首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   150篇
  免费   5篇
化学   124篇
力学   4篇
数学   14篇
物理学   13篇
  2022年   2篇
  2021年   2篇
  2019年   3篇
  2016年   4篇
  2015年   4篇
  2014年   5篇
  2013年   4篇
  2012年   7篇
  2011年   10篇
  2010年   7篇
  2009年   7篇
  2008年   5篇
  2007年   2篇
  2006年   4篇
  2005年   2篇
  2003年   9篇
  2002年   5篇
  1996年   1篇
  1994年   1篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1988年   2篇
  1987年   1篇
  1984年   1篇
  1982年   3篇
  1981年   1篇
  1957年   2篇
  1940年   1篇
  1916年   1篇
  1914年   1篇
  1913年   1篇
  1909年   7篇
  1904年   1篇
  1903年   6篇
  1902年   3篇
  1900年   4篇
  1898年   3篇
  1895年   3篇
  1890年   1篇
  1887年   5篇
  1886年   1篇
  1885年   5篇
  1884年   4篇
  1882年   1篇
  1881年   2篇
  1879年   1篇
  1878年   1篇
  1870年   1篇
  1865年   1篇
排序方式: 共有155条查询结果,搜索用时 125 毫秒
1.
In this study, thermogelation of methylcelluloses is investigated in relation to the molar mass and concentration in aqueous medium. A large hysteresis between heating and cooling ramps was observed whatever the conditions. The heating process in particular was studied to analyze the two steps of gelation using rheometry. At low temperature, in the sol state, viscosity depends on the concentration and molar mass. Over 30°C a gel-like behavior was observed including two steps (the second step is a strong gel with phase separation) having storage moduli that are nearly independent of polymer molar mass but are directly related to polymer concentration.  相似文献   
2.
Schistosomiasis is a neglected disease with large geographic distribution worldwide. Among the several different species of this parasite, S. mansoni is the most common and relevant one; its pathogenesis is also known to vary according to the worms' strain. High parasitical virulence is directly related to granulomatous reactions in the host's liver, and might be influenced by one or more molecules involved in a specific metabolic pathway. Therefore, better understanding the metabolic profile of these organisms is necessary, especially for an increased potential of unraveling strain virulence mechanisms and resistance to existing treatments. In this report, MALDI‐MSI and the metabolomic platform were employed to characterize and differentiate two Brazilian S. mansoni strains: males and females from Belo Horizonte (BH) and from Sergipe (SE). By performing direct analysis, it is possible to distinguish the sex of adult worms, as well as identify the spatial distribution of chemical markers. Phospholipids, diacylglycerols and triacylglycerols were located in specific structures of the worms' bodies, such as tegument, suckers, reproductive and digestive systems. Lipid profiles were found to be different both between strains and males or females, giving specific metabolic fingerprints for each group. This indicates that biochemical characterization of adult S. mansoni may help narrowing‐down the investigation of new therapeutic targets according to worm composition, molecule distribution and, therefore, aggressiveness of disease. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
3.
In this study, densities and speeds of sound were measured over the whole composition range, at T = (298.15, 303.15 and 308.15) K and p = 0.1 MPa, for the binary systems of ethanol, or 1-propanol, or 2-propanol and 1-butyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide, or 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. The density and speed of sound data were used to calculate the corresponding excess molar volumes and excess molar isentropic compressions, which were fitted with the Redlich–Kister equation. From the obtained results, a discussion was carried out in terms of interactions and structure factors in these binary mixtures.  相似文献   
4.
During the past century extensive uranium mining took place in Portugal for radium and uranium production. One such uranium mine was the Boco Mine, in operation during the 1960s and 70s. Mining waste and open pits were left uncovered since mine closure. During the nineties a quarry for sand extraction was operated in the same site and water from a local stream was extensively used in sand sieving. Downstream the mine area, agriculture soil is used for cattle grazing. Water from the stream, water wells, soil, pasture and sheep meat were now analyzed for radionuclides of uranium natural series. The U-series radionuclide 226Ra was generally the highest in concentrations especially in soil, pasture, and in internal organs of sheep. 226Ra concentrations were 1,093 ± 96 Bq/kg (dry weight, dw) in soil, 43 ± 3 Bq/kg (dw) in pasture, and 193 ± 84 mBq/kg (wet weight, ww) in muscle tissue of sheep. Other sheep internal organs displayed much higher 226Ra concentrations, such as the brain and kidneys with 1,850 ± 613 mBq/kg (ww) and 6,043 ± 6,023 mBq/kg (ww), respectively. Results of analyses of tissue samples from sheep grown in a comparison area were 2 to 16 times lower, depending on the organ. Absorbed radiation doses for internal organs were computed and may exceed 5.2 mGy/y in the case of kidneys, near three times higher than in animals from the reference area, but below the threshold for biological effects. Radionuclide transfer in the terrestrial food chain and radiation exposure of the human population is discussed.  相似文献   
5.
In this paper, the ionic liquids 1,2-diethylpyridinium ethylsulfate, EEpyESO4; 1-methylpyridinium methylsulfate, MpyMSO4; 1,3-dimethylpyridinium methylsulfate, MMpyMSO4; and 2-ethyl-1-methylpyridinium methylsulfate, EMpyMSO4; were synthesized in our laboratory, and their experimental densities, speeds of sound, dynamic viscosities, and refractive indices were studied as a function of temperature at atmospheric pressure. Thermal expansion coefficient, molar volume, and molar refraction of these ionic liquids were calculated from the experimental density and refractive index values.  相似文献   
6.
7.
8.
9.
10.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号