全文获取类型
收费全文 | 222篇 |
免费 | 11篇 |
国内免费 | 2篇 |
专业分类
化学 | 100篇 |
力学 | 7篇 |
数学 | 87篇 |
物理学 | 41篇 |
出版年
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 16篇 |
2016年 | 13篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 29篇 |
2012年 | 12篇 |
2011年 | 21篇 |
2010年 | 12篇 |
2009年 | 13篇 |
2008年 | 7篇 |
2007年 | 11篇 |
2006年 | 5篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 5篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1984年 | 1篇 |
1979年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有235条查询结果,搜索用时 15 毫秒
111.
Nourchaine Jelaiel Noureddine Said Soufiane Touil Mohamed Lotfi Efrit 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2382-2392
The condensation of primary amines on α- or β-ketophosphonates affords the corresponding iminophosphonates. The reaction was found to be highly stereoselective, affording the E isomer exclusively. These phosphonylimines were then treated in basic media to give pyrrolidines and quinolines through intramolecular cyclization. The structures of all obtained products were confirmed by NMR spectroscopy (1H, 31P, 13C), and in some cases by mass spectrometry. 相似文献
112.
113.
Said Lotfi Hafsaoui Mokhtar Benziane Abbas Tcharkhtchi 《Journal of Thermal Analysis and Calorimetry》2013,112(1):285-292
Simulation of thermal phenomena in rotational moulding is very important to follow the evolution of the temperature in various zones of this process. It was a question of modelling heat gradients developing in rotational moulding part. Thermal model tested take into account the temperature change (thermal transfer mechanism) of melting and crystallization pseudo-stages (enthalpy method). Series of tests in polyamide 11 (PA11) were carried out by means of rotational moulding STP LAB, and non-isothermal crystallization kinetics of rotational moulding PA11 grade are measured and analysed by DSC technique type TAQ20. A result of non-isothermal crystallization of the studied polyamide was confronted with Ozawa model. In order to test the validity degree of enthalpy method (layer to layer), another approach based on Ozawa model has also been used in the case of cooling pseudo-stage. As results, the rotational moulding of PA11 was successfully carried out. The simulation of the fusion and crystallization stages, by application of Ozawa model coupled with enthalpy method gave a good representation of experimental data. 相似文献
114.
115.
This paper presents the implementation of a multi-phase final-exam-scheduling package at a large university. The problem as it had evolved over time is discussed and a solution is presented. The implementation was undertaken over a three-year period and involved a multi-phase approach. The multi-phase final-exam-scheduling process consists of first grouping the final exams into sets called `blocks' in such a way as to minimize the number of students with simultaneous exams. Second, the blocks are assigned to exam days while minimizing the number of students with two or more exams per day. Third, the exam days and exam blocks within days are arranged so as to minimize the number of students with consecutive exams. Fourth, exams are assigned to classrooms so as to maximize the space utilization. New formulations and solution methods for the stated four phases are presented. The approach is well suited for a practical application and has been implemented at a large university. 相似文献
116.
Inès Ouerfelli Rafik Gatri Mohamed Lotfi Efrit Johann Perruchon Loïc Toupet 《Journal of organometallic chemistry》2011,696(3):670-675
A series of systematically varied ’rigid-rod’ octahedral ruthenium-acetylide complexes, bearing conjugated bis(acylamino)triazine (DAT) substituents capable of ADAD-DADA pairing, of general formula trans-[(dppe)2Ru(Cl)(CC-C6H4-DAT(R)2)] (R = Et, i-Pr, t-Bu, n-C5H11) have been synthesized and thoroughly characterized in solution by 1H NMR and in the solid state. trans-[Ru(-CC-C6H4-DAT(R)2)2(dppe)2] (R = n-C5H11) has also been designed to form discrete oligomeric chains in solution. 相似文献
117.
Najmeh Malekmohammadi Farhad Hosseinzadeh Lotfi Azmi B. Jaafar 《Central European Journal of Operations Research》2011,19(1):65-79
In the existing DEA models, we have a centralized decision maker (DM) who supervises all the operating units. In this paper,
we solve a problem in which the centralized DM encounters limited or constant resources for total inputs or total outputs.
We establish a DEA target model that solves and deals with such a situation. In our model, we consider the decrease of total
input consumption and the increase of total output production; however, in the existing DEA models, total output production
is guaranteed not to decrease. Considering the importance of imprecise data in organizations, we define our model so as to
deal with interval and ordinal data. A numerical illustration is provided to show the application of our model and the advantages
of our approach over the previous one. 相似文献
118.
G.R. Jahanshahloo F. Hosseinzadeh Lotfi V. Rezaie M. Khanmohammadi 《Applied Mathematical Modelling》2011
An original DEA model is to evaluate each DMU optimistically, but the interval DEA model proposed in this paper has been formulated to obtain an efficiency interval consisting of evaluations from both the optimistic and the pessimistic viewpoints. 相似文献
119.
Data envelopment analysis (DEA) and multiple objective linear programming (MOLP) can be used as tools in management control and planning. The existing models have been established during the investigation of the relations between the output-oriented dual DEA model and the minimax reference point formulations, namely the super-ideal point model, the ideal point model and the shortest distance model. Through these models, the decision makers’ preferences are considered by interactive trade-off analysis procedures in multiple objective linear programming. These models only consider the output-oriented dual DEA model, which is a radial model that focuses more on output increase. In this paper, we improve those models to obtain models that address both inputs and outputs. Our main aim is to decrease total input consumption and increase total output production which results in solving one mathematical programming model instead of n models. Numerical illustration is provided to show some advantages of our method over the previous methods. 相似文献
120.
ABSTRACTWe investigated the alignment director of a frustrated cholesteric liquid crystal (CLC) confined in a planar cell. Three cells with different confinement ratio (c?=?d/p) (where p is the pitch and d is the cell thickness) are prepared. Under an electric field, the CLC planar texture is transformed into a cholesteric fingerprint (CF). The results showed that CF contrast depends on c. When c?≈?2, CLC stripes are formed by a periodic CF, with a period equal to the CLC pitch. The CF is developed and slowly extended to the whole cell surface along the rubbing direction and the contrast of the grating stripes keeps unchangeable. Yet, the CLC finger borders have a different light intensity. However, when c?≈?1, the CF contrast increases with time. When c?1, an isolated CF is obtained whose borders contrast change by varying the angle θ between the polarizer and the CFs. 相似文献