全文获取类型
收费全文 | 674篇 |
免费 | 16篇 |
国内免费 | 2篇 |
专业分类
化学 | 519篇 |
晶体学 | 1篇 |
力学 | 21篇 |
数学 | 114篇 |
物理学 | 37篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 13篇 |
2021年 | 22篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 19篇 |
2017年 | 5篇 |
2016年 | 21篇 |
2015年 | 18篇 |
2014年 | 18篇 |
2013年 | 41篇 |
2012年 | 39篇 |
2011年 | 47篇 |
2010年 | 39篇 |
2009年 | 28篇 |
2008年 | 45篇 |
2007年 | 38篇 |
2006年 | 33篇 |
2005年 | 34篇 |
2004年 | 34篇 |
2003年 | 26篇 |
2002年 | 17篇 |
2001年 | 5篇 |
2000年 | 14篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有692条查询结果,搜索用时 156 毫秒
91.
92.
Correlations have been investigated between the content of short isotactic segments and thermal properties in some propylene/olefin random copolymers. Polypropylene copolymers modified by ethylene show variations different from those for copolymers modified by ethylene and butene. However, in both cases, the weldability temperature decreases on increasing the comonomer concentration. 相似文献
93.
94.
95.
96.
Maccotta A Fantazzini P Garavaglia C Donato ID Perzia P Brai M Morreale F 《Annali di chimica》2005,95(3-4):117-124
Magnetic Resonance Relaxation (MRR) and Magnetic Resonance Imaging (MRI) are powerful tools to obtain detailed information on the pore space structure that one is unlikely to obtain in other ways. These techniques are particularly suitable for Cultural Heritage materials, because they use water 1H nuclei as a probe. Interaction with water is one of the main causes of deterioration of materials. Porous structure in wood, for example, favours the penetration of water, which can carry polluting substances and promote mould growth. A particular case is waterlogged wood from underwater discoveries and moist sites; in fact, these finds are very fragile because of chemical, physical and biological decay from the long contact with the water. When wood artefacts are brought to the surface and directly dried in air, there is the collapse of the cellular structures, and wood loses its original form and dimensions and cannot be used for study and museum exhibits. In this work we have undertaken the study of some wood finds coming from Ercolano's harbour by MRR and MRI under different conditions, and we have obtained a characterization of pore space in wood and images of the spatial distribution of the confined water in the wood. 相似文献
97.
98.
Silvano Bozzini Patrizia Nitti Giuliana Pitacco Alessandro Pizzioli Claudio Russo 《Journal of heterocyclic chemistry》1996,33(4):1217-1221
Tricyclic compounds with an imidazolinone ring fused to 1,2- and 1,4-naphtoquinones were synthesized by a reaction of 4-amino-1,2-naphthoquinone and 2-amino-1,4-naphthoquinone with electrophilic symmetric and non symmetric diazenes. 相似文献
99.
Edoardo Cesarotti Patrizia Antognazza Marco Pallavicini Luigi Villa 《Helvetica chimica acta》1993,76(6):2344-2349
A number of 3-O-substituted 1,3-dihydroxypropan-2-ones have been synthesized in view of their potential use as prochiral precursors of optically active glycerols. Indeed, the oxo-ethers have been reduced to the corresponding 3-O-substituted glycerols via chiral Ru complexes derived from (S)-binap, ( =(?)-(S)-2,2′-bis(diphenylphosphino)-1,1′-binaphthalene) with enantiomeric excesses up to 93%. The steric course of the catalytic reduction appears to be essentially dependent on the steric encumbrance of the substituents; indeed, a dramatic increase of the enantiomeric excess is observed when the bulky trityl group is substituted by the less encumbering benzyl or octadecyl groups. 相似文献
100.
Malandrino G Perdicaro LM Condorelli G Fragalà IL Rossi P Dapporto P 《Dalton transactions (Cambridge, England : 2003)》2006,(8):1101-1106
A novel nickel beta-diketonate adduct, Ni(tta)2.tmeda, has been synthesized using 2-thenoyltrifluoroacetone as the beta-diketonate and N,N,N,'N'-tetramethylethylendiamine as the Lewis base. It has been characterized by elemental analyses, IR, 1H NMR, 13C NMR spectroscopy and single-crystal X-ray diffraction studies. Physical and thermal properties of Ni(tta)2.tmeda precursor have been also extensively investigated. Its efficacy as a metal-organic chemical vapour deposition (MOCVD) precursor for the growth of nickel oxide films has been fully tested by applying it to the deposition of NiO films on quartz substrate. NiO thin films have been characterized by X-ray diffraction (XRD), scanning electron microscopy and UV spectroscopy. 相似文献