全文获取类型
收费全文 | 383篇 |
免费 | 12篇 |
专业分类
化学 | 243篇 |
晶体学 | 2篇 |
力学 | 21篇 |
数学 | 64篇 |
物理学 | 65篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 3篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 3篇 |
2017年 | 2篇 |
2016年 | 10篇 |
2015年 | 15篇 |
2014年 | 14篇 |
2013年 | 21篇 |
2012年 | 23篇 |
2011年 | 16篇 |
2010年 | 15篇 |
2009年 | 25篇 |
2008年 | 28篇 |
2007年 | 22篇 |
2006年 | 16篇 |
2005年 | 20篇 |
2004年 | 13篇 |
2003年 | 6篇 |
2002年 | 13篇 |
2001年 | 8篇 |
2000年 | 13篇 |
1999年 | 15篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1985年 | 7篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有395条查询结果,搜索用时 15 毫秒
61.
62.
We present an analysis of emission spectra, obtained in polar and non-polar solvents and at different temperatures, for a series of aniline derivatives excited at different wavelengths. Important changes in the intensity and polarization of the emission are shown to be due to conformational effects of the amino group which strongly changes the molecular desactivation dynamics. This interpretation is shown to be consistent also with the absorption spectra. 相似文献
63.
In the present work, experiments have been performed to study the influence of the sheet thickness on the oscillatory movement of an air-blasted liquid sheet, based on measurements of oscillation frequencies and wavelengths. To measure the wavelengths, a novel double-beam diffraction technique has been implemented. It has been determined that the sheet oscillation frequency depends on the inverse of the square root of the sheet thickness, while the wavelength increases linearly as sheet thickness is increased. Based on these dependencies, suitable non-dimensional groups are proposed to describe the problem. Wave propagation velocities have also been calculated and discussed. 相似文献
64.
Inside Cover: Textile/Metal–Organic‐Framework Composites as Self‐Detoxifying Filters for Chemical‐Warfare Agents (Angew. Chem. Int. Ed. 23/2015) 下载免费PDF全文
65.
Data envelopment analysis (DEA) can be used as a pre-merger planning tool to estimate expected cost and profit efficiency gains. Specifically, in this paper, two alternative DEA models are presented, one to minimize post-merger input cost and the other to maximize post-merger profit. The first model assumes that input prices are known, whereas the second assumes that output prices are known. As both models explicitly consider the possibility of closing existing units, they are especially apt for in-market horizontal mergers, in which considerable overlap may exist among the branches of the merging firms. Indicative efficiency ratios are proposed based on the results of the models. The proposed approach is, in addition, rather flexible, allowing the optional inclusion of a variety of features and constraints, such as incompatibility among units, employment guarantees, etc. 相似文献
66.
Carlos García-Martínez Fred Glover Francisco J. Rodriguez Manuel Lozano Rafael Martí 《Computational Optimization and Applications》2014,58(1):161-185
The quadratic multiple knapsack problem (QMKP) consists in assigning a set of objects, which interact through paired profit values, exclusively to different capacity-constrained knapsacks with the aim of maximising total profit. Its many applications include the assignment of workmen to different tasks when their ability to cooperate may affect the results. Strategic oscillation (SO) is a search strategy that operates in relation to a critical boundary associated with important solution features (such as feasibility). Originally proposed in the context of tabu search, it has become widely applied as an efficient memory-based methodology. We apply strategic oscillation to the quadratic multiple knapsack problem, disclosing that SO effectively exploits domain-specific knowledge, and obtains solutions of particularly high quality compared to those obtained by current state-of-the-art algorithms. 相似文献
67.
Arnaldi R Banicz K Castor J Chaurand B Cicalò C Colla A Cortese P Damjanovic S David A de Falco A Devaux A Ducroux L En'yo H Fargeix J Ferretti A Floris M Förster A Force P Guettet N Guichard A Gulkanian H Heuser JM Keil M Kluberg L Lourenço C Lozano J Manso F Martins P Masoni A Neves A Ohnishi H Oppedisano C Parracho P Pillot P Poghosyan T Puddu G Radermacher E Ramalhete P Rosinsky P Scomparin E Seixas J Serci S Shahoyan R Sonderegger P Specht HJ Tieulent R Usai G Veenhof R 《Physical review letters》2007,99(13):132302
The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. In this Letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than approximately 80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results. 相似文献
68.
J.C. Burbano R.A. Vargas D. Pe?a Lara C.A. Lozano Z. H. Correa 《Solid State Ionics》2009,180(36-39):1553-1557
The first-order phase transition that leads to the superionic phase in AgI-based materials is studied by dc-conductivity measurements and a free energy model. By properly adjusting the model parameters, an abrupt change of disordering concentration, Δη?, is predicted at a transition temperature, Tt. The temperature dependence of the dc-conductivity, σ(T), is well fitted to the η?(T) equilibrium configuration obtained from the trial free energy function. The reported comparative study was done using an AgI–KI modified sample. The model also predicts a transition temperature, Tc for a continuous phase transition (Δη? = 0). 相似文献
69.
R. Arnaldi K. Banicz K. Borer J. Castor B. Chaurand W. Chen C. Cicalò A. Colla P. Cortese S. Damjanovic A. David A. de Falco A. Devaux L. Ducroux H. En’yo J. Fargeix A. Ferretti M. Floris A. F?rster P. Force N. Guettet A. Guichard H. Gulkanyan J. Heuser M. Keil L. Kluberg Z. Li C. Louren?o J. Lozano F. Manso P. Martins A. Masoni A. Neves H. Ohnishi C. Oppedisano P. Parracho P. Pillot T. Poghosyan G. Puddu E. Radermacher P. Ramalhete P. Rosinsky E. Scomparin J. Seixas S. Serci R. Shahoyan P. Sonderegger H. J. Specht R. Tieulent A. Uras G. Usai R. Veenhof H. K. W?hri 《The European Physical Journal C - Particles and Fields》2009,64(1):1-18
The NA60 experiment has measured muon pair production in In–In collisions at 158 AGeV at the CERN SPS. This paper presents a high statistics measurement of φ→μ μ meson production. Differential spectra, yields, mass and width are measured as a function of centrality and compared to previous measurements in other colliding systems at the same energy. The width of the rapidity distribution is found to be constant as a function of centrality, compatible with previous results. The decay muon polar angle distribution is measured in several reference frames. No evidence of polarization is found as a function of transverse momentum and centrality. The analysis of the p T spectra shows that the φ has a small radial flow, implying a weak coupling to the medium. The T eff parameter measured in In–In collisions suggests that the high value observed in Pb–Pb in the kaon channel is difficult to reconcile with radial flow alone. The absolute yield is compared to results in Pb–Pb collisions: though significantly smaller than measured by NA50 in the muon channel, it is found to exceed the NA49 and CERES data in the kaon channel at any centrality. The mass and width are found to be compatible with the PDG values at any centrality and at any p T : no evidence for in-medium modifications is observed. 相似文献
70.
Virginia Lozano Peter G. Jones 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(9):o653-o655
The title compounds, C7H8Cl2N+·Cl− and C7H8Br2N+·Br−, are isomorphous. In the crystal packing, layers parallel to the ac plane are formed by a classical N+—H⋯X− hydrogen bond (X = halogen) and two X⋯X contacts. A third X⋯X contact links the layers, and a fourth, which is however very long, completes a ladder‐like motif of halogen atoms. Hydrogen bonds of the form C—H⋯X play at best a subordinate role in the packing. 相似文献