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61.
Katri Huitu Ritva Kinnunen Jari Laamanen Sami Lehti Sourov Roy Tapio Salminen 《The European Physical Journal C - Particles and Fields》2008,58(4):591-608
In grand-unified theories (GUT), non-universal boundary conditions for the gaugino masses may arise at the unification scale
and may affect the observability of the neutral MSSM Higgs bosons (h/H/A) at the LHC. The implications of such non-universal gaugino masses are investigated for Higgs boson production in the SUSY
cascade decay chain
,
,
,
produced in pp interactions. In the singlet representation with universal gaugino masses only the light Higgs boson can be produced in this
cascade with the parameter region of interest for us, while with non-universal gaugino masses heavy neutral MSSM Higgs boson
production may dominate. The allowed parameter space in the light of the WMAP constraints on the cold dark-matter relic density
is investigated in the above scenarios for gaugino mass parameters. We also demonstrate that combination of representations
can give the required amount of dark matter in any point of the parameter space. In the non-universal case we show that heavy
Higgs bosons can be detected in the cascade studied in parameter regions with the WMAP preferred neutralino relic density. 相似文献
62.
Dias CL Ala-Nissila T Karttunen M Vattulainen I Grant M 《Physical review letters》2008,100(11):118101
We elucidate the mechanism of cold denaturation through constant-pressure simulations for a model of hydrophobic molecules in an explicit solvent. We find that the temperature dependence of the hydrophobic effect induces, facilitates, and is the driving force for cold denaturation. The physical mechanism underlying this phenomenon is identified as the destabilization of hydrophobic contact in favor of solvent-separated configurations, the same mechanism seen in pressure-induced denaturation. A phenomenological explanation proposed for the mechanism is suggested as being responsible for cold denaturation in real proteins. 相似文献
63.
Adamov A Sysoev AA Grigoras K Laakia J Kotiaho T 《European journal of mass spectrometry (Chichester, England)》2011,17(6):593-597
Using a simple ion source set-up, laser desorption/ionization on silicon (DIOS) was demonstrated with the use of a custom-made drift tube ion mobility spectrometer (IMS), mounted on a commercial triple quadrupole mass spectrometer, and with an IMS equipped with a Faraday plate detector. DIOS was tested by mobility measurement of tetrapropylammonium iodide, tetrabutylammonium iodide and tetrapentylammonium iodide, whilst 2,6-di-tert- butylpyridine was used as a standard. The reduced mobilities measured for the test halides are in concordance with previously obtained ion mobility spectrometry-mass spectrometry data. 相似文献
64.
Jaakko Laakia Alexey Adamov Matti Jussila Christian S. Pedersen Alexey A. Sysoev Tapio Kotiaho 《Journal of the American Society for Mass Spectrometry》2010,21(9):1565-1572
This study demonstrates how positive ion atmospheric pressure photoionization-ion mobility spectrometry-mass spectrometry
(APPI-IMS-MS) can be used to produce different ionic forms of an analy te and how these can be separated. When hexane:toluene
(9:1) is used as a solvent, 2,6-di-tert-butylpyridine (2,6-DtBPyr) and 2,6-di-tert-4-methylpyridine (2,6-DtB-4-MPyr) efficiently produce radical cations [M]+ and protonated [M + H]+ molecules, whereas, when the sample solvent is hexane, protonated molecules are mainly formed. Interestingly, radical cations
drift slower in the drift tube than the protonated molecules. It was observed that an oxygen adduct ion, [M + O2]+, which was clearly seen in the mass spectra for hexane:toluene (9:1) solutions, shares the same mobility with radical cations,
[M]+. Therefore, the observed mobility order is most likely explained by oxygen adduct formation, i.e., the radical cation forrning
a heavier adduct. For pyridine and 2-tert-butylpyridine, only protonated molecules could be efficiently formed in the conditions used. For 1- and 2-naphthol it was
observed that in hexane the protonated molecule typically had a higher intensity than the radical cation, whereas in hexane:toluene
(9:1) the radical cation [M]+ typically had a higher intensity than the protonated molecule [M + H]+. Interestingly, the latter drifts slower than the radical cation [M]+, which is the opposite of the drift pattern seen for 2,6-DtBPyr and 2,6-DtB-4-MPyr. 相似文献
65.
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67.
Kotiaho T Eberlin MN Vainiotalo P Kostiainen R 《Journal of the American Society for Mass Spectrometry》2000,11(6):526-535
Aqueous ozonation of the 22 most common amino acids and some small peptides were studied by electrospray mass (ESI-MS) and tandem mass spectrometry. After 5 min of ozonation only His, Met, Trp, and Tyr form oxidation products clearly detectable by ESI-MS. For His, the main oxidation product is formed by the addition of three oxygen atoms, His + 30; for Met and Tyr by the addition of one oxygen atom, Met + O and Tyr + O, and for Trp by the addition of two oxygen atoms, Trp + 20. Ozone oxidation occurs rapidly, products are already detected after 30 s of ozonation, and the reactivity order is Met > Trp > Tyr > His. The structures of the oxygen addition products were investigated by electrospray product ion mass spectra, and by comparing these spectra to those of protonated intact amino acids, and when available, to those of model compounds. His + 30 was assigned as 2-amino-4-oxo-4-(3-formylureido)butanoic acid (1) formed by oxidation of the His imidazole ring, Met + O as methionine sulfoxide (2), Trp + 20 as N-formylkynurenine (4), and Tyr + O as a mixture of dihydroxyphenylalanines (7 and 8). Ozonation of peptides show that the same number of oxygen atoms are added as expected from the ozonation of the free amino acids. The product ion mass spectra of both the protonated intact peptides, MH+, and the main ozonation products (M + nO)H+ (n = 1-3) revealed b and y type ions as the main fragments, which allow one to assign the type and location of modified amino acid in the model peptides. 相似文献
68.
Kinetic analysis is presented for the so-called rollover mechanism in hydrogenation of dialkylbenzenes. The theory of complex
reactions and graph theory are applied for discussing plausible mechanisms. It is demonstrated that mechanisms which involve
either desorption-readsorption of some reaction intermediate or some kind of “rollover” of an adsorbed intermediate, result
in similar kinetic equations if these steps are reversible. 相似文献
69.
The purpose of this review is to highlight the versatility of membrane introduction mass spectrometry (MIMS) in environmental applications, summarize the measurements of environmental volatile organic compounds (VOCs) accomplished using MIMS, present developments in the detection of semi-volatile organic compounds (SVOCs) and forecast possible future directions of MIMS in environmental applications. 相似文献
70.
Jorma Matikainen Seppo KaltiaMaija Ala-Peijari Ninna Petit-GrasKirsi Harju Jaakko HeikkiläRaija Yksjärvi Tapio Hase 《Tetrahedron》2003,59(4):567-573
Heating a mixture formed by alkali isomerization of methyl linolenoate (1) produces a complex mixture with the bicyclic hexahydroindenoic esters 4β-(7-methoxycarbonylheptyl)-5α-methyl-2,3,3aα,4,5,7aαhexahydroindene (CL5) and 4β-ethyl-5α-(6-methoxycarbonylhexyl)-2,3,3aα,4,5,7aα-hexahydroindene (CL6) as main components. Similar isomerization reactions of three synthetic model compounds, methyl 9Z,13E,15Z-octadecatrienoate (2), 9Z,14E,16E-octadecatrienoate (4) and 9Z,11E,15Z-octadecatrienoate (5) corroborated the results obtained with alkali isomerized methyl linolenoate. 相似文献