全文获取类型
收费全文 | 689篇 |
免费 | 41篇 |
国内免费 | 17篇 |
专业分类
化学 | 513篇 |
晶体学 | 3篇 |
力学 | 40篇 |
数学 | 92篇 |
物理学 | 99篇 |
出版年
2023年 | 1篇 |
2022年 | 15篇 |
2021年 | 25篇 |
2020年 | 30篇 |
2019年 | 42篇 |
2018年 | 39篇 |
2017年 | 35篇 |
2016年 | 72篇 |
2015年 | 38篇 |
2014年 | 47篇 |
2013年 | 101篇 |
2012年 | 56篇 |
2011年 | 47篇 |
2010年 | 44篇 |
2009年 | 28篇 |
2008年 | 25篇 |
2007年 | 33篇 |
2006年 | 8篇 |
2005年 | 16篇 |
2004年 | 8篇 |
2003年 | 8篇 |
2002年 | 7篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有747条查询结果,搜索用时 15 毫秒
741.
In this study, silica-supported titanium tetrachloride was prepared and used as a novel catalyst for rapid and efficient synthesis of 2,4,5-trisubstituted imidazoles by a three-component, one-pot condensation of 1,2-diketones and aryl aldehydes in excellent yield under solvent-free conditions using conventional heating or microwave irradiation.
742.
Abolghasem BakhodaNasser Safari Vahid AmaniHamid Reza Khavasi Mahin Gheidi 《Polyhedron》2011,30(17):2950-2956
Homo bi-copper complexes [Cu2{PhP(2-py)2}2(NO3)3] (1) and [Cu2{P(2-py)3}2Cl2] (2), were synthesized from the reaction of Cu(NO3)2·3H2O and CuCl2·2H2O with their corresponding 2-pyridylphosphine ligands. Compound 1 has a mixed valence Cu(I)-Cu(II) core with electron acceptor phosphine atoms and two NO3− anions coordinated in a monodentate fashion to Cu(I), giving it a distorted tetrahedral geometry. The environment of Cu(II) in 1 is composed of four nitrogen atoms from pyridyl and another NO3− anion in a square pyramidal geometry. This complex shows luminescence and a low energy absorption band at 969 nm corresponding to intermetallic electron transfer between the copper centers. Complex 2 was prepared from the treatment of copper(II) chloride with tris(2-pyridyl)phosphine, producing a binuclear copper complex which possesses a crystallographic inversion center. The copper geometry in this complex is distorted tetrahedral with coordination of one Cl−, two nitrogens from one bridging tris(2-pyridyl)phosphine ligand and one P atom from the other bridging tris(2-pyridyl)phosphine ligand, in a similar way observed in related complexes. The products have been characterized by spectroscopic methods and also by the single-crystal X-ray diffraction method. 相似文献
743.
Seyed Javad Ahmadi Sodeh Sadjadi Morteza Hosseinpour 《Monatshefte für Chemie / Chemical Monthly》2011,44(24):1163-1168
Abstract
An efficient method for the synthesis of 4-amino-5-pyrimidinecarbonitriles by the three-component reaction of malononitrile, aldehydes, and N-unsubstituted amidines under aqueous conditions using CuO microspheres as catalyst is reported. The catalyst exhibited remarkable reusable activity. 相似文献744.
Ali Ahmadi Mohammad Kamfiroozi Javad Beheshtian Nasser L. Hadipour 《Structural chemistry》2011,22(6):1261-1265
Our main objectives are to address the following fundamental issues: (1) A density functional theory study on the structural and electronic properties of the zigzag single-walled aluminum nitride nanotubes (AlNNTs) with various diameters, using B3LYP/6-31G* level of theory. (2) An ONIOM study on the curvature effect of AlNNTs on the NH3 adsorption process using B3LYP/6-31G* and semiempirical AM1 approaches. Furthermore, a potential energy surface is calculated for NH3 moving toward AlNNT surface. In contrast to semiconducting carbon nanotubes (Louie, Top Appl Phys 80:113, 2001) our calculations confirmed that the HOMO?CLUMO energy gap of AlNNTs increases with an increase of the tube diameter. Additionally, we showed that HOMO/LUMO interaction between NH3 and AlNNTs becomes stronger as the tube diameter decreases. 相似文献
745.
Javad Tavakoli Jesus Shrestha Sajad R. Bazaz Maryam A. Rad Majid E. Warkiani Colin L. Raston Joanne L. Tipper Youhong Tang 《Molecules (Basel, Switzerland)》2022,27(3)
The current study describes a new technology, effective for readily preparing a fluorescent (FL) nanoprobe-based on hyperbranched polymer (HB) and aggregation-induced emission (AIE) fluorogen with high brightness to ultimately develop FL hydrogels. We prepared the AIE nanoprobe using a microfluidic platform to mix hyperbranched polymers (HB, generations 2, 3, and 4) with AIE (TPE-2BA) under shear stress and different rotation speeds (0–5 K RPM) and explored the FL properties of the AIE nanoprobe. Our results reveal that the use of HB generation 4 exhibits 30-times higher FL intensity compared to the AIE alone and is significantly brighter and more stable compared to those that are prepared using HB generations 3 and 2. In contrast to traditional methods, which are expensive and time-consuming and involve polymerization and post-functionalization to develop FL hyperbranched molecules, our proposed method offers a one-step method to prepare an AIE-HB nanoprobe with excellent FL characteristics. We employed the nanoprobe to fabricate fluorescent injectable bioadhesive gel and a hydrogel microchip based on polyvinyl alcohol (PVA). The addition of borax (50 mM) to the PVA + AIE nanoprobe results in the development of an injectable bioadhesive fluorescent gel with the ability to control AIEgen release for 300 min. When borax concentration increases two times (100 mM), the adhesion stress is more than two times bigger (7.1 mN/mm2) compared to that of gel alone (3.4 mN/mm2). Excellent dimensional stability and cell viability of the fluorescent microchip, along with its enhanced mechanical properties, proposes its potential applications in mechanobiology and understanding the impact of microstructure in cell studies. 相似文献
746.
Marilyn M. Olmstead Javad J. Sahbari 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(12):o719-o720
The oxime of acetamide, viz. N‐hydroxyethanimidamide, C2H6N2O, has a complex hydrogen‐bonding arrangement in its crystal structure, featuring one strong O—H⋯N hydrogen bond together with weaker hydrogen bonding involving the amide groups. Conjugation effects lead to atypical distances and angles. 相似文献
747.
Jonathon A. Campbell Y. A. Goodwin Mohsen Safari Ardi George P. Simon Christine J. T. Landry-Coltrain 《Macromolecular Symposia》1997,118(1):383-388
This paper summarises the currently available literature concerned with measurement of free volume in miscible, amorphous polymer blends using positron annihilation lifetime spectroscopy (PALS) which probes excluded volume at the angstrom level. Previously reported data is compared with new data from a range of different blend systems. Miscible blends tend to show a negative deviation of free volume size (and to a lesser degree free volume fraction) on mixing due to the intimacy of packing of the blend component macromolecules. A largely immiscible system is also reported and shows a different behaviour (positive deviation of free volume size) and this is ascribed to additional free volume at the interface. 相似文献