全文获取类型
收费全文 | 232篇 |
免费 | 10篇 |
专业分类
化学 | 205篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 15篇 |
物理学 | 18篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 14篇 |
2019年 | 4篇 |
2018年 | 9篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 9篇 |
2013年 | 6篇 |
2012年 | 27篇 |
2011年 | 24篇 |
2010年 | 10篇 |
2009年 | 6篇 |
2008年 | 15篇 |
2007年 | 19篇 |
2006年 | 22篇 |
2005年 | 13篇 |
2004年 | 11篇 |
2003年 | 4篇 |
2002年 | 5篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1985年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有242条查询结果,搜索用时 15 毫秒
31.
Ciesienski KL Haas KL Dickens MG Tesema YT Franz KJ 《Journal of the American Chemical Society》2008,130(37):12246-12247
A photosensitive caged copper complex has been prepared from a tetradentate ligand (H2cage) composed of two pyridyl-amide arms connected by a photoreactive nitrophenyl group. H2cage binds Cu2+ in aqueous solution with a stability constant (log beta) of 10.8, which corresponds to a KD of 16 pM at pH 7.4. The neutral Cu2+ complex, [Cu(OH2)(cage)], crystallizes as a distorted trigonal bipyramid coordinated by two amide and two pyridyl N atoms, with a water molecule bound in the trigonal plane. Photolysis with 350 nm UV light cleaves the ligand backbone to release photoproducts with significantly diminished affinity for Cu2+, thereby uncaging the metal ion. When coordinated as the caged complex, copper has diminished reactivity to produce hydroxyl radicals from Fenton-like reaction mixtures containing hydrogen peroxide and ascorbic acid. Postphotolysis, uncaged copper promotes hydroxyl radical formation under the same conditions. The strategy of caging copper is promising for applications where light could be used to trigger release of copper as a pro-oxidant to increase oxidative stress or as a tool to release copper intracellularly to study mechanisms of copper trafficking. 相似文献
32.
Katie Makar 《Mathematical Thinking and Learning》2016,18(1):1-24
Informal statistical inference has now been researched at all levels of schooling and initial tertiary study. Work in informal statistical inference is least understood in the early years, where children have had little if any exposure to data handling. A qualitative study in Australia was carried out through a series of teaching experiments with a class of five- to six-year-old children in two phases over six months. The aim of the exploratory study was to understand and support the emergence of informal statistical inference in the early years of schooling. Through activities that initially built on children’s experiences with prediction and key characteristics of informal statistical inference, the children’s actions were observed in a data-based inquiry involving prediction to identify critical relationships that then supported children in making informal statistical inferences. Implications are discussed. 相似文献
33.
DeNicola Cafferky K Thompson RL Richardson DD Caruso JA 《Analytical and bioanalytical chemistry》2007,387(6):2037-2043
Metals and metal-containing compounds are known to play important roles in many biological processes, including metabolic
and detoxification pathways and the formation and function of proteins. Like all organisms, viruses are expected to contain
different metals. These metals, either by themselves or in the form of metalloproteins, may be involved in the virus’s ability
to infect healthy cells and replicate within them. Identification and speciation of metals in control cells and in cells affected
by a virus could be helpful in elucidating infection and replication mechanisms; these might, in turn, be vital to the development
of more effective treatments. There has, however, been no extensive investigation of the metals specific viruses contain or
affect. The objective of this study was to investigate changes in cellular metal content resulting from herpes simplex virus
1 (HSV-1) infection. Inductively coupled plasma mass spectrometry was used to identify differences between metal concentrations
in uninfected and HSV-1-infected mammalian cells. Although it can be assumed that decreases in metal content are a result
of cellular response to the virus, increases can be attributed either to cellular response or to the HSV-1 virus itself. Microwave
digestion and flow injection methods suitable for small sample volumes were used, and the effects of different virus inactivation
procedures were explored. This work is the first step in the identification of metals pertinent to HSV-1 infection and lays
the foundation for future studies concentrating on characterization of these metal-associated or containing molecules. 相似文献
34.
The rates of proton transfer from [pyrH]+ (pyr = pyrrolidine) to the binuclear complexes [Fe2S2Cl4]2- and [S2MS2FeCl2]2- (M = Mo or W) are reported. The reactions were studied using stopped-flow spectrophotometry, and the rate constants for proton transfer were determined from analysis of the kinetics of the substitution reactions of these clusters with the nucleophiles Br- or PhS- in the presence of [pyrH]+. In general, Br- is a poor nucleophile for these clusters, and proton transfer occurs before Br- binds, allowing direct measure of the rate of proton transfer from [pyrH]+ to the cluster. In contrast, PhS- is a better nucleophile, and a pathway in which PhS- binds preferentially to the cluster prior to proton transfer from [pyrH]+ usually operates. For the reaction of [Fe2S2Cl4]2- with PhS- in the presence of [pyrH]+ both pathways are observed. Comparison of the results presented in this paper with analogous studies reported earlier on cuboidal Fe-S-based clusters allows discussion of the factors which affect the rates of proton transfer in synthetic clusters including the nuclearity of the cluster core, the metal composition, and the nature of the terminal ligands. The possible relevance of these findings to the protonation sites of natural Fe-S-based clusters, including FeMo-cofactor from nitrogenase, are presented. 相似文献
35.
36.
The purpose of this study was to investigate the effect of parameter changes that can potentially lead to unreliable measurements in fat quantification. Chemical shift imaging was performed using spoiled gradient echo sequences with systematic variations in the following: two-dimensional/three-dimensional sequence, number of echoes, delta echo time, fractional echo factor, slice thickness, repetition time, flip angle, bandwidth, matrix size, flow compensation and field strength. Results indicated no significant (or significant but small) changes in fat fraction with parameter. The significant changes can be attributed to the known effects of T1 bias and two forms of noise bias. 相似文献
37.
Y Zhu J Wyrick KD Cohen KM Magnone C Holzke D Salib Q Ma D Sun L Bartels 《J Phys Condens Matter》2012,24(35):354005
Acetylene on Cu(111) is investigated by scanning tunnelling microscopy (STM); a surface pattern previously derived from diffraction measurements can be validated, if the variation of the STM image transfer function through absorption of an acetylene molecule onto the tip apex is taken into account. Density functional theory simulations point to a balance between short-range repulsive interactions of acetylene/Cu(111) associated with surface stress and longer range attractive interactions as the origin of the ordering. 相似文献
38.
JA Paquette CJ Yardley KM Psutka MA Cochran O Calderon VE Williams KE Maly 《Chemical communications (Cambridge, England)》2012,48(66):8210-8212
We report the synthesis and characterization of a series of novel hexaalkoxydibenz[a,c]anthracenes. While the parent compound is not mesomorphic, the introduction of substituents in the 10- and 13-positions yields compounds with columnar liquid crystalline phases over very broad temperature ranges. 相似文献
39.
Cordes J Calo F Anderson K Pfaffeneder T Laclef S White AJ Barrett AG 《The Journal of organic chemistry》2012,77(1):652-657
A five-step synthesis of the natural product angelicoin A using a late stage highly regioselective palladium(0)-catalyzed decarboxylative prenyl migration and aromatization sequence as the key step is reported. The method was extended with geranyl migration in eight-step total syntheses of hericenone J and hericenol A from geraniol. 相似文献
40.
Maxwell D. Cummings Tse‐I Lin Lili Hu Abdellah Tahri David McGowan Katie Amssoms Stefaan Last Benoit Devogelaere Marie‐Claude Rouan Leen Vijgen Jan Martin Berke Pascale Dehertogh Els Fransen Erna Cleiren Liesbet vanderHelm Gregory Fanning Kristof VanEmelen Origne Nyanguile Kenny Simmen Pierre Raboisson Sandrine Vendeville 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2012,124(19):4715-4718