全文获取类型
收费全文 | 433篇 |
免费 | 20篇 |
国内免费 | 1篇 |
专业分类
化学 | 385篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 27篇 |
物理学 | 39篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 1篇 |
2020年 | 4篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 16篇 |
2013年 | 21篇 |
2012年 | 20篇 |
2011年 | 24篇 |
2010年 | 19篇 |
2009年 | 7篇 |
2008年 | 33篇 |
2007年 | 22篇 |
2006年 | 29篇 |
2005年 | 29篇 |
2004年 | 27篇 |
2003年 | 20篇 |
2002年 | 21篇 |
2001年 | 9篇 |
2000年 | 9篇 |
1999年 | 10篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 5篇 |
1988年 | 10篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有454条查询结果,搜索用时 711 毫秒
331.
Elke Scholten Erik van der Linden Herve This 《Langmuir : the ACS journal of surfaces and colloids》2008,24(5):1701-1706
The well-known alcoholic beverage Pastis becomes turbid when mixed with water due to the poor solubility of trans-anethol, the anise-flavored component of Pastis in the water solution formed. This destabilization appears as the formation of micrometer-sized droplets that only very slowly grow in size, thus expanding the life of the anise-flavored beverage. The slow growth has been attributed to an extremely low interfacial tension of the droplets. Fitting experimental droplet growth rates to an Ostwald ripening model, interfacial tensions were deduced in the past. Direct determination of the interfacial tensions was not yet reported on these systems. We have measured the interfacial tensions and used these data to predict droplet growth rates using an Ostwald ripening model and a model for creaming of the droplets. The interfacial tension was measured to be about 11 mN/m for a 30/70 w/w % ethanol/water mixture, and it decreases slightly to a value of 1.4 mN/m in the case of a 70/30 w/w % ethanol/water mixture. These values are not as low as those deduced in the past. The theoretical predictions for both the Ostwald ripening rates and the creaming rates, using the directly measured interfacial tensions, are found to contradict with the experimental results on Ostwald ripening and creaming. While the experiments on Ostwald ripening show an increase in stability with increasing ethanol concentration, the results based on our interfacial tension measurements in combination with the same Ostwald ripening model show a decrease in stability with an increase in ethanol concentration. Further research is needed to understand fully which parameters play a role in both droplet growth and the stability of these three-component emulsions to elucidate the current discrepancy between model and experiment. This could be useful for a better control of "spontaneous emulsification" processes. 相似文献
332.
U. Risse Elke Flammenkamp A. Kettrup Stefaan Vandendriessche 《Fresenius' Journal of Analytical Chemistry》1999,363(1):33-37
A Certified Reference Material (CRM) for determination of aromatic hydrocarbons in air was developed. The CRM 562 consists
of aromatic hydrocarbons sorbed on charcoal in glass tubes. Initial feasibility studies established that a homogeneous and
stable batch could be prepared. Three intercomparisons prior to the certification allowed the identification of various sources
of error. Then, a batch of about 3000 tubes was charged and certified on the basis of analyses carried out in 15 European
laboratories. The preparation of the reference material and the results of the certification exercise is described. An overview
on the analytical techniques used and the quality control guidelines are also presented. The certified values are 15.0 ± 0.4
μg benzene, 147.3 ± 3.8 μg toluene, 96.4 ± 2.5 μg m-xylene and 93.0 ± 2.9 μg o-xylene per tube. This reference material is
recommended for quality control of measurements in the field of occupational hygiene.
Received: 12 May 1998 / Revised: 28 August 1998 / Accepted: 1 September 1998 相似文献
333.
Norbert Kuhn Stefan Fuchs Elke Niquet Markus Richter Manfred Steimann 《无机化学与普通化学杂志》2002,628(4):717-718
[{(C7H13N2)AlCl}2O]: A Dinuclear Vinamidine Aluminum Complex with a Linear Oxygen Bridge [1] [(C7H13N2)AlCl2] ( 1 ) reacts with Ag2O in the ratio 2/1 to give the dinuclear vinamidine complex [{(C7H13N2)AlCl}2O] ( 2 ) in good yield. The crystal structure investigation of 2 reveals the presence of a linear fragment Al—O—Al in the centrosymmetric space group P21/c. 相似文献
334.
Jaroslaw Chojnacki Elke Baum Ingo Krossing Duncan Carmichael Francois Mathey Hansgeorg Schnckel 《无机化学与普通化学杂志》2001,627(6):1209-1212
The solid state structure of η5‐2,5‐di‐(t‐butyl)phospholylgallium(I) 1 was determined by X‐ray diffraction at 190 K. The molecules of 1 are partly organized in a for sandwich complexes new type of structure: a Ga zigzag chain in which the aromatic phospholyl rings alternate on both sides of the chain. 相似文献
335.
3‐periodic minimal surfaces made up by catenoid‐like surface patches may be related to Laves nets. Starting from these nets four new types of such surfaces with selfintersection exclusively along straight lines could be derived. They subdivide R3 into 2‐periodic labyrinths and 1‐periodic tubes. 相似文献
336.
PeterJ. Gee FredA. Hamprecht LukasD. Schuler WilfredF. vanGunsteren Elke Duchardt Harald Schwalbe Matthias Albert Dieter Seebach 《Helvetica chimica acta》2002,85(2):618-632
The GROMOS96 molecular‐dynamics (MD) program and force field was used to calculate the conformations at 298 K in CHCl3 solution of two hexakis(3‐hydroxyalkanoic acids). One consists of (R)‐3‐hydroxybutanoate (HB) residues only: H−(OCH(Me)−CH2−CO)6−OH ( 1 ). The other one carries the side chains of valine, alanine, and leucine: H−(OCH(CHMe2)CH2−CO−O−CH(Me)−CH2−CO−O−CH(CH2 CHMe2)−CH2−CO)2−OH ( 2 ), with homochiral 3‐hydroxyalkanoate (HA) moieties. In both cases, the conformational equilibria were sampled 2500 times for 25 ns. Other than clusters of arrangements with inter‐residual hydrogen bonding (between the O‐ and C‐terminal OH and COOH groups, and with chain‐bound ester carbonyl O‐atoms; Fig. 6), there are no preferred backbone conformations in which the molecules 1 and 2 spend more than 5% of the time. Specifically, neither the 21‐ nor the 31‐helical conformation of the oligoester backbone (found in stretched fibers, in lamellar crystallites, and in single crystals of polymers PHB and of oligomers OHB) is sampled to any significant extent (Fig. 8 and 9), in spite of the high population, in both oligomers, of the (−)‐synclinal conformation around the C(2)−C(3) bond (angle ϕ2 in Fig. 2). In contrast to β‐oligopeptides, for which strongly preferred secondary structures are found after a few ns, and for which the number of conformations levels off with time, the number of conformational clusters of the corresponding oligoesters found by our force‐field MD calculations increases steadily over the observation time of 25 ns (Fig. 5). Thus, the conclusion from biological and physical‐chemical studies, according to which the PHB chain is extremely flexible, is confirmed by our computational investigation: in CHCl3 solution, the hexakis(3‐hydroxyalkanoate) chain samples its conformational space randomly! 相似文献
337.
Rolf Huisgen Grzegorz Mlosto Elke Langhals Takumi Oshima 《Helvetica chimica acta》2002,85(9):2668-2685
When ‘thiocarbonyl ylide' 1A (=(2,2,4,4‐tetramethyl‐3‐oxocyclobutylidenesulfonio)methanide) is generated from the dihydrothiadiazole 5A by N2 extrusion at 40° in the presence of 2,3‐bis(trifluoromethyl)fumaronitrile ((E)‐ 10 ), a cyclic seven‐membered ketene imine 11 and trans‐thiolane 12 are formed (81 : 19). The reaction of 1A with (Z)‐ 10 furnishes 11, 12 , and cis‐thiolane 25 in the ratio of 82 : 12 : 6. The strained ketene imine 11 is crystalline and storable as a consequence of the stabilizing ‘perfluoroalkyl effect'. The ketene imine group is stereogenic; 11 has a transoid structure with respect to the CF3 groups, and there is no evidence for the cisoid diastereoisomer. Ketene imine 11 adds H2O, MeOH, and PhNH2. In solution at 60°, 11 undergoes an irreversible ring contraction, furnishing the thiolanes 12 / 25 98 : 2. The rate constant of this first‐order rearrangement increases 850‐fold, as the solvent polarity rises from cyclohexane to CD3CN, in accordance with a zwitterionic intermediate. It is the same intermediate that is initially formed from 1A and 10 , and its intramolecular N‐ and C‐alkylation give rise to 11 and 12 + 25 , respectively. In contrast to 1A , thiocarbonyl ylide 27 , which harbors the sterically less‐demanding adamantylidene group, reacts with (E)‐ 10 to give trans‐thiolane 29 , but no ketene imine. The precursor 26 catalyzes the (Z)/(E) isomerization of 10 ((E)/(Z) ca. 95 : 5 at equilibrium), thus obviating conclusions on steric course and mechanism of this cycloaddition. 相似文献
338.
Advances in agriculture and food technology, and increases in the world population, have made food analysis and regulation very complex. Food safety is a major consumer concern today, but consumer understanding of food processing has declined for a number of reasons. Regaining consumer confidence poses a specific challenge to legislators, food producers and food chemists. 相似文献
339.
In a horizontal 2-zone resistance furnace nearly ideally formed crystals were grown at the end of an evacuated ampoule, using temperatures between 750 and 720°C, a ΔT of 15 to 10 deg between the rooms of the solution and growth. When applying single heating zone and special conditions good crystals were grown by the use of a quartz rod or a quartz plate as nucleation center. — Finally analytical data on the products of growing are given. 相似文献
340.