全文获取类型
收费全文 | 642篇 |
免费 | 11篇 |
国内免费 | 13篇 |
专业分类
化学 | 446篇 |
晶体学 | 2篇 |
力学 | 43篇 |
综合类 | 11篇 |
数学 | 47篇 |
物理学 | 117篇 |
出版年
2023年 | 7篇 |
2022年 | 27篇 |
2021年 | 24篇 |
2020年 | 28篇 |
2019年 | 21篇 |
2018年 | 29篇 |
2017年 | 18篇 |
2016年 | 26篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 54篇 |
2012年 | 56篇 |
2011年 | 46篇 |
2010年 | 29篇 |
2009年 | 22篇 |
2008年 | 28篇 |
2007年 | 33篇 |
2006年 | 21篇 |
2005年 | 22篇 |
2004年 | 6篇 |
2003年 | 19篇 |
2002年 | 31篇 |
2001年 | 6篇 |
2000年 | 2篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1961年 | 1篇 |
1960年 | 1篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有666条查询结果,搜索用时 15 毫秒
191.
The critical micelle concentration (CMC) of sodium dodecyl sulphate (SDS) in pure water and in the presence of amino acids (0.01, 0.02 and 0.03 mol kg?1), L-valine (Val) and L-leucine (Leu) was determined from conductometric and fluorometric methods using pyrene as luminescence probe. Depression in the CMC at low concentration of amino acids is attributed to the increased hydrophobic–hydrophobic interaction between the non-polar groups of the surfactant, while, at high concentration, amino acids bind strongly with the anion, DS?, head groups of SDS, thereby, delaying the micelle formation, resulting in increased CMC. A pronounced decrease in the CMC, while a marked increase in λ0+, with decrease in the solvated radius (rather than crystal radius) of the counterions is observed. Negative values of ΔG0m and ΔH0m indicate that micellisation of SDS in the presence of amino acids is thermodynamically spontaneous and exothermic. Highest negative value of ΔH0m in 0.01 m Val, with lowest CMC value, shows that 0.01 m aqueous Val is the most suitable medium favouring the micellisation of SDS. Decrease in I1/I3 from Val to Leu confirms the relative hydrophobicity of two amino acids. The observed values of the packing parameter, P, of SDS in water and in aqueous amino acids suggest that micelles formed are spherical in nature. 相似文献
192.
A new optical sensing microplate was developed for rapid screening for the presence of biogenic amines (BAs) in seafood samples with high sensitivity. The deposition of a sensing spot (containing a chameleon dye (Py-1) in a polymeric cocktail) on the bottom of the wells of a standard microplate renders the plate a new sensing tool for a rapid and parallel detection of up to 96 (real) samples. This sensing microplate enables (1) a semi-quantitative readout of analyte concentration by eye-vision, (2) a rapid fluorescence readout of 96 samples with standard instrumentation in less than two minutes (unlike chromatographic and electrophoretic methods), (3) a statistically robust data evaluation (with 8-12 replicates) and (4) a rapid parallel sample preparation with standard 8 or 12-channel micropipettes. On reaction with biogenic amines, the dye shows a significant visible color change from blue over green to red color. The appearance of red color favorably coincides with the concentration of BAs that can induce symptoms of poisoning. The linear ranges of fluorescence calibration data for six biogenic amines cover the clinical toxicological relevant range of BAs that is too low to be detected by the human nose. The LODs range from 0.16 to 0.56 μg mL(-1), with correlation coefficients (r(2)) between 0.985 and 0.999. Finally, the evolution of spoilage of four fish samples (monitored by determination of their BA status) and the increase of their total amine content were found to agree well with previous data on time-dependent evolution of BAs in fish. 相似文献
193.
Abstract: The synthesis of 5-iodo-5α-cholestan-6-one (6), its 3β-acetoxy-(7) and 3β-chloro-(8) analogues, 3β-acetoxy-5-iodo-5α-stigmastan-6-one (9) and its 3β-chloro-(10) analogue by the reacion of silver chromate-iodine and pyridine with the corresponding steroidal olefins (1-5) is described. The structures of these products have been established on the basis of their elemental, analytical and spectral data. 相似文献
194.
Mohamad Ridzwan Ishak Zulkiflle Leman Mohd Sapuan Salit Mohd Zaki Abd Rahman Mohd Khairun Anwar Uyup Riaz Akhtar 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1375-1383
This study aimed to investigate the effect of resin impregnation on the interfacial shear strength (IFSS), thermogravimetric (TG) and fourier transform infrared (FT-IR) of sugar palm (Arenga pinnata) fibres. In addition, the effect of resin impregnation on the mechanical properties of sugar palm fibre reinforced unsaturated polyester (UP) composites was also studied. The fibres were impregnated with UP via vacuum resin impregnation process at a pressure of 600 mmHg for 5 min. Composites of 10, 20, 30, 40 and 50 % fibre loadings were fabricated and tested for tensile and flexural properties. It was observed that the impregnation process caused the fibres to be enclosed by UP resin and this gave a strong influence to the increase of its interfacial bonding by the increase of its IFSS from single fibre pull-out test. It was also observed with TG and FT-IR spectra that the impregnated fibre had lower moisture uptake than the control and there was no significant increase in thermal stability of the impregnated fibre. The sequence of fibre decomposition started from the evaporation of moisture, hemicelluloses, cellulose, lignin and finally ash content and the presence of these components were proven by FT-IR spectra. For the composite specimens, due to the high interfacial bonding of the impregnated fibre and the matrix, the impregnated composites showed consistently higher tensile strength, tensile modulus, elongation at break, flexural strength, flexural modulus and toughness than the control samples. It was also observed that 30 % fibre loading gave optimum properties. 相似文献
195.
Khalil Faghihi Ashraf Sadat Abootalebi Meisam Shabanian 《Journal of Saudi Chemical Society》2013,17(2):191-197
New type of aromatic polyamide/montmorillonite nanocomposites were produced using solution intercalation technique in N-methyl-2-pyrrolidone. High-molecular-weight amide chains were synthesized from 4,4′-diaminodiphenyl ether and 4-phenylenediacrylic acid in N-methyl-2-pyrrolidone. The resulting nanocomposite films containing 5–20 wt.% of organoclay (Cloisite® 20A) were characterized for FT-IR, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), optical transparency and water absorption measurements. The distribution of organoclay and nanostructure of the composites were investigated by (XRD) and SEM analyses. Thermogravimetric analysis indicated an increase in thermal stability of nanocomposites as compared to pristine polyamide. The percentage optical transparency and water absorption of these hybrids was found to be much reduced upon the addition of modified layered silicate indicating decreased permeability. 相似文献
196.
Masoud Salavati-Niasari Mina Gholami-Daghian Mahdiyeh Esmaeili-Zare Fatemeh Sadat Sangsefidi 《Journal of Cluster Science》2013,24(4):1093-1101
A novel and simple one-step solid state reaction in the presence of a suitable surfactant, sodium dodecyl sulfate (SDS), and a novel precursor, [bis(acetylacetonato)zinc(II)]; [Zn(acac)2]; has been developed to synthesize uniform zinc oxide microflakes with an average thickness of 0.3–2.4 μm. In the absence of SDS the product samples contained microrods. The formation of zinc oxide microflakes depends on the molar ratio of Zn(II)/SDS and the experimental procedure. The products were characterized by X-ray diffraction, photoluminescence spectroscopy, FT-IR spectroscopy, surface area, scanning electron microscopy and transmission electron microscopy to depict the phase and morphology. The synthesized ZnO microflakes have a hexagonal zincite structure. 相似文献
197.
198.
Jais Abdul Azim Ali S. A. Muhammed Anwar Mustafa Somalu Mahendra Rao Muchtar Andanastuti Isahak Wan Nor Roslam Wan Baharudin Nurul Akidah Lim Kean Long Brandon Nigel P. 《Journal of Solid State Electrochemistry》2020,24(3):711-722
Journal of Solid State Electrochemistry - Nickel/scandia-ceria-stabilized-zirconia (Ni/10Sc1CeSZ) cermet is a potential anode for solid oxide fuel cells. The anode powder is prepared through a... 相似文献
199.
Fan Shuyan Khamesinia Maryam Sadat 《International Journal of Theoretical Physics》2021,60(7):2400-2411
International Journal of Theoretical Physics - Quantum-dot cellular automata (QCA) is considered as rising nanotechnology, which offers computer calculations at the stage of nano by employing... 相似文献
200.
Jiqian Liu Lijuan Han Wenzheng Han Linsheng Gui Zhenzhen Yuan Shengzhen Hou Zhiyou Wang Baochun Yang Sayed Haidar Abbas Raza Abdulaziz Faisal Saleh Alowais Alaa Ahmed Alraddadi Anwar Mohammed Alanazi 《Molecules (Basel, Switzerland)》2023,28(1)
There are limited reports about the effect of different heat treatments on the quality and flavor of Black Tibetan sheep meat. The current study examined the effect of pan-frying, deep-frying, baking, and boiling treatment on the quality of Black Tibetan sheep meat; the amino acid, fatty acid, and volatile flavor compounds (VFCs) were investigated by a texture analyzer, ultra-high-performance liquid chromatography (UHPLC), gas chromatography (GC), and headspace-gas chromatography-ion mobility (HS-GC-IMS). The key VFCs were identified through orthogonal partial least squares discrimination analysis (OPLS-DA), and variable importance projection (VIP) values. In addition, Pearson’s correlations between meat quality parameters and key VFCs were examined. The sensory scores, including texture, color, and appearance, of baked and pan-fried meat were higher than those of deep-fried and boiled meat. The protein (40.47%) and amino acid (62.93 µmol/g) contents were the highest in pan-fried meat (p < 0.05). Additionally, it contained the highest amounts of monounsaturated and polyunsaturated fatty acids, such as oleic, linoleic, and α-linolenic acids (p < 0.05). Meanwhile, pan-fried and deep-fried meat had higher amounts of VFCs than baked meat. The OPLS-DA similarity and fingerprinting analyses revealed significant differences between the three heat treatment methods. Aldehydes were the key aroma compounds in pan-fried meat. Importantly, 3-methylbutyraldehyde and 2-heptanone contents were positively correlated with eicosenoic, oleic, isooleic, linoleic, α-Linolenic, and eicosadiene acids (p < 0.05). To sum up, pan-fried Black Tibetan sheep meat had the best edible, nutritional, and flavor quality. 相似文献