Author Keywords: Infrared spectrometry; Fourier transform; Wall and canvas painting analysis; Restoration/conservation of works of art 相似文献
全文获取类型
收费全文 | 10449篇 |
免费 | 1640篇 |
国内免费 | 1119篇 |
专业分类
化学 | 6715篇 |
晶体学 | 20篇 |
力学 | 620篇 |
综合类 | 101篇 |
数学 | 2503篇 |
物理学 | 3249篇 |
出版年
2024年 | 13篇 |
2023年 | 92篇 |
2022年 | 193篇 |
2021年 | 205篇 |
2020年 | 407篇 |
2019年 | 272篇 |
2018年 | 336篇 |
2017年 | 333篇 |
2016年 | 488篇 |
2015年 | 522篇 |
2014年 | 686篇 |
2013年 | 833篇 |
2012年 | 656篇 |
2011年 | 719篇 |
2010年 | 607篇 |
2009年 | 771篇 |
2008年 | 885篇 |
2007年 | 777篇 |
2006年 | 707篇 |
2005年 | 609篇 |
2004年 | 564篇 |
2003年 | 546篇 |
2002年 | 295篇 |
2001年 | 240篇 |
2000年 | 243篇 |
1999年 | 193篇 |
1998年 | 156篇 |
1997年 | 195篇 |
1996年 | 149篇 |
1995年 | 123篇 |
1994年 | 72篇 |
1993年 | 47篇 |
1992年 | 49篇 |
1991年 | 31篇 |
1990年 | 29篇 |
1989年 | 31篇 |
1988年 | 41篇 |
1987年 | 24篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 8篇 |
1983年 | 5篇 |
1982年 | 7篇 |
1981年 | 12篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1957年 | 2篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
131.
V. A. Soloshonok N. Yu. Svistunova V. P. Kukhar' V. A. Solodenko N. A. Kuz'mina A. B. Rozhenko S. V. Galushko I. P. Shishkina A. O. Gudima Yu. N. Belokon' 《Russian Chemical Bulletin》1992,41(2):311-315
Alkylation, by -haloalkylphosphonates, of the Ni(II) complex of the Schiff base formed from glycine and (S)-2-N-(N1-benzylprolyl)-o-aminobenzophenone has been used for the asymmetric synthesis of (S)-2-amino-4-phosphonobutyric and (S)-2-amino-5-phosphonovaleric acids.Institute of Bioorganic Chemistry and Oil Chemistry, Ukrainian Academy of Sciences, 250800 Kiev. A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 2, pp. 397–402, February, 1992. 相似文献
132.
Ruifeng Liu Paula R. Moody Alex S. Vanburen Jeffrey A. Clark Joel A. Krauser Dennis R. Tate 《Vibrational Spectroscopy》1996,10(2):325-329
Results of ab initio and density functional theory calculations on the structure and vibrational frequencies of hypophosphite anion indicate earlier experimental assignments of the fundamental vibrational modes are correct while the recent reassignments of several modes proposed by Bickley et al. are inconsistent with the calculated results. 相似文献
133.
In the golden age of organocatalysis 总被引:8,自引:0,他引:8
The term "organocatalysis" describes the acceleration of chemical reactions through the addition of a substoichiometric quantity of an organic compound. The interest in this field has increased spectacularly in the last few years as result of both the novelty of the concept and, more importantly, the fact that the efficiency and selectivity of many organocatalytic reactions meet the standards of established organic reactions. Organocatalytic reactions are becoming powerful tools in the construction of complex molecular skeletons. The diverse examples show that in recent years organocatalysis has developed within organic chemistry into its own subdiscipline, whose "Golden Age" has already dawned. 相似文献
134.
Hidetake Sakuraba Hiroshi Maekawa 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(1-2):41-45
The two modified β-cyclodextrin (β-CD) derivatives having catechol-type ligand (2,3- and 3,4-dihydroxy groups on the benzoate
ring) were synthesized. The chiral catalytic activity of their MoV and CuII complexes was examined in the asymmetric oxidation of aromatic sulfides using hydrogen peroxide in water (pH 6.0). The oxidation
with the MoV complexes of two β-CD derivatives were more accelerated than that with the CuII complexes. The sign of the optical rotation of the sulfoxides obtained in the above two cases showed the opposite configuration
in the oxidation of the same sulfide. The difference of the enantioselectivity appeared also between the two complexes of
the 2,3- and 3,4-dihydroxybenzoate derivatives with the same metal ion. While the use of the MoV complexes with the catechol derivatives yielded the sulfoxides with 35–65% ee, the use of the CuII complexes gave the products with the␣opposite configuration at 26–52% ee. The chiral induction in the oxidation, observed
conversely between the␣catalysts, was reflected on the chiral conformation of the respective metal catalysts, showed in Induced
Circular Dichroism (ICD) spectra. The highest optical yield, 65%, was observed in the oxidation of butyl phenyl sulfide using
the catalytic amount (0.1 equiv) of the MoV complex with mono-6-O-(3,4-dihydroxybenzoyl)-β-CD. The reaction gave predominantly the (S)-sulfoxide in 95% chemical yield. 相似文献
135.
M. T. Dom nech Carb F. Bosch Reig J. V. Gimeno Adelantado V. Periz Martí nez 《Analytica chimica acta》1996,330(2-3):207-215
This paper is a study of the analytical capacity of Fourier transform infrared spectroscopy (FT-IR) for any type of samples from works of art. The analytical information obtained with this technique on organic and inorganic compounds is extremely useful in the preliminary studies necessary for diagnosis and to decide on the conservation process. This paper reports the analysis and study with FT-IR on samples extracted from the microlayers in several works of art from different periods (16th to 18th century) comprising wall paintings and canvas. The most outstanding of these being the frescoes by A. Palomino from two ceilings in the Santos Juanes church. The analytical procedures for the different components of the works studied such as
1. (a) varnish applied to wood panels and canvas paintings,
2. (b) binding media and pigments used by the artists,
3. (c) inerts, mortars, stuccos and grounds have been optimized. The FT-IR technique offers a quick analysis of microsamples (less than 0.5 mg) and is able to characterise the different molecular groups which provide information on the nature of the different materials of organic and inorganic origin used by the artist and thus permits the diagnosis of pathologies requiring conservation treatment.
136.
Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review. 相似文献
137.
In 1959, Horner showed that metalated alkyldiphenylphosphane oxides react with aldehydes or ketones to give alkenes. With this reaction, the diphenylphosphoryl (Ph2PO) group made its entrance into synthetic organic chemistry. In the thirty-six years since that date, extensive research has shown that this olefination, the Horner–Wittig reaction, has unique properties that make it much more than simply the phosphane oxide cousin of the more famous phosphorus-based olefinations—the Wittig reaction (based on phosphonium salts) and the Wadsworth–Emmons reaction (based on phosphonate esters). Early work on the Horner–Wittig reaction concentrated on the reactivity of phosphane oxides and the regioselectivity of their reactions, but more recently the power of the Ph2PO group to control the stereochemistry of alkenes, and to produce “on demand” either stereoisomer in high stereochemical purity, has emerged. From the study of these stereocontrolled Horner–Wittig reactions arose the realization that the Ph2PO group is useful not only for the control of the two-dimensional stereochemistry of alkenes, but also of three-dimensional stereochemistry in general. After a brief introduction to phosphane oxide chemistry, this review will examine the Horner–Wittig reaction, in both its original and “stereocontrolled” varieties. From there, we will move on to an account of the stereoselective construction of molecules containing the Ph2PO group, concentrating on the stereochemical directing effects of the Ph2PO group and on the role of its unique combination of attributes—steric bulk, electronegativity, and Lewis basicity—in controlling these reactions. Finally, we will present what is intended as a practical guide to this chemistry, covering the type of functionalized alkenes that have been made with the help of the Ph2PO group and giving guidelines that we hope will help the organic chemist to make the most of the chemistry the Ph2PO group has to offer. 相似文献
138.
水溶性金属卟啉肿瘤靶向磁共振成像造影剂的研究 总被引:5,自引:0,他引:5
利用显微荧光-阿达玛变换三维图像分析研究了Cu-TSPP,Mn-TSPP,Cu-TMAP,Mn-TMAP4种水溶性金属卟啉人细胞间质进入肿瘤细胞内的富集过程,对金属卟啉的自旋-晶格驰豫性能(R1)的天空结果表明,Mn(Ⅱ)卟啉配合物的R1、值结Gd-DTPA提高1.5-2倍。 相似文献
139.
140.
Kazimierz?DarowickiEmail author Waldemar?Felisiak Artur?Zieliński 《Journal of mathematical chemistry》2005,38(4):701-711
Oscillations of species concentration are phenomena accompanying several types of electrochemical and purely chemical processes.
Importance of analyzing of such processes results from both scientific and practical reasons. In the paper the authors deal
with investigation of time dependent spectra of various stages of Belousov-Zhabotinsky type chemical oscillations. As the
analytical tool the discrete wavelet transform is proposed. 相似文献