全文获取类型
收费全文 | 1004篇 |
免费 | 33篇 |
国内免费 | 6篇 |
专业分类
化学 | 727篇 |
晶体学 | 2篇 |
力学 | 17篇 |
数学 | 155篇 |
物理学 | 100篇 |
无线电 | 42篇 |
出版年
2023年 | 6篇 |
2022年 | 15篇 |
2021年 | 19篇 |
2020年 | 7篇 |
2019年 | 18篇 |
2018年 | 17篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 22篇 |
2013年 | 52篇 |
2012年 | 71篇 |
2011年 | 55篇 |
2010年 | 40篇 |
2009年 | 43篇 |
2008年 | 71篇 |
2007年 | 55篇 |
2006年 | 56篇 |
2005年 | 78篇 |
2004年 | 62篇 |
2003年 | 42篇 |
2002年 | 44篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 5篇 |
1998年 | 12篇 |
1997年 | 6篇 |
1995年 | 9篇 |
1994年 | 6篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1939年 | 3篇 |
1915年 | 4篇 |
1913年 | 5篇 |
1902年 | 3篇 |
1889年 | 3篇 |
排序方式: 共有1043条查询结果,搜索用时 15 毫秒
91.
Pedroso MP Ferreira EC Hantao LW Bogusz S Augusto F 《Journal of separation science》2011,34(13):1547-1554
Combining qualitative data from the chromatographic structure of 2-D gas chromatography with flame ionization detection (GC×GC-FID) and that from gas chromatography-mass spectrometry (GC/MS) should result in a more accurate assignment of the peak identities than the simple analysis by GC/MS, where coelution of analytes is unavoidable in highly complex samples (rendering spectra unsuitable for qualitative purposes) or for compounds in very low concentrations. Using data from GC×GC-FID combined with GC/MS can reveal coelutions that were not detected by mass spectra deconvolution software. In addition, some compounds can be identified according to the structure of the GC×GC-FID chromatogram. In this article, the volatile fractions of fresh and dehydrated pineapple pulp were evaluated. The extraction of the volatiles was performed by dynamic headspace extraction coupled to solid-phase microextraction (DHS-SPME), a technique appropriate for slurries or solid matrices. Extracted analytes were then analyzed by GC×GC-FID and GC/MS. The results obtained using both techniques were combined to improve compound identifications. 相似文献
92.
Diego Ernesto Dominici 《Journal of Computational and Applied Mathematics》2011,236(1):39-48
We study the relation between the coefficients of Taylor series and Kapteyn series representing the same function. We compute explicit formulas for expressing one in terms of the other and give examples to illustrate our method. 相似文献
93.
Eliandro Faoro Gelson Manzoni de Oliveira Ernesto Schulz Lang Cesar Bicca Pereira 《Journal of organometallic chemistry》2011,696(11-12):2438-2444
The syntheses and the structural characterization of the compounds [(mes)2Te–Te(I)mes], (PyH)[mesTeI3(I3)] (mes = mesityl = 2,4,6-trimethylphenyl; Py = pyridine), (PyH)3[dmephTeI2(I2)]2(I3) (dmeph = 2,6-dimethylphenyl), (PyH)2[RTeI4]2·(CH3)CO(CH3)·C6H5CH3 (R = p-tert-butylphenyl) and (PyH)2[PhTeI4]2 (Ph = phenyl) are presented. Some earlier analog preparations are compared and the influence of ortho substituents in the aryl group on the oxidation state of tellurium is discussed, as well as the observed conditions for the formation of poly-iodides chains. 相似文献
94.
95.
Ernesto Lpez-Chvez J. M. Martínez Magadn Fray de Landa Castillo-Alvarado 《Journal of magnetism and magnetic materials》2004,280(2-3):293-303
A theory of disordered binary alloys AxB1−x (A=Ni, Co; B=Fe; x0.06) is used to determine the changes in the electronic structure and magnetic properties of body centered cubic (BCC) iron induced by doping with nickel and cobalt impurities. This approximation is an extension of the cluster-Bethe lattice method, in which we incorporate electronic correlations, itinerant and localized nature of electrons 3d, and both long-range and short-range chemical correlations. The magnetism is described by means of a Hubbard Hamiltonian that in conjunction with Green's functions techniques is used to calculate local densities of electronic states. For it we take an atom in the real lattice and it is joined to a Bethe's lattice with like coordination number. The magnetic moments on sites occupied for A and B atoms are obtained self-consistently. Nickel and cobalt impurities in BCC iron can provide crucial information on the modification of the electronic band structure and magnetic moments from pure Fe. The results obtained are compared with those of both pure Fe and binary alloys of Co–Fe and Ni–Fe, which have been obtained by other authors using methods such as: first-principles electronic structure calculations using the layer Korringa–Kohn–Rostoker (KKR), the full-potential linearized augmented plane wave method, the KKR coherent potential approximation combined with the local-density functional method and by the tight-binding linear-muffin-tin orbitals method, obtained good agree. These results and other that recently we have published indicate to us that our methodology can be a new alternative for calculations of the electronic structure and magnetic properties of impurities and alloys of ferromagnetic transition metals. 相似文献
96.
Virgil Percec Anatoliy V. Popov Ernesto Ramirez‐Castillo Oliver Weichold 《Journal of polymer science. Part A, Polymer chemistry》2003,41(21):3283-3299
The first example of living radical polymerization of vinyl chloride carried out in water at 25 °C is reported. This polymerization was initiated by iodoform and catalyzed by nascent Cu0 produced by the disproportionation of CuI in the presence of strongly CuII binding ligands such as tris(2‐aminoethyl)amine or polyethyleneimine. The resulting poly(vinyl chloride) was free of structural defects, had controlled molecular weight and narrow molecular weight distribution, contained two ~CHClI active chain ends, and had a higher syndiotacticity (62%) than the one obtained by conventional free‐radical polymerization at the same temperature (56%). This novel polymerization proceeds, most probably, by a combination of competitive pathways that involves activation by single electron transfer mediated by nascent Cu0 and degenerative chain transfer. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3283–3299, 2003 相似文献
97.
98.
Ernesto Di Maio Salvatore Iannace Giuseppe Mensitieri Luigi Nicolais 《Journal of Polymer Science.Polymer Physics》2006,44(13):1863-1873
The gas concentration and pressure effects on the shear viscosity of molten polymers were modeled by using a unified approach based on a free volume theory. A concentration and pressure dependent “shift factor,” which accounts for free volume changes associated with polymer‐gas mixing and with variation of absolute pressure as well as for dilution effects, has been herein used to scale the pure polymer viscosity, as evaluated at the same temperature and atmospheric pressure. The expression of the free volume of the polymer/gas mixture was obtained by using the Simha and Somcynsky equation of state for multicomponent fluids. Experimental shear viscosity data, obtained for poly(ε‐caprolactone) with nitrogen and carbon dioxide were successfully predicted by using this approach. Good agreement with predictions was also found in the case of viscosity data reported in the literature for polystyrene and poly(dimethylsiloxane) with carbon dioxide. Free volume arguments have also been used to predict the Tg depression for polystyrene/carbon dioxide and for poly(methyl methacrylate)/carbon dioxide mixtures, based on calculations performed, again, with the Simha and Somcynsky theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1863–1873, 2006 相似文献
99.
Ernesto Joselevich 《Chemphyschem》2006,7(7):1405-1407
100.
Gleison Antonio Casagrande Ernesto Schulz Lang Prof. Dr. Bárbara Tirloni Robert Alan Burrow Gelson Manzoni de Oliveira Sebastião S. Lemos 《无机化学与普通化学杂志》2006,632(5):893-896
A three‐step one‐pot synthetic procedure to synthesize the neutral tellurium(IV) coordination compounds PhTeX3L (X = Br, I and L = ethylenethiourea) has been developed and is described in this article. Oxidative halogenation of PhTeTePh in methanol generates the tellurium(II) derivative, PhTeX, which is subsequently complexed with ethylenethiourea, and, finally, further oxidative addition of additional halogen affords the corresponding tellurium(IV) compound PhTeX3L in good yields. The final product was obtained by the slow evaporation of the reaction mixture as black crystals. The X‐ray structural analyses of the compounds show Te···X and X···X secondary interactions in the solid state and suggest a weak dependence of the formation of supramolecular assemblies on the nature of the halogen bonded to the tellurium atom. 相似文献