全文获取类型
收费全文 | 14554篇 |
免费 | 649篇 |
国内免费 | 490篇 |
专业分类
化学 | 3310篇 |
晶体学 | 122篇 |
力学 | 572篇 |
综合类 | 67篇 |
数学 | 6771篇 |
物理学 | 4851篇 |
出版年
2024年 | 20篇 |
2023年 | 159篇 |
2022年 | 188篇 |
2021年 | 251篇 |
2020年 | 390篇 |
2019年 | 384篇 |
2018年 | 350篇 |
2017年 | 307篇 |
2016年 | 310篇 |
2015年 | 342篇 |
2014年 | 622篇 |
2013年 | 764篇 |
2012年 | 439篇 |
2011年 | 1283篇 |
2010年 | 854篇 |
2009年 | 989篇 |
2008年 | 1134篇 |
2007年 | 991篇 |
2006年 | 776篇 |
2005年 | 681篇 |
2004年 | 564篇 |
2003年 | 466篇 |
2002年 | 488篇 |
2001年 | 260篇 |
2000年 | 275篇 |
1999年 | 280篇 |
1998年 | 213篇 |
1997年 | 201篇 |
1996年 | 188篇 |
1995年 | 166篇 |
1994年 | 186篇 |
1993年 | 172篇 |
1992年 | 147篇 |
1991年 | 109篇 |
1990年 | 88篇 |
1989年 | 85篇 |
1988年 | 58篇 |
1987年 | 57篇 |
1986年 | 55篇 |
1985年 | 70篇 |
1984年 | 59篇 |
1983年 | 38篇 |
1982年 | 54篇 |
1981年 | 38篇 |
1980年 | 40篇 |
1979年 | 20篇 |
1978年 | 30篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
51.
B. Harihara Venkataraman 《Journal of Physics and Chemistry of Solids》2003,64(11):2105-2112
This paper reports the dielectric and impedance characteristics of ferroelectric SrBi2Nb2O9 (SBN) ceramics in the 100 Hz-1 MHz frequency range at various temperatures (300-823 K). A strong low frequency dielectric dispersion (LFDD) associated with an impedance relaxation has been found to exist in these ceramics in the temperature range 573-823 K. The Z″ of the AC complex impedance showed two distinct slopes in the frequency range 100 Hz-1 MHz suggesting the existence of two dispersion mechanisms. This non-ideal behavior has been explained on the basis of the expression, Z*=R0/(1+(iω/ω1)m+(iω/ω2)n) [J. Phys. Chem. Solids 53 (1992) 1] where ω1 and ω2 characterize the lattice response and the charge carrier behavior, respectively. The exponents m and n were obtained from the curve fitting. The exponent n was found to exhibit a minimum at the Curie temperature, Tc (723 K) whereas the m was temperature independent. 相似文献
52.
The function lattice, or generalized Boolean algebra, is the set of ℓ-tuples with the ith coordinate an integer between 0 and a bound ni. Two ℓ-tuples t-intersect if they have at least t common nonzero coordinates. We prove a Hilton–Milner type theorem for systems of t-intersecting ℓ-tuples.Received September 29, 2004 相似文献
53.
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
54.
Regularity of multiwavelets 总被引:7,自引:0,他引:7
The motivation for this paper is an interesting observation made by Plonka concerning the factorization of the matrix symbol associated with the refinement equation for B-splines with equally spaced multiple knots at integers and subsequent developments which relate this factorization to regularity of refinable vector fields over the real line. Our intention is to contribute to this train of ideas which is partially driven by the importance of refinable vector fields in the construction of multiwavelets. The use of subdivision methods will allow us to consider the problem almost entirely in the spatial domain and leads to exact characterizations of differentiability and Hölder regularity in arbitrary L p spaces. We first study the close relationship between vector subdivision schemes and a generalized notion of scalar subdivision schemes based on bi-infinite matrices with certain periodicity properties. For the latter type of subdivision scheme we will derive criteria for convergence and Hölder regularity of the limit function, which mainly depend on the spectral radius of a bi-infinite matrix induced by the subdivision operator, and we will show that differentiability of the limit functions can be characterized by factorization properties of the subdivision operator. By switching back to vector subdivision we will transfer these results to refinable vectors fields and obtain characterizations of regularity by factorization and spectral radius properties of the symbol associated to the refinable vector field. Finally, we point out how multiwavelets can be generated from orthonormal refinable bi-infinite vector fields. 相似文献
55.
1引言大粘度(大r)和大系数(ss和sc)法是处理流动区域中障碍物的常用方法山。但当流动区域中障碍物数量较多时,宜采用空隙率来模拟障碍物,如模拟反应堆流动传热的商用程序COMMIX[’]。我们根据空隙率模拟的基本概念,针对采用交错网格的压力校正法,自行编制了多障碍物流动传热三维计算的全部源程序代码,应用于某核反应堆钠池流动传热的数值模拟,获得了比较合理的结果。2数学模型和数值方法2.1控制方程空隙率修整的质量、动量、能量及湍流动能与耗散率的守恒方程通式的三维柱坐标形式为其中中一1,。,。,。,T,k,。分别表… 相似文献
56.
57.
58.
Summary In this paper, we develop a framework suitable for performing a multiresolution analysis using univariate spline spaces of arbitrary degree and with non-uniform knot-sequences. To this end, we show, among other things, the existence of compactly supported prewavelets and of prewavelets that are globally supported, but decay exponentially. In each case we obtain a decomposition of a fine spline space as a sum of a coarse spline space plus a spline space spanned by prewavelets. 相似文献
59.
In this paper we generalize to coisotropic actions of compact Lie groups a theorem of Guillemin on deformations of Hamiltonian
structures on compact symplectic manifolds. We show how one can reconstruct from the moment polytope the symplectic form on
the manifold.
Received: 21 March 2006 相似文献
60.
Roberto E. Madariaga-Garcia 《Topology and its Applications》2007,154(7):1470-1480
Tkachenko showed in 1990 the existence of a countably compact group topology on the free Abelian group of size c using CH. Koszmider, Tomita and Watson showed in 2000 the existence of a countably compact group topology on the free Abelian group of size c2 using a forcing model in which CH holds.Wallace's question from 1955, asks whether every both-sided cancellative countably compact semigroup is a topological group. A counterexample to Wallace's question has been called a Wallace semigroup. In 1996, Robbie and Svetlichny constructed a Wallace semigroup under CH. In the same year, Tomita constructed a Wallace semigroup from MAcountable.In this note, we show that the examples of Tkachenko, Robbie and Svetlichny, and Koszmider, Tomita and Watson can be obtained using a family of selective ultrafilters. As a corollary, the constructions presented here are compatible with the total failure of Martin's Axiom. 相似文献