全文获取类型
收费全文 | 1558篇 |
免费 | 88篇 |
国内免费 | 32篇 |
专业分类
化学 | 1091篇 |
晶体学 | 14篇 |
力学 | 68篇 |
综合类 | 1篇 |
数学 | 111篇 |
物理学 | 393篇 |
出版年
2024年 | 3篇 |
2023年 | 13篇 |
2022年 | 14篇 |
2021年 | 22篇 |
2020年 | 27篇 |
2019年 | 36篇 |
2018年 | 17篇 |
2017年 | 10篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 46篇 |
2013年 | 61篇 |
2012年 | 113篇 |
2011年 | 138篇 |
2010年 | 73篇 |
2009年 | 68篇 |
2008年 | 109篇 |
2007年 | 77篇 |
2006年 | 70篇 |
2005年 | 91篇 |
2004年 | 67篇 |
2003年 | 51篇 |
2002年 | 48篇 |
2001年 | 43篇 |
2000年 | 33篇 |
1999年 | 20篇 |
1998年 | 14篇 |
1997年 | 20篇 |
1996年 | 32篇 |
1995年 | 15篇 |
1994年 | 24篇 |
1993年 | 31篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 9篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1979年 | 7篇 |
1978年 | 13篇 |
1977年 | 3篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 5篇 |
排序方式: 共有1678条查询结果,搜索用时 15 毫秒
31.
Woodfordin C, a macro-ring hydrolyzable tannin dimer with antitumor activity, and accompanying dimers from Woodfordia fruticosa flowers 总被引:1,自引:0,他引:1
T Yoshida T Chou A Nitta K Miyamoto R Koshiura T Okuda 《Chemical & pharmaceutical bulletin》1990,38(5):1211-1217
Three new dimeric hydrolyzable tannins, woodfordins A, B and C, along with seven known hydrolyzable tannins, including oenothein B, a dimer exhibiting marked host-mediated antitumor activity, were isolated from an Indonesian crude drug, Sidowayah [dried flowers of Woodfordia fruticosa (L.) Kurz (Lythraceae)]. The structures of the new tannins were elucidated based on chemical and spectral evidence. Woodfordin C, having a macro-ring structure, was also found to exhibit a significant antitumor activity. 相似文献
32.
The reactions of a new cationic complex, [Cp(CO)2Mo(η4-2-methyl-3-SPh-C4H4)]+ PF?6 (3), with carbon, hydride, and nitrogen nucleophiles were found to give only the C-1 addition products in good yield. The X-ray crystal structures of two of the addition products 4a and 4e confirm the regio- and stereochemistry of the nucleophilic additions. 相似文献
33.
Ya‐Ching Shen Yun‐Sheng Lin Shaw‐Man Hsu Ashraf Taha Khalil Shih‐Sheng Wang Ching‐Te Chien Yao‐Haur Kuo Chang‐Hung Chou 《Helvetica chimica acta》2007,90(7):1319-1329
The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells. 相似文献
34.
35.
36.
37.
38.
39.
The base alkylation of 2,3-dimercapto-1-propanol with alkyl halides leads in good yield to 2,3-bis(alkylthio)-1-propanol and dialkyl sulfide. The reaction of 2,3-bis(alkylthio)-1-propanol with catalytic concentrated sulfuric acid proceeds with rearrangement to give 1,2,3-tris(alkylthio)propane and dialkyl disulfide. The rearrangement reaction takes place through a common intermediate thiaranium intermediate 8. 相似文献
40.