全文获取类型
收费全文 | 347篇 |
免费 | 19篇 |
专业分类
化学 | 239篇 |
晶体学 | 5篇 |
力学 | 6篇 |
数学 | 53篇 |
物理学 | 63篇 |
出版年
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 18篇 |
2019年 | 24篇 |
2018年 | 10篇 |
2017年 | 14篇 |
2016年 | 25篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 46篇 |
2012年 | 24篇 |
2011年 | 36篇 |
2010年 | 16篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 3篇 |
2002年 | 6篇 |
2001年 | 1篇 |
1998年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1982年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有366条查询结果,搜索用时 437 毫秒
81.
82.
The essential oils (EOs) obtained by solvent-free microwave extraction (SFME) and hydrodistillation (HD) from endemic Origanum husnucanbaseri H. Duman, Aytac & A. Duran were investigated using the gas chromatography-mass spectrometry system. The main constituents of both oils obtained from SFME and HD from O. husnucanbaseri are borneol (15.2-12.8%), α-terpineol (12.3-10.8%) and trans-sabinene hydrate (11.8-9.92%). The EO obtained from SFME contained substantially higher amounts of oxygenated compounds and lower amounts of monoterpenes than that from HD. The antibacterial activities of the EOs from SFME and HD were evaluated by the disc diffusion method against six bacterial strains. The EO extracted by SFME was more effective than the EO extracted by HD against the tested bacteria, except for Klebsiella pneumoniae American type culture collection (ATCC) 13883. Streptococcus pyogenes ATCC 19615 and Staphylococcus aureus ATCC 25923 in particular were more sensitive against the EO extracted by SFME. 相似文献
83.
We report a detailed analysis of the potential energy surface of N-acetyl-l-tryptophan-N-methylamide, (NATMA) both in the gas phase and in solution. The minima are identified using the density-functional-theory (DFT) with the 6-31g(d) basis set. The full potential energy surface in terms of torsional angles is spanned starting from various initial configurations. We were able to locate 77 distinct L-minima. The calculated energy maps correspond to the intrinsic conformational propensities of the individual NATMA molecule. We show that these conformations are essentially similar to the conformations of tryptophan in native proteins. For this reason, we compare the results of DFT calculations in the gas and solution phases with native state conformations of tryptophan obtained from a protein library. In native proteins, tryptophan conformations have strong preferences for the beta sheet, right-handed helix, tight turn, and bridge structures. The conformations calculated by DFT, the solution-phase results in particular, for the single tryptophan residue are in agreement with native state values obtained from the Protein Data Bank. 相似文献
84.
Fraley AW Pons B Dalkara D Nullans G Behr JP Zuber G 《Journal of the American Chemical Society》2006,128(33):10763-10771
Oligonucleotide delivery is a crucial issue for therapeutical purposes and is often addressed by conjugation to short cationic peptides although with controversial results. To further examine this mechanism, a 15-mer anionic oligonucleotide was conjugated to a cationic peptide in order to obtain a diblock compound with an overall positive charge with aggregation properties. These microaggregates were efficiently internalized in cells via the expeditious pathway used by commercial gene delivery systems. Moreover, stability of the duplex formed with the complementary sequence increased without inhibiting oligonucleotide enzyme recognition as shown by the properties of the conjugate to prime chain elongation by Taq DNA polymerase in a linear amplification/sequencing process. 相似文献
85.
86.
87.
Synthesis of two-component organogelation system was performed very easy and concise manner from Nε-palmitoyl-L-lysine ethyl ester and Nε-miristoyl-L-lysine ethyl ester in which they were used as base component and N-lauroyl-L-amino acids (amino acids:, alanine, leucine and phenylalanine as acid components.). And their organogelation properties were examined in different pharmaceutical fluids such as liquid paraffin, fatty acid ethyl, and isopropyl esters. In this way, gelation efficiency was ascertained variations of alkanoyl moieties and combination of different amino acids in the gelator structures. Characterization of gelators was performed via thermal measurement such as Tg and gel–sol enthalpy change; SEM and FTIR as optical methods. 相似文献
88.
89.
Electrochemically aided solid phase microextraction: conducting polymer film material applicable for cationic analytes 总被引:1,自引:0,他引:1
Khalid R. Temsamani Özcan Ceylan Brian J. Yates Serhan Öztemiz Thompson P. Gbatu Apryll M. Stalcup Harry B. Mark Wlodzimierz Kutner 《Journal of Solid State Electrochemistry》2002,6(7):494-497
The cation uptake and release properties of a poly(pyrrole-sulfated β-cyclodextrin) (PPy-SβCD) film electrode have been investigated
under both open circuit and controlled potential conditions for prospective applications in electrochemically aided solid-phase
microextraction (EA SPME). The EDAX and ion chromatography results show that the K+ and Na+ cation uptake is enhanced if a small negative potential is applied to the electrode in the range where PPy is in its neutral
form. These cations are released rapidly from the film if the applied potential is switched to the value at which PPy is converted
to its positively charged form, i.e., oxidized state. The cation ingress and egress mechanism is affected both by the cation
exchange at the negative sulfate moiety on the cyclodextrin sites and electrostatic interactions generated by the applied
potential. The electrochemical "switching" capability increases the speed of the cation uptake and release, presumably due
to electro migration, as compared to the open circuit ion exchange which is controlled solely by diffusion. Our preliminary
fundamental results show that the PPy-SβCD film is suitable for the future design of EA SPME devices.
Electronic Publication 相似文献
90.
Reaction of 1-phenylcyclooctene and 1-phenylcycloheptene with N-bromosuccinimide (NBS) in aqueous DMSO gives the corresponding 3-bromo-2-phenylcycloalkenes and 2-phenylcycloalk-2-enols
in a ratio of 3 : 1. Unlike them, 1-phenylcyclohexene gives a mixture of 3-bromo-2-phenylcyclohexene and 2-bromo-l-phenylcyclohexanol.
The oxidation of allylic alcohols with pyridinium chlorochromate afforded the corresponding α,β-unsaturated ketones. 相似文献