全文获取类型
收费全文 | 138篇 |
免费 | 2篇 |
国内免费 | 3篇 |
专业分类
化学 | 52篇 |
数学 | 44篇 |
物理学 | 47篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2016年 | 6篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 6篇 |
2012年 | 8篇 |
2011年 | 11篇 |
2010年 | 4篇 |
2009年 | 5篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 6篇 |
2005年 | 8篇 |
2004年 | 7篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1961年 | 1篇 |
排序方式: 共有143条查询结果,搜索用时 13 毫秒
71.
Noam Zion David A. Cullen Piotr Zelenay Lior Elbaz 《Angewandte Chemie (International ed. in English)》2020,59(6):2483-2489
Aerogels are fascinating materials that can be used for a wide range of applications, one of which is electrocatalysis of the important oxygen reduction reaction. In their inorganic form, aerogels can have ultrahigh catalytic site density, high surface area, and tunable physical properties and chemical structures—important features in heterogeneous catalysis. Herein, we report on the synthesis and electrocatalytic properties of an iron–porphyrin aerogel. 5,10,15,20‐(Tetra‐4‐aminophenyl)porphyrin (H2TAPP) and FeII were used as building blocks of the aerogel, which was later heat‐treated at 600 °C to enhance electronic conductivity and catalytic activity, while preserving its macrostructure. The resulting material has a very high concentration of atomically dispersed catalytic sites (9.7×1020 sites g?1) capable of catalyzing the oxygen reduction reaction in alkaline solution (Eonset=0.92 V vs. RHE, TOF=0.25 e? site?1 s?1 at 0.80 V vs. RHE). 相似文献
72.
We report time-resolved fluorescence data for the anion of p-hydroxybenzylidene dimethylimidazolinone (p-HBDI), a model chromophore of the green fluorescence protein, in viscous glycerol-water mixtures over a range of temperatures, T. The markedly nonexponential decay of the excited electronic state is interpreted with the aid of an inhomogeneous model possessing a Gaussian coordinate-dependent sink term. A nonlinear least-squares fitting routine enables us to achieve quantitative fits by adjusting a single activation parameter, which is found to depend linearly on 1/T. We derive an analytic expression for the absolute quantum yield, which is compared with the integrated steady-state fluorescence spectra. The microscopic origins of the model are discussed in terms of two-dimensional dynamics, coupling the phenyl-ring rotation to a swinging mode that brings this flexible molecule to the proximity of a conical intersection on its multidimensional potential energy surface. 相似文献
73.
74.
Noam D. Elkies 《Periodica Mathematica Hungarica》2006,53(1-2):133-148
Summary We apply an old method for constructing points-and-lines configurations
in the plane to study some recent questions in incidence geometry. 相似文献
75.
Rodney G. Downey Noam Greenberg Carl G. Jockusch Jr. Kevin G. Milans 《Combinatorica》2011,31(3):285-303
We prove several quantitative Ramseyan results involving ternary complete trees with {0,1}-labeled edges where we attempt to find a complete binary subtree with as few labels as possible along its paths. One of these is used to answer a question of Simpson??s in computability theory; we show that there is a bounded ?? 1 0 class of positive measure which is not strongly (Medvedev) reducible to DNR3; in fact, the class of 1-random reals is not strongly reducible to DNR3. 相似文献
76.
Thekku Veedu Sreevidya Gilad Golden Noam Saper Jared Feldman Mark Botoshansky Menahem Kaftory 《Structural chemistry》2011,22(5):1105-1112
Abstract
The preparation and crystal structure of six molecular compounds consist of light-stable host molecules [(1-cyclohexyl-4-hydroxybenzene, 1,1,6,6-tetraphenyl-2,4-hexadiyne-1,6-diol, 4-((10-[4-(ethoxycarbonyl)phenoxy]decyl)oxy)benzene, 1,2,4,5-benzenetetracarboxylic acid, resorcinol] and light-sensitive guest molecules [(5-chloro-2(1H)-pyridone or 5-nitro-2(1H)-pyridone] are described in light of their failure to undergo [4 + 4] photodimerization in the solid-state upon irradiation with UV light. Unlike in many cases were pyridone and its derivatives undergo such dimerization in the solid-state due to the packing arrangement in the crystalline form in which the geometric requirement for photodimerization meet, the compounds described here failed to pack in ways to enable such photodimerization. The distances between the potentially reactive atoms ranged from 4.620 to 8.408 ? which are too long to react. 相似文献77.
78.
The g(44) grating is an electroholographic transmission grating in which the applied field is perpendicular to both the grating vector and the wave vector of the incident beam. It is argued that in this configuration the incident beam traverses through a periodically rotating index ellipsoid. It is shown that in the g(44) configuration the Bragg condition is fulfilled for a specific value of the applied field and for a diffracting beam polarization that is perpendicular to that of the incident beam. Consequently, the g(44) grating can be used as an electrically controlled filter. Tunability of 7 nm is demonstrated in a 2mm thick grating. 相似文献
79.
Soreni N Noseworthy MD Cormier T Oakden WK Bells S Schachar R 《Magnetic resonance imaging》2006,24(2):187-194
PURPOSE: To measure possible positional and diurnal physiological effects on brain metabolites in single-voxel proton magnetic resonance spectroscopy ((1)H-MRS) measurements of the right and left striatum. METHODS: (1)H-MRS measurements were performed in 10 healthy adult volunteers using a short echo PRESS sequence (TE=30 ms, TR=3000 ms). Each individual was scanned during both morning and afternoon hours. Regions of interest were right and left striatum. To control for systematic drift in scanner performance, (1)H-MRS measurements of a standard phantom solution were also acquired. Statistical analysis was performed using a repeated measures analysis of variance that included three within-subject factors: metabolite (N-acetyl-aspartate [NAA] or creatine [Cr]), laterality (left or right caudate) and time (morning or afternoon). RESULTS: A significant interaction (P<.016) between time of day and metabolite levels was observed. Further exploration of this finding revealed a significant difference between morning and afternoon levels of NAA (P<.044) but not Cr. In addition, no significant morning-to-afternoon differences were observed for the (1)H-MRS phantom measurements. CONCLUSIONS: Systematic variation due to scanner performance does not account for the changes observed in repeated measurements of striatal NAA levels. This difference may be accounted for by either repositioning effects or circadian physiological effects. Further studies are required to learn whether time of day standardization of (1)H-MRS acquisitions may contribute to improved reproducibility of measurements. 相似文献
80.
Dana Kaizerman‐Kane Maya Hadar Noam Tal Roman Dobrovetsky Yossi Zafrani Yoram Cohen 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(16):5356-5360
We describe the preparation of the first water‐soluble pH‐responsive supramolecular hexagonal boxes (SHBs) based on multiple charge‐assisted hydrogen bonds between peramino‐pillar[6]arenes 2 with the molecular “lid” mellitic acid ( 1 a ). The interaction between 2 and 1 a , as well as the other “lids” pyromellitic and trimesic acids ( 1 b and 1 c , respecively) were studied by a combination of experimental and computational methods. Interestingly, the addition of 1 a to the complexes of the protonated form of pillar[6]arene 2 , that is, 3 , with bis‐sulfonate 4 a or 4 b , immediately led to guest escape along with the formation of closed 1 a22 supramolecular boxes. Moreover, the process of the openning and closing of the supramolecular boxes along with threading and escaping of the guests, respectively, was found to be reversible and pH‐responsive. This study paves the way for the easy and modular preparation of different SHBs that may have myriad applications. 相似文献