全文获取类型
收费全文 | 203篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 158篇 |
晶体学 | 1篇 |
力学 | 8篇 |
数学 | 11篇 |
物理学 | 33篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 7篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 9篇 |
2013年 | 6篇 |
2012年 | 19篇 |
2011年 | 17篇 |
2010年 | 9篇 |
2009年 | 12篇 |
2008年 | 15篇 |
2007年 | 21篇 |
2006年 | 11篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 9篇 |
2000年 | 1篇 |
1999年 | 3篇 |
1996年 | 6篇 |
1994年 | 2篇 |
1988年 | 1篇 |
1982年 | 1篇 |
1926年 | 1篇 |
排序方式: 共有211条查询结果,搜索用时 15 毫秒
181.
182.
Katia C. U. Mugnol Marccus V. A. Martins Edvaldo C. Nascimento Otaciro R. Nascimento Frank N. Crespilho Jeverson T. Arantes Iseli L. Nantes 《Theoretical chemistry accounts》2011,130(4-6):829-837
An organized multilayer was constructed by the layer-by-layer technique in which alternating layers of metalloporphyrin and dioctadecyldimethylammonium bromide bilayers were deposited onto an indium tin oxide surface electrode. The porphyrin molecules that are organized in the different layers showed a strong electroactivity with a well-defined electrochemical process. In LbL, electroactivity could be explained only by the occurrence of electron hoping. Thus, total Kohn?CSham density functional theory (KS-DFT) was performed to better understand the conditions responsible for the electroactivity of the metalloporphyrin layers intercalated by an insulating material. Total KS-DFT theory involves local density approximation energy calculations based on spin-polarized variant of KS-DFT theory. The results revealed a magnetization switching of the metalloporphyrin induced by the interaction with the surfactant bilayer accompanied by spin polarization of the porphyrin-interacting surfactant molecule. Although discrete, the surfactant magnetization had significant repercussions on the electron conductivity. Calculations also demonstrated loss of porphyrin symmetry promoted by a parent surfactant with a shorter hydrocarbon chain, ditetradecyldimethylammonium bromide. The calculation results were corroborated by experimental results obtained by the electron paramagnetic resonance and magnetic circular dichroism techniques. 相似文献
183.
Lourdes Urpí Katia Jimnez Xavier Solans Alfonso Rodríguez‐Galn Jordi Puiggalí 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(1):o24-o26
The β‐alanine residue of the title compound, C5H8ClNO3, has a ggt folded conformation, which is mainly stabilized through intermolecular N—H⋯O=C (amide–acid) and O—H⋯O=C (acid–amide) hydrogen bonds. In addition, a cis conformation is found for the Cl—CH2—C(=O)—NH torsion angle, which is associated with the presence of an intramolecular hydrogen bond. 相似文献
184.
Katia Arena Emanuela Trovato Francesco Cacciola Ludovica Spagnuolo Elisa Pannucci Paolo Guarnaccia Luca Santi Paola Dugo Luigi Mondello Laura Dugo 《Molecules (Basel, Switzerland)》2022,27(5)
Rhus coriaria L. (Anacardiaceae), commonly known as sumac, has been used since ancient times for many different applications, and nowadays is used mostly as a spice obtained from its in the Mediterranean and the Middle ground fruits and employed for flavoring and garnishing food, predominantly Eastern regions. Traditionally, sumac has been also used in popular medicine for the treatment of many ailments including hemorrhoids, wound healing, diarrhea, ulcers, and eye inflammation. Sumac drupes are indeed rich in various classes of phytochemicals including organic acids, flavonoids, tannins, and others, which are responsible of their powerful antioxidant capacity, from which treatment of many common diseases such as cardiovascular disease, diabetes, and cancer could benefit. In this work we evaluated the influence of fruit ripeness, conservation, and processing. To this aim, a phytochemical characterization of six different samples of Rhus coriaria L. was carried out. Specifically, headspace solid-phase micro extraction gas chromatography coupled to mass spectrometry and comprehensive two-dimensional liquid chromatography coupled to photodiode array and mass spectrometry detection, were employed. A total of 263 volatile compounds, including terpene hydrocarbons, acids, and aldehydes, as well as 83 polyphenolic compounds, mainly gallic acid derivatives, were positively identified. All samples showed a significant antioxidant activity by means of oxygen radical absorbance capacity, in line with their polyphenolic content and composition. Such findings set a solid ground to support the utilization of this plant as an attractive target for novel nutraceutical approaches and for drug discovery. 相似文献
185.
Analysis of type I and IV collagens by FT-IR spectroscopy and imaging for a molecular investigation of skeletal muscle connective tissue 总被引:2,自引:0,他引:2
Petibois C Gouspillou G Wehbe K Delage JP Déléris G 《Analytical and bioanalytical chemistry》2006,386(7-8):1961-1966
Many muscular diseases result from abnormal organization of connective tissue and/or collagen network formation. Only a few
molecular imaging techniques are able to analyze this collagen network by differentiating collagen types. In this study, FT-IR
spectroscopy was used to analyze type I and IV collagens, the most important compounds of which are perimysium and endomysium,
respectively. Secondary structure of collagen types was determined by curve-fitting the 1,700–1,480 cm−1 spectral interval. Type I collagen could be differentiated from type IV by its higher amounts of triple helix and α-helix,
but lower amounts of β-sheets (P < 0.01). FT-IR imaging was then used to determine structural features of perimysium and endomysium collagen network in bovine
Flexor carpi radialis muscle. Secondary structure of proteins contained in perimysium and endomysium was found to be very close to type I and IV
collagens, respectively. FT-IR spectroscopy and imaging are thus analytical tools that might be used for investigating biodistribution
and assembly of collagen types in connective tissues.
Figure Visible (left) and full spectral FT-IR (right) images of skeletal muscle tissue section (16 μm) exhibiting a vertical arrangement of fibers. + and × in FT-IR image show
selected positions to obtain FT-IR spectra of perimysium and endomysium, respectively 相似文献
186.
Excess molar enthalpies and heat capacities of binary mixtures containing dimethyl sulfoxide (DMSO) + seven normal alkanols, namely methanol, ethanol, propan-1-ol, butan-1-ol, hexan-1-ol, octan-1-ol, and decan-1-ol, have been determined at 303.15 K and atmospheric pressure. With the exception of the DMSO-methanol system, which shows negative values, all mixtures show positive values of excess molar enthalpies over the whole range of mole fraction, increasing as the number of carbon atoms increases. Heat capacities of pure components have been determined in the range 288.15 < T (K) < 325.15. Molar heat capacities of the mixtures are always positive and decrease as the number of carbon atoms decreases. The results were fitted to the Redlich-Kister polynomial equation. Molecular interactions in the mixtures are interpreted on the basis of the results obtained. 相似文献
187.
Eduardo J. Nassar Evelisy C. de O. Nassor Lilian R. Ávila Paula F. S. Pereira Alexandre Cestari Luiz M. Luz Katia J. Ciuffi Paulo S. Calefi 《Journal of Sol-Gel Science and Technology》2007,42(1):21-26
Organic–inorganic hybrid materials have been used as fillers to reinforce dental resin composites, which require strengthening
to improve their performance in large stress-bearing applications such as crowns and multiple-unit restorations. Homogeneous
organic–inorganic hybrid materials with high performance were prepared by mixing 3-methacryloxypropyltrimethoxysilane (MPTS)
and tetraethylorthosilicate (TEOS) synthesized by the sol–gel route. The matrix was prepared by hydrolyzing and condensing
the TEOS and MPTS, using basic catalysis and excess water. The resulting xerogel was treated at 50, 100, 150, and 200 °C for
4 h, and the structure was analyzed by thermogravimetry (TG/DTA), photoluminescence (PL), nuclear magnetic resonance (NMR
29Si and 13C), transmission electron microscopy (TEM), infrared spectroscopy (IR), and Raman spectroscopy. The PL spectra displayed the
Eu3+ lines characteristic of 5D0 → 7FJ (J = 0, 1, 2, 3, 4) ions, and the blue emission was ascribed to the silica matrix. TG, MNR and infrared spectroscopy analyses indicated the hybrid
silica was stable, with the organic part present up to 150 °C. Increasing the temperature of the heat treatment was found
to increase the degree of hydrolysis. The size and morphology of the silica particles were identified by TEM. 相似文献
188.
Simultaneous determination of different antibiotic residues in bovine and in porcine kidneys by solid-phase fluorescence immunoassay 总被引:5,自引:0,他引:5
Parallux, a solid-phase fluorescence immunoassay (SPFIA) developed for antibiotic residue detection in milk, was used for analysis of bovine and porcine kidney tissue. Four tetracyclines, 2 broad-spectrum cephalosporins, 3 beta-lactam antibiotics, and cephapirin were detected in one run after minimal sample preparation. This commercially available test system is designed as cartridges, each with a combination of 1-4 tests. One cartridge can be used to detect 4 analytes in the same sample, or 1 or 2 analytes in different samples. The cartridge with the combination tetracyclines-ceftiofur-penicillin-cephapirin was selected because tetracyclines, beta-lactam antibiotics as well as cephalosporins, are registered for oral or parenteral use in bovines and pigs in Europe. The test is qualitative and is recommended only for screening. Tetracycline, oxytetracycline, chlortetracycline, and doxycycline were easily detected at 300 ppb with the tetracyclines channel; ceftiofur at 1000 ppb and cefquinome at 200 ppb with the ceftiofur channel; penicillin G, ampicillin, and amoxicillin at 50 ppb with the penicillin channel; and cephapirin at 100 ppb with the cephapirin channel. These levels are equal to or lower than the corresponding maximal residue limits in kidney tissue. Cephalexin was not detected. The SPFIA test can be used as an alternative to classical inhibition tests and for post-screening inhibitor- positive kidneys, because it detects 3 specific groups of antibiotics, which enables selection of specific confirmatory methods for identification and quantification. 相似文献
189.
Van Hoof N De Wasch K Poelmans S Noppe H De Brabander H 《Rapid communications in mass spectrometry : RCM》2004,18(23):2823-2829
A multi-residue liquid chromatography/tandem mass spectrometry method (LC/MS2) was developed for the detection of the non-steroidal anti-inflammatory drugs acetylsalicylic acid (via the marker residue salicylic acid), flunixin, phenylbutazone, tolfenamic acid, meloxicam and ketoprofen, in bovine muscle. After extraction of the bovine muscle with acetonitrile, the cleanup was performed using a Oasis HLB column. The evaporated eluate was reconstituted and analysed by LC/MS2. To obtain optimal detection of salicylic acid and phenylbutazone, the ion trap mass spectrometric parameters activation q and maximum ion injection time, respectively, were optimised. The activation q for salicylic acid was increased to obtain reliable detection of both salicylic acid and its product ion. The maximum ion injection time for the time segment containing phenylbutazone was decreased since there were not enough scans across the chromatographic peak of this compound. The multi-residue method was able to detect the different analytes below or at the maximum residue limit (MRL) or minimum required performance limit (MRPL) or, in the case of phenylbutazone and ketoprofen, at 100 and 20 microg kg(-1), respectively. 相似文献
190.
The use of estrogens, gestagens and androgens (EGAs) in animal fattening is prohibited in the European Community. Based on the general detection capabilities of Belgian laboratories, National Minimum Required Performance Limits (National MRPLs) for a number of EGAs have been imposed by the inspection services. Selective hyphenated techniques, e.g. GC–MS and GC–MS2, with high detection capability are needed. β-Trenbolone, which is meant to be a “problem” molecule for GC–MS, can be detected at the 2 μg/kg level using GC–MS2. Based on the National MRPLs in different matrices, our laboratory has divided the EGAs into a class system. In this set-up, analysis of EGAs in kidney fat and meat is discussed. 相似文献