全文获取类型
收费全文 | 3370篇 |
免费 | 246篇 |
国内免费 | 340篇 |
专业分类
化学 | 2959篇 |
晶体学 | 40篇 |
力学 | 6篇 |
综合类 | 25篇 |
数学 | 1篇 |
物理学 | 925篇 |
出版年
2024年 | 8篇 |
2023年 | 27篇 |
2022年 | 93篇 |
2021年 | 75篇 |
2020年 | 72篇 |
2019年 | 80篇 |
2018年 | 80篇 |
2017年 | 102篇 |
2016年 | 113篇 |
2015年 | 117篇 |
2014年 | 136篇 |
2013年 | 311篇 |
2012年 | 193篇 |
2011年 | 208篇 |
2010年 | 170篇 |
2009年 | 202篇 |
2008年 | 179篇 |
2007年 | 255篇 |
2006年 | 215篇 |
2005年 | 195篇 |
2004年 | 144篇 |
2003年 | 144篇 |
2002年 | 123篇 |
2001年 | 93篇 |
2000年 | 94篇 |
1999年 | 84篇 |
1998年 | 61篇 |
1997年 | 51篇 |
1996年 | 38篇 |
1995年 | 37篇 |
1994年 | 35篇 |
1993年 | 33篇 |
1992年 | 33篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 21篇 |
1987年 | 10篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 9篇 |
1979年 | 3篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 6篇 |
排序方式: 共有3956条查询结果,搜索用时 0 毫秒
11.
12.
A novel copolymer, poly(N‐hexyl‐3,7‐phenothiazylene‐1,2‐ethenylene‐2,6‐pyridylene‐1,2‐ethenylene) ( P3 ), containing N‐hexyl‐3,7‐phenothiazylene and 2,6‐pyridylene chromophores was synthesized to investigate the effect of protonation, metal complexation, and chemical oxidation on its absorption and photoluminescence (PL). Poly(N‐hexyl‐3,8‐iminodibenzyl‐1,2‐ethenylene‐1,3‐phenylene‐1,2‐ethenylene) and poly(N‐hexyl‐3,7‐phenothiazylene‐1,2‐ethenylene‐1,3‐phenylene‐1,2‐ethenylene) ( P2 ), consisting of 1,3‐divinylbenzene alternated with N‐hexyl‐3,8‐iminodibenzyl and N‐hexyl‐3,7‐phenothiazylene, respectively, were also prepared for comparison. Electrochemical investigations revealed that P3 exhibited lower band gaps (2.34 eV) due to alternating donor and acceptor conjugated units (push–pull structure). The absorption and PL spectral variations of P3 were easily manipulated by protonation, metal chelation, and chemical oxidation. P3 displayed significant bathochromic shifts when protonated with trifluoroacetic acid in chloroform. The complexation of P3 with Fe3+ led to a significant absorption change and fluorescence quenching, and this implied the coordination of ferric ions with the 2,6‐pyridylene groups in the backbone. Moreover, both phenothiazylene‐containing P2 and P3 showed conspicuous PL quenching with a slight redshift when oxidized with NOBF4. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1272–1284, 2004 相似文献
13.
14.
Ildikó Mohammed-Ziegler Ferenc Billes 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):19-42
This review summarizes different applications of optical spectroscopic methods in calixarene chemistry including UV/Vis spectrometry,
vibrational spectroscopic techniques (FTIR and Raman spectroscopy), luminescence spectroscopy (including fluorescence and
phosphorescence), ellipsometry and various optical microscopic methods. Moreover, the results of theoretical studies (AM1,
PM3, DFT, ab initio, etc.) are summarized based on selected papers in the field of conformational studies, thermodynamics and complexation features.
About 300 references are processed systematically from the results reported mainly in the recent years with emphasis on the
potential of practical application of these molecules. 相似文献
15.
Andreas Wallner Margit Hölbling Judith Baumgartner Christoph Marschner 《Silicon Chemistry》2007,3(3-4):175-185
A number of cyclo-and bicyclosilanes have been prepared and structurally characterized by X-ray crystallography and Raman
spectroscopy. 1,1,4,4- and 1,1,3,3-tetrakis(trimethylsilyl)octamethylcyclohexasilanes were found to exhibit unusual twist- and twisted boat-conformations. The UV absorption properties of all compounds were studied and found to show absorption maxima red shifted
compared to the parent compound dodecamethylcyclohexasilane.
Dedicated to Prof. Mitsuo Kira on the occasion of his reception of the Wacker Silicon Award 2005 and in recongnition of his
numerous outstanding achievements in organosilicon chemistry. 相似文献
16.
Anette Munch Elmr Patric Jannasch 《Journal of polymer science. Part A, Polymer chemistry》2006,44(7):2195-2205
Methacrylate‐functionalized poly(ethylene oxide‐co‐ethylene carbonate) macromonomers were prepared in two steps by the anionic ring‐opening polymerization of ethylene carbonate at 180 °C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number‐average molecular weight of 2650 g mol?1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self‐supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 × 10?6 S cm?1 at 20 °C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195–2205, 2006 相似文献
17.
Ecaterina Stela Dragan Marcela Mihai Anton Airinei 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):5898-5908
The thermochemical transformation of electrostatically formed complexes of methyl orange (MO) with polycations containing primary amine groups such as ammonium salts afforded new polymers with a high concentration of covalently bound 4‐N,N‐dimethylaminoazobenzene groups in the side chain. Poly(allylamine hydrochloride) and poly(β‐aminoethylene acrylamide hydrochloride) were employed as support polycations for MO. The transformation of sulfonate–ammonium ion pairs into sulfonamide bonds, via heating at an elevated temperature, was supported by the polymer properties before and after the thermal treatment. The polymer structure changes were monitored with elemental analysis, Fourier transform infrared, 1H NMR, and ultraviolet–visible absorption spectroscopy, and thermogravimetric analysis. The spacer length between the backbone and azobenzene structures used as side chains strongly influenced the polymer properties before and after the heat‐induced reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5898–5908, 2006 相似文献
18.
红外光谱法研究含CeSt3的LDPE膜紫外光氧降解 总被引:1,自引:0,他引:1
报道了硬脂酸铈(CeSt_3)、及其在各种浓度、或不同温度、或延长贮放时间下含CeSt_3的低密度聚乙烯(LDPE)膜紫外光氧化降解过程的红外光谱。结果表明,只要在LDPE膜中加入0.1wt+%~0.3wt+%CeSt_3光敏剂,即可控光降解LDPE膜的寿命。 相似文献
19.
低密度聚乙烯光引发交联机理——Ⅱ.BNB自旋捕捉ESR研究 总被引:6,自引:4,他引:2
在光引发剂二苯甲酮(BP)存在下,紫外光辐照低密度聚乙烯(LDPE)所形成的自由基中间体已被自旋捕捉剂2,4,6-三特丁基亚硝基苯(BNB)所捕捉,其自旋加合物自由基已为电子自旋共振(ESR)所特征。现已检测和鉴定到二种自旋加合物:一种是叔碳自由基;另一种是仲碳自由基。它们分别是由BP的激发三重态从LDPE链的支化点和亚甲基团上夺氢所形成的自由基中间体同自旋捕捉剂BNB反应生成的。上述的证据表明:LDPE的光引发交联点主要发生在叔碳和仲碳原子上,且H-型交联点占主导地位。 相似文献
20.
S Çak?r E Co?kunP Naumov E Biçer? Bulut H ?çbudakO Çak?r 《Journal of Molecular Structure》2002,608(1):101-107
Aspartame adduct of copper(II) chloride Cu(Asp)2Cl2·2H2O (Asp=aspartame) is synthesized and characterized by elemental analysis, FT IR, UV/vis, ESR spectroscopies, TG, DTG, DTA measurements and molecular mechanics calculations. Aqueous solution of the green solid absorbs strongly at 774 and 367 nm. According to the FT IR spectra, the aspartame moiety coordinates to the copper(II) ion via its carboxylate ends, whereas the ammonium terminal groups give rise to hydrogen bonding network with the water, the chloride ions or neighboring carboxylate groups. The results suggest tetragonally distorted octahedral environment of the copper ions. 相似文献