全文获取类型
收费全文 | 385篇 |
免费 | 7篇 |
国内免费 | 3篇 |
专业分类
化学 | 180篇 |
晶体学 | 1篇 |
力学 | 31篇 |
数学 | 121篇 |
物理学 | 62篇 |
出版年
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 10篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 14篇 |
2013年 | 39篇 |
2012年 | 22篇 |
2011年 | 33篇 |
2010年 | 21篇 |
2009年 | 16篇 |
2008年 | 21篇 |
2007年 | 15篇 |
2006年 | 15篇 |
2005年 | 19篇 |
2004年 | 13篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1940年 | 2篇 |
排序方式: 共有395条查询结果,搜索用时 31 毫秒
81.
On résoud le problème de Cauchy pour des opérateurs aux dérivées partielles à coefficients polynomiaux par rapport aux variables d'espace dans des classes de Gevrey projectives. Nos résultats sont des versions globales du théorème de Cauchy-Kowalewski et du théorème de Nagumo. 相似文献
82.
Sami Mustapha 《Journal of Theoretical Probability》2006,19(4):773-787
It is shown in this paper that the transition kernels corresponding to simple random walks on certain unimodular solvable
p-adic groups admit upper Gaussian estimates.
相似文献
83.
A numerical study of forced convection enhancement in a channel intermittently heated is presented in this work. The use
of porous blocks mounted on the heated parts of the channel to improve thermal performance is investigated. In order to account
for the inertia, drag and boundary effects, the Brinkman-Forchheimer-extended Darcy model is adopted for the flow inside the
porous regions. The effects of several parameters such as Darcy number, the block dimensions, the number of blocks and the
thermal conductivity ratio are documented. The results show that the blocks may alter substantially the flow pattern depending
on the permeability of the porous medium, and may improve the heat transfer and reduce the wall temperature under certain
circumstances.
Received on 9 June 1997 相似文献
84.
In this work we study the blow up phenomena for some scalar delay differential equations. In particular, we make connection
with the blow up of ordinary differential equations that are related to the delay differential equations.
The first author is supported by a Grant from TWAS under contract No: 03-030 RG/MATHS/AF/AC.
The second author is supported by a grant from the Lebanese National Council for Scientific Research. 相似文献
85.
Mustapha Remouche Rabah Mokdad Ayoub Chakari Patrick Meyrueis 《Optics & Laser Technology》2007,39(7):1454-1460
Curvature of a multimode integrated optical waveguide reduces the numerical aperture and induces radiation losses. In this paper, we study this phenomenon and we present a geometrical approach to calculate the local numerical aperture and the intensity attenuation. We exploit the bending effect on the local numerical aperture to make a new intrinsic temperature sensor. The simulation results are validated for the silica/silicone integrated optical case. The principal performances of the silica/silicone temperature sensor are the extended temperatures range (−50 to 200 °C) with an excellent linearity response (1%) between 20 and 200 °C. 相似文献
86.
Mustapha Khelladi Nicolas Leclerc Denis Jacquemin Antoinette De Nicola Gilles Ulrich 《Tetrahedron letters》2018,59(10):878-881
New symmetrical and non-symmetrical benzoBODIPYs have been synthesized from diketones. For the two series the 3 and 5 positions have been substituted by different aromatic rings and onto benzo sub-units different groups have been introduced. The methodology of diketones self-condensation provides symmetrical dyes. By cross-condensation reaction, these positions can be differentiated and specific functions connected to the desired positions. These molecules have been fully characterized and their optical properties analyzed by both experimental and theoretical means. They are red to NIR emitters with a range of emission from 679 to 780?nm in CH2Cl2. They show maxima of absorption between 651?nm and 732?nm, strong ε of around 100,000?M?1?cm?1 and quite good quantum yields from 16% to 75%. The thienyl moiety on α-positions of the nitrogens generates the highest red shifts. Meanwhile dimethylamino groups in the same positions bring, besides chemical properties, proton sensitive dyes. The bromine atom onto the dibenzo sub-units exhibits good reactivity through Sonogashira coupling reactions. This approach provides multifunctional red to NIR dyes with endless possibilities of combination of chemical properties. 相似文献
87.
Bruno Ameduri Bernard Boutevin Mustapha Nouiri 《Journal of polymer science. Part A, Polymer chemistry》1993,31(8):2069-2080
The radical grafting of CnF2n +1 CH2CH2SH (n = 6,8) onto the double bonds of hydroxyl-terminated liquid polybutadienes (HTPBD) was studied. Various methods for investigating the amount of grafting (titration of residual thiol and fluorine analysis) were used and compared. The nature and the amount of the initiator, the quantity of thiol, the temperature and the time of the reaction. the solvent, and the microstructure of HTPBD were optimized. The kinetic aspect showed that the thiol disappeared according to a first-norder law. A method using up to 100% of grafting fluorinated mercaptan was described and standards were set up with fluorine contents of 5–59% to evaluate the physicochemical properties of these thioether group-containing polymers: solubility, refractive index, intrinsic and dynamic viscosities, and thermal characteristics (glass transition and decomposition temperatures). Finally, the surface properties of these standards showed improvements of surface energy as low as 9 mN m?1 for a totally saturated fluorinated HTPBD. © 1993 John Wiley & Sons, Inc. 相似文献
88.
Armelle Tontsa Tsamo Haruna Mohammed Mustapha Mohammed Peter Papoh Ndibewu Felix Dapare Dakora 《Natural product research》2020,34(8):1158-1162
AbstractCowpea (Vigna unguiculata L. Walp.) is an important grain legume in Africa exhibiting high morpho-genetic diversity. However, not much information exists on the phytochemical profiles of its hulls. This study explored the metabolite profiles of seed-coats from thirteen cowpea accessions of varying phenotypes using UPLC-QTOF-MS and chemometric analysis. A total of 34 secondary metabolites were identified, which comprised phenolic acids, flavonoids, anthocyanins, sphingolipids and fatty acids. Quantification of selected phenolic compounds revealed marked variations among the cowpea accessions. The chemical profiles of the test accessions were distinguished by multivariate analysis, and the results revealed a marked influence of seed-coat pigmentation on the observed differences in their metabolite profiles. Moreover, delphinidin (traces to 2257.6 µg/g), catechin glucoside (traces to 2840.6 µg/g), catechin (traces to 2089.2 µg/g) and epicatechin (26.3 to 3222.7 µg/g) contributed to the segregation amongst the studied samples. The concentrations of the discriminant metabolites were greater in the dark seeded cowpeas compared to their lighter seeded counterparts. The findings represent a useful contribution to the literature on cowpea seed coat metabolites, and also reveal their potential for use in the development of food and pharmaceutical products. 相似文献
89.
90.
This paper deals with the study of behaviour of an idealized 2D hydroelastic system involving two inviscid liquids with an
elastic rectangular container. The main objective is to investigate the influence of the physical parameters on eigenfrequencies
and eigenmodes of the system. The study extends the previous results obtained for hydroelastic systems with one fluid. The
governing equations describing the behaviour of the system are analyzed by using the concept of normal modes and their solutions
presented in the form of infinite series. The expansion coefficients for the velocity potentials are calculated by employing
a new inner product that allows the orthogonalisation of the normal modes. An eigenfrequency equation is then derived from
the existence condition of a nontrivial solution. The numerical calculations are performed by varying only some relevant parameters. 相似文献