |
2006年 | 204篇 |
2005年 | 171篇 |
2004年 | 158篇 |
2003年 | 133篇 |
2002年 | 177篇 |
2001年 | 74篇 |
2000年 | 109篇 |
1999年 | 64篇 |
1998年 | 41篇 |
1997年 | 47篇 |
1996年 | 35篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 37篇 |
1992年 | 33篇 |
1991年 | 23篇 |
1990年 | 17篇 |
1989年 | 29篇 |
1988年 | 28篇 |
1987年 | 21篇 |
1986年 | 18篇 |
1985年 | 30篇 |
1984年 | 27篇 |
1983年 | 23篇 |
1982年 | 21篇 |
1981年 | 26篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1975年 | 17篇 |
1959年 | 8篇 |
排序方式: 共有5231条查询结果,搜索用时 15 毫秒
51.
52.
H. Ismael M. K. El Nimr A. M. Abou El Ata M. A. El Hiti M. A. Ahmed A. A. Murakhowskii 《Journal of magnetism and magnetic materials》1995,150(3):403-408
The dielectric constant (′) and dielectric loss (tan δ) for hexaferrites BaCo2−xZnxFe16O27 have been studied as a function of frequency (f), temperature (T) and composition (x). The experimental results indicate that ′ and tan δ above the relaxation frequency only decrease as the frequency increases and as the temperature decreases. Tan δ shows the dielectric relaxation at certain critical frequencies which rise as temperature increases. The activation energy for the dielectric relaxation (ED), ′, and tan δ are found to be minimum for x = 0.8. 相似文献
53.
Natural radioactivity and radon exhalation rates in building materials used in Egypt 总被引:2,自引:0,他引:2
Natural and fabricated building materials commonly used in Egypt were surveyed for both natural radionuclides content and radon exhalation rate. These include raw as well as construction products. Concentration of natural radionuclides in all samples were determined by γ-ray spectroscopy with HPGe detector. For Radon exhalation rate measurements of fabricated samples, the seal can-technique has been applied using CR-39 plastic track detectors. The radiation hazard indices of the total natural radioactivity in the studied samples were estimated. The results were compared with the corresponding results of different countries and were found to be lying within the average world values. Radon exhalation rate in the studied samples varied between 197 (cement brick) and 907 mBq m−2 h−1 (blast furnace slag cement). The results of this survey suggest that, using blast furnace slag cement for pre-coating the internal walls of buildings in the Urban region of Egypt is discouraged and the replacement of clay brick by cement brick will be more healthy for the public. 相似文献
54.
55.
In this work, the geometrical structures, the formation energies, and electronic states of the Na(ms)Arn polyatomic exciplexes with m = 3-6 and n = 2-5 are studied by using a quantum-classical method. The interaction potential between an electronically excited sodium atom and argon atoms are calculated by using a one-electron model involving electron-Ar and electron-Na+ pseudopotentials, in which the Hamiltonian is diagonalized at every optimization step in the Basin Hopping algorithm. The relationship between the position of the electronically excited levels and the cluster geometry is investigated as a function of the excitation level and of the spatial extension of the excited electron orbital. We show that the equilibrium structures of the ground state Na(3s)Arn and those of the electronically excited states Na(4s)Arn, Na(5s)Arn, and Na(6s)Arn are significantly different. As a result of the detailed examination of the relationships between the geometrical structure and density distribution of the Na valence electron of the Na∗Arn with n = 2-5 polyatomic exciplexes, we can see that for the Na(4s)Arn polyatomic exciplexes, the two extreme geometries, neutral Na(3s)Arn and ionic Na+Arn compete. It appears that none of them is the actual one. For Na(5s)Arn and Na(6s)Arn the valence electron is very weakly bound to the ionic core and described by a more diffused orbital so that the geometry and the formation energies of this excited state called Rydberg states converge towards those of the ionic cores. 相似文献
56.
A high resolution (0.0018 cm−1) Fourier transform instrument has been used to record the spectrum of an enriched 34S (95.3%) sample of sulfur dioxide. A thorough analysis of the ν2, 2ν2 − ν2, ν1, ν1 + ν2 − ν2, ν3, ν2 + ν3 − ν2, ν1 + ν2 and ν2 + ν3 bands has been carried out leading to a large set of assigned lines. From these lines ground state combination differences were obtained and fit together with the existing microwave, millimeter, and terahertz rotational lines. An improved set of ground state rotational constants were obtained. Next, the upper state rotational levels were fit. For the (0 1 0), (1 1 0) and (0 1 1) states, a simple Watson-type Hamiltonian sufficed. However, it was necessary to include explicitly interacting terms in the Hamiltonian matrix in order to fit the rotational levels of the (0 2 0), (1 0 0) and (1 0 1) states to within their experimental accuracy. More explicitly, it was necessary to use a ΔK = 2 term to model the Fermi interaction between the (0 2 0) and (1 0 0) levels and a ΔK = 3 term to model the Coriolis interaction between the (1 0 0) and (0 0 1) levels. Precise Hamiltonian constants were derived for the (0 0 0), (0 1 0), (1 0 0), (0 0 1), (0 2 0), (1 1 0) and (0 1 1) vibrational states. 相似文献
57.
Attallah M. F. Rizk S. E. El Afifi E. M. 《Journal of Radioanalytical and Nuclear Chemistry》2018,317(2):933-945
Journal of Radioanalytical and Nuclear Chemistry - Three synthetic hematite (SH) materials as iron oxides nanofibers were prepared and applied for the removal of 51Cr and radioiodine (131I) as... 相似文献
58.
Abdellatif Kamal El Bouâzzaoui Choubabi Ahmed Jellal 《The European Physical Journal B - Condensed Matter and Complex Systems》2018,91(5):91
We study the electronic band structures of massless Dirac fermions in symmetrical graphene superlattice with cells of three regions. opening gaps and additional Dirac points. Finally, we inspect the potential effect on minibands, the anisotropy of group velocity and the energy bands contours near Dirac points. We also discuss the evolution of gap edges and cutoff region near the vertical Dirac points. 相似文献
59.
S. Sidi Ahmed G. Dimitri Ngantso M. Boujnah A. Benyoussef A. El Kenz 《Physics letters. A》2019,383(2-3):121-126
By using the density functional theory (DFT) and Monte Carlo simulations (MCS) with the Heisenberg model, we have studied magnetic properties of the bulk perovskite YCrO3. The exchange couplings of the Heisenberg model and the magnetic anisotropy are investigated. The 110 direction in the crystalline structure of the compound has shown the minimum energy, it is the easy magnetic direction. Using Monte Carlo simulations, the magnetizations behavior, the effects of system parameters and the critical exponents of the compound YCrO3 are implemented. It is shown that the bulk perovskite YCrO3 belongs to the 3D Heisenberg universality class. 相似文献
60.
Elías-Zúñiga Alex Palacios-Pineda Luis Manuel Olvera-Trejo Daniel Martínez-Romero Oscar 《Nonlinear dynamics》2020,102(3):1239-1270
Nonlinear Dynamics - In this paper, the dynamics response of a finite extensibility nonlinear elastic (FENE) absorber attached to a nonlinear primary system is investigated by writing the modal... 相似文献