全文获取类型
收费全文 | 363103篇 |
免费 | 2153篇 |
国内免费 | 1021篇 |
专业分类
化学 | 163075篇 |
晶体学 | 4899篇 |
力学 | 20059篇 |
综合类 | 6篇 |
数学 | 72673篇 |
物理学 | 105565篇 |
出版年
2020年 | 2002篇 |
2019年 | 2306篇 |
2018年 | 18896篇 |
2017年 | 19330篇 |
2016年 | 12623篇 |
2015年 | 3806篇 |
2014年 | 4252篇 |
2013年 | 9716篇 |
2012年 | 13613篇 |
2011年 | 27365篇 |
2010年 | 16652篇 |
2009年 | 17044篇 |
2008年 | 22544篇 |
2007年 | 27397篇 |
2006年 | 8071篇 |
2005年 | 13943篇 |
2004年 | 10488篇 |
2003年 | 10483篇 |
2002年 | 7724篇 |
2001年 | 6332篇 |
2000年 | 5241篇 |
1999年 | 3643篇 |
1998年 | 3235篇 |
1997年 | 3195篇 |
1996年 | 3122篇 |
1995年 | 2520篇 |
1994年 | 2564篇 |
1993年 | 2608篇 |
1992年 | 2709篇 |
1991年 | 2779篇 |
1990年 | 2673篇 |
1989年 | 2660篇 |
1988年 | 2604篇 |
1987年 | 2569篇 |
1986年 | 2481篇 |
1985年 | 3159篇 |
1984年 | 3328篇 |
1983年 | 2691篇 |
1982年 | 2954篇 |
1981年 | 2828篇 |
1980年 | 2630篇 |
1979年 | 2860篇 |
1978年 | 2982篇 |
1977年 | 2907篇 |
1976年 | 2906篇 |
1975年 | 2753篇 |
1974年 | 2721篇 |
1973年 | 2914篇 |
1972年 | 1928篇 |
1967年 | 1876篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
63.
Sh. M. Khaliullin V. D. Zhuravlev V. G. Bamburov L. V. Ermakova 《Physics of Atomic Nuclei》2015,78(12):1382-1388
Submicron CaZrO3 powder is obtained in combustion reactions (solution combustion synthesis—SCS) with glycine. It is found that SCS reduces the sintering temperature of CaZrO3 powders. The dielectric properties of calcium zirconate ceramics are studied by the electrochemical impedance method. It is shown that a ceramics of powders obtained by the SCS method has high dielectric characteristics. 相似文献
64.
Susana Estopiñá-Durán Liam J. Donnelly Euan B. Mclean Bryony M. Hockin Prof. Alexandra M. Z. Slawin Dr. James E. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3950-3956
A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C−O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid. 相似文献
65.
Michiel Janssen Prof. Dirk E. De Vos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(45):10724-10734
The practical application of Shilov-type Pt catalysis to the selective hydroxylation of terminal aliphatic C−H bonds remains a formidable challenge, due to difficulties in replacing PtIV with a more economically viable oxidant, particularly O2. We report the potential of employing FeCl2 as a suitable redox mediator to overcome the kinetic hurdles related to the direct use of O2 in the Pt reoxidation. For the selective conversion of butyric acid to γ-hydroxybutyric acid (GHB), a significantly enhanced catalyst activity and stability (turnover numbers (TON)>30) were achieved under 20 bar O2 in comparison to current state-of-the-art systems (TON<10). In this regard, essential reaction parameters affecting the overall activity were identified, along with specific additives to attain catalyst stability at longer reaction times. Notably, deactivation by reduction to Pt0 was prevented by the addition of monodentate pyridine derivatives, such as 2-fluoropyridine, but also by introducing varying partial pressures of N2 in the gaseous atmosphere. Finally, stability tests revealed the involvement of PtII and FeCl2 in catalyzing the non-selective overoxidation of GHB. Accordingly, in situ esterification with boric acid proved to be a suitable strategy to maintain enhanced selectivities at much higher conversions (TON>60). Altogether, a useful catalytic system for the selective hydroxylation of primary aliphatic C−H bonds with O2 is presented. 相似文献
66.
Norbornene derivatives from a metal‐free,strain‐promoted cycloaddition reaction: New building blocks for ring‐opening metathesis polymerization reactions 下载免费PDF全文
Christopher E. Hobbs Binhong Lin Thomas Malinski 《Journal of polymer science. Part A, Polymer chemistry》2015,53(20):2357-2362
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362 相似文献
67.
68.
69.
70.
Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and... 相似文献