全文获取类型
收费全文 | 2836篇 |
免费 | 469篇 |
国内免费 | 209篇 |
专业分类
化学 | 3263篇 |
晶体学 | 6篇 |
力学 | 26篇 |
数学 | 109篇 |
物理学 | 110篇 |
出版年
2024年 | 4篇 |
2023年 | 32篇 |
2022年 | 51篇 |
2021年 | 85篇 |
2020年 | 149篇 |
2019年 | 111篇 |
2018年 | 131篇 |
2017年 | 97篇 |
2016年 | 171篇 |
2015年 | 156篇 |
2014年 | 213篇 |
2013年 | 306篇 |
2012年 | 165篇 |
2011年 | 212篇 |
2010年 | 188篇 |
2009年 | 185篇 |
2008年 | 154篇 |
2007年 | 165篇 |
2006年 | 141篇 |
2005年 | 141篇 |
2004年 | 121篇 |
2003年 | 138篇 |
2002年 | 184篇 |
2001年 | 42篇 |
2000年 | 38篇 |
1999年 | 22篇 |
1998年 | 16篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 8篇 |
1994年 | 16篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有3514条查询结果,搜索用时 15 毫秒
91.
I. Strakova A. Strakovs M. Petrova S. Belyakov 《Chemistry of Heterocyclic Compounds》2007,43(12):1512-1518
The [3+2] cycloaddition reactions of a series of 1,3-substituted 5-diazo-6,6-dimethyl-4-oxo-4,5,6,7-tetrahydroindazoles with
maleic anhydride and dimethyl acetylenedicarboxylate gave 1′,3′-substituted 3-spiro[4,6-dioxo-4,6,3a,6a-tetrahydro-3H-furo[3,4-c]pyrazole]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles]
and 1′,3′-substituted 3-spiro[4,5-di(methoxycarbonyl)-3H-pyrazole]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles]
respectively. When heated the former eliminate nitrogen and are transformed into 1′,3′-substituted 6-spiro[2,4-dioxo-3-oxabicyclo[3.1.0]hexane]-5′-[6′,6′-dimethyl-4′-oxo-4′,5′,6′,7′-tetrahydroindazoles].
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1784–1791, December, 2007. 相似文献
92.
Timoshenko VM Bouillon JP Chernega AN Shermolovich YG Portella C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(18):4324-4329
The ethyl ester of beta-bromoperfluorodithiocrotonic acid reacts with dimethyl acetylenedicarboxylate to give 1,4-difluoro-2,3-bis(trifluoromethyl)-but-2-ene-1,4-diylidene-2,2'-bis(4',5'-dicarbomethoxy-1',3'-dithiole) (4), a new type of vinylogue of tetrathiafulvalene. The thermal transformations of this compound lead, depending on the temperature, to the formation of the cyclization products: 11,14-difluoro-2,3,8,9-tetra(carbomethoxy)-12,13-bis(trifluoromethyl)-1,4,7,10-tetrathiadispiro[4.0.4.4]tetradeca-2,8,11,13-tetraene (8) or 5,8-difluoro-6,7-bis(trifluoromethyl)-2,3-bis(carboxymethyl)-1,4-benzodithiine (11). 相似文献
93.
Tsvetkov N. P. Vakhmistrov V. E. Koldobsky A. B. Korlyukov A. A. Kalinin V. N. 《Russian Chemical Bulletin》2002,51(2):326-331
Unusual cascade cycloaddition reactions with dimethylhydrazones of -trimethylsilyloxyalkylacroleins acting as azadienes were found. Depending on the nature of the dienophile, the reactions give either fused heterocyclic compounds (when two consecutive Diels—Alder reactions take place) or azabicyclic compounds, resulting from the [2+4]- and [2+3]-cycloaddition cascade. 相似文献
94.
A gauche-gauche interaction is proposed as a powerful controlling factor for the stereochemistry in the intramolecular nitrile oxide cycloaddition reaction derived from N-protected 3-(N-allylamino)propionaldehyde and 2-(N-homoallylamino)acetaldehyde oximes. High levels of stereoselectivity (76% de to perfect) were obtained from the reaction involving nitrile oxides with substituents at the adjacent carbon atom to the tether nitrogen. 相似文献
95.
综述了近年来利用一些新型的含氟砌块,通过它们的环加成反应来高效地合成 含氟杂环化合物的研究,其中包括以下两个部分:(1)用1,3—偶极环加成反应合 成五元含氟杂环化合物;(2)用杂原于Diels-Alder反应合成六元含氟杂环化合物. 相似文献
96.
Engineering a Cu‐MOF Nano‐Catalyst by using Post‐Synthetic Modification for the Preparation of 5‐Substituted 1H‐Tetrazoles
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A new nano scale Cu‐MOF has been obtained via post‐synthetic metalation by immersing a Zn‐MOF as a template in DMF solutions of copper(II) salts. The Cu‐MOF serves as recyclable nano‐catalyst for the preparation of 5‐substituted 1H‐tetrazoles via [3 + 2] cycloaddition reaction of various nitriles and sodium azide in a green medium (PEG). The post‐synthetic metalated MOF were characterized by FT‐IR spectroscopy, powder X‐ray diffraction (PXRD), atomic absorption spectroscopy (AAS), and energy dispersive X‐ray spectroscopy (EDX) techniques. The morphology and size of the nano‐catalyst were determined by field emission scanning electron microscopy (FE‐SEM). 相似文献
97.
98.
Weiping Gan Xiaosong Cao Yi Shi Lei Zou Haifeng Gao 《Journal of polymer science. Part A, Polymer chemistry》2018,56(19):2238-2244
Copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP) of AB2 monomers demonstrated a chain-growth mechanism without any external ligand because of the complexation of in situ formed triazole groups with Cu catalysts. In this study, we explored the use of various ligands that affected the polymerization kinetics to tune the polymers’ molecular weights and the degree of branching (DB). Eight ligands were studied, including polyethylene glycol monomethyl ether (PEG350, Mn = 350), tris(benzyltriazolylmethyl)amine (TBTA), 2,6-bis(1-undecyl-1H-benzo[d]imidazol-2-yl)pyridine (Py(DBim)2), 2,2′-bipyridyl (bpy), 4,4′-di-n-nonyl-2,2′-bipyridine (dNbpy), N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDETA), N,N,N′,N″,N″-penta(n-butyl)diethylenetriamine (PBuDETA), and N,N,N′,N″,N″-pentabenzyldiethylenetriamine (PBnDETA). All ligands except PEG350 exhibited stronger coordination with Cu(I) than the polytriazole polymer, which freed the Cu catalyst from polymers and resulted in dominant step-growth polymerization with simultaneous chain-growth feature. Meanwhile, the use of PEG350 ligand retained the confined Cu in the polymer, demonstrating a chain-growth mechanism, but lower polymer molecular weights as compared with the no-external-ligand polymerization. Results indicated that aliphatic substituent groups on ligands had little effect on the molecular weights and DB of the polymers, but rigid aromatic substituent groups decreased both values. By varying the ligand species and amounts, hyperbranched polymers with DB value ranging from 0.53 ([TBTA]0/[Cu]0 = 5) to 0.98 ([PMDETA]0/[Cu]0 = 2) have been achieved. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2238–2244 相似文献
99.
Formal (4+1) Cycloaddition of Methylenecyclopropanes with 7‐Aryl‐1,3,5‐cycloheptatrienes by Triple Gold(I) Catalysis
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yahui Wang Dr. Michael E. Muratore Zhouting Rong Prof. Antonio M. Echavarren 《Angewandte Chemie (International ed. in English)》2014,53(51):14022-14026
7‐Aryl‐1,3,5‐cycloheptatrienes react intermolecularly with methylenecyclopropanes in a triple gold(I)‐catalyzed reaction to form cyclopentenes. The same formal (4+1) cycloaddition occurs with cyclobutenes. Other precursors of gold(I) carbenes can also be used as the C1 component of the cycloaddition. 相似文献
100.