全文获取类型
收费全文 | 190篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 111篇 |
晶体学 | 3篇 |
力学 | 5篇 |
数学 | 44篇 |
物理学 | 35篇 |
出版年
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 13篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 8篇 |
2012年 | 12篇 |
2011年 | 14篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 11篇 |
2006年 | 10篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有198条查询结果,搜索用时 15 毫秒
31.
Mohamed Fathi El-Shahat Hisham Mohamed Kamal Reda Abd El-Gawad Ghazall Walid Mohamed Morsy 《无机化学学报》2016,32(8):1427-1433
利用三异辛胺(TOA)纯化Gattar小型试验工厂的高浓度铀溶液(洗脱液的铀浓度7 g·L-1),研究了脉冲萃取柱的性能。利用实验室级脉冲萃取柱进行了实验室规模的溶剂萃取实验和后续实验。结果表明,在室温、pH=1和有机相与水相的比例(VO/VA)约为1.8:1时,加入二(2-乙基己基)磷酸(D2EHPA)使其与TOA的比例(VD2EHPA/VTOA)为2:3,可使萃取克服Cl-的抑制效应,提高效率。将结论用于考察试验工厂级萃取柱的流体力学和传质性能,结果表明用脉冲萃取柱萃取铀可以达到97%的萃取效率,具有可行性。 相似文献
32.
Saraya Roshdy E. Hassan Yasser F. Eltukhi Walid E. Salman Baher I. 《Journal of fluorescence》2022,32(5):1725-1732
Journal of Fluorescence - Vonoprazan (VON) has been approved recently via US-FDA in 2015 as the first in class of potassium competitive acid blocker group. VON is used for management of... 相似文献
33.
Walid F. Nasrallah Raymond E. Levitt 《Computational & Mathematical Organization Theory》2001,7(2):113-144
We present a general model of a network of interacting individuals, each of whom derives a known, real-valued benefit from each possible dyadic interaction. The model views interactions as knowledge-transfer exchanges that add value to the organization. We use this model to derive interaction patterns within an organization. We assume that the value of dyadic interaction benefits is distributed as a randomly permuted geometric series. Moreover, interactions only add value when a large enough waiting period is observed between interaction attempts. We show that an organization optimized for knowledge transfer has a distribution of interaction frequencies which correlates well with observations. Organizations of differing sizes can have similar optimal structures as long they have similar normalized levels of interdependence between interactions, and distribution of interaction benefit values. This research has implications for the design of communication infrastructure in a growing organization, as well as for the predictive value of modeling organizations at different scales. 相似文献
34.
Walid K. Abou Salem 《Annales Henri Poincare》2007,8(3):569-596
The quasi-static evolution of steady states far from equilibrium is investigated from the point of view of quantum statistical mechanics. As a concrete example of a thermodynamic system,
a two-level quantum dot coupled to several reservoirs of free fermions at different temperatures is considered. A novel adiabatic theorem for unbounded
and nonnormal generators of evolution is proven and applied to study the quasi-static evolution of the nonequilibrium steady
state (NESS) of the coupled system.
Submitted: April 23, 2006. Accepted: October 4, 2006. 相似文献
35.
Preparation of fluorescein isothiocyanate (FITC)-encapsulated silica nanoparticles (F-SiNPs) via seven different approaches to be used as developing agents for fingerprints detection is presented in this report. In this study, the suitability of each synthesis route toward incorporation of the selected fluorophore into silica matrix and its efficiency in fingerprints detection were systematically studied. The composition of the particles was designed to examine the hydrophobic and dipole-dipole interactions between the silicate backbone and both of the fluorescent reporter molecules and the fingerprint residues. F-SiNPs were prepared with two conventional sol-gel approaches; the Stöber method and the water in oil reverse microemulsion (WORM) method. The alkoxysilane precursor, tetraethoxyorthosilicate (TEOS) and its binary mixtures with phenyltriethoxysilane (PTEOS) or 3-aminopropyl triethoxysilane (APTES) have been used in preparing the F-SiNPs to study the effect of nanoparticles composition on fingerprints development. In addition, FITC was conjugated with APTES so it can be covalently bonded to the silica matrix and to be compared with non-covalently FITC-doped SiNPs. Moreover, the enhancement effect of introducing polyvinylpyrrolidone (PVP) onto the surface of the less hydrophobic F-SiNP on fingerprints detection on different non-porous surfaces was also investigated. The mean diameters of the F-SiNPs were between 4.1?±?0.6 and 110.4?±?31.1 nm as obtained from the TEM size measurement for the nanoparticles prepared by the WORM and Stöber methods, respectively. The obtained results clearly highlight the advantages of using a mixture of TEOS and PTEOS alkoxysilane precursors in preparing F-SiNPs with remarkable encapsulation efficiency and clear detection of fingerprints due to efficient embedding of the fluorophore inside the silica network even without conjugation. It was also observed that both the Stöber and WORM methods can be used in preparing the F-SiNPs developing agents and that PVP coated particles did not show any significant enhancement in fingerprints visualization. 相似文献
36.
Omar Kammoun Nouha Loulou Walid Rekik Houcine Na?li Tahar Mhiri Thierry Bataille 《Journal of chemical crystallography》2012,42(2):103-110
Abstract
The new hybrid material, cobalt selenate templated by 1,4-diazabicyclo[2.2.2]octane (abbreviated dabco), has been synthesised by the slow evaporation method at room temperature. Its crystal structure was investigated using single crystal X-ray diffraction data. It crystallises in the monoclinic system (space group P21/c) with the following unit-cell parameters: a = 12.9169(2) ?, b = 11.9101(2) ?, c = 12.4951(2) ?, β = 108.484(1)°, V = 1823.10(5) ?3 and Z = 4. The supramolecular structure of (C6H14N2)[Co(H2O)6](SeO4)2 consists of isolated [Co(H2O)]2+ and (C6H14N2)2+ cations and (SeO4)2− anions linked together by three dimensional hydrogen-bond network. The infrared spectroscopy confirmed the presence of these different entities. The thermal behaviour of the precursor, studied by thermodiffractometry and thermogravimetric analyses, indicates that its decomposition proceeds through three stages giving rise to the cobalt oxide. 相似文献37.
Mouna Hnaien Walid Mohamed Hassen Adnane Abdelghani Stéphane Cotte Didier Leonard François Bessueille Nicole Jaffrezic-Renault 《Electrochemistry communications》2009,11(1):165-168
A conductometric enzyme biosensor using proteinase K was developed and then tested to relate its electrical signal to the number of proteinase K hydrolysis sites in bovine serum albumin (BSA) and angiotensin, a ten amino acid peptide, with one cleaving site.The conductometric sensor presents a large linear range of response for BSA and angiotensin ranging from 0.5 to 8 mg/l and from 4 to 8 mg/l, respectively. For a same tested concentration (mg/l), the response for native BSA is 12 times higher than for angiotensin. Aspartam was used as negative test and no response was obtained with the proteinase K biosensor. The conductometric sensor permitted also to detect difference on enzyme activity on native and non-native BSA, a response three times higher was obtained for non-native BSA. 相似文献
38.
Walid Fakhfakh Slim Kaddeche Ali Abdennadher Daniel Henry Hamda Ben Hadid 《Comptes Rendus Mecanique》2006,334(5):332-339
A numerical study is conducted in order to determine the influence of a vertical magnetic field, the Reynolds number and a temperature stratification on the instabilities occurring in the Hartmann flow heated from below. For and , the results show that the vertical magnetic field has a stabilizing effect on both transverse oscillatory travelling waves and longitudinal stationary rolls . The temperature stratification is responsible of a destabilization of the transverse modes and the appearance of longitudinal modes non-existent for the isothermal Hartmann flow. Moreover, the extent of the domains of Re where the transverse modes prevail is found to narrow when Ha increases and to widen when Ra increases for a given value of Ha. On the other hand, for the modes, the extent of the domains of Re where they prevail increases when Ha grows. To cite this article: W. Fakhfakh et al., C. R. Mecanique 334 (2006). 相似文献
39.
Walid Rekik Houcine Na?li Tahar Mhiri Thierry Bataille 《Journal of chemical crystallography》2007,37(2):147-155
The crystal structure of manganese sulfate templated by 1,4-diaza-bicyclo[2.2.2]octane (abbreviated dabco), (C6H14N2)[Mn(H2O)6](SO4)2, was investigated using single crystal X-ray diffraction data. It crystallises in the monoclinic system (space group P21/c) with the following unit-cell parameters: a = 12.1392(2) ?, b = 12.3117(2) ?, c = 12.2765(2) ?, β = 104.607(1)°, V = 1775.47(5) ?3 and Z = 4. The structure has been solved using direct methods and refined by least-squares analysis [R
1 = 0.0381, wR
2 = 0.1082]. The crystal structure of the title compound is built from isolated [Mn(H2O)6]2+ octahedral cations, 1,4-diaza-bicyclo[2.2.2]octandiium cations (C6H14N2)2+ and sulfate anions (SO4)2− connected by a three-dimensional hydrogen-bond network. The thermal decomposition of the precursor, studied by thermogravimetry
and temperature-dependent X-ray powder diffraction, proceeds through four stages giving rise to the mixture of Mn2O3and Mn3O4.
Supplementary Material CCDC 620298 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. 相似文献
40.
Abeer D. Algarni Ghada El Banby Sahar Ismail Walid El-Shafai Fathi E. Abd El-Samie Naglaa F. Soliman 《Entropy (Basel, Switzerland)》2020,22(12)
The security of information is necessary for the success of any system. So, there is a need to have a robust mechanism to ensure the verification of any person before allowing him to access the stored data. So, for purposes of increasing the security level and privacy of users against attacks, cancelable biometrics can be utilized. The principal objective of cancelable biometrics is to generate new distorted biometric templates to be stored in biometric databases instead of the original ones. This paper presents effective methods based on different discrete transforms, such as Discrete Fourier Transform (DFT), Fractional Fourier Transform (FrFT), Discrete Cosine Transform (DCT), and Discrete Wavelet Transform (DWT), in addition to matrix rotation to generate cancelable biometric templates, in order to meet revocability and prevent the restoration of the original templates from the generated cancelable ones. Rotated versions of the images are generated in either spatial or transform domains and added together to eliminate the ability to recover the original biometric templates. The cancelability performance is evaluated and tested through extensive simulation results for all proposed methods on a different face and fingerprint datasets. Low Equal Error Rate (EER) values with high AROC values reflect the efficiency of the proposed methods, especially those dependent on DCT and DFrFT. Moreover, a comparative study is performed to evaluate the proposed method with all transformations to select the best one from the security perspective. Furthermore, a comparative analysis is carried out to test the performance of the proposed schemes with the existing schemes. The obtained outcomes reveal the efficiency of the proposed cancelable biometric schemes by introducing an average AROC of 0.998, EER of 0.0023, FAR of 0.008, and FRR of 0.003. 相似文献