全文获取类型
收费全文 | 539篇 |
免费 | 17篇 |
国内免费 | 2篇 |
专业分类
化学 | 427篇 |
晶体学 | 3篇 |
力学 | 11篇 |
数学 | 65篇 |
物理学 | 52篇 |
出版年
2023年 | 3篇 |
2022年 | 13篇 |
2021年 | 28篇 |
2020年 | 13篇 |
2019年 | 14篇 |
2018年 | 11篇 |
2017年 | 11篇 |
2016年 | 15篇 |
2015年 | 27篇 |
2014年 | 13篇 |
2013年 | 44篇 |
2012年 | 31篇 |
2011年 | 45篇 |
2010年 | 30篇 |
2009年 | 20篇 |
2008年 | 32篇 |
2007年 | 26篇 |
2006年 | 28篇 |
2005年 | 24篇 |
2004年 | 21篇 |
2003年 | 24篇 |
2002年 | 13篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1995年 | 5篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1941年 | 1篇 |
1933年 | 1篇 |
排序方式: 共有558条查询结果,搜索用时 15 毫秒
21.
Liliana Castro Patricio Reyes Consuelo Montes de Correa 《Journal of Sol-Gel Science and Technology》2002,25(2):159-168
Fe-ZrO2 and Cu-ZrO2 xerogels were prepared by a sol-gel method. The effect of the hydrolysis catalyst during the gelation step, namely H2SO4 or NH4OH, on the properties of the resulting materials was investigated by XRD, BET, TGA/DTA, TPD of ammonia, FTIR, and TPR. Fe-ZrO2 and Cu-ZrO2 xerogels, with sulfuric acid introduced as the hydrolysis catalyst, mainly crystallyzed in the tetragonal phase and exhibited larger surface area and acid amount than those obtained with NH4OH. Ammonia TPD shows that copper promoted sulfated zirconia is the most acidic material. TGA and FTIR reveal that under oxidizing conditions sulfated zirconia promoted with iron and copper retains more sulfate species than unpromoted sulfated zirconia. Regardless of the hydrolysis catalyst employed, copper promoted catalysts calcined at 600°C, contain a large fraction of copper oxide specieseasily reduced at low temperatures. These copper oxide species are believed to have different environment and interactions with the surface oxygen vacancies of the zirconia support. A FeO-like phase appears to be the most probable one after reduction of Fe-ZrO2 catalysts prepared with NH4OH as the hydrolysis catalyst. The formation of Fe° species may be hindered by the high dispersion and interaction of Fe2+ ions with the zirconia support. On the other hand, the reduction peaks of iron oxide and sulfate species exhibit a considerable overlap in the TPR profiles of sulfated Fe-ZrO2 samples. Hence, the nature of the supported phase in the latter samples is rather uncertain. 相似文献
22.
Dr. Joice Thomas Dr. Liliana Dobrzańska Prof. Luc Van Meervelt Prof. Mario Alfredo Quevedo Prof. Krzysztof Woźniak Marcin Stachowicz Prof. Mario Smet Prof. Wouter Maes Prof. Wim Dehaen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):979-987
A synthetic route towards homodiselenacalix[4]arene macrocycles is presented, based on the dynamic covalent chemistry of diselenides. The calixarene inner rim is decorated with either alkoxy or tert‐butyl ester groups. Single‐crystal X‐ray analysis of two THF solvates with methoxy and ethoxy substituents reveals the high similarity of their molecular structures and alterations on the supramolecular level. In both crystal structures, solvent channels are present and differ in both shape and capacity. Furthermore, the methoxy‐substituted macrocycle undergoes a single‐crystal‐to‐single‐crystal transformation during which the molecular structure changes its conformation from 1,3‐alternate (loaded with THF/water) to 1,2‐alternate (apohost form). Molecular modelling techniques were applied to explore the conformational and energetic behaviour of the macrocycles. 相似文献
23.
A short-term aerobic stabilization of digested waste in the final methane phase was studied. The effect of aeration rate on
the reduction of leachate parameters and on the rate of CO2 production and O2 assimilation was investigated. Experimental simulation of aerobic landfill stabilization was carried out using lysimeters.
When testing the effect of aeration rate on the reduction of leachate indices (BOD5, COD, N-NH4+), it was reported that the most significant reduction was obtained at the highest rate of aeration and the smallest reduction
of leachate indices was attained not at the lowest but at medium aeration rates. Both the rate of CO2 production and the O2 assimilation reached their highest values in the lysimeters aerated at a high rate of aeration. The proposed mathematical
model which consists of a system of five differential equations describing CO2 production, O2 assimilation and the changes of organic carbon content in the leachate correspond well with the experimental data. 相似文献
24.
J. M. Ferreira Liliana Caramelo R. P. Chhabra 《International Journal of Mathematical Education in Science & Technology》2013,44(4):545-552
A curve fitting model is presented which minimizes the sum of squares of relative residues and expressions for the fit coefficients and their respective errors are derived. The new model is compared to the normal least squares model, using as an example the Reynolds number-drag coefficient data for a sphere. The results show that the best fit was obtained with the new model, indicating it may provide a useful tool for data analysis. 相似文献
25.
Giraldo Liliana Moreno-Piraján Juan Carlos 《Journal of Thermal Analysis and Calorimetry》2018,132(1):337-342
Journal of Thermal Analysis and Calorimetry - The heat capacity of monazite-type LaPO4 and PrPO4 nanocrystalline whiskers, with a diameter of 30 to 45 nm and length 1–1.5 μm,... 相似文献
26.
Implementing the plasma-lasing potential for tabletop nano-imaging on across a hot plasma medium drives short-wavelength lasing, promising for "turnkey" nano-imaging setups. A systematic study of the illumination characteristics, combined with design-adapted objectives, is presented. It is shown how the ultimate nano-scale feature is dictated by either the diffraction-limited or the wavefront-limited resolution, which imposed a combined study of both the source and the optics. For nano-imaging, the spatial homogeneity of the illumination (spot noise) was shown as critical. Plasma-lasing from a triple grazing-incidence pumping scheme compensated for the missing spot homogeneity in classical schemes. We demonstrate that a collimating mirror pre-conditions both the pointing stability and the divergence below half a mrad. 相似文献
27.
Ya-Xin Li Fang-Fang Fan Jie Wang Dr. Liliana Cseh Dr. Min Xue Dr. Xiang-Bing Zeng Prof. Goran Ungar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13739-13747
Wedge-shaped molecules, such as dendrons, are among the most important building blocks for directed supramolecular self-assembly. Here we present a new approach aimed at widening the range and complexity of potential mesophases by introducing double-tapered mesogens. Two series of compounds are presented, both alkali metal salts (Li, Na, Cs) of 3,4,5-tris-alkoxybenzoic acid with a second tapered tris-alkoxyaryl group attached at the end of an alkoxy chain. The double-tapered compounds all display an unusual hexagonal columnar phase consisting of one ionic and three non-ionic columns per unit cell. The cation size has an unexpectedly drastic effect on unit cell size. Unlike most columnar phases, the current phases show unusually high dimensional stability on heating, and high stiffness in spite of being 80–85 % aliphatic, attributed to their molecular topology. The described approach may lead to co-assemblies of multifunctional materials, for example, parallel p- and n-semiconducting nanowires or parallel ionic and electronic conductors. 相似文献
28.
Geometriae Dedicata - We prove a criterion for Benjamini-Schramm convergence of periodic orbits of Lie groups. This general observation is then applied to homogeneous spaces and the space of... 相似文献
29.
Lange Camila Neves Figueiredo Ana Maria Graciano Enzweiler Jacinta Castro Liliana 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(2):1323-1332
Journal of Radioanalytical and Nuclear Chemistry - The impact of a scrapyard of impounded vehicles in São Paulo state on topsoil was evaluated for As, Ba, Co, Cr, Cu, Mo, Ni, Pb, V, Zn and... 相似文献
30.
Blanka Wladislaw Liliana Marzorati Jonas Gruber 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):185-188
Abstract Some new norbornene thioester derivatives of endo configuration are sinthesized. Proofs are provided that thioester group has more preference for endo configuration than the ester group. 相似文献