全文获取类型
收费全文 | 378篇 |
免费 | 16篇 |
专业分类
化学 | 307篇 |
力学 | 4篇 |
数学 | 13篇 |
物理学 | 70篇 |
出版年
2021年 | 3篇 |
2019年 | 12篇 |
2018年 | 5篇 |
2016年 | 9篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 11篇 |
2012年 | 17篇 |
2011年 | 17篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 11篇 |
2007年 | 4篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 12篇 |
2003年 | 5篇 |
2002年 | 10篇 |
2001年 | 12篇 |
2000年 | 14篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 6篇 |
1996年 | 10篇 |
1995年 | 7篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 7篇 |
1989年 | 13篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1982年 | 3篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1958年 | 1篇 |
1943年 | 1篇 |
1937年 | 2篇 |
1936年 | 4篇 |
排序方式: 共有394条查询结果,搜索用时 34 毫秒
51.
Colorless single crystals of Cd2[μ8‐MTB] · 3H2O · DMF ( 1 ) were prepared in DMF/H2O solution [ 1 : space group C2/c (no. 15) with a = 1821.30(6), b = 2175.08(6), c = 1269.87(4) pm, β = 129.684(1)°]. The connection between the methane‐p‐benzoate tetraanions (MTB4–) and the Cd2+ cations leads to a three‐dimensional framework with channels extending along [1 10] and [110] with openings of 670 pm × 360 pm. The channel‐like voids accommodate water molecules and N,N‐dimethylformamide (DMF) molecules not bound to Cd2+. Colorless single crystals of [Cd4(2,2′‐bipy)4(μ7‐MTB)2] · 7DMF ( 2 ) were prepared in DMF in the presence of 2,2′‐bipyridine [ 2 : space group P1 (no. 2) with a = 1224.84(4), b = 1418.85(5), c = 2033.49(4) pm, α = 85.831(2)°, β = 88.351(2)°, γ = 68.261(1)°]. The coordination of MTB4– to Cd2+ results in infinite layers parallel to (001). The layers, not connected by any hydrogen bonds, contain small openings of about 320 pm × 340 pm. 相似文献
52.
Philipp S. Steinlandt Wei Zuo Dr. Klaus Harms Prof. Dr. Eric Meggers 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(67):15333-15340
A new class of bis-cyclometalated rhodium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole ligands and two labile acetonitriles is introduced. Single enantiomers (>99 % ee) were obtained through a chiral-auxiliary-mediated approach using a monofluorinated salicyloxazoline. The new chiral-at-metal complex is capable of catalyzing the visible-light-induced enantioselective α-cyanoalkylation of 2-acyl imidazoles in which it serves a dual function as the chiral Lewis acid catalyst for the asymmetric radical chemistry and at the same time as the photoredox catalyst for the visible-light-induced redox chemistry (up to 80 % yield, 4:1 d.r., and 95 % ee, 12 examples). 相似文献
53.
Fricke Christian Harms Hauke Maskow Thomas 《Journal of Thermal Analysis and Calorimetry》2020,141(5):1933-1942
Journal of Thermal Analysis and Calorimetry - A sudden expansion is a classical problem which is happened in different industries such as energy conversion, environmental control, and chemical... 相似文献
54.
Greg S. Harms Steve W. Pauls John F. Hedstrom Carey K. Johnson 《Journal of fluorescence》1997,7(4):283-292
We have examined the lifetimes and rotational correlation times of dityrosine emission by time-correlated single-photon counting. We first noticed dityrosine fluorescence in samples of tyrosine and tyrosine dipeptides by its characteristic red-shifted emission at 400 to 430 nm. The longer rotational correlation time relative to tyrosine proved that this fluorescence emanated from a distinct species. Comparison with the fluorescence properties of synthesized dityrosine established the identity of the emitting species. Fluorescence intensity decays of dityrosine are generally characterized by two decay components, one with a lifetime in the range of 150 to 800 ps and another between 2.5 and 4.5 ns. We found no evidence for an excited-state reaction, since a rising phase (negative-amplitude component) was not observed. In the pH range from 4 to 10, two ground-state species exist in equilibrium with pK
a 7. Both species exhibit two fluorescence decays. The average fluorescence lifetime increases gradually with pH over the pH range from 4 to 10 and decreases at pH 2. Anisotropy decays were measured for dityrosine and the alanine–dityrosine–alanine and leucine–dityrosine–leucine dipeptides. The rotational correlation times of dityrosine and dityrosine dipeptides increase linearly with van der Waals volumes. The slope indicates a stronger solute–solvent interaction than predicted with stick boundary conditions. It is suggested that these interactions result from the presence of two zwitterionic pairs. 相似文献
55.
J. Harms G. Jander J. Wierciski R. Ammon K. Hinsberg und J. Courtois 《Fresenius' Journal of Analytical Chemistry》1937,111(1):30-34
Ohne Zusammenfassung 相似文献
56.
57.
By means of metal-atom ligand-vapor cocondensation (CC) hexa(eta1-arsenine)molybdenum (11) and hexa(eta1-arsenine)tungsten (12) have been prepared; in the molybdenum case, the sandwich complex bis(eta6-arsenine)molybdenum (10) has been isolated as the primary product. The structure of 12 follows from a single-crystal X-ray diffraction study. Based on the results of CC synthesis, chromium binds to arsenine in the eta6-mode exclusively, molybdenum features both options eta1 and eta6, and for tungsten only eta1 coordination is observed. 相似文献
58.
Driller KM Libnow S Hein M Harms M Wende K Lalk M Michalik D Reinke H Langer P 《Organic & biomolecular chemistry》2008,6(22):4218-4223
N-glycosides of 6H-indolo[2,3-b]quinoxalines were prepared and structurally characterized. The synthesis relies on the cyclocondensation of isatine-N-glycosides with 1,2-diaminobenzenes. Some products exhibit weak cytotoxic activity against human ceratinocytes (HaCaT). 相似文献
59.
A cobalt(I)-catalyzed [2 + 2 + 2] cycloaddition reaction between an internal acceptor-substituted alkyne and a terminal alkene leads to the formation of regiochemically enriched polysubstituted 1,3-cyclohexadiene derivatives in acceptable yields when methyl butynoate is used, whereas regiochemically pure products are formed in good yields form phenyl propyonate. The concurrent cyclotrimerization reaction of the alkyne to the corresponding benzene derivative is dependent on the sterical bulk of the alkyne and is considerably reduced with the sterically more hindered alkyne. 相似文献
60.
Rzepecki P Hochdörffer K Schaller T Zienau J Harms K Ochsenfeld C Xie X Schrader T 《Journal of the American Chemical Society》2008,130(2):586-591
Self-association of aminopyrazole peptide hybrid 1 leads to stacked nanorosettes. This remarkable, well-ordered structure obeys the laws of nucleic acid self-assembly. In a strictly hierarchical process, formation of aminopyrazole "base" triplets via a hydrogen bond network is accompanied by pi-stacking with a second rosette and final dimerization of two double rosettes to a four-layer superstructure, stabilized by a six-fold half-crown alkylammonium lock. The final complex is soluble in organic as well as in aqueous solution. It was characterized in the solid state by X-ray crystallography, in water by NMR spectroscopy, and in silico by quantum chemical shift calculation. All these methods provide strong evidence for the same hexameric complex geometry. Its structural features bear striking similarity to nucleic acid architectures and their peptidic counterparts, especially alanyl-PNA. The whole self-assembly process is highly solvent- and temperature-dependent and occurs with a high degree of cooperativity--no intermediates are observed. Formation and dissociation of the nanorosette, however, are kinetically slow. The limitation to a hexameric aggregate can be explained by six sterically demanding valine residues, whose replacement by alanines may result in formation of infinite fibers. 相似文献