全文获取类型
收费全文 | 221篇 |
免费 | 2篇 |
国内免费 | 1篇 |
专业分类
化学 | 186篇 |
晶体学 | 8篇 |
力学 | 5篇 |
数学 | 7篇 |
物理学 | 18篇 |
出版年
2021年 | 5篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 2篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 2篇 |
2011年 | 4篇 |
2010年 | 7篇 |
2009年 | 3篇 |
2008年 | 14篇 |
2007年 | 6篇 |
2006年 | 11篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 5篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 10篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1958年 | 1篇 |
1956年 | 1篇 |
1955年 | 2篇 |
1954年 | 1篇 |
1953年 | 1篇 |
1937年 | 2篇 |
1934年 | 2篇 |
1898年 | 1篇 |
排序方式: 共有224条查询结果,搜索用时 546 毫秒
131.
Agnieszka Maria Jastrzębska Joanna Jureczko Joanna Karcz Antoni Kunicki Wanda Ziemkowska Andrzej Olszyna 《Chemical Papers》2017,71(3):579-595
The present paper gives new insight into the problem of controlling the morphology of reduced graphene oxide/alumina (RGO/Al2O3) nanocomposites. The dry and simplified sol–gel methods of RGO/Al2O3 nanocomposite synthesis were compared and the influence of six key synthesis parameters on the morphology of the resulting nanocomposite powders was investigated to optimize the morphology of RGO/Al2O3 nanocomposites in terms of reducing the undesired agglomeration of RGO/Al2O3 nanocomposite flakes to a significant minority and obtaining the uniform coverage of RGO surface with Al2O3 nanoparticles. Our investigations indicate that, despite the high excess of Al2O3 used (95 wt%), the lowest RGO/Al2O3 flake agglomeration and the formation of a uniform layer composed of Al2O3 nanoparticles with the average size of 58 nm occurred only when 5 wt% of graphene oxide was used as a substrate for the deposition of Al2O3 nanoparticles together with triethyl aluminium as an Al2O3 precursor and dry hexane as the reaction environment. The resulting organic precursor was thermally decomposed at 280 °C for 3 h in air atmosphere (R4 reaction pathway). This was confirmed by the high BET-specific surface area (242.4 m2/g) and the high open porosity (0.7 cm3/g) of the obtained RGO(5 wt%)/Al2O3 nanocomposite. This is also the first study with a detailed discussion of the reactions expected to occur during the synthesis of an RGO/Al2O3 nanocomposite. 相似文献
132.
The present investigation shows that comparing with the evaporation of vapor-liquid two-phase flow boiling system, heat transfer is enhanced by adding proper inert solid particles into the traditional Chinese medicine liquid whichis under evaporation. As a result, fouling prevention effects are evident in such three-phase flow boiling evaporator. 相似文献
133.
Izabela Pospieszna‐Markiewicz Micha Kozowski Wanda Radecka‐Paryzek Maciej Kubicki 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(9):o559-o561
In the title potential O,N,N′,O′‐tetradentate Schiff base ligand {systematic name: 2,2′‐[pentane‐1,5‐diylbis(nitrilomethylidyne)]diphenol}, C19H22N2O2, the mutual orientation of the three planar fragments determines the conformation of the molecule. The dihedral angles between the planes of the two salicylidene groups and the plane of the central extended pentane chain are 78.4 (2) and 62.0 (3)°, and the angle between the terminal ring planes is 55.4 (1)°. Strong intramolecular O—H...N hydrogen bonds close almost‐planar six‐membered rings, and the O—H bonds are elongated as a result of hydrogen‐bond formation. 相似文献
134.
Wanda K Nabors 《The Journal of Mathematical Behavior》2003,22(2):133-179
Four seventh grade students participated in a constructivist teaching experiment in which manipulatives within a computer microworld were used to solve fractional reasoning tasks followed by tasks that involve concepts of rate, ratio and proportion. Through a retrospective analysis of video tapes, their thinking processes were analyzed from the perspective of the types of cognitive schemes of operation used as they engaged in the given problem situations. One result of the study indicates that the modifications of the students’ available schemes of operation when solving the fractional reasoning tasks formed a basis for the cognitive schemes of operation used in their solutions of tasks involving proportionality. 相似文献
135.
Jerzy Peszke Barbara Mianowska Wanda ?liwa 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1997,53(14):2565-2570
For six isomeric formyl derivatives of 1,5-, 1,6- and 4,6-benzonaphthyridines the electronic structure and UV spectral values have been calculated by CI AM1 method. Correlations of the calculated and observed wave number values of considered compounds show good compatibility. 相似文献
136.
137.
Berger CM Zhao X Schaeffer DG Dobrovolny HM Krassowska W Gauthier DJ 《Physical review letters》2007,99(5):058101
We investigate, both experimentally and theoretically, the period-doubling bifurcation to alternans in heart tissue. Previously, this phenomenon has been modeled with either smooth or border-collision dynamics. Using a modification of existing experimental techniques, we find a hybrid behavior: Very close to the bifurcation point, the dynamics is smooth, whereas further away it is border-collision-like. The essence of this behavior is captured by a model that exhibits what we call an unfolded border-collision bifurcation. This new model elucidates that, in an experiment, where only a limited number of data points can be measured, the smooth behavior of the bifurcation can easily be missed. 相似文献
138.
We present an extensive ab initio study of the structural and dielectric properties of hafnium silicates Hf(x)Si(1-x)O(2) that accounts for the observed anomalous dependence on composition of the static dielectric constant in the entire x range. The results reveal that this complex behavior reflects that of the structural development with x, from silica to hafnia, and clarify how different growth processes can also lead to scattered sets of data. Several simple models proposed thus far to explain part of the experimental data are shown to be inadequate. It is argued that silicate layers with low hafnium content form at the HfO(2)/Si interface and play a crucial role in preserving high electron mobility in the channel. 相似文献
139.
Lidia Chrzastek Marian Mielniczak Zdzislaw Staroniewicz Wanda Sliwa 《Chemistry of Heterocyclic Compounds》1999,35(10):1214-1221
The synthesis of four isomeric nitro derivatives of methyldiazaphenanthrenes (DAP) has been described. The UV spectra of these
compounds have been recorded and compared with those of parent diazaphenanthrenes. The biological data of methylnitrodiazaphenanthrenes
and of other derivatives of diazaphenanthrenes are presented.
Institute of Chemistry, Pedagogical University, 42-201 Czestochowa, Poland Babimost School, 66-110 Babimost, Poland. Microbiology
Department Agricultural Academy 50-375 Wroclaw, Poland. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp.
1396–1403, October, 1999. 相似文献
140.
Jerzy Krysiak Wanda H. Midura Wanda Wieczorek Lesław Sieroń Marian Mikołajczyk 《Tetrahedron: Asymmetry》2010,21(11-12):1486-1493
A new stereocontrolled synthesis of (+)-2-aminobicyclo[3.1.0]hexane-2.6-dicarboxylic acid (LY354740) 1, a potent and selective 2mGluR agonist, has been accomplished in four steps with an overall yield of 27% starting from the enantiopure (+)-(R)-2-(p-tolylsulfinyl)cyclopent-2-enone 3. The key steps include asymmetric cyclopropanation of 3 with (dimethylsulfuranylidene)acetate (EDSA) and removal of the chiral p-tolylsulfinyl auxiliary from the cycloadduct ent-4c upon treatment with iso-propylmagnesium chloride. The stereoselective hydantoin formation from the bicyclic ketone 6 formed (Bucherer–Bergs reaction) and subsequent hydrolysis completed the synthesis of 1. The same reaction sequence has been applied in the first synthesis of enantiopure (+)-2-amino-6-phosphonobicyclo[3.0.1]hexane-2-carboxylic acid 2, a structural 6-phosphono analogue of 1. The starting bicyclic ketophosphonates 9–11 have been obtained by asymmetric cyclopropanation of (?)-(S)-3 with phosphoryl sulfonium ylides, producing only two endo-isomers. The major endo-isomer (+)-11a containing the 6-diisopropoxyphosphoryl group has been converted in three steps into (+)-endo-2 in 46% overall yield. 相似文献