全文获取类型
收费全文 | 592篇 |
免费 | 25篇 |
国内免费 | 2篇 |
专业分类
化学 | 391篇 |
晶体学 | 4篇 |
力学 | 33篇 |
数学 | 101篇 |
物理学 | 90篇 |
出版年
2023年 | 4篇 |
2022年 | 11篇 |
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 30篇 |
2015年 | 18篇 |
2014年 | 17篇 |
2013年 | 19篇 |
2012年 | 28篇 |
2011年 | 38篇 |
2010年 | 34篇 |
2009年 | 23篇 |
2008年 | 43篇 |
2007年 | 42篇 |
2006年 | 37篇 |
2005年 | 29篇 |
2004年 | 31篇 |
2003年 | 17篇 |
2002年 | 14篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 6篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1928年 | 1篇 |
排序方式: 共有619条查询结果,搜索用时 31 毫秒
81.
82.
Elisiane C. Reis Mônica Almeida Juliana C. Cardoso Maysa de A. Pereira César B.Z. de Oliveira Emanuella M. Venceslau Janice I. Druzian Rosa Mariano Francine F. Padilha 《Macromolecular Symposia》2010,296(1):347-353
The future supplies and usage of glycerol are expected to increase as biodiesel plants increase production, and the output will greatly outpace demand. Biodiesel production has already had a significant impact on the price of refined glycerol. A major concern of glycerol producers is the reduced price of glycerol resulting from the increased production of biodiesel. Some alternative uses for this glycerol that have been investigated are substrates for fermentation process or the production of biosurfactants, fatty acids, biopolymers, and others products. This work had as objective to evaluate two strains of Xanthomonas sp isolate from Brazil for xanthan gum in orbital agitator, analizing the apparent viscosity of aqueous solutions and selecting viscosity. The experiments of xanthan gum production were realized in orbital agitator with 120 rpm agitation, for cells production, and 180rpm, for biopolymer production, under a 28 °C temperature. The rheology of the fermentation broth was analyzed by apparent viscosity and the polymer was recovered with ethanol (1:3, v/v). After its recovery, the productivity evaluation was performed. The productivity were 0.157 and 0.363 gL−1 for C1 and 0.186 and 0.363 gL−1 for C9 to media glycerol or glycerol and sucrose, respectively. The viscosity analysis was performed for aqueous solutions 3%, at 25 °C, the best apparent viscosity was obtained using gum synthesized with glycerol and sucrose (50:50) at 25 °C, 143 mPa.s−1 from Xanthomonas sp C1. 相似文献
83.
84.
We present results about minimization of convex functionals defined over a finite set of vectors in a finite-dimensional Hilbert
space, that extend several known results for the Benedetto-Fickus frame potential. Our approach depends on majorization techniques.
We also consider some perturbation problems, where a positive perturbation of the frame operator of a set of vectors is realized
as the frame operator of a set of vectors which is close to the original one. 相似文献
85.
Bisconti Luca Mariano Paolo Maria 《Journal of Optimization Theory and Applications》2022,193(1-3):737-759
Journal of Optimization Theory and Applications - We describe the dynamics of fluids with scattered polymer chains through a multi-field model accounting for weakly non-local inertia and... 相似文献
86.
Carla Maria Mariano Fernandez Maurício Ferreira da Rosa Ana Claudia Aparecida Mariano Fernandez Wanessa de Campos Bortolucci Fabiana Borges Padilha Ferreira Giani Andrea Linde 《Natural product research》2020,34(5):731-735
AbstractThis study, was to evaluate the acaricidal effect of the essential oil (EO) and fractions (FR) obtained from Laurus nobilis leaves on Rhipicephalus (Boophilus) microplus. Eight fractions were obtained, however FR1: sabinene (37.83%), β-pinene (13.50%), 1,8-cineole (12.66%), α-pinene (12.56%) and FR8: α-terpineol (79.19%) were highlighted as to the larvicidal potential when submitted by Larval Packet Test. The EO was tested by the Adult Immersion Test, at concentrations of 200.00; 100.00 and 50.00?µL/mL caused mortality of engorged females, egg mass reduction and hatching inhibition. Two fractions are shown to be efficient in controlling larvae FR8 (LC50?=?0.13?µL/mL, LC99?=?0.51?µL/mL) and FR1 (LC50?=?0.20?µL/mL, LC99?=?0.56?µL/mL). The fractionation of EO was determinant to elucidate which compounds were responsible for the larvicidal potential. This study opens new perspectives to direct new bioassays with the compounds obtained in the fractionation, since they present high potential on cattle tick larvae. 相似文献
87.
88.
The sensing of a chemical environment is achieved mainly in the surface by interactions of the sensor material with its chemical surroundings. Therefore, porous structure control is key in developing good chemical sensors. The aim of this work was to obtain materials of tailored porosity to be used as support matrix for optical chemical sensors. We studied the simultaneous effect of pH, temperature, ethanol:TEOS, and water:TEOS molar ratios on gelation time, and textural and structural properties. We used a 24 factorial design that evaluates the effect of each independent variable and their interactions. Samples were characterized by XRD, SEM, FTIR, and gas adsorption (N2 at 77 K and CO2 at 273 K). The gelation time decreased with increasing temperature, water:TEOS molar ratio, and pH; and with decreasing ethanol:TEOS molar ratios. Synthesis conditions also affected the xerogels porous textures. Xerogels obtained at pH 2.5 were ultramicroporous. In general, samples synthesized at pH 4.5 and ethanol:TEOS molar ratio of 2.25:1 were mesoporous, but the material is not appropriate for use as support in fiber optical sensors. 相似文献
89.
Bizzarri M Cavaliere C Foglia P Guarino C Samperi R Laganà A 《Analytical and bioanalytical chemistry》2008,391(5):1969-1976
A label-free absolute quantitation method based on matrix-assisted laser desorption/ionization time-of-flight mass spectrometry
(MALDI-TOF MS) has been developed. This methodology was applied to mouse heart in order to quantify cardiac troponin T (cTnT),
which is considered to be a sensitive marker of heart damage. The cTnT was extracted, isolated by reversed-phase high-performance
liquid chromatography, digested, and analyzed by MALDI-TOF MS. The MS-based quantitation was performed using matrix-matched
calibration curves (due to a matrix effect) of two synthetic peptides, one cTnT-specific peptide and one internal standard
peptide, respectively. Recoveries at three spiking levels ranged from 87–96%, with relative standard deviations of below 10%.
The method detection limit and the method quantitation limit, expressed as the amount of cTnT for the amount of total sarcomeric
protein extract, were 0.03 mg g−1 and 0.15 mg g−1, respectively. This method appears to be accurate and generally suitable for improving absolute protein quantitation. 相似文献
90.
Skabara PJ Pozo-Gonzalo C Lardiés Miazza N Laguna M Cerrada E Luquin A González B Coles SJ Hursthouse MB Harrington RW Clegg W 《Dalton transactions (Cambridge, England : 2003)》2008,(23):3070-3079
A series of new metal (M) dithiolene complexes bearing terthiophene (3, 12, M = Ni; 4, M = Pd; 5, 6, M = Au) and 2,5-bis(para-methoxyphenyl)thiophene units (14, M = Ni; 15, 16, M = Au; 17, M = Pd) have been synthesised in 38-99% yield. The electrochemical properties of the materials have been characterised by cyclic voltammetry and UV-vis spectroelectrochemistry. The nickel complexes possess low oxidation potentials (-0.12 to -0.25 V vs Ag/AgCl) due to the electron-rich dithiolene centres and all complexes display ligand-based redox activity. The terthiophene derivatives have been polymerised by electrochemical oxidation to give stable films with, in the case of poly(3), broad absorption characteristics. Charge transfer materials have been isolated from 14 and 16 with conductivities in the range 9 x 10(-6) to 7 x 10(-8) S cm(-1). 相似文献