全文获取类型
收费全文 | 1412篇 |
免费 | 37篇 |
国内免费 | 8篇 |
专业分类
化学 | 784篇 |
晶体学 | 8篇 |
力学 | 19篇 |
数学 | 160篇 |
物理学 | 486篇 |
出版年
2021年 | 6篇 |
2020年 | 12篇 |
2019年 | 14篇 |
2018年 | 14篇 |
2017年 | 13篇 |
2016年 | 30篇 |
2015年 | 19篇 |
2014年 | 19篇 |
2013年 | 60篇 |
2012年 | 49篇 |
2011年 | 77篇 |
2010年 | 37篇 |
2009年 | 38篇 |
2008年 | 100篇 |
2007年 | 79篇 |
2006年 | 95篇 |
2005年 | 95篇 |
2004年 | 106篇 |
2003年 | 67篇 |
2002年 | 58篇 |
2001年 | 27篇 |
2000年 | 30篇 |
1999年 | 22篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 24篇 |
1995年 | 19篇 |
1994年 | 18篇 |
1993年 | 8篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 6篇 |
1984年 | 13篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 17篇 |
1972年 | 9篇 |
1971年 | 5篇 |
1965年 | 4篇 |
排序方式: 共有1457条查询结果,搜索用时 31 毫秒
51.
52.
53.
Dr. Steffen Bähring Dr. Luis Martín‐Gomis Gunnar Olsen Prof. Dr. Kent A. Nielsen Dr. Dong Sub Kim Dr. Troels Duedal Prof. Dr. Ángela Sastre‐Santos Prof. Dr. Jan O. Jeppesen Prof. Dr. Jonathan L. Sessler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):1958-1967
Supramolecular polymers are a class of macromolecules stabilized by weak non‐covalent interactions. These self‐assembled aggregates typically undergo stimuli‐induced reversible assembly and disassembly. They thus hold great promise as so‐called functional materials. In this work, we present the design, synthesis, and responsive behavior of a short supramolecular oligomeric system based on two hetero‐complementary subunits. These “monomers” consist of a tetrathiafulvalene‐functionalized calix[4]pyrrole (TTF‐C[4]P) and a glycol diester‐linked bis‐2,5,7‐trinitrodicyanomethylenefluorene‐4‐carboxylate (TNDCF), respectively. We show that when mixed in organic solvents, such as CHCl3, CH2ClCH2Cl, and methylcyclohexane, supramolecular aggregation takes place to produce short oligomers stabilized by hydrogen bonding and donor–acceptor charge‐transfer (CT) interactions. The self‐associated materials were characterized by 1H NMR and UV/Vis/NIR absorption spectroscopy, as well as by concentration‐ and temperature‐dependent absorption spectroscopy and dynamic light scattering (DLS) analyses of both the monomeric and oligomerized species. The self‐associated system produced from TTF‐C[4]P and TNDCF exhibits a concentration‐dependent aggregation behavior typical of supramolecular polymers. Further support for the proposed self‐assembly came from theoretical calculations. The fluorescence emitting properties of TNDCF are quenched under conditions that promote the formation of supramolecular aggregates containing TTF‐C[4]P and TNDCF. This quenching effect has been utilized as a probe for the detection of substrates in the form of anions (i.e., chloride) and nitroaromatic explosives (i.e., 1,3,5‐trinitrobenzene). Specifically, the addition of these substrates to mixtures of TTF‐C[4]P and TNDCF produced a fluorescence “turn‐on” response. 相似文献
54.
Dr. Agnes Kütt Prof. Dr. Gunnar Jeschke Dr. Lauri Toom Dr. Jaak Nerut Prof. Christopher A. Reed 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(41):8871-8874
Hydride abstraction from diarylamines with the trityl ion is explored in an attempt to generate a stable diarylnitrenium ion, Ar2N+. Sequential H-atom abstraction reactions ensue. The first H-atom abstraction leads to intensely colored aminium radical cations, Ar2NH.+, some of which are quite stable. However, most undergo a second H-atom abstraction leading to ammonium ions, Ar2NH2+. In the absence of a ready source of H-atoms, a unique self-abstraction reaction occurs when Ar=Me5C6, leading to a novel iminium radical cation, Ar=N.+Ar, which decays via a second self H-atom abstraction reaction to give a stable iminium ion, Ar=N+HAr. These products differ substantially from those derived via photochemically produced diarylnitrenium ions. 相似文献
55.
Carbon K‐edge X‐ray spectroscopy has been applied to the study of a wide range of organic samples, from polymers and coals to interstellar dust particles. Identification of carbonaceous materials within these samples is accomplished by the pattern of resonances in the 280–320 eV energy region. Carbonate minerals are often encountered in the study of natural samples, and have been identified by a distinctive resonance at 290.3 eV. Here C K‐edge and Ca L‐edge spectra from a range of carbonate minerals are presented. Although all carbonates exhibit a sharp 290 eV resonance, both the precise position of this resonance and the positions of other resonances vary among minerals. The relative strengths of the different carbonate resonances also vary with crystal orientation to the linearly polarized X‐ray beam. Intriguingly, several carbonate minerals also exhibit a strong 288.6 eV resonance, consistent with the position of a carbonyl resonance rather than carbonate. Calcite and aragonite, although indistinguishable spectrally at the C K‐edge, exhibited significantly different spectra at the Ca L‐edge. The distinctive spectral fingerprints of carbonates provide an identification tool, allowing for the examination of such processes as carbon sequestration in minerals, Mn substitution in marine calcium carbonates (dolomitization) and serpentinization of basalts. 相似文献
56.
Gunnar Aksnes Fayez Y. Khalil Piotr J. Majewski 《Phosphorus, sulfur, and silicon and the related elements》2013,188(2):157-161
Abstract This study reports rate data of the alkoxide promoted decomposition of triphenyl 3-hydroxypropyl phosphonium chloride, diphenyl di(3-hydroxypropyl)phosphonium chloride, and tetraphenyl phosphonium bromide. Comparison of kinetics, rate constants, and activation parameters of the alkoxide promoted decompositions points to different mechanism as compared to the hydroxyl promoted reaction. The alkoxide reaction is believed to proceed via a hexacovalent intermediate. Reasons for the hexacovalent route are discussed. 相似文献
57.
Lars Carlsena Klaus Bechgaardb Claus S. Jacobsen Ib Johansen 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2)
Abstract Tetrathiafulvalene S-oxide (TTF-ox) was first detected by mass spectrometry in samples of Tetrathiafulvalene (TTF) which had been exposed to oxygen. Pure TTF-ox was prepared by peracid oxidation of TTF and isolated as a relativly stable solid. Physical data will be presented. 相似文献
58.
Gunnar Aksnes Roald Gierstae Erik A. Wulvik 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):141-152
Abstract A study of alkaline decomposition of several aromatic phosphine oxides containing p- and o-nitrobenzyl, and trichloromethyl as leaving groups, is reported. The property of the trichloromethyl group as leaving group, and the CCl? 3-group's further decomposition in the hydrolysis of diethyl and disodium trichloromethanephosphonates, have also been investigated. 相似文献
59.
60.