全文获取类型
收费全文 | 181篇 |
免费 | 2篇 |
专业分类
化学 | 163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 | 4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183条查询结果,搜索用时 15 毫秒
81.
A. Venema N. M. M. Nibbering Th. J. de Boer 《Journal of mass spectrometry : JMS》1970,3(12):1589-1592
Specific 13C-labelling in the side-chain of 1-phenylethylbromide and of styrene shows that it is not necessary to assume eight-membered ring structures for the [C8H9]+- and [C8H8]++˙-ions to explain the almost complete randomization of all hydrogen atoms, as might be concluded from D-labelling data. It is now suggested that the eight-membered ring is predominantly present in [C8H9]+ and [C8H8]+˙ ions of low internal energy. In particular this appears to apply to styrene, which generates a cyclooctatetraene molecular ion with the original side-chain carbon atoms still linked together, as shown by 13C-labelling. 相似文献
82.
83.
84.
Carla B. Theissling Nico M. M. Nibbering Seymour Meyerson 《Journal of mass spectrometry : JMS》1976,11(8):838-843
Evidence has been reported that primary loss of H and of HCN from the molecular ions of propionitrile, isobutyronitrile and butyronitrile in the mass spectrometer is preferentially preceded by hydrogen migration from C-2 to C-1. Ion cyclotron double resonance spectra of proton (or deuteron-) transfer products derived from propionitrile-2-d2 and -3-d3 and a series of bases provide evidence that such migration occurs also in long-lived propionitrile molecular ions. 相似文献
85.
Guo X Duursma MC Kistemaker PG Nibbering NM Vekey K Drahos L Heeren RM 《Journal of mass spectrometry : JMS》2003,38(6):597-606
The internal energy of protonated leucine enkephalin has been manipulated in electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry with two newly designed pump-probe experiments. Blackbody infrared radiation was applied to pump an ion population into a well-defined internal energy distribution below the dissociation threshold. Following this pumping stage, the internal energy distribution was probed using on-resonance collisional activation to dissociate the ions. These pump-probe experiments were carried out in two different ways: (a) using on-resonance collisional activation with variable kinetic energies to dissociate the ions at a constant initial ion temperature (determining the precursor ion survival percentage as a function of kinetic energy) and (b) using on-resonance collisional activation with a constant kinetic energy to dissociate the ions at variable initial ion temperatures (to investigate the ion survival yield-initial ion temperature dependence). Using this approach, a detailed study of the effects of the initial ion temperature, the probing kinetic energy and the internal energy loss rate on the effective conversion efficiency of (laboratory-frame) kinetic energy to internal energy was conducted. This conversion efficiency was found to be dependent on the initial ion temperature. Depending on the experimental conditions the conversion efficiency (for collisions with argon) was estimated to be about 4.0 +/- 1.7%, which agrees with that obtained from a theoretical modeling. Finally, the reconstructed curves of the ion survival yield versus the mode of the (final) total internal energy distribution of the activated ion population (after pump and probe events) at different pump-probe conditions reveal the internal energy content of the activated ions. 相似文献
86.
Wilfrid P. M. Maas Peter A. Van Veelen Nico M. M. Nibbering 《Journal of mass spectrometry : JMS》1989,24(8):546-558
Three routes have been explored in both a high-pressure chemical ionization (CI) source and a low-pressure Fourier transform ion cyclotron resonance (FT-ICR) cell to generate the spiro[2,5]octadienyl anion in the gas phase: (i) proton abstraction from spiro[2,5]octa-4,6-diene; (ii) expulsion of trimethysilyl fluoride by phenyl ring participation following fluoride anion attack upon the silicon centre of 2-phenylethyl trimethylsilane; and (iii) collisionally induced dissociation (CID) of the carboxylate anion of 3-phenylpropanoic acid via carbon dioxide loss. From comparison of the CID spectra of various reference [C8H9]? ions with those of the [C8H9]? ions which could be generated via the routes (i) and (iii) in the CI source it can be concluded that only the third route yields a [C8H9]?ion whose CID spectrum is not inconsistent with the one expected for the spiro[2,5]octadienyl anion. In the FT-ICR cell [C8H9]? ions are generated along all three routes; their structures have been identified by specific ion-molecule reactions and appear to be different. Route (i) yields an α-methyl benzyl anion, probably due to isomerization within the ion-molecule complex formed. An ortho-ethylphenyl anion is formed along route (ii), presumably due to an intramolecular ortho proton abstraction in the generated trimethylsilyl fluoride solvated 2-phenylethyl primary carbanion. The [C8H9]? ion formed along route (iii) shows reactions similar to those of the 1,1-dimethylcyclohexadienyl anion which is structurally related to the spiro[2,5]octadienyl anion. Furthermore, the [C8H9]? ion generated via route (iii) reacts with hexafluorobenzene under expulsion of only one hydrogen fluoride molecule which contains exclusively one of the original phenyl ring hydrogen atoms. On the basis of all these observations it is therefore quite likely that the spiro[2,5]octadienyl anion is formed by collisionally induced decarboxylation of the 3-phenylpropanoic acid carboxylate anion and can be a long-lived and stable species in the gas phase. 相似文献
87.
Tineke A. Molenaar-Langeveld Roel H. Fokkens Nico M. M. Nibbering 《Journal of mass spectrometry : JMS》1986,21(1):15-21
It is shown by 15N and specific 13C labelling that ~50% of the molecules of hydrogen cyanide, eliminated within ~10?6 s upon electron impact of benzonitrile, contains the original cyano carbon atom, whereas the remaining percentage contains one of the phenyl ring carbon atoms at random. This is even more dramatic for the molecular ions of benzonitrile which decompose in the first and second field-free regions of the VG Micromass ZAB-2F high-field mass spectrometer used. Then only 5–7% of the eliminated molecules of hydrogen cyanide contains the original cyano carbon atom. A cycloaddition-cycloreversion process in the molecular ions, leading to ionized 1-cyano-1,3-hexadien-5-yne as an intermediate in the hydrogen cyanide loss, is proposed to explain this. 相似文献
88.
Klaas Jan van den Berg Steen Ingemann Nico M. M. Nibbering 《Journal of mass spectrometry : JMS》1993,28(5):527-533
The reactions of metal carbonyl anions (M(CO)n?; M = Cr, Mn and Fe; n = 1–3) with n-heptane, water and methanol were studied with use of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an external ion source. The M(CO)n? ions were formed in the FT-ICR cell by collision-induced dissociation of the most abundant primary ion generated by electron impact of the appropriate metal carbonyl compound present in the external ion source. The M(CO)n? ions were allowed subsequently to undergo non-reactive collisions with argon in order to remove possible excess internal/translational energy prior to the ion/molecule reaction. Only the Cr(CO)3?, Mn(CO)3? and Fe(CO)2? ions react with n-heptane. This reaction proceeds by loss of H2 from the collision complex and the Cr(CO)3? and Fe(CO)2? ions react about three times more efficiently than the Mn(CO)3? ion. With water, Mn(CO)? and Fe(CO)3? are unreactive, whereas the other ions react by loss of one or two CO molecules from the collision complex. The rate of the reaction with water decreases in the order Cr(CO)3?, Fe(CO)2?, Cr(CO)2?, Fe(CO)?, Mn(CO)3? and Mn(CO)2?. With methanol, the Cr(CO)2? ion reacts by loss of two CO molecules from the collision complex, whereas loss of one CO molecule and elimination of CO + H2 occur in the reaction with Cr(CO)3?. Competing loss of CO and one or two H2 molecules occurs in the reactions of Mn(CO)3? and Fe(CO)2? with methanol. The rate of the reaction with methanol decreases in the order Cr(CO)3?, Fe(CO)2?, Cr(CO)2? and Mn(CO)3?. 相似文献
89.
Rini M Holm AK Nibbering ET Fidder H 《Journal of the American Chemical Society》2003,125(10):3028-3034
We present a femtosecond UV-mid-IR pump-probe study of the photochemical ring-opening reaction of the spiropyran 1',3',3',-trimethylspiro-[-2H-1-benzopyran-2,2'-indoline] (also known as BIPS) in tetrachloroethene, using 70 fs UV excitation pulses and probing with 100 fs mid-IR pulses. The time evolution of the transient IR absorption spectrum was monitored over the first 100 ps after UV excitation. We conclude that the merocyanine product is formed with a 28 ps time constant, contrasting with a 0.9 ps time constant obtained in previous investigations where the rise of absorption bands at visible wavelengths were associated with product formation. We deduce from the observed strong recovery of the spiropyran IR absorption bleaches that, in tetrachloroethene, the main decay channel for the S(1) excited state of the spiropyran BIPS, is internal conversion to the spiropyran S(0) state with a quantum yield of > or = 0.9. This puts an upper limit of 0.1 to the quantum yield of the photochemical ring-opening reaction. 相似文献
90.
Frontispiece: The Hydrated Excess Proton in the Zundel Cation H5O2+: The Role of Ultrafast Solvent Fluctuations 下载免费PDF全文