全文获取类型
收费全文 | 218篇 |
免费 | 18篇 |
国内免费 | 16篇 |
专业分类
化学 | 210篇 |
晶体学 | 3篇 |
综合类 | 3篇 |
物理学 | 36篇 |
出版年
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 12篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 10篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 28篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 16篇 |
2008年 | 11篇 |
2007年 | 7篇 |
2006年 | 4篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 5篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 9篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1979年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有252条查询结果,搜索用时 31 毫秒
1.
A preparative one-step method for the synthesis of 1,1,1,5,5,5-hexafluoro-4-trifluoromethylpentane-2,3-dione dihydrazone from perfluoro-4-methylpent-2-ene and hydrazine hydrate has been developed. Oxidation of this dihydrazone with bromine in water gives 3-diazo-1,1,1,5,5,5-hexafluoro-4-trifluoromethylpentane-2-one. The same product is obtained from 3-hydrazono-1,1,1,5,5,5-hexafluoro-4-trifluoromethylpentane-2-one under similar conditions.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2039–2041, November, 1994.This work was supported by the Russian Foundation for Basic Research (the project code 94-03-08548). 相似文献
2.
Xiangpeng Wang Yunxiang Zheng Chunxiao Zhang Lina Zong 《International Journal of Polymer Analysis and Characterization》2020,25(5):300-314
Abstract A novel hydrolysis-resistant superabsorbent composite was prepared via the solution polymerization based on acrylic acid (AA) and sodium bentonite (SBT) as monomers, tetraallylammonium bromine (TAAB) as crosslinker and ammonium persulfate (APS) as initiator. The mechanism of polymerization and the structure of the superabsorbent polymer (SAP) were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (X-ray), and scanning electron microscopy (SEM). The reaction conditions such as different mass ratios of APS to AA, TAAB to AA, SBT to AA, neutralization degree of AA were optimized by orthogonal experiment, and the influence of each reaction condition on the capacity of water absorption at 150?°C was investigated via single-factor controlled experiment. The hydrolysis resistance and swelling kinetics of the SAP were studied in different solutions at 150?°C. Compared to traditional SAPs, the SAP synthesized with TAAB as crosslinker performed a more excellent hydrolysis resistance and water absorbency capacity at high temperatures. The water absorbency in distilled water or 0.1?mol L?1 NaCl solution could reach 392.6 and 145.2?g g?1at 150?°C, respectively. The SAP maintaining high swelling capacity in the pH range of 5–9 indicated its wide application values in the acidic or alkaline environment at high temperature. In addition, the SAP exhibited good reusability which could still retain about 73% of its initial water absorbency after reswelling six times at 150?°C. 相似文献
3.
4.
The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia 相似文献
5.
Ramin Ghorbani‐Vaghei Mohammad Ali Zolfigol Nasrin Moshfeghifar Nadiya Koukabi Gholamabbas Chehardoli 《中国化学会会志》2007,54(3):791-794
An efficient method for the oxidative coupling of thiols to their corresponding disulfides by new reagents poly(N‐bromobenzene‐1,3‐disulfonylamide) PBBS , N,N,N′,N′‐tetrabromobenzene‐1,3‐disulfonylamide TBBDA and DABCO‐bromine complex is described. The reaction was applicable to a variety of thiols with high chemoselectivity. 相似文献
6.
S. G. Zlotin O. V. Prokshits N. F. Karpenko Yu. A. Strelenko O. A. Luk'yanov 《Russian Chemical Bulletin》1992,41(8):1400-1413
We have worked out a method for the synthesis of 1,3,3-trisubstituted triazene 1-oxides based upon reaction of 1,1-disubstituted hydrazines with bromine in the presence of aryl- and heteroarylnitroso compounds in acid media. Obtained are a broad range of triazene 1-oxides, among which hitherto unknown compounds of the series of pyrazole and 3,3-dialkyltriazene 1-oxides that contain functional groups at the alkyl part of the molecule. We propose a reaction scheme which includes in situ formation of diazenium cations and reaction of them with nitroso compounds that are present in the system. By means of PMR,13C, and14N NMR spectroscopy, and mass spectroscopy, it has been shown that in all the prepared compounds the oxidated nitrogen atom is at the N1 position of the triazene N-oxide group.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 8, pp. 1804–1820, August, 1992. 相似文献
7.
8.
A multi-wall carbon nanotube (MWNT)/cetyl pyridine bromine (CPB) composite film modified glassy carbon electrode (GCE) was
developed for the electrochemical determination of hymecromone in phosphonate buffer. Electrochemical behaviour of hymecromone
at the composite film electrode was investigated with voltammetry. Compared with an irreversible oxidation of hymecromone
at the bare GCE, the oxidation peak current was enhanced greatly at the film electrode. Some parameters such as pH, scan rate,
accumulation potential and accumulation time were optimized. Under optimal conditions, an oxidation peak at 0.82 V was employed
to determine hymecromone electrochemically. A linearity between the oxidation peak current and the hymecromone concentration
was obtained in the range of 3.0 × 10−7 − 2.0 × 10−5 mol 1−1 with a detection limit of 8.0 × 10−8 mol 1−1. The proposed procedure was successfully applied to assay hymecromone in pharmaceutical formulation with satisfactory results.
The text was submitted by the authors in English. 相似文献
9.
Peter Scharfenberg 《Theoretical chemistry accounts》1985,67(3):235-243
Bromine parameters are proposed, matching well the standard values of first and second row atoms, as introduced by Pople et al. This is shown by comparisons of geometries, configurations, conformations, and dipole moments, obtained with different approaches. The new parameter set was found in a very simple and efficient way that may also be useful for other tasks, e.g. in non-empirical calculations. 相似文献
10.
CHEN Wen-Tong GUO Guo-Cong ZENG Xi-Rui LI Xin-Fa FANG Xiao-Niu KUANG Han-Mao LIU Dong-Sheng LIU Li-Min 《结构化学》2007,26(10)
The title compound (4,4'-H2bipy)[CdBr4]·H2O 1 has been synthesized via hydrothermal reaction and characterized by X-ray diffraction. The crystal belongs to monoelinic,space group P21/c with a=8.260(3), b=23.926(7), c=9.774(2) (A), β=106.777(9)°,C10H12Br4CdN2O, Mr=608.26, V=1849.4(9)(A)3, Z=4, Dc=2.185 g/cm3, S=1.005, μ(MoKα)=9.814 mm-1, F(000)=1128, R=0.0646 and wR=0.0989. The crystal structure analysis of 1reveals that the title compound features an isolated structure, based on discrete 4,4'-H2bipy moieties and lattice water molecules which are linked by hydrogen bonds together with tetrahedral cadmium atoms terminally coordinated by four bromine atoms. 相似文献