全文获取类型
收费全文 | 70912篇 |
免费 | 5221篇 |
国内免费 | 6451篇 |
专业分类
化学 | 26206篇 |
晶体学 | 290篇 |
力学 | 6839篇 |
综合类 | 1254篇 |
数学 | 26152篇 |
物理学 | 21843篇 |
出版年
2023年 | 538篇 |
2022年 | 1035篇 |
2021年 | 1201篇 |
2020年 | 1311篇 |
2019年 | 1575篇 |
2018年 | 1302篇 |
2017年 | 1559篇 |
2016年 | 1794篇 |
2015年 | 1647篇 |
2014年 | 2362篇 |
2013年 | 4534篇 |
2012年 | 2733篇 |
2011年 | 3111篇 |
2010年 | 2688篇 |
2009年 | 3842篇 |
2008年 | 4309篇 |
2007年 | 4540篇 |
2006年 | 4214篇 |
2005年 | 3570篇 |
2004年 | 3296篇 |
2003年 | 3357篇 |
2002年 | 3079篇 |
2001年 | 2612篇 |
2000年 | 2588篇 |
1999年 | 2300篇 |
1998年 | 2142篇 |
1997年 | 1768篇 |
1996年 | 1554篇 |
1995年 | 1424篇 |
1994年 | 1314篇 |
1993年 | 1135篇 |
1992年 | 1084篇 |
1991年 | 852篇 |
1990年 | 695篇 |
1989年 | 603篇 |
1988年 | 558篇 |
1987年 | 447篇 |
1986年 | 376篇 |
1985年 | 438篇 |
1984年 | 430篇 |
1983年 | 211篇 |
1982年 | 346篇 |
1981年 | 408篇 |
1980年 | 304篇 |
1979年 | 302篇 |
1978年 | 222篇 |
1977年 | 212篇 |
1976年 | 155篇 |
1974年 | 111篇 |
1973年 | 113篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
231.
The distributions of limit cycles of cubic vector fields (P2, Q3) are considered in this paper, where P2 and Q3 are polynomials of x and y of order two and three, respectively. It is possibly seven different distributions of limit cycles given in [1]. We now prove that in which three kinds of distributions are impossible and other four kinds all can be realized by concrete vector fields of (P2,Q3). Some related results are also given. 相似文献
232.
A triangulation of a connected closed surface is called weakly regular if the action of its automorphism group on its vertices
is transitive. A triangulation of a connected closed surface is called degree-regular if each of its vertices have the same
degree. Clearly, a weakly regular triangulation is degree-regular. In [8], Lutz has classified all the weakly regular triangulations
on at most 15 vertices. In [5], Datta and Nilakantan have classified all the degree-regular triangulations of closed surfaces
on at most 11 vertices.
In this article, we have proved that any degree-regular triangulation of the torus is weakly regular. We have shown that there
exists ann-vertex degree-regular triangulation of the Klein bottle if and only if n is a composite number ≥ 9. We have constructed two
distinctn-vertex weakly regular triangulations of the torus for eachn ≥ 12 and a (4m + 2)-vertex weakly regular triangulation of the Klein bottle for eachm ≥ 2. For 12 ≤n ≤ 15, we have classified all then-vertex degree-regular triangulations of the torus and the Klein bottle. There are exactly 19 such triangulations, 12 of which
are triangulations of the torus and remaining 7 are triangulations of the Klein bottle. Among the last 7, only one is weakly
regular. 相似文献
233.
反对称正交对称矩阵反问题 总被引:6,自引:0,他引:6
本文讨论一类反对称正交对称矩阵反问题及其最佳逼近.研究了这类矩阵的一些性质,利用这些性质给出了反问题解存在的一些条件和解的一般表达式,不仅证明了最佳逼近解的存在唯一性,而且给出了此解的具体表达式. 相似文献
234.
B. Amaziane M. Goncharenko L. Pankratov 《Mathematical Methods in the Applied Sciences》2005,28(15):1847-1865
We study the asymptotic behaviour of the solution of a stationary quasilinear elliptic problem posed in a domain Ω(ε) of asymptotically degenerating measure, i.e. meas Ω(ε) → 0 as ε → 0, where ε is the parameter that characterizes the scale of the microstructure. We obtain the convergence of the solution and the homogenized model of the problem is constructed using the notion of convergence in domains of degenerating measure. Proofs are given using the method of local characteristics of the medium Ω(ε) associated with our problem in a variational form. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
235.
236.
T. K. Solovykh 《Journal of Applied Spectroscopy》1997,64(5):654-657
The role of impurity ions in formation of the optical properties of rare-earth orthoferrites is investigated. Optical spectra
of the substituted against unsubstituted orthoferrites are presented. The influence of different isovalent substitutions on
the optical absorption of orthoferrites that are promising for magnetooptics is studied.
Institute of Solid-State and Semiconductor Physics of the Academy of Sciences of Belarus, 17, P. Brovka St., Minsk, 220072,
Belarus. Translated from zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 642–645, September–October, 1997. 相似文献
237.
A. P. Prishivalko 《Journal of Applied Spectroscopy》1997,64(1):94-100
A method for finding the optimum sizes of pigment particles, their volume concentration, and the paint coating thickness that
provide the covering power and the required coloristic characteristics of reflected light for the minimum flow rate of pigments
is based on using a four-flow approximation of the solution to the equation of radiation transfer in dispersion media and
is extended to coatings of complex composition. The capabilities of the method are demonstrated by examples of coatings of
mixtures of hematite and rutile particles in a binder with n=1.5 for variations of the modal size and the half-width of the
size distribution of the pigment particles.
B. I. Stepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220072, Belarus. Translated
from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 90–96, January–February, 1997. 相似文献
238.
239.
本文是[1,12]的继续,研究描述架中概念的结构;本文讨论后半部分,内容涉及概念内涵与外延的转换,清晰关系的内投影与内变换,概念的结构*以及有关问题的注记。 相似文献
240.
混合位级正交试验设计的极差分析方法 总被引:3,自引:0,他引:3
本文指出,在混合位级的正交试验设计中,以往的极差分析方法存在着不足。本文给出了极差的修正方法,并用大量实例做了数值验证,说明这个修正确实很有效 相似文献