全文获取类型
收费全文 | 190篇 |
免费 | 18篇 |
专业分类
化学 | 167篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 22篇 |
物理学 | 16篇 |
出版年
2023年 | 9篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 10篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 4篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 3篇 |
2012年 | 5篇 |
2011年 | 8篇 |
2010年 | 15篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 13篇 |
2006年 | 6篇 |
2005年 | 11篇 |
2004年 | 6篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
1971年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有208条查询结果,搜索用时 15 毫秒
51.
Eike Kirchner Frauke Thiem Rudolt Dernick Jochen Heukeshoven Joachim Thieina 《Journal of carbohydrate chemistry》2013,32(2):453-486
Abstract Glycal derivatives of N-acetylneuraminic acid were prepared and their N-iodosuccinimide-mediated glycosylation shown to proceed only with most reactive alcohols, Their reduced enol ether reactivity is attributed to the α unsaturated ester reature. Thus several reduced glycal derivatives were synthesized. These couid be glycosyiatec with simple alcohols as well as otner saccnarides as aglycones in averaae to modest yields with the trans-diaxiai additions compounas prevailing. A number or selective and specific prepparation led to both the anomeric phenylthioglycosides or N dcety Ineuraminic acid. These could be used in phenylmercurl triflate-promoted glycosylations to afford several derivatives. 相似文献
52.
53.
54.
Transition-Metal-Induced Rearrangement of [(PhSn)4S6] Towards Ternary CuI/Sn/S or CuII/Sn/S Clusters
Eike Dornsiepen Dr. Florian Weigend Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(10):2486-2490
Direct access of ternary copper-tin sulfide clusters by reactions of a binary organotin sulfide cluster, [(PhSn)4S6] ( A ), with transition metal complexes was achieved for the first time without extra addition of further chalcogenide sources. This indicates that an in situ rearrangement of the inorganic core takes place even without initial formation of anionic fragments. The use of [Cu(PPh3)3Cl] or [Cu(PPh3)2Cl2] as reactants yielded the ternary clusters [(CuPPh3)4(PhSn)18Cu6S31Cl2] ( 1 ) and [{Cu(PPh3)2}2(PhSn)3(SnCl)S8] ( 2 ), respectively. Whereas 1 represents the largest neutral Cu/Sn/S cluster known to date, compound 2 , which is the first example of a ternary Cu/Sn/E (E=S, Se) cluster containing copper in the +II oxidation state, may be viewed as a very early stage of cluster formation. Apparently, the presence of CuII inhibits effective cluster growth, which rationalizes the lack of such species so far. The two ternary clusters exhibit very similar optical absorption energies despite their markedly different cluster sizes. According to time-dependent DFT calculations, this is due to different characters of the electronic excitation in the triplet compound 2 , as compared to the excitation of the closed shell cluster 1 , which serve to compensate for the different extensions of the clusters. 相似文献
55.
Matthias A. Grasser Tobias Pietsch Jan Blasius Dr. Oldamur Hollóczki Prof. Dr. Eike Brunner Prof. Dr. Thomas Doert Prof. Dr. Michael Ruck 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(7):e202103770
Elemental tellurium readily dissolves in ionic liquids (ILs) based on tetraalkylphosphonium cations even at temperatures below 100 °C. In the case of ILs with acetate, decanoate, or dicyanamide anions, dark red to purple colored solutions form. A study combining NMR, UV-Vis and Raman spectroscopy revealed the formation of tellurium anions (Ten)2− with chain lengths up to at least n=5, which are in dynamic equilibrium with each other. Since external influences could be excluded and no evidence of an ionic liquid reaction was found, disproportionation of the tellurium is the only possible dissolution mechanism. Although the spectroscopic detection of tellurium cations in these solutions is difficult, the coexistence of tellurium cations, such as (Te4)2+ and (Te6)4+, and tellurium anions could be proven by cyclic voltammetry and electrodeposition experiments. DFT calculations indicate that electrostatic interactions with the ions of the ILs are sufficient to stabilize both types of tellurium ions in solution. 相似文献
56.
Two laboratories extensively investigated the use of HPTLC to perform assays on lamivudine-zidovudine, metronidazole, nevirapine, and quinine composite samples. To minimize the effects of differences in analysts' technique, the laboratories conducted the study with automatic sample application devices in conjunction with variable-wavelength scanning densitometers to evaluate the plates. The HPTLC procedures used relatively innocuous, inexpensive, and readily available chromatography solvents used in the Kenyon or the Global Pharma Health Fund Minilabs TLC methods. The use of automatic sample applications in conjunction with variable- wavelength scanning densitometry demonstrated an average repeatability or within-laboratory RSD of 1.90%, with 73% less than 2% and 97% at 2.60% or less, and an average reproducibility or among-laboratory RSD of 2.74%. 相似文献
57.
Eike Rietsch 《Numerical Linear Algebra with Applications》2009,16(4):319-344
Let u1, u2, …, uN with un∈? denote the values of a function recorded or computed at N real and equidistant abscissa values tn=nΔt+t0 for n=1, …, N. A consistent interpolation operator L , as defined in this paper, interpolates these function values for N new abscissas tn = (n+½)Δt+t0, the first N?1 of which are halfway between those originally given while the last one is outside of the original abscissa range. Application of L to these interpolated function values produces the last N?1 samples u2, u3, …, uN of the original data plus one extrapolated function value uN+1. Hence, L 2 is essentially a shift operator, but with a prediction component. The difference between various interpolation methods (e.g. polynomials, Fourier series) is now reduced to the way in which uN+1 is determined. This concept not only permits a uniform view at interpolation by quite different classes of functions but also allows the creation of more general interpolation, differentiation, and integration formulas, which can be tailored to particular problems. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
58.
An innovative soft chemical approach was applied, using ionic liquids as an alternative reaction medium for the synthesis of tellurium polycationic cluster compounds at room temperature. [Mo2Te12]I6, Te6[WOCl4]2, and Te4[AlCl4]2 were isolated from the ionic liquid [BMIM]Cl/AlCl3 ([BMIM]+: 1‐n‐butyl‐3‐methylimidazolium) and characterized. Black, cube‐shaped crystals of [Mo2Te12]I6, which is not accessible by conventional chemical transport reaction, were obtained by reaction of the elements at room temperature in [BMIM]Cl/AlCl3. The monoclinic structure (P21/n, a = 1138.92(2) pm, b = 1628.13(2) pm, c = 1611.05(2) pm, β = 105.88(1) °) is homeotypic to the triclinic bromide [Mo2Te12]Br6. In the binulear complex [Mo2Te12]6+, the molybdenum(III) atoms are η4‐coordinated by terminal Te42+ rings and two bridging η2‐Te22– dumbbells. Despite the short Mo···Mo distance of 297.16(5) pm, coupling of the magnetic moments is not observed. The paramagnetic moment of 3.53 μB per molybdenum(III) atom corresponds to an electron count of seventeen. Black crystals of monoclinic Te6[WOCl4]2 are obtained by the oxidation of tellurium with WOCl4 in [BMIM]Cl/AlCl3. Tellurium and tellurium(IV) synproportionate in the ionic liquid at room temperature yielding violet crystals of orthorhombic Te4[AlCl4]2. 相似文献
59.
60.
Trapping cations in specific positions in tuneable "artificial cell" channels: new nanochemistry perspectives 总被引:1,自引:0,他引:1