全文获取类型
收费全文 | 158篇 |
免费 | 3篇 |
国内免费 | 1篇 |
专业分类
化学 | 85篇 |
晶体学 | 1篇 |
力学 | 16篇 |
数学 | 38篇 |
物理学 | 22篇 |
出版年
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 4篇 |
2020年 | 7篇 |
2019年 | 13篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2014年 | 5篇 |
2013年 | 9篇 |
2012年 | 11篇 |
2011年 | 9篇 |
2010年 | 5篇 |
2009年 | 6篇 |
2008年 | 12篇 |
2007年 | 10篇 |
2006年 | 4篇 |
2005年 | 6篇 |
2004年 | 1篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 2篇 |
2000年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 5篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有162条查询结果,搜索用时 26 毫秒
71.
In(2)O(3) sol-gel thin films made with LaF(3):Ln(3+) (Ln=Er, Nd, and Eu) nanoparticles were prepared and showed sensitized emission of the lanthanide ions after In(2)O(3) matrix excitation. The excitation spectra showed an In(2)O(3) absorption band in addition to the excitation peaks of the lanthanide ions, clearly demonstrating that there is energy transfer from the In(2)O(3) matrix to Ln(3+) (Er(3+), Nd(3+), and Eu(3+)). Similarly, HfO(2) and ZrO(2) sol-gel thin films made with LaF(3):Ln(3+) nanoparticles also showed energy transfer from the semiconductor matrix to the lanthanide ions. 相似文献
72.
Sabir H. Mashraqui Shailesh Ghadigaonkar A. Sri Ranjini P.K. Das 《Tetrahedron》2007,63(40):10011-10017
A thieno[2,3-b]thiophene core has been utilized as a π-donor component to design two series of push-pull thienothiophenes by introducing various acceptor groups either via olefinic or aza-spacers. The molecules show a UV-visible cut-off wavelength below the second harmonic generation (SHG) at λ/2 of 532 nm, thereby conforming to the nonlinearity-transparency trade-off. Second order molecular nonlinearity, β measured by Hyper-Rayleigh scattering technique was found in the range of 9.58-47.66×10−30 esu, while the Kurtz powder technique produced signals of the order of 0.43-1.02 U. Thermal decomposition temperatures measured by differential scanning calorimetry revealed decomposition temperatures≥275 °C, indicating high thermal stability. 相似文献
73.
Ohashi K Winarno H Mukai M Inoue M Prana MS Simanjuntak P Shibuya H 《Chemical & pharmaceutical bulletin》2003,51(3):343-345
Six fatty acids (1-6), two xanthines (7, 8), two flavonol glycosides (9, 10), one monoterpene glucoside (11), one lignan glycoside (12), and four flavanes (13-16) were clarified by a bioassay-guided separation as chemical constituents of Scurrula atropurpurea (Loranthaceae), a parasitic plant of the tea plant Thea sinensis (Theaceae). Among these constituents, it was found that the alkynic fatty acid octadeca-8,10,12-triynoic acid (6) exhibits a more potent inhibitory effect on cancer cell invasion in vitro than flavanes [(+)-catechin (13), (-)-epicatechin (14), (-)-epicatechin-3-O-gallate (15) and (-)-epigallocatechin-3-O-gallate (16)]. 相似文献
74.
The object of this study was to develop hydroxypropyl methylcellulose (HPMC) based cephalexin extended release tablet, which can release the drug for six hours in predetermined rate. Twenty-one batches of cephalexin tablets were prepared by changing various physical and chemical parameters, in order to get required theoretical release profile. The influences of HPMC, microcrystalline cellulose powder (MCCP), granulation technique, wetting agent and tablet hardness on cephalexin release from HPMC based extended release tablets were studied. The formulated tablets were also characterized by physical and chemical parameters. The dissolution results showed that a higher amount of HPMC in tablet composition resulted in reduced drug release. Addition of MCCP resulted in faster drug release. Tablets prepared by dry granulation was released the drug slowly than the same prepared with a wet granulation technique. Addition of wetting agent in the tablets prepared with dry granulation technique showed slower release. An increase in tablet hardness resulted in faster drug release. Tablets prepared with a wet granulation technique and having a composition of 9.3% w/w HPMC with a hardness of 10-12 kg/cm(2) gave predicted release for 6 h. The in vitro release data was well fit in to Higuchi and Korsmeyer-Peppas model. Physical and chemical parameters of all formulated tablets were within acceptable limits. One batch among formulated twenty-one batches was successful and showed required theoretical release. The effect of storage on in vitro release and physicochemical parameters of successful batch was studied and was found to be in acceptable limits. 相似文献
75.
The relaxation-assisted two-dimensional infrared (RA 2DIR) method is a novel technique for probing structures of molecules, which relies on vibrational energy transport in molecules. In this article we demonstrate the ability of RA 2DIR to detect the bond connectivity patterns in molecules using two parameters, a characteristic intermode energy transport time (arrival time) and a cross-peak amplification coefficient. A correlation of the arrival time with the distance between the modes is demonstrated. An 18-fold amplification of the cross-peak amplitude for the modes separated by approximately 11 A is shown using RA 2DIR; larger cross-peak amplifications are expected for the modes separated by larger distances. The RA 2DIR method enhances the applicability of 2DIR spectroscopy by making practical the long-range measurements using a variety of structural reporters, including weak IR modes. The data presented demonstrate the analytical power of RA 2DIR which permits the speedy structural assessments of the bond connectivity patterns. 相似文献
76.
We study the use of para-orthogonal polynomials in solving the frequency analysis problem. Through a transformation of Delsarte and Genin, we present an approach for the frequency analysis by using the zeros and Christoffel numbers of polynomials orthogonal on the real line. This leads to a simple and fast algorithm for the estimation of frequencies. We also provide a new method, faster than the Levinson algorithm, for the determination of the reflection coefficients of the corresponding real Szego polynomials from the given moments.
77.
Gangireddy Sujeevan Reddy Suresh Babu Nallapati P.S.V.K. Sri Saranya B. Sridhar Varadaraj Bhat Giliyaru Raghu Chandrashekhar Hariharapura G. Gautham Shenoy Manojit Pal 《Tetrahedron letters》2018,59(52):4587-4592
Propargylamine (secondary) has been explored as a building block in synthesizing indoles via an ultrasound assisted Pd/Cu-catalyzed coupling-cyclization method. Indoles containing a pyrazole moiety at C-2 attached via the –CH2NH– linker (designed as potential anti-tubercular agents) were synthesized first and then generality/scope of the methodology was expanded by synthesizing other indoles. Unexpected formation of imine side products in first cases helped in synthesizing related (pyrazole)imines via a Cu catalyzed ultrasound assisted aerobic oxidation of precursor amines. 相似文献
78.
It has been synthesized Mg/Al layered double hydroxide anionic clay (Mg/Al hydrotalcite) through direct precipitation by adding 0.5 M NaOH solution into a mixed solution containing Mg(NO3)2 and Al(NO3)3 with molar ratio of 0.1:0.05 until the medium acidity reached pH 10.1. The synthesized Mg/Al hydrotalcite was then utilized to remove dissolved humic acid in aqueous medium. The humic acid was isolated from peat soil taken in Gambut District, South Kalimantan, Indonesia using the recommended procedure of IHSS (International Humic Substances Society). The removal of humic acid was mostly occurred through simple sorption process without accompanied by significant intercalation. The sorption was optimum at pH 9.0, with the first order rate constant, capacity and energy of sorption were 5.50 × 10−3 min−1, 0.12 mmol g−1 (69 mg g−1), and 28.32 kJ mol−1, respectively. 相似文献
79.
A validated LC method for determination of 2,3-dichlorobenzoic acid and its associated regio isomers
A simple, selective and sensitive gradient reversed-phase liquid chromatography method has been developed for the separation and determination of 2,3-dichlorobenzoic acid, which is an intermediate of the lamotrizine drug substance, and its regio isomers. The separation was achieved on a reversed-phase United States Pharmacopeia L1 (C-18) column using 0.01 M ammonium acetate buffer at pH 2.5 and methanol (50:50 v/v) mixture as mobile phase A and a methanol and water mixture (80:20 v/v) as mobile phase B in a gradient elution at flow rate 1.2 mL/min with ultraviolet detection at 210 nm. The method is found to be selective, precise, linear, accurate and robust. It was used for quality assurance and monitoring the synthetic reactions involved in the process development of lamotrizine. The method is found to be simple, rapid, specific and reliable for the determination of unreacted levels of raw materials and isomers in reaction mixtures and finished product lamotrizine. The method was fully validated as per International Conference of Harmonization guidelines and results from validation confirm that the method is highly suitable for its intended purpose. 相似文献
80.
We describe a method to detect the expression of a surface protein in single cells without prior labeling or manipulation using a microfluidic device. When the protein is expressed on a cell surface, it undergoes transient bond formation with an immobilized ligand as the cell is pumped through a microfluidic channel, resulting in a specific decrease in the cell's velocity. We were able to detect the expression of interleukin 13 receptor alpha 2 (IL13Rα2) differentially expressed on LM2 cells, a subline of MDA-MB-231 human breast cancer cells with a unique lung metastatic capability. The detection of cells with high expression of the protein was near 100% sensitive and 100% specific. We also provided proof of principle of multiplexing by tracking the same cell over two, differentially-coated patches. The method is non-destructive and cells can be collected for reanalysis. The system can identify positive cells in a cell mixture. This method will have a potential impact in analyzing cancer cells when only a few are available, such as the case with needle aspirates and when labeling and manipulation result in cell loss. 相似文献