全文获取类型
收费全文 | 178篇 |
免费 | 12篇 |
国内免费 | 1篇 |
专业分类
化学 | 110篇 |
晶体学 | 1篇 |
力学 | 6篇 |
数学 | 21篇 |
物理学 | 53篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 10篇 |
2012年 | 10篇 |
2011年 | 8篇 |
2010年 | 9篇 |
2009年 | 16篇 |
2008年 | 11篇 |
2007年 | 9篇 |
2006年 | 8篇 |
2005年 | 8篇 |
2004年 | 3篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有191条查询结果,搜索用时 31 毫秒
81.
Bardelang D Rockenbauer A Karoui H Finet JP Tordo P 《The journal of physical chemistry. B》2005,109(20):10521-10530
(1)H NMR and electron paramagnetic resonance (EPR) titrations were used to determine the association constants of the complexes of alpha-phenyl-N-tert-butylnitrone (PBN) analogues and their superoxide spin adducts, respectively, with methylated beta-cyclodextrins. A 1:1 stoichiometry for the nitrones with randomly methylated beta-cyclodextrin and 2,6-di-O-methyl-beta-cyclodextrin and 1:1 and 1:2 stoichiometries for the corresponding cyclodextrin-nitroxide complexes were observed. After the superoxide radical spin trapping reaction, EPR titrations afforded the association constants of the corresponding cyclodextrin-nitroxide complexes. Two-dimensional EPR simulations indicated a bimodal inclusion of the nitroxide free radical spin adducts into the cyclodextrins. For all the nitrone-cyclodextrin and nitroxide-cyclodextrin complexes, the association constants were always higher for the nitroxide complexes than for the nitrone complexes. A cooperative system concerning the complexation of the nitroxide spin adduct with a cyclodextrin was evidenced by EPR titrations. The efficiency of the cyclodextrin inclusion technique to trap superoxide and to resist bioreduction by sodium l-ascorbate was also investigated. 相似文献
82.
The conditions of thermal decomposition of the hippurates of Y, La and the light lanthanides from Ce(III) to Gd have been studied. When heated, the Y, Ce(III), Pr and Gd complexes decomposed in two stages, those of La, Sm and Eu in three stages, and that of Nd in four stages, the oxides finally being formed. The complexes lost crystallization water to form anhydrous (Nd) or hydrated salts, and then decomposed to oxides directly (Y, Ce(III), Pr(III) and Gd) or with intermediate formation of Ln2O2CO3 (La, Nd, Sm and Eu). The temperature of oxide formation varied periodically with the ionic potential in the lanthanide series.
Zusammenfassung Die Bedingungen der thermischen Zersetzung der Hippurate von Y, La und der leichten Lanthanide von Ce(III) bis Gd wurden untersucht. Beim Aufheizen zersetzen sich die Komplexe von Y, Ce(III), Pr und Gd in zwei Schritten, die von Sm und Eu in drei Schritten und der von Nd in vier Schritten zu den Oxiden. Die Komplexe verlieren Kristallwasser unter Bildung wasserfreier (Nd) oder hydratisierter Salze und zersetzen sich dann direkt (Y, Ce(III), Pr(III), Gd) oder über Ln2O2CO3 (Ln, Nd, Sm, Eu) zu den Oxiden. Die Temperatur der Oxidbildung verändert sich periodisch mit abnehmenden Ionenpotential in der Lanthanidenreihe.
, . , , , , — , — , . , , (, , ) Ln2O2CO3 (, , ). .相似文献
83.
Wirgau JI Spasojević I Boukhalfa H Batinić-Haberle I Crumbliss AL 《Inorganic chemistry》2002,41(6):1464-1473
pK(a) values for the hydroxamic acid, alpha-NH(3)(+), and epsilon-NH(3)(+) groups of L-lysinehydroxamic acid (LyHA, H(3)L(2+)) were found to be 6.87, 8.89, and 10.76, respectively, in aqueous solution (I = 0.1 M, NaClO(4)) at 25 degrees C. O,O coordination to Fe(III) by LyHA is supported by H(+) stoichiometry, UV-vis spectral shifts, and a shift in nu(CO) from 1648 to 1592 cm(-1) upon formation of mono(L-lysinehydroxamato)tetra(aquo)iron(III) (Fe(H(2)L)(H(2)O)(4)(4+)). The stepwise formation of tris(L-lysinehydroxamato)iron(III) from Fe(H(2)O)(6)(3+) and H(3)L(2+) was characterized by spectrophotometric titration, and the values for log beta(1), log beta(2), and log beta(3) are 6.80(9), 12.4(2), and 16.1(2), respectively, at 25 degrees C and I = 2.0 M (NaClO(4)). Stopped-flow spectrophotometry was used to study the proton-driven stepwise ligand dissociation kinetics of tris(L-lysinehydroxamato)iron(III) at 25 degrees C and I = 2.0 M (HClO(4)/NaClO(4)). Defining k(n) and k(-n) as the stepwise ligand dissociation and association rate constants and n as the number of bound LyHA ligands, k(3), k(-3), k(2), k(-2), k(1), and k(-1) are 3.0 x 10(4), 2.4 x 10(1), 3.9 x 10(2), 1.9 x 10(1), 1.4 x 10(-1), and 1.2 x 10(-1) M(-1) s(-1), respectively. These rate and equilibrium constants are compared with corresponding constants for Fe(III) complexes of acetohydroxamic acid (AHA) and N-methylacetohydroxamic acid (NMAHA) in the form of a linear free energy relationship. The role of electrostatics in these complexation reactions to form the highly charged Fe(LyHA)(3)(6+) species is discussed, and an interchange mechanism mediated by charge repulsion is presented. The reduction potential for tris(L-lysinehydroxamato)iron(III) is -214 mV (vs. NHE), and a comparison to other hydroxamic acid complexes of Fe(III) is made through a correlation between E(1/2) and pFe. 相似文献
84.
H. Bagheri M. Nekoomanesh S. Hakim Y. Jahani H. S. Tan Z. Q. Fan 《Polymer Science Series A》2016,58(2):283-291
The interfacial adhesion and molecular structure of an in-reactor polypropylene/ethylene propylene rubber alloy were studied with respect to the rheological behavior and final properties of the alloy. The polymer alloys have similar structural parameters but different impact properties. The samples were characterized by gel permeation chromatography, thermal analysis, rheological analysis and mechanical testing. Fractionation of samples showed that the quantities of components are the same. Gel permeation chromatography results showed that molecular weight distribution of all components were similar. Thermal analysis results showed that the crystal size of two samples was the same but the crystal contents were different. In studying the impact strength, it was revealed that a large difference exists between the two samples. The small amplitude oscillation rheometry indicates that the rheological parameters have a glaring difference in both samples that can be an evidence of interfacial adhesion in the in-reactor alloys having so many similar structural parameters. 相似文献
85.
Eckelbarger JD Wilmot JT Epperson MT Thakur CS Shum D Antczak C Tarassishin L Djaballah H Gin DY 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(14):4293-4306
Deoxyharringtonine (2), homoharringtonine (3), homodeoxyharringtonine (4), and anhydroharringtonine (5) are reported to be among the most potent members of the antileukemia alkaloids isolated from the Cephalotaxus genus. Convergent syntheses of these four natural products are described, each involving novel synthetic methods and strategies. These syntheses enabled evaluation of several advanced natural and non-natural compounds against an array of human hematopoietic and solid tumor cells. Potent cytotoxicity was observed in several cell lines previously not challenged with these alkaloids. Variations in the structure of the ester chain within this family of alkaloids confer differing activity profiles against vincristine-resistant HL-60/RV+, signalling new avenues for molecular design of these natural products to combat multi-drug resistance. 相似文献
86.
87.
88.
89.
90.
Nonlinear electrokinetics (EK), specifically electrophoresis of the second kind, dielectrophoresis (DEP) and electrorotation (EROT), have gained significant interest recently for their flexibility and labeless discriminant manner of operation. The current applications of these technologies are a clear advancement from what they were when first discovered, but also still show strong signs of future growth. The present review article presents a discussion of the current uses of microscale nonlinear EK technologies as analytical, sensing, and purification tools for microorganisms. The discussion is focused on some of the latest discoveries with various nonlinear EK microfluidic techniques, such as DEP particle trapping and EROT for particle assessments, for the analysis of microorganisms ranging from viruses to parasites. Along the way, special focus was given to key research articles from within the past two years to provide the most up-to-date knowledge on the current state-of-the-art within the field of microscale EK, and from there, an outlook on where the future of the field is headed is also included. 相似文献