全文获取类型
收费全文 | 1574篇 |
免费 | 63篇 |
国内免费 | 18篇 |
专业分类
化学 | 1005篇 |
晶体学 | 25篇 |
力学 | 57篇 |
综合类 | 3篇 |
数学 | 233篇 |
物理学 | 332篇 |
出版年
2023年 | 10篇 |
2022年 | 49篇 |
2021年 | 46篇 |
2020年 | 44篇 |
2019年 | 53篇 |
2018年 | 55篇 |
2017年 | 56篇 |
2016年 | 71篇 |
2015年 | 55篇 |
2014年 | 68篇 |
2013年 | 160篇 |
2012年 | 98篇 |
2011年 | 135篇 |
2010年 | 81篇 |
2009年 | 88篇 |
2008年 | 101篇 |
2007年 | 99篇 |
2006年 | 66篇 |
2005年 | 56篇 |
2004年 | 45篇 |
2003年 | 42篇 |
2002年 | 33篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 6篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 9篇 |
1992年 | 10篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1655条查询结果,搜索用时 31 毫秒
81.
A series of novel 1,2,3,4,6-pentasubstituted-4-hydroxy-cyclohexanes (3a–u) were synthesized from the reaction of aromatic ketones with aromatic aldehydes under mild reaction conditions in good yields. The stereochemistry of the synthesized compounds was established using 1D and 2D-NMR spectra. 相似文献
82.
Mustafa Imamoglu 《Journal of Dispersion Science and Technology》2013,34(9):1183-1187
In this study, a batch adsorption of Cd(II) ions onto activated carbon (AC) produced from hazelnut husks were investigated. The factors controlling the adsorption process such as initial pH, agitation time, dosage and initial concentration have been examined. The AC was showed a high affinity to Cd(II) ions at pH values between 5.0 and 7.0. The equilibrium time was found to be 300 minutes. Cd(II) adsorption equilibrium was analyzed with both Langmuir and Freundlich isotherm equations and it was found that Langmuir equations fitted well with the experimental data. Maximum Cd(II) adsorption capacity of AC was calculated to be 20.9 mg g?1. Cd(II) adsorption kinetics described well with the pseudo second order model. The activated carbon prepared from hazelnut husks is efficient sorbent material for the removal of Cd(II) ions from aqueous solutions. 相似文献
83.
S. Talegaonkar G. Mustafa S. Akhter Z. I. Iqbal 《Journal of Dispersion Science and Technology》2013,34(5):690-701
The objective of the present investigation was to design a thermodynamically stable and dilutable nanoemulsion formulation of AT-Ca with minimum surfactant concentration that could improve its solubility as well as its oral bioavailability. The composition of optimized nanoemulsion formulation was Sefsol 218 and oleic acid (1:1) 10% w/w, as an oil phase, Tween-20 (19% w/w) as a surfactant, Carbitol (19% w/w) as a cosurfactant and distilled water (52% w/w) as an aqueous phase, containing 10 mg of AT. The optimized formulation showed higher% drug release (99.34%), lower droplet size (42.8 ± 0.42 nm) with low polydispersity index (0.237 ± 0.012), less viscosity (27.51 ± 1.01 cP) and infinite dilution capability. In vitro drug release from the nanoemulsion formulations was highly significant (p < 0.01) as compared to drug suspension. 相似文献
84.
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
85.
Hyojin Lee Chi P. Huynh Stephen C. Hawkins Mustafa Musameh Dae Hyung Kim 《Liquid crystals》2013,40(3):322-327
We investigated the orientational and electro-optical properties of a nematic liquid crystal (LC) aligned with a directly spinnable carbon nanotube (CNT) web functioning both as an electrode and as an alignment layer. The LC molecules were uniformly oriented along the drawing direction of the CNT web and the spatially averaged birefringence was comparable to a rubbed polyimide sample. The CNT web sample also showed smaller residual DC and hysteresis compared to the polyimide sample. 相似文献
86.
Latif Elçi Ümit Divrikli Mustafa Soylak 《International journal of environmental analytical chemistry》2013,93(10):711-723
A simple, economic and sensitive method for selective determination of As(III) and As(V) in water samples is described. The method is based on selective coprecipitation of As(III) with Ce(IV) hydroxide in presence of an ammonia/ammonium buffer at pH 9. The coprecipitant was collected on a 0.45 µm membrane filter, dissolved with 0.5 mL of conc. nitric acid and the solution was completed to 2 or 5 mL with distilled water. As(III) in the final solutions was determined by graphite furnace atomic absorption spectrometry (GFAAS). Under the working condition, As(V) was not coprecipitated. Total inorganic arsenic was determined after the reduction of As(V) to As(III) with NaI. The concentration of As(V) was calculated by the difference of the concentrations obtained by the above determinations. Both the determination of arsenic with GF-AAS in presence of cerium and the coprecipitation of arsenic with Ce(IV) hydroxide were optimised. The suitability of the method for determining inorganic arsenic species was checked by analysis of water samples spiked with 4–20 µg L?1 each of As(III) and As(V). The preconcentration factor was found to be 75 with quantitative recovery (≥95%). The accuracy of the present method was controlled with a reference method based on TXRF. The relative error was under 5%. The relative standard deviations for the replicate analysis ( n?=?5) ranged from 4.3 to 8.0% for both As(III) and As(V) in the water samples. The limit of detection (3σ) for both As (III) and As(V) were 0.05 µg L?1. The proposed method produced satisfactory results for the analysis of inorganic arsenic species in drinking water, wastewater and hot spring water samples. 相似文献
87.
Şerife Saçmacı Şenol Kartal Mustafa Saçmacı 《International journal of environmental analytical chemistry》2013,93(14):1626-1637
A simple back-extraction method was developed for the separation and preconcentration of trace levels of zinc from different matrices. Ethyl-2-(4-methoxybenzoyl)-3-(4-methoxyphenyl)-3-oxopropanoylcarbamate (EMPC) was used as a new complexing agent for the extraction of zinc(II) from the aqueous sample phase to the methyl isobutyl ketone (MIBK) phase as Zn(EMPC)2 complexes. The Zn(II) can be selectively stripped with 1?mL of 0.5?mol?L?1 HCl from Mn+(EMPC)n complexes [Ag(I), Al(III), Cd(II), Cr(III), Cu(II), Fe(II), Fe(III), Mn(II), Ni(II), Pb(II) and Pd(II)] which dissolved in MIBK phase. Some experimental parameters, which are important for the whole extraction process, including pH, sample volume, shaking time, amount of the EMPC reagent, amount of MIBK, ionic strength, and type of back-extractant were investigated. The recovery for Zn(II) was greater than 95%. The detection limit of the method was found to be 0.2?µg?L ? 1 and the relative standard deviation as 6.4%. The concentrations of Zn(II) in the certified reference materials (LGC6019 river water and NIST-1547 peach leaves) by the presented method were in good agreement with the certified values. The proposed method was succesfully applied to the determination of zinc in some natural waters, rice, hair, soil, and tea samples. 相似文献
88.
Serkan Sayin Ilkay Hilal Gubbuk Mustafa Yilmaz 《Journal of inclusion phenomena and macrocyclic chemistry》2013,75(1-2):111-118
The present study describes the preparation of a new calix[4]arene-based sporopollenin material and its application for the removal of Na2Cr2O7 from aqueous solution. The novel calix[4]arene-based sporopollenin material was prepared via the immobilization of dihydrazine amide derivative of p-tert-butylcalix[4]arene (3) onto the modified sporopollenin. The newly prepared calix[4]arene-based sporopollenin is characterized by using different analytical techniques such as FT-IR spectroscopy, scanning electron microscope and Elemental analysis. The batch wise sorption study was carried out to optimize various experimental parameters such as the effect of sorbent dosage, pH, temperature and Cr(VI) anion concentration. It has been found that the sorption of Cr(VI) anion on calix[4]arene-based sporopollenin was highly pH dependent and maximum sorption was achieved at pH 1.5. The sorption behavior was also evaluated by Langmuir, Freundlich and Dubinin Radushkevich isotherms. The value of correlation coefficient (R 2) showed a good agreement with Freundlich isotherm model. Result of study demonstrated that calix[4]arene-based sporopollenin proved to be highly effective for the removal of Cr(VI). 相似文献
89.
Kenan Koran Ahmet Ozkaya Furkan Ozen Erol Cil Mustafa Arslan 《Research on Chemical Intermediates》2013,39(3):1109-1124
Hexachlorocylotriphosphazene (1) was reacted with 4-hydroxy-3-methoxybenzaldehyde to give hexakis[(4-formyl-2-methoxy)phenoxy]cyclotriphosphazene (2). Hexakis[(4-(hydroxyimino)2-methoxy)phenoxy]cyclotriphosphazene (3) was synthesized by reaction of 2 with hydroxlamine hydrochloride in pyridine. Compound 3 was reacted with benzyl chloride, acetyl chloride, allyl bromide, benzoyl chloride, propanoyl chloride, 4-methoxybenzoyl chloride, 2-chlorobenzoyl chloride, chloroacetyl chloride, methyl iodide, and thiophene-2-carbonyl chloride. From these reactions, full or partially substituted compounds were obtained, usually in high yields. Pure or defined products could not be obtained from reaction of 3 with methacryloyl chloride and O-acetylsalicyloyl chloride. The structures of the compounds were determined by elemental analysis, and IR, 1H, 13C, and 31P NMR spectroscopy. The synthesized compounds were screened for in-vitro antimicrobial activity against two Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis), two gram-negative bacteria (Escherichia coli and Klebsiella pneumonia), and fungal strains (Aspergillus niger, and Candida albicans) by the agar well diffusion method. Few compounds had significant activity against both Gram-positive and Gram-negative bacteria. None of the compounds had antifungal activity except compounds 7 and 9, which had moderate activity. 相似文献
90.