全文获取类型
收费全文 | 503篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
化学 | 301篇 |
晶体学 | 10篇 |
力学 | 18篇 |
数学 | 116篇 |
物理学 | 71篇 |
出版年
2023年 | 5篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 15篇 |
2019年 | 16篇 |
2018年 | 14篇 |
2017年 | 12篇 |
2016年 | 41篇 |
2015年 | 19篇 |
2014年 | 21篇 |
2013年 | 95篇 |
2012年 | 32篇 |
2011年 | 41篇 |
2010年 | 45篇 |
2009年 | 23篇 |
2008年 | 24篇 |
2007年 | 27篇 |
2006年 | 18篇 |
2005年 | 9篇 |
2004年 | 9篇 |
2003年 | 6篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有516条查询结果,搜索用时 15 毫秒
91.
Two types of Schottky Barrier Diodes (SBDs) with and without PVA (Bi2O3-doped) polymeric interfacial layer, were fabricated and measured at room temperature in order to investigate the effects of the PVA (Bi2O3-doped) interfacial layer on the main electrical parameters such as the ideality factor (n), zero-bias barrier height (ΦB0), series resistance (Rs) and interface-state density (Nss). Electrical parameters of these two diodes were calculated from the current-voltage (I-V) characteristics and compared with each other. The values of ΦB0, n and Rs for SBDs without polymeric interfacial layer are 0.71 eV, 1.44 and 4775 Ω, respectively. The values of ΦB0, n and Rs for SBDs with PVA (Bi2O3-doped) polymeric interfacial layer are 0.74 eV, 3.49 and 10,030 Ω, respectively. For two SBDs, the energy density distribution profiles of interface states (Nss) were obtained from forward-bias I-V measurements by taking the bias dependence of Rs of these devices into account. The values of Nss obtained for the SBD with PVA (Bi2O3-doped) polymeric interfacial layer are smaller than those of the SBD without polymeric interfacial layer. 相似文献
92.
93.
Zimcik P Novakova V Kopecky K Miletin M Uslu Kobak RZ Svandrlikova E Váchová L Lang K 《Inorganic chemistry》2012,51(7):4215-4223
Magnesium(II), zinc(II), and metal-free phthalocyanines (Pcs) and azaphthalocyanines (AzaPcs) containing alkylsulfanyl, aryloxy, and dialkylamino peripheral substituents have been synthesized. The complexation of magnesium(II) by metal-free Pcs and AzaPcs has been studied in detail to determine the optimal reaction conditions necessary to ensure a complete conversion. Photophysical and photochemical measurements in tetrahydrofuran showed that magnesium(II) AzaPcs with aryloxy and alkylsulfanyl substituents have excellent fluorescent properties (Φ(F) up to 0.73) and that the corresponding zinc(II) Pcs are efficient singlet oxygen producers (Φ(Δ) up to 0.68). The presence of dialkylamino substituents causes intramolecular charge transfer within the molecule that competes with fluorescence and singlet oxygen formation. Alkylsulfanyl MgAzaPc and ZnAzaPc were the most photostable compounds among the series of studied derivatives. In addition, high molar absorption coefficients (ε ~ 300,000 M(-1) cm(-1)), absorption (λ(max) ~ 650 nm), and emission (λ(em) ~ 660 nm, high Φ(F)) in the red region suggest that these molecules are potential fluorescent probes that are superior to the commercial red cyanine dye Cy5. MgAzaPc, when incorporated into lipidic bilayers of liposomes, maintains excellent fluorescence properties (Φ(F) = 0.64). Water-soluble MgAzaPc with quaternary ammonium peripheral substituents retained a high fluorescence quantum yield even in water (Φ(F) = 0.25). The described properties show that magnesium(II) AzaPcs are excellent red-emitting fluorophores with potential applications as fluorescent probes in sensing or in vitro imaging applications. 相似文献
94.
Tahir SAVRAN Abdurrahman KARAG
Z ükriye Nihan KARUK ELMAS Duygu AYDIN Furkan
ZEN Kenan KORAN Fatma Nur ARSLAN Ahmet Orhan G
RGÜLÜ brahim YILMAZ 《Turkish Journal of Chemistry》2020,44(4):1148
A fluorogenic probe based on a coumarin-derivative for Cu2+ sensing in CH3CN/H2O media (v/v, 95/5, 5.0 μM) was developed and applied in real samples. 3-(4-chlorophenyl)-6,7-dihydroxy-coumarin (MCPC) probe was obtained by synthetic methodologies and identified by spectral techniques. The probe MCPC showed remarkable changes with a “turn-off” fluorogenic sensing approach for the monitoring of Cu2+ at 456 nm under an excitation wavelength of 366 nm. The response time of the probe MCPC was founded as only 1 min. The detection limit of the probe MCPC was recorded to be 1.47 nM. The binding constant and possible stoichiometric ratio (1:1) values were determined by Benesi-Hildebrand and Job’s plot systems, respectively. The mechanism of the probe MCPC with Cu2+ was further confirmed by ESI-MS and FT-IR analyses, as well as supported by theoretical calculations. Furthermore, the probe MCPC was successfully employed for the practical applications to sense Cu2+ in different herbal and black tea samples. The proposed sensing method was also verified by ICP-OES method. 相似文献
95.
Journal of Thermal Analysis and Calorimetry - The molar heat capacity parameters of CdNb2O6 and CdTa2O6 oxides, which attracted attention for their promising catalytic and optical properties, were... 相似文献
96.
İsmail Yener Mustafa Abdullah Yilmaz Özge Tokul Ölmez Pelin Köseoğlu Yılmaz Yeter Yeşil 《Analytical letters》2019,52(7):1031-1049
The Euphorbiaceae family comprises of about 300 genera and 5000 species primarily distributed in America and tropical Africa. The Euphorbia genus is represented by 105 species and locally named as “Sütle?en” and “Xa?îl” in Turkey. The present study aimed to determine the chemical constituents of E. aleppica, E. eriophora, E. macroclada, E. grisophylla, E. seguieriana subsp. seguieriana, E. craspedia, E. denticulata, E. falcata, and E. fistulosa, and classify them by utilizing the chemometric techniques of principal component analysis (PCA) and hierarchical cluster analysis (HCA). Linoleic acid, 17-tetratriacontane, palmitic acid, and hexatriacontane were the major fatty acids from the gas chromatography–mass spectrometry (GC/MS) analyses. Characterization of 268 constituents of the studied species was achieved by liquid chromatography–ion trap–time-of-flight–mass spectrometry (LC-IT-TOF-MS). Furthermore, a new liquid chromatography–tandem mass spectrometry (LC-MS/MS) method was developed and validated for the simultaneous quantitative determination of 11 compounds (quinic acid, protocatechuic acid, rutin, hesperidin, eugenol, p-coumaric acid, piceatannol, scopoletin, dl-kavain, chrysophanic acid, and resiniferatoxin) in these species. The developed method was validated for the linearity, limit of detection, limit of quantification, repeatability, and recovery. 相似文献
97.
Cansu Uzaras Uğur Avcıbaşı Hasan Demiroğlu Emin İlker Medine Ayfer Yurt Kılçar Fazilet Zümrüt Biber Müftüler Perihan Ünak 《Journal of Radioanalytical and Nuclear Chemistry》2016,307(1):131-140
The aim of this study is to determine the incorporations of PHT radiolabeled with 131I (131I-PHT) on U-87 MG, Daoy and A549 cancerous cell lines. For this, cold and radio-labeling studies were carried out. The radio-labeling yield of 131I-PHT was obtained about 95 %. Subsequently, cell culture studies were carried out and radio-labeling yields of 131I, 131I-PHT on U-87 MG, Daoy and A549 cancerous cells were investigated. Cell culture studies demonstrated that the incorporation values of 131I-PHT on the three cell lines decreased with increasing radioactivity. Consequently, 131I-PHT may be a good radiopharmaceutical for targeting radionuclide therapy of Central Nervous System Tumors. 相似文献
98.
Schiff base oligomer of N,N′‐bis (2,4‐dihydroxybenzylidene) 1,2‐phenylenediamine (DHBPDA), with a double azomethine group, was synthesized from the oxidative polycondensation (OP) reaction with NaOCl as an oxidant in an aqueous alkaline medium at 90°C. About 75% DHBPDA was converted to O‐DHBPDA. The structures of the products were studied by UV‐Vis, FT‐IR, 1H‐NMR, 13C‐NMR and elemental analysis. According to Gel Permeation Chromatography (GPC) analysis of O‐DHBPDA, the number average molecular weight (Mn), weight average molecular weight (Mw) and PDI values were found to be 4328 g mol?1, 6228 g mol?1 and 1.43, respectively. TG/DTA analyses were shown to be stable of O‐DHBPDA against thermo‐oxidative decomposition. During the polycondensation reaction, a part of the azomethine (‐CH?N‐) groups oxidized to aldehyde (CHO) group (10–12%). Oligomer‐metal complexes of oligo‐N,N′‐bis (2,4‐dihydroxybenzylidene) 1,2‐phenylenediamine (O‐DHBPDA) with Co(II) and Mn(II) were synthesized and characterized by FT‐IR, UV‐Vis, TG‐DTA and Atomic Absorption Spectroscopy (AAS). The residue of DHBPDA, O‐DHBPDA, O‐DHBPDA‐Co and O‐DHBPDA‐Mn were found to be 0%, 3.65%, 11.67%, and 9.20%, respectively at 1000°C. 相似文献
99.
İbrahim Doymaz 《Heat and Mass Transfer》2011,47(3):277-285
The effect of blanching and drying temperature (50, 60 and 70°C) on drying kinetics and rehydration ratio of sweet potatoes
was investigated. It was observed that both the drying temperature and blanching affected the drying time and rehydration
ratio. The logarithmic model showed the best fit to experimental drying data. The values of effective moisture diffusivity
and activation energy ranged from 9.32 × 10−11 to 1.75 × 10−10 m2/s, and 22.7–23.2 kJ/mol, respectively. 相似文献
100.
İsa Karaman Hayreddin Gezegen Mustafa Ceylan Merve Dilmaç 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5):580-586
Abstract In this study, a series of novel β-mercapto carbonyl derivatives (3a–j) was prepared by addition of thiophenol (2) to chalcones (1a–j) in the presence of catalytic amount of iodine (10 mol%) in CH2Cl2. Antibacterial and antifungal in vitro properties of the synthesized compounds were tested against some human pathogenic microorganisms by employing the disk diffusion technique. For the most active compounds, also minimum inhibitory concentrations (MICs) were determined. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. 相似文献