全文获取类型
收费全文 | 319篇 |
免费 | 6篇 |
国内免费 | 2篇 |
专业分类
化学 | 161篇 |
晶体学 | 4篇 |
力学 | 14篇 |
综合类 | 1篇 |
数学 | 27篇 |
物理学 | 120篇 |
出版年
2021年 | 2篇 |
2018年 | 7篇 |
2017年 | 2篇 |
2016年 | 5篇 |
2015年 | 4篇 |
2013年 | 18篇 |
2012年 | 13篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 9篇 |
2008年 | 21篇 |
2007年 | 15篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 9篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 16篇 |
2000年 | 12篇 |
1999年 | 11篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 8篇 |
1972年 | 2篇 |
1960年 | 1篇 |
1939年 | 1篇 |
1885年 | 1篇 |
排序方式: 共有327条查询结果,搜索用时 46 毫秒
71.
Neil W. Owens Adrian Lee Kirk Marat Dr. Frank Schweizer Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(40):10649-10657
The conformations of peptides and proteins are often influenced by glycans O‐linked to serine (Ser) or threonine (Thr). (2S,4R)‐4‐Hydroxyproline (Hyp), together with L ‐proline (Pro), are interesting targets for O‐glycosylation because they have a unique influence on peptide and protein conformation. In previous work we found that glycosylation of Hyp does not affect the N‐terminal amide trans/cis ratios (Ktrans/cis) or the rates of amide isomerization in model amides. The stereoisomer of Hyp—(2S,4S)‐4‐hydroxyproline (hyp)—is rarely found in nature, and has a different influence both on the conformation of the pyrrolidine ring and on Ktrans/cis. Glycans attached to hyp would be expected to be projected from the opposite face of the prolyl side chain relative to Hyp; the impact this would have on Ktrans/cis was unknown. Measurements of 3J coupling constants indicate that the glycan has little impact on the Cγ‐endo conformation produced by hyp. As a result, it was found that the D ‐galactose residue extending from a Cγ‐endo pucker affects both Ktrans/cis and the rate of isomerization, which is not found to occur when it is projected from a Cγ‐exo pucker; this reflects the different environments delineated by the proline side chain. The enthalpic contributions to the stabilization of the trans amide isomer may be due to disruption of intramolecular interactions present in hyp; the change in enthalpy is balanced by a decrease in entropy incurred upon glycosylation. Because the different stereoisomers—Hyp and hyp—project the O‐linked carbohydrates in opposite spatial orientations, these glycosylated amino acids may be useful for understanding of how the projection of a glycan from the peptide or protein backbone exerts its influence. 相似文献
72.
Valentine KG Pometun MS Kielec JM Baigelman RE Staub JK Owens KL Wand AJ 《Journal of the American Chemical Society》2006,128(50):15930-15931
Proteins encapsulated within the aqueous core of reverse micelles are found to partially align in a magnetic field. The degree of alignment is sufficient to result in sizable residual 15N-1H dipolar couplings that can be easily measured. It is found that the magnetic susceptibility of the reverse micelle particle is not dominated by the encapsulated protein. The residual dipolar couplings are found to be structurally meaningful. 相似文献
73.
The solvent varying technique (SVT) provides a simple method for the production of uniform batches of silica nanoparticles (SNPs) of a target average diameter. SNPs synthesized using the SVT have been observed to agglomerate over increasing storage times leading to an increase in average particle diameter. Since the particle diameters of the SNPs produced using the SVT may vary over increasing storage durations, the previous model, suggested by Gao et al., which is based on the diameter of the original SNPs, is unreliable when predicting a target particle diameter using the initial volume of ethanol. A centrifuge and replacement of solvent method has been applied in this investigation to the SNP solutions created using the SV technique. This reduces the amount of unused reactants in the centrifuged colloidal suspensions, which further improves the quality of the SNPs and hence any subsequent photonic crystals. Post centrifuge and replace, the morphology of the centrifuged particles is more uniform than that of the original particles, which has been evaluated using SEM micrographs. The face-centered cubic (FCC) structures observed on the surface of the photonic crystal films have also been imaged using a SEM. A linear equation for the prediction of the SNP diameters for a given initial amount of ethanol is proposed based on the centrifuged SNP diameters. The particle diameter measurements for the new equation were recorded using a DLS instrument. The dispersion of the SNPs was also recorded using DLS. The morphology of the surface of the particles has been confirmed using TEM micrographs. 相似文献
74.
Michael MillerFrank J. Owens 《Chemical physics》2012,394(1):52-55
Density functional theory is used to calculate the bond dissociation energy to cleave the C60C60 bond of the paramagnetic X-C60C60-X and X-C60C60 dimers where X is F, OH, O and H. The results show that these dimers would not be stable much above room temperature and therefore cannot constitute the paramagnetic phase needed to form the observed ferromagnetism which has been shown to be stable up to 800 K. The calculated bond dissociation energies to remove an F, OH or H from a single C60 are large suggesting that they could be the source of the unpaired spin needed for the high temperature ferromagnetism. 相似文献
75.
Evaluation of methods aimed at complete removal of template from molecularly imprinted polymers. 总被引:1,自引:0,他引:1
A Ellwanger C Berggren S Bayoudh C Crecenzi L Karlsson P K Owens K Ensing P Cormack D Sherrington B Sellergren 《The Analyst》2001,126(6):784-792
Polymers imprinted with clenbuterol were used to study the influence of various post-polymerization treatments [e.g., thermal annealing, microwave assisted extraction (MAE), Soxhlet extraction and supercritical fluid template desorption] on the bleeding of residual template. The aim of the study was to reduce the bleeding to levels that would allow the use of the materials as affinity phases for extraction of clenbuterol from bovine urine at concentrations below 1 ng ml-1. After treatment, the clenbuterol imprinted polymers were packed into solid-phase extraction columns and the bleeding was estimated by quantifying the amount of template released in 10 ml of methanol-acetic acid (9 + 1 v/v). This was followed by an assessment of selectivity and recovery in comparison with non-treated material. The lowest bleeding level was found after MAE using 100% trifluoroacetic acid for 3 x 20 min at 100 degrees C. The collected eluate contained in this case 3 ng ml-1 of clenbuterol. The same material was subsequently used for the extraction of clenbuterol from spiked bovine urine. The resulting selectivity and recovery were lower compared with those obtained using the untreated material. A milder but still efficient method to reduce the bleeding level was found to be MAE with formic acid. In this case a bleeding level of 14 ng ml-1 was found after only a 1 h extraction time. In a second model system, using a polymer imprinted with L-phenylalanine anilide, the bleeding was reduced to a similar level by extensive on-line washing in good swelling solvents containing acid or base additives and after thermal annealing of the polymers in the dry state. 相似文献
76.
Hydrogen gas is burned in air to raise and maintain the stagnation temperature of a supersonic combustion test facility to
a desired setpoint. In order to reach the desired operating conditions for stagnation temperature, there are three phases
to the hydrogen control; H2 ignition at facility start-up, H2 ramp-up while the facility is ramped-up, and H2 iteration to achieve the desired temperature setpoint. Each phase incorporates a different type of control. Fuzzy logic is
used to design a computer based supervisory controller that recognizes the different phases of operation and chooses the appropriate
control method.
Received: 28 November 1999/Accepted: 2 November 2000 相似文献
77.
A swept-potential electrochemical detector, operating in the square-wave voltammetric mode, is used to detect a mixture of five triazine pesticides separated on a reverse-phase resin column. Limits of detection are below 1 ng injected. Two compounds, not completely separated by the column, are resolved on the potential axis. 相似文献
78.
P. J. Owens 《Journal of Graph Theory》1985,9(3):381-395
We construct infinite sequences of non-Hamiltonian graphs and use them to show that the shortness exponent (or, in some cases, the shortness coefficient) is less than one for many classes of 3-connected planar graphs whose faces are all r-gons and whose vertices are all p-valent or q-valent, where p < q. Three of the five possible values of (r, p) are considered, namely (4.3). (3,3), and (3,4), in conjunction with most of the possible corresponding values of q. 相似文献
79.
The title complexes of general formula [Cu(HL)Cl2] or [Cu(L)Cl] were isolated from boiling EtOH. The thiosemicarbazones have
been characterized by their 1H- and 13C-n.m.r., i.r. and electronic spectra. The i.r., electronic and e.s.r. spectra of the
copper(II) complexes are compared with data on previously studied complexes. The antitumour and antiviral activities of the
thiosemicarbazones and their complexes are discussed.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
80.
M. M. Britton P. T. Callaghan M. L. Kilfoil R. W. Mair K. M. Owens 《Applied magnetic resonance》1998,15(3-4):287-301
We describe several different rheometric devices for use within the nuclear-magnetic-resonance probe of a standard widebore microimaging system. These include both vertical and horizontal Couette cells and the cone- and -plate cell, which produce shearing flows, and the four-roll mill and the opposed-jet (cross-flow junction) cells which produce extensional flow. We demonstrate that velocity images can be obtained for each and that detailed information about local shear and extension rates can be extracted. These systems have considerable potential for use in the study of non-Newtonian viscosity, and of molecular ordering under shear or extension. 相似文献