全文获取类型
收费全文 | 508031篇 |
免费 | 4203篇 |
国内免费 | 1348篇 |
专业分类
化学 | 247092篇 |
晶体学 | 8095篇 |
力学 | 25296篇 |
综合类 | 12篇 |
数学 | 70420篇 |
物理学 | 162667篇 |
出版年
2021年 | 3544篇 |
2020年 | 3875篇 |
2019年 | 4271篇 |
2018年 | 12238篇 |
2017年 | 12882篇 |
2016年 | 11441篇 |
2015年 | 5618篇 |
2014年 | 8197篇 |
2013年 | 19976篇 |
2012年 | 18294篇 |
2011年 | 27764篇 |
2010年 | 18767篇 |
2009年 | 18573篇 |
2008年 | 24552篇 |
2007年 | 27224篇 |
2006年 | 15372篇 |
2005年 | 18847篇 |
2004年 | 15098篇 |
2003年 | 13730篇 |
2002年 | 12159篇 |
2001年 | 13034篇 |
2000年 | 9885篇 |
1999年 | 7647篇 |
1998年 | 6453篇 |
1997年 | 6301篇 |
1996年 | 6110篇 |
1995年 | 5397篇 |
1994年 | 5148篇 |
1993年 | 5065篇 |
1992年 | 5622篇 |
1991年 | 5770篇 |
1990年 | 5531篇 |
1989年 | 5454篇 |
1988年 | 5274篇 |
1987年 | 5365篇 |
1986年 | 5098篇 |
1985年 | 6570篇 |
1984年 | 6735篇 |
1983年 | 5593篇 |
1982年 | 5950篇 |
1981年 | 5517篇 |
1980年 | 5520篇 |
1979年 | 5787篇 |
1978年 | 5940篇 |
1977年 | 5770篇 |
1976年 | 5814篇 |
1975年 | 5506篇 |
1974年 | 5310篇 |
1973年 | 5558篇 |
1972年 | 3793篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
We construct a multiplicative group structure in the class of integro-differential operators specific for a polydisk which was introduced by I. I. Bavrin. We indicate two applications of these operators to solution of functional equations. 相似文献
992.
The synthesis of several analogues of (±)-semivioxanthin including five thiophene analogues, using directed metalation are reported. The strategy consisted of the synthesis of functionalized naphthalene or benzo[b]thiophene as building blocks followed by annelation of the pyrone. 相似文献
993.
994.
995.
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
996.
997.
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
998.
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
999.
B. G. Tagiev U. F. Kasumov N. N. Musaeva R. B. Dzhabbarov 《Physics of the Solid State》2003,45(3):426-432
The current-voltage characteristics of Ca4Ga2S7: Eu3+ single crystals are measured for the first time, and the processes affecting these characteristics are analyzed theoretically. It is demonstrated that Ca4Ga2S7: Eu3+ single crystals are high-resistance semiconductors with a resistivity of ~109 Ω cm and a relative permittivity of 10.55. The electrical properties of the studied materials are governed by traps with activation energies of 0.13 and 0.19 eV and a density ranging from 9.5×1014 to 2.7×1015 cm?3. The one-carrier injection is observed in weak electric fields. In electric fields with a strength of more than 4×103 V/cm, traps undergo thermal field ionization according to the Pool-Frenkel mechanism. At low temperatures and strong fields (160 K and 5×104 V/cm), the electric current is most likely due to hopping conduction by charge carriers over local levels in the band gap in the vicinity of the Fermi level. 相似文献
1000.
In the elastic angular distributions of the systems composed of tightly bound α-nuclei, 12C+12C, 16O+16O and 16O+12C, the higher-order Airy minima are observed in the energy region between 5 and 10 MeV per nucleon. The obtained optical potentials are deeply attractive and with incomplete absorption. The same potentials successfully describe the lower-energy (molecular resonances) and the higher-energy (first Airy minimum) data. 相似文献