全文获取类型
收费全文 | 289680篇 |
免费 | 4398篇 |
国内免费 | 968篇 |
专业分类
化学 | 153856篇 |
晶体学 | 4314篇 |
力学 | 12410篇 |
综合类 | 5篇 |
数学 | 35384篇 |
物理学 | 89077篇 |
出版年
2021年 | 2389篇 |
2020年 | 2651篇 |
2019年 | 2930篇 |
2018年 | 3857篇 |
2017年 | 3640篇 |
2016年 | 5773篇 |
2015年 | 4022篇 |
2014年 | 5654篇 |
2013年 | 13503篇 |
2012年 | 11411篇 |
2011年 | 13516篇 |
2010年 | 9182篇 |
2009年 | 8811篇 |
2008年 | 12219篇 |
2007年 | 12203篇 |
2006年 | 11389篇 |
2005年 | 10439篇 |
2004年 | 9367篇 |
2003年 | 8119篇 |
2002年 | 7814篇 |
2001年 | 8029篇 |
2000年 | 6185篇 |
1999年 | 4863篇 |
1998年 | 4082篇 |
1997年 | 3955篇 |
1996年 | 3932篇 |
1995年 | 3436篇 |
1994年 | 3422篇 |
1993年 | 3510篇 |
1992年 | 3631篇 |
1991年 | 3718篇 |
1990年 | 3456篇 |
1989年 | 3374篇 |
1988年 | 3358篇 |
1987年 | 3248篇 |
1986年 | 3055篇 |
1985年 | 4208篇 |
1984年 | 4377篇 |
1983年 | 3454篇 |
1982年 | 3755篇 |
1981年 | 3633篇 |
1980年 | 3512篇 |
1979年 | 3588篇 |
1978年 | 3668篇 |
1977年 | 3557篇 |
1976年 | 3706篇 |
1975年 | 3343篇 |
1974年 | 3362篇 |
1973年 | 3418篇 |
1972年 | 2340篇 |
排序方式: 共有10000条查询结果,搜索用时 922 毫秒
121.
András Gy. Németh Renáta Szabó Dr. Attila Domján Prof. György M. Keserű Dr. Péter Ábrányi-Balogh 《ChemistryOpen》2021,10(1):16-27
The development of a new three-component chromatography-free reaction of isocyanides, amines and elemental sulfur allowed us the straightforward synthesis of thioureas in water. Considering a large pool of organic and inorganic bases, we first optimized the preparation of aqueous polysulfide solution from elemental sulfur. Using polysulfide solution, we were able to omit the otherwise mandatory chromatography, and to isolate the crystalline products directly from the reaction mixture by a simple filtration, retaining the sulfur in the solution phase. A wide range of thioureas synthesized in this way confirmed the reasonable substrate and functional group tolerance of our protocol. 相似文献
122.
123.
Natalia L. Calvo Sebastian O. SimonettiRubén M. Maggio Teodoro S. Kaufman 《Analytica chimica acta》2015
Exposure of cimetidine (CIM) to dry heat (160–180 °C) afforded, upon cooling, a glassy solid containing new and hitherto unknown products. The kinetics of this process was studied by a second order chemometrics-assisted multi-spectroscopic approach. Proton and carbon-13 nuclear magnetic resonance (NMR), as well as ultraviolet and infrared spectroscopic data were jointly used, whereas multivariate curve resolution with alternating least squares (MCR-ALS) was employed as the chemometrics method to extract process information. It was established that drug degradation follows a first order kinetics. 相似文献
124.
Experimental Mechanics - Insufficient data are available to fully understand the effects of metal additive manufacturing (AM) defects for widespread adoption of the emerging technology.... 相似文献
125.
126.
127.
Yablokov M. Yu. Shchegolikhin A. N. Lebedev O. V. Goncharuk G. P. Ozerin A. N. 《Russian Chemical Bulletin》2021,70(9):1816-1821
Russian Chemical Bulletin - Gradient polymer composites were prepared by melt-mixing of carbon black and polypropylene in a compounder and subsequent hot pressing of pellets. The thermally treated... 相似文献
128.
129.
Mathematical Notes - 相似文献
130.
Naphthalimide‐phthalimide derivative based photoinitiating systems for polymerization reactions under blue lights 下载免费PDF全文
Pu Xiao Frédéric Dumur Jing Zhang Bernadette Graff Didier Gigmes Jean Pierre Fouassier Jacques Lalevée 《Journal of polymer science. Part A, Polymer chemistry》2015,53(5):665-674
Naphthalimide‐phthalimide derivatives (NDPDs) have been synthesized and combined with an iodonium salt, N‐vinylcarbazole, amine or 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine to produce reactive species (i.e., radicals and cations). These generated reactive species are capable of initiating the cationic polymerization of epoxides and/or the radical polymerization of acrylates upon exposure to very soft polychromatic visible lights or blue lights. Compared with the well‐known camphorquinone based systems used as references, the novel NDPD based combinations employed here demonstrate clearly higher efficiencies for the cationic polymerization of epoxides under air as well as the radical polymerization of acrylates. Remarkably, one of the NDPDs (i.e., NDPD2) based systems is characterized by an outstanding reactivity. The structure/reactivity/efficiency relationships of the investigated NDPDs were studied by fluorescence, cyclic voltammetry, laser flash photolysis, electron spin resonance spin trapping, and steady state photolysis techniques. The key parameters for their reactivity are provided. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 665–674 相似文献