全文获取类型
收费全文 | 5042篇 |
免费 | 262篇 |
国内免费 | 193篇 |
专业分类
化学 | 950篇 |
晶体学 | 52篇 |
力学 | 253篇 |
综合类 | 23篇 |
数学 | 2543篇 |
物理学 | 1676篇 |
出版年
2023年 | 37篇 |
2022年 | 41篇 |
2021年 | 100篇 |
2020年 | 124篇 |
2019年 | 124篇 |
2018年 | 106篇 |
2017年 | 69篇 |
2016年 | 91篇 |
2015年 | 109篇 |
2014年 | 159篇 |
2013年 | 465篇 |
2012年 | 171篇 |
2011年 | 212篇 |
2010年 | 170篇 |
2009年 | 262篇 |
2008年 | 308篇 |
2007年 | 344篇 |
2006年 | 249篇 |
2005年 | 166篇 |
2004年 | 153篇 |
2003年 | 171篇 |
2002年 | 217篇 |
2001年 | 171篇 |
2000年 | 196篇 |
1999年 | 167篇 |
1998年 | 166篇 |
1997年 | 79篇 |
1996年 | 64篇 |
1995年 | 66篇 |
1994年 | 70篇 |
1993年 | 44篇 |
1992年 | 58篇 |
1991年 | 48篇 |
1990年 | 49篇 |
1989年 | 47篇 |
1988年 | 34篇 |
1987年 | 54篇 |
1986年 | 27篇 |
1985年 | 60篇 |
1984年 | 38篇 |
1983年 | 27篇 |
1982年 | 37篇 |
1981年 | 14篇 |
1980年 | 18篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 20篇 |
1976年 | 15篇 |
1975年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有5497条查询结果,搜索用时 31 毫秒
31.
侯旻 《新疆大学学报(理工版)》1991,(1)
本文比较了循环图类{c_p(n_1,…,n_p)}和{c-p(n_1…,n_p,p/α)}的直径下界。对于p和α满足一定条件的循环图类{c_p(n_1,n_2,p/α)},本文给出了达到或几乎达到此图类直径下界的一类几乎最优循环图{c_p(m,m+1,p/α)}。 相似文献
32.
Simple expressions are given for the mean delay, mean waiting time, and mean busy period length in a multiplexer. Data streams with active periods having a general distribution are permitted, and the data rate during the active periods can be random. Data can also arrive in batches. The key restrictions of the model are that the sources are independent, idle periods are exponentially distributed, and a source generates at least enough data during an active period to keep the server busy throughout the period. The exact formulas allow evaluation of the error in approximations such as a heavy traffic diffusion approximation.Both continuous and discrete time models are considered. The discrete-time model includes that studied by Viterbi and subsequently generalized by Neuts. The Pollaczek-Khinchine formula for the mean amount of work in anM/GI/1 queue is retrieved as a limiting case.Preliminary version presented at IEEE INFOCOM, San Francisco, April 1993. 相似文献
33.
34.
Esa Nummelin 《Journal of Theoretical Probability》1994,7(4):739-756
The paper is concerned with characterization results for distributional regeneration. It is shown that distributional regeneration is equivalent to renewal representation of the associated (shift) Markov operator. A sufficient condition for the distributional regeneration of the transfer operator in terms of variation is also formulated. Finally, a minorization condition is formulated and proved to be sufficient for recurrent co-Feller operators. 相似文献
35.
T. Schäfer 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):403-408
We review many-body calculations of the equation of state of dilute neutron matter in the context of effective-field theories
of the nucleon-nucleon interaction. 相似文献
36.
D. Boilley A. Marchix B. Jurado K. -H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2007,33(1):47-52
We propose a new formula for the saddle-to-scission time that is more general that the one based on Kramers' approach. Its
validity and applicability is then studied in detail. Such a formula is useful for the evaluation of the fission time of very
heavy nuclei. 相似文献
37.
技术的动态发展和企业间的竞争对企业新产品策略有很大影响,直接决定新产品的引进周期。本文在产业技术动态变化的随机环境下构建随机动态规划模型,关注产业技术进步、投资成本和产品市场竞争等影响因素,探讨企业进行新产品引进的周期选择,对新产品引进的周期和质量决策进行方法设计和应用举例。利用随机动态规划模型得出新产品引进的最优时间周期,用算例分析技术进步和产品研发成本对企业引进周期策略的影响,采取策略迭代的方法进行求解,发现技术进步较快时企业的新产品引进步伐也较快,研发成本的提高使企业的新产品引入步伐降低。 相似文献
38.
We discuss determination of jumps for functions with generalized bounded variation. The questions are motivated by A. Gelb
and E. Tadmor [1], F. Móricz [5] and [6] and Q. L. Shi and X. L. Shi [7]. Corollary 1 improves the results proved in B. I.
Golubov [2] and G. Kvernadze [3].
Supported by NSFC 10671062. 相似文献
39.
Empirical minimization 总被引:3,自引:0,他引:3
We investigate the behavior of the empirical minimization algorithm using various methods. We first analyze it by comparing
the empirical, random, structure and the original one on the class, either in an additive sense, via the uniform law of large
numbers, or in a multiplicative sense, using isomorphic coordinate projections. We then show that a direct analysis of the
empirical minimization algorithm yields a significantly better bound, and that the estimates we obtain are essentially sharp.
The method of proof we use is based on Talagrand's concentration inequality for empirical processes.
Research partially supported by NSF under award DMS-0434393.
Research partially supported by the Australian Research Council Discovery Porject DP0343616. 相似文献
40.
Effect of the subdivision strategy on convergence and efficiency of some global optimization algorithms 总被引:2,自引:0,他引:2
Hoang Tuy 《Journal of Global Optimization》1991,1(1):23-36
We investigate subdivision strategies that can improve the convergence and efficiency of some branch and bound algorithms of global optimization. In particular, a general class of so called weakly exhaustive simplicial subdivision processes is introduced that subsumes all previously known radial exhaustive processes. This result provides the basis for constructing flexible subdivision strategies that can be adapted to take advantage of various problem conditions. 相似文献