全文获取类型
收费全文 | 210篇 |
免费 | 11篇 |
专业分类
化学 | 168篇 |
晶体学 | 10篇 |
数学 | 12篇 |
物理学 | 31篇 |
出版年
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 7篇 |
2014年 | 6篇 |
2013年 | 9篇 |
2012年 | 11篇 |
2011年 | 8篇 |
2010年 | 8篇 |
2009年 | 15篇 |
2008年 | 12篇 |
2007年 | 8篇 |
2006年 | 8篇 |
2005年 | 11篇 |
2004年 | 8篇 |
2003年 | 9篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 4篇 |
1999年 | 6篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 2篇 |
1977年 | 5篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 265 毫秒
131.
Kaichin Chang Maria A. Fritz Dr. Nadezhda B. Tamm Dr. Alexey A. Goryunkov Prof. Lev N. Sidorov Dr. Chuanbao Chen Prof. Shangfeng Yang Prof. Erhard Kemnitz Prof. Sergey I. Troyanov 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(2):578-587
Trifluoromethylation of higher fullerene mixtures with CF3I was performed in ampoules at 400 to 420 and 550 to 560 °C. HPLC separation followed by crystal growth and X‐ray diffraction studies allowed the structure elucidation of nine CF3 derivatives of D2‐C84 (isomer 22). Molecular structures of two isomers of C84(22)(CF3)12, two isomers of C84(22)(CF3)14, four isomers of C84(22)(CF3)16, and one isomer of C84(22)(CF3)20 were discussed in terms of their addition patterns and relative formation energies. DFT calculations were also used to predict the most stable molecular structures of lower CF3 derivatives, C84(22)(CF3)2–10. It was found that the addition of CF3 groups to C84(22) is governed by two rules: additions can only occur at para positions of C6(CF3)2 hexagons and no additions can occur at triple‐hexagon‐junction positions on the fullerene cage. 相似文献
132.
Along with X‐ray diffraction measurements, 25Mg solid state NMR experiments were performed in natural abundance at 9.4 T on crystalline and mechanically milled samples of MgO, Mg(OH)2, MgF2, and magnesium hydroxide fluorides Mg(OH)xF2–x prepared on mechanochemical and sol‐gel syntheses routes. In addition to single pulse and spin‐echo sequences, both static 1H‐25Mg CP and 19F‐25Mg CP measurements allowed the registration of 25Mg spectra in attractive short measurement times. Although an assignment of different magnesium species in magnesium hydroxide fluorides is only hardly possible, position and line shapes of 25Mg spectra of magnesium hydroxide fluorides reflect chemically reliable trends. All samples studied here show a sixfold fluorine, oxygen, or mixed fluorine / oxygen coordination of magnesium, also in highly disordered samples. 相似文献
133.
Madalina Tudorache George Ghemes Andreea Nae Elena Matei Ionel Mercioniu Erhard Kemnitz Benjamin Ritter Simona Coman Vasile I. Parvulescu 《Central European Journal of Chemistry》2014,12(12):1262-1270
A comparative study of two different biocatalytic models, e.g. enzyme immobilized on magnetic particles (EIMP) and cross-linking enzyme aggregates onto magnetic particles (CLEMPA) was performed. The first model was designed as enzyme-immobilized on the magnetic particles surface (EIMP). The second model was constructed as a network structure with the enzyme aggregates and magnetic particles placed into the nodes and polyglutaraldehyde cross-linker as the network ledges. The design was called cross-linking enzyme aggregates onto magnetic particles (CLEMPA). The biocatalysts were prepared using lipase enzyme from Aspergillus niger for catalyzing the glycerol (Gly) conversion to glycerol carbonate (GlyC). The biocatalyst characteristics for both designs (EIMP and CLEMPA) were evaluated using scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis techniques. The EIMP model was strongly influenced by the composition of the polymeric layer covering the particles surface, while the size of the magnetic particles affected mostly the CLEMPA design. Also, the biocatalytic capacity of the tested models was evaluated as maximum 52% Gly conversion with 90% GlyC selectivity for EIMP, and 73% Gly conversion with 77% GlyC selectivity for CLEMPA. Both biocatalytic models were successfully used to prepare GlyC from “crude” glycerol collected directly from the biodiesel process (e.g. 49% Gly conversion with 91% GlyC selectivity for EIMP and 70% Gly conversion with 80% GlyC selectivity for CLEMPA). 相似文献
134.
135.
Followed by X-ray diffraction, MAS NMR and elemental analysis the mechanochemical reaction between Al(OiPr)3, γ-AlOOH and Al(ac)2OH as possible aluminium sources on the one side, and NH4F as fluorinating agent on the other side was studied. Encouraged by the successful mechanochemical synthesis of CaF2 using the same fluorinating agent, the formation of AlF3 was expected. However, it can be established that as long as NH4F is supplied the formation of crystalline (NH4)3AlF6 is observed instead. 相似文献
136.
137.
138.
139.
140.
Maria A. Lanskikh Kaichin Chang Nadezhda B. Tamm Erhard Kemnitz Sergey I. Troyanov 《Mendeleev Communications》2012,22(3):136-137
The synthesis, separation and X-ray crystallographic analysis of the trifluoromethyl derivatives of fullerene C88 (isomer 33), C88(CF3)n (n = 16, 18 and 20), revealed close relations between their addition patterns, which indicate the formation of higher derivatives from lower ones by the addition of CF3 groups. 相似文献