全文获取类型
收费全文 | 442711篇 |
免费 | 2896篇 |
国内免费 | 1279篇 |
专业分类
化学 | 213984篇 |
晶体学 | 6067篇 |
力学 | 23703篇 |
综合类 | 24篇 |
数学 | 75373篇 |
物理学 | 127735篇 |
出版年
2020年 | 3518篇 |
2019年 | 4177篇 |
2018年 | 16016篇 |
2017年 | 15917篇 |
2016年 | 13757篇 |
2015年 | 4887篇 |
2014年 | 7256篇 |
2013年 | 15724篇 |
2012年 | 15371篇 |
2011年 | 23991篇 |
2010年 | 16440篇 |
2009年 | 16839篇 |
2008年 | 20003篇 |
2007年 | 21957篇 |
2006年 | 12786篇 |
2005年 | 12375篇 |
2004年 | 11622篇 |
2003年 | 11023篇 |
2002年 | 10141篇 |
2001年 | 10244篇 |
2000年 | 8168篇 |
1999年 | 6078篇 |
1998年 | 5495篇 |
1997年 | 5362篇 |
1996年 | 4900篇 |
1995年 | 4171篇 |
1994年 | 4155篇 |
1993年 | 4236篇 |
1992年 | 4372篇 |
1991年 | 4693篇 |
1990年 | 4504篇 |
1989年 | 4552篇 |
1988年 | 4388篇 |
1987年 | 4394篇 |
1986年 | 4184篇 |
1985年 | 5347篇 |
1984年 | 5469篇 |
1983年 | 4545篇 |
1982年 | 4883篇 |
1981年 | 4663篇 |
1980年 | 4311篇 |
1979年 | 4752篇 |
1978年 | 5041篇 |
1977年 | 5099篇 |
1976年 | 5145篇 |
1975年 | 4870篇 |
1974年 | 4792篇 |
1973年 | 5072篇 |
1972年 | 3764篇 |
1971年 | 3337篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A.G. Rousskikh A.V. Fedyunin A.P. Artyomov A.S. Zhigalin V.I. Oreshkin 《Current Applied Physics》2019,19(6):704-708
The aim of the study presented in this paper was to characterize quantitatively the erosion of aluminum cathodes in high-current vacuum arcs. The experimental setup comprised two current generators. The first one, capable of generating a current of amplitude up to 350 kA, was used to produce a plasma jet, that is, the object to be investigated. The second generator was used to produce a source of probe radiation for imaging the object under investigation in soft x rays of energy ?ν ≈ 0.5–3 keV. The findings of the study are based on experimental data obtained by electrophysical and radiographic methods. It has been shown that the cathode erosion rate in a high-current vacuum arc is a function of the charge passed through the cathode. 相似文献
92.
Yamshchikov V. M. Rogachev V. G. Kudryashov E. A. Kachalin G. N. 《Optics and Spectroscopy》2020,128(8):1182-1186
Optics and Spectroscopy - The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical... 相似文献
93.
Physics of Atomic Nuclei - The article presents the concept of a channel-type reactor with a combined cooled moderator. The moderator consists of ceramic beryllium oxide and a liquid... 相似文献
94.
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
95.
Romanenko G. V. Letyagin G. A. Maryunina K. Yu. Bogomyakov A. S. Nishihara S. Inoue K. Ovcharenko V. I. 《Russian Chemical Bulletin》2020,69(8):1530-1536
Russian Chemical Bulletin - The study is concerned with structural rearrangements in the crystals of heterospin complexes Cu(hfac)2 with nitroxide radicals LR (hfac is hexafluoroacetylacetonate, LR... 相似文献
96.
L. Resse L.G.S. Oliveira C.I.L. de Araujo A.R. Pereira R.L. Silva 《Physics letters. A》2019,383(14):1655-1659
In this work, we have used the MuMax3 software to simulate devices consisting of a ferromagnetic thin film placed over a heavy metal thin film. The devices are two interconnected partial-disks where a Néel domain wall is formed in the disks junction. In our simulations we investigate devices with disk radius nm and different distance d between the disks centers (from nm to nm). By applying strong sinusoidal external magnetic fields, we find a mechanism able to create, annihilate and even manipulate a skyrmion in each side of the device. This mechanism is discussed in terms of interactions between skyrmion and domain wall. The Néel domain wall formed in the center of the device interacts with the Néel skyrmion, leading to a process of transporting a skyrmion from one disk to the other periodically. Our results have relevance for potential applications in spintronics such as logical devices. 相似文献
97.
98.
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
99.
Doklady Physics - In this paper, we study the statistical characteristics of the Riemann wave and the integral of it. Such problems arise in the physics of fronts’ propagation, in particular,... 相似文献
100.
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