全文获取类型
收费全文 | 816129篇 |
免费 | 9985篇 |
国内免费 | 3165篇 |
专业分类
化学 | 423210篇 |
晶体学 | 11663篇 |
力学 | 39714篇 |
综合类 | 78篇 |
数学 | 110851篇 |
物理学 | 243763篇 |
出版年
2021年 | 6919篇 |
2020年 | 7717篇 |
2019年 | 8567篇 |
2018年 | 11402篇 |
2017年 | 11294篇 |
2016年 | 16346篇 |
2015年 | 9940篇 |
2014年 | 15353篇 |
2013年 | 36841篇 |
2012年 | 29265篇 |
2011年 | 34929篇 |
2010年 | 25013篇 |
2009年 | 24623篇 |
2008年 | 32298篇 |
2007年 | 32279篇 |
2006年 | 29745篇 |
2005年 | 26825篇 |
2004年 | 24572篇 |
2003年 | 21734篇 |
2002年 | 21532篇 |
2001年 | 22304篇 |
2000年 | 17348篇 |
1999年 | 13503篇 |
1998年 | 11584篇 |
1997年 | 11308篇 |
1996年 | 10937篇 |
1995年 | 9768篇 |
1994年 | 9836篇 |
1993年 | 9588篇 |
1992年 | 10218篇 |
1991年 | 10552篇 |
1990年 | 10009篇 |
1989年 | 9840篇 |
1988年 | 9621篇 |
1987年 | 9316篇 |
1986年 | 8919篇 |
1985年 | 11889篇 |
1984年 | 12288篇 |
1983年 | 10247篇 |
1982年 | 10790篇 |
1981年 | 10294篇 |
1980年 | 9762篇 |
1979年 | 10319篇 |
1978年 | 10718篇 |
1977年 | 10564篇 |
1976年 | 10592篇 |
1975年 | 9951篇 |
1974年 | 9963篇 |
1973年 | 10253篇 |
1972年 | 7491篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
311.
Journal of Structural Chemistry - Thermodynamic characteristics are calculated for aqueous alkanolamine solutions that are obtained by substituting alkyl radicals for the protons in the amino group... 相似文献
312.
313.
Mathematical Notes - 相似文献
314.
315.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献
316.
Anishchenko V. N. Redko A. N. Rybachenko V. I. 《Theoretical and Experimental Chemistry》2020,56(1):46-49
Theoretical and Experimental Chemistry - The effect of the structure of the catalyst and the type of base on the reaction rate and product yield of the tosylation of dihydroxybenzenes in a... 相似文献
317.
Naphthalimide‐phthalimide derivative based photoinitiating systems for polymerization reactions under blue lights
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
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
318.
319.
Gelikonov G. V. Ksenofontov S. Yu. Shilyagin P. A. Gelikonov V. M. 《Radiophysics and Quantum Electronics》2019,62(3):228-236
Radiophysics and Quantum Electronics - We propose and experimentally test a numerical method for correction of the influence of fluctuations in the distance to objects during noncontact probing in... 相似文献
320.
Roberto Morales-Cerrada Dr. Christophe Fliedel Dr. Jean-Claude Daran Dr. Florence Gayet Dr. Vincent Ladmiral Dr. Bruno Améduri Prof. Rinaldo Poli 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(1):296-308
Thermal decarbonylation of the acyl compounds [Mn(CO)5(CORF)] (RF=CF3, CHF2, CH2CF3, CF2CH3) yielded the corresponding alkyl derivatives [Mn(CO)5(RF)], some of which have not been previously reported. The compounds were fully characterized by analytical and spectroscopic methods and by several single-crystal X-ray diffraction studies. The solution-phase IR characterization in the CO stretching region, with the assistance of DFT calculations, has allowed the assignment of several weak bands to vibrations of the [Mn(12CO)4(eq-13CO)(RF)] and [Mn(12CO)4(ax-13CO)(RF)] isotopomers and a ranking of the RF donor power in the order CF3<CHF2<CH2CF3≈CF2CH3. The homolytic Mn−RF bond cleavage in [Mn(CO)5(RF)] at various temperatures under saturation conditions with trapping of the generated RF radicals by excess tris(trimethylsilyl)silane yielded activation parameters ΔH≠ and ΔS≠ that are believed to represent close estimates of the homolytic bond dissociation thermodynamic parameters. These values are in close agreement with those calculated in a recent DFT study (J. Organomet. Chem. 2018 , 864, 12–18). The ability of these complexes to undergo homolytic Mn−RF bond cleavage was further demonstrated by the observation that [Mn(CO)5(CF3)] (the compound with the strongest Mn−RF bond) initiated the radical polymerization of vinylidene fluoride (CH2=CF2) to produce poly(vinylidene fluoride) in good yields by either thermal (100 °C) or photochemical (UV or visible light) activation. 相似文献