全文获取类型
收费全文 | 1015篇 |
免费 | 44篇 |
国内免费 | 8篇 |
专业分类
化学 | 827篇 |
晶体学 | 7篇 |
力学 | 21篇 |
数学 | 128篇 |
物理学 | 84篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 15篇 |
2020年 | 30篇 |
2019年 | 15篇 |
2018年 | 15篇 |
2017年 | 10篇 |
2016年 | 26篇 |
2015年 | 24篇 |
2014年 | 26篇 |
2013年 | 55篇 |
2012年 | 55篇 |
2011年 | 107篇 |
2010年 | 38篇 |
2009年 | 39篇 |
2008年 | 101篇 |
2007年 | 71篇 |
2006年 | 87篇 |
2005年 | 83篇 |
2004年 | 58篇 |
2003年 | 53篇 |
2002年 | 44篇 |
2001年 | 16篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 7篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1970年 | 6篇 |
1938年 | 2篇 |
1937年 | 1篇 |
1934年 | 1篇 |
1931年 | 1篇 |
1929年 | 2篇 |
排序方式: 共有1067条查询结果,搜索用时 15 毫秒
971.
We report the infrared spectrum of InCl3 in solid argon. The observed spectrum is consistent with a planar D3h structure for this molecule. 相似文献
972.
973.
Mary A. Blanchette William Choy Jeffery T. Davis Amy P. Essenfeld Satoru Masamune William R. Roush Toshiya Sakai 《Tetrahedron letters》1984,25(21):2183-2186
A mild olefination procedure, utilizing LiCl and an amine, has been developed for use with base-sensitive aldehydes and phosphonates. 相似文献
974.
Yan H Lee P Armstrong NR Graham A Evmenenko GA Dutta P Marks TJ 《Journal of the American Chemical Society》2005,127(9):3172-3183
This contribution describes an organosiloxane cross-linking approach to robust, efficient, adherent hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). An example is 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi(2)), which combines the hole-transporting efficiency of N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine) (TPD, prototypical small-molecule HTL material) and the strong cross-linking/densification tendencies of organosilanol groups. Covalent chemical bonding of TPDSi(2) to PLED anodes (e.g., indium tin oxide, ITO) and its self-cross-linking enable fabrication of three generations of insoluble PLED HTLs: (1) self-assembled monolayers (SAMs) of TPDSi(2) on ITO; (2) cross-linked blend networks consisting of TPDSi(2) + a hole transporting polymer (e.g., poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine), TFB) on ITO; (3) TPDSi(2) + TFB blends on ITO substrates precoated with a conventional PLED HTL, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). PLED devices fabricated using these new HTLs exhibit comparable or superior performance vs comparable devices based on PEDOT-PSS alone. With these new HTLs, current efficiencies as high as approximately 17 cd/A and luminances as high as approximately 140,000 cd/m(2) have been achieved. Further experiments demonstrate that not only do these HTLs enhance PLED anode hole injection but they also exhibit significantly greater electron-blocking capacity than PEDOT-PSS. The present organosiloxane HTL approach offers many other attractions such as convenience of fabrication, flexibility in choosing HTL components, and reduced HTL-induced luminescence quenching, and can be applied as a general strategy to enhance PLED performance. 相似文献
975.
This paper describes the commercially-viable synthesis and isolation of 2-ethoxy-3-pyridylboronic acid on a ca. 70 g scale via a directed ortho-metalation reaction on readily-available 2-ethoxypyridine. A range of efficient cross-coupling reactions of 2-ethoxy-3-pyridylboronic acid with selected aryl/heteroaryl halides under palladium-catalysed Suzuki-Miyaura conditions yield novel 2-ethoxy-3-aryl/heteroaryl-pyridines in high yield (heteroaryl=pyridyl, pyrimidyl, pyrazyl). The X-ray crystal structure of 2-ethoxy-3-pyridylboronic acid reveals that the boronic acid group takes part in an intramolecular O-H?O bond with the adjacent ethoxy substituent, and an intermolecular O-H?N bond. 相似文献
976.
[reaction: see text] A serine-derived 1,5-dioxaspiro[3.2]hexane template is shown to be a useful precursor for both aminodiol and aminotriol sphingoid bases by its conversion to D-erythro-dihydrosphingosine and D-xylo-phytoshingosine. 相似文献
977.
ICR trapped ion techniques are used to examine the kinetics of proton transfer from MnH+ (formed as a fragment ion from HMn (CO)5 by electron impact) to bases of varying strength. Deprotonation is rapid with bases whose proton affinity exceeds 196±3 kcal mol?1. This value for PA (Mn) yields the homolytic bond dissociation energy D0(Mn+-H) = 53±5 kcal mol?1. 相似文献
978.
Doonan CJ Stockert A Hille R George GN 《Journal of the American Chemical Society》2005,127(12):4518-4522
In this paper we report the results of molybdenum K-edge X-ray absorption studies performed on the oxidized active site of xanthine oxidase at pH 6 and 10. These results indicate that the active site possesses one terminal oxygen ligand (Mo=O), two thiolate ligands (Mo-S), one terminal sulfido ligand (Mo=S), and one Mo-OH moiety. EXAFS analysis demonstrates that the Mo-OH bond shortens from 1.97 A at pH 6 to 1.75 A at pH 10, which is consistent with the generation of a Mo-O- moiety. This study provides convincing structural evidence that the catalytic oxygen donor at the oxidized active site of xanthine oxidase is Mo-OH rather than the Mo-OH2 ligation previously suggested by X-ray crystallography. These results support a mechanism initiated by base-assisted nucleophilic attack of the substrate by Mo-OH. 相似文献
979.
Two-dimensional separation of peptides using RP-RP-HPLC system with different pH in first and second separation dimensions 总被引:1,自引:0,他引:1
Two-dimensional high performance liquid chromatography is a useful tool for proteome analysis, providing a greater peak capacity than single-dimensional LC. The most popular 2D-HPLC approach used today for proteomic research combines strong cation exchange and reversed-phase HPLC. We have evaluated an alternative mode for 2D-HPLC of peptides, employing reversed-phase columns in both separation dimensions. The orthogonality of 2D separation was investigated for selected types of RP stationary phases, ion-pairing agents and mobile phase pH. The pH appears to have the most significant impact on the RP-LC separation selectivity; the greatest orthogonality was achieved for the system with C18 columns using pH 10 in the first and pH 2.6 in the second LC dimension. Separation was performed in off-line mode with partial fraction evaporation. The achievable peak capacity in RP-RP-HPLC and overall performance compares favorably to SCX-RP-HPLC and holds promise for proteomic analysis. 相似文献
980.
Yang X Yuan L Yamato K Brown AL Feng W Furukawa M Zeng XC Gong B 《Journal of the American Chemical Society》2004,126(10):3148-3162
Oligo(m-phenylene ethynylenes) (oligo(m-PE)) with backbones rigidified by intramolecular hydrogen bonds were found to fold into well-defined conformations. The localized intramolecular hydrogen bond involves a donor and an acceptor from two adjacent benzene rings, respectively, which enforces globally folded conformations on these oligomers. Oligomers with two to seven residues have been synthesized and characterized. The persistence of the intramolecular hydrogen bonds and the corresponding curved conformations were established by ab initio and molecular mechanics calculations, 1D and 2D (1)H NMR spectroscopy, and UV spectroscopy. Pentamer 5, hexamer 6, and heptamer 7 adopt well-defined helical conformations. Such a backbone-based conformational programming should lead to molecules whose conformations are resilient toward structural variation of the side groups. These m-PE oligomers have provided a new approach for achieving folded unnatural oligomers under conditions that are otherwise unfavorable for previously described, solvent-driven folding of m-PE foldamers. Stably folded structures based on the design principle described here can be developed and may find important applications. 相似文献