全文获取类型
收费全文 | 809篇 |
免费 | 25篇 |
国内免费 | 1篇 |
专业分类
化学 | 659篇 |
晶体学 | 14篇 |
力学 | 9篇 |
数学 | 27篇 |
物理学 | 126篇 |
出版年
2022年 | 5篇 |
2021年 | 10篇 |
2020年 | 10篇 |
2019年 | 16篇 |
2018年 | 11篇 |
2017年 | 6篇 |
2016年 | 15篇 |
2015年 | 16篇 |
2014年 | 16篇 |
2013年 | 29篇 |
2012年 | 32篇 |
2011年 | 38篇 |
2010年 | 24篇 |
2009年 | 23篇 |
2008年 | 43篇 |
2007年 | 60篇 |
2006年 | 51篇 |
2005年 | 49篇 |
2004年 | 43篇 |
2003年 | 40篇 |
2002年 | 32篇 |
2001年 | 13篇 |
2000年 | 20篇 |
1999年 | 13篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 13篇 |
1991年 | 9篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 9篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 16篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 7篇 |
1976年 | 3篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1969年 | 4篇 |
1923年 | 3篇 |
排序方式: 共有835条查询结果,搜索用时 31 毫秒
1.
2.
3.
4.
5.
Esters of sulphur-containing 5- and 6-membered heterocycles, tetrahydro-3- and 4-thiopyranol and their 3- and 4-methyl, phenyl derivatives, and tetrahydro-2-thiophenemethanol, were synthesized. The solvolysis of β-thioesters in 80% aqueous acetone resulted in strong transannular S-participation and the products of solvolysis substantiated formation of bicyclic episulphonium ion intermediates. Such participation is considered to be present even in a tertiary system. On the other hand, γ-thioesters were solvolysed without any transannular S-participation, 相似文献
6.
Sachiko Yamada Keiko Nakayama Hiroaki Takayama Toshimasa Shinki Tatsuo Suda 《Tetrahedron letters》1984,25(30):3239-3242
(25)-25,26-Dihydroxy-23-oxovitamin D3 was synthesized efficiently and stereoselectively, and it was converted enzymatically to (25)-1α,25,26-trihydroxy-23-oxovitamin D3, a putative metabolite of 1α,25-dihydroxyvitamin D3. The spectral and chemical properties of (25)-25,26-dihydroxy-23-oxovitamin D3 and its 1α,hydroxylated derivative disagree with those reported for the isolated metabolite. 相似文献
7.
Supranee Wiwatchaiwong Hirotoshi Matsumura Nobuhumi Nakamura Masafumi Yohda Hiroyuki Ohno 《Electroanalysis》2007,19(5):561-565
We have studied the characterization of thermophilic cytochrome P450 (P450st)‐didodecyldimethylammonium bromide (DDAB) films by using UV‐vis absorption, resonance Raman spectroscopy, and electrochemical methods. The observed Raman spectrum indicated near‐native conformation of the heme iron in DDAB film on the surface of a glass slide, while on the surface of a plastic‐formed carbon (PFC) electrode, the conformation of P450st‐DDAB was very similar to that of heme‐DDAB film, suggesting the release of heme from P450st in DDAB films on PFC electrodes. When NaBr was added as salt to the casting solution, the result of Raman spectrum indicated near‐native conformation of P450st in DDAB film even on the PFC electrode, but no redox potential of P450st which has near native structure was observed. This study suggests the essential experimental conditions when working with heme protein‐DDAB films as, in some cases, heme iron from proteins is released on the surface of the electrode. 相似文献
8.
Noboru Matsumura Atsushi Ito Masaaki Tomura Yasuyuki Okumura Kazuhiko Mizuno 《Journal of heterocyclic chemistry》2004,41(1):99-102
Tetraazathiapentalene derivative 1 reacts with heterocumulenes such as diphenylketene (2) and 2‐pyridylisothiocyanate (5) to give heterocycles 3, 6 and 7 with elimination of methylisothiocyanate. The reactions of thiadiazolopyrimidine derivatives 8a‐b with ethoxycarbonyl isothiocyanate (9) and carbon disulfide (11) gives heterocycles 10 and 12 via thermal decomposition of 1:1 cycloadducts C and D which have a hypervalent sulfur. The mechanistic and reactivity features of these reactions are described. 相似文献
9.
Masato ItoAkihide Osaku Sachiko KitaharaMakoto Hirakawa Takao Ikariya 《Tetrahedron letters》2003,44(40):7521-7523
A ternary catalyst system of Cp*RuCl(cod)-2-diphenylphosphinoethylamine-KOt-Bu (Cp*=η5-C5(CH3)5, cod=1,5-cyclooctadiene) causes rapid racemization of chiral non-racemic sec-alcohols, which results from the reversible hydrogen transfer between sec-alcohols and ketones. Both tertiary phosphine and primary amine functionalities in the ligand are responsible for the high rate. 相似文献
10.