全文获取类型
收费全文 | 109224篇 |
免费 | 16758篇 |
国内免费 | 1612篇 |
专业分类
化学 | 94529篇 |
晶体学 | 520篇 |
力学 | 3587篇 |
综合类 | 19篇 |
数学 | 12797篇 |
物理学 | 16142篇 |
出版年
2023年 | 4302篇 |
2022年 | 2202篇 |
2021年 | 3375篇 |
2020年 | 5335篇 |
2019年 | 3136篇 |
2018年 | 3359篇 |
2017年 | 1611篇 |
2016年 | 7320篇 |
2015年 | 6856篇 |
2014年 | 6527篇 |
2013年 | 8592篇 |
2012年 | 7058篇 |
2011年 | 5344篇 |
2010年 | 5757篇 |
2009年 | 5792篇 |
2008年 | 4551篇 |
2007年 | 4264篇 |
2006年 | 3226篇 |
2005年 | 3578篇 |
2004年 | 3690篇 |
2003年 | 2735篇 |
2002年 | 2211篇 |
2001年 | 1552篇 |
2000年 | 1353篇 |
1999年 | 966篇 |
1998年 | 788篇 |
1997年 | 796篇 |
1996年 | 938篇 |
1995年 | 812篇 |
1994年 | 751篇 |
1993年 | 928篇 |
1992年 | 753篇 |
1991年 | 602篇 |
1990年 | 536篇 |
1989年 | 507篇 |
1988年 | 501篇 |
1985年 | 632篇 |
1984年 | 632篇 |
1983年 | 493篇 |
1982年 | 521篇 |
1981年 | 570篇 |
1980年 | 551篇 |
1978年 | 511篇 |
1977年 | 604篇 |
1976年 | 625篇 |
1975年 | 693篇 |
1974年 | 697篇 |
1973年 | 503篇 |
1970年 | 626篇 |
1968年 | 502篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Rodríguez Ortega M. P. G. Montejo M. Marchal Ingraín A. Márquez F. López González J. J. 《Journal of Sol-Gel Science and Technology》2012,61(1):258-267
The intrinsic instability of small alkylsilanediols and their propensity toward self-condensation have been the main determiners of the scarce number of experimental works dealing with their synthesis and vibrational characterization. This is the case of the title compound, ethylmethylsilanediol (EMSD), which preparation and purification is, to the best of our knowledge, firstly reported in the present work. Hence, we also report the first records of the IR and Raman spectra of the molecule that have been thoroughly analyzed and completely assigned with the support of DFT calculations. Further, as a previous step of the vibrational assignment, we accomplished a thorough conformational analysis that allowed indentifying five conformations that represent minima on the potential energy surface (PES) of the molecule, depending on the different arrangement that both, the alkyl side chain and the –OH groups, can adopt. Finally, natural bond orbital (NBO) calculations were implemented to justify the stability order and the calculated geometries for the set of conformers in terms of the stabilization derived from the anomeric effect. 相似文献
992.
In this work, we report a sol?Cgel route to fabricate oxide nanowires of BiFeO3 using two-step anodic aluminum oxide as template. We prepared oxide nanowires with uniform dimensions that can vary from 35 to 100?nm in diameter and with 4???m in length, as confirmed by scanning electron microscopy and transmission electron microscopy measurements. Magnetization measurements, performed in a vibrating sample magnetometer, show that this nanostructures present ferromagnetism at room temperature. 相似文献
993.
Dipl.‐Chem. Alexander Zhdanko Dr. Markus Ströbele Prof. Dr. Martin E. Maier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(46):14732-14744
Coordination chemistry of gold catalysts bearing eight different ligands [L=PPh3, JohnPhos (L2), Xphos (L3), DTBP, IMes, IPr, dppf, S‐tolBINAP (L8)] has been studied by NMR spectroscopy in solution at room temperature. Cationic or neutral mononuclear complexes LAuX (L=L2, L3, IMes, IPr; X=charged or neutral ligand) underwent simple ligand exchange without giving any higher coordinate complexes. For L2AuX the following ligand strength series was determined: MeOH?hex‐3‐yne <MeCN≈OTf??Me2S<2,6‐lutidine<4‐picoline<CF3CO2?≈DMAP<TMTU<PPh3<OH?≈Cl?. Some heteroligand complexes DTBPAuX exist in solution in equilibrium with the corresponding symmetrical species. Binuclear complexes dppf(AuOTf)2 and S‐tolBINAP(AuOTf)2 showed different behavior in exchange reactions with ligands depending on the ligand strength. Thus, PPh3 causes abstraction of one gold atom to give mononuclear complexes LLAuPPh3+ and (Ph3P)nAu+, but other N and S ligands give ordinary dicationic species LL(AuNu)22+. In reactions with different bases, LAu+ provided new oxonium ions whose chemistry was also studied: (DTBPAu)3O+, (L2Au)2OH+, (L2Au)3O+, (L3Au)2OH+, and (IMesAu)2OH+. Ultimately, formation of gold hydroxide LAuOH (L=L2, L3, IMes) was studied. Ligand‐ or base‐assisted interconversions between (L2Au)2OH+, (L2Au)3O+, and L2AuOH are described. Reactions of dppf(AuOTf)2 and S‐tolBINAP(AuOTf)2 with bases provided more interesting oxonium ions, whose molecular composition was found to be [dppf(Au)2]3O22+, L8(Au)2OH+, and [L8(Au)2]3O22+, but their exact structure was not established. Several reactions between different oxonium species were conducted to observe mixed heteroligand oxonium species. Reaction of L2AuNCMe+ with S2? was studied; several new complexes with sulfide are described. For many reversible reactions the corresponding equilibrium constants were determined. 相似文献
994.
995.
996.
997.
998.
999.
1000.