全文获取类型
收费全文 | 1159篇 |
免费 | 73篇 |
国内免费 | 364篇 |
专业分类
化学 | 1470篇 |
晶体学 | 11篇 |
综合类 | 14篇 |
物理学 | 101篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 15篇 |
2021年 | 12篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 33篇 |
2017年 | 33篇 |
2016年 | 36篇 |
2015年 | 31篇 |
2014年 | 35篇 |
2013年 | 159篇 |
2012年 | 68篇 |
2011年 | 54篇 |
2010年 | 35篇 |
2009年 | 60篇 |
2008年 | 75篇 |
2007年 | 94篇 |
2006年 | 80篇 |
2005年 | 68篇 |
2004年 | 84篇 |
2003年 | 72篇 |
2002年 | 68篇 |
2001年 | 50篇 |
2000年 | 55篇 |
1999年 | 46篇 |
1998年 | 42篇 |
1997年 | 32篇 |
1996年 | 34篇 |
1995年 | 28篇 |
1994年 | 24篇 |
1993年 | 36篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
排序方式: 共有1596条查询结果,搜索用时 109 毫秒
991.
Reaction of α, β-unsaturated acid chlorides with primary enaminonitriles in presence of triethylamine affords, under very mild conditions, a simple and highly efficient regiospecific synthesis of polysubstituted 3,4-dihydro-2(1H)-pyridones. 相似文献
992.
993.
The 13C-NMR spectra of the azo dyes which were synthesized by reacting substituted benzenediazonium chloride with derivatives of some phenol have been measured. The spectral data of these compounds were described considering intramolecular hydrogen bond and not. The chemical shift assignments were made regarding substituent effects. 相似文献
994.
995.
HaiShen Kong Wei Li HaiBo Lin Zhan Shi HaiYan Lu YuanYuan Dan WeiMin Huang 《Surface and interface analysis : SIA》2013,45(3):715-721
The lead dioxide electrode (PbO2) with Ti substrate and SnO2‐Sb2O5 intermediate layer was doped by F‐ ion through the potentiostatic anode co‐deposition method. The content of F in the coating can be controlled by adjusting deposition potential. The effect of F‐ doping on the composition, surface morphology and electrochemical properties of the PbO2 electrode was characterized by X‐ray diffraction, scanning electron microscope, X‐ray photoelectron spectroscopy and electrochemical measurement methods. The results have confirmed that the content of β‐PbO2 increases with increasing that of F, and the doping can make the β‐PbO2 grains become fine and the electrode surface become smooth; the specific surface areas and conductivity increase, and the initial potential of oxygen evolution shifts toward positive direction compared with the free‐doped PbO2 electrode; the oxygen evolution potential increases with the increasing of the F‐content in the PbO2 film electrode. The bulk electrolysis result demonstrated that the performances of the F‐PbO2 electrode for anodic oxidation aniline have been improved to some extent. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
996.
997.
To find novel bleaching herbicide lead compounds, a series of novel 2‐alkyl(aryl)‐4‐amino‐3‐[alkyl(alkoxy)carbonyl]‐5‐cyano‐6‐[(3‐trifluoromethyl)phenoxy]‐pyridines was designed and synthesized by the multistep reactions. N,S‐acetal 1 reacted with 2 to obtain multisubstituted pyridines 3 in the presence of zinc nitrate as the catalyst. The target compounds 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 5k , 5l were formed by the oxidation of 3 , followed by the substitution with 3‐(trifluoromethyl)phenol in the presence of potassium carbonate. Their structures were confirmed by IR, 1H NMR, EI‐MS, and elemental analyses. The preliminary bioassays indicated that some of them displayed moderate herbicidal activity against dicotyledonous weed Brassica campestris L at the concentration of 100 mg/L. 相似文献
998.
Dinne Naresh Kumar Reddy Kothapalli Bannoth Chandrasekhar Yaddanapudi Sesha Siva Ganesh Srikanth Sharathchandra Gorantla Siddabathuni Ramanjaneyulu K. Shiva Kumar 《合成通讯》2013,43(4):513-523
A greener approach for the synthesis of 3-arylmethyl/diarylmethyl indoles has been achieved via a PMA-SiO2-mediated three-component reaction (the aza-Friedel–Crafts reaction) involving indoles, aldehydes, and N,N-disubstituted anilines in PEG-400. A variety of indole derivatives were prepared by using this operationally simple and straightforward methodology in acceptable yields. 相似文献
999.
B. Suresh Kuarm J. Venu Madhav S. Vijaya Laxmi Y. Thirupathi Reddy P. Narsimha Reddy 《合成通讯》2013,43(12):1719-1724
A series of 1-oxo-hexahydroxanthene derivatives was synthesized at room temperature in solid state from substituted salicylaldehydes and substituted 1,3-hexanediones in the presence of a catalytic amount of cellulose sulfuric acid. The results showed that the reaction performed under solid-state conditions was benign to the environment, with higher yields and more convenient workup.
1000.
Michelle Sternberg Jörg Rust Christian W. Lehmann Fabian Mohr 《Helvetica chimica acta》2013,96(2):280-288
Two glucose‐derived thiourea derivatives, 2a and 2b , were prepared by addition of the corresponding amino sugars to a solution of 4‐nitrobenzoyl isothiocyanate (Scheme 1). The thioureas were isolated as colorless solids in good yields and were fully characterized by NMR spectroscopy, optical rotation, elemental analysis, and also by single‐crystal X‐ray diffraction. Attempts to obtain CuII and NiII bis(chelate) complexes with these thioureas failed. However, the C(1)‐protected thiourea derivative 2a reacted with orthopalladated acetato‐bridged dimers to afford the corresponding monomeric PdII complexes 3 and 4 (Scheme 2). In these compounds, the thiourea coordinates to the metal as monoanionic O,S chelate ligand, which was confirmed by X‐ray crystallography. 相似文献