全文获取类型
收费全文 | 486篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 339篇 |
晶体学 | 4篇 |
力学 | 13篇 |
数学 | 100篇 |
物理学 | 38篇 |
出版年
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 7篇 |
2018年 | 8篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 3篇 |
2014年 | 16篇 |
2013年 | 25篇 |
2012年 | 30篇 |
2011年 | 34篇 |
2010年 | 24篇 |
2009年 | 13篇 |
2008年 | 35篇 |
2007年 | 26篇 |
2006年 | 26篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 8篇 |
2000年 | 7篇 |
1999年 | 12篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1989年 | 2篇 |
1984年 | 4篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1968年 | 3篇 |
1915年 | 1篇 |
1912年 | 2篇 |
1905年 | 1篇 |
1903年 | 1篇 |
1899年 | 1篇 |
1897年 | 2篇 |
1894年 | 1篇 |
1892年 | 1篇 |
1889年 | 2篇 |
1888年 | 1篇 |
1882年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 109 毫秒
491.
Energy‐dependent dead‐time correction in digital pulse processors applied to silicon drift detector's X‐ray spectra
下载免费PDF全文
![点击此处可从《Journal of synchrotron radiation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Suelen F. Barros Vito R. Vanin Alexandre A. Malafronte Nora L. Maidana Marcos N. Martins 《Journal of synchrotron radiation》2018,25(2):484-495
Dead‐time effects in X‐ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low‐energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead‐time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile‐up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead‐time fraction either from the calculations or using the value given by the detector acquisition system. The energy‐dependent dead‐time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse‐height distribution according to counting rate and energy spectrum characteristics is included. 相似文献
492.
Franco Cristiani Francesco A. Devillanova Francesco Isaia Vito Lippolis Gaetano Verani Francesco Demartin 《Heteroatom Chemistry》1993,4(6):571-578
1,4,7-Trithiacyclononane ([9]aneS3) reacts with molecular diiodine in CH2Cl2 to form a 1:1 adduct. The formation constant and the thermodynamic parameters of this adduct have been determined by UV-visible spectra of several solutions at the temperatures of 15, 20, 25, 30, and 35°C. The 13C NMR spectra show that adducts with higher ligand/diiodine molar ratios are formed. Two neutral charge-transfer molecular compounds having formula 2[9]aneS3 · 4I2 ( I ) and [9]aneS3 · 3I2 · ( II ) have been obtained as crystals. The crystals of I are triclinic (a = 8.498(2) Å, b = 13.984(4) Å, c = 14.898(6) Å, α = 65.57(2)°, γ = 89.19(2)°, γ = 81.26(2)°, Z = 2, space group P1; R = 0.025) and contain units formed by two [9]aneS3 molecules connected by a diiodine molecule; one [9]aneS3 binds two other diiodine molecules, while the second binds only one other diiodine molecule. The crystals of II are monoclinic (a = 13.810(2) Å, b = 9.829(4) Å, c = 16.198(6) Å, β = 113.41(2)°, Z = 4, space group P21/c; R = 0.019) and contain molecules of [9]aneS3 binding three diiodine molecules. FT-Raman spectra in the characteristic v(I–I) region, carried out on the solid adducts, are discussed in comparison with the structural parameters. 相似文献
493.
Dr. Giuseppe Dilauro Dr. Cosimo Luccarelli Dr. Andrea F. Quivelli Prof. Paola Vitale Prof. Filippo M. Perna Prof. Vito Capriati 《Angewandte Chemie (International ed. in English)》2023,62(30):e202304720
Advancing the development of perfecting the use of polar organometallics in bio-inspired solvents, we report on the effective generation in batch of organosodium compounds, by the oxidative addition of a C−Cl bond to sodium, a halogen/sodium exchange, or by direct sodiation, when using sodium bricks or neopentylsodium in hexane as sodium sources. C(sp3)-, C(sp2)-, and C(sp)-hybridized alkyl and (hetero)aryl sodiated species have been chemoselectively trapped (in competition with protonolysis), with a variety of electrophiles when working “on water”, or in biodegradable choline chloride/urea or L-proline/glycerol eutectic mixtures, under hydrous conditions and at room temperature. Additional benefits include a very short reaction time (20 s), a wide substrate scope, and good to excellent yields (up to 98 %) of the desired adducts. The practicality of the proposed protocol was demonstrated by setting up a sodium-mediated multigram-scale synthesis of the anticholinergic drug orphenadrine. 相似文献
494.
Dr. Giuseppe Dilauro Dr. Luciana Cicco Prof. Paola Vitale Prof. Filippo Maria Perna Prof. Vito Capriati 《European journal of organic chemistry》2023,26(3):e202200814
A Deep Eutectic Solvent, choline chloride/glycerol (1 : 2 mol mol−1), proved to be an effective and sustainable reaction medium to promote telescoped, one-pot Mizoroki-Heck cross-coupling/reduction processes between 2,3-dihydrofuran or 3,4-dihydro-2H-pyran and several (hetero)aryl halides to easily access valuable 2-(hetero)aryl tetrahydrofuran (THF) or tetrahydropyran derivatives in up to 95 % yield. Notably, the whole transformation takes place under aerobic conditions, in the absence of additional ligands, and with a good substrate scope. The practicability of the method is also exemplified by the sustainable synthesis of two key THF derivatives, which are side chains of pharmacologically relevant inhibitors of Kv1.2 channel. 相似文献