全文获取类型
收费全文 | 274篇 |
免费 | 25篇 |
专业分类
化学 | 187篇 |
力学 | 8篇 |
数学 | 35篇 |
物理学 | 69篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 13篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 20篇 |
2013年 | 15篇 |
2012年 | 23篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 4篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 2篇 |
1998年 | 4篇 |
1995年 | 2篇 |
1994年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1971年 | 1篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1955年 | 2篇 |
1954年 | 1篇 |
1953年 | 1篇 |
排序方式: 共有299条查询结果,搜索用时 281 毫秒
21.
22.
Mark E. Erupe Allegra Liberman-Martin Philip J. Silva Quentin G.J. Malloy Naomi Yonis David R. Cocker III Kathleen L. Purvis-Roberts 《Journal of chromatography. A》2010,1217(13):2070-2073
An ion chromatography method with non-suppressed conductivity detection was developed for the simultaneous determination of methylamines (methylamine, dimethylamine, trimethylamine) and trimethylamine-N-oxide in particulate matter air samples. The analytes were well separated by means of cation-exchange chromatography using a 3 mM nitric acid/3.5% acetonitrile (v/v) eluent solution and a Metrosep C 2 250 (250 mm × 4 mm i.d.) separation column. The effects of the different chromatographic parameters on the separation were also investigated. Detection limits of methylamine, dimethylamine, trimethylamine, and trimethylamine-N-oxide were 43, 46, 76 and 72 μg/L, respectively. The relative standard deviations of the retention times were between 0.42% and 1.14% while the recoveries were between 78.8% and 88.3%. The method is suitable for determining if methylamines and trimethylamine-N-oxide are a significant component of organic nitrogen aerosol in areas with high concentration of these species. 相似文献
23.
Frédéric Chazal David Cohen-Steiner Quentin Mérigot 《Foundations of Computational Mathematics》2011,11(6):733-751
Data often comes in the form of a point cloud sampled from an unknown compact subset of Euclidean space. The general goal
of geometric inference is then to recover geometric and topological features (e.g., Betti numbers, normals) of this subset
from the approximating point cloud data. It appears that the study of distance functions allows one to address many of these
questions successfully. However, one of the main limitations of this framework is that it does not cope well with outliers
or with background noise. In this paper, we show how to extend the framework of distance functions to overcome this problem.
Replacing compact subsets by measures, we introduce a notion of distance function to a probability distribution in ℝ
d
. These functions share many properties with classical distance functions, which make them suitable for inference purposes.
In particular, by considering appropriate level sets of these distance functions, we show that it is possible to reconstruct
offsets of sampled shapes with topological guarantees even in the presence of outliers. Moreover, in settings where empirical
measures are considered, these functions can be easily evaluated, making them of particular practical interest. 相似文献
24.
Quentin Araud Pascal Finaud‐Guyot Vincent Guinot Robert Mosé José Vazquez 《国际流体数值方法杂志》2012,70(12):1590-1604
Discontinuous Galerkin (DG) methods have shown promising results for solving the two‐dimensional shallow water equations. In this paper, the classical Runge–Kutta (RK) time discretisation is replaced by the eigenvector‐based reconstruction (EVR) that allows the second‐order time accuracy to be achieved within a single time‐stepping procedure. Moreover, the EVRDG approach yields stable solutions near drying and wetting fronts, whereas the classical RKDG approach yields instabilities. The proposed EVRDG technique is compared with the original RKDG approach on various test cases with analytical solutions. The EVRDG solutions are shown to be as accurate as those obtained with the RKDG scheme. Besides, the EVRDG scheme is 1.6 times faster than the RKDG method. Simulating dambreaks involving dry beds confirms that EVRDG scheme gives correct solutions, whereas the RKDG method yields instabilities. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
25.
We consider the design of multiple transit lines in a network and present a mixed integer formulation for this multiple-route
transit network design problem (MRTNDP). With the introduction of node labels, the formulation can exploit the route structure
and hence attains efficiency in obtaining a cost minimizing transit network design.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
26.
An analogy is presented between periodic persistent currents in mesoscopic rings and staggerings of gamma energy transitions
from some nuclear high-spin states. Various sources of damping of the expected periodic structures in both physical systems
are compared. This discussion provides, in the nuclear case, a tentative explanation of the scarcity of such staggerings,
their appearance near 150Gd and the existence of a spin-window for their observation.
Received: 21 July 1997 / Revised version: 13 October 1997 相似文献
27.
28.
Tailoring of carboxyl‐decorated magnetic latex particles using seeded emulsion polymerization 下载免费PDF全文
Talha Jamshaid Mohamed M. Eissa Quentin Lelong Anne Bonhommé Geraldine Augsti Nadia Zine Abdelhamid Errachid Abdelhamid Elaissari 《先进技术聚合物》2017,28(9):1088-1096
In this research, submicron and carboxyl‐functionalized magnetic latex particles were elaborated by using seeded emulsion polymerization technique in presence of oil‐in‐water (o/w) magnetic emulsion as seed. The polymerization conditions were optimized in order to get well‐defined latex particles with magnetic core and polymer shell bearing carboxylic (–COOH) functionality. Starting from (o/w) magnetic emulsion as seed, synthesis process was performed by copolymerization of styrene (St) monomer with the cross‐linker divinylbenzene (DVB) in presence of 4,4′‐azobis(4‐cyanopentanoic acid) (ACPA) as a carboxyl‐bearing initiator. The prepared magnetic latex particles were first characterized in terms of particle size, chemical composition, morphology, magnetic properties, magnetic content, and colloidal stability using various techniques, e.g. particle size analyzer using dynamic light scattering (DLS) technique, Fourier transform infrared, transmission electron microscopy, vibrating sample magnetometer, thermogravimetric analysis, and zeta potential measurements as a function of pH of the dispersion media, respectively. The prepared magnetic latex particles were then used as second seed for further functionalization with methacrylic acid (MAA) in order to enhance carboxylic groups on the magnetic particle's surface. The results showed that final magnetic latex particles possessed spherical morphology with core‐shell structure and enriched carboxylic acid functionality. More importantly, they exhibited superparamagnetism with high magnetic content (58.42 wt%) and high colloidal stability, which considered as the main requirements for their application in the biomedical diagnostic domains. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
29.
Shiran Shahar Pnina Hillman Rachel Lubart Debby Ickowicz Haim Breitbart 《Photochemistry and photobiology》2014,90(5):1077-1083
To acquire fertilization competence, spermatozoa must undergo several biochemical and motility changes in the female reproductive tract, collectively called capacitation. Actin polymerization and the development of hyperactivated motility (HAM) are part of the capacitation process. In a recent study, we showed that irradiation of human sperm with visible light stimulates HAM through a mechanism involving reactive‐oxygen‐species (ROS), Ca2+ influx, protein kinases A (PKA), and sarcoma protein kinase (Src). Here, we showed that this effect of light on HAM is mediated by ROS‐dependent activation of the epidermal growth factor receptor (EGFR). Interestingly, ROS‐mediated HAM even when the EGFR was activated by EGF, the physiological ligand of EGFR. Light irradiation stimulated ROS‐dependent actin polymerization, and this effect was abrogated by PBP10, a peptide which activates the actin‐severing protein, gelsolin, and causes actin‐depolymerization in human sperm. Light‐stimulated tyrosine phosphorylation of Src‐dependent gelsolin, resulting in enhanced HAM. Thus, light irradiation stimulates HAM through a mechanism involving Src‐mediated actin polymerization. Light‐stimulated HAM and in vitro‐fertilization (IVF) rate in mouse sperm, and these effects were mediated by ROS and EGFR. In conclusion, we show here that irradiation of sperm with visible light, enhances their fertilization capacity via a mechanism requiring ROS, EGFR and HAM. 相似文献
30.
Bricaud Q Fabre RM Brookins RN Schanze KS Reynolds JR 《Langmuir : the ACS journal of surfaces and colloids》2011,27(8):5021-5028
We present a study of Fo?rster resonance energy transfer (FRET) between two emissive conjugated polyelectrolytes (CPEs) in layer-by-layer (LbL) self-assembled films as a means of examining their organization and architecture. The two CPEs are a carboxylic acid functionalized polyfluorene (PFl-CO(2)) and thienylene linked poly(phenylene ethynylene) (PPE-Th-CO(2)). The PFl-CO(2) presents a maximum emission at 418 nm, while the PPE-Th-CO(2) has an absorption λ(max) centered at 431 nm, in sufficient proximity for effective FRET. Several LbL films have been constructed using varied concentrations of the deposition solutions and identity of the buffer layers separating the two emissive layers, using a system of either weak polyelectrolytes, poly(allylamine hydrochloride) (PAH)/poly(sodium methacrylate) (PMA), or strong polyelectrolytes, poly(diallylammonium chloride) (PDDA)/poly(styrene sulfonate) sodium (PSS). The efficiency of FRET has been monitored using fluorescence spectroscopy. Initially, the fluorescence of the PFl-CO(2) (E(g) ~ 3.0 eV), which emits at 420 nm, is quenched by the lower band gap PPE-Th-CO(2) (E(g) ~ 2.5 eV). For films using the PAH/PMA system as buffer bilayers and deposited from 1 mM solutions, the PFl-CO(2) fluorescence is progressively recovered as the number of intervening buffer bilayers is increased. Ellipsometry measurements indicate that energy transfer between the two emissive layers is efficient to a distance of ca. 7 nm. 相似文献