全文获取类型
收费全文 | 1262篇 |
免费 | 57篇 |
国内免费 | 16篇 |
专业分类
化学 | 918篇 |
晶体学 | 7篇 |
力学 | 66篇 |
数学 | 175篇 |
物理学 | 169篇 |
出版年
2023年 | 8篇 |
2022年 | 36篇 |
2021年 | 68篇 |
2020年 | 43篇 |
2019年 | 61篇 |
2018年 | 65篇 |
2017年 | 42篇 |
2016年 | 63篇 |
2015年 | 52篇 |
2014年 | 78篇 |
2013年 | 133篇 |
2012年 | 95篇 |
2011年 | 90篇 |
2010年 | 66篇 |
2009年 | 51篇 |
2008年 | 52篇 |
2007年 | 57篇 |
2006年 | 48篇 |
2005年 | 45篇 |
2004年 | 21篇 |
2003年 | 20篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 15篇 |
1999年 | 7篇 |
1998年 | 3篇 |
1997年 | 6篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1968年 | 2篇 |
1965年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1335条查询结果,搜索用时 15 毫秒
101.
Véronique Cariou Stéphane Verdun Emmanuelle Diaz El Mostafa Qannari Evelyne Vigneau 《Advances in Data Analysis and Classification》2009,3(3):227-241
Within the scope of cluster analysis of variables, the selection of the appropriate number of clusters is of paramount interest. The strategy of determination of the appropriate number of clusters adopted herein is based on a hypothesis testing approach. It consists in testing whether the variation of a partition quality criterion between two consecutive partitions is far removed from the expected variation under the null-hypothesis stipulating a lack of structure. Three hypothesis testing strategies are detailed and compared in the scope of clustering of variables: Gap, Weighted Gap and a statistic associated with CLV methodology. Finally, an illustration is presented based on data from a preference study. 相似文献
102.
Mostafa Khorramizadeh Nezam Mahdavi-Amiri 《4OR: A Quarterly Journal of Operations Research》2009,7(2):145-167
We present a new class of integer extended ABS algorithms for solving linear Diophantine systems. The proposed class contains the integer ABS (the so-called EMAS and our proposed MEMAS) algorithms and the generalized Rosser’s algorithm as its members. After an application of each member of the class a particular
solution of the system and an integer basis for the null space of the coefficient matrix are at hand. We show that effective
algorithms exist within this class by appropriately setting the parameters of the members of the new class to control the
growth of intermediate results. Finally, we propose two effective heuristic rules for selecting certain parameters in the
new class of integer extended ABS algorithms.
相似文献
103.
Mostafa Blidia 《Combinatorica》1986,6(1):23-27
We show that every digraph has a kernel (i.e. an absorbing and independent set) under the following parity condition: For
every pair of verticesx, y x ≠ y all minimal directed paths betweenx andy have the same length parity. 相似文献
104.
A. A. El-Shafei A. M. Abd Elhafeez H. A. Mostafa 《Journal of Solid State Electrochemistry》2010,14(2):185-190
Impregnated Pd–zeolite graphite (PdZG) electrodes have been tested for ethanol oxidation in 0.5 M NaOH. The results obtained
have been compared with that of Pd electrode. Cyclic voltammetric and chronoamperometric measurements indicated the activity
of PdZG electrode toward ethanol oxidation and poisoning tolerance. The influence of zeolite loading as well as impregnation
time in Pd2+ solution has been examined. Scan rate effect and ethanol concentration dependency indicated that ethanol oxidation at PdZG
electrode was governed by diffusion control. 相似文献
105.
Liliane Bokobza Mostafa Rahmani Colette Belin Jean‐Luc Bruneel Nour‐Eddine El Bounia 《Journal of Polymer Science.Polymer Physics》2008,46(18):1939-1951
The reinforcement of a styrene‐butadiene rubber (SBR) by single fillers—carbon black (CB) or multiwall carbon nanotubes (MWNTs)—or by mixtures of CB and MWNTs, is investigated. The morphologies, mechanical and electrical properties of the composites, are analyzed. A significant improvement in the tensile properties is observed for samples containing a dual phase. Using atomic force (AFM) and transmission electron (TEM) microscopies, we demonstrate that the double loading improves the dispersion of the nanotubes in SBR. Electrical measurements show lower resistivity and a lower percolation threshhold for composites containing blends of fillers, which provides further evidence of better dispersion. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 46: 1939–1951, 2008 相似文献
106.
Topological KKM theorems and generalized vector equilibria on G-convex spaces with applications 总被引:2,自引:0,他引:2
El Mostafa Kalmoun Hassan Riahi 《Proceedings of the American Mathematical Society》2001,129(5):1335-1348
In the present paper, slightly modifying the topological KKM Theorem of Park and Kim (1996), we obtain a new existence theorem for generalized vector equilibrium problems related to an admissible multifunction. We work here under the general framework of G-convex space which does not have any linear structure. Also, we give applications to greatest element, fixed point and vector saddle point problems. The results presented in this paper extend and unify many results in the literature by relaxing the compactness, the closedness and the convexity conditions.
107.
Mostafa Sahar I. El-Asmy Ahmed A. El-Shahawi Mohamed S. 《Transition Metal Chemistry》2000,25(4):470-473
New ruthenium(II) complexes with 2-hydroxybenzophenone N(4)-substituted (Me, Ph and/or piperidyl) thiosemicarbazones have
been prepared and characterised by elemental analysis, molar conductivity, thermal analysis, spectroscopy (i.r., 1H-n.m.r. and u.v.–vis.) and by cyclic voltammetry. The thiosemicarbazones coordinate to ruthenium(II) as mononegative tridentate
ligands via the deprotonated hydroxyl group, N1 nitrogen and thione sulphur centres. The redox properties, nature of the electrode processes and the stability of the complexes
towards oxidation in CH2Cl2 are discussed. The change in the E
1/2 values of the complexes can be related to the basicity of the N(4)-substituents. All the complexes display an irreversible
one-electron charge-transfer couple in the potential range studied.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
108.
Aly Ashraf A. Hassan Alaa A. Mohamed Asmaa H. Osman Esraa M. Bräse Stefan Nieger Martin Ibrahim Mahmoud A. A. Mostafa Sara M. 《Molecular diversity》2021,25(1):461-471
Molecular Diversity - During formylation of 2-quinolones by DMF/Et3N mixture, the unexpected 3,3′-methylenebis(4-hydroxyquinolin-2(1H)-ones) were formed. The discussed mechanism was proved as... 相似文献
109.
Mostafa Kiamehr Batoul Alipour Leyla Mohammadkhani Behzad Jafari Peter Langer 《Tetrahedron》2017,73(21):3040-3047
Various novel polycyclic thiopyranoindol annulated [3,4-c]quinolone derivatives were synthesized via domino Knoevenagel-hetero-Diels–Alder reactions of indoline-2-thions and novel N-acrylated anthranilaldehydes in refluxing ethanol as a solvent in the presence of 20 mol% ZnBr2 as a Lewis acid catalyst. All reactions proceed with high yields with excellent regio- and stereoselectivity. 相似文献
110.
For the purpose of exploring and modeling the relationships between a dataset Y and several datasets () measured on the same individuals, multiblock Partial Least Squares is a regression technique which is widely used, particularly in process monitoring, chemometrics and sensometrics. In the same vein, a new multiblock method, called multiblock Redundancy Analysis, is proposed. It is introduced by maximizing a criterion that reflects the objectives to be addressed. The solution of this maximization problem is directly derived from the eigenanalysis of a matrix. In addition, this method is related to other multiblock methods. Multiblock modeling methods provide to the user a large spectrum of interpretation indices for the investigation of the relationships among variables and among datasets. They are related to the criterion to maximize and therefore directly derived from the maximization problem under consideration. The interest of multiblock Redundancy Analysis and the associated interpretation tools are illustrated using a dataset in the field of veterinary epidemiology. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献