全文获取类型
收费全文 | 326篇 |
免费 | 12篇 |
专业分类
化学 | 250篇 |
晶体学 | 13篇 |
力学 | 3篇 |
数学 | 30篇 |
物理学 | 42篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 9篇 |
2021年 | 19篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 7篇 |
2014年 | 14篇 |
2013年 | 29篇 |
2012年 | 30篇 |
2011年 | 26篇 |
2010年 | 27篇 |
2009年 | 10篇 |
2008年 | 20篇 |
2007年 | 16篇 |
2006年 | 13篇 |
2005年 | 20篇 |
2004年 | 12篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1990年 | 2篇 |
1983年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有338条查询结果,搜索用时 31 毫秒
41.
We present the results for thermal expansion coefficients of Sn2P2S6 crystals determined both in the crystallographic system and the system based on eigenvectors of thermal expansion tensor. Peculiarities of temperature evolution of the indicative surface of thermal expansion tensor for Sn2P2S6 are discussed, including the region of their ferroelectric phase transition. 相似文献
42.
Wen Li Edita Mjekiqi Wessel Douma Xin Wang Dr. Oksana Kavatsyuk Prof. Dr. Ronnie Hoekstra Dr. Jean-Christophe Poully Dr. Thomas Schlathölter 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(70):16114-16119
Vacuum ultraviolet photoionization of a gas-phase oligonucleotide anion leads to the formation of a valence hole. This hole migrates towards an energetically favorable site where it can weaken bonds and ultimately lead to bond cleavage. We have studied Vacuum UV photoionization of deprotonated oligonucleotides containing the human telomere sequence dTTAGGG and G-quadruplex structures consisting of four dTGGGGT single strands, stabilized by NH4+ counter ions. The oligonucleotide and G-quadruplex anions were confined in a radiofrequency ion trap, interfaced with a synchrotron beamline and the photofragmentation was studied using time-of-flight mass spectrometry. Oligonucleotide 12-mers containing the 5'-TTAGGG sequence were found to predominantly break in the GGG region, whereas no selective bond cleavage region was observed for the reversed 5'-GGGATT sequence. For G-quadruplex structures, fragmentation was quenched and mostly non-dissociative single and double electron removal was observed. 相似文献
43.
Oksana Kharchenko Vitaliy Smokal Oksana Krupka Pavlo Virych Natalia Kutsevol 《Molecular Crystals and Liquid Crystals》2020,699(1):51-56
AbstractThe thermostability of polysterene with/without new styrylquinoline containing methacrylic fragments has been described in the present work. Polystyrene and copolymers based on styrene and new methacrylic styrylquinoline containing monomers were synthesized by free radical thermoinitiated polymerization in the presence of 2,2′-azobisisobutyronitrile (1?wt%) as initiator at inert atmosphere. The impact of 2-[2-(4-methoxyphenyl)ethenyl]quinolin-8-yl 2-methylpropyl-2-enoate (М1), 2-(2-phenylethenyl)quinolin-8-yl 2-methylpropyl-2-enoate (М2), 2-[2-(4-nitrophenyl)ethenyl]quinolin-8-yl 2-methylpropyl-2-enoate (М3) on thermal stability of polystyrene was investigated. The thermostability of polystyrene and copolymers ST:M1, ST:M2, ST:M3 were studied by dynamic thermograviametric analysis. It was shown that destruction of polystyrene with corresponding units M1-M2 starts at 41–42°С higher, than reference polystyrene. 相似文献
44.
Yu.?I.?SlyvkaEmail author B.?R.?Ardan M.?G.?Mys’kiv 《Journal of Structural Chemistry》2018,59(2):388-394
Three new Cu(I) π-complexes with 2,5-bis(allylthio)-1,3,4-thiadizole (Bialtia) ([Cu3Cl3(Bialtia)2] (1), [Cu3Cl3(Bialtia)] (2), and [Cu2Cl2(Bialtia)] (3)) are obtained by the alternating current electrochemical synthesis and studied by single crystal X-ray diffraction. A distinctive feature of Bialtia is its ability to coordinate to Cu(I) atoms by nitrogen atoms of the thiadiazole core and two allyl groups. The formation of island inorganic {Cu3Cl3} moieties occurs in 1 through π coordination of two independent Bialtia molecules by three metal atoms. Due to the absence of one Bialtia molecule in 2, inorganic {–Cu3Cl3–} subunits join into infinite chains {[Cu3Cl3(Bialtia)]}n}. The structure of [Cu2Cl2(Bialtia)] (3) contains two Cu(I) atoms with different coordination environments: distorted tetrahedral and trigonal. 相似文献
45.
Feyer V Plekan O Skála T Cháb V Matolín V Prince KC 《The journal of physical chemistry. B》2008,112(43):13655-13660
The adsorption of L-histidine on clean and oxygen-covered Cu(110) surfaces has been studied by soft X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The valence band spectra, carbon, nitrogen and oxygen 1 s XPS and N K edge absorption spectra were measured for submonolayer, monolayer, and multilayer films. The spectra provide a detailed picture of the electronic structure and adsorption geometry at each coverage. In the monolayer, the histidine molecules are randomly oriented, in contrast to the submonolayer regime, where the molecules are coordinated to the copper surface with the imidazole functional group nearly parallel to, and strongly interacting with, the surface. The pi*/sigma* intensity ratio in NEXAFS spectra at the nitrogen edge varies strongly with angle, showing the imidazole ring is oriented. Adsorption models are proposed. 相似文献
46.
Nesterova OV Petrusenko SR Kokozay VN Skelton BW Jezierska J Linert W Ozarowski A 《Dalton transactions (Cambridge, England : 2003)》2008,(11):1431-1436
A novel heterometallic 1D coordination polymer [{Ni(en)2}2(micro-NCS)4Cd(NCS)2](n) x nCH3CN (en = ethylenediamine) has been prepared using the self-assembly process in a one-pot reaction of cadmium oxide, nickel and ammonium thiocyanates with an acetonitrile solution of ethylenediamine. The complex consists of an uncommon cis-Cd(SCN)4(NCS)2(4-) fragment and a rare combination of cis-Ni(en)2(2+) and trans-Ni(en)2(2+) building blocks linked by micro(1,3)-NCS bridges into a double-stranded zigzag chain structure. Each chain is comprised of [Ni2Cd2(micro-NCS-N,S)4)] macrocycles with chair-like and rectangular-like shapes arrayed alternately. The shortest intrachain CdCd separations are 9.535(1) and 10.868(2) A, while the nearest NiNi distances are 5.418(1) and 6.612(2) A. A network of weak N-HS hydrogen bonds, involving the terminal NCS ligands and NH2-groups of en, links the infinite chains and results in the formation of an extended supramolecular three-dimensional framework. Variable-temperature (1.8-300 K) magnetic susceptibilities show a slight change of the micro(B) value at low temperature, indicative of weak antiferromagnetic interactions (J = 1.55 cm-1) between magnetic canters. High-field, high-frequency (100-400 GHz) EPR spectra were simulated using S = 1 ground state for separate Ni2+ ions with the spin Hamiltonian parameters g = 2.165, D = 0.45 cm-1 and E = 0.03 cm(-1). According to DFT calculations, the D and E parameters are -0.35 cm(-1) and 0.049 cm-1 for the cis arrangement of Ni2+ and 0.58 cm(-1) and 0.012 cm(-1) for trans. 相似文献
47.
Diev VV Stetsenko ON Tung TQ Kopf J Kostikov RR Molchanov AP 《The Journal of organic chemistry》2008,73(6):2396-2399
1,3-Dipolar cycloaddition of C-aryl,N-aryl (or N-methyl) nitrones with a number of 1,2-diphenylcyclopropenes substituted at the C(3) position occurs with the formation of expected "normal" cycloadducts (with N-methylnitrones) and products of their subsequent transformations. Among them are corresponding alpha-acetophenyl aziridines and tetra (or penta) -arylpyrroles. Aziridines and the normal cycloadducts can be also thermally converted to such arylpyrroles with moderate to good yields. Substitution at the C(3( position of cyclopropenes by an electron acceptor group decreases the reactivity of cyclopropenes. 相似文献
48.
Zaluzhna O Simmons JG Heard GL Setser DW Holmes BE 《The journal of physical chemistry. A》2008,112(27):6090-6097
The unimolecular reactions of CF3CFClCH2Cl molecules formed with 87 kcal mol(-1) of vibrational energy by recombination of CF3CFCl and CH2Cl radicals at room temperature have been characterized by the chemical activation technique. The 2,3-ClH and 2,3-FH elimination reactions, which have rate constants of (2.5 +/- 0.8) x 10(4) and (0.38 +/- 0.11) x 10(4) s(-1), respectively, are the major reactions. The 2,3-FCl interchange reaction was not observed. The trans (or E)-isomers of CF3CFCHCl and CF3CClCHCl are favored over the cis (or Z)-isomers. Density functional theory at the B3PW91/6-31G(d',p') level was used to evaluate thermochemistry and structures of the molecule and transition states. This information was used to calculate statistical rate constants. Matching the calculated to the experimental rate constants for the trans-isomers gave threshold energies of 62 and 63 kcal mol(-1) for HCl and HF elimination, respectively. The threshold energy for FCl interchange must be 3-4 kcal mol(-1) higher than for HF elimination. The results for CF3CFClCH2Cl are compared to those from CF3CFClCH3; the remarkable reduction in rate constants for HCl and HF elimination upon substitution of one Cl atom for one H atom is a consequence of both a lower E and higher threshold energies for CF3CFClCH2Cl. 相似文献
49.
Novel classes of dynamical systems are introduced, including many-body problems characterized by nonlinear equations of motion of Newtonian type (“acceleration equals forces”) which determine the motion of points in the complex plane. These models are solvable, namely their con?guration at any time can be obtained from the initial data by algebraic operations, amounting to the determination of the zeros of a known time-dependent polynomial in the independent variable z. Some of these models are multiply periodic, isochronous or asymptotically isochronous; others display scattering phenomena. 相似文献
50.
Nikolai J Loe Ø Dominiak PM Gerlitz OO Autschbach J Davies HM 《Journal of the American Chemical Society》2007,129(35):10763-10772
Quantum chemical DFT calculations at the B3LYP/6-31G(d) level have been used to study the stereochemical course of the photochemical cycloaddition of enone 9 with dienes. The observed products of this photochemically induced cycloaddition showed a stereoselectivity, which is opposite to what would be expected by FMO considerations. The quantum chemical calculations revealed that the unusual stereoselectivity of the reaction can be rationalized by assuming a stereospecific photochemical cis-trans isomerization of enone 9 to trans isomer 9a followed by a thermal Diels-Alder reaction of the diene onto the highly reactive trans enone. The photochemical reaction step involves the selective formation of a twisted triplet intermediate, which accounts for the selectivity of the reaction. 相似文献