全文获取类型
收费全文 | 134篇 |
免费 | 7篇 |
专业分类
化学 | 105篇 |
晶体学 | 7篇 |
力学 | 6篇 |
数学 | 6篇 |
物理学 | 17篇 |
出版年
2024年 | 1篇 |
2022年 | 3篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 10篇 |
2011年 | 6篇 |
2010年 | 6篇 |
2009年 | 5篇 |
2008年 | 8篇 |
2007年 | 14篇 |
2006年 | 7篇 |
2005年 | 9篇 |
2004年 | 3篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有141条查询结果,搜索用时 15 毫秒
61.
Citrus species are rich sources for various bioactive compounds such as flavonoids, adrenergic amines, limonoids, and coumarins. Six adrenergic amines and 20 flavonoids in the jams and juices of Citrus species were analyzed by high-performance liquid chromatography with a C18 reversed-phase column using gradient mobile phase of sodium acetate buffer (pH 5.5) and acetonitrile at a flow rate of 1.0 mL/min with detection at 254, 280, and 330 nm. Synephrine was present in levels from 3.65 to 60.66 mg/L in 48 Citrus juices and 0.018-1.02 mg per serving in 32 Citrus jams. The content of these amines and flavonoids varied to a large extent depending on the type of the Citrus species used. The method has been successfully applied to the determination of adrenergic amines and flavonoids in several samples of Citrus fruit juices and jams. 相似文献
62.
We introduce PMF*, a novel potential of mean force (PMF) for the Ramachandran ?/Ψ dihedral plot of the 20 standard amino acids and assess its relevance to the conformation of polypeptides by scoring structures in the protein data bank and decoy datasets. The new energy function is a linear combination of the conventional, unreferenced PMF and the ΔPMF relative to the free energy of all amino acids in the parameterization set of structures, effectively removing their respective biases toward α‐helix and β‐strand. It is shown that low‐resolution crystal structures, NMR structures, and theoretical models have on average significantly higher energies than high‐resolution crystal structures; also PMF* is more discriminative for structure quality than the individual PMF and ΔPMF energy functions. PMF* may be well suited for use as a restraint energy term in the refinement of experimental structures and theoretical models. © 2012 Wiley Periodicals, Inc. 相似文献
63.
Measurement of myocardial strain provides direct information about heart function that can be correlated with disease. We present an MRI pulse sequence that acquires in just six heartbeats both harmonic phase (HARP) and strain-encoded (SENC) images and provides dense measurements of radial, circumferential and longitudinal strains within a single short-axis slice. Normal volunteer data confirm the feasibility of this pulse sequence, and acquired data demonstrate the strain measurement reliability. 相似文献
64.
No More HF: Teflon‐Assisted Ultrafast Removal of Silica to Generate High‐Surface‐Area Mesostructured Carbon for Enhanced CO2 Capture and Supercapacitor Performance 下载免费PDF全文
Dheeraj Kumar Singh Dr. Katla Sai Krishna Dr. Srinivasan Harish Prof. Srinivasan Sampath Prof. Muthusamy Eswaramoorthy 《Angewandte Chemie (International ed. in English)》2016,55(6):2032-2036
An innovative technique to obtain high‐surface‐area mesostructured carbon (2545 m2 g?1) with significant microporosity uses Teflon as the silica template removal agent. This method not only shortens synthesis time by combining silica removal and carbonization in a single step, but also assists in ultrafast removal of the template (in 10 min) with complete elimination of toxic HF usage. The obtained carbon material (JNC‐1) displays excellent CO2 capture ability (ca. 26.2 wt % at 0 °C under 0.88 bar CO2 pressure), which is twice that of CMK‐3 obtained by the HF etching method (13.0 wt %). JNC‐1 demonstrated higher H2 adsorption capacity (2.8 wt %) compared to CMK‐3 (1.2 wt %) at ?196 °C under 1.0 bar H2 pressure. The bimodal pore architecture of JNC‐1 led to superior supercapacitor performance, with a specific capacitance of 292 F g?1 and 182 F g?1 at a drain rate of 1 A g?1 and 50 A g?1, respectively, in 1 m H2SO4 compared to CMK‐3 and activated carbon. 相似文献
65.
Density functional theory (DFT) calculations have been carried out for the compound 4-[2-(tert-butylamino)-1-hydroxyethyl]-2-hydroxymethyl) phenol (4BAHEHMP) by using the B3LYP method at the 6-311++G (d,p) basis set level. The electric dipole moment (μ) and the first hyperpolarizability (α) values of the investigated molecule were computed. Total and partial density of state (TDOS and PDOS) and also overlap population density of state (COOP or OPDOS) diagrams analysis were presented. HOMO and LUMO energies confirm that charge transfer occurs within the molecule. In addition Molecular Electrostatic Potential (MEP), Natural Bond Orbital analysis (NBO) and Non- Linear Optical (NLO) properties are studied. 相似文献
66.
Redox‐Active Metal–Organic Frameworks: Highly Stable Charge‐Separated States through Strut/Guest‐to‐Strut Electron Transfer 下载免费PDF全文
Nivedita Sikdar Dr. Kolleboyina Jayaramulu Dr. Venkayala Kiran Dr. K. Venkata Rao Prof. Srinivasan Sampath Prof. Subi J. George Prof. Tapas Kumar Maji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(33):11701-11706
Molecular organization of donor and acceptor chromophores in self‐assembled materials is of paramount interest in the field of photovoltaics or mimicry of natural light‐harvesting systems. With this in mind, a redox‐active porous interpenetrated metal–organic framework (MOF), {[Cd(bpdc)(bpNDI)] ? 4.5 H2O ? DMF}n ( 1 ) has been constructed from a mixed chromophoric system. The μ‐oxo‐bridged secondary building unit, {Cd2(μ‐OCO)2}, guides the parallel alignment of bpNDI (N,N′‐di(4‐pyridyl)‐1,4,5,8‐naphthalenediimide) acceptor linkers, which are tethered with bpdc (bpdcH2=4,4′‐biphenyldicarboxylic acid) linkers of another entangled net in the framework, resulting in photochromic behaviour through inter‐net electron transfer. Encapsulation of electron‐donating aromatic molecules in the electron‐deficient channels of 1 leads to a perfect donor–acceptor co‐facial organization, resulting in long‐lived charge‐separated states of bpNDI. Furthermore, 1 and guest encapsulated species are characterised through electrochemical studies for understanding of their redox properties. 相似文献
67.
68.
Richard Anderson Sampath Kannan Howard Karloff Richard E. Ladner 《Journal of Algorithms in Cognition, Informatics and Logic》2002,44(2):338
We present an O(n4)-time algorithm for the following problem: Given a set of items with known access frequencies, find the optimal binary search tree under the realistic assumption that each comparison can only result in a two-way decision: either an equality comparison or a less-than comparisons. This improves the best known result of O(n5) time, which is based on split tree algorithms. Our algorithm relies on establishing thresholds on the frequency of an item that can occur as an equality comparison at the root of an optimal tree. 相似文献
69.
Under what conditions can a simple polygon be tiled by parallelograms? In this paper we give matching necessary and sufficient conditions on the polygon to be tilable and characterize the set of possible tilings. We also provide an efficient algorithm for constructing a tiling. 相似文献
70.
H.M. Sampath Kumar M. Shesha RaoSipak Joyasawal J.S. Yadav 《Tetrahedron letters》2003,44(22):4287-4289
α,β-Unsaturated esters are formed in good yields when aldehydes are heated with orthoacetates in the presence of a catalytic amount of phenol. 相似文献