全文获取类型
收费全文 | 447篇 |
免费 | 8篇 |
国内免费 | 6篇 |
专业分类
化学 | 233篇 |
晶体学 | 3篇 |
力学 | 28篇 |
数学 | 158篇 |
物理学 | 39篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 13篇 |
2020年 | 12篇 |
2019年 | 6篇 |
2018年 | 16篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 45篇 |
2012年 | 29篇 |
2011年 | 25篇 |
2010年 | 24篇 |
2009年 | 36篇 |
2008年 | 21篇 |
2007年 | 16篇 |
2006年 | 16篇 |
2005年 | 25篇 |
2004年 | 19篇 |
2003年 | 15篇 |
2002年 | 16篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1993年 | 1篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 7篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1966年 | 1篇 |
1961年 | 1篇 |
1940年 | 1篇 |
排序方式: 共有461条查询结果,搜索用时 46 毫秒
1.
Jason P. Seeley Dr. Mircea Cotlet Aileen M. Eagleton Seiichiro Higashiya Prof. John T. Welch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(4):961-965
The fluorescence intensity of a C-terminal acceptor chromophore, N-(7-dimethylamino-4-methyl coumarin (DACM), increased proportionally with 280 nm irradiation of an increasing number of donor tryptophan residues located on a β-sheet forming polypeptide. The fluorescence intensity of the acceptor chromophore increased even as the length of the β-sheet edge approached 256 Å, well beyond the Förster radius for the tryptophan–acceptor chromophore pair. The folding of the peptides under investigation was verified by circular dichroism (CD) and deep UV resonance Raman experiments. Control experiments showed that the enhancement of DACM fluorescence occurred concomitantly with peptide folding. In other control experiments, the DACM fluorescence intensity of the solutions of tryptophan and DACM did not show any enhancement of DACM fluorescence with increasing tryptophan concentrations. Formation of fibrillar aggregates of the substrate peptides prepared for the fluorescence studies was undetectable by thioflavin T (ThT) fluorescence. 相似文献
2.
We consider a quasistatic problem of frictional contact between a viscoelastic body and a moving foundation. The contact is with wear and is modeled by normal compliance and a law of dry friction. The novelty in the model is that it allows for the diffusion of the wear debris over the potential contact surface. Such kind of phenomena arise in orthopaedic biomechanics and influence the properties of joint prosthesis. We derive a weak formulation of the problem and state that, under a smallness assumption on the problem data, there exists a unique weak solution for the model. To cite this article: M. Shillor et al., C. R. Mecanique 331 (2003). 相似文献
3.
We consider a fully discrete scheme for a quasistatic frictional contact problem between a viscoelastic body and an obstacle. The contact is bilateral, the friction is modeled with Tresca's law and the behavior of the material is described with a viscoelastic constitutive law with long memory. We state an existence and uniqueness result for the discrete solution, followed by error estimate results. Then, we present numerical simulations in the study of a two-dimensional test example. To cite this article: Á. Rodríguez-Arós et al., C. R. Mecanique 334 (2006). 相似文献
4.
Mircea Ştefănescu Mirela Barbu Paul Barvinschi Oana Ştefănescu 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1121-1127
This paper presents a study regarding the obtaining of NiCr2O4 by two new unconventional synthesis methods: (i) the first method is based on the formation of Cr(III) and Ni(II) carboxylate-type precursors in the redox reaction between the nitrate ion and 1,3-propanediol. The thermal decomposition of these complex combinations, at ~300 °C, leads to an oxide mixture of Cr2O3+x and NiO, with advanced homogeneity, small particles and high reactivity. On heating this mixture at 500 °C, Cr2O3 reacts with NiO to form NiCr2O4, which was evidenced by FT-IR and X-ray diffractometry (XRD) analysis; (ii) the second method starts from a mechanical mixture of (NH4)2Cr2O7 and Ni(NO3)2·6H2O. On heating this mixture, a violent decomposition at 240 °C with formation of an oxides mixture (Cr2O3 + CrO3) and NiO takes place. On thermal treatment up to 500 °C, an intermediary phase NiCrO4 is formed, which by decomposition at ~700 °C leads to NiCr2O4, evidenced by FT-IR and XRD analysis. NiCr2O4 is formed, in both cases, starting with a temperature higher than 400 °C, when the non-stoichiometric chromium oxide (Cr2O3+x ) loses the oxygen excess and turns to stoichiometric chromium oxide (Cr2O3), which further reacts with NiO. 相似文献
5.
Paul Barvinschi Oana Stefanescu Thomas Dippong Simona Sorescu Mircea Stefanescu 《Journal of Thermal Analysis and Calorimetry》2013,112(1):447-453
The study reports the preparation of CoFe2O4/SiO2 nanocomposites by a new modified sol–gel method starting from cobalt nitrate, iron nitrate, and diols: 1,2-ethanediol (EG), 1,3-propanediol (1,3PG), and tetraethylorthosilicate (TEOS), for final compositions of 30 %CoFe2O4/70 %SiO2 and 50 %CoFe2O4/50 %SiO2. The method is based on the formation of a Co(II), Fe(III)—carboxylate precursors mixture, during the redox reaction between the NO 3 ? ion and the diol (~140 °C) within the silica gels. The thermal decomposition of these complex combinations takes place at ~300 °C leading to the corresponding amorphous metal oxides within the pores of the hybrid gels. Depending on the subsequent thermal treatment, CoFe2O4 can be obtained as single phase or in a mixture with Co2SiO4. The CoFe2O4 crystallites sizes are in the nanometer range (3–10 nm). The obtained nanocomposites have a hard magnet behavior, as a result of the high anisotropy of CoFe2O4 having large hysteresis cycles. 相似文献
6.
Mircea Balaj 《Applicable analysis》2013,92(11):1049-1054
We introduce a new concept of generalized Knaster–Kuratowski–Mazurkiewicz (KKM) family of sets and related to this we obtain fixed point theorems and sections results in homotopically trivial spaces. 相似文献
7.
This study’s main objective was the development of effective low-cost sorbents for the removal of heavy metal ions from aqueous solutions. The influence of different factors on the sorption capacity of ash and modified ash as low-cost sorbents obtained by different methods was investigated. The synthesis of new ash-based materials was carried out at ambient temperature (20°C), 70°C, and 90°C, respectively, in an alkaline medium with NaOH concentrations of 2 M and 5 M, respectively, corresponding to a mixture with solid/liquid ratios of 1: 3 and 1: 5, respectively. The prepared materials (sorbents) were characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), X-ray diffraction, and BET surface measurement. Adsorption isotherms were determined using the batch equilibrium method. The results showed that these types of new materials displayed a good capacity to remove copper, nickel, and lead ions (29.97 mg of Cu2+ per g of sorbent, 303 mg of Ni2+ per g of sorbent, and 1111 mg of Pb2+ per g of sorbent) from aqueous solutions. The modified materials were prepared using an alkaline attack (a recognised method used in previous studies), but Romanian ash from a thermal power plant was studied for the above purpose for the first time. Hence, the factors which affect the sorption capacity of the prepared low-cost sorbents were determined and their behaviour was explained, taking into account the composition and structure of the new materials. 相似文献
8.
9.
10.
Two triphenylamine-based polymers were successfully prepared by the interfacial and microemulsion oxidative polymerization of triphenylamine and 4-(diphenylamino)benzyl 2-bromo-2-methylpropanoate. Ammonium peroxodisulfate ((NH4)2S2O8) was used as a chemical oxidant and dichloromethane/water was used as a solvent. Sodium dodecyl benzene sulfonate was employed as a surfactant in the microemulsion system. Polytriphenylamines were characterized via Fourier transform infrared (FTIR) spectra and 1H-NMR and UV–vis absorption spectroscopy. Molecular weights were determined by gel permeation chromatography and redox properties were studied by cyclic voltammetry. The surface morphology of thin polymer films was determined by atomic force microscopy. 相似文献