全文获取类型
收费全文 | 199篇 |
免费 | 10篇 |
国内免费 | 1篇 |
专业分类
化学 | 115篇 |
晶体学 | 3篇 |
力学 | 7篇 |
数学 | 22篇 |
物理学 | 63篇 |
出版年
2022年 | 7篇 |
2021年 | 7篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 7篇 |
2017年 | 5篇 |
2016年 | 6篇 |
2015年 | 6篇 |
2014年 | 6篇 |
2013年 | 18篇 |
2012年 | 14篇 |
2011年 | 13篇 |
2010年 | 13篇 |
2009年 | 13篇 |
2008年 | 3篇 |
2007年 | 13篇 |
2006年 | 6篇 |
2005年 | 9篇 |
2004年 | 13篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1973年 | 3篇 |
1972年 | 1篇 |
排序方式: 共有210条查询结果,搜索用时 15 毫秒
91.
92.
93.
Sari Kiviniemi Maija Nissinen Tanja Kolli Jorma Jalonen Kari Rissanen Jouni Pursiainen 《Journal of inclusion phenomena and macrocyclic chemistry》2001,40(1-2):153-159
Crown ether complexes of six-membered N-heteroaromatic cations and the closely related bicyclic purinium cation (6) have been studied by 1H NMR, mass spectrometric and crystallographic methods. The stability constants for the complexes were determined by 1H NMR titration in acetonitrile solution and the complexation stoichiometry by 1H NMR and ESI mass spectrometric methods. Altogether six crystal structures of complexes were determined to study the complexation in the solid state. Hydrogen bonding was observed to be the most important interaction for the complexation both in solution and in the solid state but – interactions also contribute to it. All crystal structures of the DB18C6 complexes with six-membered N-heteroaromatic cations, except for 4-hydroxypyridinium, are isomorphous to previously studied five-membered N-heteroaromatic cations and pyridinium complexes. Such a close resemblance is not observed in B18C6 and 18C6 complexes or DB18C6purinium (6). 相似文献
94.
Sari L McCarthy MC Schaefer HF Thaddeus P 《Journal of the American Chemical Society》2003,125(37):11409-11417
Highly correlated ab initio coupled-cluster theories (e.g., CCSD(T), CCSDT) were applied on the ground electronic states of Si(2)H(3) and Si(2)H(4), with substantive basis sets. A total of 10 isomers, which include mono- and dibridged structures, were investigated. Scalar relativistic corrections and zero-point vibrational energy corrections were included to predict reliable energetics. For Si(2)H(3), we predict an unanticipated monobridged H(2)Si-H-Si-like structure (C(s), (2)A') to be the lowest energy isomer, in constrast to previous studies which concluded that either H(3)Si-Si (C(s), (2)A') or near-planar H(2)Si-SiH (C(1), (2)A) is the global minimum. Our results confirm that the disilene isomer, H(2)Si-SiH(2), is the lowest energy isomer for Si(2)H(4) and that it has a trans-bent structure (C(2)(h), (1)A(g)). In addition to the much studied silylsilylene, H(3)Si-SiH, we also find that a new monobridged isomer H(2)Si-H-SiH (C(1), (1)A, designated 2c) is a minimum on the potential energy surface and that it has comparable stability; both isomers are predicted to lie about 7 kcal/mol above disilene. By means of Fourier transform microwave spectroscopy of a supersonic molecular beam, the rotational spectrum of this novel Si(2)H(4) isomer has recently been measured in the laboratory, as has that of the planar H(2)Si-SiH radical. Harmonic vibrational frequencies as well as infrared intensities of all 10 isomers were determined at the cc-pVTZ CCSD(T) level. 相似文献
95.
Reeta?ViitalaEmail author Mika?Jokinen Sari?Tuusa Jarl?B.?Rosenholm Harry?Jalonen 《Journal of Sol-Gel Science and Technology》2005,36(2):147-156
Amorphous, sol-gel derived SiO2 are known to biocompatible and bioresorbable materials. Bioresorbable materials have potential applications as implants or
injectable matrices in the controlled delivery of biologically active agents in the living tissue. Bioresorbable matrices
provide desirable properties, e.g., extra removal operations that have to be done with biostable matrices are avoided and
the release of large therapeutic molecules can be controlled by matrix degradation rather than by diffusion. New important
groups of drugs, such as biotechnically-produced peptides and proteins, are potential to be encapsulated in bioresorbable
SiO2, because they are typically larger in size and their direct oral administration without protecting matrix is difficult due
to digestion. The methods to achieve a wide range of SiO2 bioresorption rates (from days to months) are introduced in this study. This is done by a “conventional” alkoxy-based sol-gel
method at protein-friendly conditions by adjusting the precursor ratios, aging of the sol and by using different preparation
methods (casting, spray-drying and freeze-drying). The prepared morphologies include implantable monolithic sticks and injectable
microspheres. The importance of chemical structure is shown in comparison with the specific surface area and pore volume. 相似文献
96.
Ultrasound assisted method to increase soluble chemical oxygen demand (SCOD) of sewage sludge for digestion 总被引:3,自引:0,他引:3
Grönroos A Kyllönen H Korpijärvi K Pirkonen P Paavola T Jokela J Rintala J 《Ultrasonics sonochemistry》2005,12(1-2):115-120
The aim of this study was to clarify the possibilities to increase the amount of soluble chemical oxygen demand (SCOD) and methane production of sludge using ultrasound technologies with and without oxidising agents. The study was done using multivariate data analyses. The most important factors affected were discovered. Ultrasonically assisted disintegration increased clearly the amount of SCOD of sludge. Also more methane was produced from treated sludge in anaerobic batch assays compared to the sludge with no ultrasonic treatment. Multivariate data analysis showed that ultrasonic power, dry solid content of sludge (DS), sludge temperature and ultrasonic treatment time have the most significant effect on the disintegration. It was also observed that in the reactor studied energy efficiency with high ultrasound power together with short treatment time was higher than with low ultrasound power with long treatment time. When oxidising agents were used together with ultrasound no increase in SCOD was achieved compared the ultrasonic treatment alone and only a slight increase in total organic carbon of sludge was observed. However, no enhancement in methane production was observed when using oxidising agents together with ultrasound compared the ultrasonic treatment alone. Ultrasound propagation is an important factor in ultrasonic reactor scale up. Ultrasound efficiency rose linearly with input power in sludge at small distances from the transducer. Instead, ultrasound efficiency started even to decrease with input power at long distances from the transducer. 相似文献
97.
98.
99.
100.