全文获取类型
收费全文 | 166篇 |
免费 | 3篇 |
国内免费 | 2篇 |
专业分类
化学 | 111篇 |
晶体学 | 4篇 |
力学 | 1篇 |
数学 | 16篇 |
物理学 | 39篇 |
出版年
2023年 | 1篇 |
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 5篇 |
2013年 | 6篇 |
2012年 | 12篇 |
2011年 | 12篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 6篇 |
2007年 | 10篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 10篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1982年 | 1篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 1篇 |
排序方式: 共有171条查询结果,搜索用时 15 毫秒
101.
Radostina PALCHEVA Luděk KALUZA Alla SPOJAKINA Květue JIRTOV Georgi TYULIEV 《催化学报》2012,33(6):952-961
A hydrotreating NiMo/γ-Al2O3 catalyst(12 wt% Mo and 1.1 wt% Ni) was prepared by impregnation of the support with the Anderson-type heteropolyoxomolybdate(NH4)4Ni(OH)6Mo6O18.Before impregnation of the support,it was modified with an aqueous solution of H3BO3,Co(NO3)2,or Ni(NO3)2.The catalysts were investigated using N2 adsorption,O2 chemisorption,X-ray diffraction,UV-Vis spectroscopy,Fourier transform infrared spectroscopy,temperature-programmed reduction,temperature-programmed desorption,and X-ray photoelectron spectroscopy.The addition of Co,Ni,or B influenced the Al2O3 phase composition and gave increased catalytic activity for 1-benzothiophene hydrodesulfurization(HDS).X-ray photoelectron spectroscopy confirmed that the prior loading of Ni,Co or B increased the degree of sulfidation of the NiMo/γ-Al2O3 catalysts.The highest HDS activity was observed with the NiMo/γ-Al2O3 catalyst with prior loaded Ni. 相似文献
102.
Ivayla Pantcheva Radoslava Stamboliyska Nikolay Petkov Alia Tadjer Svetlana Simova Radostina Stoyanova Rositza Kukeva Petar Dorkov 《Molecules (Basel, Switzerland)》2022,27(12)
The veterinary 16-membered macrolide antibiotics tylosin (HTyl, 1a) and tilmicosin (HTilm, 1b) react with copper(II) ions in acetone at metal-to-ligand molar ratio of 1:2 to form blue (2) or green (3) metal(II) coordination species, containing nitrate or chloride anions, respectively. The complexation processes and the properties of 2–3 were studied by an assortment of physicochemical techniques (UV-Vis, EPR, NMR, FTIR, elemental analysis). The experimental data revealed that the main portion of copper(II) ions are bound as neutral EPR-silent dinuclear complexes of composition [Cu2(µ-NO3)2L2] (2a–b) and [Cu2(µ-Cl)2Cl2(HL)2] (3a–b), containing impurities of EPR-active mono-species [Cu(NO3)L] (2a’–b’) and [CuCl2(HL)] (3a’–b’). The possible structural variants of the dinuclear- and mono-complexes were modeled by the DFT method, and the computed spectroscopic parameters of the optimized constructs were compared to those measured experimentally. Using such a combined approach, the main coordination unit of the macrolides, involved in the complex formation, was defined to be their mycaminosyl substituent, which acts as a terminal ligand in a bidentate mode through the tertiary nitrogen atom and the oxygen from a deprotonated (2) or non-dissociated (3) hydroxyl group, respectively. 相似文献
103.
Nikola G. Todorov Marina G. Stoyanova Stefka Tosheva 《Journal of polymer science. Part A, Polymer chemistry》1997,35(10):1933-1938
The preparation of water-soluble polymers with physiological activity via ion bonding of low molecular weight physiologically active substances to a polymer carrier has been studied. The conditions for obtaining polymer salts of physiologically active substances with acid properties and amino-containing polymer carrier have been established. The maximum conversion degree has been determined. The polymer salts have been characterized by potentiometric titration, 31P-NMR and IR spectroscopy, and elemental analysis. The stability of the salts and the immobilization rate of the low molecular weight physiologically active substances have been investigated. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1933–1938, 1997 相似文献
104.
105.
106.
Gawlitza K Wu C Georgieva R Wang D Ansorge-Schumacher MB von Klitzing R 《Physical chemistry chemical physics : PCCP》2012,14(27):9594-9600
The aim of the present work is the use of a water soluble enzyme in an organic solvent, still with a pronounced catalytic activity. Therefore, lipase B from Candida antarctica (CalB) is immobilized within micron-sized thermosensitive p-NIPAM hydrogel particles using a solvent exchange from polar to organic solvents. The absorbed amount of CalB is investigated at different immobilization temperatures. Confocal laser scanning microscopy (CLSM) shows that CalB is homogeneously distributed within the polymer network. An enhanced specific activity of CalB in n-hexane is achieved after immobilization within the p-NIPAM microgels. In order to get information on the supply of the substrate depending on the temperature, the activity is determined at different reaction temperatures. Additionally, the system is stable in the organic solvent, namely n-hexane, and shows a good reusability. 相似文献
107.
Carlier D Cheng JH Berthelot R Guignard M Yoncheva M Stoyanova R Hwang BJ Delmas C 《Dalton transactions (Cambridge, England : 2003)》2011,40(36):9306-9312
Manganese substituted sodium cobaltate, Na(2/3)Co(2/3)Mn(1/3)O(2), with a layered hexagonal structure (P2-type) was obtained by a co-precipitation method followed by a heat treatment at 950 °C. Powder X-ray diffraction analysis revealed that the phase is pure in the absence of long-range ordering of Co and Mn ions in the slab or Na(+) and vacancy in the interslab space. The oxidation states of the transition metal ions were studied by magnetic susceptibility measurements, electron paramagnetic resonance (ESR) and (23)Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The charge compensation is achieved by the stabilization of low-spin Co(3+) and Mn(4+) ions. The capability of Na(2/3)Co(2/3)Mn(1/3)O(2) to intercalate and deintercalate Na(+) reversibly was tested in electrochemical sodium cells. It appears that the P2 structure is maintained during cycling, the cell parameter evolution versus the sodium amount is given. From the features of the cycling curve the formation of an ordered phase for the Na(0.5)Co(2/3)Mn(1/3)O(2) composition is expected. 相似文献
108.
Silvia Boumova Peter Boyvalenkov Hristina Kulina Maya Stoyanova 《Designs, Codes and Cryptography》2009,51(3):275-288
We investigate the structure of spherical τ-designs by applying polynomial techniques for investigation of some inner products
of such designs. Our approach can be used for large variety of parameters (dimension, cardinality, strength). We obtain new
upper bounds for the largest inner product, lower bounds for the smallest inner product and some other bounds. Applications
are shown for proving nonexistence results either in small dimensions and in certain asymptotic process. In particular, we
complete the classification of the cardinalities for which 3-designs on exist for n = 8, 13, 14 and 18. We also obtain new asymptotic lower bound on the minimum possible odd cardinality of 3-designs.
相似文献
109.
A. O. Stoyanov N. A. Chivireva I. V. Stoyanova E. V. Timukhin V. P. Antonovich 《Journal of Analytical Chemistry》2011,66(5):470-475
A procedure is proposed for the indirect spectrophotometric determination of trace europium(II) in poorly soluble inorganic
materials. The approach based on sample dissolution in the presence of excess vanadium(V) salts followed by the determination
of vanadium(IV), equivalent to the concentration of europium(II), is used. The photometric determination of V(IV) is based
on its oxidation with a potassium permanganate solution followed by the measurement of absorbance of excess MnO4−. The procedure is applied to the analysis of EuF3 − x
with low europium(II) concentrations in the study the dissolution products of europium fluorides in salt melts and in the
study the products of sorption europium(II) by strontium fluorapatite from salt melts. The proposed procedure is rapid and
simple. It possesses satisfactory performance characteristics. 相似文献
110.
V. A. Bezzubov I. A. Vasil’ev V. N. Goryachev S. P. Denisov V. N. Evdokimov S. V. Erin A. V. Kozelov A. V. Levin V. V. Lipaev D. A. Stoyanova A. A. Shchukin 《Physics of Particles and Nuclei》2018,49(1):17-20
In this work, the results of the measurements of characteristics of 40-cm and 2-m scintillation counters irradiated by a particle beam with a momentum of 7 GeV/c from the accelerator of the Institute for High Energy Physics are presented. The scintillators used in counters are BC-404 and BC-408 scintillators. The counters are viewed from both ends by R1828-01 photomultiplier tubes. The PMT signal spectra are well described by a convolution of the Landau and Gaussian distributions. Their width is determined mainly by fluctuations of ionization energy losses. The time distributions of the signals obey the Gaussian law. For the 40-cm counter, the time resolution is σ(T) = 88 ps; for the 2-m counter, it varies from 120–160 ps in its center to ~100 ps near the end. 相似文献