全文获取类型
收费全文 | 716篇 |
免费 | 14篇 |
国内免费 | 42篇 |
专业分类
化学 | 762篇 |
晶体学 | 4篇 |
综合类 | 2篇 |
物理学 | 4篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 13篇 |
2019年 | 22篇 |
2018年 | 39篇 |
2017年 | 36篇 |
2016年 | 15篇 |
2015年 | 16篇 |
2014年 | 67篇 |
2013年 | 89篇 |
2012年 | 33篇 |
2011年 | 51篇 |
2010年 | 28篇 |
2009年 | 47篇 |
2008年 | 51篇 |
2007年 | 43篇 |
2006年 | 31篇 |
2005年 | 41篇 |
2004年 | 52篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 6篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1985年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有772条查询结果,搜索用时 15 毫秒
681.
Jia Jia Dong 《Tetrahedron letters》2009,50(23):2778-513
The palladium-catalysed direct 3- or 4-arylation of 2,5-disubstituted thiophenes using aryl bromides gives a simple access to a variety of 3- or 4-arylthiophene derivatives. Moderate to good yields of 3-arylated thiophenes were obtained using 2,5-dimethylthiophene. In the presence of unsymmetrically disubstituted, 2-acetyl-5-methylthiophene, a regioselective arylation on carbon 4 of thiophene was observed. This reaction provides only HX associated to the base as by-product and reduces the number of steps to prepare these compounds. 相似文献
682.
A label-free immunosensor based on the modulation of the electrochemistry of a surface bound redox species, to detect the presence of antibodies, is demonstrated. In this proof of concept study the model epitope was biotin and the model antibody was anti-biotin IgG. Glassy carbon (GC) electrode surfaces were first modified with 4-nitrophenyl groups by electrochemical reductive adsorption of the corresponding aryl diazonium salt. Subsequently, the nitro group was reductively converted into an amine, giving 4-aminophenyl groups. Oxidatively shortened single walled carbon nanotubes (SWNTs) were then covalently attached to the electrode via self-assembly; a procedure that has previously been shown to give SWNTs aligned normal to the surface. 1,1-Di(aminomethyl)ferrocene was attached to the carboxylic acid terminated SWNTs followed by attachment of biotin to the remaining free amine of the ferrocene derivative. Binding of anti-biotin IgG to the surface bound epitope resulted in attenuation of the ferrocene electrochemistry. This label-free immunosensor was successfully able to detect anti-biotin between 30 and 450 ng mL−1. 相似文献
683.
Karen Kennedy Miroslava Macova Frederic Leusch Michael E. Bartkow Darryl W. Hawker Bin Zhao Michael S. Denison Jochen F. Mueller 《Analytical and bioanalytical chemistry》2009,394(5):1413-1421
Passive air sampling was undertaken using polyurethane foam passive air samplers at three types of locations, including indoors
(six offices) at buildings in the central business district (CBD) and at a private suburban home (indoor and outdoor) located
9 km from the CBD in Brisbane, Queensland, Australia. Estrogenic (E-SCREEN—MCF7-BOS) and aryl hydrocarbon receptor (AhR) (CAFLUX—H4G1.1c2)
activity were assessed for samples collected from each of these locations. The samples were tested either as crude extracts
(“untreated”) or were subjected to H2SO4 silica gel (“treated”) for each location in order to determine whether chemicals, which are not resistant to this treatment
like polycyclic aromatic hydrocarbons, potentially account for the observed activity. In most cases, H2SO4 treatment resulted in a statistically significant reduction of potency for both endpoints, suggesting that chemicals less
resistant to treatment may be responsible for much of the detected biological activity in these locations. Estrogenic potency
measurements (<0.22–185 pg m−3) were highest in the indoor offices, followed by the indoor suburban home and finally the outdoor suburban home (which was
not estrogenic). Total AhR activity for crude extracts (1.3–10 pg m−3) however was highest for the outdoor suburban home site. Levels of polycyclic aromatic hydrocarbons were monitored indoors
and outdoors at the suburban home. At that location, polycyclic aromatic hydrocarbon air concentrations were on average approximately
two times higher outdoor than indoor, while AhR potency was five times higher outdoor than indoor. No significant correlation
was found between the estrogenic and AhR activity (P = 0.88) for the sites in this study.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
684.
The construction of diaryl sulfides through the cross‐coupling of aryl iodides and thiols in microwave heating is described. By using this method, a variety of diaryl sulfides can be prepared in a mild condition and in high yields. Deactivated 4‐nitrothiophenol was effective to afford the product in 94% yield. Sterically hindered ortho‐substituted aryl iodides or thiophenols provided diaryl sulfides effectively by this microwave‐assisted coupling reaction. 相似文献
685.
Muthiah Senthil Kumar 《Journal of organometallic chemistry》2006,691(22):4708-4716
Reactions of [η5-carboxycyclopentadienyl][η4-tetraphenylcyclobutadiene] cobalt, Ph4C4CoC5H4COOH (1), with (Ph3Sn)2O, [(n-Bu)2SnO]n and (Ph2SnO)n in refluxing toluene resulted in the formation of the monomeric compound Ph3SnOC(O)C5H4CoC4Ph4 (2) and dimeric compounds n-Bu2Sn[OC(O)C5H4CoC4Ph4]2 (3) and Ph2Sn[OC(O)C5H4CoC4Ph4]2 (4), respectively. Reactions carried out in the solid state by mechanical grinding also yielded same results. Crystal structure determination and cyclic voltammetric studies of compounds 1, 2, 3 and 4 have been carried out and compared with similar ferrocene carboxylic acid derivatives. The structures and electrochemistry of these compounds are compared with analogous organotin ferrocene carboxylates. The results obtained from the reaction of 1 with alkyl and aryl tin oxides suggest that the formation of stannoxanes assemblies having more than two carboxylate units are not favored indicating that 1 is a highly sterically hindered metallocene carboxylic acid. 相似文献
686.
Tushar S. Basu Baul Wandondor Rynjah Antonin Ly?ka Robert Jirásko Ray J. Butcher 《Journal of organometallic chemistry》2006,691(23):4850-4862
Reactions of 5-[(E)-2-(aryl)-1-diazenyl]-2-hydroxybenzoic acids (LHH′, where the aryl group is an R-substituted phenyl ring such that for L1HH′: R = H; L2HH′: R = 2′-CH3; L3HH′: R = 3′-CH3; L4HH′: R = 4′-CH3; L5HH′: R = 4′-Cl; L6HH′: R = 4′-Br) with nBu2SnO in a 1:1 molar ratio yielded complexes of composition {[nBu2Sn(LH)]2O}2. The complexes have been characterized by 1H, 13C, 119Sn NMR, ESI-MS, IR and 119mSn Mössbauer spectroscopic techniques in combination with elemental analyses. The crystal structures of {[nBu2Sn(L1H)]2O}2 (1), {[nBu2Sn(L4H)]2O}2 (4), {[nBu2Sn(L5H)]2O}2 (5) and {[nBu2Sn(L6H)]2O}2 (6) were determined. The compounds are centrosymmetric tetranuclear bis(dicarboxylatotetrabutyldistannoxane) complexes containing a planar Sn4O2 core in which two μ3-oxo O-atoms connect an Sn2O2 ring to two exocyclic Sn-atoms. The four carboxylate ligands display two different modes of coordination where both modes involve bridging of two structurally distinct Sn-atoms. The solution structures were confirmed by 119Sn NMR spectroscopy by observing two tin resonances in compounds 1, and 4-6. The observed difference between the two tin resonances was about 3 ppm while the differences in 13C resonances were even smaller. Compounds {[nBu2Sn(L2H)]2O}2 (2) and {[nBu2Sn(L3H)]2O}2 (3) undergo a very complex exchange processes in deuteriochloroform solution. The in vitro cytotoxic activity of compounds 1 and 4 against WIDR, M19 MEL, A498, IGROV, H226, MCF7 and EVSA-T human tumour cell lines is reported. 相似文献
687.
Italo A. Sanhueza Mads C. Nielsen Marcel Ottiger Franziska Schoenebeck 《Helvetica chimica acta》2012,95(11):2231-2236
(Trifluoromethyl)stannane reagents such as Bu3SnCF3 are effective in CuI‐mediated trifluoromethylation reactions of aryl iodides. The reactions proceed via the intermediacy of [CuCF3] species. 相似文献
688.
G. NagendraC. Madhu T.M. VishwanathaVommina V. Sureshbabu 《Tetrahedron letters》2012,53(38):5059-5063
A simple and efficient method for the synthesis of alcohols from the corresponding carboxylic acids is described. Activation of carboxylic acid with 1-propanephosphonic acid cyclic anhydride (T3P) and subsequent reduction using NaBH4 yield the alcohol in excellent yields with good purity. Reduction of several alkyl/aryl carboxylic acids and Nα-protected amino acids/peptide acids as well as Nβ-protected amino acids was successfully carried out to obtain corresponding alcohols in good yields. All the products were fully characterized by 1H NMR and mass spectral analyses. The procedure is mild, simple and the isolation of the products is easy. 相似文献
689.
The use of N-bromosuccinimide as a catalyst promoted the synthesis of polycyclic indolo[2,3-b]quinoline derivatives in good to high yields in the reactions of various aryl amines with indole-3-carbaldehyde at room temperature under mild conditions. 相似文献
690.
Dayanand A. KamblePratibha U. Karabal Pandurang V. ChouthaiwaleArumugam Sudalai 《Tetrahedron letters》2012,53(32):4195-4198
Sodium periodate and sodium azide combination has been found to be an excellent reagent system suitable for the direct diazidation of styrenes, alkenes, benzylic alcohols, and aryl ketones to produce the corresponding vicinal and geminal diazides respectively in high yields under mild reaction conditions. 相似文献