全文获取类型
收费全文 | 363篇 |
免费 | 3篇 |
专业分类
化学 | 186篇 |
晶体学 | 8篇 |
力学 | 15篇 |
数学 | 69篇 |
物理学 | 88篇 |
出版年
2022年 | 3篇 |
2021年 | 2篇 |
2019年 | 3篇 |
2018年 | 2篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 9篇 |
2013年 | 15篇 |
2012年 | 10篇 |
2011年 | 10篇 |
2010年 | 12篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 12篇 |
2006年 | 20篇 |
2005年 | 11篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 12篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 3篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 2篇 |
1994年 | 14篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 12篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1987年 | 12篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1984年 | 7篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1968年 | 2篇 |
1933年 | 4篇 |
1932年 | 1篇 |
排序方式: 共有366条查询结果,搜索用时 15 毫秒
11.
12.
13.
14.
15.
16.
Summary Enantiomeric separation of (–)-menthyl chloroformate derivatives of some chiral cardioactive drugs, on porous graphitic carbon (PGC), Hypercarb-S, is described. Capacity and separation factors of derivatives of the calcium channel blockers; amlodipine and UK52.829, the -blockers; atenolol, sotalol and propranolol, and mexiletine were studied in different chromatographic systems based on dichloromethane. A high content of a carboxylic acid in the mobile phase was found to decrease the retention and positively affect the stereoselectivity of the derivatives. A mobile phase with dichloromethane, acetonitrile and formic acid gave baseline separation of the enantiomers of amlodipine in less than 8 minutes. Results show that acetic acid and formic acid, may be regarded as strong organic solvents in PGC chromatography with nearly the same elution power as dichloromethane. 相似文献
17.
J. Carlsson P. Jönsson L. Sturesson 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1990,16(2):87-90
The lifetimes of the silver 5p 2 P states have been measured with high accuracy by time-resolved laser spectroscopy using the delayed coincidence technique. Also, the hyperfine structure of107Ag and109Ag in these two states has been studied by observing quantum beats. 相似文献
18.
R. Wäppling L. Häggström T. Ericsson S. Devanarayanan E. Karlsson B. Carlsson S. Rundqvist 《Journal of solid state chemistry》1975,13(3):258-271
The para- to ferromagnetic transition in Fe2P has been studied using Mössbauer spectroscopy. The magnetic hyperfine fields drop abruptly from about half of their saturation values to zero at 214.5 K indicating a first order transition. The isomer shifts show a discontinuous change at the transition point. For some samples the transition takes place over a wide temperature range, probably due to impurities and other imperfections in the samples. From the magnetic hyperfine fields at 15 K the magnetic moments can be deduced to be 1.14 μB and 1.78 μB for Fe(1) and Fe(2), respectively. An assignment of the components in the Mössbauer spectra to the two crystallographically nonequivalent iron positions has been made from the temperature variation of the spectra.The ordering of metal vacancies has been investigated by a Mössbauer study of a nonstoichiometric Fe2P sample and by an X-ray diffraction study of a nonstoichiometric Mn2P crystal. 相似文献
19.
Anderson MW Ohsuna T Sakamoto Y Liu Z Carlsson A Terasaki O 《Chemical communications (Cambridge, England)》2004,(8):907-916
This article describes a number of important recent microscopy tools and their application in particular to the study of porous inorganic materials. The authors believe that these new techniques are on the threshold of delivering enormous new power in the chemist's arsenal for understanding new and complex behaviour in multi-component, hierarchical or composite materials. In particular we consider the contribution of electron crystallography, three-dimensional electron tomography, ultra-high resolution scanning electron microscopy as well as the combined application of high-resolution electron microscopy and atomic force microscopy to the study of surfaces and crystal growth. Much of this work has taken on a particular significance owing to the ground breaking work of scientists at Mobil and in Japan 10 years ago in the successful synthesis of materials with porosity on many length scales achieved through the cooperative self-assembly between inorganic and organic phases. This resulted in a series of materials known as M41S of which MCM-41 and MCM-48 were two of the first and most important structures to be synthesised. This has led to a wealth of new porous structures with order over many length scales and has presented new problems in characterisation. Microscopy methods properly executed are particularly important in the study of this new class of material. 相似文献
20.
Clean-up and analysis of carbazole and acridine type polycyclic aromatic nitrogen heterocyclics in complex sample matrices 总被引:1,自引:0,他引:1
A HPLC method for the analysis of polycyclic aromatic nitrogen heterocyclics (PANHs) in complex sample matrices is presented. It isolated and separated carbazole and acridine type PANHs with an absolute recovery of between 79–98%. Open column chromatography is used as an initial step to isolate a PANH fraction. By applying normal-phase liquid chromatography using a dimethylaminopropyl silica stationary phase and utilising back-flush technique it was possible to separate the PANH fraction into two fractions containing acridine type and carbazole type PANHs, respectively. The method applied on a sample of solvent refined coal heavy distillate (SRC II HD). A number of 3–5 ring acridines and carbazoles were identified with GC–electron impact MS and quantified with GC–nitrogen–phosphorous detection. Polycyclic aromatic hydrocarbons (PAHs) were determined in the SRC II HD sample by automated on-line clean-up and analysis of the obtained PAH fraction with coupled LC–GC–flame ionization detection. There was no overlap between the PANH and the PAH fractions with this method, and carbazoles and acridines were efficiently separated. 相似文献