全文获取类型
收费全文 | 23838篇 |
免费 | 2431篇 |
国内免费 | 2336篇 |
专业分类
化学 | 3767篇 |
晶体学 | 44篇 |
力学 | 1989篇 |
综合类 | 557篇 |
数学 | 15274篇 |
物理学 | 6974篇 |
出版年
2023年 | 207篇 |
2022年 | 389篇 |
2021年 | 424篇 |
2020年 | 489篇 |
2019年 | 526篇 |
2018年 | 502篇 |
2017年 | 660篇 |
2016年 | 731篇 |
2015年 | 556篇 |
2014年 | 1119篇 |
2013年 | 1503篇 |
2012年 | 1188篇 |
2011年 | 1406篇 |
2010年 | 1219篇 |
2009年 | 1564篇 |
2008年 | 1574篇 |
2007年 | 1616篇 |
2006年 | 1514篇 |
2005年 | 1387篇 |
2004年 | 1124篇 |
2003年 | 1053篇 |
2002年 | 921篇 |
2001年 | 830篇 |
2000年 | 778篇 |
1999年 | 672篇 |
1998年 | 606篇 |
1997年 | 579篇 |
1996年 | 425篇 |
1995年 | 337篇 |
1994年 | 289篇 |
1993年 | 232篇 |
1992年 | 217篇 |
1991年 | 160篇 |
1990年 | 162篇 |
1989年 | 112篇 |
1988年 | 119篇 |
1987年 | 107篇 |
1986年 | 82篇 |
1985年 | 154篇 |
1984年 | 162篇 |
1983年 | 92篇 |
1982年 | 140篇 |
1981年 | 152篇 |
1980年 | 90篇 |
1979年 | 85篇 |
1978年 | 81篇 |
1977年 | 57篇 |
1976年 | 51篇 |
1974年 | 28篇 |
1973年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
951.
952.
953.
954.
We study the filling length function for a finite presentation of a group , and interpret this function as an optimal bound on the length of the boundary loop as a van Kampen diagram is collapsed to the basepoint using a combinatorial notion of a null-homotopy. We prove that filling length is well behaved under change of presentation of . We look at 'AD-pairs' (f,g) for a finite presentation
: that is, an isoperimetric function f and an isodiametric function g that can be realised simultaneously. We prove that the filling length admits a bound of the form [g+1][log (f+1)+1] whenever (f,g) is an AD-pair for
. Further we show that (up to multiplicative constants) if
is an isoperimetric function (
) for a finite presentation then (
) is an AD-pair. Also we prove that for all finite presentations filling length is bounded by an exponential of an isodiametric function.Partially supported by NSF grant DMS-9800158Supported by EPSRC Award No. 98001683 and Corpus Christi College, Oxford. 相似文献
955.
This paper presents complete solutions of the stationary distributions of buffer occupancy and buffer content of a fluid queue driven by an M/M/1 queue. We assume a general boundary condition when compared to the model discussed in Virtamo and Norros [Queueing Systems 16 (1994) 373–386] and Adan and Resing [Queueing Systems 22 (1996) 171–174]. We achieve the required solutions by transforming the underlying system of differential equations using Laplace transforms to a system of difference equations leading to a continued fraction. This continued fraction helps us to find complete solutions. We also obtain the buffer content distribution for this fluid model using the method of Sericola and Tuffin [Queueing Systems 31 (1999) 253–264]. 相似文献
956.
André Adler 《Journal of Theoretical Probability》2002,15(4):939-949
Consider independent and identically distributed random variables {X,X
nj
, 1jn,n1} with density f(x)=px
–p–1
I(x1), where p>0. We show that there exist unusual generalized Laws of the Iterated Logarithm involving the larger order statistics from our array. 相似文献
957.
Gábor Hetyei 《Graphs and Combinatorics》2002,18(3):533-564
958.
Arie Leizarowitz 《Set-Valued Analysis》2002,10(2-3):185-207
The order reduction method for singularly perturbed optimal control systems consists of employing the system obtained while setting the small parameter to be zero. In many situations the differential-algebraic system thus obtained indeed provides an appropriate approximation to the singularly perturbed problem with a small parameter. In this paper we establish that if relaxed controls are allowed then the answer to the question whether or not this method is valid depends essentially on one simple parameter: the dimension of the fast variable, denoted n. More specifically, if n=1 then the order reduction method is indeed applicable, while if n>1 then the set of singularly perturbed optimal control systems for which it is not applicable is dense (in the L
norm). 相似文献
959.
函数的逼近及其在下半连续函数可微性中的应用 总被引:1,自引:0,他引:1
通过函数的下卷积函数列的逼近方法,在变分原理中从扰动最小值点集的“大小”入手,研究了下半连续函数的可微性。 相似文献
960.
Ralph Chill Eva Fasangová 《Proceedings of the American Mathematical Society》2002,130(3):675-681
We show that a new notion of a spectrum of a function ( is a Banach space), defined by B. Basit and the first author, coincides with the Arveson spectrum of some shift group, provided is uniformly continuous. We apply this result to prove a new version of a tauberian theorem. 相似文献