全文获取类型
收费全文 | 1791篇 |
免费 | 40篇 |
国内免费 | 57篇 |
专业分类
化学 | 159篇 |
力学 | 45篇 |
综合类 | 4篇 |
数学 | 1389篇 |
物理学 | 291篇 |
出版年
2024年 | 4篇 |
2023年 | 28篇 |
2022年 | 43篇 |
2021年 | 30篇 |
2020年 | 45篇 |
2019年 | 35篇 |
2018年 | 38篇 |
2017年 | 37篇 |
2016年 | 33篇 |
2015年 | 25篇 |
2014年 | 83篇 |
2013年 | 202篇 |
2012年 | 57篇 |
2011年 | 111篇 |
2010年 | 92篇 |
2009年 | 175篇 |
2008年 | 128篇 |
2007年 | 125篇 |
2006年 | 93篇 |
2005年 | 58篇 |
2004年 | 52篇 |
2003年 | 51篇 |
2002年 | 31篇 |
2001年 | 32篇 |
2000年 | 49篇 |
1999年 | 33篇 |
1998年 | 33篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 17篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 9篇 |
1991年 | 7篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有1888条查询结果,搜索用时 51 毫秒
91.
Charles R. Johnson 《Linear algebra and its applications》2008,429(4):875-886
There is remarkable and distinctive structure among Hermitian matrices, whose graph is a given tree T and that have an eigenvalue of multiplicity that is a maximum for T. Among such structure, we give several new results: (1) no vertex of T may be “neutral”; (2) neutral vertices may occur if the largest multiplicity is less than the maximum; (3) every Parter vertex has at least two downer branches; (4) removal of a Parter vertex changes the status of no other vertex; and (5) every set of Parter vertices forms a Parter set. Statements (3), (4) and (5) are also not generally true when the multiplicity is less than the maximum. Some of our results are used to give further insights into prior results, and both the review of necessary background and the development of new structural lemmas may be of independent interest. 相似文献
92.
Anita Mareno 《Journal of Mathematical Analysis and Applications》2008,343(2):932-937
This paper focuses on a nonlinear equation from thin plate theory of the form Δ(D(x)Δw)−(1−ν)[D,w]+c(x)f(w)=0. We obtain maximum principles for certain functions defined on the solution of this equation using P-functions or auxiliary functions of the types used by Payne [L.E. Payne, Some remarks on maximum principles, J. Anal. Math. 30 (1976) 421-433] and Schaefer [P.W. Schaefer, Solution, gradient, and laplacian bounds in some nonlinear fourth order elliptic equations, SIAM J. Math. Anal. 18 (1987) 430-434]. 相似文献
93.
We give a linear-time algorithm to find a feasible flow in a strongly connected network with fixed supplies and demands, each summing to a common value that is at most the minimum arc capacity. This algorithm speeds up the Goldberg-Rao maximum flow method by a constant factor. 相似文献
94.
Rudolf Beran 《Annals of the Institute of Statistical Mathematics》2008,60(4):843-864
The unknown matrix M is the mean of the observed response matrix in a multivariate linear model with independent random errors. This paper constructs
regularized estimators of M that dominate, in asymptotic risk, least squares fits to the model and to specified nested submodels. In the first construction,
the response matrix is expressed as the sum of orthogonal components determined by the submodels; each component is replaced
by an adaptive total least squares fit of possibly lower rank; and these fits are then summed. The second, lower risk, construction
differs only in the second step: each orthogonal component is replaced by a modified Efron-Morris fit before summation. Singular
value decompositions yield computable formulae for the estimators and their asymptotic and estimated risks. In the asymptotics,
the row dimension of M tends to infinity while the column dimension remains fixed. Convergences are uniform when signal-to-noise ratio is bounded.
This research was supported in part by National Science Foundation Grant DMS 0404547. 相似文献
95.
该文讨论了如下具有退化粘性的非齐次双曲守恒律方程的Cauchy问题$\left\{\begin{array}{l} u_t+f(u)_x=a^2t^\alpha u_{xx}+g(u),\ \ \ x\in{\bf R},\ \ \ t>0,\\u(x,0)=u_0(x) \in L^\infty({\bf R}).\end{array}\right.\eqno{({\rm I})}$其中$f(u), g(u)$是${\bf R}$上的光滑函数, $a>0, 0<\alpha<1$均为常数.在此条件下, 作者首先给出了Cauchy问题(I)的局部解的存在性, 再利用极值原理获得了解的$L^{\infty}$估计, 从而证明了Cauchy问题(I)整体光滑解的存在性. 相似文献
96.
E. Demidenko 《Journal of Optimization Theory and Applications》2008,136(3):375-395
We develop criteria for the existence and uniqueness of the global minima of a continuous bounded function on a noncompact
set. Special attention is given to the problem of parameter estimation via minimization of the sum of squares in nonlinear
regression and maximum likelihood. Definitions of local convexity and unimodality are given using the level set. A fundamental
theorem of nonconvex optimization is formulated: If a function approaches the minimal limiting value at the boundary of the
optimization domain from below and its Hessian matrix is positive definite at the point where the gradient vanishes, then
the function has a unique minimum. It is shown that the local convexity level of the sum of squares is equal to the minimal
squared radius of the regression curvature. A new multimodal function is introduced, the decomposition function, which can
be represented as the composition of a convex function and a nonlinear function from the argument space to a space of larger
dimension. Several general global criteria based on majorization and minorization functions are formulated. 相似文献
97.
Multiple UAVs path planning algorithms: a comparative study 总被引:1,自引:0,他引:1
B. Moses Sathyaraj L. C. Jain A. Finn S. Drake 《Fuzzy Optimization and Decision Making》2008,7(3):257-267
Unmanned aerial vehicles (UAVs) are used in team for detecting targets and keeping them in its sensor range. There are various
algorithms available for searching and monitoring targets. The complexity of the search algorithm increases if the number
of nodes is increased. This paper focuses on multi UAVs path planning and Path Finding algorithms. Number of Path Finding
and Search algorithms was applied to various environments, and their performance compared. The number of searches and also
the computation time increases as the number of nodes increases. The various algorithms studied are Dijkstra’s algorithm,
Bellman Ford’s algorithm, Floyd-Warshall’s algorithm and the AStar algorithm. These search algorithms were compared. The results
show that the AStar algorithm performed better than the other search algorithms. These path finding algorithms were compared
so that a path for communication can be established and monitored. 相似文献
98.
非线性双曲型积分微分方程有限元逼近的误差分析 总被引:1,自引:0,他引:1
窦纳 《高校应用数学学报(A辑)》2001,16(3):337-347
考虑非线性双曲型积分微分方程半离散有限元格式,得到H^1超收敛和最优阶L^∞和W^1,∞模误差估计,结果丰富了有限元方法的理论。 相似文献
99.
The main result of the present note states that it is consistent with the ZFC axioms of set theory (relying on Martin's Maximum MM axiom), that every Asplund space of density character ω1 has a renorming with the Mazur intersection property. Combined with the previous result of Jiménez and Moreno (based upon the work of Kunen under the continuum hypothesis) we obtain that the MIP renormability of Asplund spaces of density ω1 is undecidable in ZFC. 相似文献
100.
Costa et al. (Oper. Res. Lett. 31:21–27, 2003) presented a quadratic O(min (Kn,n
2)) greedy algorithm to solve the integer multicut and multiflow problems in a rooted tree. (n is the number of nodes of the tree, and K is the number of commodities). Their algorithm is a special case of the greedy type algorithm of Kolen (Location problems
on trees and in the rectilinear plane. Ph.D. dissertation, 1982) to solve weighted covering and packing problems defined by general totally balanced (greedy) matrices. In this communication
we improve the complexity bound in Costa et al. (Oper. Res. Lett. 31:21–27, 2003) and show that in the case of the integer multicut and multiflow problems in a rooted tree the greedy algorithm of Kolen
can be implemented in subquadratic O(K+n+min (K,n)log n) time. The improvement is obtained by identifying additional properties of this model which lead to a subquadratic transformation
to greedy form and using more sophisticated data structures.
相似文献