全文获取类型
收费全文 | 443篇 |
免费 | 12篇 |
国内免费 | 3篇 |
专业分类
化学 | 175篇 |
晶体学 | 4篇 |
力学 | 19篇 |
数学 | 176篇 |
物理学 | 84篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 16篇 |
2018年 | 9篇 |
2017年 | 11篇 |
2016年 | 18篇 |
2015年 | 19篇 |
2014年 | 17篇 |
2013年 | 36篇 |
2012年 | 35篇 |
2011年 | 25篇 |
2010年 | 31篇 |
2009年 | 37篇 |
2008年 | 32篇 |
2007年 | 31篇 |
2006年 | 20篇 |
2005年 | 19篇 |
2004年 | 17篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2000年 | 5篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1981年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
1962年 | 1篇 |
排序方式: 共有458条查询结果,搜索用时 15 毫秒
131.
Dalibor Merunka 《Solid State Communications》2004,129(6):375-377
The modified strong dipole-proton coupling (MSDPC) model, which predicted several static and dynamic dielectric properties of KH2PO4 or KDP-type ferroelectrics, was used to investigate the properties of these crystals on the local scale. Results calculated by molecular dynamics (MD) simulation show that both order-disorder and displacive characteristics of one PO4 dipole are present in KDP and KD2PO4 (DKDP). These results correlate with experimental data from NMR and neutron scattering studies of local properties. 相似文献
132.
Ar-Rh(III) pivalate complexes assembled in situ from the reaction of [RhCl(coe)2]2 (coe = cis-cyclooctene), [p-(CF3)C6H4]3P, and CsOPiv effectively catalyzed the direct C-arylation of free (NH)-indoles and (NH)-pyrroles in good yields and with high regioselectivity. The reaction displayed excellent functional group compatibility and low moisture sensitivity. Kinetics studies support a mechanism involving phosphine displacement by indole in complex 2 (resting state of the catalyst), followed by a rate-limiting C-H bond metalation. 相似文献
133.
Ciprian?FoiasEmail author Il?Bong?Jung Eungil?Ko Carl?Pearcy 《Israel Journal of Mathematics》2005,145(1):83-91
We consider the question of which operators on Hilbert space admit a moment sequence, and show, in particular, that ifT is any operator inL(itH) that can be written asT=N+K, whereN is normal andK is compact, andM⊂itH is any invariant subspace forT, then the restrictionT/itM admits such a sequence. 相似文献
134.
In this paper we first develop a theory of almost automorphic
functions with values in Frechet spaces. Then, we consider the
semilinear differential equation x'(t) = A x(t) + f(t, x(t)), t ∈ ℝ in a Frechet space X, where A is the infinitesimal generator
of a C0-semigroup satisfying some conditions of exponential stability. Under suitable conditions on f, we prove the existence and
uniqueness of an almost automorphic mild solution to the equation. 相似文献
135.
The development of a new chemical transformation, namely oxidative C-arylation of saturated (NH)-heterocycles, is described. This reaction combines dehydrogenation and arylation in one process, leading to cross-coupling of (NH)-heterocycles and haloarenes. Typical reaction conditions involve heating the reaction partners in anhydrous dioxane at 120-150 degrees C in the presence of RhCl(CO)[P(Fur)3]2 as the catalyst and Cs2CO3 as the base. Addition of tert-butylethylene as the hydrogen acceptor increases the chemical yield by diminishing the dehalogenation pathway. This method demonstrated a good substrate scope, allowing for cross-coupling of a variety of (NH)-heterocycles (e.g., pyrrolidine, piperidine, piperazine, morpholine) and halo(hetero)arenes to afford valuable heterocyclic products in one step. The preliminary mechanistic studies provided some insight regarding the key events in the proposed catalytic cycle, including beta-hydride elimination of an amido rhodium complex and carbometalation of the resulting imine. A large kinetic isotope effect [KIE (kC-H/kC-D) = 4.3] suggests that one or both beta-hydride elimination steps are rate determining. The central role for the phosphine ligand was established in controlling the partitioning between the oxidative C-arylation and N-arylation pathways. 相似文献
136.
Ciprian D. Coman Andrew P. Bassom 《Journal of the mechanics and physics of solids》2007,55(8):1601-1617
Asymptotic properties of the neutral stability curves for a linear boundary eigenvalue problem which models the wrinkling instability of an annular thin film in tension are considered. The film is subjected to imposed radial displacement fields on its inner and outer boundaries and, when these loads are sufficiently large, the film is susceptible to wrinkling. The critical values at which this onset occurs are dictated by the solution of a fourth-order ordinary differential eigensystem whose eigenvalue λ is a function of μ(?1), a quantity inversely proportional to the non-dimensional bending stiffness of the film, and n, the number of half-waves of the wrinkling pattern that sets in around the annular domain. Previously, Coman and Haughton [2006. Localised wrinkling instabilities in radially stretched annular thin films. Acta Mech. 185, 179-200] employed the compound matrix method together with a WKB technique to characterise the form of λ(μ,n) which essentially is related to a turning point in a reduced eigenproblem. The asymptotic analysis conducted therein pertained to the case when this turning point was not too close to the inner edge of the annulus. However, in the thin film limit μ→∞, the wrinkling load and the preferred instability mode are given by a modified eigenvalue problem that involves a turning point asymptotically close to the inner rim. Here WKB and boundary-layer asymptotic methods are used to examine these issues and comparisons with direct numerical simulations made. 相似文献
137.
We establish an invariance principle for a general class of stationary random fields indexed by Zd, under Hannan’s condition generalized to Zd. To do so we first establish a uniform integrability result for stationary orthomartingales, and second we establish a coboundary decomposition for certain stationary random fields. At last, we obtain an invariance principle by developing an orthomartingale approximation. Our invariance principle improves known results in the literature, and particularly we require only finite second moment. 相似文献
138.
Jan Tborský Josef Sus Jaromír Lachman Barbora ebkov Aneka Adamcov Dalibor atínský 《Molecules (Basel, Switzerland)》2021,26(13)
Apple trees (Malus domestica Borgh) are a rich source of dihydrochalcones, phenolic acids and flavonoids. Considering the increasing demand for these phytochemicals with health-benefitting properties, the objective of this study was to evaluate the profile of the main bioactive compounds—phloridzin, phloretin, chlorogenic acid and rutin—in apple tree bark, leaves, flower buds and twigs. The variety in the phenolic profiles of four apple tree cultivars was monitored during the vegetation period from March to September using chromatography analysis. Phloridzin, the major glycoside of interest, reached the highest values in the bark of all the tested cultivars in May (up to 91.7 ± 4.4 mg g−1 of the dried weight (DW), cv. ‘Opal’). In the leaves, the highest levels of phloridzin were found in cv. ‘Opal’ in May (82.5 ± 22.0 mg g−1 of DW); in twigs, the highest levels were found in cv. ‘Rozela’ in September (52.4 ± 12.1 mg g−1 of DW). In the flower buds, the content of phloridzin was similar to that in the twigs. Aglycone phloretin was found only in the leaves in relatively low concentrations (max. value 2.8 ± 1.4 mg g−1 of DW). The highest values of rutin were found in the leaves of all the tested cultivars (10.5 ± 2.9 mg g−1 of DW, cv. ‘Opal’ in September); the concentrations in the bark and twigs were much lower. The highest content of chlorogenic acid was found in flower buds (3.3 ± 1.0 mg g−1 of DW, cv. ‘Rozela’). Whole apple fruits harvested in September were rich in chlorogenic acid and phloridzin. The statistical evaluation by Scheffe’s test confirmed the significant difference of cv. ‘Rozela’ from the other tested cultivars. In conclusion, apple tree bark, twigs, and leaves were found to be important renewable resources of bioactive phenolics, especially phloridzin and rutin. The simple availability of waste plant material can therefore be used as a rich source of phenolic compounds for cosmetics, nutraceuticals, and food supplement preparation. 相似文献
139.
An Ethanol Biosensor Based on Simple Immobilization of Alcohol Dehydrogenase on Fe3O4@Au Nanoparticles 下载免费PDF全文
Anchalee Samphao Kanjana Kunpatee Sanchai Prayoonpokarach Jatuporn Wittayakun Ľubomír Švorc Dalibor M. Stankovic Kristina Zagar Miran Ceh Kurt Kalcher 《Electroanalysis》2015,27(12):2829-2837
An ethanol biosensor based on alcohol dehydrogenase (ADH) attached to Au seeds decorated on magnetic nanoparticles (Fe3O4@Au NPs) is presented. ADH was immobilized on Fe3O4@Au NPs, which were subsequently fixed by a magnet on a carbon paste electrode modified with 5 % (m : m) MnO2. Optimum conditions for the amperometric determination of ethanol with the biosensor were as follows: working potential +0.1 V (vs. Ag/AgCl); supporting electrolyte: 0.1 M phosphate buffer solution at pH 6.8 containing 0.25 mM of the coenzyme (NAD+); working electrode: carbon paste with magnetically attached Fe3O4@Au NPs (0.012 mg ? cm?2 electrode area) with immobilized alcohol dehydrogenase (120 units per cm2 of electrode area). Linearity between signal and concentration was found for the range from 0.1 to 2.0 M ethanol (r2=0.995) with a detection limit of 0.07 M, a sensitivity of 0.02 µA ? mM?1 ? cm?2, a reproducibility of 4.0 % RSD, and a repeatability of 2.7 % RSD. The results for the determination of ethanol in alcoholic beverages showed good agreement with gas chromatography (GC) with recovery of 96.0 – 108.8 %. 相似文献
140.
Jamali S Milić D Kia R Mazloomi Z Abdolahi H 《Dalton transactions (Cambridge, England : 2003)》2011,40(37):9362-9365
The preparation of two new bis(N-heterocyclic carbene) platinum(II) complexes, in which NHC rings are joined by a CH(2) linker group, is described. While, the chelate complex [PtMe(2)(bis-NHC1)], 1, was formed with large tert-butyl wingtips, the iso-propyl N-substituent analogue favors formation of the cluster complex [Pt(2)Me(4)(μ-SMe(2))(μ-bis-NHC2)](2)(μ-Ag(2)Br(2)), 2, in which two binuclear platinum(II) complexes are linked together by an Ag(2)Br(2) unit. The chelating platinum complex 1 undergoes aerial CO(2) fixation and forms platinum(II) carbonate complex [Pt(CO(3))(bis-NHC1)], 3. 相似文献