全文获取类型
收费全文 | 654篇 |
免费 | 51篇 |
国内免费 | 87篇 |
专业分类
化学 | 761篇 |
晶体学 | 8篇 |
综合类 | 2篇 |
物理学 | 21篇 |
出版年
2024年 | 1篇 |
2023年 | 10篇 |
2022年 | 38篇 |
2021年 | 39篇 |
2020年 | 44篇 |
2019年 | 17篇 |
2018年 | 25篇 |
2017年 | 16篇 |
2016年 | 34篇 |
2015年 | 29篇 |
2014年 | 36篇 |
2013年 | 85篇 |
2012年 | 24篇 |
2011年 | 27篇 |
2010年 | 19篇 |
2009年 | 19篇 |
2008年 | 27篇 |
2007年 | 32篇 |
2006年 | 24篇 |
2005年 | 30篇 |
2004年 | 24篇 |
2003年 | 34篇 |
2002年 | 85篇 |
2001年 | 18篇 |
2000年 | 12篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有792条查询结果,搜索用时 15 毫秒
21.
Katarzyna Kaa Wojciech Pajk Katarzyna Sukowska-Ziaja Agata Krakowska Jan Lazur Maciej Fidurski Krystian Marzec Piotr Ziba Agata Fijakowska Agnieszka Szewczyk Boena Muszyska 《Molecules (Basel, Switzerland)》2022,27(24)
Hypsizygus marmoreus is an edible medicinal mushroom species with a high dietary value. In this study, the fruiting bodies of commercial and self-cultivated crops and mycelium from in vitro H. marmoreus cultures (both white and brown varieties) were evaluated. This study aimed to analyze the presence of indole compounds and other biologically active substances and determine the effect that the addition of zinc and magnesium ions to the culture medium has on the content of the tested compounds in mycelial cultures. The content of indole compounds and other organic compounds was determined using high-performance liquid chromatography, the content of bioelements was determined using flame atomic absorption spectrometry, the glucan content was determined spectrophotometrically, and the antioxidant activity of extracts was estimated using DPPH, FRAP, and ABTS methods. The results showed that H. marmoreus mycelium from in vitro cultures is a good source of indole compounds, bioelements, glucans, and lovastatin. Mycelia from in vitro cultures showed the most diverse composition of indole compounds (L-tryptophan, 5-hydroxy-L-tryptophan, tryptamine, 5-methyltryptamine, and melatonin). Additionally, in vitro cultures of H. marmoreus enriched with Zn and Mg salts increased the contents of Na, Ca, Zn, 5-methyltryptamine, melatonin, protocatechuic acid, sterols, and total glucans. Only in the case of the white variety of mycelial enriched cultures, ergothioneine and Mg levels also increased. To summarize, the content of the active compounds differed depending on the H. marmoreus variety and the tested material. 相似文献
22.
23.
Xin Yuan Yu-Sheng Cui Xin-Peng Zhang Long-Zhou Qin Qi Sun Xiu Duan Lin Chen Guigen Li Jiang-Kai Qiu Prof. Kai Guo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(21):6522-6528
Considering their unique roles in organic synthesis, and pharmaceutical and agrochemical applications, the development of fluoroalkylation, cyclization, and indole oxidative cleavage are important topics. Herein, an unprecedented electrochemical tri- and difluoromethylation/cyclization/indole oxidative cleavage process occurring in an undivided cell is presented. The protocol employs a readily prepared Langlois reagent as the fluoroalkyl source, affording a series of tri- or difluoromethylated 2-(2-acetylphenyl)isoquinoline-1,3-diones in good yields with excellent stereoselectivity. It is worth noting that this new methodology merges the fluoroalkylation/cyclization of N-substituted acrylamide alkenes with the oxidative cleavage of an indole C(2)=C(3) bond under external oxidant-free conditions. 相似文献
24.
Maíra A. Carvalho Joo Bosco P. Da Silva Marcelo Z. Hernandes 《International journal of quantum chemistry》2005,102(4):379-386
The molecular electrostatic potential (MEP) of the indole molecule was calculated in a three‐dimensional grid in which the molecule was centered at the origin. To evaluate the dependence of MEP on the type of calculation, semiempirical, ab initio, and density functional theory methods with different basis sets were employed. The data matrix generated by these calculations was analyzed by principal component analysis (PCA). The appearance of outliers and the effect of wavefunction modifications such as the introduction of electron correlations and diffuse functions were highlighted by the use of PCA. The spatial localization of such effects around the molecule was possible from the loadings values associated with the graphical analysis of the grid points. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 相似文献
25.
3位含有季碳手性中心的吲哚啉并环化合物是一类非常重要的化合物, 广泛存在于各种天然产物和具有生物活性的分子中. 化学家们发展了多种有效的途径来合成这类化合物. 其中以方便易得的吲哚衍生物为起始原料, 利用不对称去芳构化\环化串联的方法最为简单高效, 但多数工作都是从色胺或色醇衍生物出发, 合成二氢吡咯并吲哚啉或二氢呋喃并吲哚啉化合物. 因此, 发展其他类型的吲哚衍生物的不对称去芳构化\环化反应显得非常有必要. 作者课题组发展了手性磷酸催化的吲哚衍生物与甲基乙烯基酮的不对称Michael加成\环化串联反应. 以5 mol% (R)-SPINOL为骨架的手性磷酸(R)-4c为催化剂, 以中等到良好的收率和优秀的对映选择性构建了一系列手性吲哚[2,3-b]并氢化喹啉化合物, 而且该催化体系对于克级规模反应同样能够获得很好的结果. 相似文献
26.
Highly Enantioselective Tandem Michael Addition of Tryptamine‐Derived Oxindoles to Alkynones: Concise Synthesis of Strychnos Alkaloids 下载免费PDF全文
Weigang He Jiadong Hu Pengyan Wang Le Chen Kai Ji Siyu Yang Yin Li Zhilong Xie Prof. Dr. Weiqing Xie 《Angewandte Chemie (International ed. in English)》2018,57(14):3806-3809
A highly enantioselective tandem Michael addition of tryptamine‐derived oxindoles to alkynones was developed by taking advantage of a chiral N,N′‐dioxide Sc(OTf)3 catalyst. The reaction enables the facile preparation of enantioenriched spiro[pyrrolidine‐3,3′‐oxindole] compounds, which provides a novel strategy for the synthesis of monoterpenoid indole alkaloids. As a demonstration, the asymmetric synthesis of strychnos alkaloids [(?)‐tubifoline, (?)‐tubifolidine, (?)‐dehydrotubifoline] was achieved in 10–11 steps. 相似文献
27.
Thiourea‐Catalyzed Asymmetric Michael Addition of Carbazolones to 2‐Chloroacrylonitrile: Total Synthesis of 5,22‐Dioxokopsane,Kopsinidine C,and Demethoxycarbonylkopsin 下载免费PDF全文
Dr. Dongshun Ni Dr. Yi Wei Prof. Dr. Dawei Ma 《Angewandte Chemie (International ed. in English)》2018,57(32):10207-10211
A modified Takemoto catalyst enabled the asymmetric Michael addition of carbazolones to 2‐chloroacrylonitrile to afford 3,3‐disubstituted carbazolones with excellent enantioselectivity. This method was successfully applied to total syntheses of three Kopsia alkaloids which featured an unprecedented MnIII‐mediated oxidative cyclization to create the caged ring system and a SmI2‐mediated reductive coupling as key steps. 相似文献
28.
29.
Colorimetric detection of anions (HSO4? and CN?) was achieved via analyte triggered colour changing of the dipodal and tripodal sensors in CH3CN–H2O (1:1). The sensors exhibited very sharp visual colour changes and fluorescence quenching–enhancing effect upon addition of the HSO4? and CN?. The large downfield shift of the NH proton signals in 1H-NMR complexation studies and quantum chemical DFT calculations proved the formation of hydrogen-bonded complexes where no proton transfer mechanism was found. 相似文献
30.
Samia R. El-ezbawy Aboel-Magd A. Abdel-wahab 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):285-289
Abstract 4-Amino-halonitrodiphenyl sulfides(I) and/or 4-amino-halonitrodiphenyl sulfones have been found to react with isatin, N-acetyl isatin, isatin-N-Mannich bases, indole-3-carboxaldehyde and N-substituted indole-3-carboxaldehyde producing the corresponding indole derivatives. The biological activity of some of these products was screened against selected strains of bacteria. 相似文献