全文获取类型
收费全文 | 182篇 |
免费 | 2篇 |
专业分类
化学 | 164篇 |
数学 | 5篇 |
物理学 | 15篇 |
出版年
2020年 | 1篇 |
2016年 | 3篇 |
2014年 | 2篇 |
2013年 | 5篇 |
2012年 | 4篇 |
2011年 | 6篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 6篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 3篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 7篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 9篇 |
1973年 | 4篇 |
1972年 | 1篇 |
1971年 | 3篇 |
1970年 | 5篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有184条查询结果,搜索用时 15 毫秒
41.
R. Hittenhausen-Gelderblom A. Venema N. M. M. Nibbering 《Journal of mass spectrometry : JMS》1974,9(9):878-883
The mass spectra of the title compounds have been studied by use of deuterium labelling. The character of the halogen atom appears to have a marked influence on the fragmentation pathways. It is shown that the acyl halide group may react with the different active atoms in the molecular ion—the α- and β-hydrogen atoms—as well as with the phenyl ring. 相似文献
42.
43.
44.
Dr. Varsha V. Kapoerchan Dr. Annemiek D. Knijnenburg Miquel Niamat Emile Spalburg Dr. Albert J. de Neeling Dr. Peter H. Nibbering Roos H. Mars‐Groenendijk Dr. Daan Noort José M. Otero Dr. Antonio L. Llamas‐Saiz Dr. Mark J. van Raaij Prof. Dr. Gijs A. van der Marel Prof. Dr. Herman S. Overkleeft Dr. Mark Overhand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(40):12174-12181
The cyclic cationic antimicrobial peptide gramicidin S (GS) is an effective topical antibacterial agent that is toxic for human red blood cells (hemolysis). Herein, we present a series of amphiphilic derivatives of GS with either two or four positive charges and characteristics ranging between very polar and very hydrophobic. Screening of this series of peptide derivatives identified a compound that combines effective antibacterial activity with virtually no toxicity within the same concentration range. This peptide acts against both Gram‐negative and Gram‐positive bacteria, including several MRSA strains, and represents an interesting lead for the development of a broadly applicable antibiotic. 相似文献
45.
Mohammed OF Banerji N Lang B Nibbering ET Vauthey E 《The journal of physical chemistry. A》2006,110(51):13676-13680
Ultrafast infrared transient absorption spectroscopy is used to study the photoinduced bimolecular electron transfer reaction between perylene in the first singlet excited state and 1,4-dicyanobenzene in acetonitrile and dichloromethane. Following vibrational marker modes on both donor and acceptor sides in real time provides direct insight into the structural dynamics during the reaction. A band narrowing on a time scale of a few tens of picoseconds observed on the antisymmetric CN stretching vibration of the dicyanobenzene radical anion indicates that a substantial part of the excess energy is channeled into vibrational modes of the product, despite the fact that the reaction is weakly exergonic. An additional narrowing of the same band on a time scale of several hundreds of picoseconds observed in acetonitrile only is interpreted as a signature of the dissociation of the geminate ion pairs into free ions. 相似文献
46.
Yang M Szyc Ł Dreyer J Nibbering ET Elsaesser T 《The journal of physical chemistry. A》2010,114(46):12195-12201
2-Pyridone (PD) tautomerises to 2-hydroxypyridine (HP) in liquid solution, the equilibrium of which is solvent dependent. Dimerization of PD and HP leads to the cyclic dimers (PD)(2), (HP)(2), and (PD-HP). A combined NMR and FT-IR study [Szyc, ?.; et al. J. Phys. Chem. A 2010, 114, 7749-7760] has shown that solutions of 2-pyridone in CD(2)Cl(2) constitute mainly PD-CD(2)Cl(2) solute-solvent complexes and cyclic dimers (PD)(2). Because of a lack of specific marker modes, a contribution of the cyclic dimer (HP)(2) to the NH/OH stretching absorption between 2400 and 3300 cm(-1) could not be fully ruled out. Here, we present the first ultrafast infrared (IR) pump-probe experiments on the NH/OH stretching region of a solution of 2-pyridone in CD(2)Cl(2). The temporally and spectrally resolved data reveal different rate-like relaxation processes with time constants between 150 fs and 20 ps as well as coherent low-frequency oscillations due to hydrogen bond modes. An analysis shows that the transient behavior is dominated by a single hydrogen bonded species. We compare the low-frequency wavepacket motions, observed with 99 and 150 cm(-1) frequencies, with literature values as well as our quantum chemical calculations and conclude that this single molecular species is cyclic (PD)(2). 相似文献
47.
48.
Tineke A. Molenaar-Langeveld Nico M. M. Nibbering 《Journal of mass spectrometry : JMS》1983,18(10):426-432
It is shown by field ionization kinetics, D and 13C labelling and metastable ion studies that the loss of a propyl radical from the molecular ion of methoxycyclohexane occurs via two routes. At a molecular ion lifetime of <10?10 s propyl is eliminated in the ‘classic’ way, i.e. by successive cleavage of the C(1)? C(2) bond, 1,5-H shift from C(6) to C(2) and cleavage of the C(4)? C(5) bond. At 10?10 s the other pathway for propyl loss starts to take place, which is initiated by a hydrogen shift from position 3 or 5 to the methoxy group. This leads in a series of steps to the formation of the 3-methoxyhexene-1 ion, which eventually eliminates a propyl radical. In some of the steps specific hydrogen-deuterium exchange processes have been observed. 相似文献
49.
A strong secondary isotope effect is observed in the preferred loss of methyl vs. trideutero-methyl from the molecular ions of appropriately labelled 4-t-butylpyridine and t-butylbenzene decomposing in the first and second field free regions of a double focusing mass spectrometer. This has been rationalised by invoking the theory of radiationless transitions2, which can account for the higher population of activated states responsible for loss of methyl vs. that for trideuteromethyl. 13C-Labelling at the central carbon atom of the t-butyl group indicates that the [M – methyl]+ ions, decomposing further by elimination of ethylene, cannot be represented exclusively by a pyridylated (or phenylated) cyclopropane ion if present at all. It is concluded that ions with structures generated by 1,2-hydrogen-, 1,2-pyridyl- (or 1,2-phenyl-) and 1,2-methyl shifts must also play a role. D-labelling further shows an extensive randomisation of side-chain hydrogen atoms in the [M-methyl]+ ions of 4-t-butylbenzene; in this case, however, the expelled ethylene also contains ring hydrogen atoms (≤2). Presumably this is caused by exchange between the side-chain and ortho-hydrogen atoms in the initially generated phenyldimethylcarbinyl carbenium ion. 相似文献
50.
van Amerom EH van Duijn D van der Hart WJ Nibbering NM 《Journal of the American Society for Mass Spectrometry》2001,12(4):359-366
By use of Fourier transform ion cyclotron resonance, it is shown that protonated naphthalene when excited with laser light of 488 nm is more reactive in proton transfer to reference bases than in its ground state. The excitation leads to reaction with bases for which proton transfer in the ground state is endothermic up to a detected maximum of 60 kJ/mol. For indene radical cations excited at 514.5 nm, it is shown that the rate constant for proton transfer to 3-pentanone is either about 10 or about 100 times lower than the rate constant for relaxation by collisions with 3-pentanone. From the energy deposited in the ions, 0.5-0.6 eV is available for proton transfer to a base which seems reasonable when taking into account a complete randomization of the initially deposited energy. 相似文献