全文获取类型
收费全文 | 218篇 |
免费 | 4篇 |
国内免费 | 2篇 |
专业分类
化学 | 169篇 |
晶体学 | 1篇 |
力学 | 1篇 |
数学 | 25篇 |
物理学 | 28篇 |
出版年
2023年 | 1篇 |
2022年 | 11篇 |
2021年 | 7篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 5篇 |
2017年 | 5篇 |
2016年 | 7篇 |
2015年 | 7篇 |
2014年 | 2篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 13篇 |
2010年 | 5篇 |
2009年 | 15篇 |
2008年 | 9篇 |
2007年 | 6篇 |
2006年 | 8篇 |
2005年 | 11篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1993年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 7篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1889年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 234 毫秒
101.
Grossel A Zeninari V Joly L Parvitte B Courtois D Durry G 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,63(5):1021-1028
Atmospheric methane was detected by combining a photoacoustic (PA) sensor with several lasers emitting in both the near- and mid-infrared spectral ranges to check the achievable detection limits. The PA spectrometer is based on differential Helmholtz resonance. Near-infrared telecommunication-type laser diodes of increasing power, from Sensors Unlimited Inc. and Anritsu, were first used to scan the 2 nu(3) band of CH(4) near 1.65 microm. The best achieved detection limit is 0.15 ppm of methane at atmospheric pressure and with a 1s integration time. The PA sensor was then operated in conjunction with a quantum cascade laser from Alpes Lasers emitting near 7.9 microm on the nu(4) band of CH(4). The achieved detection limit is then of 3 ppb. The dramatic improvement in the detection limit obtained with the QC laser is due to the stronger optical power as well as to the capability of reaching the fundamental bands of methane lying in the mid-infrared spectral range. 相似文献
102.
Lilian Buzer 《Computational Geometry》2009,42(1):45-59
For a given polygonal chain, we study the min-# problem, which consists of finding an approximate and ordered subchain with a minimum number of vertices under a given approximation criterion. We propose the first near-linear time algorithm for the min-# problem that ensures optimality in the number of vertices and that retains the shape of the input polygonal chain at the same time. Previous algorithms with near-linear time performance produced geometrical inconsistencies and former methods used to preserve the features of the original chain required a quadratic time complexity. When we set the approximation error equal to the pixel pitch, our simplification criterion guarantees that the rendering of the simplification lies at most half a pixel away from the original chain, contrary to other methods that do not offer a direct control over the rendering. Thus, we avoid producing visible topological inconsistencies. Moreover, our method is based on basic data structures, which leads to a simple and efficient implementation. 相似文献
103.
Eduardo J. Nassar Lilian R. Avila Cesar Mello Katia J. Ciuffi 《Journal of luminescence》2005,111(3):159-166
The sol-gel method using metal alkoxide has been investigated to prepare aluminum-yttrium oxide as yttrium-aluminum garnet (YAG) matrix composite fiber. In this paper we investigate the influence of yttrium content and temperature in the synthesis of Eu(III)-doped aluminum-yttrium oxide by non-hydrolytic sol-gel route. The formation process and the local structure of the samples were discussed by means of X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. For temperatures around 800 °C, initial crystallization was observed and the phases Y4Al2O9 (YAM) and Y3Al5O12 (YAG) appear. For samples treated at 800 and 1500 °C the emission spectra display preferentially the f-f transitions characteristic of the YAM monoclinic phase, whereas the YAG cubic appears as the favored phase at 1100 °C, in accordance with the Eu(III) centrosymmetrical local site. 相似文献
104.
Vibrational properties of C20-based solids 总被引:6,自引:0,他引:6
Spagnolatti I. Mussi A. Bernasconi M. Benedek G. 《The European Physical Journal B - Condensed Matter and Complex Systems》2004,38(2):143-145
The European Physical Journal B - The phonon dispersion relations and IR spectrum of a C20-based solid recently identified experimentally [Iqbal et&;nbsp;al. , Eur. Phys. J. B 31, 509 (2003)]... 相似文献
105.
Erix Wiliam Hernández‐Rodríguez Ana Lilian Montero‐Alejo Rafael López Elsa Sánchez‐García Luis Alberto Montero‐Cabrera José Manuel García de la Vega 《Journal of computational chemistry》2013,34(28):2460-2471
Spectral shifts of rhodopsin, which are related to variations of the electron distribution in 11‐cis‐retinal, are investigated here using the method of deformed atoms in molecules. We found that systems carrying the M207R and S186W mutations display large perturbations of the π‐conjugated system with respect to wild‐type rhodopsins. These changes agree with the predicted behavior of the bond length alternation (BLA) and the blue shifts of vertical excitation energies of these systems. The effect of the planarity of the central and Schiff‐base regions of retinal chain on the electronic structure of the chromophore is also investigated. By establishing nonlinear polynomial relations between BLA, chain distortions, and vertical excitation energies, we are also able to provide a semiquantitative approach for the understanding of the mechanisms regulating spectral shifts in rhodopsin and its mutants. © 2013 Wiley Periodicals, Inc. 相似文献
106.
Instrumental neutron activation analysis for assessing homogeneity of a whole rice candidate reference material 总被引:1,自引:0,他引:1
Lilian Seiko Kato Elisabete A. De Nadai Fernandes Márcio Arruda Bacchi Camila Elias Silvana R. Vicino Sarriés Gabriel Adrián Sarriés Paula Sancinetti Modolo 《Journal of Radioanalytical and Nuclear Chemistry》2013,297(2):271-275
A whole rice reference material was prepared for use in quality control of trace elements in rice and in similar matrices. This study aimed at evaluating the homogeneity of the material. As, Br, Co, Cs, Fe, K, Na, Rb and Zn were determined in the samples by instrumental neutron activation analysis. The material is homogeneous for the elements determined (p < 0.05), except for Co and Fe, which presented dispersion of results much higher than the predicted degree of repeatability. 相似文献
107.
We examine the roles of vision and leadership in creating and directing Fermi National Accelerator Laboratory from the late 1960s through the 1980s. The story divides into two administrations having different problems and accomplishments, that of Robert R. Wilson from 1967-1978, which saw the transformation from cornfield to frontier physics facility, and that of Leon M. Lederman from 1979-1989, in which the laboratory evolved into one of the world's major high-energy facilities. Lederman's pragmatic vision of a user-based experimental community helped him to convert the pioneering facility that Wilson had built frugally into a laboratory with a stable scientific, cultural, and funding environment. 相似文献
108.
1 IntroductionSpectralmethodemploysglobalpolynomialsastrialfunctionsinspatialdiscretizationofdifferentialequations.Itoftenprovidesaccuratenumericalresultswithrelativelylessdegreeoffreedoms,andthushasbeensuccessfullyusedforcomputationsinscienceandengin… 相似文献
109.
Alexandre G. S. Prado André L. F. Santos Carolina P. Pedroso Thiago O. Carvalho Lilian R. Braga Sheila M. Evangelista 《Journal of Thermal Analysis and Calorimetry》2011,106(2):415-420
Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications due to its biocompatibility,
high charge density, and non-toxicity. In this study, chitosan microspheres were successfully prepared by an adapted method
of coagulation/dispersion. The degree of deacetylation of chitosan powder was obtained by NMR 1H and FTIR techniques. Chitosan powder and chitosan microspheres were characterized by BET surface area and scanning electron
microscopy (SEM). The interactions among the chitosan microspheres and the vitamins A and E were characterized by FTIR. In order to evaluate
the ability of interaction of vitamin A and vitamin E with the chitosan microspheres, the thermodynamic parameters were followed
by calorimetric titration. Different experimental approaches were applied, such as adsorption isotherms, kinetics and thermodynamics
studies. The obtained results showed that the interactions of chitosan microspheres with the vitamins were spontaneous, enthalpically
and entropically favorable, indicating that the chitosan microspheres can be used with success in the controlled release of
these vitamins. 相似文献
110.
DNA is the biopolymer most studied by scanning probe methods, and it is now possible to obtain reliable and reproducible images of DNA using atomic force microscopy (AFM). AFM has been extensively used to elucidate morphological changes to DNA structure, such as the formation of knots, nicks, supercoiling and bends. The mitochondrial or kinetoplast DNA (kDNA) of trypanosomatids is the most unusual DNA found in nature, being unique in organization and replication. The kDNA is composed of thousands of topologically interlocked DNA circles that form a giant network. To understand the biological significance of the kinetoplast DNA, it is necessary to learn more about its structure. In the present work, we used two procedures to prepare kDNA networks of Crithidia fasciculata for observation by AFM. Because AFM allows for the examination of kDNA at high resolution, we were able to identify regions of overlapping kDNA molecules and sites where several molecules cross. This found support the earlier described kDNA structural organization as composed by interlocked circles. We also observed an intricate high-density height pattern around the periphery of the network of C. fasciculata, which appears to be a bundle of DNA fibers that organizes the border of the network. Our present data confirm that AFM is a powerful tool to study the structural organization of biological samples, including complex arrays of DNA such as kDNA, and can be useful in revealing new details of structures previously visualized by other means. 相似文献