全文获取类型
收费全文 | 1608篇 |
免费 | 32篇 |
国内免费 | 2篇 |
专业分类
化学 | 1294篇 |
晶体学 | 5篇 |
力学 | 7篇 |
数学 | 190篇 |
物理学 | 146篇 |
出版年
2021年 | 21篇 |
2020年 | 18篇 |
2019年 | 25篇 |
2017年 | 14篇 |
2016年 | 28篇 |
2015年 | 31篇 |
2014年 | 38篇 |
2013年 | 39篇 |
2012年 | 55篇 |
2011年 | 74篇 |
2010年 | 48篇 |
2009年 | 39篇 |
2008年 | 46篇 |
2007年 | 51篇 |
2006年 | 58篇 |
2005年 | 53篇 |
2004年 | 53篇 |
2003年 | 52篇 |
2002年 | 51篇 |
2001年 | 30篇 |
2000年 | 34篇 |
1999年 | 33篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 27篇 |
1995年 | 30篇 |
1994年 | 36篇 |
1993年 | 20篇 |
1992年 | 24篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 14篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 25篇 |
1984年 | 30篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 28篇 |
1979年 | 24篇 |
1978年 | 26篇 |
1977年 | 23篇 |
1976年 | 27篇 |
1975年 | 29篇 |
1974年 | 36篇 |
1973年 | 34篇 |
1972年 | 25篇 |
1971年 | 12篇 |
1970年 | 16篇 |
排序方式: 共有1642条查询结果,搜索用时 15 毫秒
101.
Heiko Schirmer Michael Duetsch Frank Stein Thomas Labahn Burkhard Knieriem Armin de Meijere 《Angewandte Chemie (International ed. in English)》1999,38(9):1285-1287
A novel mode of reaction towards arylethynes is shown by the β-trimethylsilyl-substituted α,β-unsaturated Fischer carbene complexes 1 . A mixture of the isomeric, highly substituted spiro[4.4]nonatrienes 2 and 3 is formed by the formal insertion of three alkyne molecules and subsequent cyclization (see scheme). Such selective triple insertions of alkynes into ethenylcarbene complexes have not been previously observed. 相似文献
102.
David Scheschkewitz Matthias Menzel Matthias Hofmann Paul von Ragu Schleyer Gertraud Geiseler Werner Massa Klaus Harms Armin Berndt 《Angewandte Chemie (International ed. in English)》1999,38(19):2936-2939
Remarkably short distances to the ring plane are shown by the η5-bound lithium ions in the first compound with a triply negatively charged five-membered ring, 1 , which was obtained by reduction of 2 with lithium. R=CH(SiMe3)2, Dur=2,3,5,6-tetramethylphenyl. 相似文献
103.
104.
Sautter A Kaletas BK Schmid DG Dobrawa R Zimine M Jung G van Stokkum IH De Cola L Williams RM Würthner F 《Journal of the American Chemical Society》2005,127(18):6719-6729
A molecular square with dimensions of about 4 nm, incorporating sixteen pyrene chromophores attached to four ditopic bay-functionalized perylene bisimide chromophores, has been synthesized by coordination to four Pt(II) phosphine corner units and fully characterized via NMR spectroscopy and ESI-FTICR mass spectrometry. Steady-state and time-resolved emission as well as femtosecond transient absorption studies reveal the presence of a highly efficient (>90%) and fast photoinduced energy transfer (k(en) approximately equal to 5.0 x 10(9) s(-1)) from the pyrene to the perylene bisimide chromophores and a very fast and efficient electron transfer (>94%, k(et) approximately equal to 5 x 10(11) up to 43 x 10(11) s(-1)). Spectrotemporal parametrization indicates upper excited-state electron-transfer processes, various energy and electron-transfer pathways, and chromophoric heterogeneity. Temperature-dependent time-resolved emission spectroscopy has shown that the acceptor emission lifetime increases with decreasing temperature from which an electron-transfer barrier is obtained. The extremely fast electron-transfer processes (substantially faster and more efficient than in the free ligand) that are normally only observed in solid materials, together with the closely packed structure of 20 chromophoric units, indicate that we can consider the molecular square as a monodisperse nanoaggregate: a molecularly defined ensemble of chromophores that partly behaves like a solid material. 相似文献
105.
106.
The enormous diversity of chemical compounds now available is problematic for waste disposal and recovery of essential resources such as rare earth metals. Non-renewable resources are being depleted and need to be managed more effectively. To validate the potential of strategic metals, which often are multi-functional and thus find (competitive) applications in different technologies, a criticality concept is applied. This is based on qualitative and quantitative criteria characterizing the different transformations along supply chains: ranging from the resource deposit to the product and from there into the so-called re-phases or disposal and end-of-life. The trajectories of the resources in real space and time have to be transparent in order to optimize the resource efficiency and its long-ranging compatibility but also to minimize dissipation. This approach allows developing transparent narratives (“Stoffgeschichten”, “Stories of Stuff”) for a responsible and benign use of resources. Only then can re-integration of functional materials be achieved. 相似文献
107.
Hans-Georg Schmarr Birgit Maas Armin Mosandl Stephan Bihler Hans-Peter Neukom Konrad Grob 《Journal of separation science》1991,14(5):317-321
An unusual peak defocusing effect influencing chromatographic performance over a limited range of elution temperatures is described for hexakis(2,6-di-O-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase. Since this phenomenon is likely to be dependent on minor details of the cyclodextrin molecule, full assignment of the 1H- and 13C-NMR-spectra are given. 相似文献
108.
Georgios Papazoglou Jorge Sierra Katharina Homberger Armin Guggisberg Wolf-Dietrich Woggon Manfred Hesse 《Helvetica chimica acta》1991,74(3):565-571
Aphelandrine ( 1 ) is shown to be biosynthesized in the root cells of Aphelandra tetragona (VAHL ) NEES from labelled putrescine ( 4 ), spermidine ( 5 ), and cinnamic acid ( 3 ). Whether spermine ( 6 ) and the (p-hydroxycinnamoyl)spermidine 8 are precursors of 1 is uncertain, since the latter is hydrolysed to a large extent before incorporation, and the former is metabolized to 4 and 5 . Methionine ( 7 ) is the source of the 3-aminopropyl unit of 5 and 6 . 相似文献
109.
110.