全文获取类型
收费全文 | 3729篇 |
免费 | 427篇 |
国内免费 | 733篇 |
专业分类
化学 | 4615篇 |
晶体学 | 95篇 |
力学 | 2篇 |
综合类 | 10篇 |
数学 | 1篇 |
物理学 | 166篇 |
出版年
2024年 | 3篇 |
2023年 | 25篇 |
2022年 | 59篇 |
2021年 | 146篇 |
2020年 | 222篇 |
2019年 | 172篇 |
2018年 | 145篇 |
2017年 | 145篇 |
2016年 | 223篇 |
2015年 | 186篇 |
2014年 | 222篇 |
2013年 | 319篇 |
2012年 | 457篇 |
2011年 | 245篇 |
2010年 | 215篇 |
2009年 | 235篇 |
2008年 | 244篇 |
2007年 | 246篇 |
2006年 | 214篇 |
2005年 | 182篇 |
2004年 | 231篇 |
2003年 | 154篇 |
2002年 | 82篇 |
2001年 | 61篇 |
2000年 | 53篇 |
1999年 | 69篇 |
1998年 | 45篇 |
1997年 | 45篇 |
1996年 | 36篇 |
1995年 | 30篇 |
1994年 | 27篇 |
1993年 | 23篇 |
1992年 | 30篇 |
1991年 | 14篇 |
1990年 | 15篇 |
1989年 | 6篇 |
1988年 | 19篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有4889条查询结果,搜索用时 31 毫秒
61.
手性有机硼化合物在有机合成、医药、材料等诸多领域中有广泛的应用,发展该类化合物的高效合成方法一直广受关注.此前,我们发展了过渡金属催化卡宾对硼氢键(B—H)的插入反应,并实现了α-重氮酯对B—H键的不对称插入反应.本文以手性螺环双噁唑啉配体和铜的络合物作为催化剂,首次实现了α-重氮酮对膦-硼烷加合物的B—H键不对称插入反应,获得了较高的收率和高达83%ee的对映选择性.该研究成果是为数不多的以α-重氮酮作为卡宾前体的不对称杂原子氢键插入反应,为手性α-硼取代酮化合物这类新的有机硼化合物的合成提供了有效方法. 相似文献
62.
Catalytic Asymmetric Michael Reaction of 5H‐Oxazol‐4‐Ones with α,β‐Unsaturated Acyl Imidazoles 下载免费PDF全文
Bangzhi Zhang Fengxia Han Linqing Wang Dan Li Dongxu Yang Xiaoli Yang Junxian Yang Xiaofang Li Dr. Depeng Zhao Prof. Dr. Rui Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17234-17238
The asymmetric Michael reaction between 5H‐oxazol‐4‐ones and α,β‐unsaturated acyl imidazoles is reported. A novel 2‐benzo[b]thiophenyl‐modified chiral ProPhenol species is synthesized and used as a ligand, leading to good enantioselectivities in this asymmetric conjugate addition reaction. Furthermore, the introduction of phenol additives as achiral co‐ligands is found to improve the reaction’s chemical yields, diastereoselectivities, and enantioselectivities. 相似文献
63.
考察了双亚磷酸酯配体Bisphosphite 1、Bisphosphite 2及双膦配体DPPE、DPPP、DPPB、BISBI在丁烯氢甲酰化反应中的反应活性和选择性,并对双亚磷酸酯配体和双膦配体进行混合,应用到丁烯氢甲酰化反应当中,对混合配体进行筛选发现Bisphosphite 1与DPPB混合配体的反应效果最佳,明显提高了1-丁烯氢甲酰化产物醛的正异构比,并通过31P NMR等方法推测了混合配体与铑配位的关键配合物中间体.通过正交实验优选了铑催化剂浓度、Bisphosphite 1浓度与DPPB浓度,其优化的催化剂配方对1-丁烯氢甲酰化的正异构比达到76.3,平均TOF 1821 h-1. 相似文献
64.
Carboxylic‐Acid‐Passivated Metal Oxide Nanocrystals: Ligand Exchange Characteristics of a New Binding Motif 下载免费PDF全文
Jonathan De Roo Dr. Yolanda Justo Katrien De Keukeleere Freya Van den Broeck Prof. Dr. José C. Martins Prof. Dr. Isabel Van Driessche Prof. Dr. Zeger Hens 《Angewandte Chemie (International ed. in English)》2015,54(22):6488-6491
Ligand exchange is central in the processing of inorganic nanocrystals (NCs) and requires understanding of surface chemistry. Studying sterically stabilized HfO2 and ZrO2 NCs using 1H solution NMR and IR spectroscopy as well as elemental analysis, this paper demonstrates the reversible exchange of initial oleic acid ligands for octylamine and self‐adsorption of oleic acid at NC surfaces. Both processes are incompatible with an X‐type binding motif of carboxylic acids as reported for sulfide and selenide NCs. We argue that this behavior stems from the dissociative adsorption of carboxylic acids at the oxide surface. Both proton and carboxylate moieties must be regarded as X‐type ligands yielding a combined X2 binding motif that allows for self‐adsorption and exchange for L‐type ligands. 相似文献
65.
66.
Inside Back Cover: Intermolecular Enantioselective Dearomatization Reaction of β‐Naphthol Using meso‐Aziridine: A Bifunctional In Situ Generated Magnesium Catalyst (Angew. Chem. Int. Ed. 7/2015) 下载免费PDF全文
67.
Rhodium‐Catalyzed Enantioselective Intramolecular CH Silylation for the Syntheses of Planar‐Chiral Metallocene Siloles 下载免费PDF全文
Dr. Qing‐Wei Zhang Kun An Li‐Chuan Liu Yuan Yue Prof. Dr. Wei He 《Angewandte Chemie (International ed. in English)》2015,54(23):6918-6921
Reported herein is the rhodium‐catalyzed enantioselective C? H bond silylation of the cyclopentadiene rings in Fe and Ru metallocenes. Thus, in the presence of (S)‐TMS‐Segphos, the reactions took place under very mild conditions to afford metallocene‐fused siloles in good to excellent yields and with ee values of up to 97 %. During this study it was observed that the steric hindrance of chiral ligands had a profound influence on the reactivity and enantioselectivity of the reaction, and might hold the key to accomplishing conventionally challenging asymmetric C? H silylations. 相似文献
68.
Fragment‐Based De Novo Design Reveals a Small‐Molecule Inhibitor of Helicobacter Pylori HtrA 下载免费PDF全文
Thomas P. Schmidt Dr. Manja Böhm Katharina Stutz Daniel Reker Dr. Bernhard Pfeiffer Prof. Dr. Karl‐Heinz Altmann Prof. Dr. Steffen Backert Prof. Dr. Silja Wessler Prof. Dr. Gisbert Schneider 《Angewandte Chemie (International ed. in English)》2015,54(35):10244-10248
Sustained identification of innovative chemical entities is key for the success of chemical biology and drug discovery. We report the fragment‐based, computer‐assisted de novo design of a small molecule inhibiting Helicobacter pylori HtrA protease. Molecular binding of the designed compound to HtrA was confirmed through biophysical methods, supporting its functional activity in vitro. Hit expansion led to the identification of the currently best‐in‐class HtrA inhibitor. The results obtained reinforce the validity of ligand‐based de novo design and binding‐kinetics‐guided optimization for the efficient discovery of pioneering lead structures and prototyping drug‐like chemical probes with tailored bioactivity. 相似文献
69.
Different Types of Nickel,Cobalt, and Manganese Complexes originating from 2‐Imidazolecarboxaldiimine of Triethylenetetraamine 下载免费PDF全文
The reactivity of the 2‐imidazolecarboxaldiimine of triethylenetetraamine (H2imida) towards divalent manganese, cobalt, and nickel ions differs. It forms a cationic nickel(II) complex by acting as a hexa‐dentate ligand, whereas the cobalt(II) complex formation took place by deprotonation of the H2imida forming a neutral complex with imida. Deprotonation of the ligand by H2imida by cobalt(II) ions caused quenching of the fluorescence emission at 312 nm, such a quenching effect was not observed with the nickel ions. On the other hand, a mononuclear manganese(II) complex of a new tetradentate ligand was formed by manganese(II) assisted intramolecular cyclization reactions of H2imida. 相似文献
70.
Four Metal Complexes Based on Bulky Imidazole Ligands: Solvothermal Syntheses,Crystal Structures,and Fluorescence Properties 下载免费PDF全文
Xue Zhang Sai Li Yue‐Jiao He Tong Han Xiao‐Ling Wang Bang Chen Kang‐Yu Zou Zuo‐Xi Li 《无机化学与普通化学杂志》2015,641(11):1874-1880
In order to explore the influences of (de‐)protonation of the imidazole ring on the structural diversity of the resulting complexes, the imidazole‐based ligands 4, 5‐diphenylimidazole (Hdpi) and 1H‐phenanthro[9, 10‐d]imidazole (Hpi) were utilized as bulky building blocks to construct four complexes by solvothermal reactions, i.e. [Ag(Hdpi)2](NO3) · (H2O) ( 1 ), [Cu(dpi)]∞ ( 2 ), [Cu(Hpi)(NO3)]∞ ( 3 ), and [(H2pi)(NO3)] · H2O ( 4 ). In complex 1 , two Hdpi ligands adopt a monodentate pattern and coordinate with one AgI ion to form a mononuclear unit, which is further connected by hydrogen bonds into a 1D supramolecular helix. The deprotonated dpi ligand of 2 acts in bidentate mode, and bridges CuI ions to afford a 1D chain. In 3 , the NO3– ion, acts as a monodentate bridging ligand and joins CuI ions to generate a 1D chain. The Hpi ligand employs a monodentate mode to bond with CuI ions of the 1D chain. 4 is protonated and two H2pi nitrogen atoms are free of coordination. Interestingly, hydrogen bonds among the NO3– ion, the H2pi ligand, and the water molecule yield a macro ring R44(14). The resulting structural diversity reveals that the (de‐)protonation of imidazole ring directly steers the coordination number of ligand, and thus causes a significant effect on the structure, especially the dimensionality. Furthermore, the solid‐state fluorescence properties of the free ligands and compounds 1 – 4 were studied at room temperature. 相似文献