全文获取类型
收费全文 | 6089篇 |
免费 | 216篇 |
国内免费 | 903篇 |
专业分类
化学 | 4801篇 |
晶体学 | 84篇 |
力学 | 132篇 |
综合类 | 37篇 |
数学 | 156篇 |
物理学 | 1998篇 |
出版年
2024年 | 13篇 |
2023年 | 136篇 |
2022年 | 170篇 |
2021年 | 131篇 |
2020年 | 176篇 |
2019年 | 182篇 |
2018年 | 140篇 |
2017年 | 202篇 |
2016年 | 226篇 |
2015年 | 224篇 |
2014年 | 264篇 |
2013年 | 381篇 |
2012年 | 297篇 |
2011年 | 458篇 |
2010年 | 382篇 |
2009年 | 428篇 |
2008年 | 401篇 |
2007年 | 430篇 |
2006年 | 330篇 |
2005年 | 286篇 |
2004年 | 256篇 |
2003年 | 230篇 |
2002年 | 182篇 |
2001年 | 146篇 |
2000年 | 134篇 |
1999年 | 128篇 |
1998年 | 130篇 |
1997年 | 96篇 |
1996年 | 92篇 |
1995年 | 64篇 |
1994年 | 77篇 |
1993年 | 46篇 |
1992年 | 65篇 |
1991年 | 56篇 |
1990年 | 34篇 |
1989年 | 30篇 |
1988年 | 29篇 |
1987年 | 10篇 |
1986年 | 20篇 |
1985年 | 10篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 7篇 |
1978年 | 11篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1974年 | 6篇 |
排序方式: 共有7208条查询结果,搜索用时 15 毫秒
991.
G.V. Kurlyandskaya S.M. Bhagat J.C. Aphesteguy 《Journal of Physics and Chemistry of Solids》2011,72(4):276-285
Microwave absorption was studied for magnetic nanoparticles of Fe3O4 (A) prepared by co-precipitation and Ni0.35Cu0.15Zn0.5Fe2O4 (B) nanoparticles prepared by the sol-gel combustion method at different temperature. In all cases only one ferromagnetic resonance line was observed which indicated that the materials were magnetically uniform. The linewidths were large mainly because of the wide variations in particle sizes, shapes and orientations. As expected, A type nanoparticles showed no absorption at zero-field. However, B type nanoparticles exhibited a sizable loss at a zero-field and the effect increases with the increase of reaction temperature. Mechanical crushing of the sample further enhanced the absorption. 相似文献
992.
Beata Zielińska Ewa Borowiak-Palen Ryszard J. Kalenczuk 《Journal of Physics and Chemistry of Solids》2011,72(2):117-123
Fe-, Ni-, Co- and Ag- loaded NaNbO3 catalysts were prepared and their activities have been investigated in the reaction of photocatalytic hydrogen generation. Me/NaNbO3 were synthesized by impregnation of NaNbO3 in an aqueous solution of metal nitrates and then by calcination at the temperature of 400 °C. The crystallographic phases and optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-Ray spectrometer (EDX) as its mode. The detailed analysis has revealed that all the investigated catalysts exhibit high crystallinity and the presence of Fe2O3, NiO, Co3O4 and Ag2O oxides on Me/NaNbO3 was confirmed. Finally, the influence of different metal loadings (Fe, Ni, Co and Ag) on the photocatalytic activity of NaNbO3 for photocatalytic hydrogen generation has been investigated. Here we report that among all the Me/NaNbO3 photocatalysts Ag-loaded NaNbO3 exhibited higher photocatalytic efficiency for photocatalytic hydrogen generation than NaNbO3. 相似文献
993.
Swarup Kumar Maji Anup Mondal Bibhutosh Adhikary Basudeb Karmakar 《Journal of Physics and Chemistry of Solids》2011,72(6):784-788
We report the formation of mesoporous zinc sulphide, composed by the fine network of nanoparticles, which was formed via a single precursor Zn(SOCCH3)2Lut2 complex. The complex was chemically synthesized using zinc carbonate basic, 3,5-lutidine and thioacetic acid, in air. The metal precursor complex was characterized using different conventional techniques. Thermogravimetric analysis (TGA) result indicates that the decomposition of the complex starts at 100 °C and continues up to 450 °C, finally yielding ZnS. ZnS nanocrystals were characterized by powder X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM), N2-sorption isotherm, UV-vis spectroscopy and photoluminescence (PL) spectroscopy. The grain diameter of nanocrystals was found to be 4-5 nm. The material followed Type-IV N2-sorption isotherm, which is the characteristic of mesoporous materials. The band gap energy, as obtained from optical measurements was around 3.8 eV. 相似文献
994.
Nanosized zinc oxide has been synthesized through a novel single step solution combustion route using citric acid as fuel. The X-ray diffraction (XRD) analysis revealed that the synthesized ZnO nanopowder has the pure wurtzite structure. The phase purity of the nanopowder has been confirmed using differential thermal analysis (DTA), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). The morphology and crystalline size of the as-prepared nanopowder characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that the powder consisted of a mixture of nanoparticles and nanorods. The nanocrystalline ZnO could be sintered to ∼97% of the theoretical density at 1200 °C in 4 h. The dielectric constant (εr) and dielectric loss (εi) of sintered ZnO pellets at 5 MHz were 1.38 and 9×10−2, respectively, at room temperature. 相似文献
995.
The equilibrium process of plasma nitrogen species by chemical kinetic reactions along various pressures is successfully investigated. The equilibrium process is required in industrial application to obtain the stable condition when heating up the material for having homogenous reaction. Nitrogen species densities is modeled by a continuity equation and extended Arrhenius form. These equations are used to integrate the change of density over the time. The integration is to acquire density and the reaction rate of each reaction where temperature and time dependence are imposed. A comparison is made with global model within pressure range of 1-100 mTorr and the temperature of electron is set to be higher than other nitrogen species. The results show that the chemical kinetic model only agrees for high pressure because of no power imposed; while the global model considers the external power along the pressure range then the electron and nitrogen species give highly quantity densities by factor of 3-5. 相似文献
996.
Mohammadreza Saeidi Majid VaezzadehFarzaneh Badakhshan 《Physica B: Condensed Matter》2011,406(4):1038-1040
Influence of DC electric field on carbon nanotube (CNT) growth in chemical vapor deposition is studied. Investigation of electric field effect in van der Waals interaction shows that increase in DC electric field raises the magnitude of attractive term of the Lennard-Jones potential. By using a theoretical model based on phonon vibrations of CNT on catalyst, it is shown that there is an optimum field for growth. Also it is observed that CNT under optimum electric field is longer than CNT in the absence of field. Finally, the relation between optimum DC electric field and type of catalyst is investigated and for some intervals of electric field, the best catalyst is introduced, which is very useful for experimental researches. 相似文献
997.
X.D. OuY.X. Wang L.Q. ShiW. Ding M. WangY.S. Zhu 《Physica B: Condensed Matter》2011,406(23):4460-4465
Using the first principles method based on the density functional theory, we investigated the effect of hydrogen-doping on bonding properties of Ti3SiC2. The formation energies of hydrogen interstitials in three possible positions were calculated. The results show that hydrogen favors residing near the (0 0 1) Si plane. In these positions, hydrogen is hybridized most with 1s states of lattice atoms (Si and C), instead of Ti. The presence of hydrogen does not substantially influence the bonding nature of Ti3SiC2; chemical bonding is characterized by the hybridizations of Ti d-Si p and Ti d-C p states, and yields high strength. This is contrary to hydrogen-doping in transition metals, where the electron of hydrogen fills in the d bands of the metals and, as a consequence, decreases the cohesive strength of the lattice. 相似文献
998.
The structural, microstructural, polarization, magnetization, dielectric constant, and relaxor characteristics of 0.7BiFeO3-0.3BaTiO3 (BF-BT) nanocrystals have been studied. BF-BT nanocrystals were prepared by a chemical route using polyvinyl alcohol as surfactant. The phase structure is confirmed by X-ray diffraction and average particle size by transmission and scanning electron microscopy. The magnetoelectric coupling is studied by polarization hysteresis loops under the influence of applied magnetic field and the phase transition anomaly. The diffuse phase transition is studied by modified Curie-Weiss law and relaxor characteristics by Vogel-Fulcher relation. 相似文献
999.
TiO2 nanowires were grown on titanium foil by an alkali hydrothermal growth method. The as-synthesized nanowires are structurally uniform with diameters of 50-100 nm and lengths of up to a few micrometers. The as-prepared TiO2 nanowires were coated with Ag nanoparticles by reducing AgNO3 in solution. The experimental results indicate that the Ag nanoparticles can aggregate together on the surfaces of TiO2 nanowires by interconnection between nanoparticles. The degree of aggregation of Ag nanostructures can be controlled by changing the concentrations of Ag nanoparticles. The as-prepared nanostructures exhibit a wide optical absorption from 387 to 580 nm that can be easily tuned by controlling the degree of aggregation of Ag nanostructures. The results reveal that optical properties of the Ag-coated TiO2 nanowires can be enhanced by plasmon coupling of Ag nanoparticles. The as-prepared nanostructures may find potential applications in the field of solar cells. 相似文献
1000.
Effects of doping on the surface energies of nanocrystals and evidence from studies at high pressure
Zn1−XMnXS (X=0.85% and 1.26%) nanoparticles have been synthesized using a specially designed equipment and we have studied the influence of doping Mn2+ on the surface energy of ZnS. The high pressure behaviors of ZnS nanocrystals with different dopant contents have been investigated using angle-dispersive synchrotron X-ray powder diffraction up to 45.1 GPa. Theoretical calculations show that doping with Mn2+ increases the surface energy of the nanocrystals. The theoretical result has been further corroborated by our experimental observation of an increase in the phase transition pressure of Mn2+ doped ZnS nanocrystals in diamond-anvil-cell studies. 相似文献