全文获取类型
收费全文 | 2271篇 |
免费 | 141篇 |
国内免费 | 1篇 |
专业分类
化学 | 1635篇 |
晶体学 | 18篇 |
力学 | 50篇 |
数学 | 255篇 |
物理学 | 455篇 |
出版年
2024年 | 6篇 |
2023年 | 18篇 |
2022年 | 69篇 |
2021年 | 87篇 |
2020年 | 84篇 |
2019年 | 112篇 |
2018年 | 109篇 |
2017年 | 81篇 |
2016年 | 138篇 |
2015年 | 94篇 |
2014年 | 111篇 |
2013年 | 152篇 |
2012年 | 142篇 |
2011年 | 182篇 |
2010年 | 104篇 |
2009年 | 82篇 |
2008年 | 117篇 |
2007年 | 114篇 |
2006年 | 111篇 |
2005年 | 91篇 |
2004年 | 68篇 |
2003年 | 52篇 |
2002年 | 51篇 |
2001年 | 19篇 |
2000年 | 18篇 |
1999年 | 18篇 |
1998年 | 7篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 6篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 8篇 |
1983年 | 4篇 |
1980年 | 6篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1974年 | 9篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1970年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有2413条查询结果,搜索用时 15 毫秒
991.
A. G. Druganov V. V. Lapachev O. P. Petrenko V. A. Raldugin 《Chemistry of Natural Compounds》1994,30(6):739-741
The 3-O-palmitate and 3-O-tridecanoate of gibberellin A3 have been synthesized and monomolecular Langmuir-Blodgett films have been obtained from them.
Novosibirsk Institute of Organic Chemistry, Siberian Division of the Russian Academy of Sciences. Translated from Khimiya
Prirodnykh Soedinenii, No. 6, pp. 793–795, November–December, 1994. 相似文献
992.
We consider twisted convolution operators with kernels having singularities on a sphere and having as Fourier transform the oscillatory symbol mα(|ξ|) = |ξ|–αei|ξ|, 0 ≤ ??α < 2n. We give integral representations for such operators and, as a principal result, we study Lp–Lq estimates for them. 相似文献
993.
994.
Alexey V. Samokhin 《Acta Appl Math》1995,41(1-3):299-309
Quantities which are conserved in nondissipative media decay in the presence of dissipation. The velocity of such a decay (or the balance law) may be found explicitly using the generating function of the conservation law. The general approach is illustrated with a system of MHD equations for incompressible magnetofluids. 相似文献
995.
996.
Group 13-15 inorganic analogues of benzene, [HMYH](3) (M = B, Al, Ga; Y = N, P, As), mixed heterocycles of the type [BAlGaNPAs]H(6) and their dimers have been theoretically examined at the B3LYP/TZVP level of theory. Six different isomers have been structurally characterized for the mixed compounds [BAlGaNPAs]H(6). B-N bonding strongly (about approximately 90-100 kJ mol(-)(1)) stabilizes the mixed heterocycles, followed by the preference of the Al-N bonded structures over Ga-N bonded ( approximately 30-40 kJ mol(-1)), while B-P bonding is slightly (5-10 kJ mol(-1)) more favorable compared to B-As. Thus, the bonding pattern is predicted to be the most stable, followed by the core. Processes of [HMYH](3) formation from donor-acceptor complexes H(3)MYH(3) are predicted to be thermodynamically favorable for all MY combinations. Dimerization reactions of the coordinationally unsaturated [HMYH](3) heterocycles yielding hexamer clusters [HMYH](6) are found to be exothermic, with the exception of borazine, for which, as for benzene, dimerization is strongly endothermic due to the aromaticity of C(6)H(6) and [HBNH](3). Despite the high endothermicity of [HBNH](3) dimerization, the B-N bond formation is the driving force of the dimerization of mixed species [BAlGaNPAs]H(6). The dimerization enthalpies of [BAlGaNPAs]H(6) may be both exo- and endothermic, depending on the bonding pattern of the isomers. A complete set of mean MY bond energies in four- and six-membered cycles of [HMYH](6) was derived. The MY energies were found to be transferable quantities and may serve for a qualitative prediction of the relative stability of different isomers of mixed cluster compounds. [BAlGaNPAs](2)H(12) clusters are promising synthetic targets, they are expected to serve as single-source precursors for the stoichiometry-controlled CVD processes of the group 13-15 composites. A strategy of their synthesis and the most suitable starting systems have been also predicted. 相似文献
997.
Mazur AK 《Journal of the American Chemical Society》2003,125(26):7849-7859
Reversible transitions between the A- and B-forms of DNA are obtained in free molecular dynamics simulations of a single double helix immersed in a water drop with Na(+) counterions. The dynamics of the transitions agrees with their supposed cooperative character. In silico titration of the transitions was carried out by smooth variation of the drop size. The estimated range of hydration numbers corresponding to the transition roughly agrees with experimental data. The chain length dependence was studied for double helices from 6 to 16 base pairs. It appeared that the B --> A transition is hindered for DNA shorter than one helical turn. With increased NaCl concentration in the drop, stabilization of the B-form is observed accompanied by the salt crystallization. The results strongly suggest that the B --> A transition at low hydration is caused by Na(+) ions sandwiched between phosphate strands in the major groove and is driven by direct medium range electrostatic interactions. The role of the reduced water shell apparently consists of increasing the counterion concentration in the opening of the major groove. Analysis of the available experimental data suggests that this mechanism is perhaps generally responsible for the A/B polymorphism in DNA. 相似文献
998.
Alexey A. Nazarov Mikhail P. Koroteev Christian G. Hartinger Bernhard K. Keppler Eduard E. Nifantev 《Monatshefte für Chemie / Chemical Monthly》2005,136(2):137-146
Summary. The coordination behavior of newly developed bicyclophosphite ligands toward Mo(0), Rh(I), and Pt(II) was studied.Reactions at different ratios of metal to ligand were done. It was found that the ligands act as monodentate ones and form with hexacarbonylmolybdenum(0) complexes with the general formula Mo(CO)5L by replacing only one carbonyl ligand. Coordination experiments toward acetylacetonatodicarbonylrhodium(I) resulted in the formation of undefined compounds. Toward dichlorocyclooctadienylplatinum(II) the monomeric phosphorus ligands act as monodentate ligands forming complexes of the general structure cis-PtCl2L2. All the synthesized platinum-complexes possess cis-configuration (proven by 31P NMR). The corresponding coordination compounds were isolated and characterized by elemental analyses and 1H, 13C, and 31P NMR. 相似文献
999.
G. V. Grishina A. A. Borisenko I. S. Veselov A. M. Petrenko 《Russian Journal of Organic Chemistry》2005,41(2):272-278
A series of 1-benzyl-3-hydroxy-1,2,3,6-tetrahydropyridines, multipurpose synthons for fine organic synthesis and potential antiviral compounds, was prepared by the rearrangement of a number of 1-benzyl-3,4- epoxypiperidines under treatment with lithium amides. 3,4-Epoxypiperidines were obtained by oxidation of 1,2,5,6- tetrahydropyridines trifluoroacetates with a trifluoroperacetic acid. Convenient synthetic routes were found and developed. A conformation analysis of the series of stable 3,4-epoxypiperidines and 3-hydroxy-1,2,3,6- tetrahydropyridines was carried out.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 2, 2005, pp. 281–287.Original Russian Text Copyright © 2005 by Grishina, Borisenko, Veselov, Petrenko. 相似文献
1000.
Alexey N. Ryabov 《Journal of organometallic chemistry》2005,690(19):4213-4221
Constrained geometry complexes (CGCs) of titanium (IV) and zirconium (IV) containing isomeric cyclopentadienyls fused to thiophene fragment, i.e., 4,5-dimethylcyclopenta[b]thienyl and 5,6-dimethylcyclopenta[b]thienyl, have been prepared and unambiguously characterized. The molecular structure of the titanium complex [η5-(5,6-dimethylcyclopenta[b]thienyl)SiMe2(NtBu)-η1]TiCl2 was established by X-ray crystal structure analysis. Preliminary studies showed that the studied CGCs/MAO are active olefin polymerization catalysts. 相似文献