全文获取类型
收费全文 | 390139篇 |
免费 | 3825篇 |
国内免费 | 1093篇 |
专业分类
化学 | 213924篇 |
晶体学 | 6417篇 |
力学 | 15623篇 |
综合类 | 17篇 |
数学 | 41451篇 |
物理学 | 117625篇 |
出版年
2020年 | 3430篇 |
2019年 | 3854篇 |
2018年 | 5011篇 |
2017年 | 5031篇 |
2016年 | 7177篇 |
2015年 | 4282篇 |
2014年 | 6862篇 |
2013年 | 17387篇 |
2012年 | 12588篇 |
2011年 | 15333篇 |
2010年 | 11018篇 |
2009年 | 10890篇 |
2008年 | 14287篇 |
2007年 | 14248篇 |
2006年 | 13278篇 |
2005年 | 12051篇 |
2004年 | 10845篇 |
2003年 | 9976篇 |
2002年 | 9640篇 |
2001年 | 11126篇 |
2000年 | 8587篇 |
1999年 | 6550篇 |
1998年 | 5390篇 |
1997年 | 5408篇 |
1996年 | 5073篇 |
1995年 | 4471篇 |
1994年 | 4446篇 |
1993年 | 4325篇 |
1992年 | 5054篇 |
1991年 | 5029篇 |
1990年 | 4880篇 |
1989年 | 4914篇 |
1988年 | 4851篇 |
1987年 | 4835篇 |
1986年 | 4613篇 |
1985年 | 5965篇 |
1984年 | 6126篇 |
1983年 | 4855篇 |
1982年 | 5191篇 |
1981年 | 5129篇 |
1980年 | 4757篇 |
1979年 | 5267篇 |
1978年 | 5376篇 |
1977年 | 5477篇 |
1976年 | 5341篇 |
1975年 | 4931篇 |
1974年 | 4872篇 |
1973年 | 4952篇 |
1972年 | 3369篇 |
1967年 | 3278篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
I. P. Dobrovol’skaya M. V. Mokeev Yu. N. Sazanov A. V. Gribanov T. E. Sukhanova 《Russian Journal of Applied Chemistry》2006,79(8):1312-1315
Variation of the supramolecular structure of heat-resistant polymide films in the course of high-temperature treatment was studied by X-ray diffraction analysis and NMR spectroscopy in solids. 相似文献
992.
P. K. Sazonov G. A. Artamkina I. P. Beletskaya 《Russian Journal of Organic Chemistry》2006,42(3):438-447
The nucleophilic aromatic and vinyl substitution using diaza-18-crown-6 as nucleophile afforded a number of its N,N’-diaryl-[aryl = 2,4-(NO2)2C6H3, 4-C5F4N, 4-CF3C6F4] and N,N’-dialkenyl-substituted derivatives [alkenyl = PhC(O)CH=CH, MeOCOCH=CH, (EtO2C)2C=C(Ph), etc.]. Arylation of diaza-18-crown-6 with nonactivated aryl bromides, such as 4-Me2NC6H4Br, 4-MeOC6H4Br, C6H5Br, and 4-CF3C6H4Br, was effected under catalysis by palladium complexes. N,N’-Diaryldiaza-18-crowns-6 having electron-acceptor substituents in the aromatic rings turned out to be incapable of forming complexes with metal cations, while their analogs containing electron-donor para-methoxy and para-dimethylamino groups gave complexes with barium perchlorate. 相似文献
993.
陈永静 朱胜江 J.H.Hamilton A.V.Ramayya J.K.Hwang Y.X.Luo J.O.Rasmussen 车兴来 丁怀博 李明亮 《中国物理 C》2006,30(8):740-744
通过测量252Cf自发裂变所产生的瞬发γ射线, 对146Ce核的高自旋结构进行了重新研究, 结果更新了以前报道的能级纲图, 把八级形变集体带扩展到更高的自旋, 并且重新构建了可能的准γ带结构. 此外, 用反射不对称壳模型(RASM)对146Ce核的八级形变带进行了计算, 低自旋处的计算结果与实验数据符合得很好. 相似文献
994.
K.E. Lee T.L. Phan N.D. Ha M.H. Phan S.C. Yu C.O. Kim 《Journal of magnetism and magnetic materials》2006
Influences of oxygen-partial pressure and annealing on the electrical and magnetic properties of CoFeAlO thin films were systematically investigated by means of resistivity, permeability, magnetization and ferromagnetic resonance (FMR) measurements. It was found that, with increasing oxygen-partial pressure or under annealing, the electrical resistivity of the film increased and the magnetic softness decreased, which is attributed to the microstructural change of the film. Interestingly, an as-deposited Co45.30Fe20.65Al19.34O14.71 film was found to exhibit an inverted hysteresis loop with negative coercivity, and this peculiar phenomenon disappeared upon effects of oxygen-partial pressure and annealing. It was also found that the as-deposited films owned a narrow FMR line width that increased with increasing oxygen-partial pressure or under annealing. 相似文献
995.
W. Gao M. Li R. Klie E.I. Altman 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):136-149
Oxide catalysts are frequently used to convert toxic species to environmentally benign molecules, and to prevent the formation of toxic species in the first place. In this paper, growth and characterization of model oxide systems employed in both approaches is discussed. An example of the former approach is the selective catalytic reduction (SCR) of NO emitted from power plants by NH3, which employs tungsten and vanadium oxides supported on the anatase polymorph of TiO2. To model SCR catalysts, epitaxial titanium, vanadium and tungsten oxide films were grown using molecular beam epitaxy and magnetron sputtering. Two different anatase orientations were grown on LaAlO3 substrates and their interactions with vanadia were characterized. On LaAlO3 (0 0 1), anatase exposed a (4 × 1) reconstructed (0 0 1) surface. Vanadia lifted the reconstruction and at 1 ML a (1 × 1) surface with mostly V5+ was observed. Continued V2O5 growth led to loss of order, but at high temperatures epitaxial VO2 could be grown; vanadia behaved similarly on anatase films on LaAlO3 (1 1 0). Results suggested that the monolayer is pseudomorphic with O adsorption oxidizing the surface V to 5+, since the anatase structure cannot accommodate more bulk oxygen, only a monolayer can be pseudomorphic and have only V5+. Thus the vanadia monolayer has unique structural and chemical properties that can help explain why vanadia monolayers on TiO2 are much more active than bulk V2O5. For WO3, a series of added row reconstructions were observed as the epitaxial films were reduced. The effect of these structures on surface chemistry was characterized by studying 1-propanol adsorption. The results indicated that the structure of the WO3 surface did not alter its catalytic function but had a strong effect on reaction kinetics. As an example of a system where catalysts prevent the formation of toxic species, the reactivity of oxidized Pd surfaces used in CH4 catalytic combustion were studied. An ordered PdO-like monolayer was found to be less reactive towards CO than adsorbed O on Pd. On the other hand, the PdO layer favored a lower activation energy C3H6 oxidation pathway. The results indicated that Pd oxidation reduces the sticking coefficient of reactive species but once molecules adsorb, the oxide surface can reduce the activation energy for subsequent reaction. 相似文献
996.
The possibility that pairs of quarks will form diquark clusters in the regime above deconfinement transition for hadron matter
at finite density is revisited. Here we present the results on the diquark-diquark (dq-dq) interaction in the framework of
constituent quark model taking account of spin, isospin and color degrees of freedom in the spirit of generalized Pauli principle.
By constructing the appropriate spin and color states of the dq-dq clusters we compute the expectation values of the interaction
Hamiltonian involving pairwise quark—quark interaction. We find that the effective interaction between two diquark clusters
is quite sensitive to different configurations characterized by color and spin states, obtained after the coupling of two
diquark states. The value of the coupling parameter for a particular color—spin state, i.e., -3, 1 is compared to the one
obtained earlier by Donoghue and Sateesh,Phys. Rev.
D38, 360 (1988) based on the effective Φ4-theory. This new value of λ derived for different color-spin dq-dq states, may lead to several important implications in
the studies of diquark star and diquark gas. 相似文献
997.
T. Kasahara H.S. Park D. Shindo H. Yoshikawa T. Sato K. Kondo 《Journal of magnetism and magnetic materials》2006
Domain wall motion in Mn–Zn and Ni–Zn ferrites with applied magnetic fields is investigated by in situ observations with Lorentz microscopy and electron holography. It is found that both Mn–Zn and Ni–Zn ferrites have a mean grain size of approximately 10 μm and several pores with sizes ranging from 0.2 to 1.1 μm. In situ observations by Lorentz microscopy with an applied magnetic field reveals that in Mn–Zn ferrite, the domain walls move easily across the grain boundary, while in Ni–Zn ferrite, the domain walls move along the grain boundary but are pinned at the grain boundary and pores. From in situ observations of Ni–Zn ferrite by electron holography, it is clarified that domain wall pinning at the grain boundary retards a sensitive increase in magnetic flux parallel to the applied field direction, which is considered to result in high hysteresis loss. 相似文献
998.
999.
YoungJu Choie Olav K. Richter 《Proceedings of the American Mathematical Society》2007,135(8):2309-2315
We determine a class of functions spanned by theta series of higher degree. We give two applications: A simple proof of the inversion formula of such theta series and a classification of skew-holomorphic Jacobi forms.
1000.
B. D. Kabulov K. A. Akhundzhanov F. U. Yunusov O. A. Shpigun S. S. Negmatov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2007,81(3):354-356
The hydrolytic polycondensation of tetraethoxysilane in the presence of various polymers (polyacrylonitrile, polycaproamide, and chitosan) as templates was performed with the use of the sol-gel technology to obtain nanohybrid composite polymer-silica sorbents-nanofractals. 相似文献