全文获取类型
收费全文 | 51322篇 |
免费 | 9969篇 |
国内免费 | 16380篇 |
专业分类
化学 | 37733篇 |
晶体学 | 1842篇 |
力学 | 3706篇 |
综合类 | 1754篇 |
数学 | 7990篇 |
物理学 | 24646篇 |
出版年
2024年 | 150篇 |
2023年 | 627篇 |
2022年 | 1883篇 |
2021年 | 1825篇 |
2020年 | 1892篇 |
2019年 | 1958篇 |
2018年 | 1775篇 |
2017年 | 2355篇 |
2016年 | 2072篇 |
2015年 | 2796篇 |
2014年 | 3225篇 |
2013年 | 4269篇 |
2012年 | 4255篇 |
2011年 | 4616篇 |
2010年 | 4355篇 |
2009年 | 4418篇 |
2008年 | 4900篇 |
2007年 | 4286篇 |
2006年 | 4296篇 |
2005年 | 3620篇 |
2004年 | 2916篇 |
2003年 | 2082篇 |
2002年 | 2224篇 |
2001年 | 2072篇 |
2000年 | 2239篇 |
1999年 | 1290篇 |
1998年 | 682篇 |
1997年 | 556篇 |
1996年 | 523篇 |
1995年 | 437篇 |
1994年 | 420篇 |
1993年 | 402篇 |
1992年 | 328篇 |
1991年 | 265篇 |
1990年 | 235篇 |
1989年 | 220篇 |
1988年 | 206篇 |
1987年 | 189篇 |
1986年 | 141篇 |
1985年 | 100篇 |
1984年 | 106篇 |
1983年 | 95篇 |
1982年 | 59篇 |
1981年 | 55篇 |
1980年 | 51篇 |
1979年 | 46篇 |
1978年 | 18篇 |
1977年 | 12篇 |
1965年 | 24篇 |
1959年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
3.
4.
The Ramanujan Journal - We calculate the dimensions of the spaces of invariant vectors under the Klingen congruence subgroup of level $${\mathfrak {p}}^2$$ for all irreducible, admissible... 相似文献
5.
Wacker oxidation is an industry-adopted process to transform olefins into value-added epoxides and carbonyls. However, traditional Wacker oxidation involves the use of homogeneous palladium and copper catalysts for the olefin addition and reductive elimination. Here, we demonstrated an ultrahigh loading Cu single atom catalyst(14% Cu, mass fraction) for the palladium-free Wacker oxidation of 4-vinylanisole into the corresponding ketone with N-methylhydroxylamine hydrochloride as an additive under mild conditions. Mechanistic studies by 18O and deuterium isotope labelling revealed a hydrogen shift mechanism in this palladium-free process using N-methylhydroxylamine hydrochloride as the oxygen source. The reaction scope can be further extended to Kucherov oxidation. Our study paves the way to replace noble metal catalysts in the traditional homogeneous processes with single atom catalysts. 相似文献
6.
利用n维有限射影空间上的一些性质,构作了组合群验的数学模型de-析取矩阵,并研究了它的参数和Hamming距离. 相似文献
7.
Nonlinear Dynamics - With an increasing number of people sharing feelings and opinions online, the online platforms have become one of the most important channels for public opinion dissemination.... 相似文献
8.
Yi Han Zibo Xue Dr. Guangwu Li Dr. Yanwei Gu Dr. Yong Ni Dr. Shaoqiang Dong Prof. Chunyan Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(23):9111-9116
Incorporation of a non-hexagonal ring into a nanographene framework can lead to new electronic properties. During the attempted synthesis of naphthalene-bridged double [6]helicene and heptagon-containing nanographene by the Scholl reaction, an unexpected azulene-embedded nanographene and its triflyloxylated product were obtained, as confirmed by X-ray crystallographic analysis and 2D NMR spectroscopy. A 5/7/7/5 ring-fused substructure containing two formal azulene units is formed, but only one of them shows an azulene-like electronic structure. The formation of this unique structure is explained by arenium ion mediated 1,2-phenyl migration and a naphthalene to azulene rearrangement reaction according to an in-silico study. This report represents the first experimental example of the thermodynamically unfavorable naphthalene to azulene rearrangement and may lead to new azulene-based molecular materials. 相似文献
9.
10.
In the view of substrate availability, atomic efficiency and cost, directly using arenols as coupling partners in cross‐coupling, would be one of the most attractive goals. Up to date, many efforts have been made to activate the C—O bond of phenols with different strategies, for example, through in‐situ formed intermediates, through a catalytic reductive dearomatization‐condensation‐rearomatization sequence or catalytic deoxygenation. In this review, we summarized recent advances in cross‐couplings of arenols as the electrophiles via C—O activation. 相似文献