全文获取类型
收费全文 | 21323篇 |
免费 | 190篇 |
国内免费 | 107篇 |
专业分类
化学 | 10878篇 |
晶体学 | 427篇 |
力学 | 611篇 |
综合类 | 7篇 |
数学 | 1860篇 |
物理学 | 7837篇 |
出版年
2017年 | 170篇 |
2016年 | 268篇 |
2015年 | 183篇 |
2014年 | 299篇 |
2013年 | 894篇 |
2012年 | 627篇 |
2011年 | 684篇 |
2010年 | 501篇 |
2009年 | 499篇 |
2008年 | 668篇 |
2007年 | 713篇 |
2006年 | 681篇 |
2005年 | 618篇 |
2004年 | 540篇 |
2003年 | 495篇 |
2002年 | 501篇 |
2001年 | 707篇 |
2000年 | 546篇 |
1999年 | 451篇 |
1998年 | 358篇 |
1997年 | 353篇 |
1996年 | 320篇 |
1995年 | 395篇 |
1994年 | 359篇 |
1993年 | 328篇 |
1992年 | 358篇 |
1991年 | 393篇 |
1990年 | 370篇 |
1989年 | 370篇 |
1988年 | 341篇 |
1987年 | 336篇 |
1986年 | 334篇 |
1985年 | 413篇 |
1984年 | 428篇 |
1983年 | 321篇 |
1982年 | 331篇 |
1981年 | 351篇 |
1980年 | 328篇 |
1979年 | 338篇 |
1978年 | 338篇 |
1977年 | 315篇 |
1976年 | 334篇 |
1975年 | 293篇 |
1974年 | 284篇 |
1973年 | 299篇 |
1972年 | 182篇 |
1969年 | 159篇 |
1968年 | 189篇 |
1967年 | 334篇 |
1966年 | 285篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A model is developed for the flow of a slightly compressible fluid through a saturated inelastic porous medium. The initial‐boundary‐value problem is a system that consists of the diffusion equation for the fluid coupled to the momentum equation for the porous solid together with a constitutive law which includes a possibly hysteretic relation of elasto‐visco‐plastic type. The variational form of this problem in Hilbert space is a non‐linear evolution equation for which the existence and uniqueness of a global strong solution is proved by means of monotonicity methods. Various degenerate situations are permitted, such as incompressible fluid, negligible porosity, or a quasi‐static momentum equation. The essential sufficient conditions for the well‐posedness of the system consist of an ellipticity condition on the term for diffusion of fluid and either a viscous or a hardening assumption in the constitutive relation for the porous solid. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
32.
T. N. Mamedov V. N. Duginov A. V. Stoykov I. L. Chaplygin D. Herlach U. Zimmermann V. N. Gorelkin J. Major M. Schefzik 《JETP Letters》1998,68(1):64-70
The residual polarization of negative muons in crystal silicon samples with phosphorus (P: 1.6×1013 cm−3) and antimony (Sb: 2×1018 cm−3) impurities is investigated. The measurements are made in a 1000 G magnetic field oriented in a direction transverse to the
muon spin in the temperature range 4–300 K. The relaxation rate and shift of the precession frequency in the silicon sample
with the phosphorus impurity are measured more accurately than previously. It is found that in antimony-doped silicon the
acceptor center
μ
A1 at temperatures below 30 K can be in both ionized and neutral states. The experimental data are interpreted on the basis
of spin-lattice relaxation of the magnetic moment of an acceptor center, formation of acceptor-donor pairs, and recombination
of charge carriers at the acceptor. Preliminary measurements showed a nonzero residual polarization of negative muons in germanium.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 61–66 (10 July 1998) 相似文献
33.
34.
35.
M. U. Belyi N. E. Bartnitskaya I. F. Mel'nik B. A. Okhrimenko S. M. Yablochkov 《Journal of Applied Spectroscopy》1995,62(3):564-567
T. Shevchenko Kiev University, 252022 Kiev, Pr. Akad. Glushakova, 6, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii,
Vol. 62, No. 3, pp. 192–196, May–June, 1995. 相似文献
36.
G.J. Babonas A. Reza I. Simkiene M. Baran U.O. Karlsson 《Applied Surface Science》2006,252(15):5391-5394
Optical properties of Fe-doped silica films on Si were investigated by ellipsometric technique in the region 1-5 eV. Samples were produced by sol-gel method. Precursors were prepared by mixing tetraethoxysilane (TEOS) solution in ethanol and water with aqueous solution of Fe-chloride or Fe-acetate. The coating solution was deposited on Si substrates by spin on technique. The size of Fe-containing nanometric-sized particles depended on technology and varied from 20 to 100 nm. Optical response of complex hybrid samples SiO2:Fe/Si was interpreted in a multi-layer model. In the inverse problem, the Maxwell equations were solved by transfer matrix technique. Dielectric function of Fe-doped silica layers was calculated in the model of effective media. Analysis of optical data has shown that various Fe-oxides formed. Experimental data for films obtained from precursors with Fe-acetate and annealed in hydrogen were well described by the model calculations taking into account a small contribution 1-5% of metal Fe imbedded in silica. The Fe/Fe-O contribution to optical response increased for samples grown from FeCl3-precursor. Ellipsometric data for Fe-doped silica films on Si were interpreted taking into account the structural AFM studies as well as the results of magnetic measurements. 相似文献
37.
38.
R.G. Abhilash Kumar K. Vinod U. Syamaprasad 《Applied Physics A: Materials Science & Processing》2007,88(2):243-247
MgB2/Fe wires were prepared by electrical self-heating of in situ powder-in-tube wires for the first time at ambient conditions.
Characterization of the wires processed at 750 °C, 800 °C and 850 °C for 15 min by XRD, SEM, ϱ–T, susceptibility and JC measurements shows that the MgB2 formed is of high quality particularly with respect to phase purity and transport JC. The method considerably reduces the overall energy consumption vis-à-vis the production cost, simplifies the complexity
of the fabrication procedure and is promising for manufacture of high-quality MgB2 superconducting wires.
PACS 74.70.Ad; 74.62.Bf; 74.25.Fy; 74.25.Ha; 81.20.Hy 相似文献
39.
Several Pd-catalyzed reactions were explored to further functionalize the bromo-substituted 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one scaffold (Aba). We report in this paper suitable reaction conditions for Suzuki, Buchwald-Hartwig, and Heck reactions. The substitution pattern of the starting aminobenzazepinone turned out to be crucial for the success of these transition metal-catalyzed reactions, which often required modifications of standard literature procedures. The Pd-catalyzed methods provide access to novel substitution patterns of the Aba scaffold. 相似文献
40.
Differentiation of functions w.r.t. finite atomless measures with compact support on the real line is introduced. The related harmonic calculus is similar to that of the classical Lebesgue case. As an application we obtain the Weyl exponent for the spectral asymptotics of the Laplacians w.r.t. linear Cantor-type measures with arbitrary weights. 相似文献