全文获取类型
收费全文 | 156篇 |
免费 | 2篇 |
专业分类
化学 | 116篇 |
力学 | 7篇 |
数学 | 21篇 |
物理学 | 14篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 5篇 |
2011年 | 10篇 |
2010年 | 2篇 |
2009年 | 5篇 |
2008年 | 7篇 |
2006年 | 5篇 |
2005年 | 3篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1980年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有158条查询结果,搜索用时 187 毫秒
1.
El-Shazly RM Al-Hazmi GA Ghazy SE El-Shahawi MS El-Asmy AA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(1-2):243-252
Several complexes of thiosemicarbazone derivatives with Ni(II) have been prepared. Structural investigation of the ligands and their complexes has been made based on elemental analysis, magnetic moment, spectral (UV-Vis, i.r., (1)H NMR, ms), and thermal studies. The i.r. spectra suggest the bidentate mononegative and tridentate (neutral, mono-, and binegative) behavior of the ligands. Different stereochemistries were suggested for the isolated complexes. The thermogravimetry (TG) and derivative thermogravimetry (DTG) have been used to study the thermal decomposition and kinetic parameters of some ligands and complexes using the Coats-Redfern and Horowitz-Metzger equations. The redox properties and stability of the complexes toward oxidation waves explored by cyclic voltammetry are related to the electron withdrawing or releasing ability of the substituent of thiosemicarbazone moiety. The samples displayed Ni(II)/Ni(I) couples irreversible waves associated with Ni(III)/Ni(II) process. 相似文献
2.
A first-derivative spectrophotometric (1D) method and a derivative-ratio zero-crossing spectrophotometric (1DD) method were used to determine pyritinol dihydrochloride (I) in the presence of its precursor (II) and its degradation product (III) with 0.1N hydrochloric acid as a solvent. Linear relationships were obtained in the ranges of 6-22 microg/mL for the (1D) method and 6-20 microg/mL for the (1DD) method. By applying the proposed methods, it was possible to determine pyritinol dihydrochloride in its pure powdered form with an accuracy of 100.36 +/- 1.497% (n = 9) for the (1D) method and an accuracy of 99.92 +/- 1.172% (n = 8) for the (1DD) method. Laboratory-prepared mixtures containing different ratios of (I), (II), and (III) were analyzed, and the proposed methods were valid for concentrations of < or = 10% (II) and < or = 50% (III). The proposed methods were validated and found to be suitable as stability-indicating assay methods for pyritinol in pharmaceutical formulations. 相似文献
3.
A simple, reliable and selective high-performance liquid chromatographic method for the determination of metoclopramide hydrochloride in pharmaceutical dosage forms has been developed and evaluated. The drug and the internal standard (phenobarbitone) were eluted from a 5-micron C8 reversed-phase column at ambient temperature with a mobile phase consisting of phosphate buffer (10 mM)-methanol-acetonitrile (50 + 28 + 22) adjusted to pH 4.8 with orthophosphoric acid. The mobile phase was pumped at a flow-rate of 1.5 ml min-1 and the effluent was monitored spectrophotometrically at 214 nm. The retention times of the internal standard and metoclopramide hydrochloride were 3.0 and 7.5 min, respectively. Quantification was achieved by measuring the peak-height ratio of the drug to the internal standard. A linear relationship was found over the range 1-10 micrograms ml-1. Within-day coefficients of variation (CVs) ranged from 0.50 to 1.70% and between-day CVs from 0.68 to 4.07% at three different concentrations. The developed procedure was compared with the current BP method for the assay of metoclopramide hydrochloride in tablets. The proposed method was also used to study the stability of metoclopramide hydrochloride. 相似文献
4.
el-Daly SA Abdel-Kader MH Issa RM el-Sherbini el-SA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(2):405-411
Electronic absorption, and excitation spectra of 1-methyl-4-[4-aminostyryl] pyridinum iodide (M-NH2) were measured in solvents of different polarity. The (M-NH2) dye exhibits negative solvatochromism, i.e. a hypsochromic band shift as the solvent polarity increases. The fluorescence quantum yield is also sensitive to the polarity and viscosity of the medium. The ground and excited state protonation constants were calculated and amount to 3.35 and 0.62, respectively. The effect of micellization on the emission spectrum of (M-NH2) are also studied in sodium dodecyl sulphate (SDS). The fluorescence intensity increases as the concentration of SDS increases with an abrupt change at cmc. The quantum yield of the cis trans photoisomerization is also determined in aqueous buffer solution of pH 1.1. 相似文献
5.
6.
Sameh E. Shaban Nagdya M. Ibrahiem Sayed A. El-mongy Elsayed E. Elshereafy 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(3):1219-1224
Ten ore samples, two unpurified yellow cake samples and natural uranyl nitrate hexahydrate sample were analyzed by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) method to verify source nuclear material. Samples represent source nuclear material as possible. All samples were scanned at ideal conditions; working distance = 10 mm, voltage = 30 kV, magnification value = × 100, spot size = 50 to screen samples for the presence of uranium and thorium, Also Hyper pure germanium (HPGe) gamma spectrometers were applied to estimate the uranium and thorium contents in Bq/kg (ppm). For the ore samples uranium-238 ranges from 1,049.23 Bq/kg (85.30 ppm) to 2,096.06 Bq/kg (170.41 ppm), uranium-235 ranges from 47.51 to 105.61 Bq/kg and thorium-232 ranges from 22.84 Bq/kg (5.65 ppm) to 41.78 Bq/kg (10.34 ppm). For the yellow cake samples and uranyl nitrate hexahydrate uranium-238 ranges from 42.99 Bq/kg (3.50 ppm) to 71,887.2 Bq/kg (5,844.49 ppm) and thorium-232 is 4.78 Bq/kg (1.83 ppm) and the other two samples are lower than the detection limit. 相似文献
7.
Mokhtar A. Abd ul-Malik Adel M. Kamal El-Dean Shaban M. Radwan Remon M. Zaki 《Journal of heterocyclic chemistry》2021,58(11):2067-2077
A new series of pyrazolopyrazinoselenolotriazolopyrimidines was synthesized by a facile method based on condensation of 5-amino-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]selenolo[3,2-e]pyrazine-6-carbonitrile ( 3 ) with triethyl orthoformate followed by intramolecular cyclization with hydrazine to afford 7-amino-8-imino-3-methyl-1-phenyl-1,8-dihydro-7H-pyrazolo[3″,4″:5′,6′]pyrazino[2′,3′:4,5] selenolo[3,2-d]pyrimidine ( 5 ). The latter compound was utilized as a multipurpose precursor for the construction of other new triazoles fused to the pyrazolopyrazino- selenolopyrimidine moiety. Alternatively, acetylation and chloro-acetylation of compound 3 using acetic anhydride and chloroacetyl chloride yielded the acetyl amino 11 and chloroacetamido 12 derivatives, respectively. Compound 12 underwent nucleophilic substitution upon reaction with morpholine to provide the morpholinyl acetamide 13 . Furthermore, the pyrazolopyridoselenolopyrazine ring system 14 was synthesized by the reaction of the o-amino-carbonitrile 3 with malononitrile. Assignment of the chemical structures for the new compounds was confirmed depending on elemental and spectral techniques. On the other hand, most of the synthesized compounds revealed promising results against various bacterial and fungal strains. 相似文献
8.
Mehdi?AlaeiyanEmail author Shaban?Sedghi 《Southeast Asian Bulletin of Mathematics》2003,26(2):181-184
Let G be a intransitive permutation group on a set with no fixed point in ; let m, n be a positive integer and let |g – | m, for every
and g G. When G has t orbits and degree n close to [2mp/(p – 1)] + t – 1, this paper constructs such a group with m close to [n(p – 1)/2p].AMS Subject Classification: 20BXX. 相似文献
9.
Shaban Sedghi Ishak Altun Nabi Shobe 《Nonlinear Analysis: Theory, Methods & Applications》2010,72(3-4):1298-1304
In the present work, we prove a coupled fixed point theorem for contractive mappings in complete fuzzy metric spaces. 相似文献
10.