全文获取类型
收费全文 | 243篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
化学 | 156篇 |
晶体学 | 3篇 |
力学 | 23篇 |
数学 | 44篇 |
物理学 | 30篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 14篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 8篇 |
2014年 | 11篇 |
2013年 | 25篇 |
2012年 | 11篇 |
2011年 | 23篇 |
2010年 | 13篇 |
2009年 | 17篇 |
2008年 | 10篇 |
2007年 | 14篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 6篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 31 毫秒
141.
Corina Constantinescu Enkelejd Hashorva Lanpeng Ji 《Insurance: Mathematics and Economics》2011,49(3):487-495
In this paper we discuss the link between Archimedean copulas and L1 Dirichlet distributions for both finite and infinite dimensions. With motivation from the recent papers Weng et al. (2009) and Albrecher et al. (2011) we apply our results to certain ruin problems. 相似文献
142.
Chiara Mongioví Nadia Morin-Crini Dario Lacalamita Corina Bradu Marina Raschetti Vincent Placet Ana Rita Lado Ribeiro Aleksandra Ivanovska Mirjana Kosti Grgorio Crini 《Molecules (Basel, Switzerland)》2021,26(14)
Lignocellulosic fibers extracted from plants are considered an interesting raw material for environmentally friendly products with multiple applications. This work investigated the feasibility of using hemp- and flax-based materials in the form of felts as biosorbents for the removal of metals present in aqueous solutions. Biosorption of Al, Cd, Co, Cu, Mn, Ni and Zn from a single solution by the two lignocellulosic-based felts was examined using a batch mode. The parameters studied were initial metal concentration, adsorbent dosage, contact time, and pH. In controlled conditions, the results showed that: (i) the flax-based felt had higher biosorption capacities with respect to the metals studied than the hemp-based felt; (ii) the highest removal efficiency was always obtained for Cu ions, and the following order of Cu > Cd > Zn > Ni > Co > Al > Mn was found for both examined biosorbents; (iii) the process was rapid and 10 min were sufficient to attain the equilibrium; (iv) the efficiency improved with the increase of the adsorbent dosage; and (v) the biosorption capacities were independent of pH between 4 and 6. Based on the obtained results, it can be considered that plant-based felts are new, efficient materials for metal removal. 相似文献
143.
Marin Cernea Corina Elisabeta Secu Bogdan Stefan Vasile Mihail Secu 《Current Applied Physics》2013,13(1):137-141
Nanocrystalline Tm3+(5%)-doped BaTiO3 (BT-Tm) has been synthesized by the sol–gel method. The morphology, structure, and optical properties of powders and ceramics were characterized. The average grain size of the gel precursor annealed at 700 and 900 °C was 20 nm and 30 nm, respectively. These powders were single phase and crystallized with a cubic structure while the BT-Tm sintered ceramics were crystallized with the tetragonal BaTiO3 structure. The photoluminescence spectra showed typical transitions of Tm3+ ions and a structure consistent with the Tm3+ ions incorporation in the BaTiO3 crystalline lattice. Thermoluminescence peaks recorded at 300 °C (for annealed samples) or at 230 °C for the ceramic sample were assigned to the recombination of the Tm2+-electron traps located mainly at the surface of the nano-crystals or inside the microcrystals, respectively. 相似文献
144.
145.
146.
Chiara Mongioví Dario Lacalamita Nadia Morin-Crini Xavier Gabrion Aleksandra Ivanovska Federico Sala Vincent Placet Vito Rizzi Jennifer Gubitosa Ernesto Mesto Ana Rita Lado Ribeiro Paola Fini Nicoletta De Vietro Emanuela Schingaro Mirjana Kosti Cesare Cosentino Pinalysa Cosma Corina Bradu Gilles Chanet Grgorio Crini 《Molecules (Basel, Switzerland)》2021,26(15)
FINEAU (2021–2024) is a trans-disciplinary research project involving French, Serbian, Italian, Portuguese and Romanian colleagues, a French agricultural cooperative and two surface-treatment industries, intending to propose chènevotte, a co-product of the hemp industry, as an adsorbent for the removal of pollutants from polycontaminated wastewater. The first objective of FINEAU was to prepare and characterize chènevotte-based materials. In this study, the impact of water washing and treatments (KOH, Na2CO3 and H3PO4) on the composition and structure of chènevotte (also called hemp shives) was evaluated using chemical analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray computed nanotomography (nano-CT), attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, solid state NMR spectroscopy and thermogravimetric analysis. The results showed that all these techniques are complementary and useful to characterize the structure and morphology of the samples. Before any chemical treatment, the presence of impurities with a compact unfibrillated structure on the surfaces of chènevotte samples was found. Data indicated an increase in the crystallinity index and significant changes in the chemical composition of each sample after treatment as well as in surface morphology and roughness. The most significant changes were observed in alkaline-treated samples, especially those treated with KOH. 相似文献
147.
Servilia Oancea Florin Grosu Anca Lazar Ioan Grosu 《Chaos, solitons, and fractals》2009,41(5):2575-2580
A single controller for synchronization of two Lorenz systems is obtained by using Lyapunov function. Numerical results are given for the all three cases with one controller in each equation. Controller contains two or three variables of the master system. 相似文献
148.
149.
Claudia Lar Mӑdӑlina Elena Moisӑ Elena Bogdan Anamaria Terec Niculina Daniela Hӑdade Ion Grosu Luminiţa David Csaba Paizs Ioana Georgeta Grosu 《Tetrahedron letters》2019,60(4):335-340
A new class of axially-chiral o,o′-bridged biphenyls containing etheroxime chains was obtained in good yields by the macrocyclisation reaction of o,o′-diformylbiphenyl dioxime with several ditosylated or dibrominated reagents. In all cases the enantiomers of the compounds were separated by HPLC using a chiral column (Chiralpack IC) and the stability of the enantiomers (barriers of racemisation) was investigated employing chiral HPLC or chiral Dynamic HPLC techniques. A slight influence on the barrier to rotation was noticed when the enantiomerisation was performed in the presence of suitable alkali cations. 相似文献
150.
Dr. Nivedita Sikdar João R. C. Junqueira Dr. Denis Öhl Stefan Dieckhöfer Thomas Quast Michael Braun Dr. Harshitha B. Aiyappa Dr. Sabine Seisel Prof. Corina Andronescu Prof. Wolfgang Schuhmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(12):e202104249
Bimetallic tandem catalysts have emerged as a promising strategy to locally increase the CO flux during electrochemical CO2 reduction, so as to maximize the rate of conversion to C−C-coupled products. Considering this, a novel Cu/C−Ag nanostructured catalyst has been prepared by a redox replacement process, in which the ratio of the two metals can be tuned by the replacement time. An optimum Cu/Ag composition with similarly sized particles showed the highest CO2 conversion to C2+ products compared to non-Ag-modified gas-diffusion electrodes. Gas chromatography and in-situ Raman measurements in a CO2 gas diffusion cell suggest the formation of top-bound linear adsorbed *CO followed by consumption of CO in the successive cascade steps, as evidenced by the increasingνC−H bands. These findings suggest that two mechanisms operate simultaneously towards the production of HCO2H and C−C-coupled products on the Cu/Ag bimetallic surface. 相似文献