全文获取类型
收费全文 | 283篇 |
免费 | 7篇 |
国内免费 | 2篇 |
专业分类
化学 | 196篇 |
晶体学 | 2篇 |
力学 | 4篇 |
数学 | 18篇 |
物理学 | 72篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 17篇 |
2012年 | 16篇 |
2011年 | 36篇 |
2010年 | 18篇 |
2009年 | 13篇 |
2008年 | 11篇 |
2007年 | 11篇 |
2006年 | 16篇 |
2005年 | 16篇 |
2004年 | 5篇 |
2003年 | 13篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 7篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1972年 | 3篇 |
1969年 | 1篇 |
排序方式: 共有292条查询结果,搜索用时 31 毫秒
101.
In this paper, we present a validated UPLC‐MS/MS assay for determination of ramipril and ramiprilat from human plasma samples. The assay is capable of isolating phase II metabolites (acylglucornides) of ramipril from in vivo study samples which is otherwise not possible using conventional HPLC conditions. Both analytes were extracted from human plasma using solid‐phase extraction technique. Chromatographic separation of analytes and their respective internal standards was carried out using an Acquity UPLC BEH C18 (2.1 × 100 mm), 1.7 µm column followed by mass spectrometric detection using an Waters Quattro Premier XE. The method was validated over the range 0.35–70.0 ng/mL for ramipril and 1.0–40.0 ng/mL for ramiprilat. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
102.
Bloch et al. mapped the precession of the spin-half in a magnetic field of variable magnitude and direction to the rotations of a rigid sphere rolling on a curved surface utilizing SU(2)–SO(3) isomorphism. This formalism is extended to study the behaviour of spin–orbit interactions and the mechanical analogy for Rashba–Dresselhauss spin–orbit interaction in two dimensions is presented by making its spin states isomorphic to the rotations of a rigid sphere rolling on a ring. The change in phase of spin is represented by the angle of rotation of sphere after a complete revolution. In order to develop the mechanical analogy for the spin filter, we find that perfect spin filtration of down spin makes the sphere to rotate at some unique angles and the perfect spin filtration of up spin causes the rotations with certain discrete frequencies. 相似文献
103.
We describe a NMR strategy to resolve temperature-gradient-monitored real-time chemical reaction involving a [3 + 3]-cyclocondensation reaction between alkynone and ethyl 2-amino-1H-indole-3-carboxylate toward the synthesis of pyrimido[1,2-a]indole catalyzed by Cs2CO3. The in situ NMR study clearly indicates that the reactant undergoes [3 + 3]-cyclocondensation reaction through a concerted mechanism, resulting in the product formation. The detailed NMR spectroscopic data led to the optimization of the reaction conditions and quantitative analysis of the product accurately and efficiently. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file. 相似文献
104.
Baryon-antibaryon widths of the “true” diquoniums are calculated using the quark-pair-creation model, otherwise very successful for the decays of ordinary baryons and mesons. The resulting widths are one order of magnitude smaller than generally believed. Combined with an earlier study of diquonium decays into mesonic channels, this would avoid the need for “mock” configurations and make it difficult to interpret structures with widths ≈ 100 MeV as diquoniums. 相似文献
105.
Rane MR Sarode PD Chaudhari BL Chincholkar SB 《Applied biochemistry and biotechnology》2008,151(2-3):665-675
Biocontrol ability of Pseudomonas aeruginosa ID 4365, a biocontrol agent of groundnut phytopathogens from marine origin, was previously attributed to the production of pyoverdin type of siderophores. However, pyoverdin-rich supernatants of this organism showed better antifungal activity compared to equivalent amount of purified pyoverdin indicating presence of undetected metabolite(s) in pyoverdin rich supernatants. On the basis of observation that antagonistic activity was iron-dependent and iron-independent, an attempt was made to detect the presence of additional metabolites. In addition to pyoverdin, strain produced additional siderophores, viz. pyochelin and salicylic acid. Two broad spectrum antifungal compounds, viz. pyocyanin and phenazine-1-carboxylic acid, were detected, characterized, and activity against phytopathogens was demonstrated. Iron- and phosphate-dependent co-production of siderophores and phenazines was confirmed. Strain showed additional features like production of hydrogen cyanide, indol-3-acetic acid, and phosphate solubilization. 相似文献
106.
Jacob JA Mahal HS Biswas N Mukherjee T Kapoor S 《Langmuir : the ACS journal of surfaces and colloids》2008,24(2):528-533
We demonstrate that dihydroxy benzenes are excellent reducing agents and may be used to reduce silver ions to synthesize stable silver nanoparticles in air-saturated aqueous solutions. The formation of Ag nanoparticles in deaerated aqueous solution at high pH values suggests that the reduction of silver ions occurs due to oxidation of dihydroxy benzenes and probably on the surface of Ag2O. Pulse radiolysis studies show that the semi-quinone radical does not participate in the reduction of silver ions at short time scales. Nevertheless, results show that primary intermediates undergo slower transformation in the presence of dihydroxy benzenes than in their absence. This slow transformation eventually leads to the formation of silver nanoparticles. The Ag nanoparticles were characterized by UV-vis absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). XRD and TEM techniques showed the presence of Ag nanoparticles with an average size of 30 nm. 相似文献
107.
P. Shanmugavadivu V. Sivakumar Rashmi Sudhir 《The European physical journal. Special topics》2016,225(1):137-146
A new Fractal Dimension-based diagnosis technique for the change detection and time-series analysis of masses in the temporal digital mammogram is presented in this paper. As the digital mammograms are confirmed as a reliable source for the prognosis of breast cancer, the demand for the development of precise computer aided detection techniques is constantly on the increase. This formed the basis for the development of this method using Fractal geometry, which is an efficient mathematical approach that deals with self-similar and irregular geometric objects called fractals. This work comprises of the detection of spatial masses using Fractal Hurst bound enhancement and segmentation of those temporal masses using Fractal Thresholding. The consultant radiologist’s assessment of mass lesions forms the baseline for comparison and validation of the detected masses. Further, this research work performs temporal analysis of mass lesions, detected from the mammograms of the current and the respective prior view using the principle of Fractal Dimension. The precision of Fractal-dimension based temporal texture analysis of malignant masses of digital mammograms subsequently attributes to their characterization. 相似文献
108.
Aqueous solutions of amphiphilic polymers usually comprise of inter- and intramolecular associations of hydrophobic groups often leading to a formation of a rheologically significant reversible network at low concentrations that can be identified using techniques such as static light scattering and rheometry. However, in most studies published till date comparing water soluble polymers with their respective amphiphilic derivatives, it has been very difficult to distinguish between the effects of molecular mass versus hydrophobic associations on hydrodynamic (intrinsic viscosity [η]) and thermodynamic parameters (second virial coefficient A 2), owing to the differences between their degrees of polymerization. This study focuses on the dilute and semi-dilute solutions of hydroxyethyl cellulose (HEC) and its amphiphilic derivatives (hmHEC) of the same molecular mass, along with other samples having a different molecular mass using capillary viscometry, rheometry and static light scattering. The weight average molecular masses (M W ) and their distributions for the non-associative HEC were determined using size exclusion chromatography. Various empirical approaches developed by past authors to determine [η] from dilute solution viscometry data have been discussed. hmHEC with a sufficiently high degree of hydrophobic modification was found to be forming a rheologically significant network in dilute solutions at very low concentrations as opposed to the hmHEC with a much lower degree of hydrophobic modification which also enveloped the hydrophobic groups inside the supramolecular cluster as shown by their [η] and A 2. The ratio A 2 M W /[η], which takes into account hydrodynamic as well as thermodynamic parameters, was observed to be less for associative polymers compared to that of the non-associative polymers. 相似文献
109.
Chita Ranjan Sahoo Jyotirmaya Sahoo Monalisa Mahapatra Debananda Lenka Pratap Kumar Sahu Budheswar Dehury Rabindra Nath Padhy Sudhir Kumar Paidesetty 《Arabian Journal of Chemistry》2021,14(2):102922
Nowadays, bacterial infections epitomize significant health threats globally with an increased morbidity and mortality. Most contemporary antibacterial agents are resisted by pathogenic bacteria - the multidrug resistant (MDR) bacterial strains arising from cross resistances operative in natural bacterial consortia inside human body and in environments. Consequently, the development of newer potential drug candidate(s) is required against the broad spectrum of MDR bacteria. Indeed, the phytochemical coumarin and its derivatives had been reported with broad biological inhibitory properties, including antibacterial activities. In this review, several methods of synthetic strategies of coumarin derivatives as antibacterials were considered with individual schematic compounds by structure-activity relationship (SAR) studies as essential corollaries. Overall, substituents at positions C-3 and C-4 of coumarin are coveted for the development of newer antibacterial agents. 相似文献
110.
Improving carbon dioxide solubility in ionic liquids 总被引:4,自引:0,他引:4
Muldoon MJ Aki SN Anderson JL Dixon JK Brennecke JF 《The journal of physical chemistry. B》2007,111(30):9001-9009
Previously we showed that CO2 could be used to extract organic molecules from ionic liquids without contamination of the ionic liquid. Consequently a number of other groups demonstrated that ionic liquid/CO2 biphasic systems could be used for homogeneously catalyzed reactions. Large differences in the solubility of various gases in ionic liquids present the possibility of using them for gas separations. More recently we and others have shown that the presence of CO2 increases the solubility of other gases that are poorly soluble in the ionic liquid phase. Therefore, a knowledge and understanding of the phase behavior of these ionic liquid/CO2 systems is important. With the aim of finding ionic liquids that improve CO2 solubility and gaining more information to help us understand how to design CO2-philic ionic liquids, we present the low- and high-pressure measurements of CO2 solubility in a range of ionic liquids possessing structures likely to increase the solubility of CO2. We examined the CO2 solubility in a number of ionic liquids with systematic increases in fluorination. We also studied nonfluorinated ionic liquids that have structural features known to improve CO2 solubility in other compounds such as polymers, for example, carbonyl groups and long alkyl chains with branching or ether linkages. Results show that ionic liquids containing increased fluoroalkyl chains on either the cation or anion do improve CO2 solubility when compared to less fluorinated ionic liquids previously studied. It was also found that it was possible to obtain similar, high levels of CO2 solubility in nonfluorous ionic liquids. In agreement with our previous results, we found that the anion frequently plays a key role in determining CO2 solubility in ionic liquids. 相似文献