全文获取类型
收费全文 | 364218篇 |
免费 | 1362篇 |
国内免费 | 349篇 |
专业分类
化学 | 156446篇 |
晶体学 | 5381篇 |
力学 | 22483篇 |
综合类 | 3篇 |
数学 | 61516篇 |
物理学 | 120100篇 |
出版年
2021年 | 3095篇 |
2020年 | 3412篇 |
2019年 | 4192篇 |
2018年 | 11864篇 |
2017年 | 12350篇 |
2016年 | 10666篇 |
2015年 | 3968篇 |
2014年 | 6932篇 |
2013年 | 12167篇 |
2012年 | 13163篇 |
2011年 | 20442篇 |
2010年 | 14693篇 |
2009年 | 15024篇 |
2008年 | 18741篇 |
2007年 | 21158篇 |
2006年 | 10086篇 |
2005年 | 12392篇 |
2004年 | 10251篇 |
2003年 | 10149篇 |
2002年 | 9151篇 |
2001年 | 7768篇 |
2000年 | 6339篇 |
1999年 | 4523篇 |
1998年 | 4290篇 |
1997年 | 4135篇 |
1996年 | 3904篇 |
1995年 | 3403篇 |
1994年 | 3452篇 |
1993年 | 3455篇 |
1992年 | 3449篇 |
1991年 | 3863篇 |
1990年 | 3865篇 |
1989年 | 3881篇 |
1988年 | 3640篇 |
1987年 | 3719篇 |
1986年 | 3405篇 |
1985年 | 3944篇 |
1984年 | 4195篇 |
1983年 | 3588篇 |
1982年 | 3782篇 |
1981年 | 3468篇 |
1980年 | 3225篇 |
1979年 | 3733篇 |
1978年 | 3807篇 |
1977年 | 3889篇 |
1976年 | 3999篇 |
1975年 | 3725篇 |
1974年 | 3578篇 |
1973年 | 3780篇 |
1972年 | 3217篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
V. G. Bozhkov 《Radiophysics and Quantum Electronics》2003,46(8-9):631-656
The state of the art in the development of semiconductor detectors, mixers, and frequency multipliers based on Schottky-barrier diodes (SBDs) and heterojunction structures for uncooled terahertz receivers is reviewed. The present status of this field features a transition from quasi-optical designs based on dot-matrix, whisker-contacted SBDs to the designs with hybrid-integrated and monolithic constructions on the planar SBD base, which are positioned in a waveguide mount. The high-level performance of these planar devices is achieved by partially or completely removing or changing semiconductor substrates and/or using membrane constructions incorporated in the waveguide. 相似文献
952.
953.
954.
955.
Makarov V. L. Khlobystov V. V. Kashpur E. F. Mikhal'chuk B. R. 《Ukrainian Mathematical Journal》2003,55(6):942-955
We construct an integral Newton-type interpolation polynomial with a continual set of nodes. This interpolant is unique and preserves an operator polynomial of the corresponding degree. 相似文献
956.
M. M. Glazov 《Physics of the Solid State》2003,45(6):1162-1165
A precession mechanism of spin relaxation of conduction electrons in a square quantum well is analyzed. The dependence of the spin relaxation time on the width of a quantum well and the height of its barriers is calculated under the assumption that the electron-electron collisions dominate over other processes of carrier scattering. 相似文献
957.
958.
A solution to the phase problem in optics is considered within the context of registration and analysis of two-dimensional stationary optical fields transformed by the object under study or fields forming an image. To obtain information on amplitude and phase distributions of the light field analyzed, a method of registration of two intensity distributions is used. The first distribution corresponds directly to the amplitude distribution. The other is formed for the sum of the initial field and the field shifted along a certain direction. The intensity distributions obtained allow one to calculate the two-dimensional structure of the field under study. It is noteworthy that the method requires no iteration procedures in solving the problem. This leads to speeding up of the processing and analysis of the information. Two variants of optical schemes for the analysis of light fields are considered. The first one corresponds to registration of the image of the analyzed plane and the second to registration of the spectrum of the spatial frequencies. 相似文献
959.
The shape of lines in the radiospectroscopic (NMR and EPR) and dielectric spectra of materials formed by nanoparticles (hereafter, nanomaterials) is analyzed theoretically. The theory is developed in the framework of the core and shell model according to which a nanoparticle consists of two regions whose properties are affected and unaffected by the surface, respectively. The changes in the resonance frequency, the relaxation time, and the static permittivity due to the surface tension are taken into account, and the Gaussian and Lorentzian shapes of homogeneously broadened lines are considered. The inhomogeneous broadening of the spectral lines is examined for several types of nanoparticle size distributions. It is demonstrated that the splitting of the initial lines in the spectra of bulk systems into pairs of lines with a decrease in the particle size is a specific feature of the spectra of nanoparticles. The intensities and half-widths of the lines are investigated as functions of the parameters of the size distribution of nanoparticles. The results of theoretical calculations are compared with recent experimental data on the 17O and 25Mg NMR spectra of nanocrystalline MgO. The theoretical dependences of the intensity, the resonance frequency, and the half-width of the spectral lines are in good agreement with the experimental data. The proposed theory offers a satisfactory explanation of the behavior of the static permittivity in BaTiO3 ceramic materials with nanometer-sized grains. 相似文献
960.
Synchronized whistlers recorded at Varanasi 总被引:1,自引:0,他引:1
Some interesting events of synchronized whistlers recorded at low latitude station Varanasi during magnetic storm period of
the year 1977 are presented. The dynamic spectrum analysis shows that the component whistlers are Eckersley whistlers having
dispersion 10 s1/2 and 30 s1/2. An attempt has been made to explain the dynamic spectra using lightning discharge generated from magnetospheric sources 相似文献