全文获取类型
收费全文 | 656篇 |
免费 | 61篇 |
国内免费 | 29篇 |
专业分类
化学 | 499篇 |
晶体学 | 3篇 |
力学 | 22篇 |
数学 | 79篇 |
物理学 | 143篇 |
出版年
2023年 | 11篇 |
2022年 | 13篇 |
2021年 | 14篇 |
2020年 | 25篇 |
2019年 | 32篇 |
2018年 | 22篇 |
2017年 | 15篇 |
2016年 | 40篇 |
2015年 | 25篇 |
2014年 | 28篇 |
2013年 | 39篇 |
2012年 | 42篇 |
2011年 | 41篇 |
2010年 | 29篇 |
2009年 | 26篇 |
2008年 | 39篇 |
2007年 | 41篇 |
2006年 | 28篇 |
2005年 | 21篇 |
2004年 | 19篇 |
2003年 | 8篇 |
2002年 | 20篇 |
2001年 | 6篇 |
2000年 | 16篇 |
1999年 | 9篇 |
1998年 | 10篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 8篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 3篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 8篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有746条查询结果,搜索用时 31 毫秒
21.
22.
23.
The emission spectra of a series of naphthalene end-labeled oligo-oxyethylene(N-Pn-N) and their facilitated transport of cations across liquid membranes have been investigated.Alkali-metal cations enhance or inhibit the intramolecular excimer formation of N-Pn-N remarkably,suggesting that the polyether chain of N-Pn-N in solution complexes with the cations,and the orientation of the terminal chromophores depends on the cation size and the length of the polyether chain. These compounds are able to act as carriers to facilitate transport of alkali-metal cations through organic liquid membranes.The transport efficiencies are comparable with those of cyclic carriers such as crown ethers,and show remarkable selectivity. 相似文献
24.
Using 1 MHz pulse-echo ultrasound externally applied to detect mastoid effusion: cadaver experiments
The objective of this study is to explore the feasibility of using ultrasound to detect mastoid effusion (ME). In the past, ultrasound has been used to measure middle ear effusion (MEE) by injecting water into the external ear canal to measure echoes from the tympanic membrane, which is uncomfortable for the patient. It has been shown that air cells in the mastoid of patients with MEE are filled with fluid, which implies that ME could be a useful indicator of MEE. This study suggests using ultrasound to detect ME as a potentially noninvasive approach for MEE detection. In vitro experiments were performed on ten cadaver samples of the human ear. A single-element 1 MHz transducer was used to measure the mastoid of each cadaver before and after injecting water into the mastoid. The experimental results showed that the relative amplitudes of ultrasonic signals differed significantly between before (0.24 ± 0.09, mean ± standard deviation) and after (0.15 ± 0.03) the water injection (p < 0.05, t-test), demonstrating that the ultrasonic reflection can be used to detect ME. The location of the human mastoid under the skin behind the ear allows external measurements, and hence ultrasound-based ME detection may be an alternative, noninvasive diagnostic approach to detecting MEE in the future, providing an examination that avoids discomfort. 相似文献
25.
26.
27.
A Phosphorescent Platinum(II) Bipyridyl Supramolecular Polymer Based on Quadruple Hydrogen Bonds 下载免费PDF全文
Fang‐Wei Liu Dr. Li‐Ya Niu Prof. Yong Chen Prof. Vaidhyanathan Ramamurthy Prof. Li‐Zhu Wu Prof. Chen‐Ho Tung Prof. Yu‐Zhe Chen Prof. Qing‐Zheng Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(50):18132-18139
A platinum(II) bipyridyl complex bearing bis‐ureidopyrimidinone (Pt‐bisUPy) has been designed and its self‐assembling behavior has been thoroughly investigated by 1H NMR, DOSY NMR, Ubbelohde viscometry analysis, UV/Vis, and emission spectroscopies. Pt‐bisUPy underwent concentration‐dependent ring‐chain polymerization in apolar solvents. Hydrogen‐bonding interactions play an important role during the formation of the supramolecular polymers. Hydrogen‐bonded supramolecular polymers were transformed to nanoparticles in water through the miniemulsion method. These nanoparticles showed strong π–π excimeric emission. Metal‐metal‐to‐ligand charge transfer (MMLCT) from Pt–Pt interactions was not significant in the emission spectrum. The phosphorescence of the nanoparticle persisted even under aerobic conditions. The triplet state of these phosphorescent nanomaterials were long‐lived and possessed moderate emission quantum yields. Furthermore, the low toxicity of these materials promises a place for them in in vitro and in vivo bioimaging. 相似文献
28.
Inside Cover: High‐Nuclear Organometallic Copper(I)–Alkynide Clusters: Thermochromic Near‐Infrared Luminescence and Solution Stability (Chem. Eur. J. 49/2016) 下载免费PDF全文
29.
Jing Wang Ke Feng Nan Xie Zhi-Jun Li Qing-Yuan Meng Bin Chen Chen-Ho Tung Li-Zhu Wu 《中国科学:化学(英文版)》2016,59(8):1018-1024
We develop here a simple wet chemistry to prepare covalent functionalized graphenes(FGs) through epoxide aminolysis especially under alkaline aqueous condition. Remarkably, a series of typical monoamines, such as industrial Huntsman Jeffamine~ M-2070 and M-2005 polymer with hydrophilic or hydrophobic polyetheramine chains, positively-charged 2-amino-N,N,Ntrimethylpropanaminium,negatively-charged sulfanilic acid, even oligopeptide sequence, can be effectively grafted on the platelets of graphene oxide precursor with covalent functionalization and partially reduced features. This strategy provides the researchers a facile and convenient approach to design and synthesize solution processable, biocompatible and functionalized graphenes for the potent applications in electronic inks, drug carriers and biomedicines. Expansion of the current study is actively ongoing in our laboratory. 相似文献
30.