全文获取类型
收费全文 | 336篇 |
免费 | 18篇 |
国内免费 | 62篇 |
专业分类
化学 | 393篇 |
晶体学 | 4篇 |
力学 | 1篇 |
综合类 | 4篇 |
物理学 | 14篇 |
出版年
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 6篇 |
2013年 | 44篇 |
2012年 | 14篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 21篇 |
2007年 | 27篇 |
2006年 | 24篇 |
2005年 | 25篇 |
2004年 | 17篇 |
2003年 | 21篇 |
2002年 | 24篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 2篇 |
1996年 | 4篇 |
1995年 | 11篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1979年 | 2篇 |
排序方式: 共有416条查询结果,搜索用时 46 毫秒
121.
122.
123.
A facile route for the synthesis of dimethyl adipate (DAP) from cyclopentanone and dimethyl carbonate (DMC) in the presence of solid base catalysts has been developed.It was found that the intermediate carbomethoxycyclopentanone (CMCP) was produced from cyclopentanone with DMC in the first step,and then CMCP was further converted to DAP by reacting with a methoxide group.The role of the basic catalysts can be mainly ascribed to the activation of cyclopentanone via the abstraction of a proton in the α-position by base sites,and solid bases with moderate strength,such as MgO,favor the formation of DAP. 相似文献
124.
采用毛细管气相色谱法(GC)测定了二乙基二硫的含量.结果表明,二乙基二硫含量在0.010.4g/L范围内具有良好的线性关系,平均回收率为99.91%;该方法简便、准确、重复性好,可方便地用于二乙基二硫含量的测定. 相似文献
125.
126.
Jinjun Yang Zhenguo Li Pengju Pan Bo Zhu Tungalag Dong Yoshio Inoue 《Journal of Polymer Science.Polymer Physics》2009,47(20):1997-2007
The polymorphic crystalline structure and melting behavior of biodegradable poly(butylene adipate) (PBA) samples melt‐crystallized at different crystallization temperatures were studied by differential scanning calorimetry (DSC) and fourier transform infrared (FTIR) spectroscopy. The crystalline structure and melting behavior of PBA were found to be greatly dependent on the crystallization temperature. By comparison of the FTIR spectra and the corresponding second derivatives between the α‐ and β‐crystal of PBA, the spectral differences were identified for the IR bands appeared at 1485, 1271, 1183, and 930 cm?1 and the possible reasons were presented. Especially, the 930 cm?1 band was found to be a characteristic band for the β‐crystal. Combining the DSC data with the analysis of normalized intensity changes of several main IR bands during the melting process, the melting behaviors of the α‐ and β‐crystal were clarified in detail. It is demonstrated by the in situ IR measurement that the β‐crystalline phase would transform into the α‐crystalline phase during the melting process, and the solid–solid phase transition from the β‐ to α‐crystal was well elucidated by comparing the intensity changes of the 1170 and 930 cm?1 bands. The dependence of the β‐ to α‐crystal phase transition on the heating rate was revealed by monitoring the intensity ratio of the 909 and 930 cm?1 band. It was suggested that at the heating rate of 0.5 or 1 °C/min, the percent amount of the transformed α‐crystal from the β‐crystal was much higher than that at the higher heating rate. The β‐crystal transforms into the α‐crystal incompletely at the higher heating rate because of the less time available for the phase transition. In addition, the β‐ to α‐crystal phase transition was further confirmed by the IR band shifts during the melting process. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1997–2007, 2009 相似文献
127.
Jingang Fang Baowei Wang Zhenhua Li Genhui Xu 《Reaction Kinetics and Catalysis Letters》2003,80(2):293-301
The synthesis of diethyl oxalate from ethyl nitrite and carbon monoxide in gaseous phase has been studied at atmospheric pressure.
Kinetics of coupling - regeneration reaction has been determined and the optimization of the reaction has been simulated.
The influences of gas impurities has also been studied. Scale-up circulating shows that the concentrate and selectivity were
stable in the product and the process is suitable for industrial production.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
128.
129.
Visible-light transparent high-quality substrate-supported poly(2,3-benzofuran) (PBF) film has been successfully electrosynthesized by direct anodic oxidation of 2,3-benzofuran on stainless steel sheet in boron trifluoride diethyl etherate (BFEE) containing 10% poly(ethylene glycol) (PEG) with molar mass of 400 (by volume). The oxidation potential of 2,3-benzofuran in this medium was measured to be only 1.0 V vs. SCE, which is lower than that determined in acetonitrile + 0.1 M Bu4NBF4 (1.2 V vs. SCE). The PBF films obtained in this media showed good electrochemical behaviors and good thermal stability with conductivity of 10−2 S cm−1, and the doping level of as-prepared PBF films was determined to be only 8.9%. The structure and morphology of the polymer were investigated by UV-vis, infrared spectroscopy and scanning electron microscopy (SEM), respectively. To the best of our knowledge, this is the first case for the syntheses of PBF films. 相似文献
130.
从磷硅试剂合成烃基膦酯类化合物 总被引:1,自引:1,他引:0
本文报导三甲基硅氧基亚磷酸酯(一种活性较高的磷硅试剂)与醛酮反应而获得十四个二乙基三甲硅氧基烃基膦酸酯。产物结构经IR,~1HNMR,~(31)PNMR,MS测试和元素分析表征;对反应机理作了初步讨论。 相似文献