全文获取类型
收费全文 | 1140篇 |
免费 | 84篇 |
国内免费 | 25篇 |
专业分类
化学 | 983篇 |
晶体学 | 8篇 |
力学 | 14篇 |
数学 | 90篇 |
物理学 | 154篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 46篇 |
2021年 | 49篇 |
2020年 | 77篇 |
2019年 | 75篇 |
2018年 | 107篇 |
2017年 | 76篇 |
2016年 | 80篇 |
2015年 | 57篇 |
2014年 | 90篇 |
2013年 | 119篇 |
2012年 | 98篇 |
2011年 | 77篇 |
2010年 | 55篇 |
2009年 | 45篇 |
2008年 | 57篇 |
2007年 | 43篇 |
2006年 | 19篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 12篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 1篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1249条查询结果,搜索用时 0 毫秒
101.
Younes Ghasemi Abdolali Mohagheghzadeh Zahra Ostovan Maryam Moshavash Sara Rasoul-Amini Mohammad Hossein Morowvat 《Chemistry of Natural Compounds》2010,46(5):734-737
Biotransformation of several monoterpene ketones, including carvone, pulegone, piperitone, menthone, and fenchone, was carried
out by the locally isolated unicellular microalgae Chlorella vulgaris. The microalgal strain was isolated during a screening program from soil samples collected from paddy-fields of Fars Province,
in the south of Iran. Chlorella vulgaris was cultured in 250 mL conical flasks, each containing 50 mL of BG-11 liquid medium and 20 μL levels of terpene substrates,
incubated at a temperature of 28±2°C and illuminated continuously with fluorescent lamps with shaking at 80 rpm. The metabolites
were identified by thin-layer chromatography and GC-MS. Chlorella vulgaris has the ability to reduce the C=C double bond of carvone to yield trans-dihydrocarvone and cis-dihydrocarvone. The cell line reduced menthone and pulegone to the same product and gave menthol. Study of Chlorella vulgaris with substrates of piperitone and fenchone showed no reaction in these substrates. Chlorella vulgaris MCCS 012 was assigned according to the 18S rRNA gene sequence. The DNA sequence of the 18S rRNA gene of Chlorella vulgaris MCCS 012 was recorded in the NCBI under the accession number EU374170. 相似文献
102.
In the present study a second-order calibration strategy for high performance liquid chromatography with diode-array detection (HPLC-DAD) has been developed using parallel factor analysis (PARAFAC) and has been applied for simultaneous determination of aflatoxins B1, B2, G1 and G2 in pistachio nuts in the presence of matrix interferences. Sample preparation was based on solvent extraction (SE) followed by solid phase extraction (SPE) on Bond Elut C18 cartridges. Since the sample preparation procedure was not selective to the analytes of interest, exploiting second-order advantage to obtain concentrations of individual analytes in the presence of uncalibrated interfering compounds seemed necessary. Appropriate pre-processing steps have been applied to correct background signals and the effect of retention time shifts. Transferred calibration data set obtained from standardization of solvent based calibration data has been used in prediction step. The results of PARAFAC on a set of spiked and naturally contaminated pistachio nuts indicated that the four aflatoxins could be successfully determined. The method was validated and multivariate analytical figures of merit were calculated. The advantages of the proposed method are using a low-cost SPE step relative to standard method of aflatoxin analysis (immune affinity column assay), a unique and simple isocratic elution program for all samples and a calibration transfer for saving both chemicals and time of analysis. This study show that coupling of SPE-HPLC-DAD with PARAFAC as a powerful second-order calibration method can be considered as an alternative method for resolution and quantification of aflatoxins in the presence of unknown interferences obtained through analysis of highly complex matrix of pistachio samples and cost per analysis can be reduced significantly. 相似文献
103.
Anglin EJ Salisbury C Bailey S Hor M Macardle P Fenech M Thissen H Voelcker NH 《Lab on a chip》2010,10(24):3413-3421
We report on surface-engineered microarrays that provide in situ cell sorting, localization, and immobilization of various subsets of human primary lymphocytes, followed by an on-chip bioassay for ionizing-radiation-induced cytogenetic damage. The microarray format eliminates the necessity of separating cell sub-populations by alternative means (such as fluorescence- or magnetic-activated cell sorting) prior to performing informational bioassays. To exemplify the potential of this on-chip cytometry approach, we have integrated the cytokinesis-block micronucleus cytome (CBMNcyt) assay with the microarray platform for analysis of the chromosome damage profile of specific subsets of human peripheral lymphocytes. Microarray results were compared with data obtained from the traditional CBMNcyt assay on heterogeneous lymphocyte populations, and with flow cytometry data. Our results suggest that cytogenetic damage caused by ionizing radiation is not uniformly distributed across all lymphocytes subsets, but rather concentrated in specific subsets. The salient features of our approach are that it requires very small volumes of reagents, allows sorting of lymphocyte subsets in situ, increases parallelism of cell assays and is amenable to high content microscopy analysis. The on-chip cytometry format opens new vistas for advanced cell-based assays, potentially bringing to light important information which remains hidden with conventional assays and hence engendering new discoveries in cell biology. 相似文献
104.
Maryam Ezoddin Farzaneh Shemirani Mohammad Reza Jamali 《Journal of Analytical Chemistry》2010,65(2):153-158
In this research, simple, rapid and efficient method, dispersive liquid-liquid microextraction (DLLME) combined fiber optic
-linear array detection spectrophotometry (FO-LADS) was developed using a cylindrical micro-cell for preconcentration and
determination of Cu(II) in samples. DLLME and FO-LADS methods have good matching conditions for being combined since FO-LADS
is a suitable method for the determination of analytes in low volume of the remained phase obtained after DLLME. Molar absorptivity
of complex Cu with (4-benzylp iperidineditiocarbamate potassium salt) (BPDC) was determined as 2.75 × 104 L mol-1 cm-1 at 7nmax = 436 nm. Under the optimum conditions the calibration graph was linear in the rage of 2–70 fug L-1 with detection limit of 0.34 fug L-1. The proposed procedure was successfully applied to the determination of Cu(II) in real water samples and human urine sample. 相似文献
105.
A selective and sensitive method for simultaneous determination of lead, zinc and copper by adsorptive differential pulse
cathodic stripping voltammetry is presented. The method is based on adsorptive accumulation of the complexes of Pb(II), Zn(II),
and Cu(II) ions with dopamine onto hanging mercury drop electrode (HMDE), followed by reduction of adsorbed species by differential
pulse cathodic stripping voltammetry. The effect of experimental parameters such as pH, dopamine concentration, accumulation
time and potential and scan rate were examined. Under the optimized conditions, linear calibration curves were established
for the concentration of Pb, Zn, and Cu in the ranges of 5–150, 5–250, and 1–150 ng/mL, respectively. Detection limits of
0.06, 0.25, and 0.04 ng/mL for Pb, Zn, and Cu were obtained. An application of the proposed method is reported for the determination
of these elements in some real samples such as natural waters and alloys. 相似文献
106.
Mozaffar Asadi Maryam Mohammadikish Khosro Mohammadi 《Central European Journal of Chemistry》2010,8(2):291-299
Four Schiff base ligands, salabza-H2 = N,N′-bis(salicylidene)-2-aminobenzylamine, were synthesized by condensation of one mole of 2-aminobenzylamine and two moles of
salicylaldehyde and/or two moles of substituted salicylaldehyde (5-OMe, 5-Br, 5-NO2). All the four Schiff bases and their Mn(II), Co(II), Cu(II) and Zn(II) complexes are characterized by UV-Vis, FT-IR, 1H NMR spectroscopy, mass spectrometry and elemental analysis. The formation constants and the Gibbs free energies were measured
spectrophotometrically for 1:1 complexes in methanol in constant ionic strength (I = 0.1 mol dm−3 NaClO4) and at 25°C. The data refinement was carried out with the SQUAD program. The trend of formation constants of H2L1 with M(II) follows the order: Mn(II) (3.97) < Zn(II) (4.30) < Co(II) (4.89) < Cu(II) (5.73) 相似文献
107.
Ester Sagristà Estelle Larsson Maryam Ezoddin Manuela Hidalgo Victòria Salvadó Jan Åke Jönsson 《Journal of chromatography. A》2010,1217(40):6153-6158
In this study, a three-phase hollow fiber liquid-phase microextraction (HF-LPME) method combined with liquid chromatography–mass spectrometry was developed for direct determination of four non-steroidal anti-inflammatory drugs (ketoprofen, naproxen, diclofenac and ibuprofen) in sewage sludge. The drugs were extracted from non-spiked and spiked slurry samples with different amounts of sludge into an organic phase and then back-extracted into an aqueous phase held in the lumen of the hollow fiber. High enrichment factors ranging from 2761 to 3254 in pure water were achieved. In sludge samples, repeatability and inter-day precision were tested with relative standard deviation values between 10–18% and 7–15%, respectively. Average concentrations of 29 ± 9, 138 ± 2, 39 ± 5 and 122 ± 7 ng/g were determined in dried sludge from Källby sewage treatment plant (Sweden) for ketoprofen, naproxen, diclofenac and ibuprofen, respectively. 相似文献
108.
109.
Effect of Copper Substitution and Preparation Methods on the LaMnO3 Structure and Catalysis of Methane Combustion and CO Oxidation 总被引:1,自引:0,他引:1
LaMn1-xCuxO3刡冊 perovskite oxides (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were prepared by two different methods, the Pechini and sol-gel methods. The catalysts were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray fluorescence spectroscopy, N2 adsorption, and temperature-programmed reduction. Their catalytic activity in the oxidation of methane and CO was evaluated. EDS and SEM results showed that the Pechini samples had more homogeneity and smaller particles (higher specific surface area). The catalytic activity for methane combustion was highest for x = 0.2. In CO oxidation, the oxides with x = 0.2 and x = 0.4 were the most active. The Pechini samples had higher activity and stability than the sol-gel samples. 相似文献
110.
Nanoplates of the three-dimensional coordination polymer, {[Cd(3)(3-pyc)(4)(N(3))(2)(H(2)O)](n) (1), 3-pyc(-)=pyridine-3-carboxylate), have been synthesized by a sonochemical process and characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy and elemental analyses. Cadmium(II) oxide nanoparticles were prepared from thermal decomposition in oleic acid and direct calcination of compound 1 at different temperatures. The thermal stability of nano-sized compound 1 was studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Results show that the size and morphology of the CdO nanoparticles are dependent upon the particles size of compound 1 and the thermolysis temperature. A decrease in the particle size of compound 1 leads to a decrease in the particle size of the CdO, while an increase in the processing temperature leads to an increase in the particle size of the produced cadmium(II) oxide nano-particles. 相似文献