全文获取类型
收费全文 | 212篇 |
免费 | 8篇 |
国内免费 | 4篇 |
专业分类
化学 | 159篇 |
力学 | 3篇 |
数学 | 37篇 |
物理学 | 25篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 11篇 |
2019年 | 1篇 |
2018年 | 5篇 |
2017年 | 4篇 |
2016年 | 6篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 13篇 |
2012年 | 20篇 |
2011年 | 20篇 |
2010年 | 11篇 |
2009年 | 5篇 |
2008年 | 17篇 |
2007年 | 13篇 |
2006年 | 20篇 |
2005年 | 13篇 |
2004年 | 6篇 |
2003年 | 11篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1970年 | 1篇 |
1937年 | 1篇 |
1936年 | 2篇 |
1885年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 15 毫秒
31.
Biomimetic strategies which utilise hydrogels have been targeted due to favourable hydrogel characteristics such as the presentation of a large surface area for crystal nucleation within a structured yet responsive scaffold. Chitosan hydrogels were prepared and mineralised using a combined method which involves alternate soaking of the films with precursor solutions, followed by treatment with saturated mineral solution. This method has been shown to be effective for the synthesis of calcium carbonate-chitosan composite materials with tensile strength comparable to nacre. The ratio of organic to inorganic is readily controlled through the presoaking solution concentrations. The ubiquity of this method is shown here with respect to switching out both the anion (CaHPO(4)) and the cation (BaSO(4)). Cation doping is also readily achieved allowing formation of Mg-rich CaCO(3). Poly(acrylic acid) added to (Mg,Ca)CO(3)-chitosan systems induces the formation of two polymorphs (vaterite and calcite) which coexist within the composite material. The mineralised scaffolds were analysed by SEM and powder XRD. The successful mineralisation of chitosan templates with various inorganic compounds shows that this combined approach is widely applicable as a biomimetic approach. 相似文献
32.
Melissa M. Cadelis Natasha S. L. Nipper Alex Grey Soeren Geese Shara J. van de Pas Bevan S. Weir Brent R. Copp Siouxsie Wiles 《Molecules (Basel, Switzerland)》2022,27(1)
Screening of several fungi from the New Zealand International Collection of Microorganisms from Plants identified two strains of Penicillium, P. bissettii and P. glabrum, which exhibited antimicrobial activity against Escherichia coli, Klebsiella pneumoniae, and Staphylococcus aureus. Further investigation into the natural products of the fungi, through extraction and fractionation, led to the isolation of five known polyketide metabolites, penicillic acid (1), citromycetin (2), penialdin A (3), penialdin F (4), and myxotrichin B (5). Semi-synthetic derivatization of 1 led to the discovery of a novel dihydro (1a) derivative that provided evidence for the existence of the much-speculated open-chained form of 1. Upon investigation of the antimicrobial activities of the natural products and derivatives, both penicillic acid (1) and penialdin F (4) were found to inhibit the growth of Methicillin-resistant S. aureus. Penialdin F (4) was also found to have some inhibitory activity against Mycobacterium abscessus and M. marinum along with citromycetin (2). 相似文献
33.
Smits R Warner N McQueen JM Cutler A 《The Journal of the Acoustical Society of America》2003,113(1):563-574
We present the results of a large-scale study on speech perception, assessing the number and type of perceptual hypotheses which listeners entertain about possible phoneme sequences in their language. Dutch listeners were asked to identify gated fragments of all 1179 diphones of Dutch, providing a total of 488,520 phoneme categorizations. The results manifest orderly uptake of acoustic information in the signal. Differences across phonemes in the rate at which fully correct recognition was achieved arose as a result of whether or not potential confusions could occur with other phonemes of the language (long with short vowels, affricates with their initial components, etc.). These data can be used to improve models of how acoustic-phonetic information is mapped onto the mental lexicon during speech comprehension. 相似文献
34.
Georgieva I Trendafilova N Bauer G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(2):403-415
The paper presents a detailed experimental and theoretical study of five metal complexes of glyoxilic acid oxime (gaoH2), Cu(gaoH)2(H2O)2 (1), Zn(gaoH)2(H2O)2 (2), Co(gaoH)2(H2O)2 (3), Ni(gaoH)2(H2O)2 (4) and [Cd(gaoH)2(H2O)2].H2O (5). The electronic and vibrational spectra were measured and discussed as to the most sensitive to the M-L binding bands. Two different types of coordination were considered for gaoH- ligand: bidentate through the carboxylic oxygen and oxime nitrogen in 1-4 and mixed bidentate and bridging through the COO group in 5. It is shown that the spectral behavior of the nu(COO) modes can be used to predict bridging ligand coordination. DFT(B3LYP/6-31++G(d,p)) calculations on model compounds: neutral, anionic and radical forms of gao and Cu(gaoH)2, have been carried out to correlate geometries, electronic and vibrational structures. The results obtained were used to assist the electronic and vibrational analysis of the complexes studied. The effect of the metal-ligand interactions (electrostatic and covalent) on the geometry structure of the ligand was investigated. 相似文献
35.
Natasha Samko 《Integral Equations and Operator Theory》2005,51(3):417-433
For the singular integral operators with Carleman shift, preserving or changing orientation, and piecewise continuous coefficients we prove the theorem on Fredholmness and obtain the formula for index in the generalized Hölder spaces
defined by an arbitrary continuity modulus from the Bari-Stechkin class and some general weights on a closed or open finite Lyapunov curve . 相似文献
36.
Natasha Samko 《Positivity》2013,17(3):683-706
In this paper we study $p\rightarrow q$ -boundedness of the multi-dimensional Hardy type operators in the vanishing local generalized Morrey spaces $V\mathcal L ^{p,\varphi }_\mathrm{{loc}}(\mathbb R ^n,w)$ defined by an almost increasing function $\varphi (r)$ and radial type weight $w(|x|)$ . We obtain sufficient conditions, in terms of some integral inequalities imposed on $\varphi $ and $w$ , for such a boundedness. In the case where the function $\varphi (r)$ and the weight are power functions, these conditions are also necessary. 相似文献
37.
Natasha S. Adamson Ashton G. Theakstone Lachlan C. Soulsby Egan H. Doeven Emily Kerr Conor F. Hogan Paul S. Francis Lynn Dennany 《Chemical science》2021,12(28):9770
We present a new approach to explore the potential-dependent multi-colour co-reactant electrochemiluminescence (ECL) from multiple luminophores. The potentials at both the working and counter electrodes, the current between these electrodes, and the emission over cyclic voltammetric scans were simultaneously measured for the ECL reaction of Ir(ppy)3 and either [Ru(bpy)3]2+ or [Ir(df-ppy)2(ptb)]+, with tri-n-propylamine as the co-reactant. The counter electrode potential was monitored by adding a differential electrometer module to the potentiostat. Plotting the data against the applied working electrode potential and against time provided complementary depictions of their relationships. Photographs of the ECL at the surface of the two electrodes were taken to confirm the source of the emissions. This provided a new understanding of these multifaceted ECL systems, including the nature of the counter electrode potential and the possibility of eliciting ECL at this electrode, a mechanism-based rationalisation of the interactions of different metal-complex luminophores, and a previously unknown ECL pathway for the Ir(ppy)3 complex at negative potentials that was observed even in the absence of the co-reactant.Exploration of potential-dependent, multi-colour co-reactant electrochemiluminescence from multiple luminophores at the working and counter electrodes reveals new pathways to emission. 相似文献
38.
Two experimental values (?19.3 ± 0.3 and ?17.8 ± 0.1 kcal/mol) for the gas phase heat of formation (δfH) (298k) of nitromethane have been reported. Although these values differ by only 1.5 kcal/mol, substantially greater differences in theoretical and experimental results occur when these differing values are used to calculate thermodynamic properties. This is especially evident when these two values for the δfH of nitromethane are used to calculate thermodynamic properties of polynitro compounds. For example, when density functional theory (DFT) is coupled with the use of isodesmic reactions, the ΔfH of octanitrocubane is calculated to be 160.6 or 172.6 kcal/mol, depending on which value is used. It should also be appreciated that several computational theories depend upon having access to reliable experimental data for testing and development. We have examined this discrepancy using several computational models and several levels of theory. Our results coupled with a comprehensive review of the literature support the lower (?19.3 ± 0.3 kcal/mol) experimental value. This is problematic because the higher value (?17.8 ± 0.1 kcal/mol) has been used in the development and/or testing of several semiempirical quantum mechanical models as well as ab initio Gaussian theory (G2 and G3). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
39.
H. H. Willard J. J. Thompson E. Kasper P. Slawik A. W. Middleton K. Seelkopf H. Taeger P. Schmidt F. Weyrauch A. Necke H. Müller A. J. Lindsey B. Park E. J. Lewis O. B. Winter Helen M. Robinson F. W. Lamb E. J. Miller C. E. Willoughby E. S. Wilkins E. O. Kraemer A. Jílek J. Kota 《Analytical and bioanalytical chemistry》1936,106(4-6):200-207
40.
Michael I. Bruce Natasha N. Zaitseva Brian W. Skelton 《Journal of organometallic chemistry》2008,693(17):2887-2897
Several complexes containing Co3 carbonyl clusters end-capping carbon chains of various lengths are described. Pd(0)/Cu(I)-catalysed reactions between {Co3{μ3-C(CC)2Au(PPh3)}(μ-dppm)(CO)7 and I(CC)2SiMe3 or FcCCI gave {Co3{μ3-C(CC)xR}(μ-dppm)(CO)7 [x = 4, R = SiMe33; x = 3, R = Fc 8]; treatment of 3 with NaOMe and AuCl(PPh3) gave 4 [x = 4, R = Au(PPh3)]. Related preparations of Co3{μ3-C(CC)2[Ru(PP)Cp′]}(μ-dppm)n(CO)9−2n [PP = (PPh3)2, Cp’ = Cp, n = 1, 5; PP = dppe, Cp′ = Cp∗, n = 1, 6; 0, 7] are also described. Syntheses of bis-cluster complexes {Co3(μ-dppm)(CO)7}2(μ-Cx) (x = 14, 12; 16, 9; 18, 11; 26, 10) - the latter being the longest cluster-capped Cx chains so far described - and the mercury-bridged compounds Hg{(CC)xC[Co3(μ-dppm)(CO)7]}2 (x = 1, 13; 2, 14) are reported. The molecular structures of 7, 12, 13 and 14, as well as of Co3(μ3-CCCSiMe3)(μ-dppm)(CO)6(PPh3) (15) and Co3{μ3-CC(O)OEt}(μ-dppm)(CO)7 (16), are reported. 相似文献