全文获取类型
收费全文 | 24859篇 |
免费 | 4405篇 |
国内免费 | 3344篇 |
专业分类
化学 | 18096篇 |
晶体学 | 324篇 |
力学 | 1729篇 |
综合类 | 216篇 |
数学 | 2695篇 |
物理学 | 9548篇 |
出版年
2024年 | 53篇 |
2023年 | 531篇 |
2022年 | 771篇 |
2021年 | 872篇 |
2020年 | 1164篇 |
2019年 | 1010篇 |
2018年 | 874篇 |
2017年 | 825篇 |
2016年 | 1227篇 |
2015年 | 1216篇 |
2014年 | 1389篇 |
2013年 | 1795篇 |
2012年 | 2272篇 |
2011年 | 2346篇 |
2010年 | 1567篇 |
2009年 | 1476篇 |
2008年 | 1679篇 |
2007年 | 1433篇 |
2006年 | 1412篇 |
2005年 | 1176篇 |
2004年 | 943篇 |
2003年 | 770篇 |
2002年 | 779篇 |
2001年 | 636篇 |
2000年 | 538篇 |
1999年 | 587篇 |
1998年 | 377篇 |
1997年 | 361篇 |
1996年 | 393篇 |
1995年 | 331篇 |
1994年 | 299篇 |
1993年 | 241篇 |
1992年 | 225篇 |
1991年 | 177篇 |
1990年 | 156篇 |
1989年 | 122篇 |
1988年 | 133篇 |
1987年 | 75篇 |
1986年 | 77篇 |
1985年 | 62篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1982年 | 30篇 |
1981年 | 25篇 |
1980年 | 14篇 |
1979年 | 14篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1957年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
992.
A Hexagonal Covalent Porphyrin Framework as an Efficient Support for Gold Nanoparticles toward Catalytic Reduction of 4‐Nitrophenol
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zheng‐Dong Ding Yu‐Xia Wang Sai‐Fei Xi Prof. Dr. Yunxing Li Prof. Dr. Zaijun Li Prof. Dr. Xuehong Ren Prof. Dr. Zhi‐Guo Gu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(47):17029-17036
A hexagonal porphyrin‐based porous organic polymer, namely, CPF‐1, was constructed by 3+2 ketoenamine condensation of the C2‐symmetric porphyrin diamine 5,15‐bis(4‐aminophenyl)‐10,20‐diphenylporphyrin and 1,3,5‐triformylphloroglucinol. This material exhibits permanent porosity and excellent thermal and chemical stability. CPF‐1 can be employed as a superior supporting substrate to immobilize Au nanoparticles (NPs) as a result of the strong interactions between Au NPs and the CPF support. An Au@CPF‐1 hybrid was synthesized by an interfacial solution infiltration method with NaBH4 as reducing agent. Au NPs (5 nm) grew on CPF‐1 and were distributed without aggregation. Moreover, Au@CPF‐1 exhibits superior catalytic activity compared to many other reported Au‐based catalysts for the reduction of 4‐nitrophenol in the presence of NaBH4. In addition, Au@CPF‐1 has excellent stability and recyclability, and it can be reused for three successive reaction cycles without loss of activity. The dense distribution of phenyl rings on the channel walls of the CPF support can reasonably be regarded as the active sites that adsorb the 4‐nitrophenol molecule through hydrogen‐bonding and C?H ??? π interactions, as was confirmed by the X‐ray structure of model compound DAPP‐Benz. 相似文献
993.
994.
995.
De-Yang Zhang Chang-Bin Yu Min-Can Wang Kai Gao Yong-Gui Zhou 《Tetrahedron letters》2012,53(20):2556-2559
A new electronically deficient atropisomeric diphosphine ligand (S)-CF3O-BiPhep was synthesized from 1-bromo-3-(trifluoromethoxy)benzene in high yield. The key steps included oxidative coupling with anhydrous ferric chloride and optical resolution by (+)-DMTA. The ligand afforded high performance for Ir-catalyzed asymmetric hydrogenation of quinolines with ee up to 92% and TON up to 25,000. It was also successfully applied to the Pd-catalyzed asymmetric hydrogenation of simple indoles with ee up to 87% and Rh-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone with 97% ee. 相似文献
996.
997.
By adding one variable to the equality-or inequality-constrained minimization problems, a new simple penalty function is proposed. It is proved to be exact in the sense that under mild assumptions, the local minimizers of this penalty function are precisely the local minimizers of the original problem, when the penalty parameter is sufficiently large. 相似文献
998.
Hongliu Zheng 《代数通讯》2013,41(4):1403-1417
999.
Dongyao Li Chunmiao Ma Prof. Junfeng Xiang Kai Zhang Ling Yang Prof. Quan Gan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(45):11663-11669
A strategy to reversibly switch the parallel/antiparallel helical conformation of aromatic double helices through the formation/breakage of a disulfide bond is presented. Single-crystal X-ray structures, NMR, and circular dichroism spectroscopy demonstrate that the double helices with terminal thiol groups favor an antiparallel helical arrangement both in the solid state and in solution, while the P/M bias of helicity induced by chiral segments from another extremity of the sequence is weak in this structural motif. The antiparallel helices can be rearranged to parallel helices through the disulfide connection of the sequences. This change enhances the bias of helical handedness and results in absolute chirality control of the double helices. The handedness-mediated process can be governed by the oxidation-reduction cycle, thereby switching the structural arrangement and the enhancement of chiral bias. In addition, we find that the sequences can dimerize into an intermolecular double helix with the disulfide connection. And the helical handedness is also fully controlled due to the head-to-head structural motif. 相似文献
1000.
A simple and efficient synthetic route of 2′‐amino‐2′‐deoxyuridine was studied. 2′‐Amino‐2′‐deoxyuridine was incorporated into 1,8‐naphthalimides in the 2′‐position of 2′‐sugar via linking arms of different lengths. A convenient method for the synthesis of the conjugates was adopted. 相似文献