全文获取类型
收费全文 | 465篇 |
免费 | 20篇 |
国内免费 | 4篇 |
专业分类
化学 | 315篇 |
力学 | 5篇 |
数学 | 65篇 |
物理学 | 104篇 |
出版年
2022年 | 4篇 |
2021年 | 7篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 8篇 |
2014年 | 17篇 |
2013年 | 26篇 |
2012年 | 40篇 |
2011年 | 47篇 |
2010年 | 21篇 |
2009年 | 13篇 |
2008年 | 33篇 |
2007年 | 31篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 31篇 |
2003年 | 28篇 |
2002年 | 24篇 |
2001年 | 9篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有489条查询结果,搜索用时 15 毫秒
21.
Platinum‐Promoted Ga/Al2O3 as Highly Active,Selective, and Stable Catalyst for the Dehydrogenation of Propane
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)
Jesper J. H. B. Sattler Dr. Ines D. Gonzalez‐Jimenez Dr. Lin Luo Brien A. Stears Dr. Andrzej Malek Dr. David G. Barton Dr. Beata A. Kilos Dr. Mark P. Kaminsky Tiny W. G. M. Verhoeven Eline J. Koers Prof. Dr. Marc Baldus Prof. Dr. Bert M. Weckhuysen 《Angewandte Chemie (International ed. in English)》2014,53(35):9251-9256
A novel catalyst material for the selective dehydrogenation of propane is presented. The catalyst consists of 1000 ppm Pt, 3 wt % Ga, and 0.25 wt % K supported on alumina. We observed a synergy between Ga and Pt, resulting in a highly active and stable catalyst. Additionally, we propose a bifunctional active phase, in which coordinately unsaturated Ga3+ species are the active species and where Pt functions as a promoter. 相似文献
22.
Inside Cover: Fluoride‐Bridged {GdIII3MIII2} (M=Cr,Fe, Ga) Molecular Magnetic Refrigerants (Angew. Chem. Int. Ed. 9/2014)
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)
23.
Christian Fabiansen Charles W. Yaméogo Sarita Devi Henrik Friis Anura Kurpad Jonathan C. Wells 《Isotopes in environmental and health studies》2017,53(4):344-355
Childhood malnutrition is highly prevalent and associated with high mortality risk. In observational and interventional studies among malnourished children, body composition is increasingly recognised as a key outcome. The deuterium dilution technique has generated high-quality data on body composition in studies of infants and young children in several settings, but its feasibility and accuracy in children suffering from moderate acute malnutrition requires further study. Prior to a large nutritional intervention trial among children with moderate acute malnutrition, we conducted pilot work to develop and adapt the deuterium dilution technique. We refined procedures for administration of isotope doses and collection of saliva. Furthermore, we established that equilibration time in local context is 3?h. These findings and the resulting standard operating procedures are important to improve data quality when using the deuterium dilution technique in malnutrition studies in field conditions, and may encourage a wider use of isotope techniques. 相似文献
24.
We observe twofold shell filling in the spectra of closed one-dimensional quantum dots formed in single-wall carbon nanotubes. Its signatures include a bimodal distribution of addition energies, correlations in the excitation spectra for different electron number, and alternation of the spins of the added electrons. This provides a contrast with quantum dots in higher dimensions, where such spin pairing is absent. We also see indications of an additional fourfold periodicity indicative of K-K' subband shells. Our results suggest that the absence of shell filling in most isolated nanotube dots results from disorder or nonuniformity. 相似文献
25.
A series of molecularly imprinted polymer (MIP) synthetic receptors selective for the sedative thalidomide (5) have been designed and synthesized based upon the functional monomer 9-(2'-methacryloyloxyethyl)adenine (2). (1)H-NMR studies were used to establish the existence of DNA-like binding interactions between 2 and the template (5). A series of ethylene glycol dimethacrylate cross-linked copolymers was synthesized using either 2 or methacrylic acid, or a combination of these functional monomers. Zonal HPLC studies demonstrated enantioselectivity (alpha = 2.11) and ligand selectivity which could be attributed to the interaction of 2 with the imide moiety of 5. Compound 2 provided a more significant contribution to the binding of 5 than methacrylic acid, though a combination of these two functional monomers resulted in improved enantioselectivity. Frontal chromatographic and batch binding studies confirmed the observed differences in affinity of the imprinted and reference polymers for the template. 相似文献
26.
We generalize the concept of a 2-coloring of a graph to what we call a semi-balanced coloring by relaxing a certain discrepancy condition on the shortest-paths hypergraph of the graph. Let G be an undirected, unweighted, connected graph with n vertices and m edges. We prove that the number of different semi-balanced colorings of G is: (1) at most n+1 if G is bipartite; (2) at most m if G is non-bipartite and triangle-free; and (3) at most m+1 if G is non-bipartite. Based on the above combinatorial investigation, we design an algorithm to enumerate all semi-balanced colorings of G in O(nm2) time.Acknowledgments The authors thank Tetsuo Asano, Naoki Katoh, Kunihiko Sadakane, and Hisao Tamaki for helpful discussions and comments.Supported in part by Sweden-Japan FoundationFinal version received: November 17, 2003 相似文献
27.
Bromine-lithium exchange using tert-butyllithium at -78 degrees C initiates a cascade process whereby either xanthone derivatives or pentacyclic 13-azadibenzo[a,de]anthracenes are produced in high yields. The reaction proceeds via a sequential intramolecular trapping of organolithium intermediates. 相似文献
28.
De novo design and total chemical synthesis of proteins provide powerful approaches to critically test our understanding of protein folding, structure, and stability. The 4-alpha-helix bundle is a frequently studied structure in which four amphiphilic alpha-helical peptide strands form a hydrophobic core. Assembly of protein models on a template has been suggested as a way to reduce the entropy of folding. We have previously developed the concept of carbohydrates as templates in the de novo design of protein models termed 'carboproteins'. Here we present the chemical synthesis of three 8.1 kDa 4-alpha-helix bundles by oxime ligation of tetra-aminooxyacetyl functionalized D-galacto-, D-gluco-, and D-altropyranoside templates with an amphiphilic C-terminal hexadecapeptide aldehyde sequence. CD spectroscopy indicated that the choice of template has an effect on the overall structure of the carboprotein, as the altro-based carboprotein was found to be more alpha-helical than the corresponding galacto- and gluco-carboproteins. However, an influence on stability could not be detected in the present experiments, as the three carboproteins gave similar free energy of foldings (deltaG(F)H2O) and melting points in chemical and thermal denaturation experiments. 相似文献
29.
Tsang WC Jernelius JA Cortez GA Weatherhead GS Schrock RR Hoveyda AH 《Journal of the American Chemical Society》2003,125(9):2591-2596
An enantiomerically pure Mo-based complex that bears an alkylimido ligand is prepared and characterized through NMR spectroscopy and X-ray analysis. Mo complex 4 is the only reported chiral alkylimido catalyst; all previous chiral complexes are arylimido systems. These studies show that the chiral Mo catalyst exists exclusively as the syn isomer and that it offers unique reactivity and selectivity profiles in asymmetric olefin metathesis. 相似文献
30.
The aim of this paper is to formulate a conjecture for an arbitrary simple Lie
algebra g in terms of the geometry of principal nilpotent pairs. When g is specialized to sln,
this conjecture readily implies the n! result and it is very likely that, in fact, it is equivalent
to the n! result in this case. In addition, this conjecture can be thought of as generalizing an
old result of Kostant. In another direction, we show that to prove the validity of the n! result
for an arbitrary n and an arbitrary partition of n, it suffices to show its validity only for the
staircase partitions. 相似文献