全文获取类型
收费全文 | 457篇 |
免费 | 18篇 |
国内免费 | 1篇 |
专业分类
化学 | 309篇 |
晶体学 | 6篇 |
力学 | 18篇 |
数学 | 22篇 |
物理学 | 121篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 20篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 19篇 |
2016年 | 27篇 |
2015年 | 16篇 |
2014年 | 40篇 |
2013年 | 53篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 15篇 |
2009年 | 14篇 |
2008年 | 19篇 |
2007年 | 20篇 |
2006年 | 9篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 9篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1973年 | 6篇 |
1971年 | 1篇 |
排序方式: 共有476条查询结果,搜索用时 296 毫秒
101.
Mahima Goel Dr. Manickam Jayakannan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(10):2867-2874
We report CH/π hydrogen‐bond‐driven self‐assembly in π‐conjugated skeletons based on oligophenylenevinylenes (OPVs) and trace the origin of interactions at the molecular level by using single‐crystal structures. OPVs were designed with appropriate pendants in the aromatic core and varied by hydrocarbon or fluorocarbon tails along the molecular axis. The roles of aromatic π‐stack, van der Waals forces, fluorophobic effect and CH/π interactions were investigated on the theromotropic liquid crystallinity of OPV molecules. Single‐crystal structures of hydrocarbon OPVs provided direct evidence for the existence of CH/π interactions between the π‐ring (H‐bond acceptor) and alkyl C? H (H‐bond donor). The four important crystallographic parameters, dc?x=3.79 Å, θ=21.49°, φ=150.25° and dHp?x=0.73 Å, matched in accordance with typical CH/π interactions. The CH/π interactions facilitate the close‐packing of mesogens in x–y planes, which were further protruded along the c axis producing a lamellar structure. In the absence of CH/π interactions, van der Waals interactions drove the assembly towards a Schlieren nematic texture. Fluorocarbon OPVs exhibited smectic liquid‐crystalline textures that further underwent Smectic A (SmA) to Smectic C (SmC) phase transitions with shrinkage up to 11 %. The orientation and translational ordering of mesogens in the liquid‐crystalline (LC) phases induced H‐ and J‐type molecular arrangements in fluorocarbon and hydrocarbon OPVs, respectively. Upon photoexcitation, the H‐ and J‐type molecular arrangements were found to emit a blue or yellowish/green colour. Time‐resolved fluorescence decay measurements confirmed longer lifetimes for H‐type smectic OPVs relative to that of loosely packed one‐dimensional nematic hydrocarbon‐tailed OPVs. 相似文献
102.
G. Chandra Sekhar Reddy M. Veera Narayana Reddy C. Radha Rani N. Bakthavatchala Reddy K. Uma Maheswara Rao S.K. Nayak C. Suresh Reddy 《Heteroatom Chemistry》2012,23(3):247-253
A new family of di(1‐oxo/thioxoper‐hydro‐1λ5‐[1,3,2]diazaphospholo[1,5‐a]pyridine‐1‐yl)(4‐substituted phenyl) boronates ( 4a – j ) has been synthesized in a two‐step process. A reaction of (±)‐piperidin‐2‐yl‐methanamine ( 1 ) phosphoryl/phosphorothioyl chloride in the presence of triethylamine in dry tetrahydrofuran formed the intermediate monochloride ( 2 ), which on condensation with p‐substituted phenylboronic acids ( 3a – j ) afforded the titled compounds ( 4a – j ). They were characterized by elemental, IR, 1H, 13C, 31P NMR, and mass spectral analyses. All these compounds showed moderate to high antiosteoclast and osteoblast activity. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:247–253, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21010 相似文献
103.
A quartz crystal microbalance can be used as a biosensor if biological receptor molecules (ligands) are attached to the crystal.
To improve the sensitivity, the surface area of the gold electrodes on the crystal was increased by rendering the electrodes
porous. This increased the response up to a factor of 3. A protein model system with human anti-myoglobin as ligand and sheep
skeletal myoglobin at different concentrations as analyte was used. The quartz crystal was mounted in a flow-cell, where immobilisation,
binding and regeneration of the surface were carried out. The kinetics of the model system was monitored under various experimental
conditions.
Received February 2, 2000. Revision June 30, 2000. 相似文献
104.
Lal Sohan Arora Sanjiv Kumar Vinod Rani Shikha Jagdeva Geetanjali 《Journal of Thermal Analysis and Calorimetry》2021,143(4):3267-3274
Journal of Thermal Analysis and Calorimetry - The different concentrations of chitosan were applied on cotton fabrics using glutaraldehyde as a cross-linking agent. The fabric samples were... 相似文献
105.
Saravanan M. Dhivakar S. Mohapatra M. Kutti Rani S. Vijayakumaran K. 《Journal of fluorescence》2022,32(4):1557-1563
The present work describes the synthesis and characterization of pyrene derivatives, N-(1-Pyrenoylmethyl) pyridinium bromide (PM-PB) and N-(1-Pyrenoylmethyl)-N,N,N-triethylammonium bromide (PM-TAB). The photophysical behavior of these molecules has been studied in various protic and aprotic solvents. Using steady state fluorescence intensity, fluorescence anisotropy and dynamic fluorescence lifetime studies, the sensitivity of these molecules towards the micellization process of bile salts has been monitored. These derivatives have been effectively used in estimating critical micellar concentration (CMC) of bile salt, sodium deoxycholate (NaDC).
相似文献106.
The γ- and conversion electron spectra following131Ba ε-decay are investigated, using HPGe detector and mini-orange electron spectrometer. Attention is particularly focussed
on identifying weak transitions associated with low energy high spin levels in131Cs level scheme earlier inferred in reaction studies but not yet observed in131Ba decay. Our experiment identifies 15 new gammas and 6 new conversion lines in this decay. Internal conversion coefficients
and multipolarities of several transitions are determined. Five new levels (3 with Iπ = 7/2+ and one each with Iπ 9/2+ and 11/2−) are introduced in the131Cs level scheme based on our observations taken together with the results from reaction studies. Spin-parity assignments to
a few other levels are also suggested 相似文献
107.
108.
Sol-Gel Synthesis of Nanocrystalline PZT Using a Novel System 总被引:2,自引:0,他引:2
Jacob K. Stanly Panicker N. Rani Selvam I. Packia Kumar V. 《Journal of Sol-Gel Science and Technology》2003,28(3):289-295
A simple system has been developed for the preparation of lead zirconate titanate, Pb(Zr
x
Ti1 – x
)O3 powders by sol-gel process. To achieve stable and homogeneous precursor solutions, chelating ligands such as acetic acid and acetylacetone have been used for the chemical modification of titanium and zirconium starting precursors. Phase-pure PZT powders were obtained, through a pyrochlore-free pathway, from the amorphous xerogel after heat treatment at 600°C. The formation of the crystalline phase, compositional homogeneity, sinterability, dielectric and piezoelectric characteristics of PZT are reported. 相似文献
109.
V. Srinivasa Rao M. Srinivasa Reddy K. Thomas S. S. Raju B. L. Rani B. Hari Babu 《Journal of solution chemistry》2018,47(3):430-448
The density (ρ), speed of sound (u) and refractive index (nD) of [Bmim][PF6], 2-pyrrolidone and their binary mixtures were measured over the whole composition range as a function of temperature between (303.15 and 323.15)?K at atmospheric pressure. Experimental values were used to calculate the excess molar volumes \( \left( {V_{m}^{\text{E}} } \right) \), excess partial molar volumes \( \left( {\overline{V}_{m}^{\text{E}} } \right) \), partial molar volumes at infinite dilution \( \left( {\overline{V}_{m}^{{{\text{E}},\infty }} } \right) \), excess values of isentropic compressibility \( \left( {\kappa_{S}^{\text{E}} } \right) \), free length \( \left( {L_{\text{f}}^{\text{E}} } \right) \) and speeds of sound \( \left( {u^{\text{E}} } \right) \) for the binary mixtures. The calculated properties are discussed in terms of molecular interactions between the components of the mixtures. The results reveal that interactions between unlike molecules take place, particularly through intermolecular hydrogen bond formation between the C2–H of [Bmim][PF6] and the carbonyl group of pyrrolidin-2-one. An excellent correlation between thermodynamic and IR spectroscopic measurements was observed. The observations were further supported by the Prigogine–Flory–Patterson (PFP) theory of excess molar volume. 相似文献
110.
Sundaravel Vivek Kumar Mani Anusha Rani Abdulrahman I. Almansour Raju Suresh Kumar S. Athimoolam Raju Ranjith Kumar 《Tetrahedron》2018,74(35):4569-4577
A facile syntheses of novel poly-substituted pyridine/benzo fused cyclododecane hybrid heterocycles have been achieved through one-pot multi-component tandem strategy employing cyclododecanone, aromatic aldehydes and malononitrile. 相似文献