全文获取类型
收费全文 | 1100篇 |
免费 | 199篇 |
国内免费 | 88篇 |
专业分类
化学 | 177篇 |
晶体学 | 8篇 |
力学 | 97篇 |
综合类 | 24篇 |
数学 | 679篇 |
物理学 | 402篇 |
出版年
2023年 | 11篇 |
2022年 | 14篇 |
2021年 | 37篇 |
2020年 | 27篇 |
2019年 | 29篇 |
2018年 | 35篇 |
2017年 | 47篇 |
2016年 | 36篇 |
2015年 | 30篇 |
2014年 | 54篇 |
2013年 | 86篇 |
2012年 | 65篇 |
2011年 | 68篇 |
2010年 | 59篇 |
2009年 | 66篇 |
2008年 | 70篇 |
2007年 | 64篇 |
2006年 | 54篇 |
2005年 | 51篇 |
2004年 | 61篇 |
2003年 | 57篇 |
2002年 | 66篇 |
2001年 | 44篇 |
2000年 | 41篇 |
1999年 | 19篇 |
1998年 | 33篇 |
1997年 | 24篇 |
1996年 | 16篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 5篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有1387条查询结果,搜索用时 593 毫秒
81.
Matthias Kriesell 《Graphs and Combinatorics》2007,23(5):545-557
We study the distribution of small contractible subgraphs in 3-connected graphs under local regularity conditions. 相似文献
82.
确定Lotka-Volterra生态系统模型高精度参数的研究 总被引:1,自引:0,他引:1
研究确定Lotka-Volterra生态系统模型的高精度参数估计问题.利用周期性,先对测量数据进行预处理;然后用三种不同的方法构造了误差函数,进行非线性最小二乘法参数估计;再用计算机仿真对其进行验证.结果表明该方法能够有效地解决高精度参数估计中消除测量数据误差的问题. 相似文献
83.
Linn I. Sennott 《Mathematical Methods of Operations Research》1997,45(1):45-62
The Approximating Sequence Method for computation of average cost optimal stationary policies in denumerahle state Markov decision chains, introduced in Sennott (1994), is reviewed. New methods for verifying the assumptions are given. These are useful for models with multidimensional state spaces that satisfy certain mild structural properties. The results are applied to four problems in the optimal routing of packets to parallel queues. Numerical results are given for one of the models. 相似文献
84.
Linn I. Sennott 《Mathematical Methods of Operations Research》1994,39(2):209-225
Zero-sum stochastic games with countable state space and with finitely many moves available to each player in a given state are treated. As a function of the current state and the moves chosen, player I incurs a nonnegative cost and player II receives this as a reward. For both the discounted and average cost cases, assumptions are given for the game to have a finite value and for the existence of an optimal randomized stationary strategy pair. In the average cost case, the assumptions generalize those given in Sennott (1993) for the case of a Markov decision chain. Theorems of Hoffman and Karp (1966) and Nowak (1992) are obtained as corollaries. Sufficient conditions are given for the assumptions to hold. A flow control example illustrates the results. 相似文献
85.
θ-Fuzzy关系方程的分解与求解 总被引:3,自引:0,他引:3
在有限论域上首先给出θ-Fuzzy关系方程的分解,然后针对NR-蕴涵θ,探讨θ-Fuzzy关系方程的求解问题,基于解矩阵给出解的存在性的几个新判据,并在解集非空时,证明θ-Fuzzy关系方程的每一个解都存在一个极大解。 相似文献
86.
SpeckleaveragingbyphaseshiftfordigitalshearographyfringeF.Chen;Y.Y.Hung(DepartmentofmechanicalEngineering,OaklandUniversity,R... 相似文献
87.
本文对可数状态集、非空决策集、报酬无界的平均准则马氏决策过程,提出了一组新的条件,在此条件下存在(ε)最优平稳策略,且当最优不等式中的和有定义时最优不等式也成立。 相似文献
88.
关于n进制及其有关计数函数 总被引:23,自引:0,他引:23
给出了n进制中数字之和函数均值A(N)的一个精确的计算公式。 相似文献
89.
Tadeus Nawka Lutz Christian Anders Mario Cebulla David Zurakowski 《Journal of voice》1997,11(4):422-428
Spectral analysis of vowels during connected speech can be performed using the spectral intensity distribution within critical bands corresponding to a natural scale on the basilar membrane. Normalization of the spectra provides the opportunity to make objective comparisons independent from the recording level. An increasing envelope peak between 3,150 and 3,700 Hz has been confirmed statistically for a combination of seven vowels in three groups of male speakers with hoarse, normal, and professional voices. Each vowel is also analyzed individually. The local energy maximum is called “the speaker's formant” and can be found in the region of the fourth formant. The steepness of the spectral slope (i.e. the rate of decline) becomes less pronounced when the sonority or the intensity of the voice increases. The speaker's formant is connected with the sonorous quality of the voice. It increases gradually and is approximately 10 dB higher in professional male voices than in normal male voices at neutral loudness (60 dB at 0.3 min). The peak intensity becomes stronger (30 dB above normal voices) when the overall speaking loudness is increased to 80 dB. Shouting increases the spectral energy of the adjacent critical bands but not the speaker's formant itself. 相似文献
90.
Zhan-jie SONG Wen-chang SUN Shou-yuan YANG & Guang-wen ZHU School of Science Tianjin University Tianjin China Department of Mathematics LPMC Nankai University Tianjin China National Ocean Technology Center Tianjin China 《中国科学A辑(英文版)》2007,50(4):457-463
We show that a weak sense stationary stochastic process can be approximated by local averages. Explicit error bounds are given. Our result improves an early one from Splettstosser. 相似文献