全文获取类型
收费全文 | 662148篇 |
免费 | 6206篇 |
国内免费 | 1773篇 |
专业分类
化学 | 335388篇 |
晶体学 | 9711篇 |
力学 | 33037篇 |
综合类 | 22篇 |
数学 | 87405篇 |
物理学 | 204564篇 |
出版年
2021年 | 5825篇 |
2020年 | 6361篇 |
2019年 | 7197篇 |
2018年 | 10012篇 |
2017年 | 10184篇 |
2016年 | 13786篇 |
2015年 | 7729篇 |
2014年 | 12565篇 |
2013年 | 29415篇 |
2012年 | 23158篇 |
2011年 | 27353篇 |
2010年 | 19993篇 |
2009年 | 19805篇 |
2008年 | 25413篇 |
2007年 | 25377篇 |
2006年 | 23248篇 |
2005年 | 22686篇 |
2004年 | 21355篇 |
2003年 | 18520篇 |
2002年 | 17266篇 |
2001年 | 18482篇 |
2000年 | 14387篇 |
1999年 | 11145篇 |
1998年 | 9517篇 |
1997年 | 9369篇 |
1996年 | 8770篇 |
1995年 | 7976篇 |
1994年 | 7854篇 |
1993年 | 7588篇 |
1992年 | 8152篇 |
1991年 | 8572篇 |
1990年 | 8225篇 |
1989年 | 8008篇 |
1988年 | 7912篇 |
1987年 | 7718篇 |
1986年 | 7336篇 |
1985年 | 9365篇 |
1984年 | 9961篇 |
1983年 | 8324篇 |
1982年 | 8713篇 |
1981年 | 8309篇 |
1980年 | 7876篇 |
1979年 | 8345篇 |
1978年 | 8698篇 |
1977年 | 8554篇 |
1976年 | 8582篇 |
1975年 | 8150篇 |
1974年 | 7979篇 |
1973年 | 8369篇 |
1972年 | 5961篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Within the framework of microscopic fluctuation-dissipation theory, we obtain the stochastic equation describing the Brownian motion of an electron in the phonon field of the crystal lattice. An expression for the Green’s function of the phonon field is found in general form and for the case of linear phonon-variable interaction of an electron with the phonon field with allowance for the potential screening of crystal-lattice nuclei. An expression for the phonon drag acting on a conduction electron in the lattice field is found and analyzed with allowance for the interaction. Frequency dependence of the coefficient of the phonon drag acting on a conduction electron is studied and the contribution of the electron-phonon interaction to the effective mass of a charge carrier is determined.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 3, pp. 249–268, March 2005. 相似文献
992.
Complex impedance spectra were obtained on a crystal of CaCu3Ti4O12 (CCTO) from 289 to 456 K. As in the case of ceramic CCTO, these spectra can be interpreted as arising from a conducting material containing insulating barriers. This is then further evidence for the existence of planar defects within crystals of CCTO that act as insulating barriers and produce the large dielectric constant through a space charge mechanism. 相似文献
993.
The aim of this work is to study the dynamic formation and dissociation of trions and excitons in double barrier resonant tunneling diodes. We propose a system of rate equations that takes into account the formation, dissociation and annihilation of these complexes inside the quantum well. From the solutions of the coupled equations, we are able to study the modulation of excitons and trions formation in the device as a function of the applied bias. The results of our model agree qualitatively with the experiments showing the viability of these rate equations system to study the dynamics of complex systems. 相似文献
994.
A MCSCF-method for minimization of the variance yielding an optimal basisset of variance minimizing orbitals in analogy to Löwdin's natural orbitals for minimal energy is developed. 相似文献
995.
996.
997.
The oxides A(Ti0.5Te1.5)O6 (A = K, Rb, Cs, Tl), A(Ti0.5W1.5)O6 (A = Rb, Cs, Tl), and Cs(B0.5W1.5)O6 (B = Zr, Hf) have been obtained as polycrystalline powders giving X-ray diffraction patterns characteristic of defect cubic pyrochlores, space group
(No. 227), Z = 8. The best discrepancy R factors, from 0.0265 for Rb(Ti0.5Te1.5)O6 to 0.0554 for Cs(Zr0.5W1.5)O6, were obtained for the B cations randomly distributed at 16(d), A ions at one quarter of 32(e), and oxygen atoms at 48(f) positions. A linear relationship is observed between the a unit cell parameters and the ionic radii of the A cations, as well as the average ionic radii of the B atoms. The results of electrical resistivity measurements for A(Ti0.5Te1.5)O6 (A = K, Rb, Cs, Tl) are given. 相似文献
998.
T. T. Vasil'eva V. A. Kochetkova V. I. Dostovalova B. V. Nelyubin R. Kh. Freidlina 《Russian Chemical Bulletin》1989,38(11):2346-2349
The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989. 相似文献
999.
1000.
V. A. Maihara M. B. A. Vasconcellos 《Journal of Radioanalytical and Nuclear Chemistry》1989,132(2):329-337
Instrumental neutron activation analysis was applied to the determination of the elements Na, K, Br, As, Rb, Zn, Co, Fe and Sc in Brazilian rice samples and in biological standards. Hg and Se concentrations were determined by using a simple radiochemical separation. The chemical procedure was carried out by means of distillation of Hg and Se in HBr medium and subsequent precipitation of selenium by sodium metabisulfite and mercury by thioacetamide. The accuracy of the instrumental and radiochemical methods was evaluated by means of analysis of the Reference Materials NBS-Bovine Liver, Bowen's Kale and NBS-Rice Flour. 相似文献