全文获取类型
收费全文 | 1015篇 |
免费 | 50篇 |
国内免费 | 18篇 |
专业分类
化学 | 857篇 |
晶体学 | 7篇 |
力学 | 15篇 |
数学 | 62篇 |
物理学 | 142篇 |
出版年
2024年 | 1篇 |
2023年 | 13篇 |
2022年 | 53篇 |
2021年 | 38篇 |
2020年 | 56篇 |
2019年 | 63篇 |
2018年 | 78篇 |
2017年 | 62篇 |
2016年 | 72篇 |
2015年 | 52篇 |
2014年 | 68篇 |
2013年 | 117篇 |
2012年 | 86篇 |
2011年 | 80篇 |
2010年 | 52篇 |
2009年 | 44篇 |
2008年 | 31篇 |
2007年 | 16篇 |
2006年 | 15篇 |
2005年 | 15篇 |
2004年 | 7篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 2篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1992年 | 3篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 4篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1083条查询结果,搜索用时 0 毫秒
61.
62.
Samadi N Manayi A Vazirian M Samadi M Zeinalzadeh Z Saghari Z Abadian N Mozaffarian VO Khanavi M 《Natural product research》2012,26(20):1931-1934
The essential oil obtained from the flowering parts of Anthemis altissima L. var. altissima was analysed by gas chromatography and gas chromatography mass spectroscopy. In this study, 34 compounds representing 98.76% of the essential oil were identified. The main components were α-terpineol (26.42%), β-pinene (9.23%), cis-chrysanthenyl acetate (6.30%), globulol (5.36%), n-tricosane (4.41%), terpinen-4-ol (4.08%) and 1,8 cineole (3.84%). Antibacterial activities of the essential oil and its two major components (α-terpineol and β-pinene) were determined using microdilution method against both Gram-positive (Staphylococcus aureus, Bacillus subtilis, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae) bacteria. The essential oil showed a broad-spectrum antibacterial activity (MICs ranged from 3.13 to 6.25?μL?mL(-1)). It was found that α-terpineol with minimum inhibitory concentration (MIC) values of the range 0.87-1.56?μL?mL(-1) was a more potent antibacterial agent than β-pinene with MIC values of the range 1.56-6.25?μL?mL(-1). All of them, the essential oil, β-pinene and α-terpineol, were more effective against Gram-positive bacteria than Gram-negative ones. 相似文献
63.
Bassam Abu Thaher Jalal A. Zahra Mustafa M. El-Abadelah Hans-Hartwig Otto 《Monatshefte für Chemie / Chemical Monthly》2004,40(9):435-439
Nitrilimines were prepared from N-arylhydrazono chlorides and reacted with -alanine yielding the corresponding amidrazones, which were treated with 1,1-carbonyldiimidazole in THF affording the hitherto unknown 3-acetyl-1-aryl-1,4,5,6-tetrahydro-1,2,4-triazepin-7-ones. 相似文献
64.
65.
Azizian J Karimi AR Kazemizadeh Z Mohammadi AA Mohammadizadeh MR 《The Journal of organic chemistry》2005,70(4):1471-1473
[reaction: see text] 11-(1H-Pyrrol-1-yl)-11H-indeno[1,2-b]quinoxaline and 3-(1H-pyrrol-1-yl)indolin-2-one derivatives have been synthesized in good yields in a novel, one-pot, and efficient process by condensation of 11H-indeno[1,2-b]quinoxalin-11-one or isatin derivatives with 4-hydroxyproline on solid-support montmorillonite K10 under microwave irradiation. 相似文献
66.
Malek T. Maghsoodlou Nourallah Hazeri Sayed M. Habibi-Khorassani Reza Heydari Ghasem Marandi Mojtaba Lashkari Khatereh Bagherpour Zahra Gharechaei 《Monatshefte für Chemie / Chemical Monthly》2010,39(5):351-356
Abstract
Synthesis of five phosphonato esters has been accomplished via reaction between dimethyl acetylenedicarboxylate and triphenyl phosphite in the presence of biological compounds such as theophylline, 4-hydroxypyrimidine, 2H-3,1-benzoxazine-2,4(1H)-dione, 2-chloroaniline, or 3-nitroaniline at ambient temperature. The configuration of the compounds was determined on the basis of coupling constants emerging from the Karplus equation. 相似文献67.
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
68.
In the present work,an easy solid phase extraction method using alumina modified with polyethylenimine as a new adsorbent was applied to the simultaneous extraction of copper,silver,and palladium ions prior to their determination with electrothermal atomic absorption spectrometry.The analytical procedure involved the complex formation of these cations with polyethylenimine as a chelating agent in buffer media of pH 7.0.Under the optimum conditions,a preconcentration factor of200,150,and 200,precision of ±5.4%,±4.7%,and ±5.2%and linear calibration ranges of 15.0-140,4.0-93,and 7.5-125 ng/L(in original solution) for Cu,Ag,and Pd were obtained,respectively.Also detection limits of3.9,1.1,and 2.0 ng/L were obtained for Cu,Ag,and Pd,respectively.The proposed method was applied to the determination of copper,silver,and palladium in some real samples with satisfactory results. 相似文献
69.
Sebastian Grieger Beata M. Szydowska Vaishnavi J. Rao Eva Steinmann Marcus Dodds Zahra Gholamvand Georg S. Duesberg Jana Zaumseil Claudia Backes 《Angewandte Chemie (International ed. in English)》2020,59(33):13785-13792
In recent years, various functionalization strategies for transition‐metal dichalcogenides have been explored to tailor the properties of materials and to provide anchor points for the fabrication of hybrid structures. Herein, new insights into the role of the surfactant in functionalization reactions are described. Using the spontaneous reaction of WS2 with chloroauric acid as a model reaction, the regioselective formation of gold nanoparticles on WS2 is shown to be heavily dependent on the surfactant employed. A simple model is developed to explain the role of the chosen surfactant in this heterogeneous functionalization reaction. The surfactant coverage is identified as the crucial element that governs the dominant reaction pathway and therefore can severely alter the reaction outcome. This study shows the general importance of the surfactant choice and how detrimental or beneficial a certain surfactant can be to the desired functionalization. 相似文献
70.
A poly acrylate-ethylene glycol (PA-EG) thin film is introduced for the first time as a novel polar sorbent for sorptive extraction method coupled directly to solid-state spectrofluorimetry without the necessity of a desorption step. The structure, polarity, fluorescence property and extraction performance of the developed thin film were investigated systematically. Carvedilol was used as the model analyte to evaluate the proposed method. The entire procedure involved one-step extraction of carvedilol from plasma using PA-EG thin film sorptive phase without protein precipitation. Extraction variables were studied in order to establish the best experimental conditions. Optimum extraction conditions were the followings: stirring speed of 1000 rpm, pH of 6.8, extraction temperature of 60 °C, and extraction time of 60 min. Under optimal conditions, extraction of carvedilol was carried out in spiked human plasma; and the linear range of calibration curve was 15–300 ng mL−1 with regression coefficient of 0.998. Limit of detection (LOD) for the method was 4.5 ng mL−1. The intra- and inter-day accuracy and precision of the proposed method were evaluated in plasma sample spiked with three concentration levels of carvedilol; yielding a recovery of 91–112% and relative standard deviation of less than 8%, respectively. The established procedure was successfully applied for quantification of carvedilol in plasma sample of a volunteer patient. The developed PA-EG thin film sorptive phase followed by solid-state spectrofluorimetric method provides a simple, rapid and sensitive approach for the analysis of carvedilol in human plasma. 相似文献