全文获取类型
收费全文 | 165篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
化学 | 94篇 |
力学 | 3篇 |
数学 | 26篇 |
物理学 | 45篇 |
出版年
2021年 | 1篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 1篇 |
2012年 | 9篇 |
2011年 | 19篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 5篇 |
2007年 | 10篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 7篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1969年 | 2篇 |
1958年 | 1篇 |
1947年 | 1篇 |
排序方式: 共有168条查询结果,搜索用时 78 毫秒
121.
John G. Hefner Paul M. Zizelman Loren D. Durfee Glenn S. Lewandos 《Journal of organometallic chemistry》1984,260(3):369-380
The copper(I) trifluoromethanesulfonate π complexes of 1,8-cyclotetradecadiyne and 1,7-octadiyne have been synthesized. For a series of terminal alkyne (CuO3SCF3) π complexes, vibrational spectra show weakening of both C ≡C and Csp-H bonds upon copper(I) coordination. NMR analysis shows less Cu(I) caused deshielding of C(1) than C(2) of the alkyne and increased Csp-H coupling. Copper(I) π coordination to terminal alkynes increases the rate of exchange of protium on C(1) for deuterium from CD3COOD. Copper enhances the rate of exchange by a factor of 1.2 x 105 with 1,7-octadiyne. The exchange is catalytic in copper(I) and is faster than the rate of copper alkynide formation in the absence of deuterium donor. Copper(I) catalyzes deuterium exchange for protium at C(1) between 1,7-octadiyne and 1-hexyne-1-d1. 相似文献
122.
[reaction: see text] Conformational analysis, van der Waals attractions, and transition structure calculations are combined to design an asymmetric Lewis acid-catalyzed Diels-Alder reaction for simple acyclic alpha,beta-unsaturated ketones and alpha,beta-unsaturated acid chlorides, giving up to 83 and 92% ee, respectively. The two-point-binding chiral recognition mechanism, Lewis acid-Lewis base coordination with boron and a van der Waals attraction with the naphthyl group, uses the inherent enone unit of simple alpha,beta-unsaturated carbonyl compounds, ending the need for auxiliary oxygen binding sites on the dienophile. 相似文献
123.
Loren?S?Scuro PU?Simioni DL?Grabriel Elzira?E?Saviani Luzia?V?Modolo Wirla?MSC?Tamashiro Ione?SalgadoEmail author 《BMC biochemistry》2004,5(1):5
Background
The anti-inflammatory properties of some flavonoids have been attributed to their ability to inhibit the production of NO by activated macrophages. Soybean cotyledons accumulate certain flavonoids following elicitation with an extract of the fungal pathogen Diaporthe phaseolorum f. sp. meridionalis (Dpm). Sodium nitroprusside (SNP), a nitric oxide donor, can substitute for Dpm in inducing flavonoid production. In this study, we investigated the effect of flavonoid-containing diffusates obtained from Dpm- and SNP-elicited soybean cotyledons on NO production by lipopolysaccharide (LPS)- and LPS plus interferon-γ (IFNγ)-activated murine macrophages.Results
Significant inhibition of NO production, measured as nitrite formation, was observed when macrophages were activated in the presence of soybean diffusates from Dpm- or SNP-elicited cotyledons. This inhibition was dependent on the duration of exposure to the elicitor. Daidzein, genistein, luteolin and apigenin, the main flavonoids present in diffusates of elicited cotyledons, suppressed the NO production by LPS + IFNγ activated macrophages in a concentration-dependent manner, with IC50 values of 81.4 μM, 34.5 μM, 38.6 μM and 10.4 μM respectively. For macrophages activated with LPS alone, the IC50 values were 40.0 μM, 16.6 μM, 10.4 μM and 2.8 μM, respectively. Western blot analysis showed that iNOS expression was not affected by daidzein, was reduced by genistein, and was abolished by apigenin, luteolin and Dpm- and SNP-soybean diffusates at concentrations that significantly inhibited NO production by activated macrophages.Conclusions
These results suggest that the suppressive effect of flavonoids on iNOS expression could account for the potent inhibitory effect of Dpm- and SNP-diffusates on NO production by activated macrophages. Since the physiological concentration of flavonoids in plants is normally low, the treatment of soybean tissues with SNP may provide a simple method for substantially increasing the concentration of metabolites that are beneficial for the treatment of chronic inflammatory diseases associated with NO production.124.
Jan J. Spitzer Prem Paul Singh Inger V. Olofsson Loren G. Hepler 《Journal of solution chemistry》1978,7(8):623-630
We have used a flow calorimeter and a flow densimeter for measurements leading to apparent molar heat capacities and apparent molar volumes of aqueous solutions of Cd(ClO4)2, Ca(ClO4)2, Co(ClO4)2, Mn(ClO4)2, Ni(ClO4)2, and Zn(ClO4)2. The resulting apparent molar quantities have been extrapolated to infinite dilution to obtain the corresponding standardstate apparent and partial molar heat capacities and volumes. These latter values have been used for calculation of conventional ionic heat capacities and volumes. 相似文献
125.
Frontispiece: NMR Spectroscopic Assignment of Backbone and Side‐Chain Protons in Fully Protonated Proteins: Microcrystals,Sedimented Assemblies,and Amyloid Fibrils
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Jan Stanek Dr. Loren B. Andreas Dr. Kristaps Jaudzems Dr. Diane Cala Dr. Daniela Lalli Andrea Bertarello Dr. Tobias Schubeis Dr. Inara Akopjana Dr. Svetlana Kotelovica Prof. Kaspars Tars Dr. Andrea Pica Dr. Serena Leone Prof. Delia Picone Dr. Zhi‐Qiang Xu Prof. Nicholas E. Dixon Dr. Denis Martinez Mélanie Berbon Nadia El Mammeri Dr. Abdelmajid Noubhani Dr. Sven Saupe Dr. Birgit Habenstein Dr. Antoine Loquet Dr. Guido Pintacuda 《Angewandte Chemie (International ed. in English)》2016,55(50)
126.
Ground-state two-particle reduced density matrices (2-RDMs) are used to calculate excited-state energy spectra. Solving the Schrodinger equation for excited states dominated by single excitations from the ground-state wavefunction requires the ground-state 2- and 3-RDMs. The excited states, however, can be obtained without a knowledge of the ground-state 3-RDM by two methods: (i) cumulant expansion methods which build the 3-RDM from the 2-RDM, and (ii) double commutator methods which eliminate the 3-RDM. Previous work [Mazziotti, Phys. Rev. A 68, 052501 (2003)] examined the accuracy of excited states extracted from ground-state 2-RDMs, which were calculated by full configuration interaction or the variational 2-RDM method. In this work we employ (i) advances in semidefinite programming to treat the excited states of water and hydrogen fluoride and chains of hydrogen atoms, and (ii) the addition of partial three-particle N-representability conditions to compute more accurate ground-state 2-RDMs. With the hydrogen chains we examine the metal-to-insulator transition as measured by the band gap (the difference between the ground-state and the first excited-state energies), which is difficult for excited-state methods to capture. 相似文献
127.
Kai Xue Kumar Tekwani Movellan Xizhou Cecily Zhang Eszter E. Najbauer Marcel C. Forster Stefan Becker Loren B. Andreas 《Chemical science》2021,12(43):14332
Solid-state NMR (ssNMR) is a versatile technique that can be used for the characterization of various materials, ranging from small molecules to biological samples, including membrane proteins. ssNMR can probe both the structure and dynamics of membrane proteins, revealing protein function in a near-native lipid bilayer environment. The main limitation of the method is spectral resolution and sensitivity, however recent developments in ssNMR hardware, including the commercialization of 28 T magnets (1.2 GHz proton frequency) and ultrafast MAS spinning (<100 kHz) promise to accelerate acquisition, while reducing sample requirement, both of which are critical to membrane protein studies. Here, we review recent advances in ssNMR methodology used for structure determination of membrane proteins in native and mimetic environments, as well as the study of protein functions such as protein dynamics, and interactions with ligands, lipids and cholesterol.Solid-state NMR (ssNMR) is a versatile technique that can be used for the characterization of various materials, ranging from small molecules to biological samples, including membrane proteins, as reviewed here. 相似文献
128.
Loren G. Kaake 《Chemical record (New York, N.Y.)》2019,19(6):1131-1141
A perspective on the operating principles of organic bulk heterojunction solar cells is outlined and used to suggest an alternative device configuration, employing two type II semiconductor heterojunctions in series. Guiding principles to the implementation of this configuration, called a double heterojunction, are summarized. Assuming an exciton binding energy of 0.3 eV or less, results in a maximum achievable power conversion efficiency of well over 25 %. Achieving a high efficiency organic double heterojunction requires a specific energy level alignment, charge separation in the absence of driving forces, high phase purity and excellent diode quality. Fully conjugated triblock polymers of the form [D1‐A1]‐[D1‐A2]‐[D2‐A2] appear to be a system that can fulfill these requirements. Going forward, the primary challenge is the identification and development of synthetically tractable materials which have the necessary properties. 相似文献
129.