全文获取类型
收费全文 | 228篇 |
免费 | 24篇 |
国内免费 | 9篇 |
专业分类
化学 | 134篇 |
晶体学 | 2篇 |
力学 | 12篇 |
数学 | 65篇 |
物理学 | 48篇 |
出版年
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 10篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 23篇 |
2012年 | 7篇 |
2011年 | 9篇 |
2010年 | 12篇 |
2009年 | 9篇 |
2008年 | 7篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 3篇 |
2004年 | 7篇 |
2003年 | 13篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1966年 | 1篇 |
1937年 | 1篇 |
1921年 | 1篇 |
1902年 | 1篇 |
1900年 | 1篇 |
排序方式: 共有261条查询结果,搜索用时 15 毫秒
1.
Acid/Base‐Triggered Switching of Circularly Polarized Luminescence and Electronic Circular Dichroism in Organic and Organometallic Helicenes 下载免费PDF全文
Nidal Saleh Barry Moore II Monika Srebro Nicolas Vanthuyne Loïc Toupet J. A. Gareth Williams Christian Roussel Kirandeep K. Deol Gilles Muller Jochen Autschbach Jeanne Crassous 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1673-1681
Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene‐bipyridine proligand 1 a and in its “rollover” cycloplatinated derivative 2 a . Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum‐chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene‐bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge‐transfer‐type transition rather than a π–π* transition) as well as an increase in the HOMO–LUMO character of the transition and stabilization of the LUMO level upon protonation. 相似文献
2.
3.
4.
Dr. Amey Nimkar Dr. Sandeepan Maity Prof. Robert A Flowers II Prof. Shmaryahu Hoz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(44):10499-10504
The work described herein compares the effect of additives (HMPA, methanol, ethylene glycol, pinacol, N-methylethanolamine) on thermal and photochemical reactions of samarium diiodide (SmI2). In thermal reactions, additives that coordinate to SmI2 induce a significant increase in reaction rate. In photochemical reactions, the presence of an electronegative atom with a highly localized negative charge on the substrate leads to a rate deceleration. In order to benefit from the columbic interaction with the positively charged samarium cation, these substrates react preferentially by an inner sphere reduction mechanism. The addition of ligands prevents this close interaction causing rate retardation. Furthermore, studies demonstrate that excited state quenching of SmII by ethylene glycol and other additives indicate that it is unlikely to be the major cause for the observed rate retardation. This effect provides a simple diagnostic tool to distinguish between an inner and an outer sphere reduction mechanism. 相似文献
5.
James T. Brewster II Apolonio Aguilar Gonzalo Anguera Hadiqa Zafar Matthew D. Moore 《Journal of Coordination Chemistry》2018,71(11-13):1808-1813
AbstractThe reaction between amethyrin and non-aqueous uranyl silylamide (UO2[N(SiMe3)2]2) under anaerobic conditions affords a bench-stable uranyl complex. UV–vis spectroscopy, cyclic voltammetry, as well as proton NMR spectroscopic analyses provide support for the conclusion that all six pyrrole subunits participate in coordination of the uranyl dication and that, upon complexation, the amethyrin-core undergoes a 2-electron oxidation to yield a formal 22 π-electron aromatic species. 相似文献
6.
7.
8.
9.
Timothy P. Moneypenny II Huiying Liu Anna Yang Ian D. Robertson Jeffrey S. Moore 《Journal of polymer science. Part A, Polymer chemistry》2017,55(18):2935-2948
Alkene metathesis has proven to be a powerful method for carbon carbon bond formation, particularly in the field of polymer and materials science. The availability of various tailor-made catalysts not only enables the synthesis of well-defined polymers but facilitates the development of functional, stimuli–responsive materials. This highlight, dedicated to Professor Robert Grubbs on his 75th birthday, focuses on the various research efforts in our group utilizing both alkene and alkyne metatheses and the interesting materials derived from them. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2935–2948 相似文献
10.
Over the last 23 years, the U.S. Securities and Exchange Commission has required over 34,000 companies to file over 165,000 annual reports. These reports, the so-called “Form 10-Ks,” contain a characterization of a company’s financial performance and its risks, including the regulatory environment in which a company operates. In this paper, we analyze over 4.5 million references to U.S. Federal Acts and Agencies contained within these reports to measure the regulatory ecosystem, in which companies are organisms inhabiting a regulatory environment. While individuals across the political, economic, and academic world frequently refer to trends in this regulatory ecosystem, far less attention has been paid to supporting such claims with large-scale, longitudinal data. In this paper, in addition to positing a model of regulatory ecosystems, we document an increase in the regulatory energy per filing, i.e., a warming “temperature.” We also find that the diversity of the regulatory ecosystem has been increasing over the past two decades. These findings support the claim that regulatory activity and complexity are increasing, and this framework contributes an important step towards improving academic and policy discussions around legal complexity and regulation. 相似文献