全文获取类型
收费全文 | 428篇 |
免费 | 32篇 |
国内免费 | 37篇 |
专业分类
化学 | 244篇 |
晶体学 | 4篇 |
力学 | 30篇 |
综合类 | 12篇 |
数学 | 31篇 |
物理学 | 176篇 |
出版年
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 11篇 |
2016年 | 3篇 |
2015年 | 6篇 |
2014年 | 15篇 |
2013年 | 36篇 |
2012年 | 18篇 |
2011年 | 23篇 |
2010年 | 11篇 |
2009年 | 18篇 |
2008年 | 26篇 |
2007年 | 28篇 |
2006年 | 25篇 |
2005年 | 24篇 |
2004年 | 26篇 |
2003年 | 5篇 |
2002年 | 9篇 |
2001年 | 24篇 |
2000年 | 25篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 5篇 |
1995年 | 12篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1975年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1899年 | 2篇 |
排序方式: 共有497条查询结果,搜索用时 31 毫秒
111.
Silica supported heteropoly acids are active in n-hexane cracking, while the pure compounds (except H3PW12O40) are inactive. This result is explained by a partial transformation of H6P2W18O62 and H6P2W21O71 (H2O)3 into H3PW12O40. In the case of H4SiW12O40, the polyanion in interaction with silica leads to superacidic species upon thermal treatment.
, , -, ( H3PW12O40) . H6P2W18O62 H6P2W21O71 (H2O)3 H3PW12O40. H4SiW12O40 , , .相似文献
112.
Molodtsov SG Elyashberg ME Blinov KA Williams AJ Martirosian EE Martin GE Lefebvre B 《Journal of chemical information and computer sciences》2004,44(5):1737-1751
The elucidation of chemical structures from 2D NMR data commonly utilizes a combination of COSY, HMQC/HSQC, and HMBC data. Generally COSY connectivities are assumed to mostly describe the separation of protons that are separated by 1 skeletal bond (3JHH), while HMBC connectivities represent protons separated from carbon atoms by 1 to 2 skeletal bonds (2JCH and 3JCH). Obviously COSY and HMBC connectivities of lengths greater than those described have been detected. Though experimental techniques have recently been described to aid in the identification of the nature of the couplings the detection of whether a coupling is 2-bond or greater still remains a challenge in most laboratories. In the StrucEluc software system the common lengths of the connectivities, 1-bond for COSY and 1- or 2-bond for HMBC, derived from 2D NMR data are set as the default. Therefore, in the presence of any extended connectivities contradictions can appear in the 2D NMR data. In this article, algorithmic methods for the detection and removal of contradictions in 2D NMR data that have been developed in support of StrucEluc are described. The methods are based on the analysis of molecular connectivity diagrams, MCDs. These methods have been implemented in the StrucEluc system and tested by solving 50 structural problems with 2D NMR spectral data containing contradictions. The presence of contradictions was detected by the algorithm in 90% of the cases, and the contradictions were automatically removed in approximately 50% of the problems. A method of "fuzzy" structure generation in the presence of contradictions has been suggested and successfully tested in this work. This work will demonstrate examples of the application of developed methods to a number of structural problems. 相似文献
113.
114.
115.
116.
117.
AB_3型超支化聚(酰胺-酯)的合成及缩聚动力学研究 总被引:6,自引:0,他引:6
采用丁二酸酐、三羟甲基氨基甲烷为主要原料 ,在冰水浴条件下 ,合成AB3型单体 ,然后进行熔融缩聚制得超支化聚 (酰胺 酯 ) ,没有出现凝胶现象 .采用Fourier变换红外谱仪 (FTIR)、粘度测试、端基分析等方法对其结构、特性粘数进行了表征 .同时对AB3型超支化聚 (酰胺 酯 )的缩聚反应动力学进行了研究 ,得出了130℃、14 0℃和 15 0℃时的缩聚反应速率常数 ,并进一步得出了缩聚反应活化能 .实验结果证明缩聚过程为自催化过程 ,且为三级反应 相似文献
118.
Laser excitation spectra of the A2Σ-X2Πi system have been recorded for 63CuS and 65CuS isotopic molecules with a single-mode dye laser operating in the region 17000–18000 cm?1. For highly overlapped sequences, use of a monochromator as a narrow band filter was necessary to allow rotational analysis. A simultaneous fit of all eight analyzed bands has led to the following spectroscopic constants for 63CuS (in cm?1):
State | |||||||
0 | 17924.335 (7) | 0.17989 (4) | 0.177 (7) | 0.03853 (7) | |||
1 | 842.574 (7) | 0.18701 (4) | 0.163 (7) | 0.01496 (9) | |||
0 | 432.566 (6) | 0.18818 (4) | 0.162 (7) | 0.01508 (9) | |||
1 | 411.289 (7) | 0.18724 (4) | 0.184 (7) | ?0.96 (6) | |||
0 | — | 0.18839 (4) | 0.160 (7) | ?0.11 (6) |