全文获取类型
收费全文 | 314篇 |
免费 | 26篇 |
国内免费 | 51篇 |
专业分类
化学 | 340篇 |
晶体学 | 2篇 |
综合类 | 2篇 |
数学 | 1篇 |
物理学 | 46篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 16篇 |
2020年 | 21篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 23篇 |
2012年 | 27篇 |
2011年 | 11篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 12篇 |
2007年 | 12篇 |
2006年 | 13篇 |
2005年 | 19篇 |
2004年 | 16篇 |
2003年 | 12篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 13篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 8篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1982年 | 1篇 |
排序方式: 共有391条查询结果,搜索用时 15 毫秒
191.
Jacobs T Lloyd GO Gertenbach JA Müller-Nedebock KK Esterhuysen C Barbour LJ 《Angewandte Chemie (International ed. in English)》2012,51(20):4913-4916
Crystallographic pressure-lapse snapshots of a porous material responding to gas loading were used to investigate the stepwise uptake of carbon dioxide and acetylene molecules into discrete confined spaces. Based on the data, a qualitative statistical mechanical model was devised that reproduces even subtle features in the experimental gas sorption isotherms. 相似文献
192.
The experimentally motivated question of the acetylene bromoboration mechanism was addressed in order to suggest possible radical isomerization pathways for the syn-adduct. Addition–elimination mechanisms starting with a bromine radical attack at the “bromine end” or the “boron end” of the C=C bond were considered. Dispersion-corrected DFT and MP2 methods with the SMD solvation model were employed using three all-electron bases as well as the ECP28MWB ansatz. The rate-determining, elimination step had a higher activation energy (12 kcal mol−1) in case of the “bromine end” attack due to intermediate stabilization at both the MP2 and DFT levels. In case of the “boron end” attack, two modes of C–C bond rotation were followed and striking differences in MP2 vs. DFT potential energy surfaces were observed. Employing MP2, addition was followed by either a 180° rotation through an eclipsed conformation of vicinal bromine atoms or by an opposite rotation avoiding that conformation, with 5 kcal mol−1 of elimination activation energy. Within B3LYP, the addition and rotation proceeded simultaneously, with a 9 (7) kcal mol−1 barrier for rotation involving (avoiding) eclipsed conformation of vicinal bromines. For weakly bound complexes, ZPE corrections with MP2 revealed significant artifacts when diffuse bases were included, which must be considered in the Gibbs free energy profile interpretation. 相似文献
193.
194.
195.
A. M. Vasil'tsov E. Yu. Shmidt A. I. Mikhaleva A. V. Afonin A. B. Zaitsev 《Chemistry of Heterocyclic Compounds》2001,37(12):1488-1492
The oxime of 5-pregnen-3-ol-20-one reacts with acetylene in the KOH-DMSO system to form a mixture of products containing 3-vinyloxy-17-(1-vinyl-2-pyrrolyl)-5-androstene as the major product (63% yield) and also the O-vinyloxime of 3-vinyloxy-5-pregnen-20-one (10%), 3-vinyloxy-17- and 3-vinyloxy-17-5-pregnen-20-one (25%, 1:4 ratio). 相似文献
196.
197.
R. S. Mitchenko A. A. Shubin A. N. Vdovichenko 《Theoretical and Experimental Chemistry》2006,42(3):186-189
The hydrochlorination of acetylene by gaseous HCl is catalyzed at room temperature on the surface of dry K2PtCl4 subjected to mechanical preactivation in an acetylene atmosphere. The acetylene hydrochlorination product is formed by trans
addition. The kinetic isotope effect (KIE) upon replacing HCl by DCl is 5 ± 1, which is much greater than the KIE found in
the catalytic hydrochlorination of acetylene on the surface of mechanically preactivated K2PtCl6 (1.9). This discrepancy suggests different reaction mechanisms in these two systems.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 173–177, May–June, 2006. 相似文献
198.
199.
Nadezhda M. Vitkovskaya Vladimir B. Orel Vladimir B. Kobychev Alexander S. Bobkov Damir Z. Absalyamov Boris A. Trofimov 《International journal of quantum chemistry》2020,120(9):e26158
The mechanisms of fundamental base-promoted acetylene reactions, namely, nucleophilic addition to the triple C ≡ C bond (vinylation) and nucleophilic addition of acetylenic carbanion to a carbonyl group (ethynylation), are addressed using three models of different complexity—pentasolvate, monosolvate, and anionic—which describe the catalytic superbasic systems MOH(OBut)/DMSO (suspensions of alkali hydroxides or tert-butoxides in dimethyl sulfoxide). The above acetylene reactions and sequential transformations of reagents arranged by the superbasic center are modeled within the framework of the most complete pentasolvate model, in which the superbase is represented by the KOH·5DMSO (KOBut·5DMSO) complexes. We have developed approaches to the construction of simplified models (monosolvate and anionic) to describe transformations in complex systems. The mechanisms of cascade assemblies of 6,8-dioxabicyclo[3.2.1]octanes, cyclopentenones, and furan cycles from ketones and acetylenes in the superbasic environment are investigated using a uniform B2PLYP/6-311+G**//B3LYP/6-31+G* approach, and the energy profiles of these different carbo- and heterocycles are analyzed. 相似文献
200.
The first total synthesis of the natural product (−)-petrosiol D has been achieved in a linear fashion. Sharpless asymmetric epoxidation, base induced elimination reaction for the formation of chiral propargyl alcohol and Cadiot–Chodkiewicz coupling reaction are the key steps utilized for the synthesis. 相似文献