全文获取类型
收费全文 | 1193篇 |
免费 | 70篇 |
国内免费 | 3篇 |
专业分类
化学 | 1054篇 |
晶体学 | 5篇 |
力学 | 5篇 |
数学 | 91篇 |
物理学 | 111篇 |
出版年
2024年 | 2篇 |
2023年 | 22篇 |
2022年 | 26篇 |
2021年 | 32篇 |
2020年 | 44篇 |
2019年 | 34篇 |
2018年 | 29篇 |
2017年 | 23篇 |
2016年 | 35篇 |
2015年 | 50篇 |
2014年 | 49篇 |
2013年 | 66篇 |
2012年 | 96篇 |
2011年 | 106篇 |
2010年 | 52篇 |
2009年 | 40篇 |
2008年 | 83篇 |
2007年 | 82篇 |
2006年 | 91篇 |
2005年 | 69篇 |
2004年 | 60篇 |
2003年 | 52篇 |
2002年 | 32篇 |
2001年 | 8篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 12篇 |
1995年 | 3篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 5篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1987年 | 4篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有1266条查询结果,搜索用时 15 毫秒
21.
Catalytic and Atom‐Economic C
−C
Bond Formation: Alkyl Tantalum Ureates for Hydroaminoalkylation 下载免费PDF全文
Rebecca C. DiPucchio Dr. Sorin‐Claudiu Roşca Prof. Laurel L. Schafer 《Angewandte Chemie (International ed. in English)》2018,57(13):3469-3472
Atom‐economic and regioselective C ?C bond formation has been achieved by rapid C?H alkylation of unprotected secondary arylamines with unactivated alkenes. The combination of Ta(CH2SiMe3)3Cl2, and a ureate N,O‐chelating‐ligand salt gives catalytic systems prepared in situ that can realize high yields of β‐alkylated aniline derivatives from either terminal or internal alkene substrates. These new catalyst systems realize C?H alkylation in as little as one hour and for the first time a 1:1 stoichiometry of alkene and amine substrates results in high yielding syntheses of isolated amine products by simple filtration and concentration. 相似文献
22.
Aoife M. Foley Declan P. Gavin Rebecca E. Deasy Sinéad E. Milner Thomas S. Moody Kevin S. Eccles Simon E. Lawrence Anita R. Maguire 《Tetrahedron》2018,74(13):1435-1443
Efforts to combine the intramolecular nitroaldol reaction with lipase-catalysed resolution of the resulting nitroaldol adduct in a one-pot dynamic kinetic resolution (DKR) are described. Significant challenges were encountered in the combination of the two systems. trans-2-Methyl-2-nitrocyclohexyl acetate (±)-3b was isolated in excellent enantiopurity (>98% ee) via a sequential DKR sequence where the lipase-mediated resolution and base-mediated interconversion of 2-methyl-2-nitrocyclohexanol 2 were effected alternately, demonstrating the feasibility of this approach initially. Further work showed, for the first time, evidence that a DKR-type system is possible for 2. Reaction engineering allowed the design of a sequential one-pot reaction system which furnished the products with excellent enantioselectivity, and good diastereoselectivity. 相似文献
23.
Selective Hydrogen Atom Abstraction through Induced Bond Polarization: Direct α‐Arylation of Alcohols through Photoredox,HAT, and Nickel Catalysis 下载免费PDF全文
Jack Twilton Melodie Christensen Dr. Daniel A. DiRocco Dr. Rebecca T. Ruck Dr. Ian W. Davies Prof. Dr. David W. C. MacMillan 《Angewandte Chemie (International ed. in English)》2018,57(19):5369-5373
The combination of nickel metallaphotoredox catalysis, hydrogen atom transfer catalysis, and a Lewis acid activation mode, has led to the development of an arylation method for the selective functionalization of alcohol α‐hydroxy C?H bonds. This approach employs zinc‐mediated alcohol deprotonation to activate α‐hydroxy C?H bonds while simultaneously suppressing C?O bond formation by inhibiting the formation of nickel alkoxide species. The use of Zn‐based Lewis acids also deactivates other hydridic bonds such as α‐amino and α‐oxy C?H bonds. This approach facilitates rapid access to benzylic alcohols, an important motif in drug discovery. A 3‐step synthesis of the drug Prozac exemplifies the utility of this new method. 相似文献
24.
Perfluoroaryl Bicyclic Cell‐Penetrating Peptides for Delivery of Antisense Oligonucleotides 下载免费PDF全文
Justin M. Wolfe Colin M. Fadzen Rebecca L. Holden Monica Yao Gunnar J. Hanson Prof. Bradley L. Pentelute 《Angewandte Chemie (International ed. in English)》2018,57(17):4756-4759
Exon‐skipping antisense oligonucleotides are effective treatments for genetic diseases, yet exon‐skipping activity requires that these macromolecules reach the nucleus. While cell‐penetrating peptides can improve delivery, proteolytic instability often limits efficacy. It is hypothesized that the bicyclization of arginine‐rich peptides would improve their stability and their ability to deliver oligonucleotides into the nucleus. Two methods were introduced for the synthesis of arginine‐rich bicyclic peptides using cysteine perfluoroarylation chemistry. Then, the bicyclic peptides were covalently linked to a phosphorodiamidate morpholino oligonucleotide (PMO) and assayed for exon skipping activity. The perfluoroaryl cyclic and bicyclic peptides improved PMO activity roughly 14‐fold over the unconjugated PMO. The bicyclic peptides exhibited increased proteolytic stability relative to the monocycle, demonstrating that perfluoroaryl bicyclic peptides are potent and stable delivery agents. 相似文献
25.
Christina Heroven Victoria Georgi Gaurav K. Ganotra Prof. Paul Brennan Finn Wolfreys Prof. Dr. Rebecca C. Wade Amaury E. Fernández‐Montalván Apirat Chaikuad Prof. Dr. Stefan Knapp 《Angewandte Chemie (International ed. in English)》2018,57(24):7220-7224
Prolonged drug residence times may result in longer‐lasting drug efficacy, improved pharmacodynamic properties, and “kinetic selectivity” over off‐targets with high drug dissociation rates. However, few strategies have been elaborated to rationally modulate drug residence time and thereby to integrate this key property into the drug development process. Herein, we show that the interaction between a halogen moiety on an inhibitor and an aromatic residue in the target protein can significantly increase inhibitor residence time. By using the interaction of the serine/threonine kinase haspin with 5‐iodotubercidin (5‐iTU) derivatives as a model for an archetypal active‐state (type I) kinase–inhibitor binding mode, we demonstrate that inhibitor residence times markedly increase with the size and polarizability of the halogen atom. The halogen–aromatic π interactions in the haspin–inhibitor complexes were characterized by means of kinetic, thermodynamic, and structural measurements along with binding‐energy calculations. 相似文献
26.
Dr. Darren M. C. Ould Dr. Rebecca L. Melen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):9835-9845
The past 20 years has seen significant advances in main group chemistry and their use in catalysis. This Minireview showcases the recent emergence of phosphorus and arsenic containing heterocycles as catalysts. With that, we discuss how the Group 15 compounds diazaphospholenes, diazaarsolenes, and their cationic counterparts have proven to be highly effective catalysts for a wide range of reduction transformations. This Minireview highlights how the initial discovery by Gudat of the hydridic nature of the P−H bond in these systems led to these compounds being used as catalysts and discusses the wide range of examples currently present in the literature. 相似文献
27.
28.
Katherine E. BashfordMatthew B. Burton Stuart CameronAnthony L. Cooper Rebecca D. HoggPeter D. Kane David A. MacManusChristopher A. Matrunola Christopher J. Moody Avril A.B. Robertson Mark R. Warne 《Tetrahedron letters》2003,44(8):1627-1629
The Bohlmann-Rahtz reaction has been used to prepare 2,3,6-trisubstituted pyridines suitable for use in library synthesis. The synthesis of piperidine substituted nicotinic acid derivative 9 has been optimised and carried out on a large scale to give ca. 500 g of scaffold which was used in the generation of the pyridine library 11. 相似文献
29.
Longbo Li Andy T. Tek Rudy J. Wojtecki Rebecca Braslau 《Journal of polymer science. Part A, Polymer chemistry》2019,57(17):1821-1835
Internal plasticization of polyvinyl chloride (PVC) using thermal azide‐alkyne Huisgen dipolar cycloaddition between azidized PVC and electron‐poor acetylenediamides incorporating a branched glutamic acid linker resulted in incorporation of four plasticizing moieties per attachment point on the polymer chain. A systematic study incorporating either alkyl or polyethylene glycol esters provided materials with varying degrees of plasticization, with depressed Tg values ranging from ?1 °C to 62 °C. Three interesting trends were observed. First, Tg values of PVC bearing various internal plasticizers were shown to decrease with increasing chain length of the plasticizing ester. Second, branched internal plasticizers bearing triethylene glycol chains had lower Tg values compared to those with similar length long‐chain alkyl groups. Finally, thermogravimetric analysis of these internally plasticized PVC samples revealed that these branched internal plasticizers bearing alkyl chains are more thermally stable than similarity branched plasticizers bearing triethylene glycol units. These internal tetra‐plasticizers were synthesized and attached to PVC‐azide in three simple synthetic steps. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1821–1835 相似文献
30.
Rebecca Beveridge Lukasz G. Migas Richard W. Kriwacki Perdita E. Barran 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(10):3146-3150
Intrinsically disordered proteins have been reported to undergo disorder‐to‐order transitions upon binding to their partners in the cell. The extent of the ordering upon binding and the lack of order prior to binding is difficult to visualize with classical structure determination methods. Binding of p27 to the Cdk2/cyclin A complex is accompanied by partial folding of p27 in the KID domain, with the retention of dynamic behavior for function, particularly in the C‐terminal half of the protein. Herein, native ion mobility mass spectrometry (IM‐MS) is employed to measure the intrinsic dynamic properties of p27, both in isolation and within the trimeric complex with Cdk2/cyclin A. The trimeric Cdk2/cyclin A/p27‐KID complex possesses significant structural heterogeneity compared to Cdk2/cyclin A. These findings support the formation of a fuzzy complex in which both the N‐ and C‐termini of p27 interact with Cdk2/cyclin A in multiple, closely associated states. 相似文献