全文获取类型
收费全文 | 299篇 |
免费 | 2篇 |
国内免费 | 4篇 |
专业分类
化学 | 212篇 |
晶体学 | 10篇 |
力学 | 11篇 |
数学 | 41篇 |
物理学 | 19篇 |
无线电 | 12篇 |
出版年
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2018年 | 3篇 |
2016年 | 7篇 |
2014年 | 3篇 |
2013年 | 6篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 7篇 |
2008年 | 6篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 9篇 |
2003年 | 8篇 |
2002年 | 10篇 |
2001年 | 7篇 |
2000年 | 11篇 |
1999年 | 4篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 9篇 |
1975年 | 2篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1965年 | 1篇 |
1959年 | 2篇 |
1958年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有305条查询结果,搜索用时 0 毫秒
301.
Ma K Somashekhar BS Gowda GA Khetrapal CL Weiss RG 《Langmuir : the ACS journal of surfaces and colloids》2008,24(6):2746-2758
The influence of covalently attaching hydroxymethylene to the methyl groups of methyl-tri-n-alkylphosphonium halides (where the alkyl chains are decyl, tetradecyl, or octadecyl and the halide is chloride or bromide) or adding methanol as a solute to the salts on their solid, liquid-crystalline (smectic A2), and isotropic phases has been investigated using a variety of experimental techniques. These structural and compositional changes are found to induce liquid crystallinity in some cases and to enhance the temperature range and lower the onset temperature of the liquid-crystalline phases in some others. The results are interpreted in terms of the lengths of the three n-alkyl chains attached to the phosphorus cation, the nature of the halide anion, the influence of H-bonding interactions at the head group regions of the layered phases, and other solvent-solute interactions. The fact that at least 1 molar equiv of methanol must be added to effect complete (isothermal) conversion of a solid methyl-tri-n-alkylphosphonium salt to a liquid crystal demonstrates a direct and strong association between individual methanol molecules and the phosphonium salts. Possible applications of such systems are suggested. 相似文献
302.
Chandrashekhar N Thomas B Gayathri V Ramanathan KV Gowda NM 《Magnetic resonance in chemistry : MRC》2008,46(8):769-774
Synthesis and NMR spectral studies of multidentate N and S heterocycles, 1,3,5-tris(N-methylbenzimidazolyl)benzene, 1,3,5-tris(benzimidazolyl)benzene,1,3,5-tris(benzothiazolyl) benzene, 2,2'-bipyridine 3,3'-bis(benzothiazolyl)benzene and 1,2,4,5-tetrakis(benzothiazolyl) benzene have been carried out. 2D (1)H-(1)H PFG-COSY as well as (1)H-(13)C single and multiple bond correlated (2D GRASP-HSQC and GRASP-HMBC) experiments have been employed to characterize the compounds. 1D NOE experiments have been useful in understanding the structure of 1,3,5-tris(N-methylenzimidazolyl)benzene. 相似文献
303.
Ma K Shahkhatuni AA Somashekhar BS Gowda GA Tong Y Khetrapal CL Weiss RG 《Langmuir : the ACS journal of surfaces and colloids》2008,24(17):9843-9854
Tri- n-decylmethylphosphonium chloride and bromide ( 1P10X) salts are not liquid crystalline. However, mesophases are induced by adding very small amounts of an alcohol or water. The temperature ranges of the induced smectic A 2 (SmA 2) liquid-crystalline phases can be very broad and the onset temperatures can be below room temperature depending upon the concentration of the alcohol or water and the structure of the alcohol. At least one molar equivalent of hydroxyl groups is necessary to convert the 1P10X completely into a liquid crystal. Strong association between the hydroxyl groups of an alcohol or water and the head groups of the 1P10X is indicated by spectroscopic, diffraction, and thermochemical data. Unlike many other smectic phases, those of the 1P10X/alcohol complexes are easily aligned in strong magnetic fields and the order parameters of selectively deuterated alcohols as measured by (2)H NMR spectroscopy, approximately 10 (-2), are much lower than the values found when the host is a commonly employed thermotropic liquid crystal. The dependence of the specific values of the order parameters on temperature, the nature of the halide anion, and the structure and concentration of the alcohol are reported. In sum, a detailed picture is presented to explain how and why an alcohol or water induces liquid crystallinity in the 1P10X salts. The data also provide a blueprint for designing media with even lower order parameters that can be hosts to determine the conformations and shapes of guest molecules. 相似文献
304.
The essential oil was extracted from the seeds of Heracleum rigens by hydrodistillation and a total of twenty compounds accounting for 98.5% of the total oil composition were identified. Physicochemical properties and chemical composition of the oil was determined by a combination GC/FID and GC/MS analysis. The major compounds identified were bornyl acetate (51.2%), alpha-pinene (22.6%), limonene (9.62%), octyl acetate (3.94%), rho-cymene (2.85%) and gamma-terpinene (1.93%). The antimicrobial activity of the oil was screened by the disc diffusion method against nine pathogenic bacterial strains. Maximum antimicrobial activity was noted against Klebsiella pneumonia and Bacillus subtillis. This investigation corroborates the traditional claim of H. rigens as an effective antimicrobial agent. 相似文献
305.
Papanna Roopa Kothathi Kanakapura Basavaiah Gowda Shankara Bujuvally Shivaiah Basavaraju Mahesh Puttegowda Veena Keregodu 《Journal of Analytical Chemistry》2021,76(11):1262-1270
Journal of Analytical Chemistry - Four simple, precise and sensitive visible spectrophotometric methods were developed for the determination of solifenacin succinate in pure and pharmaceutical... 相似文献