全文获取类型
收费全文 | 955篇 |
免费 | 18篇 |
国内免费 | 5篇 |
专业分类
化学 | 679篇 |
晶体学 | 3篇 |
力学 | 9篇 |
数学 | 157篇 |
物理学 | 130篇 |
出版年
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 13篇 |
2014年 | 17篇 |
2013年 | 53篇 |
2012年 | 47篇 |
2011年 | 59篇 |
2010年 | 26篇 |
2009年 | 19篇 |
2008年 | 48篇 |
2007年 | 57篇 |
2006年 | 49篇 |
2005年 | 39篇 |
2004年 | 47篇 |
2003年 | 30篇 |
2002年 | 33篇 |
2001年 | 19篇 |
2000年 | 18篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 13篇 |
1996年 | 16篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 10篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 17篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 13篇 |
1983年 | 16篇 |
1982年 | 6篇 |
1980年 | 11篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1974年 | 10篇 |
1971年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有978条查询结果,搜索用时 15 毫秒
1.
Dielectric studies are presented of a banana-shaped compound that exhibits the antiferroelectric B2 phase. Upon application and subsequent removal of strong electric fields the textures and dielectric properties of the phase drastically change. Most notable is the huge increase of the low frequency permittivity. This behaviour would suggest the induction of ferroelectricity by the electric field. 相似文献
2.
Rosés M 《Journal of chromatography. A》2004,1037(1-2):283-298
The measurement of pH in chromatographic mobile phases has been a constant subject of discussion during many years. The pH of the mobile phase is an important parameter that determines the chromatographic retention of many analytes with acid-base properties. In many instances a proper pH measurement is needed to assure the accuracy of retention-pH relationships or the reproducibility of chromatographic procedures. Three different methods are common in pH measurement of mobile phases: measurement of pH in the aqueous buffer before addition of the organic modifier, measurement of pH in the mobile phase prepared by mixing aqueous buffer and organic modifier after pH calibration with standard solutions prepared in the same mobile phase solvent, and measurement of pH in the mobile phase prepared by mixing aqueous buffer and organic modifier after pH calibration with aqueous standard solutions. This review discusses the different pH measurement and calibration procedures in terms of the theoretical and operational definitions of the different pH scales that can be applied to water-organic solvent mixtures. The advantages and disadvantages of each procedure are also presented through chromatographic examples. Finally, practical recommendations to select the most appropriate pH measurement procedure for particular chromatographic problems are given. 相似文献
3.
A preferential solvation model that relates solute properties with solvent composition in binary mixtures has been applied to the dissociation pKa values of a set of 28 substituted phenols in methanol-water mixtures. The parameters of the model allow estimation of the pKa value of each phenol for any methanol-water composition. Moreover, it is demonstrated that the pKa values of the whole set of phenols at any methanol-water composition are linearly related to the pKa values of the phenols in water. Equations that relate the correlations' slope and intercept values with the solvent composition have been derived and tested with the set of phenols. The general parameters obtained for these equations allow an accurate calculation of the pKa value of any phenol, even of those not included in the original set, at any methanol-water composition solely from the pKa value of the phenol in water. These calculated pKa values can be used for quantitative structure-HPLC retention relationships. The method is tested by comparison of the calculated pKa values with the HPLC determined pKa values of 26 phenols in a polymeric column with a 50% methanol as mobile phase. 相似文献
4.
Peak distortion in the column liquid chromatographic determination of omeprazole dissolved in borax buffer. 总被引:1,自引:0,他引:1
Injection of a sample containing omeprazole dissolved in borax buffer (pH 9.2) into a reversed-phase liquid chromatographic system consisting of a mixture of acetonitrile and phosphate buffer (pH 7.6) as the mobile phase and a C18 surface-modified silica as the solid phase resulted under special conditions in split peaks of omeprazole. The degree of peak split and the retention time of omeprazole varied with the concentration of borax in the sample solution and the ionic strength of the mobile phase buffer as well as with the column used. Borax is eluted from the column in a broad zone starting from the void volume of the column. The retention is probably due to the presence of polyborate ions. The size of the zone varies with the concentration of borax in the sample injected. In the borax zone the pH is increased compared with the pH of the mobile phase, and when omeprazole (a weak acid) is co-eluting in the borax zone its retention is affected. In the front part and in the back part of the borax zone, pH gradients are formed, and these gradients can induce the peak splitting. When the dissolving medium is changed to a phosphate buffer or an ammonium buffer at pH 9 no peak distortion of omeprazole is observed. 相似文献
5.
A new method is presented to calculate binding energies and eigenfunctions for molecules, using the relativistic Dirac hamiltonian. A numerical basis set of four component wavefunctions is obtained from atom-like Dirac-Slater wavefunctions. A discrete variational method has been developed and applied to the linear XeF2 molecule. 相似文献
6.
Summary A global LSER model that relates HPLC retention to mobile phase composition and pH is tested for a varied group of solutes,
both neutral and ionizable, in a polymeric column and methanol-water mobile phases. It is compared to the local LSER model
developed only for a given mobile phase, i.e., a fixed organic modifier content, and to the global LSER model set only for
neutral solutes. The global LSER model for neutral and ionizable solutes requires a few supplementary parameters over the
other models tested, but it accounts for retention under any experimental conditions for a given column and methanol-water
mobile phases, describing properly the interactions established in the HPLC system (hydrophobicity, hydrogen-bond acidity
and basicity, dipolarity/polarizability…).
This paper is number 13 of a series with the same general title: “Retention of Ionizable Compounds on HPLC” published in various
journals. 相似文献
7.
B. Wästberg A. Rosén D. E. Ellis 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1989,12(1-4):377-380
Theoretical X-ray absorption near-edge spectra have been evaluated for different bond lengths of Mn2, Co2 and Ni2 using a modified Xα scattered-wave procedure. 相似文献
8.
Hans-Peter Seidel 《Geometriae Dedicata》1990,33(3):337-354
In this paper we relate the theory of stable planes to the theory of generalized symmetric spaces in the sense of differential geometry where the symmetries may be of arbitrary order. This leads to the notion of a generalized symmetric plane. We assign to every generalized symmetric plane an associated infinitesimal model and show that the associated infinitesimal model essentially determines a generalized symmetric plane up to global isomorphism. In particular, every generalized symmetric plane with an abelian group of transvections is a topological translation plane. 相似文献
9.
R. Euler B. Fricke T. Morović W. -D. Sepp A. Rosén 《Zeitschrift für Physik A Hadrons and Nuclei》1980,297(2):101-104
Total energy SCF calculations were performed for noble gas difluorides in a relativistic procedure and compared with analogous non-relativistic calculations. The discrete variational method with numerical basis functions was used. Rather smooth potential energy curves could be obtained. The theoretical Kr-F and Xe-F bond distances were calculated to be 3.5 a.u. and 3.6 a.u. which should be compared with the experimental values of 3.54 a.u. and 3.7 a.u. Although the dissociation energies are off by a factor of about five it was found that ArF2 may be a stable molecule. Theoretical ionization energies for the outer levels reproduce the experimental values for KrF2 and XeF2 to within 2 eV. 相似文献
10.