全文获取类型
收费全文 | 1740篇 |
免费 | 181篇 |
国内免费 | 40篇 |
专业分类
化学 | 1590篇 |
晶体学 | 39篇 |
力学 | 19篇 |
综合类 | 4篇 |
数学 | 13篇 |
物理学 | 296篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 16篇 |
2021年 | 25篇 |
2020年 | 56篇 |
2019年 | 52篇 |
2018年 | 59篇 |
2017年 | 38篇 |
2016年 | 90篇 |
2015年 | 67篇 |
2014年 | 77篇 |
2013年 | 140篇 |
2012年 | 65篇 |
2011年 | 80篇 |
2010年 | 80篇 |
2009年 | 72篇 |
2008年 | 61篇 |
2007年 | 66篇 |
2006年 | 65篇 |
2005年 | 73篇 |
2004年 | 74篇 |
2003年 | 57篇 |
2002年 | 40篇 |
2001年 | 34篇 |
2000年 | 51篇 |
1999年 | 38篇 |
1998年 | 25篇 |
1997年 | 37篇 |
1996年 | 33篇 |
1995年 | 36篇 |
1994年 | 21篇 |
1993年 | 27篇 |
1992年 | 25篇 |
1991年 | 20篇 |
1990年 | 25篇 |
1989年 | 22篇 |
1988年 | 23篇 |
1987年 | 23篇 |
1986年 | 26篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 18篇 |
1979年 | 17篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1961条查询结果,搜索用时 15 毫秒
41.
A family of layered bismuth oxyhalides, LI0.5Bi1.5O2X and LIIBiO2X has been reinvestigated. Formation of X1-type Sillén compounds has been established for LI=Li, Na, LII=Ca, Sr, Ba, and X=Cl, Br, I, but the details of their crystal structures are different. While all LI0.5Bi1.5O2X, CaBiO2Br, and CaBiO2I adopt the disordered tetragonal Nd2O2Te structure, all compounds of LII=Sr and Ba are orthorhombic and isostructural to PbSbO2Cl, due to L/Bi cation ordering. Crystal structures have been determined for CaBiO2I, SrBiO2Br, SrBiO2I, and BaBiO2I. We discuss the factors which determine the occurrence and type of cation ordering in the quaternary bismuth and antimony X1-type oxyhalides. We also predict that more isostructural compounds can be prepared with antimony. 相似文献
42.
43.
Summary A numer of bonded stationary phases were investigated for the separation of Cd2+, Cu2+, Fe3+, Mn2+, Ni2+, Pb2+, and Zn2+ by thin-layer chromatography. The effect of structure, surface loading, type of silica gel and mobile phase concentration was considered. 相似文献
44.
The CGC analysis of 25 organophosphorus and organonitrogen pesticides was optimized on two different stationary phases, namely a 5% diphenyl dimethyl silicone (SE-54 type) and a 50% diphenyl dimethyl silicone (OV-17 type) by selecting the best temperature program conditions, using computer simulation. 相似文献
45.
Four new stationary phases for HPLC were prepared by modifying silica gel with a trifrnctional aminoalkyl silane. A conjugated π-electron system was linked to the amino group either directly or with a carboxylic anhydride as a spacer in between. Characterization and dynamic measurements of the new stationary phases were performed by solid state NMR spectroscopy. The results of the 29si and 13C CP/MAS techniques were compared with the recently developed 1H MAS-only technique. Despite strong homonuclear dipole-dipole interactions it was possible to obtain well resolved 1H MAS spectra of those stationaru phases with a high degree of crosslinking. Limited mobility of the aromatic ligand fragments is common for all examined stationaryu phases. The chromatographic properties of the new phases were tested by their ability tio sepatate a mixture of eight PAHS. It could be shown that the π-π interaction mechanism is responsible for the separation of the eight PAHs, because the elution order of the PAHs did not changem despite the use of both a nonpolar mobile phase (n-heptane) and a polar mobile phase (methanol/ water mixture). 相似文献
46.
In this paper the equation for thin-layer adsorption chromatography with multicomponent mobile phases, proposed by O?cik in 1965 is extended to energetically heterogeneous solid surfaces. Other forms of this equation, more convenient in practical applications, are presented. Model calculations are made for TLC with binary mobile phases according to the modified form of O?cik's equation. Finally, this equation is compared with that of Snyder. 相似文献
47.
M. Baru A. Danilov I. Vagenina E. Gorbunova S. Moshnikov L. Mustaeva V. Cherskii 《Chromatographia》1997,45(1):351-354
Summary The design of new dynamic, axial-compression columns with a system for continous packed bed adjustment and monitoring of the
floating adapter position is described. The columns are meant for liquid chromatography at low pressures (up to 8 bar) in
aqueous and organic media with stationary phases of all types. The columns have adapter position pickups for continuous automatic
monitoring of the bed height (original “swellographic” monitoring). The column described with gas pressurisation was tested
with soft Sephadex G-10 and G-25. In spite of the reduction in external porosity there was no dramatic increase in back-pressure.
The column proved to provide long-term stability of the packed bed and improvement in resolution.
Presented at the 21st ISC held in Stuttgart, Germany, 15th–20th September, 1996 相似文献
48.
Quanwei?Yu Jens?Fr?mmel Thomas?WolffEmail author Karel?Procházka 《Colloid and polymer science》2004,282(9):1039-1043
Solid stoichiometric complexes of [3,12]-ionene and dodecyl sulfate form upon reaction of the bromide of the ionene and the silver salt of dodecyl sulfate in methanol. IR, DSC, and TG investigations indicated that the solid complexes are stable between 30 and 120 °C. TG and DSC also showed that the complexes easily take up water at ambient conditions. These samples are optically isotropic. When exposed to an increased humidity they exhibit optical anisotropy, i.e., birefringence, which is caused by the formation of a hexagonal mesogenic phase. Mesogenicity is necessarily accompanied by a further uptake of water (4–5 H2O molecules per ionic unit), which is dependent on the relative humidity. The phase behavior as a function of temperature and controlled relative humidity was studied using birefringence measurements and polarizing microscopy. 相似文献
49.
A. Meddour J. Courtieu W. Abdelhadi S. Guermouche M. H. Guermouche 《Chromatographia》1996,43(7-8):387-392
Summary Comparative gas chromatographic properties of two thermotropic Poly(L-glutamates) with long alkyl side chains (10 and 16 carbons called Poly 10 and Poly 16 respectively) are studied.Their thermal properties were established with differential scanning calorimetry (DSC) and gas chromatography. They present a cholesteric liquid crystal in a large temperature range.The chromatographic separation abilities of the two polymers in the liquid crystal state were studied using capillary glass columns. Interesting analytical performances were obtained in different fields: isomeric separation of alkanes, aromatics, polyaromatics, volatile aroma compounds and cis and trans isomers. Some differences were noticed in their behaviours; 2 and 3-methyloctane and xylene isomers are separated only on Poly 10 while limonene and eucalyptol are separated only on Poly 16. 相似文献
50.
Sameena Ashraf Keith D. Bartle Anthony A. Clifford Robert Moulder 《Journal of separation science》1992,15(8):535-538
Lubricating oil additives have been analyzed by supercritical fluid chromatography on open tubular and packed capillary columns. Carbon dioxide and modified carbon dioxide were used as mobile phases and detection was accomplished by flame ionization and micro UV. Rapid and efficient analysis of the lubricating oil additives was demonstrated. 相似文献