全文获取类型
收费全文 | 8525篇 |
免费 | 719篇 |
国内免费 | 1100篇 |
专业分类
化学 | 349篇 |
晶体学 | 22篇 |
力学 | 344篇 |
综合类 | 188篇 |
数学 | 8078篇 |
物理学 | 1363篇 |
出版年
2024年 | 15篇 |
2023年 | 79篇 |
2022年 | 92篇 |
2021年 | 135篇 |
2020年 | 192篇 |
2019年 | 234篇 |
2018年 | 234篇 |
2017年 | 239篇 |
2016年 | 280篇 |
2015年 | 183篇 |
2014年 | 400篇 |
2013年 | 642篇 |
2012年 | 351篇 |
2011年 | 506篇 |
2010年 | 492篇 |
2009年 | 671篇 |
2008年 | 633篇 |
2007年 | 670篇 |
2006年 | 565篇 |
2005年 | 507篇 |
2004年 | 433篇 |
2003年 | 451篇 |
2002年 | 409篇 |
2001年 | 265篇 |
2000年 | 292篇 |
1999年 | 289篇 |
1998年 | 241篇 |
1997年 | 229篇 |
1996年 | 139篇 |
1995年 | 78篇 |
1994年 | 72篇 |
1993年 | 43篇 |
1992年 | 39篇 |
1991年 | 24篇 |
1990年 | 17篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 7篇 |
1986年 | 5篇 |
1985年 | 16篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 24篇 |
1981年 | 14篇 |
1980年 | 20篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
L. Shao D. Shao C. G. Shao H. Noda 《International Journal of Theoretical Physics》2008,47(6):1663-1691
Using the recoupling theorem and graph calculation in loop quantum gravity, it is demonstrated that the action of metric matrix
operator on Gaussian weave state is an eigenaction, the representation matrix elements of the metric operator and their expectation
values are calculated. The values of length of tangent vectors of edges adjacent to the vertex of Gaussian weave state, as
well as the angles between them are also obtained in the cases of k=0 and k=2. 相似文献
63.
64.
65.
《Journal of Physics and Chemistry of Solids》2014,75(4):558-569
We present the structural, cation distribution, electrical and magnetic studies of CoAlxFe2−xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8) ferrites. The Rietveld-fitted X-ray diffraction (XRD) patterns confirm the formation of single-phase cubic spinel structures with space group for all the samples. A comprehensive analysis of XRD-based cation distribution has been performed to see the effect of Al3+ ions substitution on various structural parameters such as site ionic radii, edge length, bond length and interionic distances. The dielectric constant and direct current (DC) conductivity decreases with increasing Al3+ substitution up to x = 0.4. However, with further increase in Al3+ substitution, both the dielectric constant and the DC conductivity increase. The presentation of dielectric data in the complex electric modulus form reveals the presence of a non-Debye-type relaxation behaviour in the considered ferrites. The power law behaviour of alternating current (AC) conductivity indicates a strong correlation among electrons in these systems. The isothermal magnetisation versus applied field curves with high-field slope and significant coercivity suggest that the studied materials are highly anisotropic with canted spin structures. The samples exhibit ferrimagnetic behaviour at 300 K and the magnetisation decreases with increasing Al3+ concentration. The as-prepared samples are promising candidates for various industrial applications. 相似文献
66.
Microstructure and high-temperature corrosion behaviors of aluminide coatings by low-temperature pack aluminizing process 总被引:1,自引:0,他引:1
Zhaolin Zhan Zhong Liu Jianxiong Liu Li Li Zeng Li Pibo Liao 《Applied Surface Science》2010,256(12):3874-3879
Aluminide coatings were produced on carbon steel and Fe-5Cr-Mo alloy at a relatively lower temperature below 600 °C in shorter treatment time by a combination of surface refinement process and pack aluminizing process. Repetitive ball impact, generated by mechanical vibration, caused the top-layer refinement of substrates in a conventional pack aluminizing process. The effects of temperature and treatment time on the formation of aluminide coatings were analyzed. The microstructure of the coatings was investigated by SEM, AFM and XRD. The aluminide coatings were one-layer, compacted structure with ultrafine grains and uniform elemental distribution. High-temperature oxidation and sulphidation tests were carried out at 600 °C in air for 200 h and 10% SO2 + Ar gas mixture atmosphere for 50 h, respectively. The mass gains and spallation indicated that the aluminide coatings significantly improved the high-temperature oxidation and sulphidation resistance. 相似文献
67.
FAN Hong-Yi GUO Qin 《理论物理通讯》2008,49(4):859-862
We introduce the quantum Hadamard operator in continuum state vector space and find that it can be decomposed into a single-mode squeezing operator and a position-momentum mutual transform operator. The two-mode Hadamard operator in bipartite entangled state representation is also introduced, which involves the two-mode squeezing operator and [η〉 ←→|ξ〉 mutual transformation operator, where [η〉 and |ξ〉 are mutual conjugate entangled states. All the discussions are proceeded by virtue of the IWOP technique. 相似文献
68.
The q-p phase-space distribution function is a popular tool to
study semiclassical physics and to describe the quantum aspects of a system. In this paper by using the pure state density operator formula of the Husimi operator
Δh(q,p;κ)=|p,q〉κκ〈p,q| we deduce the Husimi function of the excited squeezed vacuum state. Then we study the behavior of Husimi distribution graphically. 相似文献
69.
Gerd Wellenreuther Venkataraman Parthasarathy Wolfram Meyer‐Klaucke 《Journal of synchrotron radiation》2010,17(1):25-35
In biological systems, X‐ray absorption spectroscopy (XAS) can determine structural details of metal binding sites with high resolution. Here a method enabling an automated analysis of the corresponding EXAFS data is presented, utilizing in addition to least‐squares refinement the prior knowledge about structural details and important fit parameters. A metal binding motif is characterized by the type of donor atoms and their bond lengths. These fit results are compared by bond valance sum analysis and target distances with established structures of metal binding sites. Other parameters such as the Debye–Waller factor and shift of the Fermi energy provide further insights into the quality of a fit. The introduction of mathematical criteria, their combination and calibration allows an automated analysis of XAS data as demonstrated for a number of examples. This presents a starting point for future applications to all kinds of systems studied by XAS and allows the algorithm to be transferred to data analysis in other fields. 相似文献
70.
The absorption spectrum of the 16O3 isotopologue of ozone has been recorded in the 7000-7920 cm−1 region by high sensitivity CW-Cavity Ring Down Spectroscopy. This report is devoted to the analyses of the 7065-7300 cm−1 region dominated by the ν1 + 2ν2 + 5ν3 and ν1 + 5ν2 + 3ν3 A-type bands at 7130.8 and 7286.8 cm−1 respectively. 289 transitions were assigned to the ν1 + 2ν2 + 5ν3 band. The corresponding line positions were modeled with an effective Hamiltonian involving Coriolis resonance interactions between the (1 2 5) upper state and the (4 4 0), (0 2 6) and (6 1 0) dark states, and an anharmonic resonance interaction with the (2 0 5) state. The very strong interaction (up to 50% mixing of the wavefunctions) between the (1 2 5) and (6 1 0) states leads to the observation of two extra lines of the 6ν1 + ν2 band due to a resonance intensity transfer. 213 transitions of the ν1 + 5ν2 + 3ν3 band were assigned and modeled taking into account a Coriolis resonance interaction with the (3 6 0) state.We take the opportunity of the present work to report the analysis of the very weak 4ν2 + 4ν3 B-type band at 6506.1 cm−1 which was assigned from previously recorded CRDS spectra. 286 transitions were modeled using the effective Hamiltonian approach.The dipole transition moment parameters of the three analyzed bands were determined by a least-squares fit to the measured line intensities. For the three studied band systems, the effective Hamiltonian and transition moment operator parameters were used to generate line lists provided as Supplementary Materials. 相似文献