全文获取类型
收费全文 | 141篇 |
免费 | 13篇 |
专业分类
化学 | 127篇 |
力学 | 2篇 |
数学 | 4篇 |
物理学 | 21篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2016年 | 4篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 9篇 |
2012年 | 10篇 |
2011年 | 17篇 |
2010年 | 5篇 |
2009年 | 5篇 |
2008年 | 12篇 |
2007年 | 17篇 |
2006年 | 17篇 |
2005年 | 2篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1981年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有154条查询结果,搜索用时 203 毫秒
81.
Daisuke Kinoshita Youhei Kimura Masaru Tada Kin-ya Akiba 《Phosphorus, sulfur, and silicon and the related elements》2013,188(5-6):1339-1343
Abstract 1,8-dimethoxy-10-methyl-9-methylene-9H-thioxanthenium salt (4) was prepared and the structure was determined by X-ray analysis to show the bond length between O─C is 2.80 A. This is too long to effect a hypervalent bonding. Bis[(1,8-dimethoxy) thioxanthylidene]allene (5) was prepared to be a symmetric compound in solution. Methylation of 5 with Meerwein reagent afforded S-monomethylated product (6) in solution and 6 gradually decomposed to C (or S)-monoprotonated allene (7), which was separately prepared as stable compound. 相似文献
82.
Mayumi Matsushita-Morita Hiroyuki Nakagawa Sawaki Tada Junichiro Marui Ryota Hattori Satoshi Suzuki Youhei Yamagata Hitoshi Amano Hiroki Ishida Michio Takeuchi Ken-Ichi Kusumoto 《Applied biochemistry and biotechnology》2013,171(1):145-164
β-Aminopeptidases exhibit both hydrolytic and aminolytic (peptide bond formation) activities and have only been reported in bacteria. We identified a gene encoding the β-aminopeptidase homolog from a genome database of the filamentous fungus Aspergillus oryzae. The gene was overexpressed in A. oryzae, and the resulting recombinant enzyme was purified. Apart from bacterial homologs [β-Ala-para-nitroanilide (pNA)], the enzyme preferred d-Leu-pNA and d-Phe-pNA as substrates. Therefore, we designated this gene as d-stereoselective aminopeptidase A (damA). The purified recombinant DamA was estimated to be a hexamer and was composed of two subunits with molecular masses of 29.5 and 11.5 kDa, respectively. Optimal hydrolytic activity of DamA toward d-Leu-pNA was observed at 50 °C and pH 8.0. The enzyme was stable up to 60 °C and from pH 4.0–11.0. DamA also exhibited aminolytic activity, producing d-Leu-d-Leu-NH2 from d-Leu-NH2 as a substrate. In the presence of 3.0 M NaCl, the amount of pNA liberated from d-Leu-pNA by DamA was 3.1-fold higher than that in the absence of NaCl. Thus, DamA is a halophilic enzyme. The enzyme was utilized to synthesize several hetero-dipeptides containing a d-amino acid at the N-terminus as well as physiologically active peptides. 相似文献
83.
An organocatalyst formed from a binaphthyl‐substituted diamine and trifluoromethanesulfonic acid exhibited unprecedented levels of exo selectivity in the Diels–Alder reaction of α,β‐unsaturated aldehydes with cyclopentadiene. A novel axially chiral diamine was also designed as an organocatalyst for an asymmetric variant of this reaction, in which the desired cycloadducts were formed with high diastereo‐ and enantioselectivities. The highest diastereoselectivity observed was greater than 20:1 in favor of the exo cycloadduct in the asymmetric Diels–Alder reaction of crotonaldehyde with cyclopentadiene. 相似文献
84.
Chiral quaternary ammonium salt-catalyzed diastereoselective aziridination of electron-deficient olefins that possess a chiral auxiliary with N-chloro-N-sodiocarbamates was developed. The key to high stereoselectivity was found to be the employment of the "matching" stereochemical combination of chiral auxiliary/ammonium salt. For example, when 3-phenyl-(4R,7S)-4-methyl-7-isopropyl-4,5,6,7-tetrahydroindazole (L-menthopyrazole) as a chiral auxiliary and a cinchonidine-derived chiral ammonium salt as a catalyst were applied to the reaction system, perfect diastereoselectivity was realized. Furthermore, the preparation of enantiomerically pure aziridines by removal of the chiral auxiliary was demonstrated. 相似文献
85.
Hosohama T Megumi K Terakawa S Nishimura J Iida Y Ban T Shioi A 《Langmuir : the ACS journal of surfaces and colloids》2011,27(23):14131-14142
An oil/water interface containing bis(2-ethylhexyl)phosphate and Ca(2+) or Fe(3+) exhibits spontaneous Marangoni instability associated with the fluctuation in interfacial tension. This instability rarely appears for oil/water systems with Mg(2+), Sr(2+), Ba(2+), Cu(2+), or Co(2+). The same ion selectivity is observed for n-heptane and nitrobenzene despite their significant differences in density, viscosity, and the dielectric constant of oil. We studied this instability under acidic pH conditions to avoid the neutralization reaction effects. The result of the equilibrium interfacial tension and the extraction ratio of cations indicates that a large number of oil-soluble complexes form at the interfaces of Ca(2+)-containing systems and probably for Fe(3+)-containing systems. The results obtained by oscillating drop tensiometry and Brewster angle microscopy indicate that desorption, rather than adsorption, is more significant to the onset of instability and that the resulting complex tends to form aggregates in the interface. This aggregation gives the nonlinear desorption rate of the oil-soluble complex. Then, exfoliation of the aggregating matter occurs, which triggers the Marangoni instability. The induced convection removes the oil-soluble complex accumulated at the interface, creating a renewed interface, which is necessary for the successive occurrence of the Marangoni instability. For the other cations, the oil-soluble compounds are insignificant, and they rarely form aggregates. In such cases, adsorption/desorption proceeds without instability. 相似文献
86.
Mitsuhiro Terakawa Yuto Tanaka Go Obara Tatsunori Sakano Minoru Obara 《Applied Physics A: Materials Science & Processing》2011,102(3):661-665
We investigate the dependence of the size parameter in the Mie scattering theory on the near-field enhanced Raman scattering
properties for high dielectric constant ZnO nanorods grown randomly by PLD (pulsed laser deposition). High Raman signals of
Rhodamine 6G (R6G) at 532 nm excitation wavelength were observed with nanorods of 400 nm average diameter. This experimental
result was explained theoretically by the size parameter described in the Mie scattering theory, not by surface plasmon polaritons.
This was also confirmed by the near-field distribution calculated by the FDTD (Finite-Difference Time Domain) method. The
ZnO nanorods with 400 nm average diameter can detect as low as 1 μM of R6G. This near-field enhancement factor is equivalent
to that with 10-nm-thick gold-coated ZnO nanorods (nanoshells) with an average core diameter of 100 nm. Controlling the diameter
of bare ZnO nanorods is effective for obtaining large enhancement factors without an additional process of gold thin film
coating on them. 相似文献
87.
Organic emitting compounds that are based on π‐conjugated skeletons have emerged as promising next‐generation materials for application in optoelectronic devices. In this Minireview, recent advances in the development of organic emitters that irradiate room‐temperature phosphorescence and/or thermally activated delayed fluorescence with extraordinary luminescence properties, such as aggregation‐induced emission, mechanochromic luminescence, and circularly polarized luminescence, are discussed. 相似文献
88.
Paola Zimmermann Crocomo Dr. Masato Okazaki Takumi Hosono Prof. Dr. Satoshi Minakata Prof. Dr. Youhei Takeda Prof. Dr. Przemyslaw Data 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202200826
Previous work has reported the synthesis of donor–acceptor–donor molecules based on dibenzophenazine acceptor group, presenting thermally activated delayed fluorescent (TADF) properties and their application in the assembly of highly efficient electroluminescent devices. Herein, we focus on the characterisation of charge carrier species through UV-Vis-NIR spectroelectrochemical and potentiostatic EPR techniques, in addition to the investigation of electropolymerisation properties of some compounds depicted in this study. The promising electrochromic features of both small molecules and conjugated polymers led to the assembly and investigation of electrochromic devices, evidencing the materials’ versatility, applied in such different approaches as electrochromic windows and electroluminescent devices. Furthermore, the assembled OLEDs provided high efficiencies, with small roll-off, EQEs up to 20.5 % and luminance values up to 85 000 cd/m2. 相似文献
89.
90.