全文获取类型
收费全文 | 443篇 |
免费 | 20篇 |
国内免费 | 5篇 |
专业分类
化学 | 272篇 |
晶体学 | 1篇 |
力学 | 7篇 |
数学 | 75篇 |
物理学 | 113篇 |
出版年
2023年 | 5篇 |
2022年 | 2篇 |
2021年 | 13篇 |
2020年 | 8篇 |
2019年 | 13篇 |
2018年 | 5篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 10篇 |
2014年 | 16篇 |
2013年 | 33篇 |
2012年 | 33篇 |
2011年 | 24篇 |
2010年 | 15篇 |
2009年 | 27篇 |
2008年 | 33篇 |
2007年 | 19篇 |
2006年 | 17篇 |
2005年 | 16篇 |
2004年 | 16篇 |
2003年 | 9篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1999年 | 4篇 |
1998年 | 4篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 2篇 |
1992年 | 12篇 |
1991年 | 3篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 1篇 |
1959年 | 1篇 |
1958年 | 1篇 |
1937年 | 2篇 |
1931年 | 1篇 |
1927年 | 1篇 |
排序方式: 共有468条查询结果,搜索用时 250 毫秒
81.
Ana M. Gutierrez Antoine Brimont Mariam Aamer Pablo Sanchis 《Optics Communications》2012,285(6):1144-1147
In this paper, a method for measuring waveguide propagation losses by means of a Mach–Zehnder Interferometer (MZI) structure is reported. The method, based on the analysis of the transmission spectra of asymmetric MZIs, enables the propagation losses of the optical waveguides to be calculated without the requirement of identical coupling conditions for each measurement. In addition, the power imbalance of the branching structure in the MZI can also be obtained. Our theoretical analysis is supported by experimental measurements. 相似文献
82.
A general and easy-to-code numerical method based on radial basis functions
(RBFs) collocation is proposed for the solution of delay differential equations
(DDEs). It relies on the interpolation properties of infinitely smooth RBFs, which allow
for a large accuracy over a scattered and relatively small discretization support.
Hardy's multiquadric is chosen as RBF and combined with the Residual Subsampling
Algorithm of Driscoll and Heryudono for support adaptivity. The performance
of the method is very satisfactory, as demonstrated over a cross-section of
benchmark DDEs, and by comparison with existing general-purpose and specialized
numerical schemes for DDEs. 相似文献
83.
Cesar Hervs Pedro Antonio Gutierrez Manuel Silva Juan Manuel Serrano 《Journal of Chemometrics》2007,21(12):567-577
This is a study of the potential of neural networks built by using different transfer functions (sigmoidal, product and sigmoidal–product units) designed by an evolutionary algorithm to quantify highly overlapping electrophoretic peaks. To test this approach, two aminoglycoside antibiotics, amikacin and paramomycin, were quantified from samples containing either only one component or mixtures of them though capillary zone electrophoresis (CZE) with laser‐induced fluorescence (LIF) detection. The three models assayed used as input data the four‐parameter Weibull curve associated with the profile of the electrophoretic peak and in some cases the class label for each sample estimated by cluster analysis. The combination of classification and regression approaches allowed the establishment of straightforward network topologies enabling the analytes to be quantified with great accuracy and precision. The best models for mixture samples were provided by product unit neural networks (PUNNs), 4:4:1 (14 weights) for both analytes, after discrimination by cluster analysis, allowing the analytes to be quantified with great accuracy: 8.2% for amikacin and 5.6% for paromomycin within the standard error of prediction for the generalization test, SEPG. For comparison, partial least square regression was also used for the resolution of these mixtures; it provided a minor accuracy: SEPG 11.8 and 15.7% for amikacin and paramomycin, respectively. The reduced dimensions of the neural networks models selected enabled the derivation of simple quantification equations to transform the input variables into the output variable. These equations can be more easily interpreted from a chemical point of view than those provided by other ANN models. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
84.
Jhoel S. Gutierrez 《代数通讯》2020,48(4):1510-1527
AbstractWe study homological approximations of the profinite completion of a limit group (see Thm. A) and obtain the analogous of Bridson and Howie’s Theorem for the profinite completion of a non-abelian limit group (see Thm. B). 相似文献
85.
C. J. Gutierrez S. H. Mayer J. C. Walker 《Journal of magnetism and magnetic materials》1989,80(2-3):299-304
We have grown good quality single crystal heterostructures of Fe(110) / Ag(111) with a high degree of epitaxy not previously achieved for films this thin. The iron-free mica substrates are transparent to gamma rays and aid in the epitaxial growth process. These films were characterized by reflection high-energy electron diffraction (RHEED), residual gas analysis (RGA), and transmission Mössbauer spectroscopy. The film with the thickest Fe component (8 monolayers) showed a hyperfine field comparable to bulk while the films with the thinnest Fe components (1.3 and 2.0 monolayers) showed an enhanced hyperfine field at 4.2 K. All the films were magnetically ordered at all the temperatures measured. Most importantly, and in contrast to other work, the direction of magnetization was in-plane for all of the films. 相似文献
86.
87.
88.
In terms of a standard model for English auctions and sealed-bid auctions, we study the impact of an increase in bidding competition and in variance of the distribution of valuations on the winner's expected rent using tools from order statistics and stochastic ordering. 相似文献
89.
Alverson G Baker WF Ballocchi G Benson R Berg D Blusk S Bromberg C Brown D Carey D Chand T Chandlee C Choudhary BC Chung WH de Barbaro L DeSoi W Dlugosz W Dunlea J Easo S Engels E Faissler W Fanourakis G Ferbel T Garelick D Ginther G Glass G Glaubman M Gutierrez P Hartman K Huston J Johnstone C Kapoor V Kourbanis I Lanaro A Lirakis C Lobkowicz F Lukens P Mani S Maul A Mansour J Miller R Nelson CA Oh B Orris D Pothier E Prebys E Rajaram BM Roser R Ruddick K Shepard P Shivpuri RK Sinanidis A 《Physical review letters》1992,68(17):2584-2587
90.
Araujo K Colina M Mazurek R Delgado J Ledo H Gutierrez E Herrera L 《Analytical and bioanalytical chemistry》1996,355(3-4):319-320
The mercury concentrations in wastewater and sewage sludge of a stabilization pond system have been evaluated. The system is built by three parallel facultative ponds followed by two systems of three maturation ponds in series. The samples of wastewater and sludge were digested using nitric acid and placed into a Parr-type bomb for 4 h at 110 degrees C. Mercury was measured by Cold Vapour Atomic Absorption Spectrometry (CV-AAS) at 253.7 nm with sodium tetrahydroborate as reductant. The methodologies were checked with an USEPA quality control sample, a standard reference material from NIST and with another method of mineralization (cold mineralization) showing good results. Concentrations of mercury in wastewater between 1.47 +/- 0.75 microgl(-1) have been found at the entrance of the system and 0.74 +/- 0.0 microgl(-1) at the exit, while in sludge the results were between 0.29 +/- 0.12 microgkg(-1) in the facultative pond and 0.04 +/- 0.02 microgkg(-1) in the second maturation pond (exit). 相似文献