全文获取类型
收费全文 | 1840篇 |
免费 | 127篇 |
国内免费 | 32篇 |
专业分类
化学 | 1282篇 |
晶体学 | 21篇 |
力学 | 56篇 |
综合类 | 3篇 |
数学 | 185篇 |
物理学 | 452篇 |
出版年
2023年 | 12篇 |
2022年 | 38篇 |
2021年 | 36篇 |
2020年 | 29篇 |
2019年 | 40篇 |
2018年 | 23篇 |
2017年 | 22篇 |
2016年 | 54篇 |
2015年 | 55篇 |
2014年 | 85篇 |
2013年 | 85篇 |
2012年 | 145篇 |
2011年 | 156篇 |
2010年 | 86篇 |
2009年 | 104篇 |
2008年 | 138篇 |
2007年 | 125篇 |
2006年 | 79篇 |
2005年 | 92篇 |
2004年 | 58篇 |
2003年 | 46篇 |
2002年 | 51篇 |
2001年 | 46篇 |
2000年 | 42篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 13篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 28篇 |
1992年 | 13篇 |
1991年 | 17篇 |
1990年 | 8篇 |
1989年 | 7篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 22篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1980年 | 12篇 |
1979年 | 11篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1976年 | 12篇 |
1975年 | 9篇 |
1973年 | 9篇 |
1971年 | 5篇 |
排序方式: 共有1999条查询结果,搜索用时 15 毫秒
41.
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
42.
Density functional theory and ab initio calculations have been used to determine structures and stabilities of the protonated aromatics species AH^+ and AH2^2+ (A=pyrrole, furan). Possible mechanisms and relative energetics for protonation of pyrrole and furan by H3O^+ and AH^+ in the gas phase have been explored. Calculations show that the Cα-protonated species was the most stable structure for AH^+, and the protonated AH^+ might accommodate the second proton to yield AH2^2+ if the free proton was available. The gas-phase H3O^+ could protonate pyrrole and furan with significant exothermiCity and almost without barrier. The proton transfer from AH4^+ to pyrrole and furan has a barrier ranging from 33.5 to 39.3 kJ/mol in the gas phase. 相似文献
43.
We propose a numerical procedure for the calculation of the electrostatic repulsion force between two identical, parallel surfaces immersed in anab electrolyte solution. These surfaces are coated with an ion-penetrable membrane carrying fixed charges. The amount of fixed charges is governed by the dissociation of the functional groups in the membrane phase. The effect of pH on the degree of dissociation of these functional groups is taken into account. The difficulty of extensive use of Jacobi elliptic function in the numerical treatment of Poisson-Boltzmann equation can be circumvented by resorting to the present algorithm. 相似文献
44.
45.
46.
47.
48.
49.
50.
Biflavonoids, widely distributed in natural plants, had strong biological activities including spasmolysis, peripheral vasodilatation, antibradykinin activity and antispasmogenic action against prostaglandin PGE1, inhibition of cyclic GMP and cyclic AMP phosphodiesterase and inhibition of hepatoma cells. Recently, some biflavonoids were demonstrated to enhance suppersion of lymphocyte proliferation, inhibition of phospholipaseCr1, anti-inflammatory activity, anti-HIV activity, anticompleme… 相似文献