全文获取类型
收费全文 | 110961篇 |
免费 | 19039篇 |
国内免费 | 11069篇 |
专业分类
化学 | 75671篇 |
晶体学 | 1283篇 |
力学 | 7243篇 |
综合类 | 611篇 |
数学 | 12627篇 |
物理学 | 43634篇 |
出版年
2024年 | 385篇 |
2023年 | 2219篇 |
2022年 | 3854篇 |
2021年 | 4086篇 |
2020年 | 4490篇 |
2019年 | 4402篇 |
2018年 | 3771篇 |
2017年 | 3492篇 |
2016年 | 5453篇 |
2015年 | 5249篇 |
2014年 | 6351篇 |
2013年 | 8233篇 |
2012年 | 9919篇 |
2011年 | 10254篇 |
2010年 | 6750篇 |
2009年 | 6483篇 |
2008年 | 6885篇 |
2007年 | 6283篇 |
2006年 | 5767篇 |
2005年 | 4841篇 |
2004年 | 3634篇 |
2003年 | 2878篇 |
2002年 | 2698篇 |
2001年 | 2231篇 |
2000年 | 1919篇 |
1999年 | 2209篇 |
1998年 | 1955篇 |
1997年 | 1780篇 |
1996年 | 1954篇 |
1995年 | 1555篇 |
1994年 | 1512篇 |
1993年 | 1210篇 |
1992年 | 1135篇 |
1991年 | 1026篇 |
1990年 | 829篇 |
1989年 | 589篇 |
1988年 | 479篇 |
1987年 | 401篇 |
1986年 | 392篇 |
1985年 | 329篇 |
1984年 | 249篇 |
1983年 | 164篇 |
1982年 | 144篇 |
1981年 | 110篇 |
1980年 | 77篇 |
1979年 | 45篇 |
1978年 | 34篇 |
1976年 | 36篇 |
1975年 | 33篇 |
1974年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
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
43.
44.
Lijuan Shen Li Li Sheng Lu Xiaohan Zhang Jie Liu Junlin An Guojun Zhang Bo Wu Fei Wang 《中国颗粒学报》2015,(3):10-15
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion. 相似文献
45.
JPC – Journal of Planar Chromatography – Modern TLC - A new high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous estimation of... 相似文献
46.
47.
48.
49.
We investigate terahertz radiation(T-rays) from a pentacene organic diode at room temperature. The quantum chemistry calculation for frequency-related Huang–Rhys factor of pentacene is also carried out. The results demonstrate that the T-rays can come from a bending vibration of pentacene skeleton after the energy of pentacene exciton transferring to the vibrational excited state via electron–phonon coupling. Frequency and natural bond orbital analytics of pentacene and its derivatives are performed in order to explain the result and develop new materials to get higher emission. This work provides a new way to produce T-rays with a simple device at room temperature. 相似文献
50.
Efficient control of regioselectivity is a key concern in transition-metal-catalyzed direct C–H functionalization reactions. Various strategies for regiocontrol have been established by tuning the selectivity of the C–H activation step as a common mode. Herein, we present our study on an alternative mode of regiocontrol, in which the selectivity of the C–H activation step is no longer a key concern. We found that, in a reaction where the C–H activation step exhibits a different regio-preference from the subsequent functionalization step, a ligand-enabled switch of the regioselectivity-determining step could provide efficient regiocontrol. This mode has been exemplified by the Pd(ii)-catalyzed aerobic oxidative Heck reaction of indoles, in which a ligand-controlled C3-/C2-selectivity was achieved for the first time by the development of sulfoxide-2-hydroxypyridine (SOHP) ligands.Ligand-enabled switch of the regioselectivity-determining step allowed for efficient regiocontrol in the aerobic oxidative Heck reaction of indole. 相似文献