全文获取类型
收费全文 | 1716篇 |
免费 | 71篇 |
国内免费 | 11篇 |
专业分类
化学 | 1127篇 |
晶体学 | 3篇 |
力学 | 75篇 |
数学 | 300篇 |
物理学 | 293篇 |
出版年
2023年 | 14篇 |
2022年 | 45篇 |
2021年 | 46篇 |
2020年 | 35篇 |
2019年 | 36篇 |
2018年 | 26篇 |
2017年 | 18篇 |
2016年 | 69篇 |
2015年 | 55篇 |
2014年 | 80篇 |
2013年 | 102篇 |
2012年 | 122篇 |
2011年 | 137篇 |
2010年 | 83篇 |
2009年 | 62篇 |
2008年 | 103篇 |
2007年 | 107篇 |
2006年 | 105篇 |
2005年 | 109篇 |
2004年 | 85篇 |
2003年 | 75篇 |
2002年 | 46篇 |
2001年 | 22篇 |
2000年 | 14篇 |
1999年 | 15篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 4篇 |
1985年 | 6篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1978年 | 6篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
1921年 | 2篇 |
1868年 | 1篇 |
排序方式: 共有1798条查询结果,搜索用时 0 毫秒
51.
Nora Jannsen Dr. Stefano Diodati Nicola Dengo Francesca Tajoli Dr. Nicola Vicentini Dr. Giacomo Lucchini Prof. Adolfo Speghini Prof. Denis Badocco Prof. Paolo Pastore Prof. Silvia Gross 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(59):13624-13634
The aim of this work was i) to develop a hydrothermal, low-temperature synthesis protocol affording the upconverting hexagonal phase NaYF4 with suitable dopants while adhering to the “green chemistry” standards and ii) to explore the effect that different parameters have on the products. In optimizing the synthesis protocol, short reaction times and low temperatures (below 150 °C) were considered. Yb3+ and Er3+ ions were chosen as dopants for the NaYF4 material. Within the context of the second goal, parameters including nature of the precursors, treatment temperature, and treatment time were investigated to afford a pure hexagonal crystalline phase, both in the doped and undoped materials. To fully explore the synthesis results, the prepared materials were characterized from a structural (XRD), compositional (XPS, ICP-MS), and morphological (SEM) point of view. The upconverting properties of the compounds were confirmed by photoluminescence measurements. 相似文献
52.
Nicola Polloni 《Ambix》2020,67(2):135-152
The article examines the two Latin versions of Artephius's Clavis sapientiae (Key of Wisdom) that have been preserved in early modern collections of alchemical texts. A comparative analysis of the two versions shows that one of them has undergone a process of textual manipulation. In particular, an interpolation of short philosophical passages concerning the doctrine of prime matter has relevant interpretative implications. These additions appear to be grounded in the early thirteenth-century philosophical debate on cosmology and the first Latinate reception of Aristotle’s metaphysics. 相似文献
53.
54.
Andrea Giuntoli Nicola Calonaci Sebastiano Bernini Dino Leporini 《Journal of Polymer Science.Polymer Physics》2017,55(23):1760-1769
The relation between elasticity and yielding is investigated in a model polymer solid by Molecular‐Dynamics simulations. By changing the bending stiffness of the chain and the bond length, semicrystalline and disordered glassy polymers — both with bond disorder — as well as nematic glassy polymers with bond ordering are obtained. It is found that in systems with bond disorder the ratio τY/G between the shear yield strength τY and the shear modulus G is close to the universal value of the atomic metallic glasses. The increase of the local nematic order in glasses leads to the increase of the shear modulus and the decrease of the shear yield strength, as observed in experiments on nematic thermosets. A tentative explanation of the subsequent reduction of the ratio τY/G in terms of the distributions of the per‐monomer stress is offered. © 2017 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2017 , 55, 1760–1769 相似文献
55.
56.
57.
Roberto Terzano Matthias Alfeld Koen Janssens Bart Vekemans Tom Schoonjans Laszlo Vincze Nicola Tomasi Roberto Pinton Stefano Cesco 《Analytical and bioanalytical chemistry》2013,405(10):3341-3350
Iron (Fe) is an essential element for plant growth and development; hence determining Fe distribution and concentration inside plant organs at the microscopic level is of great relevance to better understand its metabolism and bioavailability through the food chain. Among the available microanalytical techniques, synchrotron μ-XRF methods can provide a powerful and versatile array of analytical tools to study Fe distribution within plant samples. In the last years, the implementation of new algorithms and detection technologies has opened the way to more accurate (semi)quantitative analyses of complex matrices like plant materials. In this paper, for the first time the distribution of Fe within tomato roots has been imaged and quantified by means of confocal μ-XRF and exploiting a recently developed fundamental parameter-based algorithm. With this approach, Fe concentrations ranging from few hundreds of ppb to several hundreds of ppm can be determined at the microscopic level without cutting sections. Furthermore, Fe (semi)quantitative distribution maps were obtained for the first time by using two opposing detectors to collect simultaneously the XRF radiation emerging from both sides of an intact cucumber leaf. Figure
Elemental distribution maps within intact tomato roots as determined by confocal micro X‐ray fluorescence 相似文献
58.
S-methyl dinucleoside phosphorothioates are prepared from 0-2,4-dichlorophenyl S-methyl nucleoside phosphorothioates by selective removal of the transient 0-2,4-dichlorophenyl protecting group followed by condensation with appropriate nucleosides in the presence of MSNT activating reagent. 相似文献
59.
Nicola A. Bailey Darran R. Cairns Gregory P. Crawford James N. Hay 《Liquid crystals》2013,40(12):1761-1765
A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T a, exhibited an endotherm at the transition which developed with extent of ageing time, t a. We attribute this endotherm to the relaxation of the glass towards the equilibrium liquid. The progress of the relaxation process was measured using differential scanning calorimetry. On subsequent reheating, the aged glass showed an apparent shift in the glass transition to higher temperatures. The endotherm was used to define the extent of enthalpic relaxation and the maximum value observed was found to increase initially then decrease, with the extent of undercooling from the glass transition temperature, Δ T, passing through a maximum for a Δ T = 15 K. From the temperature dependence of the relaxation times, an apparent activation enthalpy for the relaxation process of 85 ± 10 kJ mol-1 was determined. The small value of the activation enthalpy compared with that found in the ageing of polymers reflects differences in the molecular species involved in relaxation processes. 相似文献
60.
ABSTRACT Acyloxymethylation of an acylated silver salt of α-trinositol gives, after deprotection, membrane permeable 1D-myo-inositol 1,2,6-tris(ethoxycarbonyloxymethyl sodium phosphate). The acyl groups, 3-(4,5-methylenedioxy-2-nitrophenyl)propanoyl, are cleaved by hydrogenolysis. 相似文献