全文获取类型
收费全文 | 3853篇 |
免费 | 523篇 |
国内免费 | 724篇 |
专业分类
化学 | 1650篇 |
晶体学 | 25篇 |
力学 | 36篇 |
综合类 | 2篇 |
数学 | 1686篇 |
物理学 | 1701篇 |
出版年
2024年 | 3篇 |
2023年 | 70篇 |
2022年 | 122篇 |
2021年 | 139篇 |
2020年 | 137篇 |
2019年 | 99篇 |
2018年 | 92篇 |
2017年 | 63篇 |
2016年 | 88篇 |
2015年 | 134篇 |
2014年 | 209篇 |
2013年 | 243篇 |
2012年 | 304篇 |
2011年 | 328篇 |
2010年 | 270篇 |
2009年 | 298篇 |
2008年 | 253篇 |
2007年 | 358篇 |
2006年 | 346篇 |
2005年 | 213篇 |
2004年 | 156篇 |
2003年 | 141篇 |
2002年 | 144篇 |
2001年 | 157篇 |
2000年 | 120篇 |
1999年 | 118篇 |
1998年 | 95篇 |
1997年 | 87篇 |
1996年 | 51篇 |
1995年 | 42篇 |
1994年 | 42篇 |
1993年 | 29篇 |
1992年 | 34篇 |
1991年 | 22篇 |
1990年 | 17篇 |
1989年 | 5篇 |
1988年 | 31篇 |
1987年 | 40篇 |
排序方式: 共有5100条查询结果,搜索用时 31 毫秒
41.
Enumeration on Nonseparable Planar Maps 总被引:1,自引:0,他引:1
This paper provides some functional equations satisfied by the generating functions for nonseparable rooted planar maps with the valency of root-vertex, the number of edges and the valency of root-faces of the maps as three parameters. But the solutions of these equations can only be obtained indirectly by considering some relations between nonseparable and general rooted planar maps. One of them is an answer to the open problem 6.1 in Liu (1983, Comb. Optim. CORR83-26, University of Waterloo). 相似文献
42.
玻璃中CdSeS纳米晶体的室温光致发光谱 总被引:4,自引:3,他引:1
对掺有过饱和的镉、硒和少量硫的玻璃在500~800℃分别退火4h,生长了不同尺寸的CdSe1-xSx纳米晶体。测量了纳米晶体的室温吸收光谱和光致发光(PL)光谱,550℃生长的样品在300~800nm的范围没有观察到吸收和发光峰,表明温度低于550℃玻璃中不能形成纳米晶体。生长温度在600~650℃,纳米晶体的PL光谱主要为两个宽的发光带,即带边激子发光带和通过表面态复合的发光带。随着生长温度的升高,带边复合发光的蓝移减小,通过表面态的发光逐渐消失,并出现了叠加于宽发光带上的一系列明显的弱发射峰。不同温度生长的样品中,叠加峰的能量相同。同一样品中叠加峰的能量不随激发光波长的变化而变化。 相似文献
43.
In this paper, the authors obtain the endpoint estimates for a class of non-standard commutators with higher order remainders and their variants. Moreover, the authors show that these operators are actually not bounded in certain cases.
44.
杨大春 《中国科学A辑(英文版)》2003,46(5)
This paper introduces the fractional Sobolev spaces on spaces of homogeneous type,includingmetric spaces and fractals. These Sobolev spaces include the well-known Hajfasz-Sobolev spaces as specialmodels.The author establishes varions chaaracterizations of(sharp)maximal functions for these spaces.Asapplications,the author identifies the fractional Sobolev spaces with some Lipscitz-type spaces.Moreover;some embedding theorems are also given. 相似文献
45.
In this paper we investigate the
probabilistic linear $(n,\delta)$-widths and $p$-average linear
$n$-widths of the Sobolev space $W^r_2$ equipped with the Gaussian
measure $\mu$ in the $L_{\infty}$-norm, and determine the
asymptotic equalities
\begin{eqnarray*}
\lambda_{n,\delta}(W^r_2,\mu,L_{\infty})
&\asymp&\frac{\sqrt{\ln
(n/\delta)}}{n^{r+(s-1)/2}},\\[3pt]
\lambda^{(a)}_n(W^r_2,\mu,L_{\infty})_p &\asymp&\frac{\sqrt{\ln
n}}{n^{r+(s-1)/2}}, \qquad 0 < p < \infty.
\end{eqnarray*} 相似文献
46.
CHEN Bao-Zhen HUANG Zu-Qia 《理论物理通讯》2004,42(9)
The theoretical signal-pressure curves are calculated from approximate analytical solutions of the coupledequations describing the third order parametric wave mixing in a gas-filled capillary of femto-second laser pulses. Thecomparison with the corresponding experimental curves suggests that the following three factors exert important influ-ences on the degree of fitting between the theoretical and experimental results: the walk-off, the phase modulation, andthe third order harmonic of idler pulse. 相似文献
47.
Feng-Yu Wang 《Probability Theory and Related Fields》1994,98(3):299-306
Summary By using coupling methods, some lower bounds are obtained for the first Neumann eigenvalue on Riemannian manifolds. This method is new and the results improve some known estimates. An example shows that our estimates can be sharp.Research supported in part by the Foundation of Beijing Normal University 相似文献
48.
Three novel zinc complexes [Zn(dbsf)(H2O)2] ( 1 ), [Zn(dbsf)(2,2′‐bpy)(H2O)]·(i‐C3H7OH) ( 2 ) and [Zn(dbsf)(DMF)] ( 3 ) (H2dbsf = 4,4′‐dicarboxybiphenyl sulfone, 2,2′‐bpy = 2,2′‐bipyridine, i‐C3H7OH = iso‐propanol, DMF = N,N‐dimethylformamide) were first obtained and characterized by single crystal X‐ray crystallography. Although the results show that all the complexes 1–3 have one‐dimensional chains formed via coordination bonds, unique three‐dimensional supramolecular structures are formed due to different coordination modes and configuration of the dbsf2? ligand, hydrogen bonds and π–π interactions. Iso‐propanol molecules are in open channels of 2 while larger empty channels are formed in 3 . As compared with emission band of the free H2dbsf ligand, emission peaks of the complexes 1–3 are red‐shifted, and they show blue emission, which originates from enlarging conjugation upon coordination. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
49.
We give a Euclidean wormhole solution in the vacuum Bergmann-Wagoner scalar-tensor gravitational theory. We show that this wormhole, unlike others, has complex charge and is a baby universe (half a wormhole). 相似文献
50.