全文获取类型
收费全文 | 439篇 |
免费 | 19篇 |
国内免费 | 6篇 |
专业分类
化学 | 242篇 |
晶体学 | 3篇 |
力学 | 23篇 |
数学 | 85篇 |
物理学 | 111篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 13篇 |
2016年 | 14篇 |
2015年 | 25篇 |
2014年 | 23篇 |
2013年 | 40篇 |
2012年 | 34篇 |
2011年 | 23篇 |
2010年 | 18篇 |
2009年 | 37篇 |
2008年 | 30篇 |
2007年 | 21篇 |
2006年 | 19篇 |
2005年 | 11篇 |
2004年 | 22篇 |
2003年 | 9篇 |
2002年 | 2篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1972年 | 1篇 |
1967年 | 2篇 |
1939年 | 1篇 |
1935年 | 1篇 |
1934年 | 2篇 |
1933年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有464条查询结果,搜索用时 156 毫秒
101.
102.
smet Kaya Fatma Moral Didem Erdener 《Journal of polymer science. Part A, Polymer chemistry》2004,42(11):2717-2724
The reaction conditions of the oxidative polycondensation of 2‐[(pyridine‐2‐yl‐methylene) amino] phenol (2‐PMAP) with air O2, H2O2, and NaOCl were studied in an aqueous alkaline medium between 60 and 90 °C. Oligo‐2‐[(pyridine‐2‐yl‐methylene) amino] phenol (O‐2‐PMAP) was characterized with 1H NMR, Fourier transform infrared, ultraviolet–visible, size exclusion chromatography (SEC), and elemental analysis techniques. Moreover, solubility testing of the oligomer was performed in polar and nonpolar organic solvents. With the NaOCl, H2O2, and air O2 oxidants, the conversions of 2‐PMAP into O‐2‐PMAP were 98, 87, and 62%, respectively, in an aqueous alkaline medium. According to SEC, the number‐average molecular weight, weight‐average molecular weight, and polydispersity index of O‐2‐PMAP were 2262 g mol?1, 2809 g mol?1, and 1.24 with NaOCl, 3045 g mol?1, 3861 g mol?1, and 1.27 with air O2, and 1427 g mol?1, 1648 g mol?1, and 1.16 with air H2O2, respectively. Also, thermogravimetric analysis showed that O‐2‐PMAP was stable against thermooxidative decomposition. The weight loss of O‐2‐PMAP was 96.68% at 900 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2717–2724, 2004 相似文献
103.
AzaPCs containing tetra- and octaguaiacol moieties have not been investigated up to now. In this study, an unusual method is used for the synthesis of metalloAzaPCs (M: Zn, Co, Cu) containing guaiacol moieties. All compounds are characterized by a combination of FT-IR, 1H NMR, 13C NMR, mass and UV/vis spectroscopy techniques. The molecular structure of starting pyrazine compounds 1 and 2 is also determined by the single crystal X-ray diffraction technique. The aggregation behavior of new Zn(II) AzaPCs is investigated in DMSO at different concentrations. The fluorescence properties of Zn(II) AzaPCs are investigated in different solvents. The fluorescence quantum yields of Zn(II) AzaPCs are calculated in DMSO. 相似文献
104.
The oxidative polycondensation reaction conditions of 4-[(4-hydroxybenzylidene)amino]phenol(4-HBAP)were studied with H_2O_2,air oxygen and NaOCl in an aqueous alkaline medium between 50 and 90℃.The structures of the obtained monomer and polymer were confirmed by FT-IR,UV-Vis,~1H-and ~(13)C-NMR and elemental analysis.The characterization was made by TG-DTA,size exclusion chromatography(SEC)and solubility tests.At the optimum reaction conditions,the yield of poly[4-(4-hydroxybenzylidene amino)phenol](P-4-HBAP)was found to be 48.3%(for H_2O_2 oxidant),80.5%(for air O_2 oxidant)and 86.4%(for NaOCl oxidant).According to the SEC analysis,the number-average molecular weight(M_n),weight-average molecular weight(M_w)and polydispersity index(PDI)values of P-4-HBAP was found to be 8950,10970 g mol~(-1) and 1.225,respectively,using H_2O_2;and 11610,15190 g mol~(-1) and 1.308 respectively, using air O_2 and 7900,9610 g mol~(-1) and 1.216,respectively,using NaOCl.According to TG-DTA analyses,P-4-HBAP was more stable than 4-HBAP against thermal decomposition.The weight loss of P-4-HBAP was found to be 49.27% at 1000℃. The highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)values calculated from electrochemical measurement.Electrochemical energy gaps(E′_g)of 4-HBAP and P-4-HBAP were found to be-5.46, -5.28;-2.26,-2.67;3.20 and 2.61 eV,respectively.According to UV-Vis measurements,optical band gap(E_g)of 4-HBAP and P-4-HBAP were found to be 3.34 and 3.01 eV,respectively.Also,antimicrobial activities of 4-HBAP and P-4-HBAP were examined against selected some bacteria.The electrical conductivity of the polymer was measured after doping with iodine. 相似文献
105.
Hosoya K Watabe Y Kubo T Hoshino N Tanaka N Sano T Kaya K 《Journal of chromatography. A》2004,1030(1-2):237-246
A pair of polymeric selectors potentially responding to stimulation was introduced onto monosized porous polymer particles to be evaluated as a packing material for HPLC. Possible complexes formed between polyacrylamide (PAAm) and poly(methacrylic acid) (PMAA) were utilized as stimulus responsive polymeric selectors. Uniformly sized base polymer particle was prepared by multi-step swelling and polymerization method, while the introduction of PAAm and PMAA was done by newly invented modification technique. In this technique, a solvent in which both acrylamide (AAm) and methacrylic acid (MAA) monomers are soluble, but PAAm and PMAA are insoluble, was utilized as a modification medium. The polymer particle doubly modified with PAAm and PMAA was utilized as packing material for HPLC and the stimulus responses were evaluated by changing temperature or pH to check change of the slope of a Van't Hoff plot. By using water as a mobile phase, the expected inflection point of the Van't Hoff plot was observed at upper critical solution temperature (UCST) of the polymer complexes and the temperature responsive ability was observed. Moreover, pH responsive ability was studied by using buffer of either pH 4 or 10 as mobile phase. Slope of the plot was changed in buffer of pH 4, but no change of slope was observed in the buffer of pH 10. 相似文献
106.
Alraqa Shaya Y. Kaya Esra Nur Taşci Neşe Erbahar Dogan Durmuş Mahmut 《Journal of fluorescence》2022,32(5):1801-1813
Journal of Fluorescence - In this current study, the novel bis[4,5-(pyrene-2-yl)-3,6-(hexyloxy)] phthalonitrile (SPN) fluorophore has been successfully synthesized. Structural characterization of... 相似文献
107.
Kaya Irfan Özdemir Yalçın Kaya Eren Keskin Mehmet Emin 《Journal of Thermal Analysis and Calorimetry》2020,139(2):817-822
Journal of Thermal Analysis and Calorimetry - In this study, the effects of heating and cooling rate on the thermal properties of high nickel-rich Ni55Ti45 shape memory alloy were investigated.... 相似文献
108.
109.
The asymmetry and fringe inclination of the sawtooth-like waveform observed in the self-mixing signal obtained from a semiconductor laser with optical feedback enable the direction discrimination of line-of-sight motion of external target surfaces. We investigated the effects of linewidth enhancement factor and feedback strength on the asymmetry and the direction of fringe inclination of the signal by numerical simulations. For the first time, we show that direction of the fringe inclination is determined not only by the direction of the target motion but also by the value of the linewidth enhancement factor. 相似文献
110.
Glass transition during bulk polymerization was studied in free-radical cross-linking copolymerization (FCC) of methyl methacrylate (MMA) using the steady-state fluorescence (SSF) technique. Naphthalene (N) was used as a monomer and excimer forming probe. Changes in the viscosity of the pregel solutions due to gel formation dramatically enhance both monomer and excimer fluorescent yield of N molecules. The reaction time at which the monomer and excimer intensities exhibit a sudden increase corresponds to the reaction time at which the rate of polymerization becomes maximum resulting from the gel effect. This effect was used to study the gelation of MMA, as a function of time, in various N concentrations. The results were interpreted in the view of percolation theory. The gel fraction, β, and weight average degree of polymerization, γ, exponents β?=?0.40?±?0.02 and γ?=?1.70?±?0.07 were found in agreement with percolation results for both monomer and excimer measurements, respectively. 相似文献