全文获取类型
收费全文 | 50089篇 |
免费 | 11849篇 |
国内免费 | 3569篇 |
专业分类
化学 | 51390篇 |
晶体学 | 494篇 |
力学 | 1329篇 |
综合类 | 184篇 |
数学 | 3891篇 |
物理学 | 8219篇 |
出版年
2024年 | 33篇 |
2023年 | 264篇 |
2022年 | 526篇 |
2021年 | 622篇 |
2020年 | 1754篇 |
2019年 | 3072篇 |
2018年 | 1470篇 |
2017年 | 1106篇 |
2016年 | 3924篇 |
2015年 | 4121篇 |
2014年 | 4125篇 |
2013年 | 5086篇 |
2012年 | 4225篇 |
2011年 | 3414篇 |
2010年 | 3801篇 |
2009年 | 3672篇 |
2008年 | 3352篇 |
2007年 | 2612篇 |
2006年 | 2296篇 |
2005年 | 2328篇 |
2004年 | 2039篇 |
2003年 | 1880篇 |
2002年 | 2724篇 |
2001年 | 1997篇 |
2000年 | 1718篇 |
1999年 | 718篇 |
1998年 | 334篇 |
1997年 | 283篇 |
1996年 | 274篇 |
1995年 | 200篇 |
1994年 | 198篇 |
1993年 | 153篇 |
1992年 | 131篇 |
1991年 | 120篇 |
1990年 | 105篇 |
1989年 | 89篇 |
1988年 | 80篇 |
1987年 | 56篇 |
1986年 | 79篇 |
1985年 | 65篇 |
1984年 | 64篇 |
1983年 | 50篇 |
1982年 | 33篇 |
1981年 | 28篇 |
1980年 | 38篇 |
1979年 | 22篇 |
1978年 | 33篇 |
1977年 | 25篇 |
1976年 | 30篇 |
1975年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
83.
The present paper determines the form of automorphisms of $\[{E_2}(R)\]$ and $\[G{E_2}(R)\]$ over commutative rings provided 2, 3 and 5 are units. 相似文献
84.
85.
86.
A graph G is N2‐locally connected if for every vertex ν in G, the edges not incident with ν but having at least one end adjacent to ν in G induce a connected graph. In 1990, Ryjá?ek conjectured that every 3‐connected N2‐locally connected claw‐free graph is Hamiltonian. This conjecture is proved in this note. © 2004 Wiley Periodicals, Inc. J Graph Theory 48: 142–146, 2005 相似文献
87.
ZHU Yabin ZHOU Yueliang LIU Zhen WANG Shufang CHEN Zhenghao U Huibin YANG Guozhen XlAO Ling Ren Hongtao JIAO Yulei Zheng Minghui 《中国科学G辑(英文版)》2004,47(2):165-172
The irreversibility field (Hirr) of Y-based superconductor is much higher than that of Bi-based superconductor. Y-based superconductor is capable of maintaining stable electrical currents in high magnetic field and electric field, so it is a better suited mate-rial for electric-current applications. Commonly, the Y-based tapes comprise a YBCO thick film deposited on a flexible substrate, typically with an intermediate buffer layer, and an overcoat of noble metal. In this process, the interm… 相似文献
88.
This paper is devoted to a detailed theoretical study of an ion pair SN2 reaction LiNCO+CH3F in the gas phase and in solution at the level of MP2(full)/6-31+G**//HF/6-31+G**. Two possible reaction mechanisms, inversion and retention, are discussed. There are eight possible reaction pathways. The inversion mechanism is more favorable no matter in the gas phase or in solution based on analyses of the transition structures. Methyl isocyanate should form preferentially in the gas phase and more stable methyl cyanate is the main product in solution. The retardation of the reaction in solvents was attributed to the difference in solvation in the separated reactants and in the transition state. 相似文献
89.
Song LI Guo Mao WANG Zhi Song LIU 《数学学报(英文版)》2005,21(6):1475-1486
The purpose of this paper is to investigate the mean size formula of wavelet packets in Lp for 0 〈 p ≤ ∞. We generalize a mean size formula of wavelet packets given in terms of the p-norm joint spectral radius and we also give some asymptotic formulas for the Lp-norm or quasi-norm on the subdivision trees. All results will be given in the general setting, 相似文献
90.
Ching‐Yuan Cheng Kuan‐Jiuh Lin 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(8):m363-m365
In the title compound, catena‐poly[lithium‐μ3‐ethylenediphosphonato], [Li(C2H7O6P2)]n, the supramolecular monoclinic (C2/c) structure consists of one‐dimensional lithium chains [Li⋯Li = 2.7036 (8) Å] that are embedded within ethylenediphosphonate anions linked by strong symmetric hydrogen bonds [O⋯O = 2.473 (3) Å]. The Li atoms and the H atom in the symmetric hydrogen bond reside on twofold rotation axes and there is an inversion center at the mid‐point of the C—C bond of the ethylenediphosphonate ligand. 相似文献