全文获取类型
收费全文 | 218篇 |
免费 | 8篇 |
国内免费 | 30篇 |
专业分类
化学 | 231篇 |
晶体学 | 2篇 |
综合类 | 2篇 |
物理学 | 21篇 |
出版年
2023年 | 3篇 |
2022年 | 10篇 |
2021年 | 10篇 |
2020年 | 2篇 |
2019年 | 8篇 |
2018年 | 4篇 |
2017年 | 6篇 |
2016年 | 2篇 |
2015年 | 9篇 |
2014年 | 4篇 |
2013年 | 15篇 |
2012年 | 8篇 |
2011年 | 19篇 |
2010年 | 11篇 |
2009年 | 12篇 |
2008年 | 12篇 |
2007年 | 11篇 |
2006年 | 19篇 |
2005年 | 16篇 |
2004年 | 13篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 2篇 |
1998年 | 7篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有256条查询结果,搜索用时 156 毫秒
101.
Sulfuric acid ([3-(3-silicapropyl)sulfanyl]propyl)ester is employed as a recyclable catalyst for the condensation reaction between aromatic aldehydes and 3-methyl-l-phenyl-5-pyrazolone. This condensation reaction was performed in ethanol under refluxing conditions giving 4,4'-alkylmethylene-bis(3-methyl-5-pyrazolones) in 74-90% yields. The heterogeneous catalyst was recycled and used in eleven runs for the reaction between benzaldehyde and 3-methyl-l-phenyl-5-pyrazolone without losing catalytic activity. 相似文献
102.
Kwak IH Shin YH Kim M Cha HY Nam HJ Lee BS Chaudhary SC Pai KS Lee JH 《Experimental & molecular medicine》2011,43(2):111-120
Aberrant activation of hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, Met, is involved in the development and progression of many human cancers. In the cell-based screening assay, (-)epigallocatechin-3-gallate (EGCG) inhibited HGF/SF-Met signaling as indicated by its inhibitory activity on HGF/SF-induced cell scattering and uPA activation (IC50=15.8 microgram/ml). Further analysis revealed that EGCG at low doses specifically inhibited HGF/SF-induced tyrosine phosphorylation of Met but not epidermal growth factor (EGF)-induced phosphorylation of EGF receptor (EGFR). On the other hand, high-dose EGCG decreased both Met and EGFR proteins. We also found that EGCG did not act on the intracellular portion of Met receptor tyrosine kinase, i.e., it inhibited InlB-dependent activation of Met but not NGF-induced activation of Trk-Met hybrid receptor. This inhibition decreased HGF-induced migration and invasion by parental or HGF/SF-transfected B16F10 melanoma cells in vitro in either a paracrine or autocrine manner. Furthermore, EGCG inhibited the invasion/metastasis of HGF/SF-transfected B16F10 melanoma cells in mice. Our data suggest the possible use of EGCG in human cancers associated with dysregulated paracrine or autocrine HGF/SF-Met signaling. 相似文献
103.
A highly selective synthesis of 2‐aryl‐1‐arylmethyl‐1H‐1,3‐benzimidazoles from the reaction of o‐phenylenediamine and aromatic aldehydes in the presence of silica‐bonded propyl‐S‐sulfonic acid (SBSSA) at 80°C in water in good to excellent yields was developed. 相似文献
104.
Gilles Toussaint Miguel Angel Rodriguez Rudi Cloots Juan Rubio Fausto Rubio Bénédicte Vertruyen Catherine Henrist 《Journal of Non》2011,357(3):951-957
Synthetic lamellar silica and hybrid lamellar silicas have been prepared by liquid crystal templating, template extraction and silanization. The samples have been characterized by thermogravimetric analysis (TGA), carbon analysis, spectroscopy, X-ray diffraction (XRD) and nitrogen adsorption. The XRD analyses have shown that the lamellar periodic stacking is preserved for all samples. The quantity and type of organic molecules at the silica surface have been evaluated by carbon analysis, TGA and spectroscopy. The covalent grafting of the solvent used for extraction of the initial surfactant has been highlighted by these analyses. The nitrogen adsorption analyses have revealed three categories of pores and two types of samples. The initial lamellar silica exhibits a very low specific surface area and plate-like type of pores. The second type of samples is made up of the hybrid samples and the initial substrate from whom the surfactant has been extracted. These samples show a significantly higher specific surface area with interlamellar spaces corresponding to narrow-slit like mesopores around 4 nm. The nitrogen adsorption data analysis has highlighted the presence of micropores within the silica sheets. The difference of the specific surface is due to pore blocking by the surfactant impeding the access to nitrogen into interlamellar spaces and by the silanes covering the pores once the surface modified. The presence of micro and mesopores combined to a high BET specific surface of 612 m²/g makes these lamellar silicas interesting materials for catalysis applications. 相似文献
105.
Dandekar P Jain R Stauner T Loretz B Koch M Wenz G Lehr CM 《Macromolecular bioscience》2012,12(2):184-194
A hydrophobic starch derivative is used for safe and enhanced delivery of anticancer agents. The synthesis and characterization of propyl starch with a controlled degree of substitution to modulate the release of the encapsulated hydrophobic drug is reported. The application of this polymer for formulating nanoparticles of docetaxel, an anti-cancer agent effective against numerous types of cancers but possessing intrinsic formulation difficulties is described. The solvent emulsification/diffusion technique is used and the synthesis is optimized with respect to several formulation parameters. Uptake studies with these nanoparticles indicate their enhanced internalization by the cancerous cells and their peri-nuclear localization. 相似文献
106.
107.
2-羟基-3-(三乙胺基)丙基正癸基硫醚修饰碳糊电极测定痕量金 总被引:4,自引:0,他引:4
制备了2_羟基_3_(三乙胺基)丙基正癸基硫醚修饰碳糊电极,用于痕量金的测定。研究了电极的伏安特性及分析条件。在0.2mo/LKCl-HCl缓冲溶液中(pH1),Au(Ⅲ)被富集到电极表面,然后介质交换到0.2mol/LKCl-HCl空白溶液中(pH1)进行阳极溶出伏安测定,对于5min富集,Au(Ⅲ)浓度在2×10-8~1×10-6mol/L范围内呈线性关系,检出限为1×10-8mol/L,相对标准偏差5.2%,一般常见离子不干扰。 相似文献
108.
Hisanori Yamane Ryota Yagi Akira Hosono Yuji Masubuchi 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(6):702-706
A new quaternary oxide, BiGaTi4O11 (bismuth gallium tetratitanium undecaoxide), was prepared by heating a mixture of the binary oxides at 1373 K in air. BiGaTi4O11 melts at 1487 K and prismatic single crystals were obtained from a sample melted at 1523 K and solidified by furnace cooling. The structure of BiGaTi4O11 was analyzed using single‐crystal X‐ray diffraction to be of a new type that crystallized in the space group Cmcm. A Bi3+ site is coordinated by nine O2? anions, and three oxygen‐coordinated octahedral sites are statistically occupied by Ga3+ and Ti4+ cations. A relative dielectric constant of 46 with a temperature coefficient of 57 ppm K?1 in the temperature range 297–448 K was measured for a polycrystalline ceramic sample at 150 Hz–1 MHz with a dielectric loss tan δ of less than 0.01. Electrical resistivities measured at 1073 K by alternating‐current impedance spectroscopic and direct‐current methods were 1.16 × 10?4 and 1.14 × 10?4 S cm?1, respectively, which indicates that electrons and/or holes were conduction carriers at high temperature. The optical band gap estimated by the results of diffuse reflectance analysis was 2.9–3.0 eV, while the band gap obtained from the activation energy for electrical conduction was 3.5 eV. 相似文献
109.
V. Kahlenberg 《无机化学与普通化学杂志》2001,627(10):2386-2390
Single crystals of a new barium oxogallate were obtained by growth from a melt at 1500 °C. The compound is monoclinic, with cell parameters a = 17.7447(10) Å, b = 10.6719(5) Å, c = 7.2828(5) Å, β = 98.962(7)°, V = 1362.3(2) Å3. The diffraction pattern shows systematic absences corresponding to the space group P121/c1. The structure was solved by direct methods followed by Fourier syntheses, and refined using a single crystal diffraction data set (R1 = 0.032 for 2173 reflections with I > 2σ(I)). The chemical composition derived from structure solution is Ba4Ga2O7, with a unit cell content of Z = 6. Main building units of the structure are GaO4 tetrahedra sharing one oxygen atom to form Ga2O7 groups. The Ga–O–Ga bridging angle of one of the two symmetrically independent groups is linear by symmetry. The dimers are crosslinked by barium cations coordinated by six to eight oxygen ligands. 相似文献
110.
Triphenyl(propyl‐3‐sulfonyl)phosphoniumtrifluoromethanesulfonate {[TPPSP]OTf} as a reusable, green and benign ionic liquid catalyst has been used in the Hantzsch four‐component (synthesis of polyhydroquinolines) and three‐component (synthesis of acridines) condensation reactions of 1,3‐diones, β‐ketoesters, aldehydes, ammonium acetate and aniline derivatives in the presence of 0.5 mol% of {[TPPSP]OTf} at room temperature under solvent‐free conditions. The new ionic liquid catalyst was fully characterized using infrared, 1H NMR, 13C NMR, 31P NMR, 19F NMR and mass spectroscopies, and thermogravimetric and derivative thermogravimetric analyses. Additionally, the recovered catalyst can be recycled at least five times in subsequent reactions without significant loss in catalytic activity. The new synthesis technique presented offers numerous advantages of safety, mild conditions, simplicity, short reaction time, high yields and easy workup compared to the traditional synthesis method. Twenty products have been reported for the first time. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献