全文获取类型
收费全文 | 1698篇 |
免费 | 48篇 |
国内免费 | 11篇 |
专业分类
化学 | 1240篇 |
晶体学 | 8篇 |
力学 | 32篇 |
数学 | 270篇 |
物理学 | 207篇 |
出版年
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 27篇 |
2019年 | 8篇 |
2018年 | 17篇 |
2017年 | 23篇 |
2016年 | 31篇 |
2015年 | 35篇 |
2014年 | 35篇 |
2013年 | 62篇 |
2012年 | 98篇 |
2011年 | 118篇 |
2010年 | 48篇 |
2009年 | 39篇 |
2008年 | 102篇 |
2007年 | 81篇 |
2006年 | 98篇 |
2005年 | 106篇 |
2004年 | 85篇 |
2003年 | 76篇 |
2002年 | 71篇 |
2001年 | 19篇 |
2000年 | 17篇 |
1999年 | 25篇 |
1998年 | 27篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 21篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 14篇 |
1991年 | 12篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 13篇 |
1986年 | 13篇 |
1985年 | 25篇 |
1984年 | 25篇 |
1983年 | 16篇 |
1982年 | 20篇 |
1981年 | 28篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1976年 | 21篇 |
1975年 | 13篇 |
1974年 | 8篇 |
1973年 | 9篇 |
排序方式: 共有1757条查询结果,搜索用时 15 毫秒
41.
42.
Gianfranco Denti Mauro Ghedini Jon A. McCleverty Harry Adams Neil A. Bailey 《Transition Metal Chemistry》1982,7(4):222-224
Summary Treatment of [Mo{HB(3,5-Me2C3HN2)3}(NO)I2] with one or two moles of AgPF6 in acetonitrile afforded the paramagnetic (one unpaired electron) complex [Mo{HB(3,5-Me2C3NH2)3}(NO)(NCMe)2][PF6]. The structure of this complex was determined crystallographically, and the six-coordinate geometry of the complex cation confirmed. 相似文献
43.
44.
45.
46.
47.
48.
[reaction: see text] The combination of catalytic palladium(0) and Trost ligand provides an effective catalyst for the rearrangement of allyl beta-ketoesters. The mechanism of the transformation involves formation of pi-allyl palladium intermediates which undergo enantioselective attack by ketone enolates. Decarboxylation of beta-ketocarboxylates allows regiospecific generation of enolates under extremely mild conditions. 相似文献
49.
Jon Volden Yngvar Thomassen Tyge Greibrokk Syvert Thorud Paal Molander 《Analytica chimica acta》2005,530(2):263-271
The storage stability of the occupationally frequently occurring compounds, methylethylketone, methylisobutylketone, benzene, toluene, tetrachloroethylene, n-butylacetate, -pinene, β-pinene, limonene and n-decane, has been investigated on the adsorbents Tenax TA, Chromosorb 106 and Carbotrap using thermally desorbable tube type samplers, commonly utilized in ambient and workroom atmospheric measurements. Fifty and 500 ng of each compound were loaded on the various adsorbents tubes, stored at both ambient (20 °C) and refrigerated (4 °C) temperatures and analysed by means of thermal gas chromatography with mass spectrometric detection on days 0, 7, 14 and 28 after exposure. A 90% storage recovery was chosen as acceptance criteria for storage stability, and statistical testing by Student's t-test, analysis of variance and Bonferroni post hoc tests were employed to investigate the effect of the categorical variables storage time, storage temperature and analyte loading on the different adsorbents. Chromosorb 106 showed the overall best behaviour with recoveries of 90% or better for all analytes during the 28-day test period. Tenax TA and Carbotrap yielded lower recoveries and were more influenced by variations in storage time, storage temperature and analyte loading. Refrigerated temperatures were best avoided for storage on Tenax TA, but may increase the recovery of some compounds on Carbotrap (e.g. n-butylacetate). The blank build-up on the adsorbents was also investigated, and Carbotrap and Tenax TA showed no signs of artefact development over time. Chromosorb 106, however, contained inherently more artefacts that build up over time, which in spite of the excellent storage capability, may limit its use in field studies where long storage times are normal. 相似文献
50.
The structure and configuration of gilmaniellin, a metabolite of Gilmaniella humicola BARRON , has been shown to be 2 by X-ray analysis. By comparison of spectral data structure 1 has been assigned to dechlorogilmaniellin. 相似文献