全文获取类型
收费全文 | 30336篇 |
免费 | 3932篇 |
国内免费 | 2895篇 |
专业分类
化学 | 14681篇 |
晶体学 | 210篇 |
力学 | 1571篇 |
综合类 | 199篇 |
数学 | 2366篇 |
物理学 | 8047篇 |
综合类 | 10089篇 |
出版年
2024年 | 141篇 |
2023年 | 537篇 |
2022年 | 880篇 |
2021年 | 981篇 |
2020年 | 981篇 |
2019年 | 882篇 |
2018年 | 788篇 |
2017年 | 718篇 |
2016年 | 1108篇 |
2015年 | 1260篇 |
2014年 | 1483篇 |
2013年 | 1824篇 |
2012年 | 2089篇 |
2011年 | 2329篇 |
2010年 | 1589篇 |
2009年 | 1559篇 |
2008年 | 1635篇 |
2007年 | 1628篇 |
2006年 | 1484篇 |
2005年 | 1396篇 |
2004年 | 1123篇 |
2003年 | 844篇 |
2002年 | 835篇 |
2001年 | 790篇 |
2000年 | 725篇 |
1999年 | 904篇 |
1998年 | 821篇 |
1997年 | 794篇 |
1996年 | 745篇 |
1995年 | 645篇 |
1994年 | 601篇 |
1993年 | 496篇 |
1992年 | 518篇 |
1991年 | 421篇 |
1990年 | 395篇 |
1989年 | 339篇 |
1988年 | 229篇 |
1987年 | 198篇 |
1986年 | 136篇 |
1985年 | 86篇 |
1984年 | 47篇 |
1983年 | 44篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1977年 | 5篇 |
1975年 | 6篇 |
1969年 | 4篇 |
1957年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Bomin Feng Xiuju Wu Ling Li Wei Gao Dr. Weihua Hu Prof. Chang Ming Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(49):11560-11565
It remains challenging to rationally synthesize iron/nitrogen-doped carbon (Fe/N-C) catalysts with rich Fe−Nx atomic active sites for improved oxygen reduction reaction (ORR) electrocatalysis. A highly efficient Fe/N-C catalyst, which has been synthesized through a spatial isolation strategy, is reported. Derived from bioinspired polydopamine (PDA)-based hybrid microsphere precursors, it is a multifunctional carrier that loads atomically dispersed Fe3+/Zn2+ ions through coordination interactions and N-rich melamine through electrostatic attraction and covalent bonding. The Zn2+ ions and melamine in the precursor efficiently isolate Fe3+ atoms upon pyrolysis to form rich Fe−Nx atomic active sites, and generate abundant micropores during high-temperature treatment; as a consequence, the resultant Fe-N/C catalyst contains rich catalytically active Fe−Nx sites and a hierarchical porous structure. The catalyst exhibits improved ORR activity that is superior to and close to that of Pt/C in alkaline and acidic solutions, respectively. 相似文献
992.
Porous multipod Cu2O microcrystals were found to be an efficient, highly recyclable and eco‐friendly catalyst for the cross‐coupling reactions of aryl halides and terminal alkynes with high yields in aqueous media. Noteworthy, the Cu2O catalyst can be reused for several times without significant decrease in catalytic activity. 相似文献
993.
994.
995.
996.
采用EDTA-甘氨酸联合法(EGCP)合成具有钙钛矿结构的La0.90Sr0.10Al0.97Mg0.03O3-δ(LSAM)粉体。采用TG-DSC,XRD,ICP-OES和TEM对粉体进行表征。在750℃下,无定形结构的粉末直接转化为钙钛矿结构的LSAM粉体。经1000℃煅烧3 h后的粉体,团聚程度低,粒径分布均匀,平均粒径约为77 nm,具有良好的烧结性能。通过SEM对材料的显微结构进行观察并分析其对电性能的影响。采用直流四电极法在空气中测定材料的总电导率,在800℃时,EGCP合成的LSAM电解质的总电导率为1.50×10-2S.cm-1,比固相法的高47.1%。 相似文献
997.
998.
Copper(I) catalyzed radical benzylation and cyclization reaction of tertiary enamides was investigated and 3,3-disubstituted N-Alkyl isoindolin-1-ones were obtained in moderate to good yields. In this reaction, two new C–C bonds were formed in one step with high atom economy. Possible reaction pathway for the formation of the products was also discussed in this paper. 相似文献
999.
A series of imidazolium chlorides for the formation of tridentate CNO‐donor palladium(II) complexes featuring N‐heterocyclic carbene moieties have been developed from cheap and readily available starting materials with high yields. Their palladium complexes were prepared by reactions between the ligand precursors and PdCl2 using K2CO3 as base in pyridine with reasonable yields. These air‐stable metal complexes were characterized using 1H NMR and 13C{1H} NMR spectroscopy and elemental analyses. Heteronuclear multiple bond correlation experiments were performed to identify key NMR signals of these compounds. The structures of two of the complexes were also established by single‐crystal X‐ray diffraction analysis. One of these complexes was successfully applied in the direct C―H functionalization reactions between heterocyclic compounds and aryl bromides, producing excellent yields of coupled products. The coupling reactions were scalable, allowing grams of coupled products to be obtained with a mere 2 mol% of Pd loading. The catalyst system developed allowed the large‐scale preparation of several push–pull chromophores straightforwardly. Photophysical properties based on UV–visible and fluorescence spectroscopy for these chromophores were investigated. Deep blue photoluminescence with moderate quantum efficiency and twisted intramolecular charge transfer excited state were observed for these chromophores. Density functional theory (DFT) and time‐dependent DFT calculations were performed to support the experimental results. 相似文献
1000.
Yuan Hu Brad Sherborne Tai-Sung Lee David A. Case Darrin M. York Zhuyan Guo 《Journal of computer-aided molecular design》2016,30(7):533-539
In drug discovery, protonation states and tautomerization are easily overlooked. Through a Merck–Rutgers collaboration, this paper re-examined the initial settings and preparations for the Thermodynamic Integration (TI) calculation in AMBER Free-Energy Workflows, demonstrating the value of careful consideration of ligand protonation and tautomer state. Finally, promising results comparing AMBER TI and Schrödinger FEP+ are shown that should encourage others to explore the value of TI in routine Structure-based Drug Design. 相似文献