全文获取类型
收费全文 | 1262篇 |
免费 | 147篇 |
国内免费 | 221篇 |
专业分类
化学 | 1486篇 |
晶体学 | 17篇 |
力学 | 3篇 |
综合类 | 4篇 |
数学 | 2篇 |
物理学 | 118篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 35篇 |
2021年 | 58篇 |
2020年 | 71篇 |
2019年 | 49篇 |
2018年 | 49篇 |
2017年 | 39篇 |
2016年 | 78篇 |
2015年 | 61篇 |
2014年 | 61篇 |
2013年 | 74篇 |
2012年 | 81篇 |
2011年 | 73篇 |
2010年 | 67篇 |
2009年 | 71篇 |
2008年 | 64篇 |
2007年 | 75篇 |
2006年 | 54篇 |
2005年 | 61篇 |
2004年 | 47篇 |
2003年 | 48篇 |
2002年 | 90篇 |
2001年 | 41篇 |
2000年 | 31篇 |
1999年 | 33篇 |
1998年 | 36篇 |
1997年 | 19篇 |
1996年 | 16篇 |
1995年 | 17篇 |
1994年 | 16篇 |
1993年 | 16篇 |
1992年 | 14篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有1630条查询结果,搜索用时 266 毫秒
991.
Secondary amines are obtained in moderate-good yields by reduction of crude imines prepared from N-alkyltriethoxyiminophosphoranes and aldehydes via the aza-Wittig reaction. N-Alkyltriethoxyiminophosphoranes are synthesized by one-pot azidation of alkyl bromides followed by Staudinger reaction. 相似文献
992.
Lorenzo Lombardi Prof. Marco Bandini 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(47):20951-20962
Graphene oxide (GO) is experiencing growing interest by synthetic organic chemists as a promoter of chemical transformations. The synergistic role of the multiple functionalities featuring the nanostructured carbon materials and their π-domains enables the interplay of specific activation modes towards organic compounds that can explore unprecedented chemical modifications. A detailed comprehension of the mechanistic details that govern the transformations guided by GO is a not fully solved task in the field. In this direction, more sophisticated and diversified techniques are employed, providing insights towards intriguing activation modes exerted by the π-matrix and the oxygenated/sulfonate groups decorating the functionalized nano-carbon material. The present Minireview accounts for a critical survey of the most recent developments in the area of GO-mediated organic transformations with a specific focus on mechanist aspects. 相似文献
993.
Sliding threshold of spike‐rate dependent plasticity of a semiconducting polymer/electrolyte cell 下载免费PDF全文
Wenshuai Dong Fei Zeng Yuandong Hu Chiating Chang Xiaojun Li Feng Pan Guoqi Li 《Journal of Polymer Science.Polymer Physics》2016,54(23):2412-2417
Spike‐rate dependent plasticity, one of the conventional learning protocols in neuroscience, has been achieved in semiconducting polymer/electrolyte cells. The frequency threshold θm of spike‐rate dependent plasticity is sliding in requirement of stability. In this work, various prior signal inputs are applied to poly[2‐methoxy‐5‐(2‐ethylhexyloxy)?1,4‐phenylenevinylene]/polyethylene oxide ‐Nd3+ cells to explore their effects on θm.The study find that a prior inhibitory input, i.e., a weak stimulation, moves θm in the low frequency direction, while a prior excitatory input, i.e., an intensive stimulation, moves θm in the high frequency direction. Our results demonstrate the adaptivity of ionic kinetics in macromolecules systems for signal handling and learning. We suggest that a sliding threshold is due to the variable active ionic domains depending on stimulation strength and history. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2412–2417 相似文献
994.
Yuqing Xiao Dr. Yueying Chu Prof. Shenhui Li Dr. Fang Chen Wei Gao Prof. Jun Xu Prof. Feng Deng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(44):11303-11308
The separation of ethane/ethylene mixture by using metal-organic frameworks (MOFs) as adsorbents is strongly associated with the pore size-sieving effect and the adsorbent-adsorbate interaction. Herein, solid-state NMR spectroscopy is utilized to explore the host-guest interaction and ethane/ethylene separation mechanism on zeolitic imidazolate frameworks (ZIFs). Preferential access to the ZIF-8 and ZIF-8-90 frameworks by ethane compared to ethylene is directly visualized from two-dimensional 1H-1H spin diffusion MAS NMR spectroscopy and further verified by computational density distributions. The 1H MAS NMR spectroscopy provides an alternative for straightforwardly extracting the adsorption selectivity of ethane/ethylene mixture at 1.1∼9.6 bar in ZIFs, which is consistent with the IAST predictions. 相似文献
995.
996.
Hydrochlorination of acetylene using expanded multilayered vermiculite (EML-VMT)-supported catalysts
Catalyst supports have very important effects on catalyst performance.A novel expanded multilayered vermiculite(EML-VMT) is successfully used as the catalyst support for the acetylene hydrochlorination.By mixing carbon on the surface of EML-VMT[i.e.,EML-VMT-C),the HgCl_2/EML-VMT-C achieved a high acetylene conversion of 97.3%,a vinyl chloride selectivity of 100%and a turn over frequency(TOF) value of 8.83 × 10~(-3)s~(-1) at a temperature of 140 C,an acetylene gas hourly space velocity(GHSV) of 108 h~(-1)',and a feed volume ratio V(HC1)/V(C_2H_2) of 1.15.Moreover,the HgCl_2/EML-VMT-C shows good stability.The EML-VMT also shows potential in the preparation of other EML-VMT-supported catalysts. 相似文献
997.
998.
Kang Cheng Lars I. van der Wal Hideto Yoshida Jogchum Oenema Justine Harmel Zhaorong Zhang Glenn Sunley Jovana Ze
evi Krijn P. de Jong 《Angewandte Chemie (International ed. in English)》2020,59(9):3592-3600
Improving product selectivity by controlling the spatial organization of functional sites at the nanoscale is a critical challenge in bifunctional catalysis. We present a series of composite bifunctional catalysts consisting of one‐dimensional zeolites (ZSM‐22 and mordenite) and a γ‐alumina binder, with platinum particles controllably deposited either on the alumina binder or inside the zeolite crystals. The hydroisomerization of n‐heptane demonstrates that the catalysts with platinum particles on the binder, which separates platinum and acid sites at the nanoscale, leads to a higher yield of desired isomers than catalysts with platinum particles inside the zeolite crystals. Platinum particles within the zeolite crystals impose pronounced diffusion limitations on reaction intermediates, which leads to secondary cracking reactions, especially for catalysts with narrow micropores or large zeolite crystals. These findings extend the understanding of the “intimacy criterion” for the rational design of bifunctional catalysts for the conversion of low‐molecular‐weight reactants. 相似文献
999.
1000.
《中国化学》2018,36(5):417-420
Osmotic power generation in biomimetic nanofluidic systems has attracted considerable research interest owing to the enhanced performance and long‐term stability. Towards practical applications, when extrapolating the materials from single‐nanopore to multi‐pore membranes, conventional viewpoint suggests that, to gain high electric power density, the porosity should be as high as possible. However, recent experimental observations show that the commonly‐used linear amplification method largely overestimates the actual performance, particularly at high pore density. Herein, we provide a theoretical investigation to understand the reason. We find a counterintuitive pore‐density dependence in high porosity nanofluidic systems that, once the pore density approaches more than 1×109 pores/cm2, the overall output electric power goes down with the increasing pore density. The excessively high pore density impairs the charge selectivity and induces strong ion concentration polarization, which undermines the osmotic power generation process. By optimizing the geometric size of the nanopores, the performance degradation can be effectively relieved. These findings clarify the origin of the unsatisfactory performance of the current osmotic nanofluidic power sources, and provide insights to further optimize the device. 相似文献