全文获取类型
收费全文 | 259篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 215篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 33篇 |
物理学 | 19篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 18篇 |
2020年 | 7篇 |
2019年 | 4篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 14篇 |
2015年 | 4篇 |
2014年 | 10篇 |
2013年 | 15篇 |
2012年 | 17篇 |
2011年 | 22篇 |
2010年 | 17篇 |
2009年 | 10篇 |
2008年 | 14篇 |
2007年 | 14篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 14篇 |
2003年 | 16篇 |
2002年 | 9篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1985年 | 1篇 |
排序方式: 共有270条查询结果,搜索用时 15 毫秒
151.
152.
Dr. Concetta Avitabile Dr. Carlo Diaferia Dr. Valentina Roviello Dr. Davide Altamura Dr. Cinzia Giannini Dr. Luigi Vitagliano Dr. Antonella Accardo Prof. Alessandra Romanelli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(65):14850-14857
Studies carried out in recent decades have revealed that the ability to self-assemble is a widespread property among biomolecules. Small nucleic acid moieties or very short peptides are able to generate intricate assemblies endowed with remarkable structural and spectroscopic properties. Herein, the structural/spectroscopic characterization of aggregates formed by nucleobases and peptide nucleic acid (PNA)–peptide conjugates are reported. At high concentration, all studied nucleobases form aggregates characterized by previously unreported fluorescence properties. The conjugation of these bases, as PNA derivatives, to the dipeptide Phe–Phe leads to the formation of novel hybrid assemblies, which are characterized by an amyloid-like association of the monomers. Although these compounds share the same basic cross-β motif, the nature and number of PNA units have an important impact on both the level of structural order and the intrinsic fluorescence of the self-assembled nanostructure. 相似文献
153.
Anatoly P. Sobolev Arianna Di Lorenzo Simone Circi Cristina Santarcangelo Cinzia Ingallina Maria Daglia Luisa Mannina 《Molecules (Basel, Switzerland)》2021,26(17)
Untargeted (NMR) and targeted (RP-HPLC-PDA-ESI-MSn, RP-HPLC-FD) analytical methodologies were used to determine the bioactive components of 19 tea samples, characterized by different production processes (common tea and GABA tea), degrees of fermentation (green and oolong teas), and harvesting season (autumn and spring). The combination of NMR data and a multivariate statistical approach led to a statistical model able to discriminate between GABA and non-GABA teas and green and oolong teas. Targeted analyses showed that green and GABA green teas had similar polyphenol and caffeine contents, but the GABA level was higher in GABA green teas than in regular green tea samples. GABA oolong teas showed lower contents of polyphenols, caffeine, and amino acids, and a higher content of GABA, in comparison with non-GABA oolong teas. In conclusion, the results of this study suggest that the healthy properties of teas, especially GABA teas, have to be evaluated via comprehensive metabolic profiling rather than only the GABA content. 相似文献
154.
Advances in Data Analysis and Classification - Topic detection in short textual data is a challenging task due to its representation as high-dimensional and extremely sparse document-term matrix.... 相似文献
155.
Walter Baratta Prof. Cinzia Barbato Dr. Santo Magnolia Dr. Katia Siega Dr. Pierluigi Rigo Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(10):3201-3206
The osmium complexes trans‐[OsCl2(dppf)(diamine)] (dppf: 1,1′‐bis(diphenylphosphino)ferrocene; diamine: ethylenediamine in 3 , propylenediamine in 4 ) were prepared by the reaction of [OsCl2(PPh3)3] ( 1 ) with the ferrocenyl diphosphane, dppf and the corresponding diamine in dichloromethane. The reaction of derivative 3 with NaOCH2CF3 in toluene afforded the alkoxide cis‐[Os(OCH2CF3)2(dppf)(ethylenediamine)] ( 5 ). The novel precursor [Os2Cl4(P(m‐tolyl)3)5] ( 2 ) allows the synthesis of the chiral complexes trans‐[OsCl2(diphosphane)(1,2‐diamine)] ( 6 – 9 ; diphosphane: (R)‐[6,6′‐dimethoxy(1,1′‐biphenyl)‐2,2′‐diyl]bis[1,1‐bis(3,5‐dimethylphenyl)phosphane] (xylMeObiphep) or (R)‐(1,1′‐binaphthalene)‐2,2′‐diylbis[1,1‐bis(3,5‐dimethylphenyl)phosphane] (xylbinap); diamine=(R,R)‐1,2‐diphenylethylenediamine (dpen) or (R,R)‐1,2‐diaminocyclohexane (dach)), obtained by the treatment of 2 with the diphosphane and the 1,2‐diamine in toluene at reflux temperature. Compounds 3 – 5 in ethanol and in the presence of NaOEt catalyze the reduction of methyl aryl, dialkyl, and diaryl ketones and aldehydes with H2 at low pressure (5 atm), with substrate/catalyst (S/C) ratios of 10 000–200 000 and achieving turnover frequencies (TOFs) of up to 3.0×105 h?1 at 70 °C. By employment of the chiral compounds 6 – 9 , different ketones, including alkyl aryl, bulky tert‐butyl, and cyclic ketones, have successfully been hydrogenated with enantioselectivities up to 99 % and with S/C ratios of 5000–100 000 and TOFs of up to 4.1×104 h?1 at 60 °C. 相似文献
156.
Lara Bianchi Dr. Gianluca Giorgi Prof. Massimo Maccagno Dr. Giovanni Petrillo Prof. Fernando Sancassan Prof. Elda Severi Dr. Domenico Spinelli Prof. Marco Stenta Dr. Cinzia Tavani Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(4):1312-1318
When Ar is a low‐aromaticity homo‐ or heterosystem, the sulfonyl‐stabilized anion of nitrobutadienes 4 (which derive from the initial ring opening of 3‐nitrothiophene) undergoes a rather surprising addition onto the aromatic ring itself, thereby leading to the construction of an unusual eight‐membered sulfur heterocycle condensed with the original Ar ring. The competitiveness of such a pathway with respect to the formation of the thiopyran ring (i.e., addition onto the nitrovinyl moiety) is favored at low temperatures, thus revealing its nature as a kinetically controlled process. 相似文献
157.
Rubino FM Verduci C Buratti M Fustinoni S Campo L Omodeo-Salè E Giglio M Iavicoli S Brambilla G Colombi A 《Biomedical chromatography : BMC》2006,20(3):257-266
The validation of an analytical method for the measurement of the unnatural amino acid alpha-fluoro-beta-alanine (AFBA), the main metabolite of the antineoplastic drug 5-fluorouracil (5FU), in urine for the biological monitoring of the exposure of hospital workers to the drug when preparing the therapeutical doses and administering to cancer patients is described. The method employed a two-step extractive derivatization of the analyte from urine to the N-trifluoroacety-n-butyl ester derivative and detection by selected-ion monitoring gas chromatography-mass spectrometry of structurally specific fragments. The limit of detection was 20 ng/mL with quantification accuracy better than +/-20% and precision (CV%) better than +/-20% in the range 0.020-10 microg/mL. Norleucine was used as the internal standard and the sample-to-sample analysis time was less than 15 min. The validated method has been applied to the biological monitoring of some hospital workers potentially exposed to 5FU and to matched control subjects. On a total number of 65 analyzed urine samples from control and exposed subjects, only three, obtained from exposed subjects, were found to be positive, with values of 20, 30 and 1150 ng/mL, respectively. 相似文献
158.
Barreca D Gasparotto A Maccato C Maragno C Tondello E 《Langmuir : the ACS journal of surfaces and colloids》2006,22(21):8639-8641
We report on the preparation of supported columnar CeO(2) nanostructures by a simple catalyst-free chemical vapor deposition process at temperatures as low as 623 K. A suitable choice of experimental parameters enables us to control the structural and morphological features of the resulting ceria nanosystems. 相似文献
159.
160.
Many experiments on high-temperature superconductors have shown paramagnetic behavior when the sample is field cooled. The paramagnetism was attributed to a d-wave order parameter creating pi-junctions in the samples. However, the same effect was later discovered in traditional low-temperature superconductors and conventional Josephson-junction arrays which are s wave. By simulating both conventional and mixed pi/conventional Josephson-junction arrays we determine that differences exist which may be sufficient to clearly identify the presence of pi junctions. In particular, the pi junctions cause a symmetry breaking providing a measurable signature of their presence. 相似文献