全文获取类型
收费全文 | 325篇 |
免费 | 9篇 |
国内免费 | 2篇 |
专业分类
化学 | 148篇 |
晶体学 | 3篇 |
力学 | 24篇 |
数学 | 61篇 |
物理学 | 100篇 |
出版年
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 3篇 |
2018年 | 7篇 |
2017年 | 7篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 16篇 |
2013年 | 8篇 |
2012年 | 23篇 |
2011年 | 21篇 |
2010年 | 12篇 |
2009年 | 19篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 3篇 |
2004年 | 8篇 |
2003年 | 19篇 |
2002年 | 9篇 |
2001年 | 2篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1968年 | 2篇 |
1963年 | 3篇 |
1959年 | 3篇 |
排序方式: 共有336条查询结果,搜索用时 15 毫秒
1.
Ionel Rosenthal Joe Z. Sostaric Peter Riesz 《Research on Chemical Intermediates》2004,30(7-8):685-701
Sonochemistry and photochemistry are initiated by high-energy transient species, which may be prone to mutual interaction. Electronic excitation of solutes by energy transfer from high energy species generated in collapsing bubbles is already supported by experimental evidence. The rates of photochemical reactions can be affected by ultrasound-induced mixing of liquids caused by microstreaming near pulsating cavitation bubbles and shockwaves due to bubble collapse. This may not only improve light absorption but also modify the pathway of reaction by increasing the contact between reagents. Finally, one may speculate about a potentially new chemistry of photoexcited solutes under the extreme conditions inside cavitation microreactors. This work reviews research on the excitation of solutes by sonoluminescence, the combined effects of ultrasound and light on liquid systems and the effect of ultrasound on photocatalytic reactions. 相似文献
2.
Marilena Vasilescu Titus Constantinescu Mariana Voicescu Helge Lemmetyinen Elina Vuorimaa 《Journal of fluorescence》2003,13(4):315-322
The spectrophotometric study of luminol (LH2) in dimethyl sulfoxide (DMSO), DMSO-water solutions, and alkaline DMSO and DMSO-water solutions has been done, focusing on the effect of the KOH additon on LH2 absorption and fluorescence properties. The absorption spectra indicate an acid-base equilibrium, and the luminol dianion (L2–) formation at 3 × 10–4 – 2.4 × 10–3
M KOH. The decrease of the fluorescence intensity and the variation of the excitation spectra of LH2-DMSO-KOH solutions with KOH concentration have been similarly explained. The acid-base process is reversible. The addition of HCl to the solution with 3.0 × 10–3 M KOH leads to an increase of the fluorescence intensity to its highest value, observed in pure DMSO. The addition of HCl to the LH2-DMSO solution leads to the decrease of the fluorescence intensity as a result of the LH+
3 cation formation. In LH2-DMSO-water, the fluorescence band is shifted from 405 nm to 424 nm and increased in the intensity. In the presence of KOH (in LH2-DMSO-water-KOH solution) a new band appears, with the maximum at 485 nm and the band at 405 nm decreased. The changes in fluorescence lifetimes also evidence the different chemical species formed. 相似文献
3.
Alina Constantinescu 《Applications of Mathematics》2007,52(4):321-326
In one if his paper Luo transformed the problem of sum-fuzzy rationality into artificial learning procedure and gave an algorithm
which used the learning rule of perception. This paper extends the Luo method for finding a sum-fuzzy implementation of a
choice function and offers an algorithm based on the artificial learning procedure with fixed fraction. We also present a
concrete example which uses this algorithm. 相似文献
4.
Let B(N) be the power set of the set of natural numbers endowed with the usual structure of a compact abelian group and letμ be the normed Haar measure on it. The paper studies the properties ofμ-measurable additive maps of B(N) into Hausdorff abelian groups. 相似文献
5.
P. Spacu C. Gheorghiu M. Constantinescu I. Pascaru O. Contantinescu 《无机化学与普通化学杂志》1971,384(2):184-190
Copper(II) coordination compounds with p-chlorphenylbiguanide of the type: [Cu(Cl-PhBig)2]X2 and [Cu(Cl–PhBig)X2] with X =Cl?, Br? NO3, OH?, NCS?, NCO?, N3, have been studied by EPR spectroscopy using polycrytalline powders and solutions in DMF. The parameters of the EPR spectra have been used to estimate molecular orbital coefficient, in these compounds and to discuss details of the chemical bonding. 相似文献
6.
7.
Ionel I Mangalagiu Geanina C MangalagiuCalin Deleanu Gabi DrochioiuMagda Ghe Petrovanu 《Tetrahedron》2003,59(1):111-114
The ability of 4-methylpyrimidinium ylides (as 1,3-dipoles) to react with activated non-symmetrical substituted dipolarophiles (alkenes and alkynes) is presented. 4-Methylpyrimidinium ylides did not react with alkenes. With alkynes the reactions are regiospecific, a single regioisomer being obtained. A possible mechanism for the reaction pathway is proposed. For the first time in the pyrimidinium ylides series both isomers resulting from bonding to the 2-and 6-positions of the heterocycle ring were obtained. The appropriate conditions in order to increase the selectivity of one of the isomers were determined. 相似文献
8.
Organotin derivatives of dimethyldithioarsinic (dithocacodylic) acid have been obtained from the appropriate organotin chloride and the sodium salt of the latter. Tin(IV) chloride and NaS2AsMe2 · 2 H2O yielded only two products, namely Cl2Sn(S2AsMe2)2 and Sn (S2AsMe2)4, regardless of the reagent ratio. Spectroscopic characterization of the compounds (infrared and1H NMR) provides structural information suggesting that the dimethyldithioarsinato group behaves as monodentate (or anisobidentate) ligand in Me2Sn(S2AsMe2)2, Bu2Sn-(S2AsMe2)2 and Cy3Sn(S2AsMe2), as bidentate in Ph2Sn(S2AsMe2)2, Ph3Sn(S2AsMe2) and Cl2As(S2AsMe2)2, whereas Sn(S2AsMe2)4 contains both mono- and bidentate ligands, presumably in a six-coordinate structure. 相似文献
9.
Sorin Mager Ionel Hopârtean Dan Bini§or 《Monatshefte für Chemie / Chemical Monthly》1978,109(6):1393-1401
The spectra of some 9-chloro-6-nitroacridines with methoxy substituents in position 1,4; 2,4; 3,4; 2,3; and ethoxy substituents in positions 1, 2, 3, were recorded. The influence of electron releasing alkoxy groups and electron withdrawing nitro groups on chemical shifts of protons in the 9-chloroacridinic cycle was discussed and PMR parameters were determined, comparatively with those of acridine and 9-chloroacridine. Good agreement between calculated and experimental values is observed. The spectrum of 9-chloro-1,2,3-triethoxyacridine shows for the four protons of the ringC. (H-5, H-6, H-7, H-8) anAMNX coupling pattern whose parameters were determined. 相似文献
10.
G. Surpateanu A. Lablache-Combier M. Constantinescu J. Marko 《Tetrahedron letters》1984,25(50):5751-5754
E and Z isomers of p-nitrobenzoyl, 4-p-tolyl[1-2-4]triazolum methylide 5b and p-nitrobenzoyl, 4-p-phenyl[1-2-4]triazolium methylide 5e, have been characterised. 相似文献