全文获取类型
收费全文 | 452038篇 |
免费 | 3827篇 |
国内免费 | 1345篇 |
专业分类
化学 | 234457篇 |
晶体学 | 7334篇 |
力学 | 21036篇 |
综合类 | 9篇 |
数学 | 52355篇 |
物理学 | 142019篇 |
出版年
2020年 | 3514篇 |
2019年 | 3978篇 |
2018年 | 5279篇 |
2017年 | 5184篇 |
2016年 | 7629篇 |
2015年 | 4613篇 |
2014年 | 7497篇 |
2013年 | 19041篇 |
2012年 | 14182篇 |
2011年 | 17434篇 |
2010年 | 12399篇 |
2009年 | 12243篇 |
2008年 | 16255篇 |
2007年 | 16396篇 |
2006年 | 15441篇 |
2005年 | 13930篇 |
2004年 | 12884篇 |
2003年 | 11559篇 |
2002年 | 11449篇 |
2001年 | 12773篇 |
2000年 | 9848篇 |
1999年 | 7665篇 |
1998年 | 6698篇 |
1997年 | 6549篇 |
1996年 | 6244篇 |
1995年 | 5731篇 |
1994年 | 5812篇 |
1993年 | 5637篇 |
1992年 | 6122篇 |
1991年 | 6279篇 |
1990年 | 6008篇 |
1989年 | 5811篇 |
1988年 | 5938篇 |
1987年 | 5711篇 |
1986年 | 5396篇 |
1985年 | 7359篇 |
1984年 | 7676篇 |
1983年 | 6378篇 |
1982年 | 6633篇 |
1981年 | 6540篇 |
1980年 | 6431篇 |
1979年 | 6508篇 |
1978年 | 6885篇 |
1977年 | 6706篇 |
1976年 | 6857篇 |
1975年 | 6333篇 |
1974年 | 6367篇 |
1973年 | 6535篇 |
1972年 | 4592篇 |
1971年 | 3844篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
An attempt is made to find out the suitable entrainment and exit boundary conditions in laminar flow situations. Streamfunction vorticity formulation of the Navier–Stokes equations are solved by ADI method. Two‐dimensional laminar plane wall jet flow is used to test different forms of the boundary conditions. Results are compared with the experimental and similarity solution and the proper boundary condition is suggested. The Kind 1 boundary condition is recommended. It consists of zero first derivative condition for velocity variable and for streamfunction equation, mixed derivative at the entrainment and exit boundaries. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
4.
This paper deals mainly with generalizations of results in finitary combinatorics to infinite ordinals. It is well-known that for finite ordinals ∑bT<αβ is the number of 2-element subsets of an α-element set. It is shown here that for any well-ordered set of arbitrary infinite order type α, ∑bT<αβ is the ordinal of the set M of 2-element subsets, where M is ordered in some natural way. The result is then extended to evaluating the ordinal of the set of all n-element subsets for each natural number n ≥ 2. Moreover, series ∑β<αf(β) are investigated and evaluated, where α is a limit ordinal and the function f belongs to a certain class of functions containing polynomials with natural number coefficients. The tools developed for this result can be extended to cover all infinite α, but the case of finite α appears to be quite problematic. 相似文献
5.
S. A. Gurevich T. A. Zaraiskaya S. G. Konnikov V. M. Mikushkin S. Yu. Nikonov A. A. Sitnikova S. E. Sysoev V. V. Khorenko V. V. Shnitov Yu. S. Gordeev 《Physics of the Solid State》1997,39(10):1691-1695
The concentration and chemical state of copper in the subsurface region of Cu/SiO2 composite films obtained by simultaneous magnetron sputtering from two sources (Cu and SiO2) are determined by x-ray photoelectron spectroscopy (XPS). It is established that copper in the as-grown film is primarily in the form of unoxidized atoms dispersed in a SiO2 matrix. Annealing of the film results in practically no oxidation, but about 70% of the copper atoms condense into metallic clusters with sizes below 10 Å in the subsurface region and about 50 Å in the bulk of the film. The changes in the binding energy of core electrons, and especially in the energies of Auger electrons, are so large in this situation that photoelectron and Auger spectroscopy are efficient methods for monitoring the chemical state of this composite material. 相似文献
6.
The changes in the magnetization of yttrium iron garnet (YIG) when irradiated by a pulsed neodymium laser beam with wavelength
λ=1.06 μm are investigated. Measurements are performed in the temperature range from 100 K to 600 K in various external magnetic
fields. YIG single crystals grown along the crystallographic (100), (110), and (111) directions are chosen so that the external
anisotropy of the indicated processes can be determined. Characteristic temperature intervals dominated by different mechanisms
of variation of the magnetization under the influence of a laser pulse are discussed.
Fiz. Tverd. Tela (St. Petersburg) 39, 1263–1266 (July 1997) 相似文献
7.
L. K. Aminov I. N. Kurkin D. A. Lukoyanov K. P. Chernov 《Physics of the Solid State》1997,39(8):1184-1186
Results are reported for measurements of the spin-lattice relaxation times of E′1 centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz
over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of
the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm−1. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency
dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation
of irradiation centers in crystalline quartz and quartz glass.
Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997) 相似文献
8.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis 相似文献
9.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991. 相似文献
10.