全文获取类型
收费全文 | 2168篇 |
免费 | 91篇 |
国内免费 | 11篇 |
专业分类
化学 | 1774篇 |
晶体学 | 31篇 |
力学 | 41篇 |
数学 | 112篇 |
物理学 | 312篇 |
出版年
2022年 | 8篇 |
2021年 | 19篇 |
2020年 | 29篇 |
2019年 | 47篇 |
2018年 | 21篇 |
2017年 | 12篇 |
2016年 | 50篇 |
2015年 | 40篇 |
2014年 | 63篇 |
2013年 | 93篇 |
2012年 | 136篇 |
2011年 | 160篇 |
2010年 | 89篇 |
2009年 | 63篇 |
2008年 | 156篇 |
2007年 | 138篇 |
2006年 | 138篇 |
2005年 | 147篇 |
2004年 | 134篇 |
2003年 | 113篇 |
2002年 | 63篇 |
2001年 | 27篇 |
2000年 | 30篇 |
1999年 | 18篇 |
1998年 | 27篇 |
1997年 | 24篇 |
1996年 | 20篇 |
1995年 | 13篇 |
1994年 | 18篇 |
1993年 | 7篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 20篇 |
1987年 | 13篇 |
1986年 | 16篇 |
1985年 | 21篇 |
1984年 | 21篇 |
1983年 | 17篇 |
1982年 | 23篇 |
1981年 | 21篇 |
1980年 | 17篇 |
1979年 | 27篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1976年 | 9篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 11篇 |
排序方式: 共有2270条查询结果,搜索用时 0 毫秒
1.
Kento Nishikibe Keisuke Nishikawa Momochika Kumagai Matsumi Doe Yoshiki Morimoto 《化学:亚洲杂志》2022,17(1):e202101137
There are marine cytotoxic bromotriterpenoids, named the thyrsiferol family that are structurally characterized by some tetrahydropyran (THP) and tetrahydrofuran (THF) rings. The thyrsiferol family belongs to natural products that are often difficult to determine their stereostructures even by the current, highly advanced spectroscopic methods, especially in acyclic systems including stereogenic tetrasubstituted carbon centers. In such cases, it is effective to predict and synthesize the possible stereostructures. Herein, to elucidate ambiguous stereostructures and unassigned absolute configurations of aplysiol B, laurenmariannol, and saiyacenol A, members of the thyrsiferol family, we carried out their asymmetric chemical syntheses featuring 6-exo and 5-exo oxacyclizations of epoxy alcohol precursors and 6-endo bromoetherification of a bishomoallylic alcohol. In this paper, we report total assignments of their stereostructures through their asymmetric chemical syntheses and also their preliminary cytotoxic activities against some tumor cells. These results could not have been achieved without depending on asymmetric total synthesis. 相似文献
2.
Annals of the Institute of Statistical Mathematics - 相似文献
3.
Watanabe Sou Senzaki Tatsuya Shibata Atsuhiro Nomura Kazunori Takeuchi Masayuki Nakatani Kiyoharu Matsuura Haruaki Horiuchi Yusuke Arai Tsuyoshi 《Journal of Radioanalytical and Nuclear Chemistry》2019,322(3):1273-1277
Journal of Radioanalytical and Nuclear Chemistry - Extraction chromatography flow-sheet employing octyl(phenyl)-N,N-diisobutylcarbonoylmethylphosphine oxide and bis(2-ethylhexyl) hydrogen phosphate... 相似文献
4.
5.
6.
Dr. Yohei Hattori Tatsuya Maejima Yumi Sawae Jun-ichiro Kitai Prof. Masakazu Morimoto Dr. Ryojun Toyoda Prof. Hiroshi Nishihara Prof. Satoshi Yokojima Dr. Shinichiro Nakamura Prof. Kingo Uchida 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11441-11450
The cyclization reaction of diarylethenes having an azulene ring occurs only via higher excited states. Novel diarylethenes having an azulene ring with a strong donor or acceptor were synthesized and examined in these reactions. A derivative having an electron-donating 1,3-benzodithiol-2-ylidenemethyl group at the 1-position of the azulene ring showed photochromism, whereas neither a derivative having a π-conjugated electron-donating group at the 3-position of the azulene ring nor derivatives having a π-conjugated electron-withdrawing group at the 1- or 3-position of the azulene ring showed any photochromism. The photoreactivities of these compounds were explained by calculating forces and bond orders on the excited states using density functional theory (DFT) and time-dependent (TD)-DFT. 相似文献
7.
Dr. Sudhir Kumar Keshri Dr. Waka Nakanishi Dr. Atsuro Takai Prof. Dr. Tomoya Ishizuka Prof. Dr. Takahiko Kojima Prof. Dr. Masayuki Takeuchi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(58):13288-13294
The design and synthesis of a tweezer-shaped naphthalenediimide (NDI)–anthracene conjugate ( 2NDI ) are reported. In the structure of the closed form (πNDI ⋅⋅⋅ πNDI stack) of 2NDI , which was elucidated by single-crystal XRD, the existence of C−H ⋅⋅⋅ O hydrogen bonding involving the nearest carbonyl oxygen atom of an NDI unit was suggested. The tunability of πNDI ⋅⋅⋅ πNDI interactions was studied by means of UV/Vis absorption, fluorescence and NMR spectroscopy and molecular modelling. This revealed that the πNDI ⋅⋅⋅ πNDI interactions in 2NDI affect the absorption and emission properties depending on the temperature. Furthermore, in polar solvents, 2NDI prefers the stronger πNDI ⋅⋅⋅ πNDI stack, whereas the πNDI ⋅⋅⋅ πNDI interaction is diminished in nonpolar solvents. Importantly, the conformational variations of 2NDI can be reversibly switched by variation in temperature, and this suggests potential application for fluorogenic molecular switches upon temperature changes. 相似文献
8.
Togueu Motcheyo Alain Bertrand Kimura Masayuki Doi Yusuke Tchawoua Clément 《Nonlinear dynamics》2019,95(3):2461-2468
Nonlinear Dynamics - We numerically analyzed the supratransmission phenomenon in the discrete nonlinear Schrödinger equation with the cubic–quintic nonlinearity. It has been reported... 相似文献
9.
10.
Synthesis of Disaccharide Nucleosides by the O‐Glycosylation of Natural Nucleosides with Thioglycoside Donors 下载免费PDF全文
Prof. Shin Aoki Taketo Fukumoto Taiki Itoh Masayuki Kurihara Shigeto Saito Shin‐ya Komabiki 《化学:亚洲杂志》2015,10(3):740-751
Disaccharide nucleosides constitute an important group of naturally‐occurring sugar derivatives. In this study, we report on the synthesis of disaccharide nucleosides by the direct O‐glycosylation of nucleoside acceptors, such as adenosine, guanosine, thymidine, and cytidine, with glycosyl donors. Among the glycosyl donors tested, thioglycosides were found to give the corresponding disaccharide nucleosides in moderate to high chemical yields with the above nucleoside acceptors using p‐toluenesulfenyl chloride (TolSCl) and silver triflate (AgOTf) as promoters. The interaction of these promoters with nucleoside acceptors was examined by 1H NMR spectroscopic experiments. 相似文献