全文获取类型
收费全文 | 3365篇 |
免费 | 200篇 |
国内免费 | 208篇 |
专业分类
化学 | 572篇 |
晶体学 | 28篇 |
力学 | 274篇 |
综合类 | 74篇 |
数学 | 1973篇 |
物理学 | 852篇 |
出版年
2023年 | 21篇 |
2022年 | 18篇 |
2021年 | 43篇 |
2020年 | 49篇 |
2019年 | 48篇 |
2018年 | 40篇 |
2017年 | 64篇 |
2016年 | 65篇 |
2015年 | 56篇 |
2014年 | 111篇 |
2013年 | 132篇 |
2012年 | 116篇 |
2011年 | 136篇 |
2010年 | 129篇 |
2009年 | 196篇 |
2008年 | 240篇 |
2007年 | 215篇 |
2006年 | 204篇 |
2005年 | 203篇 |
2004年 | 154篇 |
2003年 | 179篇 |
2002年 | 152篇 |
2001年 | 158篇 |
2000年 | 123篇 |
1999年 | 108篇 |
1998年 | 80篇 |
1997年 | 75篇 |
1996年 | 85篇 |
1995年 | 71篇 |
1994年 | 78篇 |
1993年 | 52篇 |
1992年 | 57篇 |
1991年 | 35篇 |
1990年 | 23篇 |
1989年 | 20篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1986年 | 15篇 |
1985年 | 18篇 |
1984年 | 24篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 21篇 |
1979年 | 24篇 |
1978年 | 18篇 |
1977年 | 16篇 |
1976年 | 11篇 |
1975年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有3773条查询结果,搜索用时 140 毫秒
21.
提出一种单光子探测器量子效率的绝对自身标定方案,利用光参量下转换过程中产生的光子对在时间上的相关性,先将参量光束分为两路,然后引入相对延时,使同时产生的孪生光子先后进入单光子探测器,然后将探测器之后的电路分为三路,其中一路直接进入计数器得到探测器所探测到的光子的总计数率,另两路用电路方法引入和光路相当的相对延时,经符合电路后进入计数器,得到前后到达探测器的光子对之间的符合计数率.这样,从符合计数率与总光子计数率之比即可在不需要任何其他探测器或者参照标准的情况下获得探测器的量子效率.文中给出两种方案,分别适 相似文献
22.
Let E\subset \Bbb R
s
be compact and let d
n
E
denote the dimension of the space of polynomials of degree at most n in s variables restricted to E . We introduce the notion of an asymptotic interpolation measure (AIM). Such a measure, if it exists , describes the asymptotic behavior of any scheme τ
n
={ \bf x
k,n
}
k=1
dnE
, n=1,2,\ldots , of nodes for multivariate polynomial interpolation for which the norms of the corresponding interpolation operators do
not grow geometrically large with n . We demonstrate the existence of AIMs for the finite union of compact subsets of certain algebraic curves in R
2
. It turns out that the theory of logarithmic potentials with external fields plays a useful role in the investigation. Furthermore,
for the sets mentioned above, we give a computationally simple construction for ``good' interpolation schemes.
November 9, 2000. Date revised: August 4, 2001. Date accepted: September 14, 2001. 相似文献
23.
24.
A Q-algebra can be represented as an operator algebra on an infinite dimensional Hilbert space. However we don’t know whether a finite n-dimensional Q-algebra can be represented on a Hilbert space of dimension n except n = 1, 2. It is known that a two dimensional Q-algebra is just a two dimensional commutative operator algebra on a two dimensional Hilbert space. In this paper we study a finite n-dimensional semisimple Q-algebra on a finite n-dimensional Hilbert space. In particular we describe a three dimensional Q-algebra of the disc algebra on a three dimensional Hilbert space. Our studies are related to the Pick interpolation problem for a uniform algebra. 相似文献
25.
一个稳定的补偿器可同时镇定n个对象(同时强镇定)等价于一个补偿器(不一定稳定)同时镇定n 1个对象(同时镇定).两个以上对象的同时强镇定和三个以上对象的伺时镇定是线性系统中一个急待解决的公开问题.文中所作的基本假定是所有的对象具有相同的简单不稳定零点,在此条件下给出了n个对象同时强镇定的一个充分条件.当仅有一个不稳定零点时.容易检验是否同时强镇定,否则仅需确定n个对象的不稳定零点并且判定由不稳定零点导出一个相应矩阵是正定的,就能判定n个对象同时强镇定.因此是一个易于检验的充分条件.文章同时给出了n个对象同时强镇定的算法,丰富了同时强镇定的充分条件. 相似文献
26.
In this paper we prove three conjectures of Revers on Lagrange interpolation for fλ(t)=|t|λ,λ>0, at equidistant nodes. In particular, we describe the rate of divergence of the Lagrange interpolants LN( fλ,t) for 0<|t|<1, and discuss their convergence at t=0. We also establish an asymptotic relation for max|t|1| |t|λ−LN( fλ,t)|. The proofs are based on strong asymptotics for |t|λ−LN( fλ,t), 0|t|<1. 相似文献
27.
For exponential weights, a necessary condition of weighted mean convergence for Lagrange interpolation is given. 相似文献
28.
S.N. Vdovichev B.A. Gribkov S.A. Gusev E. Il’ichev Yu.N. Nozdrin G.L. Pakhomov A.V. Samokhvalov R. Stolz A.A. Fraerman 《Journal of magnetism and magnetic materials》2006
The effect of an array of ferromagnetic nanoparticles on the field-dependent critical current of the short overlap Josephson junction is experimentally studied. Large reversible variations of the maximum critical current are observed depending on the magnetic state of the particles. The pronounced commensurability effects are detected which are proved by the additional peaks of magnetic field induced diffraction pattern. 相似文献
29.
Y.T. Chen S.U. Jen Y.D. Yao J.M. Wu G.H. Hwang T.L. Tsai Y.C. Chang A.C. Sun 《Journal of magnetism and magnetic materials》2006
Co50Fe50 films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10−6 mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co50Fe50 is increased, the saturation magnetization (Ms) and coercivity (Hc) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C. 相似文献
30.
Carl Boor 《Advances in Computational Mathematics》2006,24(1-4):143-153
A lemma of Micchelli's, concerning radial polynomials and weighted sums of point evaluations, is shown to hold for arbitrary
linear functionals, as is Schaback's more recent extension of this lemma and Schaback's result concerning interpolation by
radial polynomials. Schaback's interpolant is explored.
Happy 60th and beyond, Charlie!
Mathematics subject classifications (2000) 41A05, 41A6. 相似文献