全文获取类型
收费全文 | 879篇 |
免费 | 11篇 |
国内免费 | 3篇 |
专业分类
化学 | 627篇 |
晶体学 | 9篇 |
力学 | 23篇 |
数学 | 86篇 |
物理学 | 148篇 |
出版年
2022年 | 6篇 |
2021年 | 25篇 |
2020年 | 12篇 |
2019年 | 12篇 |
2018年 | 10篇 |
2017年 | 6篇 |
2016年 | 24篇 |
2015年 | 11篇 |
2014年 | 9篇 |
2013年 | 62篇 |
2012年 | 41篇 |
2011年 | 39篇 |
2010年 | 40篇 |
2009年 | 37篇 |
2008年 | 58篇 |
2007年 | 53篇 |
2006年 | 45篇 |
2005年 | 50篇 |
2004年 | 41篇 |
2003年 | 29篇 |
2002年 | 49篇 |
2001年 | 12篇 |
2000年 | 10篇 |
1999年 | 9篇 |
1998年 | 8篇 |
1997年 | 12篇 |
1996年 | 15篇 |
1995年 | 11篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 11篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 3篇 |
1973年 | 4篇 |
1968年 | 2篇 |
排序方式: 共有893条查询结果,搜索用时 250 毫秒
41.
Franco Cataldo Giancarlo Angelini Donatella Capitani Marco Gobbino Ornella Ursini Fabrizio Forlini 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):839-849
This paper is dedicated to the memory of our friend and colleague Annalaura Segre. The chemical structure of a series of β (-)-pinene polymers (PBP) obtained by radiation-induced polymerization, free radical initiation, cationic polymerization over a Friedel-Craft catalyst and by coordinative polymerization over a Ziegler-Natta catalyst has been fully elucidated by 1H and 13C-NMR spectroscopy. 2D NMR techniques have been applied in order to assign all the NMR resonances to the structures of the PBP investigated. The NMR spectra show that the most regular PBP structure is obtained by radiation-induced polymerization followed by the free radical initiated polymerization. The most defective structure has been observed in the case of PBP prepared by cationic mechanism over a Friedel-Crafts catalyst. The discussion accounts for different types of defects and cross-links present in the PBPs investigated whose fundamental structure is based on the p-menthene repeating unit. NMR self-diffusion measurements have been performed to evaluate the molecular weight of all the PBP investigated. The highest molecular weight (2600 Dalton) was found in the case of PBP prepared by Ziegler-Natta catalyst, while the lowest molecular weight was found in the case of PBP prepared by radiation-induced polymerization (about 1000 Dalton). 相似文献
42.
43.
44.
Reaction between 6‐(un)substituted‐2‐thiouracils and E‐ethyl 4‐bromocrotonate under basic conditions at room temperature is an easy, mild, high‐yielding, and regioselective method for the preparation of 7‐(un)substituted dihydrothiazolo[3,2‐a]pyrimidinone derivatives. 相似文献
45.
Giovanni Appendino Giancarlo Cravotto Giovanni Palmisano Rita Annunziata 《合成通讯》2013,43(18):3359-3371
In the presence of one-electron metal oxidants (CAN, MAH), 4-hydroxycoumarin (1) adds to alkenes to give 2,3-dihydro-4H-furo[3,2-c][1]benzopyran-4-ones. 相似文献
46.
Enrico Dalcanale Giancarlo Antonioli Mauro Ricco Herbert Groothues Friedrich Kremer 《Liquid crystals》2013,40(9):1161-1169
The dynamic and conformational behaviour of four mesogenic resorcinarenes exhibiting columnar mesophases have been studied by a combination of broadband dielectric spectroscopy and deuterium solid state NMR. Broadband dielectric spectroscopy provided evidence for two relaxation processes present both in the mesophase and in the isotropic liquid. The high frequency process II, common to all mesogens, has been assigned to the libration of the carbonyl groups of the ester junctions between the core and the side chains. The low frequency process I, present in conformationally mobile mesogens 1 and 2, has been attributed to the ring inversion process of the macrocyclic core associated with dipole inversion along the columnar axis. Deuterium solid state NMR performed on 4, the deuteriated analogue of 1, confirmed the molecular dynamics attribution for process I, assigning the ring inversion to the interconversion of the two equivalent crown conformations. 相似文献
47.
Dr. Alessandro Barge Marina Caporaso Prof. Giancarlo Cravotto Dr. Katia Martina Dr. Paolo Tosco Prof. Silvio Aime Dr. Carla Carrera Dr. Eliana Gianolio Dr. Giorgio Pariani Dr. Davide Corpillo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(36):12086-12092
We report the synthesis and characterization of a water‐soluble, star‐shaped macromolecular platform consisting of eight β‐cyclodextrin (β‐CD) units anchored to the narrower rim of a γ‐CD core through bis(triazolyl)alkyl spacers. The efficient synthetic protocol is based on the microwave (MW)‐promoted Cu‐catalyzed 1,3‐dipolar cycloaddition of CD monoazides to CD monoacetylenes. The ligand‐hosting capability of the construct has been assessed by relaxometric titration and nuclear magnetic relaxation dispersion (NMRD) profiling, which showed it to be good, and this was supported by molecular dynamics simulations. To demonstrate the feasibility of obtaining supramolecular structures with high hosting ability, we designed a dimeric platform, formed by joining two nonamers through the γ‐CD cores through a bis(lithocholic acid) linker. With a view to the potential biological applications, cytotoxicity and extent of binding to human serum albumin were assessed. The properties of this dendrimeric multicarrier make it suitable for pharmaceutical and diagnostic purposes, ranging from targeted drug delivery to molecular imaging. 相似文献
48.
Dr. Ulrich Hintermair Dr. Giancarlo Franciò Prof. Dr. Walter Leitner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(14):4538-4547
A continuous‐flow process based on a chiral transition‐metal complex in a supported ionic liquid phase (SILP) with supercritical carbon dioxide (scCO2) as the mobile phase is presented for asymmetric catalytic transformations of low‐volatility organic substrates at mild reaction temperatures. Enantioselectivity of >99 % ee and quantitative conversion were achieved in the hydrogenation of dimethylitaconate for up to 30 h, reaching turnover numbers beyond 100 000 for the chiral QUINAPHOS–rhodium complex. By using an automated high‐pressure continuous‐flow setup, the product was isolated in analytically pure form without the use of any organic co‐solvent and with no detectable catalyst leaching. Phase‐behaviour studies and high‐pressure NMR spectroscopy assisted the localisation of optimum process parameters by quantification of substrate partitioning between the IL and scCO2. Fundamental insight into the molecular interactions of the metal complex, ionic liquid and the surface of the support in working SILP catalyst materials was gained by means of systematic variations, spectroscopic studies and labelling experiments. In concert, the obtained results provided a rationale for avoiding progressive long‐term deactivation. The optimised system reached stable selectivities and productivities that correspond to 0.7 kg L ?1 h?1 space–time yield and at least 100 kg product per gram of rhodium, thus making such processes attractive for larger‐scale application. 相似文献
49.
Dipl.‐Chem. Nicolas Dietl Dr. Anna Troiani Dr. Maria Schlangen Dr. Ornella Ursini Dr. Giancarlo Angelini Prof. Dr. Yitzhak Apeloig Prof. Dr. Giulia de Petris Prof. Dr. Helmut Schwarz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(21):6662-6669
The reactivity of the two diatomic congeneric systems [CO].+ and [SiO].+ towards methane has been investigated by means of mass spectrometry and quantum‐chemical calculations. While [CO].+ gives rise to three different reaction channels, [SiO].+ reacts only by hydrogen‐atom transfer (HAT) from methane under thermal conditions. A theoretical analysis of the respective HAT processes reveals two distinctly different mechanistic pathways for [CO].+ and [SiO].+, and a comparison to the higher metal oxides of Group 14 emphasizes the particular role of carbon as a second‐row p element. 相似文献
50.
Dr. Maria Petrosino Dr. Francesco Stellato Prof. Roberta Chiaraluce Prof. Valerio Consalvi Dr. Giovanni La Penna Dr. Alessandra Pasquo Dr. Olivier Proux Prof. Giancarlo Rossi Prof. Silvia Morante 《ChemistryOpen》2021,10(11):1133-1141
We present in this work a first X-ray Absorption Spectroscopy study of the interactions of Zn with human BST2/tetherin and SARS-CoV-2 orf7a proteins as well as with some of their complexes. The analysis of the XANES region of the measured spectra shows that Zn binds to BST2, as well as to orf7a, thus resulting in the formation of BST2-orf7a complexes. This structural information confirms the the conjecture, recently put forward by some of the present Authors, according to which the accessory orf7a (and possibly also orf8) viral protein are capable of interfering with the BST2 antiviral activity. Our explanation for this behavior is that, when BST2 gets in contact with Zn bound to the orf7a Cys15 ligand, it has the ability of displacing the metal owing to the creation of a new disulfide bridge across the two proteins. The formation of this BST2-orf7a complex destabilizes BST2 dimerization, thus impairing the antiviral activity of the latter. 相似文献