全文获取类型
收费全文 | 17508篇 |
免费 | 2801篇 |
国内免费 | 2084篇 |
专业分类
化学 | 12670篇 |
晶体学 | 286篇 |
力学 | 910篇 |
综合类 | 156篇 |
数学 | 1937篇 |
物理学 | 6434篇 |
出版年
2024年 | 49篇 |
2023年 | 349篇 |
2022年 | 517篇 |
2021年 | 579篇 |
2020年 | 642篇 |
2019年 | 701篇 |
2018年 | 570篇 |
2017年 | 562篇 |
2016年 | 780篇 |
2015年 | 773篇 |
2014年 | 978篇 |
2013年 | 1332篇 |
2012年 | 1572篇 |
2011年 | 1704篇 |
2010年 | 1146篇 |
2009年 | 1138篇 |
2008年 | 1147篇 |
2007年 | 1109篇 |
2006年 | 894篇 |
2005年 | 776篇 |
2004年 | 649篇 |
2003年 | 513篇 |
2002年 | 484篇 |
2001年 | 392篇 |
2000年 | 355篇 |
1999年 | 285篇 |
1998年 | 238篇 |
1997年 | 188篇 |
1996年 | 215篇 |
1995年 | 182篇 |
1994年 | 180篇 |
1993年 | 151篇 |
1992年 | 155篇 |
1991年 | 119篇 |
1990年 | 116篇 |
1989年 | 108篇 |
1988年 | 65篇 |
1987年 | 64篇 |
1986年 | 65篇 |
1985年 | 70篇 |
1984年 | 61篇 |
1983年 | 41篇 |
1982年 | 21篇 |
1981年 | 22篇 |
1979年 | 30篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1975年 | 19篇 |
1974年 | 19篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Surajit Sen 《Physica A》2006,360(2):304-324
There are very few formalisms available to solve the Liouville equation for energy-conserved systems. The continued fraction formalism, introduced through the works of Zwanzig, Mori, Kubo, Lee, Grigolini and others is described here. A detailed discussion is presented on ways to apply the continued fraction formalism to solve for relaxation functions and for the dynamical variable itself for a simple and exactly solvable quantum spin system. 相似文献
82.
83.
84.
原伊鲁烷型倍半萜醇芳香酸酯的碳谱研究 总被引:4,自引:0,他引:4
作者自人工发酵得到的蜜环菌Armillaria mellea (Vahl.ex Fr.) Quel.菌丝体中分离出十七个原伊鲁烷型倍半萜醇芳香酸翻,在研究这些化合物的化学结构中,对其全去偶碳谱,偏共振谱或INEPT谱,C-H COSY谱和远程C-H COSY谱进行比较仔细地分析,指定了每个化合物各碳的归属,讨论了其碳谱的特征,并指出13C NMR谱是对新的该类型化合物结构测定的有效方法. 相似文献
85.
采用ππ偏振激光,通过两步激发和光电离方法,在0-154V/cm电场范围内,测定了Yb原子n-18附近m=0的斯塔克光谱,首次把包含斯塔克效应的能量矩阵对角化方法推广到Yb原子,所获得的理论斯塔克图与实验结果基本符合,观察到低场中斯塔克簇随电场增加呈现线性结构以及^1P1态与斯塔克簇在抗交叉过程中振子强度发生转移的现象,讨论了结构与量子亏损的关系。 相似文献
86.
From flash photolysis data of benzil and 2,2′-dichlorobenzil, the role of conformeric triplets in the formation of hydrogen
adduct radicals has been discussed. The planar relaxed triplet absorbing at 470 nm is less efficient in forming a hydrogen
adduct radical as compared to its puckered conformeric partner. Among the hydrogen donors, triethyl amine and isopropanol,
the former is more efficient in converting puckered triplets and less efficient in the case of planar conformers. Absorptions
of radicals and radical anions of 2,2′-dichlorobenzil appear at 355 nm and 460 nm respectively. These are blue-shifted as
compared to those of the parent compound benzil appearing at 370 nm and 540 nm, respectively. This blue-shift has been discussed
in terms of steric hindrance due to ortho-substitution. 相似文献
87.
We describe one convenient synthesis route to boron nitride (BN) nanotube by the reaction of boron powder, iron oxide, and ammonium chloride at 600 °C for 12 h. Characterized by XRD, FTIR, XPS, TEM and SAED, the composition and morphology of the products are confirmed. The possible reaction mechanism is also discussed. 相似文献
88.
本在无向网络中,建立了带有边集限制的最均匀支撑树问题的网络模型.中首先解决最均匀支撑树问题,并给出求无向网络中最均匀支撑树的多项式时间算法;然后,给出了求无向网络中带有边集限制的最小树多项式时间算法;最后,在已解决的两个问题的基础上解决了带有边集限制的最均匀支撑树问题. 相似文献
89.
90.
A theoretical approach was made to find out a complete fluorine incorporation zone on a ternary diagram which serves as a useful graphical representation to select the flows of the supplied reagents for incorporation of the suitable amount of fluorine into cladding glass of optical fiber preform made by the MCVD process using CCl2F2 as a source of fluorine under oxygen abundance, oxygen deficiency and intermediate oxygen state conditions. The possible mechanism for incorporation of fluorine into cladding glass of optical fiber is also evaluated on the basis of the thermodynamical data. The fluorine incorporation mechanism in silica glass by the MCVD process is found to be dependent on the CCl2F2/SiCl4 ratio in the input gas mixture. Fluorine doping is found to be effective for removing the strained Si–O–Si bonds, which govern the optical transparency in deep ultra-violet (DUV) and vacuum ultra-violet (VUV) regions. The maximum refractive index depression of ?0.5 × 10?3 is obtained with incorporation of fluorine into silica cladding glass by the MCVD process using CCl2F2 as a dopant precursor with suitable flow of SiCl4 vapor along with O2 through backward deposition pass. The structure of fluorine doped silica glass preform samples containing 1.70–1.79 mol% fluorine incorporated by the MCVD process based on the analyses of 19F MAS spectra done by high-resolution 19F NMR spectroscopy reveal the presence of two distinct types of fluorine environments. The majority of the fluorine environments are formed in SiO1.5F polyhedral and less abundant species is observed to be highly unusual, yielding a fivefold coordinated silicon of the type SiO2F polyhedral which become increased with increasing the fluorine content. 相似文献