全文获取类型
收费全文 | 8331篇 |
免费 | 265篇 |
国内免费 | 275篇 |
专业分类
化学 | 4085篇 |
晶体学 | 119篇 |
力学 | 176篇 |
综合类 | 31篇 |
数学 | 2902篇 |
物理学 | 1558篇 |
出版年
2023年 | 24篇 |
2022年 | 80篇 |
2021年 | 52篇 |
2020年 | 114篇 |
2019年 | 146篇 |
2018年 | 133篇 |
2017年 | 143篇 |
2016年 | 142篇 |
2015年 | 117篇 |
2014年 | 168篇 |
2013年 | 252篇 |
2012年 | 199篇 |
2011年 | 464篇 |
2010年 | 373篇 |
2009年 | 583篇 |
2008年 | 449篇 |
2007年 | 476篇 |
2006年 | 407篇 |
2005年 | 404篇 |
2004年 | 514篇 |
2003年 | 435篇 |
2002年 | 395篇 |
2001年 | 306篇 |
2000年 | 266篇 |
1999年 | 195篇 |
1998年 | 162篇 |
1997年 | 170篇 |
1996年 | 198篇 |
1995年 | 157篇 |
1994年 | 199篇 |
1993年 | 152篇 |
1992年 | 132篇 |
1991年 | 77篇 |
1990年 | 60篇 |
1989年 | 60篇 |
1988年 | 53篇 |
1987年 | 70篇 |
1986年 | 56篇 |
1985年 | 47篇 |
1984年 | 44篇 |
1983年 | 13篇 |
1982年 | 38篇 |
1981年 | 41篇 |
1980年 | 48篇 |
1979年 | 67篇 |
1978年 | 52篇 |
1977年 | 52篇 |
1976年 | 37篇 |
1974年 | 13篇 |
1973年 | 17篇 |
排序方式: 共有8871条查询结果,搜索用时 15 毫秒
991.
A solid-state rotational-echo double resonance (REDOR) NMR method was introduced to identify the ?- and ψ-torsion angle from a 1H–15N or 1H–13C′ spin system of alanine-like residues in a selectively, uniformly, or extensively 15N-/13C-labeled peptide. When a Cα(i) or a 15N peak is site-specifically obtainable in the NMR spectrum of a uniformly 15N/13C-labeled sample system, the ψ- or ?-torsion angle specified by the conformational structure of peptide geometry involving 15N(i)–1Hαi–15N(i + 1) or 13C′(i − 1)–1HNi–13C′(i) spin system can be identified based on 13Cα- or 15N-detected 1Hα–15N or 1HN–13C REDOR experiment. This method will conveniently be utilized to identify major secondary motifs, such as α-helix, β-sheet, and β-turn, from a uniformly 15N-/13C-labled peptide sample system. When tested on a 13C-/15N-labeled model system of a three amino acid peptide Gly–[U–13C, 15N]Ala–[U–13C, 15N]Leu, the ψ-angle of alanine obtained experimentally, ψ = −40 ± 30°, agreed reasonably well with the X-ray determined angle, ψ = −39°. 相似文献
992.
Qi Li Chen Bo LiGuang Zheng Kai Hua He An Shou Zheng 《Physica B: Condensed Matter》2011,406(20):3841-3846
The electronic structures of Fe-doped TiO2 anatase (1 0 1) surfaces have been investigated by all spin-polarized density functional theory (DFT) plane-wave pseudopotential method. The general gradient approximation (GGA)+U (Hubbard coefficient) method has been adopted to describe the exchange-correlation effects. Through the density functional calculations for the formation energies of various configurations, the complex of a substitutional Fe plus an O vacancy was found to form easily in the most range of O chemical potential. The calculated density of the states of the system of Fe-doped surface with a surface oxygen vacancy shows a band gap narrowing from 2.8 to 1.9 eV comparing with the pure surface due to the synergistic effects of surface Fe impurities with O vacancies. The system processes high visible light sensitivity and photocatalytic ability by decreasing extrinsic absorption energy. By comparing the partial DOS of some O and Ti atoms lying in the outermost and bottom layers of Fe-doped surfaces, it was found that the influence of Fe impurities on the electronic structure of the system is localized. 相似文献
993.
S. Aoki 《Progress in Particle and Nuclear Physics》2011,66(4):687-726
Progress on the potential method, recently proposed to investigate hadron interactions in lattice QCD, is reviewed. The strategy to extract the potential in lattice QCD is explained in detail. The method is applied to extract NN potentials, hyperon potentials and the meson–baryon potentials. A theoretical investigation is made to understand the origin of the repulsive core using the operator product expansion. Some recent extensions of the method are also discussed. 相似文献
994.
995.
Gisèle Ruiz Goldstein 《Physica D: Nonlinear Phenomena》2011,240(8):754-766
We consider in this article a Cahn-Hilliard model in a bounded domain with non-permeable walls, characterized by dynamic-type boundary conditions. Dynamic boundary conditions for the Cahn-Hilliard system have recently been proposed by physicists in order to account for the interactions with the walls in confined systems and are obtained by writing that the total bulk mass is conserved and that there is a relaxation dynamics on the boundary. However, in the case of non-permeable walls, one should also expect some mass on the boundary. It thus seems more realistic to assume that the total mass, in the bulk and on the boundary, is conserved, which leads to boundary conditions of a different type. For the resulting mathematical model, we prove the existence and uniqueness of weak solutions and study their asymptotic behavior as time goes to infinity. 相似文献
996.
Koji Hashimoto 《Applied Surface Science》2011,257(19):8141-8150
Amorphous alloys have many attractive characteristics including extremely high corrosion resistance if the sufficient amounts of corrosion-resistant elements are added. The superiority of amorphous alloys is based on the homogeneous single phase nature without any chemical and physical heterogeneities. Although there are processing limitations to avoid the formation of heterogeneous crystalline structure in addition to no welding technology without crystallization, the application of corrosion-resistant amorphous alloys is expected particularly to the very aggressive environments, where any conventional crystalline metallic materials cannot be used. Some amorphous bulk alloys showed zero corrosion mass loss due to spontaneous passivation even in 12 M HCl. Production of amorphous bulk alloys became possible for selected compositions. The homogeneous single phase nature is also effective to form useful catalysts with unique composition and structure. An example of catalysts is for carbon dioxide methanation useful for supply of renewable energy in the form of methane. 相似文献
997.
?smail Aslan 《Physics letters. A》2011,375(47):4214-4217
We analyze the discrete nonlinear Schrödinger equation with a saturable nonlinearity through the (G′/G)-expansion method to present some improved results. Three types of analytic solutions with arbitrary parameters are constructed; hyperbolic, trigonometric, and rational which have not been explicitly computed before. 相似文献
998.
The endcap of time-of-flight (ETOF) detector in BES (Beijing Spectrometer) III is planned to be upgraded by using multi-gap resistive plate chambers (MRPCs) and the designed time resolution of the MRPCs is around 50 ps. Thus a time-zero (T0) detector needs to be built to offer a high quality reference time for the MRPCs beam test. So a T0 detector is built using plastic scintillator tiles (BC420) to couple with four fast phototubes (PMTs, Hamamatsu H6533). The timing properties of the detector is studied by using a cosmic ray test and factors related to the time resolution, such as plastic scintillator size, readout mode and angle effects, are discussed. T0 detector timing resolutions of ~41-62 ps are achieved, which means that the T0 detector can be used in the MRPC beam test. 相似文献
999.
1000.