全文获取类型
收费全文 | 24502篇 |
免费 | 2236篇 |
国内免费 | 1402篇 |
专业分类
化学 | 1660篇 |
晶体学 | 29篇 |
力学 | 2866篇 |
综合类 | 255篇 |
数学 | 18634篇 |
物理学 | 4696篇 |
出版年
2024年 | 47篇 |
2023年 | 229篇 |
2022年 | 230篇 |
2021年 | 385篇 |
2020年 | 598篇 |
2019年 | 620篇 |
2018年 | 621篇 |
2017年 | 664篇 |
2016年 | 704篇 |
2015年 | 569篇 |
2014年 | 1042篇 |
2013年 | 2391篇 |
2012年 | 1061篇 |
2011年 | 1346篇 |
2010年 | 1140篇 |
2009年 | 1517篇 |
2008年 | 1532篇 |
2007年 | 1479篇 |
2006年 | 1366篇 |
2005年 | 1137篇 |
2004年 | 1007篇 |
2003年 | 945篇 |
2002年 | 976篇 |
2001年 | 826篇 |
2000年 | 780篇 |
1999年 | 745篇 |
1998年 | 603篇 |
1997年 | 546篇 |
1996年 | 437篇 |
1995年 | 332篇 |
1994年 | 291篇 |
1993年 | 236篇 |
1992年 | 199篇 |
1991年 | 169篇 |
1990年 | 140篇 |
1989年 | 112篇 |
1988年 | 87篇 |
1987年 | 93篇 |
1986年 | 76篇 |
1985年 | 111篇 |
1984年 | 146篇 |
1983年 | 65篇 |
1982年 | 98篇 |
1981年 | 81篇 |
1980年 | 73篇 |
1979年 | 79篇 |
1978年 | 63篇 |
1977年 | 46篇 |
1976年 | 35篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
101.
Let Cld
AW
(X) be the hyperspace of nonempty closed subsets of a normed linear space X with the Attouch–Wets topology. It is shown that the space Cld
AW
(X) and its various subspaces are AR's. Moreover, if X is an infinite-dimensional Banach space with weight w(X) then Cld
AW
(X) is homeomorphic to a Hilbert space with weight 2
w(X). 相似文献
102.
Zhu Yongliang; Pagilla Prabhakar R. 《IMA Journal of Mathematical Control and Information》2005,22(2):181-186
We derive some useful and easily computable necessary conditionsfor the existence of a positive semi-definite solution to thealgebraic Ricatti equation (ARE). A motivating example is givento highlight the usefulness of the conditions for controllerand observer designs for nonlinear systems. Further, an upperbound on the trace of the solution to the ARE is also derived. 相似文献
103.
Máté Matolcsi 《Acta Mathematica Hungarica》2005,108(1-2):129-136
Summary He present work deals with estimations of the n-th linear polarization constant c(H)n of an n-dimensional real Hilbert space H. We provide some new lower bounds on the value of sup║y║=1 │1,y> ... n,y>│, where x1, ... ,xn are unit vectors in H. In particular, the results improve an earlier estimate of Marcus. However, the intriguing conjecture c(H) n= nn/2 remains open. 相似文献
104.
105.
An efficient way of obtaining travelling waves in a periodic fluid system is described and tested. We search for steady states in a reference frame travelling at the wave phase velocity using a first‐order pseudospectral semi‐implicit time scheme adapted to carry out the Newton's iterations. The method is compared to a standard Newton–Raphson solver and is shown to be highly efficient in performing this task, even when high‐resolution grids are used. This method is well suited to three‐dimensional calculations in cylindrical or spherical geometries. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
106.
周焕松 《数学物理学报(B辑英文版)》1998,(2)
1IntroductionIntillspaper,weare(follccrlledwitlltileexistellccofPositly(tsollltiollsoftilefollowillgnonhonlogelleousellipticProblclll:whereg(x)EL'(R'),g(:v)Z0alldg(x)t0,f(x,t)=h(x,t).hi=withb>0,h(x,t)EC(R=xR,R)alldtilefollowing(CI)-(C3)11old:(CI)sliphillM0.linljfl- x,h(T,t)(t--if-=011llif'orllllyforxeR2.hill}t:l-:,t)(axle(~ltJ')= lx,11lliforllllyl'Ora:6RZ.ltl~la(C3)ThereexistM>0,aE(0,1]sucllthatFOllowing[1,5],wesaythatf(x,t)=h(x,f… 相似文献
107.
The Modeling of Velocity Enhancement in Polymer Flooding 总被引:1,自引:0,他引:1
In single-phase polymer flooding experiments it has repeatedly been observed that the average velocity of the polymer molecules is higher than the average velocity of the water molecules. This effect is incorporated in many conventional Enhanced Oil Recovery (EOR) simulators by the introduction of a constant velocity enhancement factor. In this paper we show that, in absence of dispersion, a constant enhancement factor in the mathematical model for two-phase polymer flow (Buckley--Leverett displacement) leads to ill-posedness of the model equations. We propose a saturation dependent enhancement factor, derived from a model based on percolation concepts, for which this problem does not occur. 相似文献
108.
In the present article, we aim at treating the existence of fundamental solutions of linear partial differential operators with constant coefficients from the viewpoint of setting up explicit formulae yielding fundamental solutions. 相似文献
109.
The equivalent geometrical configurations of linear ordered orthogonal arrays are determined when their strengths are 3 and 4. Existence of such geometrical configurations is investigated. They are also useful in the study of (T, M, S)-nets. 相似文献
110.
This paper describes a method and the corresponding algorithms for simplification of large-scale linear programming models. It consists of the elimination of the balance constraints (i.e. constraints with zero RHS term). The idea is to apply some linear transformations to the original problem in order to nullify the balance constraints. These transformations are able to simultaneously eliminate more balance rows. The core of this contribution is the introduction of the reduction matrix and the associated theorems on the equivalent linear programs (original and reduced). The numerical experiments with this method of simplification proved this approach to be beneficial for a large class of LP problems.This research work was done while the first author was at Duisburg University, Mess-, Steuer und Regelungstechnik, Germany, under the greatly appreciated financial assistance given by the Alexander-von-Humboldt Foundation. 相似文献