全文获取类型
收费全文 | 1436篇 |
免费 | 32篇 |
国内免费 | 11篇 |
专业分类
化学 | 745篇 |
晶体学 | 10篇 |
力学 | 50篇 |
数学 | 84篇 |
物理学 | 385篇 |
无线电 | 205篇 |
出版年
2023年 | 18篇 |
2022年 | 27篇 |
2021年 | 47篇 |
2020年 | 53篇 |
2019年 | 46篇 |
2018年 | 28篇 |
2017年 | 41篇 |
2016年 | 47篇 |
2015年 | 23篇 |
2014年 | 52篇 |
2013年 | 89篇 |
2012年 | 70篇 |
2011年 | 87篇 |
2010年 | 55篇 |
2009年 | 51篇 |
2008年 | 74篇 |
2007年 | 71篇 |
2006年 | 60篇 |
2005年 | 59篇 |
2004年 | 46篇 |
2003年 | 31篇 |
2002年 | 30篇 |
2001年 | 28篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 8篇 |
1997年 | 10篇 |
1996年 | 6篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 12篇 |
1992年 | 12篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 21篇 |
1979年 | 5篇 |
1978年 | 14篇 |
1977年 | 7篇 |
1976年 | 7篇 |
1974年 | 9篇 |
1969年 | 4篇 |
排序方式: 共有1479条查询结果,搜索用时 15 毫秒
81.
An investigation is made of the influence of band non-parabolicity on the relation between the Fermi energies in the presence and absence of magnetic quantization in degenerate semi-conductors through derivation of a simplified form of the relation.On leave of absence from theDept. of Physics, B. N. College, Patna University, Patna 800004. 相似文献
82.
A. N. Chakravarti A. K. Chowdhury K. P. Ghatak D. R. Choudhury 《Czechoslovak Journal of Physics》1980,30(10):1161-1166
An expression is derived for the diffusivity-mobility ratio of the carriers in n-channel inversion layers on semiconductors like the ternary compounds which have strongly non-parabolic energy bands. The dependence of the ratio on alloy composition is also studied under the weak-field limit taking n-channel Hg1–xCdx.Te as an example.On leave of absence fromthe Department of Physics, Patna University, Patna, India. 相似文献
83.
We have obtained the inverse scattering equations associated with a new pair of coupled nonlinear evolution equations in two dimensions. The spectral parameter is introduced by invoking the invariance of the equation set, and imposing those on the Lax pair. 相似文献
84.
Hydromagnetic turbulent shear flow of viscous, incompressible, electrically conducting fluid between two infinite uniformly porous moving parallel planes in the presence of axial and transverse magnetic field has been studied by the semi-empirical method. The expressions for the mean distributions for velocity and magnetic field for turbulent shear flow have been obtained for both the cases. As particular cases, the results have been obtained if the planes are fixed. The solutions obtained when the magnetic field is axial have been shown graphically for turbulent and laminar flows. 相似文献
85.
M.?Pal Chowdhury R. K.?Roy S. R.?Bhattacharyya A. K.?PalEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2005,45(1):47-53
Undoped, Be-doped and Si-doped polycrystalline GaN films were deposited by
R.F. sputtering onto fused silica substrates. The films were deposited at various deposition temperatures ranging from 300 K
to 623 K and characterized by optical measurements while the microstructural information was obtained from SEM and XRD studies.
The compositional study for the GaN film was carried out using SIMS. Residual stresses in these films were evaluated from
the band tail of the absorption spectra as well as from direct measurements of hardness by commercially available depth sensing
indentometer. It was observed that undoped GaN films had the highest hardness followed by that for Be-doped and Si-doped films.
The values of hardness obtained form the above optical measurement tallied quite well with those obtained from direct indentation
measurement. 相似文献
86.
Motivated by experiments on single-headed kinesin KIF1A, we develop a model of intracellular transport by interacting molecular motors. It captures explicitly not only the effects of adenosine triphosphate hydrolysis, but also the ratchet mechanism which drives individual motors. Our model accounts for the experimentally observed single-molecule properties in the low-density limit and also predicts a phase diagram that shows the influence of hydrolysis and Langmuir kinetics on the collective spatiotemporal organization of the motors. Finally, we provide experimental evidence for the existence of domain walls in our in vitro experiment with fluorescently labeled KIF1A. 相似文献
87.
Wen J Chowdhury P Fulton DB Datta A Das K Andreotti AH Petrich JW 《Photochemistry and photobiology》2003,77(1):5-9
Nuclear magnetic resonance measurements indicate that hypericin exists in the same "normal" tautomeric form irrespective of whether the solvent is dimethyl sulfoxide or tetrahydrofuran. This result is discussed in the context of previous experimental and theoretical work. It is concluded that solvent perturbations cannot induce tautomerization in hypericin. 相似文献
88.
We derive a relationship between the bandwidth and active length and a figure of merit for velocity- and near-velocity-matched lithium niobate traveling-wave electro-optic modulators. The figure of merit is given by the bandwidth per unit drive voltage squared and is independent of the length of the device. Alternatively, this figure of merit can be described by its inverse, which is proportional to the device's switching energy. 相似文献
89.
90.
Residual stress can adversely affect the mechanical, electronic, optical and magnetic properties of thin films. This work describes a simple stress measurement instrument based on the bending beam method together with a sensitive non-contact fibre optical displacement sensor. The fibre optical displacement sensor is interfaced to a computer and a Labview programme enables film stress to be determined from changes in the radius of curvature of the film-substrate system. The stress measurement instrument was tested for two different kinds of thin film, hard amorphous carbon nitride (CN) and soft copper (Cu) films on silicon substrates deposited by RF magnetron sputtering. Residual stress developed in 500 nm thick CN thin films deposited at substrate temperatures in the range 50-550 °C was examined and it was found that stress in CN films decreased from 0.83 to 0.44 GPa compressive with increase of substrate temperature. Residual stress was found to be tensile (121 MPa) for Cu films of thickness 1500 nm deposited at room temperature. 相似文献