全文获取类型
收费全文 | 236篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 199篇 |
力学 | 4篇 |
数学 | 30篇 |
物理学 | 21篇 |
出版年
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 11篇 |
2014年 | 5篇 |
2013年 | 16篇 |
2012年 | 10篇 |
2011年 | 20篇 |
2010年 | 17篇 |
2009年 | 13篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 16篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有254条查询结果,搜索用时 281 毫秒
91.
This contribution describes use of a separation method based on on-line coupling of a multisyringe flow system with a chromatographic
monolithic column for simultaneous determination of hydrochlorothiazide and losartan potassium in tablets. The system comprised
a multisyringe module, three low-pressure solenoid valves, a monolithic C18 column (25 mm × 4.6 mm i.d.), and a diode-array detector. The mobile phase was 10 mmol L−1 potassium dihydrogen phosphate (pH 3.1)-acetonitrile-methanol (65:33:2 v/v/v) at a flow rate 0.8 mL min−1. UV detection was carried out at 226 nm. The multi-syringe chromatographic (MSC) method with UV spectrophotometric detection
was optimized and validated. Results from validation were very good. The analysis time was about 400 s. The method was found
to be applicable to routine analysis of both compounds in tablets. The coupling of the monolithic columns with a multi-syringe
flow-injection analysis manifold provides an excellent and inexpensive tool to solve the separation problems without use of
HPLC instrumentation. 相似文献
92.
Montserrat Mancera-Arteu Estela GiménezJosé Barbosa Victòria Sanz-Nebot 《Analytica chimica acta》2016
In this study, a ZIC-HILIC-MS methodology for the analysis of N-glycan isomers was optimized to obtain greater detection sensitivity and thus identify more glycan structures in hAGP. In a second step, this method was combined with glycan reductive isotope labelling (GRIL) through [12C6]/[13C6]-aniline and exoglycosidase digestion to characterize the different glycan isomers. The GRIL method allows the peak areas resulting from two different labelled samples to be compared, since neither retention time shifts nor variations in the ionization of glycans between these samples are obtained. First, sialic acid linkage assignations were performed for most hAGP glycan isomers with α2-3 sialidase digestion. Bi-, tri- and tetraantennary glycan isomers with different terminal sialic acid linkages to galactose (α2-3 or α2-6) were assigned, and the potential of this technique for the structural characterization of isobaric isomers was therefore demonstrated. Furthermore, fucose linkage isomers of hAGP glycans were also characterized using this isotope-labelling approach in combination with α1-3,4 fucosidase and β1-4 galactosidase digestion. α1-3 antennary fucoses and α1-6 core fucosylation were detected in hAGP fucosylated glycans. These established methodologies can be extremely useful for patho-glycomic studies to characterize glycoproteins of biomedical interest and find novel glycan isomers that could be used as biomarkers in cancer research. 相似文献
93.
In this paper, a flow-through optosensor based on diffuse reflectance spectroscopy and multivariate regression modelling is proposed for simultaneous multiresidue determination of trace level concentrations of nitro-substituted phenols. The optrode integrates on-line anion-exchange sorptive preconcentration and matrix removal with direct detection of sorbed species onto the sensing layer and chemometric deconvolution of overlapped spectra. After recording of the reflectometric spectrum, fast chemosensor regeneration is accomplished with an acidic methanolic eluent followed by a metered volume of alkaline solution. The full automation of the analytical procedure is ensured by flow-programming as executed via a software-controlled multisyringe pump and a set of multiposition and solenoid valves.
Under the optimized chemical and physical variables, the 3σblank detection limits for 2-, and 4-nitrophenol and 2,4-dinitrophenol were 0.69, 0.42 and 0.37 μg L−1, respectively, for a sample loading volume of 4.0 mL with enrichment factors of 73, 74 and 81, respectively, and repeatability better than 3.0%. The analytical applicability of the optosensing system was asserted by the satisfactory results attained in its application to monitoring of nitrophenol derivatives in spiked environmental waters including highly saline matrices via the standard additions method. 相似文献
94.
Carmona-Novillo E Bartolomei M Hernández MI Campos-Martínez J 《The Journal of chemical physics》2007,126(12):124315
Quasiclassical trajectory calculations have been carried out for H(2)(v(1)=high)+H(2)(v(2)=low) collisions within a three degrees of freedom model where five different geometries of the colliding complex were considered. Within this approach, probabilities for different competitive processes are studied: four center reaction, collision induced dissociation, reactive dissociation, and three-body complex formation. The purpose is to compare in detail with equivalent quantum-mechanical wave packet calculations [Bartolomei et al., J. Chem. Phys 122, 064305 (2005)], especially the behavior of the probabilities near reaction thresholds. Quasiclassical calculations compare quite well with the quantum-mechanical ones for collision induced dissociation as well as for the four center reaction, although quantum effects become very important near thresholds, particularly for lower v(1)'s and for the four center process. Less quantitative agreement is found for reactive dissociation and three-body complex formation. It is found that most quantum effects are due to differences between quantum and classical vibrational distributions of H(2)(v(1)=high). Zero point energy violation has been found in the classical reactive-dissociative probabilities. Extension of these findings to full-dimensional treatments is examined. 相似文献
95.
Francisco Javier García-Fernndez Alba Estela García-Fernndez Ichiro Ikuta Eduardo Nava Julian Solis García del Pozo Joaquin Jordan Maria F. Galindo 《Molecules (Basel, Switzerland)》2021,26(4)
Dimethyl fumarate is a cytoprotective and immunomodulatory drug used in the treatment of multiple sclerosis. We performed a bibliometric study examining the characteristics and trends of the top 100 cited articles that include dimethyl fumarate in the title. On 21 September 2020 we carried out an electronic search in the Web of Science (WOS), seeking articles that include the following terms within the title: dimethyl fumarate, BG-12, or Tecfidera. To focus our investigation on original research, we refined the search to include only articles, early access, others, case report, and clinical trials. We obtained a total of 1115 items, which were cited 7169 times, had a citation density of 6.43 citations/item, and an h-index of 40. Around 2010, there was a jump in the number of published articles per year, rising from 5 articles/year up to 12 articles/year. We sorted all the items by the number of citations and selected the top 100 most cited (T100). The T100 had 4164 citations, with a density of 37 citations/year and contained 16 classic research articles. They were published between 1961 and 2018; the years 2010–2018 amassed nearly 80% of the T100. We noted 17 research areas with articles in the T100. Of these, the number one ranking went to neurosciences/neurology with 39 articles, and chemistry ranked second on the T100 list with 14 items. We noticed that the percentage of articles belonging to different journals changed depending on the time period. Chemistry held the highest number of papers during 1961–2000, while pharmacology andneurosciences/neurology led the 2001–2018 interval. A total of 478 authors from 145 institutions and 25 countries were included in the T100 ranking. The paper by Gold R et al. was the most successful with 14 articles, 1.823 citations and a density of 140.23 citations/year. The biotechnological company Biogen led the T100 list with 20 articles. With 59 published articles, the USA was the leading country in publications. We concluded that this study analyzed the use of and research on dimethyl fumarate from a different perspective, which will allow the readership (expert or not) to understand the relevance of classic and recent literature on this topic. 相似文献
96.
Miranda Paulo H. de S. Lourenço Estela M. G. Morais Alexander M. S. de Oliveira Pedro I. C. Silverio Priscilla S. de S. N. Jordão Alessandro K. Barbosa Euzébio G. 《Molecular diversity》2021,25(1):1-12
Molecular Diversity - Tuberculosis, caused by Mycobacterium tuberculosis (M. tuberculosis), is still responsible for a large number of fatal cases, especially in developing countries with alarming... 相似文献
97.
Hernández D Vilar G Riego E Cañedo LM Cuevas C Albericio F Alvarez M 《Organic letters》2007,9(5):809-811
[structure: see text] An efficient and versatile convergent synthesis of IB-01211 based on a combination of peptide and heterocyclic chemistry is described. The key step in the synthesis is macrocyclization through intramolecular Hantzsch formation of the thiazole ring. Dehydration of a free primary alcohol to furnish the exocyclic methylidene present in the natural product was applied during the macrocyclization. 相似文献
98.
Pereira RM Andrades NE Paulino N Sawaya AC Eberlin MN Marcucci MC Favero GM Novak EM Bydlowski SP 《Molecules (Basel, Switzerland)》2007,12(7):1352-1366
The antioxidant activity of flavonoids is believed to increase when they are coordinated with transition metal ions. However, the literature on this subject is contradictory and the outcome seems to largely depend on the experimental conditions. In order to understand the contribution of the metal coordination and the type of interaction between a flavonoid and the metal ion, in this study a new metal complex of Cu (II) with naringin was synthesized and characterized by FT-IR, UV-VIS, mass spectrometry (ESI-MS/MS), elemental analysis and 1H-NMR. The results of these analyses indicate that the complex has a Cu (II) ion coordinated via positions 4 and 5 of the flavonoid. The antioxidant, anti-inflammatory and antimicrobial activities of this complex were studied and compared with the activity of free naringin. The Naringin-Cu (II) complex 1 showed higher antioxidant, anti-inflammatory and tumor cell cytotoxicity activities than free naringin without reducing cell viability. 相似文献
99.
Study of immobilized metal affinity chromatography sorbents for the analysis of peptides by on‐line solid‐phase extraction capillary electrophoresis‐mass spectrometry
下载免费PDF全文
![点击此处可从《Electrophoresis》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Lorena Ortiz‐Martin Fernando Benavente Silvia Medina‐Casanellas Estela Giménez Victoria Sanz‐Nebot 《Electrophoresis》2015,36(6):962-970
Several commercial immobilized metal affinity chromatography sorbents were evaluated in this study for the analysis of two small peptide fragments of the amyloid β‐protein (Aβ) (Aβ(1–15) and Aβ(10–20) peptides) by on‐line immobilized metal affinity SPE‐CE (IMA‐SPE‐CE). The performance of a nickel metal ion (Ni(II)) sorbent based on nitrilotriacetic acid as a chelating agent was significantly better than two copper metal ion (Cu(II)) sorbents based on iminodiacetic acid. A BGE of 25 mM phosphate (pH 7.4) and an eluent of 50 mM imidazole (in BGE) yielded a 25‐fold and 5‐fold decrease in the LODs by IMA‐SPE‐CE‐UV for Aβ(1–15) and Aβ(10–20) peptides (0.1 and 0.5 μg/mL, respectively) with regard to CE‐UV (2.5 μg/mL for both peptides). The phosphate BGE was also used in IMA‐SPE‐CE‐MS, but the eluent needed to be substituted by a 0.5% HAc v/v solution. Under optimum preconcentration and detection conditions, reproducibility of peak areas and migration times was acceptable (23.2 and 12.0%RSD, respectively). The method was more sensitive for Aβ(10–20) peptide, which could be detected until 0.25 μg/mL. Linearity for Aβ(10–20) peptide was good in a narrow concentration range (0.25–2.5 μg/mL, R2 = 0.93). Lastly, the potential of the optimized Ni(II)‐IMA‐SPE‐CE‐MS method for the analysis of amyloid peptides in biological fluids was evaluated by analyzing spiked plasma and serum samples. 相似文献
100.
Albert Barroso Estela GiménezFernando Benavente José BarbosaVictoria Sanz-Nebot 《Analytica chimica acta》2015
In this study, the classical semiempirical relationships between the electrophoretic mobility and the charge-to-mass ratio (me vs. q/Mα) were used to model the migration behaviour of peptides and glycopeptides originated from the digestion of recombinant human erythropoietin (rhEPO), a biologically and therapeutically relevant glycoprotein. The Stoke’s law (α = 1/3), the classical polymer model (α = 1/2) and the Offord’s surface law (α = 2/3) were evaluated to predict migration of peptides and glycopeptides, with and without sialic acids (SiA), in rhEPO digested with trypsin and trypsin–neuraminidase. The Stoke’s law resulted in better correlations for the set of peptides used to evaluate the models, while glycopeptides fitted better with the classical polymer model. Once predicted migration times with both models, it was easy to simulate their separation electropherogram. Results were later validated predicting migration and simulating separation of a different set of rhEPO glycopeptides and also human transferrin (Tf) peptides and glycopeptides. The excellent agreement between the experimental and the simulated electropherograms with rhEPO and Tf digests confirmed the potential applicability of this simple strategy to predict, in general, the peptide–glycopeptide electrophoretic map of any digested glycoprotein. 相似文献