全文获取类型
收费全文 | 260篇 |
免费 | 4篇 |
专业分类
化学 | 164篇 |
晶体学 | 1篇 |
力学 | 5篇 |
数学 | 70篇 |
物理学 | 24篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 5篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 5篇 |
2016年 | 2篇 |
2015年 | 7篇 |
2014年 | 18篇 |
2013年 | 36篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 16篇 |
2009年 | 22篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 8篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1941年 | 1篇 |
1936年 | 1篇 |
1935年 | 1篇 |
1901年 | 1篇 |
排序方式: 共有264条查询结果,搜索用时 0 毫秒
81.
We study the existence of positive solutions for systems of second‐order nonlinear ordinary differential equations, subject to multipoint boundary conditions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
82.
83.
Romain Lafay Dr. German Montes‐Hernandez Dr. Emilie Janots Dr. Rodica Chiriac Nathaniel Findling François Toche 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(17):5417-5424
Herein, we report new insights into the nucleation and growth processes of chrysotile nanotubes by using batch and semi‐continuous experiments. For the synthesis of this highly carcinogenic material, the influences of temperature (90, 200, and 300 °C), Si/Mg molar ratio, and reaction time were investigated. From the semi‐continuous experiments (i.e., sampling of the reacting suspension over time) and solid‐state characterization of the collected samples by XRPD, TGA, FTIR spectroscopy, and FESEM, three main reaction steps were identified for chrysotile nucleation and growth at 300 °C: 1) formation of the proto‐serpentine precursor within the first 2 h of the reaction, accompanied by the formation of brucite and residual silica gel; 2) spontaneous nucleation and growth of chrysotile between about 3 and 8 h reaction time, through a progressive dissolution of the proto‐serpentine, brucite, and residual silica gel; and 3) Ostwald ripening growth of chrysotile from 8 to 30 h reaction time, as attested to by BET and FESEM measurements. Complementary results from batch experiments confirmed a significant influence of the reaction temperature on the kinetics of chrysotile formation. However, FESEM observations revealed some formation of chrysotile nanotubes at low temperatures (90 °C) after 14 days of reaction. Finally, doubling the Si/Mg molar ratio promoted the precipitation of pure smectite (stevensite‐type) under the same P (8.2 MPa)/T (300 °C)/pH (13.5) conditions. 相似文献
84.
Florentina Pătraşcu Mihaela Badea Maria Nicoleta Grecu Nicolae Stanică Luminiţa Măruţescu Dana Marinescu Cezar Spînu Cristian Tigae Rodica Olar 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1421-1429
New species of type MLCl2·nH2O (M:Ni, n = 6; M:Cu, n = 1.5 and M:Zn, n = 1; L: 1,8-bis(3′-ketopyridil)-1,3,6,8,10,13-hexaazacyclotetradecane, ligand resulted by 1,2-diaminoethane, nicotinamide and formaldehyde template condensation) were synthesised. The compounds were characterised by chemical analysis, ESI–MS, IR, NMR, UV–Vis-NIR and EPR spectroscopy as well as magnetic data at room temperature. The modifications in the IR and NMR spectra are in accordance with the condensation process. Electronic spectra indicate that Ni(II) adopts an octahedral stereochemistry while the surrounding of Cu(II) is square-pyramidal. The proposed stereochemistry was furthermore confirmed by magnetic moments and EPR spectrum at room temperature. The water is eliminated in one or two steps, respectively, while the oxidative degradation of the ligand and chloride decomposition occur in two steps. The final residues consist of the most stable metallic oxides as X-ray powder diffraction indicates. The newly synthesised compounds were evaluated for their antimicrobial effect against different bacterial and fungal strains. 相似文献
85.
Ioana Dorina Vlaicu Madalina Constand Rodica Olar Dana Marinescu Maria Nicoleta Grecu Veronica Lazar Mariana Carmen Chifiriuc Mihaela Badea 《Journal of Thermal Analysis and Calorimetry》2013,113(3):1369-1377
Three new coordinative compounds that contain mixed ligands (5,6-dimethylbenzimidazole and acrylato anion) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV–Vis and EPR spectra as well as thermal analysis. IR data are in accordance with unidentate nature of 5,6-dimethylbenzimidazole while the acrilato ion acts as uni- or bidentate ligand. The electronic spectra display the characteristic pattern of square pyramidal or octahedral stereochemistry, which were confirmed by the EPR spectra. Antibacterial and antifungal activities of the complexes have been determined in vitro, against various Gram-negative and Gram-positive bacteria and fungi. The tested complexes exhibited different spectra of antimicrobial activity and inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. Thermal decomposition evidenced several well-defined steps as dehydration (complex 2), 5,6-dimethylbenzimidazole molecule release (all complexes) and the acrylate decomposition in carbonate (complex 3). The final residue is in all cases copper (II) oxide. 相似文献
86.
Mihaela Badea Elica Iosub Carmen Mariana Chifiriuc Luminita Marutescu Emilia Elena Iorgulescu Veronica Lazar Dana Marinescu Coralia Bleotu Rodica Olar 《Journal of Thermal Analysis and Calorimetry》2013,111(3):1753-1761
New complexes [Pd(HDMBG)2]Cl2·H2O, [PdL1]Cl2·0.5H2O and [PdL2]Cl2·1.5H2O (HDMBG: dimethylbiguanide, L1 and L2: ligands resulted from HDMBG, ammonia/hydrazine and formaldehyde template condensation) were synthesized and characterized. The features of complexes have been assigned from microanalytical, IR, UV–Vis and cyclic voltammetry data. The thermal transformations are complex processes according to TG and DTA curves including water and hydrochloric acid elimination, thermolysis processes leading to paracyanide formation as well as PdO decomposition, final product being palladium. Complexes were screened for their antimicrobial properties against some pathogenic Gram-positive and Gram-negative bacterial as well as fungal Candida albicans strains. The complexes exhibit specific antibacterial and/or antifungal activity, depending on their structure and the tested microbial strains. All complexes inhibit the microbial biofilm development on the inert substratum. It was also observed that PdCl2 complexation minimized their cytotoxic effect on the eukaryotic cells. 相似文献
87.
Gina Vasile Rodica Olar Dana Marinescu Angela Kriza Luminita Marutescu Mariana Carmen Chifiriuc Veronica Lazar Mihaela Badea 《Journal of Thermal Analysis and Calorimetry》2013,111(3):1783-1790
Five new coordinative compounds that contain mixed ligands (4,4′-bipyridine and methacrylate anion) were synthesized and characterized (elemental analysis, IR and UV–Vis spectroscopy, and thermal studies). The complexes are of the type [M(4,4′-bipy)(C4H5O2)2]·nH2O ((1) M:Mn, n = 0; (2) Co, n = 0.5; (3) M:Ni, n = 1.5; (4) M:Cu, n = 0.5; (5) M:Zn, n = 0.5; 4,4′-bipy: 4,4′-bipyridine; C4H5O2: methacrylate anion). All the tested complexes exhibited very low MIC values against Escherichia coli strains and one compound against Staphylococcus aureus. Besides the specific antimicrobial spectrum, these compounds also inhibited the microbial ability to colonize the inert surfaces, acting as potential anti-adherence and biofilm-controlling agents. The thermal behavior provided confirmation of the complexes' compositions as well as the number and the nature of water molecules and the intervals of thermal stability. 相似文献
88.
Mihaela Badea Rodica Olar Monica Iliş Rodica Georgescu Mirela Călinescu 《Journal of Thermal Analysis and Calorimetry》2013,111(3):1763-1770
Three new copper (II) complex compounds with chlorhexidine (CHX) as ligand have been prepared and characterized by elemental and thermogravimetrical analyses, molar conductances, infrared, and UV–Vis spectra. Chlorhexidine acts as neutral tetradentate NNNN donor, coordinating through the four imine nitrogen atoms. Based on the experimental data the following formulas have been proposed for the complex compounds: [Cu(CHX)](NO3)2 (1), [Cu2(CHX)Br2Cl2]·4H2O (2), and [Cu(CHX)Cl]Cl (3). Thermal decomposition evidenced dehydration (complex 2), anionic moieties release and the ligand cleavage with chlorobenzene moieties removal for all complexes. The final residue is in all cases copper oxide. Antibacterial and antifungal activities of the complexes have been determined in vitro, by the cup-plate agar diffusion method, against Escherichia coli, Staphyloccocus aureus, and Candida albicans. The complexes present an activity comparable to that of chlorhexidine, the most active being [Cu2(CHX)Br2Cl2]·4H2O. 相似文献
89.
Anca Dumbravă Rodica Olar Mihaela Badea Maria Nicoleta Grecu Florentina Pătrascu Luminita Măruţescu Nicolae Stănică 《Journal of Thermal Analysis and Calorimetry》2014,115(3):2447-2455
New complexes ML(CNS)·nH2O [M = Ni, n = 0.5; M = Cu, n = 4.5; M = Zn, n = 0.5, HL: 6-mercapto-(1,4,8,11-tetraazaundecanyl)-6-carboxylic acid)] have been synthesised, chemical analysed, and characterised by different spectroscopic techniques (IR, UV–Vis–NIR, 1H NMR, EPR, ESI–MS), and magnetic measurements. Based on the IR spectra a dinuclear structure with the 1,3-CSN coordination was proposed for Ni(II) and Cu(II) complexes. The dinuclear structure of Cu(II) complex is also consistent with both magnetic behaviour and EPR spectrum. According to TG, DTG and DTA curves the thermal transformations are complex processes, including dehydration, Mannich base oxidative degradation and thiocyanate decomposition. The final product of decomposition is the most stable metallic oxide, as XRD data indicates. The new complexes were also screened for their microbicidal and antibiofilm properties. 相似文献
90.
We introduce a notion of solution to the wave equation on a suitable class of time-dependent domains and compare it with a previous definition. We prove an existence result for the solution of the Cauchy problem and present some additional conditions which imply uniqueness. 相似文献