全文获取类型
收费全文 | 184篇 |
免费 | 5篇 |
国内免费 | 5篇 |
专业分类
化学 | 151篇 |
晶体学 | 1篇 |
力学 | 2篇 |
数学 | 7篇 |
物理学 | 33篇 |
出版年
2023年 | 1篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 6篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 21篇 |
2012年 | 15篇 |
2011年 | 12篇 |
2010年 | 12篇 |
2009年 | 10篇 |
2008年 | 7篇 |
2007年 | 10篇 |
2006年 | 8篇 |
2005年 | 2篇 |
2004年 | 2篇 |
2003年 | 3篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 3篇 |
1991年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1973年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有194条查询结果,搜索用时 15 毫秒
1.
Summary Extraction of scandium and calcium radioactivities with 1% HDEHP in benzene from nitric acid solution was investigated. The effect of potassium titanium oxalate concentration on the extraction from 1.5M nitric acid was studied. From the data obtained, two procedures based on batch solvent extraction and extraction chromatography were developed for separation and production of radioscandium from a neutron-irradiated potassium titanium oxalate target. The radiochemical purity of the separated scandium radioactivities was more than 98%.
Zusammenfassung Die Extraktion der Aktivitäten des Scandiums und Calciums aus salpetersaurer Lösung mit 1% Diäthylhexylphosphorsäure in Benzol wurde untersucht. Der Einfluß der Kalium-Titanoxalat-Konzentration auf die Extraktion aus 1,5-m Salpetersäure wurde geprüft. Auf Grund der Ergebnisse wurden zwei Verfahren zur Trennung und Gewinnung von Radio-Scandium aus einem neutronenbestrahlten Kalium-Titanoxalat-Target ausgearbeitet, die auf einmaliger Extraktion mit dem Lösungsmittel bzw. auf Extraktionschromatographie beruhen. Die radiochemische Reinheit der Sc-Aktivitäten war besser als 98%.相似文献
2.
Synergistic extraction of samarium with TTA(HA) and TPPO or TOPO (B) mixtures were investigated. The extracted complex was proved to have the general formula SmA3 · 2B. A graphical determination for the formation constants of these complexes gave the values 3.9 × 1013 and 8.2 × 1010 for SmA3 · 2TOPO and SmA3 · 2TPPO in benzene, respectively. 相似文献
3.
Ramadan Ahmed Mekheimer Kamal Usef Sadek Hisham Ahmed Abd El‐Nabi Afaf Abd El‐Hameid Mohamed Ehab Anwer Ebraheem Michael B. Smith 《Journal of heterocyclic chemistry》2005,42(4):567-574
Ethyl 3‐amino‐4‐chlorothieno[3,2‐c]quinoline‐2‐carboxylate ( 4 ) is a versatile synthon, prepared by reacting an equimolar amount of 2,4‐dichloroquinoline‐3‐carbonitrile ( 1 ) with ethyl mercaptoacetate ( 2 ). Ethyl 5‐alkyl‐5H‐1‐thia‐3,5,6‐triazaaceanfhrylene‐2‐carboxylates 9a‐c , novel perianellated tetracyclic heteroaro‐matics, were prepared by refluxing 4 with excess of primary amines 7a‐c to yield the corresponding amino‐thieno[3,2‐c]quinolines 8a‐c . Subsequent reaction with an excess of triethyl orthoformate (TEO) furnished 9a‐c . Reaction of 4 with TEO in Ac2O at reflux, gave the simple acetylated compounds, thieno[3,2‐c]‐quinolines 12 and 13 . Refluxing 4 with benzylamine ( 7d ) gave 10 , and subsequent treatment with TEO gave the tetracyclic compound 11 . Refluxing 13 with an excess of alkylamines 7a‐d gave the fhieno[3,2‐c]quino‐lines 15 . Refluxing the aminothienoquinolines 8b with an excess of triethyl orthoacetate gave thieno[3,2‐c]quinoline 17 , while heating with Ac2O gave 18 and 19 , with small amounts of 16 . Reaction of 8a,b with ethyl chloroformate and phenylisothiocyanate generated the new 1‐thia‐3,5,6‐triazaaceanthrylenes 20a,b and 21a,b , respectively. Diazotization of 8a‐c afforded the novel tetracyclic ethyl 5‐alkyl‐5H‐1‐fhia‐3,4,5,6‐tetraazaaceanthrylene‐2‐carboxylates 22a‐c in good yields. 相似文献
4.
We demonstrate a switchable Q-switched and mode-locked erbium-doped fiber laser (EDFL) operating in the L-band region using the nonlinear polarization rotation effect. The switching operation is achieved by controlling intensity-dependent loss using a polarization controller. In Q-switching mode, the EDFL produces a pulse train with a repetition rate of 21.1 kHz, pulse width of 7.7 #s, and pulse energy of 13.6 nJ. The EDFL also generates a multi-wavelength comb with a very narrow and constant wavelength spacing of 0.045 nm and optical signal-to-noise ratio of at least l0 dB. During mode locking, the EDFL produces stretched pulses with 3-dB bandwidth of 26.2 nm, pulse width of 350 fs, repetition rate of 2.38 MHz, and pulse energy of 48.56 pJ. 相似文献
5.
Hisham J. Y. El-Aila 《Journal of Dispersion Science and Technology》2013,34(9):1208-1211
In this article, a mononuclear Mn(Niten)2H2O complex was prepared to catalyze hydrolysis of p-nitrophenyl acetate (PNPA) in presence of Cetyltrimethylammonium bromide (CTAB) micellar system in different pH range from 6.5–10 at 25°C. These results obtained indicate that the complex exhibits good catalytic function. It also appears the complex accelerates the hydrolytic cleavage of PNPA in cationic CTAB micellar solution which may be due to coordinating ability of substrate to complex, electrostatic interaction between micelles and complex and due to electrostatic interaction between micelles with reactant. 相似文献
6.
Determination of total arsenic in soil and arsenic-resistant bacteria from selected ground water in Kandal Province, Cambodia 总被引:1,自引:0,他引:1
A. Hamzah K. K. Wong F. N. Hasan S. Mustafa K. S. Khoo S. B. Sarmani 《Journal of Radioanalytical and Nuclear Chemistry》2013,297(2):291-296
Cambodia has geological environments conducive to generation of high-arsenic groundwater and people are at high risk of chronic arsenic exposure. The aims of this study are to investigate the concentration of total arsenic and to isolate and identify arsenic-resistant bacteria from selected locations in Kandal Province, Cambodia. The INAA technique was used to measure the concentration of total arsenic in soils. The arsenic concentrations in soils were above permissible 5 mg/kg, ranging from 5.34 to 27.81 mg/kg. Bacteria resistant to arsenic from two arsenic-contaminated wells in Preak Russey were isolated by enrichment method in nutrient broth (NB). Colonies isolated from NB was then grown on minimal salt media (MSM) added with arsenic at increasing concentrations of 10, 20, 30, 50, 100 and 250 ppm. Two isolates that can tolerate 750 ppm of arsenic were identified as Enterobacter agglomerans and Acinetobacter lwoffii based on a series of biochemical, physiological and morphological analysis. Optimum growth of both isolates ranged from pH 6.6 to 7.0 and 30–35 °C. E. agglomerans and A. lwoffii were able to remove 66.4 and 64.1 % of arsenic, respectively at the initial concentration of 750 ppm, within 72 h of incubation. Using energy dispersive X-ray technique, the percentage of arsenic absorbed by E. agglomerans and A. lwoffii was 0.09 and 0.15 %, respectively. This study suggested that arsenic-resistant E. agglomerans and A. lwoffii removed arsenic from media due to their ability to absorb arsenic. 相似文献
7.
I. A. Alnour H. Wagiran N. Ibrahim S. Hamzah B. S. Wee M. S. Elias J. A. Karim 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(3):1231-1237
In standardization NAA, it is necessary to characterize the neutron spectrum parameters such as epithermal neutron flux shape factor (α), thermal to epithermal neutron flux ratio (f), thermal neutron flux (φ th) and epithermal neutron flux (φ epi) in the irradiation facility to determine the concentration of an element in the sample using absolute and k 0 standardization methods. The α and f were determined using Cd-ratio multi monitor method using experimental data obtained in PUSPATI TRIGA Mark II research reactor at four irradiation positions (10, 20, 30 and 40) of the rotary rack. The calculated values of α and f ranged from 0.006 to 0.0281 and 18.56 to 19.12 respectively. The average values of φ th and φ epi were found as 2.33 × 1012 and 1.23 × 1011 n cm?2 s?1 respectively. Moreover, a comparison of the neutron flux parameters in the present study shows an acceptable level of consistency with those of previous studies. 相似文献
8.
I. A. Alnour H. Wagiran N. Ibrahim S. Hamzah B. S. Wee M. S. Elias 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):177-186
This work aimed to study the capability of INAA absolute method in determining the elemental concentration of 238U and 232Th in the rock samples. The INAA absolute method was implemented in PUSPATI TRIGA Mark II research reactor, Malaysian Nuclear Agency (NM). The accuracy of INAA absolute method was performed by analyzing the IAEA certified reference material (CRM) Soil-7. The analytical results showed the deviations between experimental and certified values were mostly less than 10 % with Z-score in most cases less than 1. In general, the results of analysed CRM Soil-7 show a good agreement between certified and experimental results which mean that the INAA absolute method can be used accurately for elemental analysis of uranium and thorium in various types of samples. The concentration of 238U and 232Th ranged from 1.77 to 24.25 and 0.88 to 95.50 ppm respectively. The highest value of 238U and 232Th was recorded for granite rock sample G17 of 238U and sample G9 of 232Th, whereas the lower value was 1.77 ppm of 238U recorded in sandstone rock and 0.88 ppm of 232Th for gabbro. Moreover, a comparison of the 238U and 232Th results obtained by the INAA absolute method shows an acceptable level of consistency with those obtained by the INAA relative method. 相似文献
9.
A 1H NMR spectroscopic study of tetra-n-butylammonium halides (TBAX: X = Cl? , Br? or I? ) in CDCl3 solutions was conducted. Complexation studies of TBAX salts with different host molecules using 1H NMR in CDCl3 have previously revealed that the reference residual CHCl3 proton signal had been shifted downfield. The aim of the study was to quantify the extent of these chemical shift changes with TBAX salts. Linear concentration–chemical shift relationships in each case were obtained from the resulting titration plots obtained from the addition of the TBAX salts alone to CDCl3. Interactions in the solid state as determined by X-ray crystallography support the solution-state investigations indicating halide ion–chloroform proton interactions. 相似文献
10.
An efficient gain-flattened C-band optical amplifier is demonstrated using a hybrid configuration with a Zirconia-based Erbium-doped
fibre (Zr-EDF) and a semiconductor optical amplifier (SOA). The amplifier utilizes a two-stage structure with a midway isolator
to improve flat gain characteristic and reduce noise figure. At input signal power of −30 dBm, a flat gain of 28 dB is obtained
from wavelength region of 1530 to 1560 nm with gain variation of less than 4 dB. The noise figure is maintained below 11 dB
at the flat-gain region. This amplifier has the potential to be used in the high channel count dense wavelength division multiplexing
system due to its simplicity and compact design. 相似文献