全文获取类型
收费全文 | 368篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
化学 | 283篇 |
晶体学 | 3篇 |
力学 | 12篇 |
数学 | 25篇 |
物理学 | 60篇 |
出版年
2023年 | 3篇 |
2021年 | 2篇 |
2019年 | 5篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 19篇 |
2010年 | 16篇 |
2009年 | 7篇 |
2008年 | 16篇 |
2007年 | 16篇 |
2006年 | 13篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 16篇 |
2002年 | 20篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 5篇 |
1998年 | 3篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 12篇 |
1978年 | 4篇 |
1977年 | 11篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 2篇 |
1972年 | 2篇 |
1968年 | 1篇 |
1934年 | 1篇 |
排序方式: 共有383条查询结果,搜索用时 15 毫秒
101.
Kenshu Fujiwara Yu-ichi Aki Fuyuki Yamamoto Mariko Kawamura Masanori Kobayashi Azusa Okano Daisuke Awakura Shunsuke Shiga Akio Murai Hidetoshi Kawai Takanori Suzuki 《Tetrahedron letters》2007,48(26):4523-4527
In this study, we synthesized the C8-C20 and C21-C30 segments of the diarrhetic shellfish toxin pectenotoxin 2. The C8-C20 segment was assembled from a phosphonate corresponding to the C8-C15 segment (prepared from l-malic acid in 19 steps) and an aldehyde corresponding to the C16-C20 segment (synthesized from 3-methyl-3-butenol in nine steps) by a twelve-step process including the Horner-Wadsworth-Emmons reaction, regio- and stereoselective reduction of the resulting enone, diastereoselective epoxidation, and 5-exo epoxide cleavage forming the C-ring. The C21-C30 segment was constructed in 13 steps from (S)-glycidol via a route involving E-ring formation by 5-exo epoxide cleavage and stereoselective methylation at C27 by the Evans method. 相似文献
102.
G. Yuan Y. Kato H. Daido R. Kodama K. Murai S. Nakai 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,32(1):1-5
Classification of 3-3 transitions in neonlike germanium in laser-produced plasma has been made. The spectra have been observed in the range of 185–290 Å using a high resolving power (λ/Δλ ~ 13000) grazing-incidence spectrometer in XUV laser experiment. A total of 21 lines (including five lasing lines) have been classified as transitions between the 2s 22p 53s, 3p, 3d or 2s2p 63p, 3d and sodiumlike germanium configurations. The identified transitions have been used to derive energy levels of 2s 22p 53l in neonlike germanium. The experimental results have been compared with theoretical predictions from Dirac-Fock (MCDF) calculations. 相似文献
103.
Harusawa S Murai Y Moriyama H Imazu T Ohishi H Yoneda R Kurihara T 《The Journal of organic chemistry》1996,61(13):4405-4411
A synthetic route to 4(5)-(beta-D-ribofuranosyl)imidazole (1), starting from 2,3,5-tri-O-benzyl-D-ribose (5), was developed via a Mitsunobu cyclization. Reaction of 5 with the lithium salt of bis-protected imidazole afforded the corresponding 5-ribosylimidazole 7RS. Hydrolysis of 7RS gave a 1:1 mixture of diol isomers 8R and 8S having an unsubstituted imidazole. Mitsunobu cyclization of the mixture 8RS using N,N,N',N'-tetramethylazodicarboxamide and Bu(3)P exclusively afforded benzylated beta-ribofuranosyl imidazole 9beta in 92% yield, accompanied by alpha-anomer 9alpha, in a ratio of 26.3:1. The configuration of 9beta was established by X-ray crystallography of ethoxycarbonyl derivative 10beta. Reductive debenzylation of 9beta over Pd/C was carried out, and the synthesis of 1 was attained from starting 5 in four steps and 87% overall yield. This synthetic methodology was extended to the synthesis of 4(5)-(2-deoxy-beta-D-ribofuranosyl)imidazole (2). Mitsunobu cyclization of a 1:1 mixture of the corresponding diol isomers 14RS produced 15beta and 15alpha in a ratio of 5.4:1. The synthesis of 2 was attained in a 59% overall yield from the starting 3,5-di-O-benzyl-2-deoxy-D-ribose (12). beta-Stereoselective glycosylation in the key step is discussed and explained by intramolecular hydrogen bonding between an NH in the imidazole and the oxygen functional group in the sugar moiety. 相似文献
104.
Takashi Nishino Ryousuke Matsui Katsuhiko Nakamae 《Journal of Polymer Science.Polymer Physics》1999,37(11):1191-1196
The elastic moduli El of the crystalline regions of α‐chitin and chitosan in the direction parallel to the chain axis were measured by X‐ray diffraction. The El values were 41 GPa for α‐chitin, and 65 GPa for chitosan, respectively, at 20°C. The contracted skeletons of α‐chitin and chitosan are the key factor for the low El values compared with that (138 GPa) of cellulose I. The El value of α‐chitin was constant at 41 GPa both at −190°C and 150°C, which indicates that the molecular chain of α‐chitin is stable against heat within the temperature and stress range studied. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1191–1196, 1999 相似文献
105.
The preparation and optical properties of the novel silicon-related material named oxygen-crosslinked polysilane were investigated. The oxygen-crosslinked polysilane was prepared by the thermal annealing of the precursor polysilane bearing alkoxyl groups. The photoluminescence consisting of a broad visible band at about 440 nm and a relatively sharp band at about 360 nm was observed at room temperature. The relative intensities of the visible emission were changed during the crosslinking. The visible emission was greatly affected by the steric hindrance of the alkoxyl groups of the precursor. The visible electroluminescene (EL) was also observed uniformly from the EL cell consisting of the oxygen-crosslinked polysilane film sandwiched between A1 electrode and indium-tin-oxide (ITO) electrode. The current densities of the EL cell increased with an increase in the oxygen-crosslinking. © 1997 John Wiley & Sons, Ltd. 相似文献
106.
Ammonium eneselenolate 2 derived from selenothioic acid S-ester 1 was reacted with electron-deficient alkenes 4 and alkynes 9 . Ammonium eneselenolate 2 underwent Michael addition with 4 to give two types of Michael adducts, 5 and 6 . Products 6 incorporated two molecules of 4 . In contrast, the reaction of 2 with 9 took place at the selenium atom to give γ-oxo divinyl selenides 10 with high Z-stereoselectivity. During the further elaboration of the reactivity of the products derived from 2 and carbonyl compounds, unexpected reaction was found in the addition of vinylmagnesium bromide to Se-vinyl ester 3 . The spectroscopic data supported the formation of the enol form 12 of β-oxo selenothioic acid S-ester 13 . © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:187–192, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20003 相似文献
107.
108.
109.
We characterize componentwise linear monomial ideals with minimal Taylor resolution and consider the lower bound for the Betti
numbers of componentwise linear ideals. 相似文献
110.
Array illumination built on a binary phase grating with a green, Q-switched, pulse Nd:YAG laser is used for patterning indium-tin-oxide films into electrodes of liquid crystal display panels. To this end, even-fanout gratings are recursively designed by simulated-annealing algorithm and are realized in quartz glasses by dry etching. While an array of identically intense beam spots strikes the film, a table supporting the film moves in a direction orthogonal to said spots array at a constant speed, forming a large group of equispaced grooves in the film. A machining yield of 1600 mm/s has been attained using a 32×1 grating.To whom correspondence should be addressed 相似文献