全文获取类型
收费全文 | 4232篇 |
免费 | 943篇 |
国内免费 | 259篇 |
专业分类
化学 | 1500篇 |
晶体学 | 192篇 |
力学 | 108篇 |
综合类 | 23篇 |
数学 | 42篇 |
物理学 | 2370篇 |
综合类 | 1199篇 |
出版年
2024年 | 13篇 |
2023年 | 29篇 |
2022年 | 68篇 |
2021年 | 88篇 |
2020年 | 78篇 |
2019年 | 70篇 |
2018年 | 91篇 |
2017年 | 137篇 |
2016年 | 191篇 |
2015年 | 131篇 |
2014年 | 237篇 |
2013年 | 519篇 |
2012年 | 303篇 |
2011年 | 254篇 |
2010年 | 253篇 |
2009年 | 219篇 |
2008年 | 241篇 |
2007年 | 258篇 |
2006年 | 270篇 |
2005年 | 217篇 |
2004年 | 187篇 |
2003年 | 185篇 |
2002年 | 197篇 |
2001年 | 125篇 |
2000年 | 132篇 |
1999年 | 133篇 |
1998年 | 102篇 |
1997年 | 97篇 |
1996年 | 98篇 |
1995年 | 84篇 |
1994年 | 72篇 |
1993年 | 56篇 |
1992年 | 46篇 |
1991年 | 35篇 |
1990年 | 23篇 |
1989年 | 33篇 |
1988年 | 28篇 |
1987年 | 19篇 |
1986年 | 17篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1982年 | 19篇 |
1981年 | 13篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有5434条查询结果,搜索用时 100 毫秒
31.
Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice
coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized
soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method
of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities,
temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which
compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease
with electric field. 相似文献
32.
The 8-mol percentage Y2O3-stabilized Porous Zirconia was prepared using sol–gel method. Zirconium oxalate gel was prepared by the addition of appropriate
amount of oxalic acid solution into the 1 M aqueous solution of zirconium-oxy chloride. A cubic phase zirconia powder was
obtained by calcination and milling of the zirconium oxalate gel. Crystallization temperature was found about 450 °C from
the Differential thermal analysis. The phase analysis by X-ray diffraction shows the presence of cubic phase. Pellets sintered
at 1,350 °C were highly porous, and the electrical conductivity was found with lower value due to the porosity, and the hardness
was about 8.0 GPa.
Paper presented at the Third International Conference on Ionic Devices (ICID 2006), Chennai, Tamilnadu, India, Dec. 7–9, 2006. 相似文献
33.
We study theoretically a nonlinear response of the planar metal/dielectric nanostructures constituted from periodical array
of ultra thin silver layers and the layers of Kerr-like nonlinear dielectric. We predict hysteresis-type dependences of the
components of the tensor of effective dielectric permittivity on the field intensity allowing the change in material transmission
properties from transparent to opaque and back at extremely low intensities of the light. It makes possible to control the
light by light in all-optical nanoscale devices and circuits. 相似文献
34.
M.Yu. Tretyakov V.V. Parshin M.A. Koshelev A.P. Shkaev A.F. Krupnov 《Journal of Molecular Spectroscopy》2006,238(1):91-97
Extension of the working frequency of modern resonator spectrometers into submillimeter wave range is described. Experimental record of atmospheric absorption spectrum covering 45-370 GHz range is demonstrated for the first time, and measured water vapor J′ka′, kc′-Jka, kc = 51,5-42,2 at 325 GHz line parameters are presented. For the first time pressure lineshift for the 325-GHz water vapor line is measured. Further extension of working range is discussed. New estimations of physical limits of time needed for measurements of absorption in the whole Backward Wave Oscillator (BWO) range are given for phase continuous synthesizer regime. Basic schemes of fast broadband continuous phase synthesized sources are discussed. Verification of the previous measurements of water vapor 31,3-22,0 at 183 GHz line parameters is presented. Comparisons with ringdown resonator spectrometers are given. 相似文献
35.
36.
Recent experiments revealed that the dielectric dispersion spectrum of fission yeast cells in a suspension was mainly composed of two sub-dispersions. The low-frequency sub-dispersion depended on the cell length, while the high-frequency one was independent of it. The cell shape effect was simulated by an ellipsoidal cell model but the comparison between theory and experiment was far from being satisfactory. Prompted by the discrepancy, we proposed the use of spectral representation to analyze more realistic cell models. We adopted a shell-spheroidal model to analyze the effects of the cell membrane. It is found that the dielectric property of the cell membrane has only a minor effect on the dispersion magnitude ratio and the characteristic frequency ratio. We further included the effect of rotation of dipole induced by an external electric field, and solved the dipole-rotation spheroidal model in the spectral representation.Good agreement between theory and experiment has been obtained. 相似文献
37.
It is shown that the condition υ > υp (ω), which is necessary in order to trigger the Vavilov-Cherenkov effect, determines the interval of radiated frequencies
and it alone cannot establish a strong restriction to the velocity of the particle. It is exhibited that it is possible to
define a general lower bound for the velocity of the particle, which does not depend on the frequency when both, a specific
response of the medium is taken into account and the mentioned condition is considered. The minimum value of the phase velocity
of light in the medium determines the existence of such general lower bound. 相似文献
38.
For the methylsilsesquioxane film whose optical birefringence is almost zero, it was recently reported that its vertical thermal expansion coefficient (CTE) was approximately one order of magnitude larger than the lateral CTE. Though the birefringence is not an absolute predictor of anisotropic behavior, the discrepancy in both the CTEs was so remarkable that it was essential to investigate whether the anisotropy was intrinsic property or not. If the effect of Poisson's ratio is considered in the calculation of the vertical CTE and when elastic modulus measured by surface acoustic wave spectroscopy is used in the assessment of the lateral CTE, both the CTEs are coincident with each other. Therefore, it can be concluded that the discrepancy in the CTEs can be attributed to a higher in‐plane polymer chain orientation but it can also arise from the misleadingly assumed modulus and Poisson's ratio. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3109–3120, 2006 相似文献
39.
40.
针对二聚物三能级蒸气激光系统增益相对于泵浦光方向显著的不对称特性,本文设计了一种稳定的能够充分利用介质增益特性的环形谐振腔,给出了象散和慧差补偿及泵浦激光与谐振腔匹配的条件。文中还给出了Na_2B~1Ⅱ_u-X~1∑_g~+跃迁激光谐振腔设计数据。 相似文献