全文获取类型
收费全文 | 5465篇 |
免费 | 695篇 |
国内免费 | 441篇 |
专业分类
化学 | 2057篇 |
晶体学 | 29篇 |
力学 | 237篇 |
综合类 | 39篇 |
数学 | 1510篇 |
物理学 | 2729篇 |
出版年
2024年 | 5篇 |
2023年 | 44篇 |
2022年 | 63篇 |
2021年 | 126篇 |
2020年 | 132篇 |
2019年 | 146篇 |
2018年 | 139篇 |
2017年 | 172篇 |
2016年 | 239篇 |
2015年 | 167篇 |
2014年 | 241篇 |
2013年 | 634篇 |
2012年 | 315篇 |
2011年 | 338篇 |
2010年 | 287篇 |
2009年 | 320篇 |
2008年 | 303篇 |
2007年 | 373篇 |
2006年 | 303篇 |
2005年 | 243篇 |
2004年 | 255篇 |
2003年 | 224篇 |
2002年 | 199篇 |
2001年 | 188篇 |
2000年 | 176篇 |
1999年 | 137篇 |
1998年 | 128篇 |
1997年 | 94篇 |
1996年 | 76篇 |
1995年 | 89篇 |
1994年 | 73篇 |
1993年 | 58篇 |
1992年 | 33篇 |
1991年 | 44篇 |
1990年 | 26篇 |
1989年 | 27篇 |
1988年 | 30篇 |
1987年 | 19篇 |
1986年 | 40篇 |
1985年 | 23篇 |
1984年 | 14篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 10篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1973年 | 2篇 |
1972年 | 3篇 |
排序方式: 共有6601条查询结果,搜索用时 31 毫秒
971.
In response to recent helium atom scattering (HAS) and neutron scattering results, Monte Carlo simulations and perturbation theory calculations have been performed for D2 on MgO(0 0 1). Monte Carlo simulations predict that D2 molecules form a series of interesting structures, p(2 × 2) → p(4 × 2) → p(6 × 2), with coverages Θ = 0.5, 0.75, 0.83 respectively, and followed by a formation of a top layer of p(6 × 2) unit cell symmetry. The three types of mono-layers are stable up to 13 K, whereas the top layer still exists up to 10 K. This is in partial agreement with the neutron scattering and HAS results that report c(2 × 2), c(4 × 2) and c(6 × 2); they agree in terms of coverage and stability, but disagree in terms of symmetry. A quantum mechanical examination of the D2 molecules’ rotational motion shows the molecular axes are azimuthally delocalized and hence the simulated structures are c-type rather than p-type. These calculations also indicate that ortho-D2 and helicoptering para-D2 prefer cationic sites, while cartwheeling para-D2 prefers anionic sites. 相似文献
972.
Phase behaviors of argon in several types of cylindrical and slit pores are examined by grand-canonical Monte Carlo simulations. Condensation processes in single- and multi-walled carbon nanotubes along with those in hard-wall tubes are compared. Effects of the pore size on pressure-tensor components, the fluid-wall surface tension, and the adsorption are also compared for the different fluid-pore interactions. The chemical potential at which the fluid begins to condense in the single-walled nanotube is greater than that in the multi-walled nanotube by an amount nearly equal to the difference in the potential-well depth of the fluid-pore interaction, and the adsorption isotherms overlap each other almost completely for narrow pores and partially for wider pores. Similar analyses are performed for slit pores of two different hydrocarbon models. 相似文献
973.
K. Yamaji T. Yanagisawa M. Miyazaki R. Kadono 《Physica C: Superconductivity and its Applications》2009,469(15-20):1037-1040
Naito et al. reported that some non-doped T′-214-type compounds drive high-Tc superconductivity. The compounds are considered to be metallic since on-site Coulomb energy U is moderate and the Fermi surface is much deformed in these compounds. In order to confirm this picture and extract electronic structure information, we have examined the phase diagram of the metallic state of the 2D Hubbard model as a function of U and t′ (with t″ we fixed at − t′/2 here; t′ and t″ are the second- and third-neighbor transfer energies, respectively) by means of the variational Monte–Carlo method. We employed a Jastrow-type Gutzwiller trial wave function. In the studied range of U = 2–12, the boundary value for |t′| at which SDW disappears increases almost linearly with U. Jump-wise transition to the Mott insulator state was not observed. Using the boundary curve and experimental band parameter values, we estimate U 5 for T′-214 compounds. Preceding works are discussed in the last part. 相似文献
974.
T. Watanabe H. Yokoyama M. Ogata 《Physica C: Superconductivity and its Applications》2009,469(15-20):1009-1012
To consider the origin of a pseudogap and a superconducting (SC) gap found in the high-Tc cuprates, we evaluated the momentum dependence of the singlet gap corresponding to the pseudogap and the SC gap in the t–J model, using an optimization variational Monte Carlo (VMC) method. In the underdoped regime, the singlet gap is significantly modified from the simple dx2-y2(d)-wave gap (∝ cos kx − cos ky) by the contribution of long-range pairings. Its angular dependence at the quasi Fermi surface is qualitatively consistent with those experimentally observed in both hole and electron-doped cuprates. On the other hand, a SC gap is almost unchanged, preserving the original simple d-wave form. Thus, it seems that the incoherent part of the singlet gap mainly influences the forms of observed gaps. 相似文献
975.
The accelerators should be properly designed to make the radiation field produced by beam loss satisfy the dose limits. The radiation field for high intensity H- cyclotron includes prompt radiation and residual radiation field. The induced radioactivity in accelerator components is the dominant source of occupational radiation exposure if the accelerator is well shielded. The source of radiation is the beam loss when cyclotron is operating. In this paper, the radiation field for CYCIAE-100 is calculated using Monte Carlo method and the radioactive contamination near stripping foil is studied. A method to reduce the dose equivalent rate of maintenance staff is also given. 相似文献
976.
SONG Yu-Shou YE Yan-Lin GE Yu-Cheng L Lin-Hui Faisal Q. JIANG Dong-Xing HUA Hui ZHENG Wao LI Zhi-Huan LI Xiang-Qing LOU Jian-Ling LU Fei FAN Feng-Ying CAO Zhong-Xin LI Qi-Te XIAO Jun 《中国物理C(英文版)》2009,33(10)
To perform a kinematically complete measurement of the dissociation reaction for neutron-rich nuclei, a multi-neutron correlation spectrometer is proposed at Peking University.A Monte Carlo simulation code based on GEANT4 is developed for a single scintillation bar which processes not only the energy deposition but also the light propagation in the scintillator and the light collection and conversion to signal at the end of the bar in a realistic way. The simulating method is described in detail in this paper, and the timing and position resolutions and detector efficiency are studied based on the simulation and compared with the experimental results.A new method of crosstalk rejection has been demonstrated to be important for the design of the whole spectrometer. 相似文献
977.
Total reaction and fusion cross sections at sub- and near-barrier energies for the system 7Li + 28Si
A. Pakou K. Rusek N. Alamanos X. Aslanoglou M. Kokkoris A. Lagoyannis T. J. Mertzimekis A. Musumarra N. G. Nicolis D. Pierroutsakou D. Roubos 《The European Physical Journal A - Hadrons and Nuclei》2009,39(2):187-194
Fusion cross sections are extracted for the 7Li$ + $28Si system, via reaction cross section and transfer measurements at sub- and near-barrier energies ( E
lab = 5.7 to 14MeV). The energy evolution of transfer to reaction cross section ratios is determined with the aid of CDCC calculations,
which subsequently allows the deduction of fusion cross sections at sub- and near-barrier energies. It is shown that fusion
can be well represented in a BPM context. Fusion cross sections are compared for the systems 7Li$ + $28Si and 6Li$ + $28Si, the latter studied previously, and are found to exhibit different strengths. Last, the direct channels determined at 13MeV,
are found to be dominated by a 2n -transfer mechanism. 相似文献
978.
R. V. Chamberlin G. H. Wolf 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,67(4):495-499
The entropy per particle in most Monte-Carlo simulations is size dependent
due to correlated energy fluctuations. Guided by nanothermodynamics, we find
a constraint for the Ising model that enhances the fluctuations and lowers
the free energy, while making the entropy homogeneous, additive, and
extensive. Although the average interaction energy becomes size dependent,
the resulting distribution of energies provides a mechanism for the
heterogeneity found in the dynamics of many materials. 相似文献
979.
F. Calvo P. Poulain 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(1):15-23
Monte Carlo simulations of gas-phase polyalanine peptides have been carried out with the Amber ff96 force field. A low-temperature structural transition takes place between the α-helix stable conformation and β-sheet structures,
followed by the unfolding phase change. The transition state ensembles connecting the helix and sheet conformations are investigated
by sampling the energy landscape along specific geometric order parameters as putative reaction coordinates, namely the electric
dipole μ, the end-to-end distance d, and the gyration radius Rg. By performing series of shooting trajectories, the committor probabilities and their distributions are obtained, revealing
that only the electric dipole provides a satisfactory transition coordinate for the α↔β interconversion. The nucleus at the
transition is found to have a high helical content. 相似文献
980.
采用Potts模型Monte Carlo方法研究了晶粒棱长、尺寸与拓扑学特征之间的统计关系.结果表明,晶粒棱长与晶粒面数之间呈线性统计关系,并且平均N面体晶粒模型和Poisson-Voronoi组织均支持该结论.不同时刻的晶粒长大仿真数据表明,在准稳态晶粒长大阶段晶粒棱长的分布具有自相似性.个体晶粒的平均棱长随晶粒面数(或晶粒尺寸)的增加而逐渐增大,这说明一些理论模型中采用的“不同面数的晶粒平均棱长均相等”的假设具有局限性.仿真数据和纯铁实验数据均表明,晶粒尺寸与晶粒面数之间的统计关系表现为一条单调递增的凸曲线.
关键词:
晶粒棱长
晶粒尺寸
拓扑学
Monte Carlo仿真 相似文献