全文获取类型
收费全文 | 45228篇 |
免费 | 7472篇 |
国内免费 | 6164篇 |
专业分类
化学 | 33927篇 |
晶体学 | 659篇 |
力学 | 2449篇 |
综合类 | 480篇 |
数学 | 4967篇 |
物理学 | 16382篇 |
出版年
2024年 | 103篇 |
2023年 | 869篇 |
2022年 | 1512篇 |
2021年 | 1570篇 |
2020年 | 1770篇 |
2019年 | 1795篇 |
2018年 | 1498篇 |
2017年 | 1522篇 |
2016年 | 2108篇 |
2015年 | 2110篇 |
2014年 | 2575篇 |
2013年 | 3305篇 |
2012年 | 4118篇 |
2011年 | 4310篇 |
2010年 | 3107篇 |
2009年 | 2866篇 |
2008年 | 3174篇 |
2007年 | 3012篇 |
2006年 | 2738篇 |
2005年 | 2293篇 |
2004年 | 1658篇 |
2003年 | 1362篇 |
2002年 | 1277篇 |
2001年 | 1053篇 |
2000年 | 955篇 |
1999年 | 934篇 |
1998年 | 692篇 |
1997年 | 657篇 |
1996年 | 563篇 |
1995年 | 536篇 |
1994年 | 521篇 |
1993年 | 409篇 |
1992年 | 336篇 |
1991年 | 329篇 |
1990年 | 293篇 |
1989年 | 197篇 |
1988年 | 157篇 |
1987年 | 140篇 |
1986年 | 118篇 |
1985年 | 93篇 |
1984年 | 61篇 |
1983年 | 42篇 |
1982年 | 43篇 |
1981年 | 24篇 |
1980年 | 19篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1971年 | 4篇 |
1957年 | 8篇 |
1936年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
21.
This minireview describes the strategies for synthesis of fiuorinated surfactants potentially nonbioaccumulable.Various strategies have been focused on(Ⅰ) reducing the length of the perfluorocarbon chain,(Ⅱ) introducing hetero atoms into the fluorocarbon chain,(Ⅲ) introducing branch(herein and after branch means the fluoro-carbon chain section is not straight).In most cases,the surface tensions versus the surfactant concentrations have been assessed.These above strategies led to various highly fiuorinated(perfluorinated or not perfluorinated) surfactants whose chemical changes enabled to obtain novel alternatives to perfluorooctanoic acid(PFOA) and perfluorooctane sulphonate(PFOS). 相似文献
22.
23.
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
24.
25.
Sulfur hexafluoride (SF6) is considered as a potent greenhouse gas, whose effective degradation is challenging. Here we report a computational study on the nucleophilic activation of sulfur hexafluoride by N-heterocyclic carbenes and N-heterocyclic olefins. The result shows that the activation of SF6 is both thermodynamically and kinetically favorable at mild condition using NHOs with fluoro-substituted azolium and sulfur pentafluoride anion being formed. The Gibbs free energy barrier during the activation of SF6 has a linear relationship with the energy of HOMO of substrates, which could be a guideline for applying those compounds that feature higher energy in HOMO to activate SF6 in high efficiency. 相似文献
26.
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
27.
Hui Li Jian Liu Juan Zhao Huiting He Dr. Dabo Jiang Prof. Steven Robert Kirk Prof. Qiong Xu Dr. Xianxiang Liu Prof. Dulin Yin 《ChemistryOpen》2021,10(4):477-485
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss. 相似文献
28.
Guo Yan Li Zhuang Wei Yuxi Zhang Xinxu Shi Kexin 《Journal of Solid State Electrochemistry》2022,26(4):1051-1065
Journal of Solid State Electrochemistry - Polyvinylpyrrolidone (PVP) and graphene (G)-modified iron oxides (Fe2O3-PVP-G) are prepared by a simple hydrothermal reaction. Their morphology and... 相似文献
29.
Peng-Yan Gui Xiao-Hui Yan Wen-Juan Yuan Yuan-Liang Ma Xiao Ding Shuai Liu 《Natural product research》2019,33(19):2830-2836
A new A, D-seco limonoid, named 12-acetyloxyperforatin (1), along with three known ones, were isolated from the leaves of Harrisonia perforata. Their structures were elucidated on the basis of spectroscopic analysis, including extensive NMR techniques and computational modelling. These compounds showed no inhibitory activity against the 11β-HSD1 enzyme. 相似文献
30.