全文获取类型
收费全文 | 469篇 |
免费 | 19篇 |
国内免费 | 2篇 |
专业分类
化学 | 337篇 |
晶体学 | 1篇 |
力学 | 16篇 |
数学 | 72篇 |
物理学 | 64篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 16篇 |
2021年 | 19篇 |
2020年 | 10篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 8篇 |
2016年 | 23篇 |
2015年 | 22篇 |
2014年 | 17篇 |
2013年 | 38篇 |
2012年 | 35篇 |
2011年 | 54篇 |
2010年 | 27篇 |
2009年 | 28篇 |
2008年 | 29篇 |
2007年 | 25篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 11篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 5篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1983年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有490条查询结果,搜索用时 15 毫秒
31.
Leandro M. de Carvalho Mariele Martini Solange C. Garcia Denise Bohrer 《Microchemical Journal》2010,96(1):114-7376
In this work, a method for simultaneous determination of amfepramone, fenproporex, sibutramine and fluoxetine was developed by capillary zone electrophoresis with capacitively coupled contactless conductivity detection (C4D) using a homemade capillary electrophoretic system. The optimized conditions for the separation of the pharmaceuticals by CZE were as follows: 50 mmol L− 1 phosphate buffer (pH 5.0) in 50/50 (v/v) mixture of water/acetonitrile as the working electrolyte, 15 kV separation voltage, 25 °C separation temperature, hydrodynamic injection by gravity using 20 cm injection height and 60 s injection time. The detection by C4D was carried out by using a homemade detector, which employs a sinusoidal wave generator operating at 600 kHz frequency and 2 Vpp wave amplitude. The optimized and validated CZE-C4D method was applied for the determination of the studied pharmaceuticals as adulterants in phytotherapeutic formulations commercialized in Brazil for slimming purposes. 相似文献
32.
Vicenţiu D. Rădulescu Gelson C. G. dos Santos Leandro S. Tavares 《Mathematische Nachrichten》2023,296(6):2555-2574
This paper is concerned with the existence and multiplicity of solutions for a class of problems involving the Φ-Laplacian operator with general assumptions on the nonlinearities, which include both semipositone cases and critical concave convex problems. The research is based on the subsupersolution technique combined with a truncation argument and an application of the Mountain Pass Theorem. The results in this paper improve and complement some recent contributions to this field. 相似文献
33.
Santiago PS Neto Dde S Barbosa LR Itri R Tabak M 《Journal of colloid and interface science》2007,316(2):730-740
Small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been used to investigate the interaction of the water-soluble meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS(4)) with cationic cethyltrimethylammonium chloride (CTAC) micelles. To evaluate if the porphyrin protonation state affects its interaction with the micelle, both SAXS and EPR measurements were performed at pH 4.0 and 9.0. The best-fit SAXS curves were obtained assuming for CTAC micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS(4). SAXS results show that the presence of porphyrin impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. Lineshapes of EPR spectra of 5- and 16-doxyl stearic acids (5- and 16-DSA, respectively) bound to 100 mM CTAC micelles exhibited slight changes as a function of porphyrin concentration. Spectral simulations revealed an increase of mobility restriction for both spin probes, especially at higher porphyrin concentration, where a small reduction of environment polarity was also observed for 16-DSA. The spin labels monitored only slight differences between pH 4.0 and 9.0, in agreement with the SAXS results. 相似文献
34.
Pedroso MP Ferreira EC Hantao LW Bogusz S Augusto F 《Journal of separation science》2011,34(13):1547-1554
Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications. 相似文献
35.
Jan Janczak Mayura M. M. Rubinger Leandro C. Alves Marcelo R. L. Oliveira 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(11):m312-m316
The rigid organic linkers N‐(4‐bromophenylsulfonyl)dithiocarbimate(2−) and N‐(4‐iodophenylsulfonyl)dithiocarbimate(2−) crystallize with two potassium cations and two water molecules in their asymmetric units, forming the title coordination polymers, [K2(C7H4BrNO2S3)(H2O)2]n and [K2(C7H4INO2S3)(H2O)2]n. The anions and the water molecules link the potassium cations into broad two‐dimensional networks, which are further linked by K...halide interactions. 相似文献
36.
Puebla P Oshima-Franco Y Franco LM Santos MG Silva RV Rubem-Mauro L Feliciano AS 《Molecules (Basel, Switzerland)》2010,15(11):8193-8204
The effect of four sub-extracts prepared from the lyophilized hydroalcoholic bark of Dipteryx alata (Leguminosae-Papilionoideae) dissolved in a methanol-water (80:20) mixture through a liquid-liquid partition procedure has been investigated against the neuromuscular blockade of the venom of the snake Bothrops jararacussu. The active CH?Cl? sub-extract has been extensively analyzed for its chemical constituents, resulting in the isolation of four lupane-type triterpenoids: lupeol, lupenone, 28-hydroxylup-20(29)-en-3-one, betulin, nine isoflavonoids: 8-O-methylretusin, 7-hydroxy-5,6,4'-trimethoxyisoflavone, afrormosin, 7-hydroxy-8,3',4'-trimethoxyisoflavone, 7,3'-dihydroxy-8,4'-dimethoxyisoflavone, odoratin, 7,8,3'-trihydroxy-4'-methoxyisoflavone, 7,8,3'-trihydroxy-6,4'-dimethoxyisoflavone, dipteryxin, one chalcone: isoliquiritigenin, one aurone: sulfuretin and three phenolic compounds: vanillic acid, vanillin, and protocatechuic acid. Their chemical structures were elucidated on the basis of spectroscopic analysis, including HRMS, 1D- and 2D-NMR techniques. 相似文献
37.
Mayara Cristina Mombach Lorenz Leandro Silva de Almeida Ana Paula de Oliveira Lopes Inacio Flávio Manoel Rodrigues da Silva Júnior Eliézer Quadro Oreste Daiane Dias 《Electroanalysis》2023,35(7):e202200354
Nowadays, carbon-based materials applied to the development of chemically modified sensors have been highlighted once they can generate methods with high sensitivity, stability, conductivity, accuracy and low cost. Hence, these sensors have been used in environmental monitoring in aneco-friendlyy, sensitive, fast, efficient, inexpensive and robust way. In this review, firstly we described about carbon-based materials and their derivatives, followed by the chemically modified carbon-based sensors manufacturing overview and their applications in environmental analytical chemistry related to inorganic and organic compounds determinations. Future perspectives on trends of the carbon-based materials applications in the sensor modifications are also described. 相似文献
38.
39.
40.
Jorge AmimJr. Leandro S. Blachechen Denise F. S. Petri 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1259-1265
Thermal behavior of mixtures composed of cellulose acetate butyrate (CAB), carboxymethylcellulose acetate butyrate (CMCAB),
or cellulose acetate phthalate (CAPh), and sorbitan-based surfactants was investigated as a function of mixture composition
by means of differential scanning calorimetry (DSC). Surfactants with three different alkyl chain lengths, namely, polyoxyethylenesorbitan
monolaurate (Tween 20), polyoxyethylenesorbitan monopalmitate (Tween 40), and polyoxyethylene sorbitan monostearate (Tween
60) were chosen. DSC measurements revealed that Tween 20, 40, and 60 act as plasticizers for CAB, CMCAB, and CAPh (except
for Tween 60), leading to a dramatic reduction of glass transition temperature (T
g). The dependence of experimental T
g values on the mixture composition was compared with theoretical predictions using the Fox equation. Plasticization was strongly
dependent on mixture composition, surfactant hydrophobic chain length, and type of cellulose ester functional group. 相似文献