全文获取类型
收费全文 | 477篇 |
免费 | 19篇 |
国内免费 | 4篇 |
专业分类
化学 | 285篇 |
晶体学 | 1篇 |
力学 | 36篇 |
数学 | 104篇 |
物理学 | 74篇 |
出版年
2023年 | 2篇 |
2022年 | 10篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 7篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 13篇 |
2015年 | 18篇 |
2014年 | 15篇 |
2013年 | 29篇 |
2012年 | 26篇 |
2011年 | 42篇 |
2010年 | 34篇 |
2009年 | 20篇 |
2008年 | 28篇 |
2007年 | 31篇 |
2006年 | 27篇 |
2005年 | 22篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 23篇 |
2001年 | 10篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 10篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有500条查询结果,搜索用时 0 毫秒
51.
Dimitris S. Achilias Alexandros K. Nikolaidis George P. Karayannidis 《Journal of Thermal Analysis and Calorimetry》2010,102(2):451-460
Kinetics of the in situ bulk polymerization of methyl methacrylate in the presence of organomodified montmorillonite (MMT)
was investigated using differential scanning calorimetry (DSC) and gravimetrically. Different amount and types of MMT under
the trade names Cloisite were employed. Using DSC, the amount of heat released versus time, under isothermal conditions, was
recorded, and eventually, the time evolution of polymerization rate and monomer conversion was calculated. Results on the
variation of monomer conversion with reaction time were in good agreement to corresponding from the gravimetric measurements.
The nanocomposites prepared were characterized with WAXD, TEM and FTIR, and their glass transition temperature, T
g, was measured with DSC. Depending on the added amount of nano-MMT, either exfoliated or intercalated structures were obtained.
An enhancement of the polymerization rate with the presence of the nanoparticles was observed especially in the gel effect
region. This was accompanied by a higher T
g and average molecular weight, as measured by GPC, of all nanocomposites compared to neat PMMA. 相似文献
52.
Sotiria Karagiovanaki Alexandros Koutsioubas Nikolaos Spiliopoulos Dimitris L. Anastassopoulos Alexandros A. Vradis Chris Toprakcioglu Angeliki Elina Siokou 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):1676-1682
We have studied the adsorption of end-attaching block copolymer chains inside the cylindrical pores of nanoporous alumina. Highly asymmetric PS-PEO block copolymers, with a small PEO anchoring block and a long PS dangling block, were allowed to adsorb onto porous alumina substrates with an average pore diameter of ∼200 nm from toluene solution. The adsorption process was monitored using FTIR spectroscopy, whereas depth profile analysis was performed by means of XPS and Ar+ ion sputtering. It is found that the PS-PEO adsorption kinetics in porous alumina are ∼4 orders of magnitude slower than the corresponding case of a flat alumina substrate. It appears that chains adsorbed near the pore entrance early on tend to form a barrier for chains entering the pore at later times, thereby slowing down the adsorption process significantly. This effect is much more pronounced for large chains whose dimensions are comparable with the pore diameter. The equilibrium adsorbance value is also affected by chain size due to the additional entropic penalty associated with chain confinement, the adsorbance falling substantially when the chain dimensions become comparable with the pore diameter. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1676–1682, 2010 相似文献
53.
A general framework for a combined land use and water management is described. An optimization problem is formulated that combines combinatorial and spatial characteristics. The aim of the planning is to maximize economic benefit, while minimizing water extraction and transportation cost under ecological constraints. A genetic algorithm is employed endowed with a new neighborhood operator. This operator acts on a local level, but it produces global results. Although the computational scheme does not include compactness as a separate objective, compact patterns are produced as emergent results. The algorithm is tested on a fictive area represented as a grid with 15×15 land blocks and, also, on a real-world case study. 相似文献
54.
Dimitris Gavalas 《International Journal of Mathematical Education in Science & Technology》2013,44(2):261-268
The traditional triadic 'Teaching System' (the teacher, the student and mathematics) and the new quaternary version (the teacher, the student, mathematics and new technologies), are studied according to Systems Theory. Systems Theory is described and the model of the traditional 'Teaching System' and that of the new system are analysed with the aid of this theory; that is the structure of each system (elements, interactions) and its function are described. Finally, comments are made about the application of the new system on didactic, on the one hand, and the philosophical background of the incorporation of the fourth element (new technologies) in the traditional system, on the other. 相似文献
55.
The task of monitoring for a change in the mean of a sequence of Bernoulli random variables has been widely studied. However most existing approaches make at least one of the following assumptions, which may be violated in many real-world situations: (1) the pre-change value of the Bernoulli parameter is known in advance, (2) computational efficiency is not paramount, and (3) enough observations occur between change points to allow asymptotic approximations to be used. We develop a novel change detection method based on Fisher’s exact test which does not make any of these assumptions. We show that our method can be implemented in a computationally efficient manner, and is hence suited to sequential monitoring where new observations are constantly being received over time. We assess our method’s performance empirically via using simulated data, and find that it is comparable to the optimal CUSUM scheme which assumes both pre- and post-change values of the parameter to be known. 相似文献
56.
Mathematical Programming - Decision rules provide a flexible toolbox for solving computationally demanding, multistage adaptive optimization problems. There is a plethora of real-valued decision... 相似文献
57.
Dimitris Arabadjis Constantin Papaodysseus Panayiotis Rousopoulos Michalis Panagopoulos 《Journal of Applied Mathematics and Computing》2010,34(1-2):81-100
In this paper two new theorems are proved in association with the problem of matching three dimensional solid bodies. Rigorous mathematical criteria are given in order to test if two such bodies actually match in a certain position. Since this problem finds important application to the actual problem of reassembling fragmented objects e.g. archaeological, special care is taken to account for small gaps between matching fragments and fuzziness of the matching parameters. 相似文献
58.
Dimitris I. Ioannou Prof. Dr. Luca Capaldo Jiri Sanramat Prof. Dr. Joost N. H. Reek Prof. Dr. Timothy Noël 《Angewandte Chemie (International ed. in English)》2023,62(52):e202315881
Electrophotocatalytic transformations are garnering attention in organic synthesis, particularly for accessing reactive intermediates under mild conditions. Moving these methodologies to continuous-flow systems, or flow ElectroPhotoCatalysis (f-EPC), showcases potential for scalable processes due to enhanced irradiation, increased electrode surface, and improved mixing of the reaction mixture. Traditional methods sequentially link photochemical and electrochemical reactions, using flow reactors connected in series, yet struggle to accommodate reactive transient species. In this study, we introduce a new flow reactor concept for electrophotocatalysis (EPC) that simultaneously utilizes photons and electrons. The reactor is designed with a transparent electrode and employs cost-effective materials. We used this technology to develop an efficient process for electrophotocatalytic heteroarylation of C(sp3)−H bonds. Importantly, the same setup can also facilitate purely electrochemical and photochemical transformations. This reactor represents a significant advancement in electrophotocatalysis, providing a framework for its application in flow for complex synthetic transformations. 相似文献
59.
Mathematical Programming - We address the problem of prescribing an optimal decision in a framework where the cost function depends on uncertain problem parameters that need to be learned from... 相似文献
60.
McElroy Tucker S. Politis Dimitris N. 《Statistical Inference for Stochastic Processes》2022,25(3):471-483
Statistical Inference for Stochastic Processes - The problem of linear interpolation in the context of a multivariate time series having multiple (possibly non-consecutive) missing values is... 相似文献