全文获取类型
收费全文 | 936篇 |
免费 | 157篇 |
国内免费 | 97篇 |
专业分类
化学 | 1171篇 |
晶体学 | 3篇 |
物理学 | 16篇 |
出版年
2024年 | 2篇 |
2023年 | 14篇 |
2022年 | 42篇 |
2021年 | 39篇 |
2020年 | 67篇 |
2019年 | 50篇 |
2018年 | 43篇 |
2017年 | 39篇 |
2016年 | 47篇 |
2015年 | 55篇 |
2014年 | 72篇 |
2013年 | 70篇 |
2012年 | 56篇 |
2011年 | 92篇 |
2010年 | 59篇 |
2009年 | 65篇 |
2008年 | 58篇 |
2007年 | 60篇 |
2006年 | 51篇 |
2005年 | 43篇 |
2004年 | 48篇 |
2003年 | 35篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 1篇 |
排序方式: 共有1190条查询结果,搜索用时 15 毫秒
101.
《中国化学会会志》2017,64(4):420-426
Six new silver complexes containing symmetrical N ‐heterocyclic carbene (NHC ) ligands were synthesized by the reaction of azolium salts with Ag2O in CH2Cl2 . These complexes were tested against Gram‐negative bacterial strains (Escherichia coli and Pseudomonas aeruginosa ), Gram‐positive bacterial strains (Enterococcus faecalis and Staphylococcus aureus ), and fungal strains (Candida albicans and Candida tropicalis ), and all tested complexes showed good activity against the different microorganisms. 相似文献
102.
合成了12个吡啶氮桥联的双环三唑鎓盐2a~2l卡宾催化剂前体,用于催化苯偶姻缩合反应和酯交换反应,考察了反应条件对催化反应的影响,并与其它三唑鎓盐的催化活性进行了比较.结果表明,在较低催化剂用量下,催化剂2c表现出优良的催化活性,分离产率最高分别达到98%和93%. 相似文献
103.
Xiu Hui Lu Wei Rong Wu Xin Che Jun Feng Han Le Yi Shi 《International journal of quantum chemistry》2010,110(6):1273-1278
The cycloaddition mechanism of forming a polycyclic compound between singlet dimethylmethylene carbene(R1) and formaldehyde(R2) has been investigated with MP2/6‐31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated with CCSD(T)//MP2/6‐31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction between singlet dimethylmethylene carbene and formaldehyde consists of two steps: (1) the two reactants(R1, R2) firstly form an energy‐enricheded intermediate (INT1a) through a barrier‐free exothermic reaction of ΔE = 11.3 kJ/mol. (2) Intermediate (INT1a) then isomerizes to a three‐membered product (P1) via a transition state (TS1a) with an energy barrier of 20.0 kJ/mol. The dominant reaction has an excellent selectivity and differs considerably from its competitive reactions in reaction rate. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
104.
Paul Le Maux 《Tetrahedron》2010,66(25):4462-14895
The transfer of the metallocarbene derived from N- and O-protected 6-diazo-5-oxo-l-norleucine (DON) catalyzed by metalloporphyrins undergoes dimerization, cyclopropanation, N-H and S-H insertion reactions, respectively. An efficient and direct synthesis of 5-oxo-l-pipecolic acid from DON is described from unprotected 6-diazo-5-oxo-l-norleucine. 相似文献
105.
Xiu-Hui Lu Xin Che Jun-Feng Han Le-Yi Shi Zhen-Xia Lian 《Journal of organometallic chemistry》2010,695(4):524-529
The mechanism of the cycloaddition reaction of forming germanic bis-heterocyclic compound between singlet germylene carbene and acetone has been investigated with MP2/6-31G* method, including geometry optimization and vibrational analysis for the involved stationary points on the potential energy surface. The energies of the different conformations are calculated by CCSD (T)//MP2/6-31G* method. From the potential energy profile, it can be predicted that the dominant reaction pathway of the cycloadditional reaction of forming germanic bis-heterocyclic compound consists of three steps: (1) the two reactants firstly form an intermediate INT4 through a barrier-free exothermic reaction of 181.4 kJ/mol; (2) INT4 further reacts with acetone (R2) to form an intermediate (INT5), which is also a barrier-free exothermic reaction of 148.9 kJ/mol; (3) INT5 then isomerizes to a germanic bis-heterocyclic product P5 via a transition state TS5 with an energy barrier of 53.3 kJ/mol. 相似文献
106.
107.
The preparation of divalent chromium N-heterocyclic carbene(NHC,1,3-diisopropyl4,5-dimethylimidazole-2-ylidene) compounds is reported.The reaction of 1:1 molar ratio of NHC with CrCl2 led to an isolation of [(NHC)CrCl(μ-Cl)(THF)]2(1),while that of 2:1 ratio resulted in the formation of(NHC)2CrCl2(2).1 can be considered as an intermediate in the formation of 2 and further converted into 2 by the addition of another equiv.of NHC.The reaction of 2 with CpNa afforded an ion pair compound [(NHC)2CrCp]+[Cp]-(3),indicating a strong coordination ability of NHC supplanting one of the ionic Cr-Cp bonding.In combination of methylalumoxane(MAO) as cocatalyst 1 and 2 both are active for catalyzing ethylene polymerization. 相似文献
108.
The reaction of 2‐(2‐bromoethyl)‐1,3‐dioxane with 1‐alkylbenzimidazole derivatives results in the formation of the new benzimidazolium salts (1). The reaction of Pd(OAc)2 with 1,3‐dialkylbenzimidazolium salts (1a–c) yields palladium N‐heterocyclic carbene (NHC) complexes (2a–c). All synthesized compounds were characterized by 1H NMR, 13 C NMR, IR and elemental analysis techniques which support the proposed structures. As catalysts, these new palladium complexes offer a simple and efficient methodology for the synthesis of triarylamines and secondary amines from anilines and amines and in a single step with potassium tertiary butoxide as a base. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
109.
110.