全文获取类型
收费全文 | 300篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
化学 | 122篇 |
晶体学 | 1篇 |
力学 | 12篇 |
数学 | 131篇 |
物理学 | 39篇 |
出版年
2020年 | 4篇 |
2019年 | 5篇 |
2017年 | 4篇 |
2015年 | 4篇 |
2014年 | 5篇 |
2013年 | 13篇 |
2012年 | 8篇 |
2011年 | 9篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 3篇 |
2005年 | 8篇 |
2004年 | 5篇 |
2003年 | 3篇 |
2002年 | 7篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1974年 | 3篇 |
1972年 | 3篇 |
1971年 | 6篇 |
1970年 | 6篇 |
1969年 | 6篇 |
1968年 | 3篇 |
1965年 | 3篇 |
1962年 | 4篇 |
1959年 | 3篇 |
排序方式: 共有305条查询结果,搜索用时 15 毫秒
121.
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
122.
Seymour Meyerson 《Journal of mass spectrometry : JMS》1970,3(1):119-125
Mass spectra of isotope-labeled triptycenes, triphenylmethanes and diphenylmethanes rule out the bulk of postulated decomposition mechanisms and fragment-ion structures. The formation of [M ? H]+ and [M ? 2H]2+ from triptycene, of [M ? H]+, [M ? CH3]+ and [M ? CH4]+ from triphenylmethane, and of [M ? H]2+ and [M ? 2H]2+-as well as the previously reported [M ? H]+ and [M ? CH3]+-from diphenylmethane all seem to be preceded or accompanied by complete loss of position identity of the α and ring hydrogens in the original molecules. A statistical preference for loss of α hydrogens is found in the process leading to [M ? 2H]+ and [M ? H]2+ from triptycene, as in the formation of [M ? H]2+ from toluene. 相似文献
123.
Ultraviolet absorption spectra of 66 metal ions in aqueous 6M hydrochloric acid were recorded and the spectra of 36 metal ions that absorb appreciably are reported. The absorption of these metal ions is sufficient to permit their detection in liquid chromatography. 相似文献
124.
Summary Collocation at Gaussian points for a scalarm-th order ordinary differential equation has been studied by C. de Boor and B. Swartz. J. Douglas, Jr. and T. Dupont, using collocation at Gaussian points, and a combination of energy estimates and approximation theory have given a comprehensive theory for parabolic problems in a single space variable. While the results of this report parallel those of Douglas and Dupont, the approach is basically different. The Laplace transform is used to lift the results of de Boor and Swartz to linear parabolic problems. This indicates a general procedure that may be used to lift schemes for elliptic problems to schemes for parabolic problems. Additionally there is a section on longtime integration and A-stability.Supported by the Office of Naval Research under contract N-00014-67-A-0128-0004 相似文献
125.
Consider the boundary value problem where β ? 0, τ ? 0. We are concerned with a mathematically rigorous numerical study of the number of solutions in any bounded portion of the positive quadrant (τ ? 0, β ? 0) of the τ, β plane. These correct computational results may then be matched with asymptotic (β→∞, τ ? 0) results developed earlier. These numerical results are based on the development of a posteriori error estimates for the numerical solution of an associated initial-value problem and a priori bounds on . 相似文献
126.
A two-coloring of the verticesX of the hypergraphH=(X, ε) by red and blue hasdiscrepancy d ifd is the largest difference between the number of red and blue points in any edge. A two-coloring is an equipartition ofH if it has discrepancy 0, i.e., every edge is exactly half red and half blue. Letf(n) be the fewest number of edges in ann-uniform hypergraph (all edges have sizen) having positive discrepancy. Erd?s and Sós asked: isf(n) unbounded? We answer this question in the affirmative and show that there exist constantsc 1 andc 2 such that $$\frac{{c_1 \log (snd(n/2))}}{{\log \log (snd(n/2))}} \leqq f(n) \leqq c_2 \frac{{\log ^3 (snd(n/2))}}{{\log \log (snd(n/2))}}$$ where snd(x) is the least positive integer that does not dividex. 相似文献
127.
Gas-phase ternary complexes with Cu(II) and 2,2'-bipyridine (bpy) of tyrosine, 3-aminotyrosine, 3-nitrotyrosine and 3-nitrotyrosine methyl ether are formed readily upon electrospraying aqueous methanol solutions containing the components. In contrast to Cu(bpy) complexes of tyrosine, 3-aminotyrosine and other aromatic amino acids, the complexes of 3-nitrotyrosine and its methyl ether undergo unusual collisionally activated dissociations (CADs) that involve Cu-mediated transfer of an oxygen atom from the nitro group. With 3-nitrotyrosine this results in an expulsion of carbonic acid, H(2)CO(3), whereas with 3-nitrotyrosine methyl ether an OH migration forms Cu(OH)bpy(+) as the predominant product. To the best of our knowledge, this is the first case of an intra-ligand redox reaction in a gas-phase organometallic complex. The reaction mechanism of this unusual dissociation was elucidated by a combination of isotope labeling, accurate mass measurements, energy-resolved CAD mass spectra and density functional theory calculations of ion structures and relative energies. 相似文献
128.
Maria Chudnovsky Gérard Cornuéjols Xinming Liu? Paul Seymour? Kristina Vu?kovi?? 《Combinatorica》2005,25(2):143-186
A graph is Berge if no induced subgraph of G is an odd cycle of length at least five or the complement of one. In this paper we give an algorithm to test if a graph G is Berge, with running time O(|V (G)|9). This is independent of the recent proof of the strong perfect graph conjecture.* Currently this author is a Clay Mathematics Institute Research Fellow.** Supported by NSF grant DMI-0352885 and ONR grant N00014-97-1-0196. Supported by ONR grant N00014-01-1-0608, and NSF grant DMS-0070912. Supported by EPSRC grant GR/R35629/01. 相似文献
129.
M. S. Andreaco R. S. Seymour G. N. Martin 《Journal of Radioanalytical and Nuclear Chemistry》1992,156(2):323-340
A comparison of an HPGe planar detector and an HPGe coaxial detector, both with short length-to-diameter ratios, provides empirical evidence for the advantage of the coaxial configuration in measurements of actinide radionuclides. The principal advantage is related to the lower capacitance of a coaxial detector relative to that of a planar detector, both with large active frontal areas. In addition, the higher interaction probability (efficiency) of Ge versus Si underscores the advantages of Ge for measurements of samples with -ray energies from 5 to 200 keV (235U and241Pu). The advantages are also dependent on the presence of other higher-energy -rays collimated versus diffuse-sample geometry, and (for bioassay applications) the intervening scattering mediums of bone and tissue. 相似文献
130.
Michael H. Seymour 《Zeitschrift fur Physik C Particles and Fields》1992,56(1):161-170
A method is described for the inclusion ofq→qγ branchings within a QCD parton showering event generator. Special attention is paid to the ‘back-to-back’ region ine + e ? events, where a very hard photon recoils from a nearly collinear quark-antiquark pair. The resulting algorithm is also applied to back-to-backq \(\bar q\) g configurations. Results for theq \(\bar q\) γ cross-section are compared against various theoretical predictions, models and experimental data. 相似文献