全文获取类型
收费全文 | 195篇 |
免费 | 3篇 |
专业分类
化学 | 111篇 |
晶体学 | 2篇 |
力学 | 10篇 |
数学 | 21篇 |
物理学 | 54篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 9篇 |
2020年 | 5篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 4篇 |
2014年 | 6篇 |
2013年 | 21篇 |
2012年 | 11篇 |
2011年 | 25篇 |
2010年 | 6篇 |
2009年 | 11篇 |
2008年 | 6篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1995年 | 3篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1979年 | 1篇 |
排序方式: 共有198条查询结果,搜索用时 31 毫秒
91.
E. S. Freitas Neto S. W. da Silva P. C. Morais M. I. Vasilevskiy M. A. Pereira‐da‐Silva N. O. Dantas 《Journal of Raman spectroscopy : JRS》2011,42(8):1660-1669
Optical phonon modes, confined in CdSxSe1−x nanocrystal (NC) quantum dots (≈2 nm in radius) grown in a glass matrix by the melting‐nucleation method, were studied by resonant Raman scattering (RRS) spectroscopy and theoretical modeling. The formation of nanocrystalline quantum dots (QDs) is evidenced by the observation of absorption peaks and theoretically expected resonance bands in the RRS excitation spectra. This system, a ternary alloy, offers the possibility to investigate the interplay between the effects of phonon localization by disorder and phonon confinement by the NC/matrix interface. Based on the concept of propagating optical phonons, which is accepted for two‐mode pseudo‐binary alloys in their bulk form, we extended the continuous lattice dynamics model, which has successfully been used for nearly spherical NCs of binary materials, to the present case. After determining the alloy composition for NCs (that was evaluated with only 2–3% uncertainty using the bulk longitudinal optical phonon wavenumbers) and the NC size (using atomic force microscopy and optical absorption data), the experimental RRS spectra were described rather well by this theory, including the line shape and polarization dependence of the scattering intensity. Even though the presence of a compressive strain in the NCs (introduced by the matrix) masks the expected downward shift owing to the phonons' spatial quantization, the asymmetric broadening of both Raman peaks is similar to that characteristic of NCs of pure binary materials. Although with some caution, we suggest that both CdSe‐like and CdS‐like optical phonon modes indeed are propagating within the NC size unless the alloy is considerably heterogeneous. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
92.
E. A. Oliveira E. N. Silva A. R. Paschoal S. M. Dantas I. Guedes J. Mendes‐Filho G. Polla A. P. Ayala 《Journal of Raman spectroscopy : JRS》2011,42(7):1567-1573
Raman spectroscopy, polarized microscopy and thermal measurements were used to investigate the sequence of phase transition in the lead oxide salts Pb8O5(XO4)2 (where X = As and V). For Pb8O5(AsO4)2, a second‐order phase transition is observed at 500 K. For Pb8O5(VO4)2, a second‐order and a first‐order structural phase transitions are observed at 425 and 525 K, respectively. The ferroelastic character of Pb8O5(VO4)2 is also discussed. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
93.
A compact miniaturized continuous flow system for the determination of urea content in milk 总被引:1,自引:0,他引:1
Willian Toito Suarez Osmundo Dantas Pessoa-Neto Vagner Bezerra dos Santos Ana Rita de Araujo Nogueira Ronaldo Censi Faria Orlando Fatibello-Filho Mar Puyol Julián Alonso 《Analytical and bioanalytical chemistry》2010,398(3):1525-1533
A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed
with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically
integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase
reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the
urea concentration range from 1.0 × 10−4 to 5.0 × 10−3 mol L−1 with a limit of detection of 8.0 × 10−6 mol L−1. The relative standard deviation (RSD) for a 2.0 × 10−3 mol L−1 urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h−1. To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different
days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the
data are in close agreement, at a 95% confidence level. 相似文献
94.
Caris JA Silva BJ Moisés EC Lanchote VL Queiroz ME 《Journal of separation science》2012,35(5-6):734-741
A sensitive, selective, and reproducible in-tube solid-phase microextraction and liquid chromatographic (in-tube SPME/LC-UV) method for determination of lidocaine and its metabolite monoethylglycinexylidide (MEGX) in human plasma has been developed, validated, and further applied to pharmacokinetic study in pregnant women with gestational diabetes mellitus (GDM) subjected to epidural anesthesia. Important factors in the optimization of in-tube SPME performance are discussed, including the draw/eject sample volume, draw/eject cycle number, draw/eject flow rate, sample pH, and influence of plasma proteins. The limits of quantification of the in-tube SPME/LC method were 50 ng/mL for both metabolite and lidocaine. The interday and intraday precision had coefficients of variation lower than 8%, and accuracy ranged from 95 to 117%. The response of the in-tube SPME/LC method for analytes was linear over a dynamic range from 50 to 5000 ng/mL, with correlation coefficients higher than 0.9976. The developed in-tube SPME/LC method was successfully used to analyze lidocaine and its metabolite in plasma samples from pregnant women with GDM subjected to epidural anesthesia for pharmacokinetic study. 相似文献
95.
Atienza CM Fernández G Sánchez L Martín N Dantas IS Wienk MM Janssen RA Rahman GM Guldi DM 《Chemical communications (Cambridge, England)》2006,(5):514-516
A light absorbing pi-conjugated oligomer-tetrafullerene nanoarray has been synthesized and its photophysical study reveals the presence of an intramolecular energy transfer. A phototovoltaic device fabricated from this nanoarray and poly(3-hexylthiophene) shows an external quantum efficiency of 15% at 500 nm. 相似文献
96.
A. L. P. Fernandes W. A. Morais A. I. B. Santos A. M. L. de Araújo D. E. S. dos Santos D. S. dos Santos F. J. Pavinatto O. N. Oliveira Jr. T. N. C. Dantas M. R. Pereira J. L. C. Fonseca 《Colloid and polymer science》2005,284(1):1-9
Chitosan nanoparticles were obtained via ionic crosslinking by using the sulfate ion. Chitosan molecular weight was varied by oxidative degradation of the chitosan β-glycoside bond, the molecular weight being indirectly monitored as the chitosan solution reduced viscosity at a fixed polymer concentration. The dependence between some physical properties of the resultant dispersions (turbidity, viscosity, zeta potential, and sedimentation column profile) and reduced viscosity was established. Atomic force microscopy images have shown the resultant particles formed to be clusters of chitosan nanoparticles with a diameter of ca. 70 nm, the interaction between these particles being characterized by FTIR spectroscopy as the result of sulfate bridging. At the end of the paper, the potential of these dispersions for the incorporation of anionic drugs via adsorption was evaluated using a model compound. The resultant dispersions were capable of adsorbing more than 25% of mass of chitosan, being the partition coefficient higher than 3,500. 相似文献
97.
Raoul Plessius Rosa Kromhout Dr. André Luis Dantas Ramos Dr. Marilena Ferbinteanu Dr. Marjo C. Mittelmeijer‐Hazeleger Prof. Rajamani Krishna Prof. Gadi Rothenberg Dr. Stefania Tanase 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):7922-7925
We present a new metal–organic framework (MOF) built from lanthanum and pyrazine‐2,5‐dicarboxylate (pyzdc) ions. This MOF, [La(pyzdc)1.5(H2O)2] ? 2 H2O, is microporous, with 1D channels that easily accommodate water molecules. Its framework is highly robust to dehydration/hydration cycles. Unusually for a MOF, it also features a high hydrothermal stability. This makes it an ideal candidate for air drying as well as for separating water/alcohol mixtures. The ability of the activated MOF to adsorb water selectively was evaluated by means of thermogravimetric analysis, powder and single‐crystal X‐ray diffraction and adsorption studies, indicating a maximum uptake of 1.2 mmol g?1 MOF. These results are in agreement with the microporous structure, which permits only water molecules to enter the channels (alcohols, including methanol, are simply too large). Transient breakthrough simulations using water/methanol mixtures confirm that such mixtures can be separated cleanly using this new MOF. 相似文献
98.
99.
Clecio Dantas Romà Tauler Márcia Miguel Castro Ferreira 《Analytical and bioanalytical chemistry》2013,405(4):1293-1302
In this work, the application of multivariate curve resolution-alternating least squares (MCR-ALS) is proposed for extracting information from multitechnique fused multivariate data (UV–VIS absorption, fluorescence, and liquid chromatography–mass spectrometry) gathered during the biosynthesis of violacein pigment. Experimental data sets were pretreated and arranged in a row-wise augmented data matrix before their chemometric investigation. Five different chemical components were resolved. Kinetic and spectral information about these components were obtained and their relationship with violacein biosynthesis was established. Three new chemical compounds with molar masses of 453, 465, and 479 u, until now not reported in the literature, were identified and proposed as intermediates in the biosynthesis of other indolocarbazoles. The precursor (tryptophan), one intermediate (deoxyviolacein), and the final product (violacein) of violacein biosynthesis were identified and characterized using the proposed approach. The chemometric procedure based on the MCR-ALS method has proved to be a powerful tool to investigate violacein biosynthesis and its application can be easily extended to the study of other bioprocesses. 相似文献
100.
F. Sato A.S. Moreira P.Z. Coura S.O. Dantas S.B. Legoas D. Ugarte D.S. Galvão 《Applied Physics A: Materials Science & Processing》2005,81(8):1527-1531
Metallic nanowires (NWs) have been the object of intense theoretical and experimental investigations in the last years. In
this work we present and review a new methodology we developed to study NW formation from mechanical stretching. This methodology
is based on tight-binding molecular dynamics techniques using second-moment approximations. This methodology had been proven
to be very effective in the study of NWs, reliably reproducing the main experimentally observed structural features. We have
also investigated the problem of determining from what regions the atoms composing the linear atomic chains come. Our results
show that ∼90% of these atoms come from outmost external layers.
Electronic supplementary material Supplementary material is available in the online version of this article at
and is accessible for authorized users.
PACS 66.30.Pa; 68.65.-k; 68.03.Hj 相似文献