全文获取类型
收费全文 | 5652篇 |
免费 | 536篇 |
国内免费 | 638篇 |
专业分类
化学 | 4143篇 |
晶体学 | 19篇 |
力学 | 115篇 |
综合类 | 119篇 |
数学 | 1060篇 |
物理学 | 1370篇 |
出版年
2024年 | 14篇 |
2023年 | 41篇 |
2022年 | 165篇 |
2021年 | 253篇 |
2020年 | 211篇 |
2019年 | 154篇 |
2018年 | 149篇 |
2017年 | 161篇 |
2016年 | 255篇 |
2015年 | 220篇 |
2014年 | 329篇 |
2013年 | 415篇 |
2012年 | 285篇 |
2011年 | 353篇 |
2010年 | 277篇 |
2009年 | 362篇 |
2008年 | 345篇 |
2007年 | 344篇 |
2006年 | 340篇 |
2005年 | 328篇 |
2004年 | 284篇 |
2003年 | 234篇 |
2002年 | 164篇 |
2001年 | 145篇 |
2000年 | 123篇 |
1999年 | 130篇 |
1998年 | 111篇 |
1997年 | 104篇 |
1996年 | 81篇 |
1995年 | 85篇 |
1994年 | 72篇 |
1993年 | 39篇 |
1992年 | 39篇 |
1991年 | 60篇 |
1990年 | 29篇 |
1989年 | 40篇 |
1988年 | 30篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 4篇 |
1969年 | 1篇 |
排序方式: 共有6826条查询结果,搜索用时 46 毫秒
11.
12.
13.
14.
15.
在工农业产品评定级别中,专家组的水平是至关重要的。文中给出一个挑选专家组成员的数学模型,可以检验专家对参评产品的决策水平,为评价所评结论的可信度提供参考依据。 相似文献
16.
We study the expected delay in cyclic polling models with general ‘branching-type’ service disciplines. For this class of
models, which contains models with exhaustive and gated service as special cases, we obtain closed-form expressions for the
expected delay under standard heavy-traffic scalings. We identify a single parameter associated with the service discipline
at each queue, which we call the ‘exhaustiveness’. We show that the scaled expected delay figures depend on the service policies
at the queues only through the exhaustiveness of each of the service disciplines. This implies that the influence of different
service disciplines, but with the same exhaustiveness, on the expected delays at the queues becomes the same when the system
reaches saturation. This observation leads to a new classification of the service disciplines. In addition, we show monotonicity
of the scaled expected delays with respect to the exhaustiveness of the service disciplines. This induces a complete ordering
in terms of efficiency of the service disciplines. The results also lead to new rules for optimization of the system performance
with respect to the service disciplines at the queues. Further, the exact asymptotic results suggest simple expected waiting-time
approximations for polling models in heavy traffic. Numerical experiments show that the accuracy of the approximations is
excellent for practical heavy-traffic scenarios.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
17.
属性区间识别理论模型研究及其应用 总被引:15,自引:3,他引:12
根据程乾生教授创立的属性识别理论模型[1] ,提出了属性测度区间的概念 ,建立了属性区间识别理论模型 ,并在自然科学学术期刊质量评价中进行了应用 . 相似文献
18.
An approach to dealing with missing data, both during the design and normal operation of a neuro-fuzzy classifier is presented in this paper. Missing values are processed within a general fuzzy min–max neural network architecture utilising hyperbox fuzzy sets as input data cluster prototypes. An emphasis is put on ways of quantifying the uncertainty which missing data might have caused. This takes a form of classification procedure whose primary objective is the reduction of a number of viable alternatives rather than attempting to produce one winning class without supporting evidence. If required, the ways of selecting the most probable class among the viable alternatives found during the primary classification step, which are based on utilising the data frequency information, are also proposed. The reliability of the classification and the completeness of information is communicated by producing upper and lower classification membership values similar in essence to plausibility and belief measures to be found in the theory of evidence or possibility and necessity values to be found in the fuzzy sets theory. Similarities and differences between the proposed method and various fuzzy, neuro-fuzzy and probabilistic algorithms are also discussed. A number of simulation results for well-known data sets are provided in order to illustrate the properties and performance of the proposed approach. 相似文献
19.
A. A. Dokukin 《Computational Mathematics and Mathematical Physics》2006,46(5):914-918
To validate approximate optimization schemes for estimate calculation algorithms (ECAs), it is necessary to compute the optimal height, which cannot be done in a reasonable amount of time. A variety of samples are built for which the optimal height of the ECAs is known by construction. 相似文献
20.
Jie Xue Liang Chen Li Zhou Zhifeng Jia Yanping Wang Xinyuan Zhu Deyue Yan 《Journal of Polymer Science.Polymer Physics》2006,44(15):2050-2057
α‐Cyclodextrin (α‐CD) has been complexed with various poly(ethylene glycol) (PEG) derivatives in aqueous solution. It has been found that the end groups of PEG derivatives affect the complexation kinetics greatly, but have only a little influence on the thermodynamic behavior. By increasing the hydrophobicity of end groups, the complexation speeds up rapidly. On the other hand, the bulky end groups slow down the threading of polymeric guests into the cavity of CD. By changing the hydrophobicity and the size of end groups, the complexation rate can be adjusted in the range of several orders of magnitudes, which should be quite useful in the design of new supramolecular systems. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2050–2057, 2006 相似文献