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排序方式: 共有198条查询结果,搜索用时 15 毫秒
41.
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42.
43.
Walid F. Nasrallah Karim A. Cheaib 《Computational & Mathematical Organization Theory》2016,22(4):383-411
This paper investigates how pre-existing institutions foster economic development through trade. A non-cooperative game-theoretic model is proposed that combines three strands of social science: economics, political science, and sociology. Idealized market participants follow rational decision theory within a reward structure that embodies two types of institutions. Regulative institutions operate on threat of punishment, and normative institutions on perceptions of what is good and right. This composite model allows a more quantitative analysis of the question, raised by Douglas North, of how societies diverge from the efficient state predicted by classical micro-economics. The main finding is that value can be created by different types of institution even when they are imperfect, and the range of minimum–maximum effectiveness varies with the types of economic transactions that are technologically possible. It is hoped that further refinements of the model will yield greater understanding of how the success of societies and organizations can be predicted by a few simple rules. 相似文献
44.
45.
Yi‐He Zhang Zhi‐Min Dang John H. Xin Walid A. Daoud Jun‐Hui Ji Yuyang Liu Bin Fei Yuanqing Li Juntao Wu Shiyong Yang Lai‐Feng Li 《Macromolecular rapid communications》2005,26(18):1473-1477
Summary: Polyimide‐mica hybrid films were prepared via ultrasonic dispersion and in situ polymerization process from a solution of a polyimide precursor and mica in N,N‐dimethylacetamide, and their structure was characterized by FTIR and XRD techniques. The dependence of dielectric properties, such as dielectric constant and electrical breakdown strength, of the hybrid films on the content of mica was studied at room and cryogenic temperatures. The results show that the dielectric constant of PI‐mica hybrid films decreases with the increase of the mica content at temperatures from −150 to 150 °C and at frequency range from 1 kHz to 1 MHz. It was found that the cryogenic electrical breakdown strength of the PI‐mica hybrid films could meet the requirements of cryogenic insulating materials.
46.
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
47.
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
48.
Stachybotrys microspora is a filamentous fungus secreting multiple β-glucosidases. Two of them were characterized. The third one, named bglG, was also characterized and used for various investigations. The current work undertakes the plausible role played by some cultural conditions and physico-chemical properties to improve bglG time course synthesis and also its catalytic efficiency. Indeed, bglG time course synthesis is slightly affected by light, but it is clearly affected by aeration and presence of baffle. On the same case, optimization of substrate and enzyme concentration contributes to the improvement of the catalytic efficiency of bglG. This biocatalyst tolerates a high ionic strength during its activity assay; β-mercaptoethanol increases the enzymatic rate. BglG has the capacity to hydrolyse efficiently oleuropéin, with a recovery of 88 %. 相似文献
49.
50.
We study the time evolution of a periodically driven quantum-mechanical system coupled to several reservoirs of free fermions
at different temperatures. This is a paradigm of a cyclic thermodynamic process. We introduce the notion of a Floquet Liouvillean
as the generator of the dynamics of the coupled system on an extended Hilbert space. We show that the time-periodic state
which the state of the coupled system converges to after very many periods corresponds to a zero-energy resonance of the Floquet
Liouvillean. We then show that the entropy production per cycle is (strictly) positive, a property that implies Carnot's formulation
of the second law of thermodynamics. 相似文献