全文获取类型
收费全文 | 12434篇 |
免费 | 2029篇 |
国内免费 | 1754篇 |
专业分类
化学 | 9128篇 |
晶体学 | 164篇 |
力学 | 740篇 |
综合类 | 127篇 |
数学 | 1605篇 |
物理学 | 4453篇 |
出版年
2024年 | 27篇 |
2023年 | 173篇 |
2022年 | 296篇 |
2021年 | 377篇 |
2020年 | 427篇 |
2019年 | 442篇 |
2018年 | 391篇 |
2017年 | 380篇 |
2016年 | 544篇 |
2015年 | 567篇 |
2014年 | 711篇 |
2013年 | 895篇 |
2012年 | 1066篇 |
2011年 | 1213篇 |
2010年 | 873篇 |
2009年 | 891篇 |
2008年 | 1009篇 |
2007年 | 868篇 |
2006年 | 793篇 |
2005年 | 604篇 |
2004年 | 456篇 |
2003年 | 370篇 |
2002年 | 411篇 |
2001年 | 346篇 |
2000年 | 313篇 |
1999年 | 268篇 |
1998年 | 199篇 |
1997年 | 173篇 |
1996年 | 204篇 |
1995年 | 172篇 |
1994年 | 107篇 |
1993年 | 105篇 |
1992年 | 87篇 |
1991年 | 84篇 |
1990年 | 67篇 |
1989年 | 66篇 |
1988年 | 39篇 |
1987年 | 40篇 |
1986年 | 36篇 |
1985年 | 25篇 |
1984年 | 19篇 |
1983年 | 22篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1974年 | 4篇 |
1972年 | 4篇 |
1971年 | 3篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
991.
<正>A novel polyester containing ferrocenyl was prepared by low-temperature interface polycondensation of 1,1'-ferrocenedicarboxylic acid chloride with 4-(4-hydroxyphenyl)-2,3-phthalazin-1-one(DHPZ),which is a twisted non-coplanar heterocyclic bisphenol-like monomer.The newly generated polymer was evaluated based on characterization of its solubility,viscosity measurements,elemental analysis,FTIR spectroscopy,differential scanning calorimetric and thermogravimetric studies. 相似文献
992.
993.
Enhanced Catalytic Activity in Liquid‐Exfoliated FeOCl Nanosheets as a Fenton‐Like Catalyst 下载免费PDF全文
Jian Zhang Prof. Xiu‐Ling Jiao Dr. Yu‐Guo Xia Fang‐Fang Liu Ying‐Ping Pang Xin‐Fu Zhao Prof. Dai‐Rong Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(27):9321-9329
A facile liquid‐phase exfoliation method to prepare few‐layer FeOCl nanosheets in acetonitrile by ultrasonication is reported. The detailed exfoliation mechanism and generated products were investigated by combining first‐principle calculations and experimental approaches. The similar cleavage energies of FeOCl (340 mJ m?2) and graphite (320 mJ m?2) confirm the experimental exfoliation feasibility. As a Fenton reagent, FeOCl nanosheets showed outstanding properties in the catalytic degradation of phenol in water at room temperature, under neutral pH conditions, and with sunlight irradiation. Apart from the increased surface area of the nanosheets, the surface state change of the nanosheets also plays a key role in improving the catalytic performance. The changes of charge density, density of states (DOS), and valence state of Fe atoms in the exfoliated FeOCl nanosheets versus plates illustrated that surface atomistic relationships made the few‐layer nanosheets higher activity, indicating the exfoliation process of the FeOCl nanosheets also brought about surface state changes. 相似文献
994.
The elasto-plastic-damage behavior of anisotropic aluminum alloys is investigated under finite deformation using a physical mechanism based constitutive model. With an application to the structural calculation, the present model is used to describe and analyze the mechanical response of anisotropic 6260-T6 aluminum alloy extrusions. For the tensile specimens extracted along three different material orientations from the extruded aluminum profile, twelve simulations are carried out covering four different specimen geometries. The simulation results in force-displacement response and central logarithmic axial strain evolution are compared with experimental results. From the comparisons, it can be concluded that the present model has the capacity to describe the behavior of anisotropic material. From the force-displacement curves, the anisotropy is observed in different material orientations, and the physical mechanism of anisotropy is analyzed. 相似文献
995.
Youneng Guo Maofa Fang Shiyang Zhang Jiang Huang Xiang Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2014,68(11):1-7
The nonlinear interaction between electron-acoustic shock waves in a dissipative, non-Maxwellian plasma composed of cold fluid electrons, stationary background ions, and inertialess superthermal electrons has been studied. The effects of plasma parameters on the trajectory changes (i.e., phase shifts) of shock waves after their head-on collision is our main concern. The results indicate that the interactions between shocks are different from those of solitons. Also, it is found that the occurrence and variation of trajectory shifts may be due to the combined role played by the dispersion and dissipation of the colliding nonlinear structure. 相似文献
996.
Z. J. Chen J. W. Fang S. Y. Zhang 《The European physical journal. Special topics》2008,153(1):195-198
For a film-on-substrate system, in the case of thin films
with lower thermal diffusivities compared to substrates, the phase
characterization of the photothermal signals is analyzed. Moreover, the
numerical estimations of multiparameter are performed, which show the
feasibility of simultaneous determination of the thermal diffusivities of
the film and the substrate, as well as the thermal interface resistance of
the film/substrate. Because the thermal diffusivity of the thin-film and the
thermal interface resistance may be highly correlated, a genetic algorithm
is used as an estimation method for the determination of the thermal
properties of thin films with low thermal diffusivity. 相似文献
997.
This paper simulates the dendrite growth process during non-isothermal solidification in the Al-Cu binary alloy by using the phase-field model. The heat transfer equation is solved simultaneously. The thermodynamic and kinetic parameters are directly obtained from existing database by using the Calculation of Phase Diagram (CALPHAD) method. The effects of the latent heat and undercooling on the dendrite growth, solute and temperature profile during the solidification of binary alloy are investigated. The results indicate that the dendrite growing morphologies could be simulated realistically by linking the phase-field method to CALPHAD. The secondary arms of solidification dendritic are better developed with the increase of undercooling. Correspondingly, the tip speed and the solute segregation in solid-liquid interface increase, but the tip radius decreases. 相似文献
998.
Perturbation to Mei symmetry and Mei adiabatic invariants for mechanical systems in phase space 下载免费PDF全文
For a perturbed mechanical system in phase space, considering d/dt in the structure equation and process of proof including infinitesimal parameter ε obviously, this paper studies the perturbation to Mei symmetry and adiabatic invariants. Firstly, the exact invariant induced directly from the Mei symmetry of the system without perturbation is given. Secondly, based on the concept of high-order adiabatic invariant, the determining equations of the perturbation to Mei symmetry are established, the condition of existence of the Mei adiabatic invariant led by the perturbation to Mei symmetry is obtained, and its form is presented. Lastly, an example is given to illustrate the application of the results. 相似文献
999.
Magnetic domain structures of precipitation-hardened SmCo 2:17-type sintered magnets: Heat treatment effect 下载免费PDF全文
The typical magnetic domains of Sm(CObalFe0.25Cuo.07Zr0.02)7.4 magnets quenched through various heattreatment steps have been revealed by using magnetic force microscopy (MFM). For the specimens in which the nominal c-axis is perpendicular to the imaging plane, the domain configurations change from plate-like for the as-sintered magnet to corrugation and spike-like for the homogenized one, and then to a coarse and finally to a finer domain structure when isothermally aged at 830℃ and then annealed at 400℃. However, only plate-like domains can be detected on the surfaces with the nominal c-axis parallel to the imaging plane. The finer domain (so-called interaction domain) is a characteristic magnetic domain pattern of the SmCo 2:IT-type magnets with high coercivities. Domain walls in a zigzag shape are revealed by means of MFM in final bulk SraCo 2:17-type sintered magnets. 相似文献
1000.
Scheme for implementing quantum dense coding with four-particle decoherence-free states in an ion trap 下载免费PDF全文
This paper proposes an experimentally feasible scheme for implementing quantum dense coding of trapped-ion system in decoherence-free states. As the phase changes due to time evolution of components with different eigenenergies of quantum superposition are completely frozen, quantum dense coding based on this model would be perfect. The scheme is insensitive to heating of vibrational mode and Bell states can be exactly distinguished via detecting the ionic state. 相似文献