首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   137篇
  免费   1篇
  国内免费   2篇
化学   92篇
力学   7篇
数学   34篇
物理学   7篇
  2023年   1篇
  2022年   5篇
  2021年   3篇
  2020年   1篇
  2018年   2篇
  2016年   2篇
  2015年   3篇
  2014年   2篇
  2013年   3篇
  2012年   11篇
  2011年   8篇
  2010年   8篇
  2009年   6篇
  2008年   3篇
  2007年   3篇
  2006年   5篇
  2005年   3篇
  2004年   3篇
  2003年   10篇
  2002年   5篇
  2001年   1篇
  2000年   2篇
  1999年   4篇
  1997年   1篇
  1996年   2篇
  1995年   4篇
  1992年   1篇
  1991年   4篇
  1989年   1篇
  1988年   2篇
  1985年   2篇
  1984年   1篇
  1983年   1篇
  1982年   2篇
  1981年   1篇
  1980年   4篇
  1979年   4篇
  1978年   3篇
  1977年   6篇
  1976年   3篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
  1969年   1篇
排序方式: 共有140条查询结果,搜索用时 0 毫秒
1.
In this paper we give a method for constructing sharply 1-transitive permutation sets inside a finite permutation group with certain properties and we apply this method to obtain a family of sharply 1-transitive permutation subsets of the sharply 3-transitive permutation group M(p 2f ) on PG(1, p 2f ) for p f 1 (mod 4).Work supported by G.N.S.A.G.A. and M.P.I.  相似文献   
2.
A mild and practical procedure of Horner-Wadsworth-Emmons olefination promoted by lithium hydroxide and α-cyano phosphonates has been set up for the synthesis of α,β-unsaturated nitriles. The reaction conditions are tolerated by functionalized ketones and the exclusive formation of E-γ-hydroxy α,β-unsaturated nitriles has been observed.  相似文献   
3.
Preparation and reactions of the 2-furyl steroid 4 is described. In acidic medium, a product, 8, arising from furan ring opening with the introduction of functional groups in 23,25 and 26 carbon atoms, is observed. In slightly different experimental conditions, 4 yields a product 10 of a new molecular rearrangement, involving the 3 oxocyclopentene-5 hydroxy unit in the steroid side chain.  相似文献   
4.
Flavonoids are plant bioactives that are recognized as hormone-like polyphenols because of their similarity to the endogenous sex steroids 17β-estradiol and testosterone, and to their estrogen- and androgen-like activity. Most efforts to verify flavonoid binding to nuclear receptors (NRs) and explain their action have been focused on ERα, while less attention has been paid to other nuclear and non-nuclear membrane androgen and estrogen receptors. Here, we investigate six flavonoids (apigenin, genistein, luteolin, naringenin, quercetin, and resveratrol) that are widely present in fruits and vegetables, and often used as replacement therapy in menopause. We performed comparative computational docking simulations to predict their capability of binding nuclear receptors ERα, ERβ, ERRβ, ERRγ, androgen receptor (AR), and its variant ART877A and membrane receptors for androgens, i.e., ZIP9, GPRC6A, OXER1, TRPM8, and estrogens, i.e., G Protein-Coupled Estrogen Receptor (GPER). In agreement with data reported in literature, our results suggest that these flavonoids show a relevant degree of complementarity with both estrogen and androgen NR binding sites, likely triggering genomic-mediated effects. It is noteworthy that reliable protein–ligand complexes and estimated interaction energies were also obtained for some suggested estrogen and androgen membrane receptors, indicating that flavonoids could also exert non-genomic actions. Further investigations are needed to clarify flavonoid multiple genomic and non-genomic effects. Caution in their administration could be necessary, until the safe assumption of these natural molecules that are largely present in food is assured.  相似文献   
5.
Arrigo Scettri 《Tetrahedron》1985,41(22):5141-5144
4-methoxy-cyclopent-2-en-1-ones 6 are easily obtained through a simple procedure involving in the key-step the conversion of 2-furylcarbinols 1 into 1,1,2-trimethoxy-al-kan-4-ones 3, a masked form of 1,4-dicarbonyl compounds, by treatment with Amberlyst H15 in methanolic solution. Then, the regeneration of the aldehydic function and a base-catalysed aldolic condensation lead in high yields to the final products 6.  相似文献   
6.
7.
SiCl4 can be conveniently activated by catalytic amounts of dimethyl sulfoxide or other readily-available sulfoxides for the allylation of aromatic, hetero-aromatic and unsaturated aldehydes in the presence of allyltributyl stannane. Chiral aryl methyl sulfoxides have been used to develop asymmetric allylation methods, as well as probe the aldehyde substrate scope.  相似文献   
8.
In this paper two systems, polyethylene (LDPE) and polyethylene/commercial organo-modified montmorillonite (LDPE/OMMT) nanocomposite, were subjected to e-beam irradiation at different doses and both the molecular modifications and mechanical properties have been investigated through solubility, FT-IR, calorimetric and tensile tests. Moreover, in some of the irradiated systems photo-oxidation aging was performed and its effects were studied. The results show an enhancement with irradiation of the positive effect of the nano-filler loading, related to the increase of the mechanical properties, due to the increase of the nano-filler polymer interaction.Nevertheless calorimetric and FT-IR data indicate that the well known reduction of LDPE/OMMT nanocomposite resistance to photo-oxidation ageing, with respect to LDPE, is amplified by ionizing radiation.  相似文献   
9.
10.
Studies carried out using three different in vitro assays and a biological setting (Escherichia coil) demonstrated the antioxidant activity of Scutellaria lateriflora microshoot extract. Moreover, the extract exhibited no toxicity in a brine shrimp lethality bioassay. These results indicated that microshoots are a rich, safe source of antioxidants, which encouraged us to enhance their production in vitro. In agar and agitated cultures, two biotechnological strategies were applied: feeding the cultures with the biogenetic precursors of the phenolics—phenylalanine and tyrosine, and eliciting them with methyl jasmonate. Specific Scutellaria flavonoids and verbascoside were analysed by HPLC. Feeding with precursors (1 g/L) in agar cultures decreased the production of the metabolites. In agitated cultures, different concentrations of precursors (1.0–2.5 g/L) and the elicitor (10; 50; 100 µM) were tested. Additionally, parallel feeding with the precursor and elicitor in a concentration of 50 µM were applied. The best strategy for total flavonoid and verbascoside production was phenylalanine feeding (1.5 g/L), max. 3765 and 475 mg/100 g DW, respectively, after 7 days. This is the first report documenting the high antioxidant production in S. lateriflora microshoots after feeding with phenylalanine. Moreover, for the first time, bioreactor cultures were successfully maintained, obtaining attractive results (max. total flavonoid content 2348 and verbascoside 485 mg/100 g DW).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号