全文获取类型
收费全文 | 37040篇 |
免费 | 490篇 |
国内免费 | 189篇 |
专业分类
化学 | 18375篇 |
晶体学 | 684篇 |
力学 | 1646篇 |
综合类 | 2篇 |
数学 | 3633篇 |
物理学 | 13379篇 |
出版年
2022年 | 324篇 |
2021年 | 370篇 |
2020年 | 345篇 |
2019年 | 338篇 |
2018年 | 530篇 |
2017年 | 458篇 |
2016年 | 728篇 |
2015年 | 431篇 |
2014年 | 735篇 |
2013年 | 1605篇 |
2012年 | 1549篇 |
2011年 | 1899篇 |
2010年 | 1374篇 |
2009年 | 1374篇 |
2008年 | 1566篇 |
2007年 | 1534篇 |
2006年 | 1424篇 |
2005年 | 1221篇 |
2004年 | 1157篇 |
2003年 | 997篇 |
2002年 | 945篇 |
2001年 | 1353篇 |
2000年 | 972篇 |
1999年 | 804篇 |
1998年 | 607篇 |
1997年 | 587篇 |
1996年 | 509篇 |
1995年 | 473篇 |
1994年 | 443篇 |
1993年 | 390篇 |
1992年 | 466篇 |
1991年 | 471篇 |
1990年 | 459篇 |
1989年 | 422篇 |
1988年 | 447篇 |
1987年 | 430篇 |
1986年 | 375篇 |
1985年 | 440篇 |
1984年 | 470篇 |
1983年 | 344篇 |
1982年 | 386篇 |
1981年 | 375篇 |
1980年 | 318篇 |
1979年 | 400篇 |
1978年 | 378篇 |
1977年 | 394篇 |
1976年 | 392篇 |
1975年 | 342篇 |
1974年 | 322篇 |
1973年 | 340篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
The revival of the nondiffracting vortex beam after its interaction with the 2D on axis obstacle is examined. We show that the phase topology and the spatial distribution of the orbital angular momentum of the beam transmitted through the obstacle regenerate to the initial form during further free propagation. We verify that the healing effect appears even if the interaction is accompanied by the exchange of the orbital angular momentum. 相似文献
32.
Bond covalency and valence of elements in HgBa2Can−1CunO2n+2+δ (n=1, 2, 3, 4) were calculated and their relationship with Tc was discussed. For both oxygen and argon annealed samples, the results indicated that with the increase of n, the trend of bond covalency of Hg-O and Cu-O was the same or opposite compared with that of superconducting temperature. This may suggest that the magnitudes of Cu-O and Hg-O bond covalency are important in governing the superconducting temperature. For the highest Tc sample, Hg had the lowest valence, implying that lower valence of Hg was preferred in order to produce higher Tc. For fixed n, the valence of Cu in oxygen annealed samples was larger than that in argon annealed samples, indicating that oxygen annealed samples produced more carriers than argon annealed samples. 相似文献
33.
An experimental study of the aerodynamic damping of oscillating plates has been undertaken. Plates of various shapes were placed into an air flow normal to the plate and excited to oscillate parallel to the flow direction by electromagnetic forces of equal amplitudes and random frequencies. The aerodynamic damping of oscillating plates, evaluated in terms of a quality Q-factor from a frequency response resonance curve, was found to vary linearly with the absolute pressure in stationary surrounding air and with the air flow velocity in moving air. The flow velocity was also found to affect the aerodynamic damping more than the absolute pressure. A simple empirical model has been developed to predict the variation of the aerodynamic damping with the flow velocity. 相似文献
34.
High-temperature series expansions of the susceptibility and second moment to 15th order are calculated for zero external field on the linear chain (LC), plane square (PSQ), simple cubic (SC), and body-centered cubic (BCC) lattices. Checks for specific models against pertinent work in the literature are detailed. 相似文献
35.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献
36.
The effects of surface preparation and illumination on electric parameters of Au/InSb/InP(100) Schottky diode were investigated, in the later diode InSb forms a fine restructuration layer allowing to block In atoms migration to surface. In order to study the electric characteristics under illumination, we make use of an He-Ne laser of 1 mW power and 632.8 nm wavelength. The current-voltage I(VG), the capacitance-voltage C(VG) measurements were plotted and analysed. The saturation current Is, the serial resistance Rs and the mean ideality factor n are, respectively, equal to 2.03 × 10−5 A, 85 Ω, 1.7 under dark and to 3.97 × 10−5 A, 67 Ω, 1.59 under illumination. The analysis of I(VG) and C(VG) characteristics allows us to determine the mean interfacial state density Nss and the transmission coefficient θn equal, respectively, to 4.33 × 1012 eV−1 cm−2, 4.08 × 10−3 under dark and 3.79 × 1012 eV−1 cm−2 and 5.65 × 10−3 under illumination. The deep discrete donor levels presence in the semiconductor bulk under dark and under illumination are responsible for the non-linearity of the C−2(VG) characteristic. 相似文献
37.
The orientation-selective growth of LaNiO3 films on Si(100) by pulsed laser deposition using a MgO buffer 总被引:4,自引:0,他引:4
X.Y. Chen K.H. Wong C.L. Mak J.M. Liu X.B. Yin M. Wang Z.G. Liu 《Applied Physics A: Materials Science & Processing》2002,75(4):545-549
Highly (100)-oriented, (110)-oriented and polycrystalline LaNiO3 (LNO) films were successfully prepared on Si(100) using an oriented MgO film as a buffer. It was somewhat surprising to find
that that the orientation relation between the LNO film and the corresponding MgO buffer was: LNO(100)\MgO(110), LNO(110)\MgO(111)
and LNO(polycrystalline)\MgO(100). The crystalline quality of the LNO films was shown to be sensitive to the preparation conditions
of the MgO buffer. The film surface was very smooth, without micrometer-sized droplets being observed. All LNO films were
of metallic conductivity, with a room-temperature resistivities of approximately 250, 280 and 420 μΩ cm for the (110)-oriented,
(100)-oriented and polycrystalline LNO, respectively.
Received: 2 April 2001 / Accepted: 23 October 2001 / Published online: 3 June 2002 相似文献
38.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
39.
Z. V. Golubenko A. S. Kamzin L. P. Ol’khovik M. M. Khvorov Z. I. Sizova V. P. Shabatin 《Physics of the Solid State》2002,44(9):1698-1702
Magnetization and remagnetization processes in a close-packed nanodispersed barium hexaferrite powder sample in the magnetically stable state were analyzed. Reversibility effects were discussed in terms of interparticle interaction. Judging from the magnetization curve and the parameters characterizing remagnetization irreversibility, the sample under study is a model system of small Stoner-Wohlfarth particles. 相似文献
40.
By using two sections of erbium doped fiber and a fiber optical reflector, a novel, highly efficient L bandamplifier is demonstrated with significantly power-conversion-efficiency enhancement and the gain increasing of as much as 13 dB. 相似文献