全文获取类型
收费全文 | 875篇 |
免费 | 26篇 |
国内免费 | 2篇 |
专业分类
化学 | 541篇 |
晶体学 | 4篇 |
力学 | 22篇 |
数学 | 173篇 |
物理学 | 163篇 |
出版年
2023年 | 5篇 |
2022年 | 16篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 12篇 |
2016年 | 36篇 |
2015年 | 21篇 |
2014年 | 29篇 |
2013年 | 37篇 |
2012年 | 61篇 |
2011年 | 54篇 |
2010年 | 29篇 |
2009年 | 29篇 |
2008年 | 37篇 |
2007年 | 45篇 |
2006年 | 40篇 |
2005年 | 36篇 |
2004年 | 47篇 |
2003年 | 48篇 |
2002年 | 19篇 |
2001年 | 13篇 |
2000年 | 12篇 |
1999年 | 8篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 13篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1976年 | 4篇 |
1969年 | 4篇 |
1934年 | 4篇 |
1915年 | 5篇 |
1891年 | 3篇 |
1880年 | 3篇 |
排序方式: 共有903条查询结果,搜索用时 15 毫秒
881.
We present the synthesis, properties, and biological applications of Leadfluor-1 (LF1), a new water-soluble, turn-on fluorescent sensor that is capable of selectively imaging Pb2+ in aqueous solution and in living cells. LF1 combines a fluorescein chromophore and a pseudocrown receptor to provide good selectivity for Pb2+ over a range of biologically and environmentally relevant metal ions in aqueous solution, with sensitivity to parts per billion EPA limits for allowable lead in drinking water. In addition to these attributes, imaging experiments further show that LF1 is the first small-molecule reagent that can be delivered into living cells and report changes in intracellular Pb2+ levels. 相似文献
882.
An analytical methodology for quality control analyses of IgG and their impurities is presented using a new UV‐LIF (266 nm) detector inside the cassette of a CE instrument and its performance was evaluated. The observed sensitivity was very close to that obtained by silver staining of slab gels (LOD of 25 ng/mL), while the sensitivity of the analysis is 80 times better than with CE/UV absorption (214 nm). Examples of the analysis of pharmaceutical and other commercial IgGs are provided and the kinetics of the reduction of IgG by β‐mercaptoethanol is reported, demonstrating the ease of performing the analysis. 相似文献
883.
Bimetallic clusters display new characteristics that could not be obtained by varying either the size of pure metallic systems or the composition of bulk bimetals alone. Coating of pre-deposited clusters by vapour deposition is a typical synthesis process of bimetallic clusters. Here, we have demonstrated that hierarchical, gold cluster-decorated copper clusters as well as both heterogeneous and homogeneous Cu?CAu bimetallic clusters (4.6 to 10.7?nm) can be prepared by coating pre-deposited, size-selected Cu5000 (4.6?±?0.2?nm) with Au evaporation at various temperatures. These bimetallic clusters were analyzed by aberration-corrected scanning transmission electron microscopy and associated electron energy loss spectroscopy. The results indicate that the growth of bimetallic clusters is controlled by a competition between nucleation and diffusion of the coating Au atoms. 相似文献
884.
Regioselective Synthesis and Characterization of Multinuclear Convex‐Bound Ruthenium‐[n]Cycloparaphenylene (n=5 and 6) Complexes 下载免费PDF全文
Dr. Eiichi Kayahara Dr. Vijay Kumar Patel Audrey Mercier Prof. Dr. E. Peter Kündig Prof. Dr. Shigeru Yamago 《Angewandte Chemie (International ed. in English)》2016,55(1):302-306
Mono‐ and multinuclear complexes of ruthenium and [n]cycloparaphenylene (CPP, n=5 and 6) were synthesized in excellent yields through ligand exchange of the cationic complex [(Cp)Ru(CH3CN)3](PF6) with CPP. In the multinuclear complexes, ruthenium selectively coordinated to alternate paraphenylene units to give bis‐ and tris‐coordinated Ru complexes for [5] and [6]CPPs, respectively. Single‐crystal X‐ray analysis revealed the Ru was coordinated with η6‐hapticity on the convex surface of CPP. 相似文献
885.
Agnieszka Kapałka Audrey Cally Stefano Neodo Christos Comninellis Michael Wächter Kai M. Udert 《Electrochemistry communications》2010,12(1):18-21
The electrochemical oxidation of ammonia was investigated on a Ni/Ni(OH)2 electrode prepared by potential cycling of a Ni electrode in 1 M NaClO4. It was found that oxidation of ammonia is strongly pH dependent and proceeds mainly at pH values above 7. This indicates that NH3 rather than is oxidized on nickel electrodes. Oxidation of ammonia occurs in the potential region of Ni(II)/Ni(III) redox activity resulting in formation of a clear peak. Ni/Ni(OH)2 is not deactivated during ammonia oxidation even at high ammonia concentrations. A considerable fraction of the ammonia was oxidized to nitrate (11%), while the rest were gaseous nitrogen compounds. It is postulated that nitrogen was formed via a mechanism involving direct electron transfer from ammonia to the anode whereas the formation of nitrate involved oxygen transfer from water to an ammonia molecule. 相似文献
886.
Conforti F Statti GA Tundis R Bianchi A Agrimonti C Sacchetti G Andreotti E Menichini F Poli F 《Natural product research》2005,19(3):295-303
The biovariability of Hypericum perforatum L. (St. John's Wort) grown wild in Calabria and Sardinia (Italy) was reported with the aim to characterize the species through the isolation, detection, and quantitative evaluations of chemical markers (hypericin, quercetin, rutin) by HPLC analysis. Antioxidant activity of the methanolic H. perforatum extracts showed that the Calabrian samples were more active than those from Sardinia. The antibacterial activity evidenced the best performance on the gram positive bacteria with a MIC value of 50 microg/mL. Moreover, antifungal activity of all the extracts was also tested which showed interesting results particularly on the phytopathogene fungus P. ultimum. The variability shown by the samples could be attributed to environmental factors such as chemical-physical properties, composition of the soil, geographical coordinate, altitude, and solar exposure. The phytochemical analysis and the biological activity data suggested a possible use of H. perforatum extracts in the alimentary, cosmetic, and pharmaceutical fields. 相似文献
887.
γ-Al2O3 samples, both pure and Cr doped, were prepared by heating at 470°C sol–gel precursors obtained by using aluminum tri-sec-butoxide [Al(OC4H9)3] as the starting compound. The samples were characterised for phase composition (X-ray diffraction) and surface area (BET). Electrochemical determinations of the double layer reactivity of the pure and doped oxides were performed both by surface charge and by electrokinetic sonic amplitude (ESA) determinations. The interfacial electrostatic response is discussed and analysed also with reference to the sample surface state obtained by X-ray photoelectron spectroscopy (XPS). 相似文献
888.
Austin M. Mroz Audrey M. Davenport Jasper Sterling Joshua Davis Christopher H. Hendon 《Chemical science》2022,13(22):6558
Chemical shape and size play a critical role in chemistry. The van der Waals (vdW) radius, a familiar manifold used to quantify size by assuming overlapping spheres, provides rapid estimates of size in atoms, molecules, and materials. However, the vdW method may be too rigid to describe highly polarized systems and chemical species that stray from spherical atomistic environments. To deal with these exotic chemistries, numerous alternate methods based on electron density have been presented. While each boasts inherent generality, all define the size of a chemical system, in one way or another, by its electron density. Herein, we revisit the longstanding problem of assessing sizes of atoms and molecules, instead through examination of the local electric field produced by them. While conceptually different than nuclei-centered methods like that of van der Waals, the field assesses chemically affected volumes. This approach implicitly accounts for long-range fields in highly polar systems and predicts that cations should affect more space than neutral counterparts.Computing atomic and molecular volumes from DFT and ab initio-based electric fields. 相似文献
889.
Dupont A Eastoe J Barthélémy P Pucci B Heenan R Penfold J Steytler DC Grillo I 《Journal of colloid and interface science》2003,261(1):184-190
Dilute aqueous phase behavior of a novel tris(hydroxymethyl)acrylamidomethane (THAM)-derived telomer bearing a perfluorohexyl hydrophobic chain, F6THAM6, has been investigated. Fluorinated polyhydroxy surfactants of this kind find use in emerging biomedical applications. Neutron reflection (NR) and drop volume surface tension (DVT) methods have been used to determine the critical micelle concentration (cmc=4.7 x 10(-4) mol x dm(-3)) and surface adsorption parameters (at the cmc NR gives a molecular area a(cmc)=67.4 and 62 A(2) and surface excess gamma(cmc)=2.46 x 10(-6) mol x m(-2)). The aggregation structures were determined by small-angle neutron scattering (SANS), indicating globular (polydisperse spheres) micelles of radius approximately 30 A are present. These findings are compared with literature on surfactants with related structures, to identify how the unusual molecular structure of F6THAM6 affects surfactant properties. 相似文献
890.
Abbiati G Arcadi A Bianchi G Di Giuseppe S Marinelli F Rossi E 《The Journal of organic chemistry》2003,68(18):6959-6966
A general one-pot synthesis of pyridines 4a-t from the reaction of dialkyl acyclic/cyclic ketones 1a-i, methyl, aryl/heteroaryl ketones 1m-r, and aldehydes bearing alpha-hydrogens 1s,t with propargylamine 2 is described. Gold and copper salts are efficient catalysts for the reaction of ketones with 2. The formation of the pyridines 4 is suggested to proceed through the sequential amination of carbonyl compounds followed by regioselective 6-endo-dig cyclization of the N-propargylenamine (N-propargyldienamine) intermediate 3(5) and aromatization reaction. Whereas the preparation of linear polycyclic pyridine 4i can be carried out by reacting cholestan-3-one 1i with 2, the angular polycyclic pyridine 4j has been obtained starting from cholest-5-en-3-one 1j. Selectivity of the reaction of polycyclic dicarbonyls 1k,l with 2 has also been investigated. 相似文献