全文获取类型
收费全文 | 121539篇 |
免费 | 18779篇 |
国内免费 | 11688篇 |
专业分类
化学 | 84571篇 |
晶体学 | 1389篇 |
力学 | 7256篇 |
综合类 | 559篇 |
数学 | 14406篇 |
物理学 | 43825篇 |
出版年
2024年 | 244篇 |
2023年 | 2230篇 |
2022年 | 2651篇 |
2021年 | 4052篇 |
2020年 | 4578篇 |
2019年 | 4469篇 |
2018年 | 3781篇 |
2017年 | 3480篇 |
2016年 | 5736篇 |
2015年 | 5307篇 |
2014年 | 6474篇 |
2013年 | 8886篇 |
2012年 | 10733篇 |
2011年 | 11416篇 |
2010年 | 7389篇 |
2009年 | 7351篇 |
2008年 | 7712篇 |
2007年 | 7118篇 |
2006年 | 6448篇 |
2005年 | 5566篇 |
2004年 | 4634篇 |
2003年 | 3550篇 |
2002年 | 3223篇 |
2001年 | 2404篇 |
2000年 | 2115篇 |
1999年 | 2344篇 |
1998年 | 2073篇 |
1997年 | 1923篇 |
1996年 | 2116篇 |
1995年 | 1681篇 |
1994年 | 1601篇 |
1993年 | 1318篇 |
1992年 | 1195篇 |
1991年 | 1078篇 |
1990年 | 882篇 |
1989年 | 637篇 |
1988年 | 539篇 |
1987年 | 441篇 |
1986年 | 442篇 |
1985年 | 408篇 |
1984年 | 333篇 |
1983年 | 223篇 |
1982年 | 197篇 |
1981年 | 165篇 |
1980年 | 126篇 |
1979年 | 75篇 |
1978年 | 62篇 |
1977年 | 63篇 |
1976年 | 62篇 |
1974年 | 72篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
Jia Tian-Cong Guo Jin-Tao Wang Zhen Zhu Xiao-Shan Zhang Qian-Xin Chen Ping Yao Kun Lv Wen-Ying Liu Guo-Guang 《Journal of Radioanalytical and Nuclear Chemistry》2019,321(3):823-829
Journal of Radioanalytical and Nuclear Chemistry - In the present work the final products of coumarin radiation chemical transformation are investigated by chromatography. During radiolysis of... 相似文献
92.
93.
Theoretical study of (e,2e) triple differential cross sections of pyrimidine and tetrahydrofurfuryl alcohol molecules using multi-center distorted-wave method
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We report theoretical studies of electron impact triple differential cross sections of two bio-molecules,pyrimidine and tetrahydrofurfuryl alcohol,in the coplanar asymmetric kinematic conditions with the impact energy of 250 eV and ejected electron energy of 20 eV at three scattering angles of-5°,-10°,and-15°.Present multi-center distorted-wave method well describes the experimental data,which was obtained by performing(e,2e)experiment.The calculations show that the secondary electron produced by the primary impact electron is strongly influenced by the molecular ionic multi-center potential,which must be considered when the low energy electron interacts with DNA analogues. 相似文献
94.
95.
Journal of Thermal Analysis and Calorimetry - The fire behavior of one flame-retardant PVC cable used as building wire is investigated in this work. Bench scale tests were performed using a cone... 相似文献
96.
97.
98.
99.
100.
When dealing with simple phenols such as caffeic acid (CA) and ferulic acid (FA), found in a variety of plants, it is very important to have control over the most important factors that accelerate their degradation reactions. This is the first report in which the stabilities of these two compounds have been systematically tested by exposure to various different factors. Forced degradation studies were performed on pure standards (trans-CA and trans-FA), dissolved in different solvents and exposed to different oxidative, photolytic and thermal stress conditions. Additionally, a rapid, sensitive, and selective stability-indicating gas chromatographic-mass spectrometric method was developed and validated for determination of trans-CA and trans-FA in the presence of their degradation products. Cis-CA and cis-FA were confirmed as the only degradation products in all the experiments performed. All the compounds were perfectly separated by gas chromatography (GC) and identified using mass spectrometry (MS), a method that additionally elucidated their structures. In general, more protic solvents, higher temperatures, UV radiation and longer storage times led to more significant degradation (isomerization) of both trans-isomers. The most progressive isomerization of both compounds (up to 43%) was observed when the polar solutions were exposed to daylight at room temperature for 1 month. The method was validated for linearity, precision as repeatability, limit of detection (LOD) and limit of quantitation (LOQ). The method was confirmed as linear over tested concentration ranges from 1−100 mg L−1 (r2s were above 0.999). The LOD and LOQ for trans-FA were 0.15 mg L−1 and 0.50 mg L−1, respectively. The LOD and LOQ for trans-CA were 0.23 mg L−1 and 0.77 mg L−1, respectively. 相似文献