全文获取类型
收费全文 | 592篇 |
免费 | 16篇 |
国内免费 | 102篇 |
专业分类
化学 | 135篇 |
晶体学 | 2篇 |
综合类 | 1篇 |
数学 | 503篇 |
物理学 | 69篇 |
出版年
2024年 | 4篇 |
2023年 | 12篇 |
2022年 | 10篇 |
2021年 | 15篇 |
2020年 | 15篇 |
2019年 | 24篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 12篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 31篇 |
2012年 | 11篇 |
2011年 | 37篇 |
2010年 | 18篇 |
2009年 | 40篇 |
2008年 | 48篇 |
2007年 | 42篇 |
2006年 | 40篇 |
2005年 | 30篇 |
2004年 | 32篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 24篇 |
2000年 | 9篇 |
1999年 | 21篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 6篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有710条查询结果,搜索用时 265 毫秒
111.
In this paper we propose a new version of the Controlled Random Search(CRS) algorithm of Price. The new algorithmhas been tested on thirteen global optimization test problems. Numericalexperiments indicate that the resulting algorithm performs considerablybetter than the earlier versions of the CRS algorithms. The algorithm,therefore, could offer a reasonable alternative to many currently availablestochastic algorithms, especially for problems requiring 43tu0212w62725/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">direct search43tu0212w62725/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">type methods. Also a classification of the CRS algorithms is made based on43tu0212w62725/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">global technique43tu0212w62725/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0"> – 43tu0212w62725/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0">local technique43tu0212w62725/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0"> and the relative performance ofclasses is numerically explored. 相似文献
112.
In this paper we establish the spectral decomposition of the Berezin transforms on the space Mat(2,) of complex 2×2 matrices related to the two-sided action ofU(2)×U(2). The eigenspaces are described explicitly by means of the matrix elements of a certain representation ofGL(2,) and each eigenvalue is expressed as a finite sum involving the MeijerG-functions evaluated at 1 and the Hahn polynomials. 相似文献
113.
Cvetan Jardas Josip Peari Nikola Sarapa 《Rendiconti del Circolo Matematico di Palermo》1998,47(3):481-492
In this paper we study the problem of convergence in the weak and the vague topology of the sequence
where μ and ν are probability measures on locally compact commutative semigroupS andA
n
=[a
ij
(n)
(i, j, n ɛ N) are double stochastic matrices satisfying some additional conditions. Our results generalize the results in [9]. Theorem
1 also holds if we make some changes on the topological assumptions onS, i.e. if we suppose thatS is a polish space. 相似文献
114.
In (Kaniuth and Kumar in Math. Proc. Camb. Phil. Soc. 131, 487–494, 2001) Hardy’s uncertainty principle for was generalized to connected and simply connected nilpotent Lie groups. In this paper, we extend it further to connected
nilpotent Lie groups with non-compact centre. Concerning the converse, we show that Hardy’s theorem fails for a connected
nilpotent Lie group G which admits a square integrable irreducible representation and that this condition is necessary if the simply connected
covering group of G satisfies the flat orbit condition. 相似文献
115.
We prove L p Poincaré inequalities with suitable dimension free constants for functions on the discrete cube {?1, 1} n . As well known, such inequalities for p an even integer allow to recover an exponential inequality hence the concentration phenomenon first obtained by Bobkov and Götze. We also get inequalities between the L p norms of $ \left\vert \nabla f\right\vert We prove L
p
Poincaré inequalities with suitable dimension free constants for functions on the discrete cube {−1, 1}
n
. As well known, such inequalities for p an even integer allow to recover an exponential inequality hence the concentration phenomenon first obtained by Bobkov and
G?tze. We also get inequalities between the L
p
norms of 43x3/440_2007_94_Article_IEq1.gif" alt="$$ \left\vert \nabla f\right\vert $$" align="middle" border="0"> and 43x3/440_2007_94_Article_IEq2.gif" alt="$$\Delta ^{\alpha }f,\alpha > 0;$$" align="middle" border="0"> moreover L
p
spaces may be replaced by more general ones. Similar results hold true, replacing functions on the cube by matrices in the
*-algebra spanned by n fermions and the L
p
norm by the Schatten norm C
p
. 相似文献
116.
117.
We consider wave scattering in a forked-shaped waveguide which consists of two finite and one half-infinite intervals having
one common vertex. We describe the spectrum of the direct scattering problem and introduce an analogue of the Jost function.
In case of the potential which is identically equal to zero on the half-infinite interval, the problem is reduced to a problem
of the Regge type. For this case, using Hermite-Biehler classes, we give sharp results on the asymptotic behavior of resonances,
that is, the corresponding eigenvalues of the Regge-type problem. For the inverse problem, we obtain sufficient conditions
for a function to be the S-function of the scattering problem on the forked-shaped graph with zero potential on the half-infinite edge, and present
an algorithm that allows to recover potentials on the finite edges from the corresponding Jost function. It is shown that
the solution of the inverse problem is not unique. Some related general results in the spectral theory of operator pencils
are also given.
This work was supported by the grant UM1-2567-OD-03 from the Civil Research and Development Foundation (CRDF). YL was partially
supported by the NSF grants 0338743, 0354339 and 0754705, by the Research Board and Research Council of the University of
Missouri, and by the EU Marie Curie “Transfer of Knowledge” program. 相似文献
118.
采用具有白磷钙矿结构的磷酸盐作为目标产物,通过高温固相法制备了发光颜色可调的Ca8MgBi(PO4)7∶Ce3+,Tb3+荧光粉。利用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)和荧光光谱等表征手段对其物相组成、微观形貌及发光性能进行了详细研究。结果表明:掺杂少量的Ce3+、Tb3+并没有改变Ca8MgBi(PO4)7基质的晶体结构。荧光光谱和荧光寿命曲线确定了Ce3+-Tb3+之间存在能量传递,其能量传递机制为四极-四极相互作用,能量传递效率可达81%。固定Ce3+浓度而逐渐增加Tb3+的掺杂量时,系列Ca8MgBi(PO4)7∶0.08Ce3+,yTb3+荧光粉的发... 相似文献
119.
Let G be an additive subgroup of a normed space X. We say that a point is weakly separated (resp. -separated) from G if it can be separated from G by a continuous character (resp. by a continuous positive definite function). Let T : X → Y be a continuous linear operator. Consider the following conditions:
(ws) if , then x is weakly separated from G;
(ps) if , then x is -separated from G;
(wp) if Tx is -separated from T(G), then x is weakly separated from G.
By (resp. , ) we denote the class of operators T : X → Y which satisfy (ws) (resp. (ps), (wp)) for all and all subgroups G of X. The paper is an attempt to describe the above classes of operators for various Banach spaces X, Y. It is proved that if X, Y are Hilbert spaces, then is the class of Hilbert-Schmidt operators. It is also shown that if T is a Hilbert-to-Banach space operator with finite ℓ-norm, then .
相似文献
120.
Rasoul Nasr-Isfahani 《Quaestiones Mathematicae》2016,39(8):1005-1017
For a Lau algebra A, we study the Banach space WAP(A) of all weakly almost periodic functionals on A to obtain some equivalent conditions for the existence of topological left invariant means on a topological left introverted subspace X of A contained in WAP(A). Finally, we consider relations between the existence of a topological left invariant mean on X and a common fixed point property. 相似文献