全文获取类型
收费全文 | 2083篇 |
免费 | 64篇 |
专业分类
化学 | 1170篇 |
晶体学 | 39篇 |
力学 | 74篇 |
数学 | 121篇 |
物理学 | 743篇 |
出版年
2023年 | 15篇 |
2022年 | 26篇 |
2021年 | 31篇 |
2020年 | 44篇 |
2019年 | 40篇 |
2018年 | 45篇 |
2017年 | 32篇 |
2016年 | 82篇 |
2015年 | 47篇 |
2014年 | 67篇 |
2013年 | 132篇 |
2012年 | 137篇 |
2011年 | 139篇 |
2010年 | 84篇 |
2009年 | 68篇 |
2008年 | 120篇 |
2007年 | 103篇 |
2006年 | 93篇 |
2005年 | 101篇 |
2004年 | 73篇 |
2003年 | 49篇 |
2002年 | 45篇 |
2001年 | 40篇 |
2000年 | 24篇 |
1999年 | 18篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 25篇 |
1995年 | 31篇 |
1994年 | 20篇 |
1993年 | 30篇 |
1992年 | 17篇 |
1991年 | 19篇 |
1989年 | 18篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 17篇 |
1985年 | 35篇 |
1984年 | 16篇 |
1983年 | 14篇 |
1982年 | 27篇 |
1981年 | 25篇 |
1980年 | 10篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 10篇 |
1975年 | 9篇 |
1974年 | 14篇 |
1973年 | 10篇 |
1955年 | 12篇 |
排序方式: 共有2147条查询结果,搜索用时 281 毫秒
71.
72.
The study describes a new wet chemical technique, termed ANM, for the isolation of secondary phases in magnesite processed at a temperature of 1650 degrees C. The major MgO (periclase) phase in processed magnesite was preferentially extracted as ammonium nitrate magnesium double salt by ammonium nitrate in ethanol medium. The residues containing enriched secondary phases were identified by XRD. 相似文献
73.
Pranab Kumar Som Amar Nath Banerjee 《Journal of polymer science. Part A, Polymer chemistry》1993,31(4):1007-1012
Isatoic anhydride (IA) alone did not initiate photopolymerization of methyl metacrylate (MMA) at 40°C when exposed to visible light for about 180 min. But IA, when used in combination with bromine (Br2) as the initiator, initiated the photopolymerization of MMA readily under the same conditions. This behavior was explained by the formation of a donor-acceptor type of complex between IA and Br2 in the presence of MMA. The polymerization was found to proceed via a free radical mechanism and the radical generation process was considered to follow an initial complexation reaction between the initiator components and monomer. The complex initiator showed nonideal kinetics for the present system (initiator exponent < 0.5) and was analyzed. The monomer exponents varied from 0.83 to 1.15 normally depending on the nature of solvent used. Initiator-dependent chain termination was significant as well as the bimolecular mode of chain termination. © 1993 John Wiley & Sons, Inc. 相似文献
74.
Biswanath Das Joydeep Banerjee Nasi Ravindranath Bollu Venkataiah 《Tetrahedron letters》2004,45(11):2425-2426
The stereoselective synthesis of (2Z)-2-(chloromethyl)alk-2-enoates has been achieved efficiently and in high yields and in short reaction times from Baylis-Hillman adducts, 3-hydroxy-2-methylene-alkanoates, by treatment with FeCl3 or InCl3 at room temperature. 相似文献
75.
ESCA and ESR studies on TMI incorporating alumina-boria catalyst systems for CO conversion show the presence of carbidic phase and no valence change of the incorporated copper in the spent catalyst. 相似文献
76.
Sumanta Bhattacharya Sandip K. Nayak Subrata Chattopadhyay Manas Banerjee 《Journal of solution chemistry》2006,35(4):485-506
Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I
D
V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E
A
V) of [60]- and [70]fullerenes in solution. The value of E
A
V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes. 相似文献
77.
Aryl bromides (3 equiv) were coupled efficiently with triarylbismuths (1 equiv) in an atom-efficient way using the Pd(OAc)2/PPh3 catalytic system in the presence of K3PO4 as base in DMF at 90 °C, providing excellent yields of the cross-coupled biaryls in short reaction times. 相似文献
78.
Sreemanta Mitra Amrita Mandal Anindya Datta Sourish Banerjee Dipankar Chakravorty 《Journal of magnetism and magnetic materials》2012
Nanosheets of nickel with thickness equal to 0.6 nm have been grown within the interlayer spaces of Na-4 mica. The sheets are made up of percolative clusters of nanodisks. Magnetization characteristics indicate a superparamagnetic behavior with a blocking temperature of 428 K. The magnetic anisotropy constant as extracted from the coercivity data has been found to be higher than that of bulk nickel by two orders of magnitude. This is ascribed to a large aspect ratio of the nickel nanophase. The Bloch exponent is also found to be considerably different from that of bulk nickel because of a size effect. The Bloch equation is still found to be valid for the two dimensional structures. 相似文献
79.
Thionyl chloride-pyridine mediated rearrangement of cylohexadienyl alcohols (2) and (8) has provided hyposantonin (3) and tetrahydronaphthalene (9), respectively, which in turn have served as potential intermediates for the synthesis of optically active and racemic occidol (6), respectively. 相似文献
80.