全文获取类型
收费全文 | 246篇 |
免费 | 10篇 |
国内免费 | 2篇 |
专业分类
化学 | 214篇 |
力学 | 5篇 |
数学 | 8篇 |
物理学 | 31篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 8篇 |
2020年 | 12篇 |
2019年 | 11篇 |
2018年 | 9篇 |
2017年 | 12篇 |
2016年 | 15篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 27篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 3篇 |
2008年 | 10篇 |
2007年 | 8篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 1篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1972年 | 1篇 |
1918年 | 1篇 |
排序方式: 共有258条查询结果,搜索用时 15 毫秒
251.
Sharmistha Das M. Mehedi Masud Lutfun Nahar Simon Gibbons Satyajit D. Sarker 《Tetrahedron》2008,64(37):8642-8645
6-Fluoroindan-1-carboxylic acid (4) was conveniently synthesised from 3-fluorobenzaldehyde in six steps. The structure of this new compound and three other intermediates, 3-fluorophenylcyanoethylacrylate (1), 3-fluorophenyl succinic acid (2) and 6-fluoro-3-oxo-indan-1-carboxylic acid (3) was elucidated by comprehensive spectral data analyses. The analgesic activity of compounds 3 and 4 was assessed by the acetic acid induced writhing in Swiss albino mice. 相似文献
252.
Ankur?Kanti?Guha Bidisha?Konwar Satyajit?Sarmah Ashwini?K.?PhukanEmail author 《Theoretical chemistry accounts》2012,131(3):1134
Density functional calculations have been carried out to investigate the effect of substituents attached to the heteroatoms
of N-heterocyclic carbenes (NHCs) on the structure and ligating properties of carbon(0) [C(NHC)2] and silicon(0) [Si(NHC)2] compounds. The substituents were found to have a profound role on the structure and ligating properties of these classes
of compounds. Fluoro- and chloro-substituted carbon(0) compounds were found to have quasi-linear geometries in which their
C(0) characteristics are “masked.” However, their C(0) characteristics become prominent in their protonated species. Large
negative charges and shallow bending potential of the central Cc–C0–Cc angle provide evidence for the “hidden C(0) characteristics” of these two compounds. Electron withdrawing substituents at
N-atoms of the two NHCs dramatically decreases the basicity of these compounds. Both natural bonding and atoms in molecules
analysis suggest that the most favorable Lewis structure of C(NHC)2 and Si(NHC)2 in their equilibrium geometries should be described (portrayed) as L=C=L and L → Si ← L, respectively, where L = NHCs. 相似文献
253.
Chavan S Vitillo JG Gianolio D Zavorotynska O Civalleri B Jakobsen S Nilsen MH Valenzano L Lamberti C Lillerud KP Bordiga S 《Physical chemistry chemical physics : PCCP》2012,14(5):1614-1626
The recently discovered UiO-66/67/68 class of isostructural metallorganic frameworks (MOFs) [J. H. Cavka et al. J. Am. Chem. Soc., 2008, 130, 13850] has attracted great interest because of its remarkable stability at high temperatures, high pressures and in the presence of different solvents, acids and bases [L. Valenzano et al. Chem. Mater., 2011, 23, 1700]. UiO-66 is obtained by connecting Zr(6)O(4)(OH)(4) inorganic cornerstones with 1,4-benzene-dicarboxylate (BDC) as linker resulting in a cubic MOF, which has already been successfully reproduced in several laboratories. Here we report the first complete structural, vibrational and electronic characterization of the isostructural UiO-67 material, obtained using the longer 4,4'-biphenyl-dicarboxylate (BPDC) linker, by combining laboratory XRPD, Zr K-edge EXAFS, TGA, FTIR, and UV-Vis studies. Comparison between experimental and periodic calculations performed at the B3LYP level of theory allows a full understanding of the structural, vibrational and electronic properties of the material. Both materials have been tested for molecular hydrogen storage at high pressures and at liquid nitrogen temperature. In this regard, the use of a longer ligand has a double benefit: (i) it reduces the density of the material and (ii) it increases the Langmuir surface area from 1281 to 2483 m(2) g(-1) and the micropore volume from 0.43 to 0.85 cm(3) g(-1). As a consequence, the H(2) uptake at 38 bar and 77 K increases from 2.4 mass% for UiO-66 up to 4.6 mass% for the new UiO-67 material. This value is among the highest values reported so far but is lower than those reported for MIL-101, IRMOF-20 and MOF-177 under similar pressure and temperature conditions (6.1, 6.2 and 7.0 mass%, respectively) [A. G. Wong-Foy et al. J. Am. Chem. Soc., 2006, 128, 3494; M. Dinca and J. R. Long. Angew. Chem., Int. Ed., 2008, 47, 6766]. Nevertheless the remarkable chemical and thermal stability of UiO-67 and the absence of Cr in its structure would make this material competitive. 相似文献
254.
As a natural outgrowth of the work done in Chavan (Proc Edin Math Soc 50:637–652, 2007; Studia Math 203:129–162, 2011), we introduce an abstract framework to study generating m-tuples, and use it to analyze hypercontractivity and hyperexpansivity in several variables. These two notions encompass (joint) hyponormality and subnormality, as well as toral and spherical isometric-ness; for instance, the Drury–Arveson 2-shift is a spherical complete hyperexpansion. Our approach produces a unified theory that simultaneously covers toral and spherical hypercontractions (and hyperexpansions). As a byproduct, we arrive at a dilation theory for completely hypercontractive and completely hyperexpansive generating tuples. We can then analyze in detail the Cauchy duals of toral and spherical 2-hyperexpansive tuples. We also discuss various applications to the theory of hypercontractive and hyperexpansive tuples. 相似文献
255.
Delazar A Modarresi M Shoeb M Nahar L Reid RG Kumarasamy Y Majinda RR Sarker SD 《Natural product research》2006,20(2):167-172
The reversed-phase preparative HPLC analysis of the methanol extract of the rhizomes of Eremostachys glabra (Lamiaceae) led to the isolation of two furanolabdane diterpene glycosides, phlomisoside II, and beta-D-glucopyranosyl-(1-->2)-beta-D-glucopyranosyl ester of phlomisoic acid (named eremostachiin), the latter being a novel natural product. The structure of the new compound has been elucidated unambiguously by HRMS and a series of 1D- and 2D-NMR spectroscopic techniques. The free radical scavenging activity of these compounds was assessed using the DPPH assay. 相似文献
256.
Amol Mhatre Vivek Chavan P. C. Kalsi V. S. Nadkarni 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(1):99-101
The gamma irradiation effects on the bulk etch rate, V
b of an indigenously prepared new nuclear track detector which is a copolymer of allyl bis-(2-nitroxy-ethyl) carbomate (ABNEC)
and allyl diglycol carbonate (ADC) [ABNEC:ADC (1:9)] were studied in the dose range of 25.0–250.0 kGy and etching temperature
range of 60–80 °C. The bulk etch rates increase and the activation energy values for bulk etching of gamma-irradiated detectors
decrease with the increase in gamma dose indicating the scission of the detector. UV–visible spectra of the unirradiated and
the irradiated films were also taken to explore the possibility of using this new detector for gamma dose measurements. 相似文献
257.
Organocatalytic enantioselective synthesis of β-blockers: (S)-propranolol and (S)-naftopidil 总被引:1,自引:0,他引:1
Sharad P. Panchgalle Rohitkumar G. Gore Subhash P. Chavan Uttam R. Kalkote 《Tetrahedron: Asymmetry》2009,20(15):1767-1770
An efficient enantioselective synthesis of β-adrenergic blockers (S)-propranolol and (S)-naftopidil with >98% ee using an l-proline-catalyzed α-aminoxylation of an aldehyde as a key step is described. 相似文献
258.
A Case Study on the Use of Binding Free Energies to Screen Inhibitors of Human Carbonic Anhydrase II
We present in this article a case study on the thermodynamics of binding to human carbonic anhydrase II (HCA II) by three well-known inhibitors, viz. (a) acetazolamide (AZM) that directly binds to the catalytic Zn(II) ion at the active site, (b) non-zinc binding 6-hydroxy-2-thioxocoumarin (FC5) (c) 2-[(S)-benzylsulfinyl]benzoic acid (3G1). In each case, the crystal structure or its analogue of inhibitor-bound HCA II has been used to perform classical molecular dynamics (MD) simulation in water till . AZM and FC5 are found to undergo repeated binding and unbinding with markedly different dynamics from the partially buried, substrate-binding hydrophobic pocket near the active site. 3G1, on the other hand, is found to remain mostly at its crystallographic binding site occluded from the active site of HCA II. The associated binding free energies ( ) have been computed using the known MM/GBSA method and compared to the available experimental data. Our results show that encounters several issues including limited sampling of multiple binding sites and incorrect prediction of the affinity of the chosen ligands. Possible use of the simulation results in further construction of Markov state models is also discussed. 相似文献