全文获取类型
收费全文 | 38819篇 |
免费 | 6190篇 |
国内免费 | 4741篇 |
专业分类
化学 | 27240篇 |
晶体学 | 538篇 |
力学 | 2355篇 |
综合类 | 344篇 |
数学 | 4745篇 |
物理学 | 14528篇 |
出版年
2024年 | 72篇 |
2023年 | 766篇 |
2022年 | 852篇 |
2021年 | 1316篇 |
2020年 | 1528篇 |
2019年 | 1401篇 |
2018年 | 1218篇 |
2017年 | 1181篇 |
2016年 | 1662篇 |
2015年 | 1724篇 |
2014年 | 2111篇 |
2013年 | 2763篇 |
2012年 | 3453篇 |
2011年 | 3492篇 |
2010年 | 2477篇 |
2009年 | 2356篇 |
2008年 | 2533篇 |
2007年 | 2234篇 |
2006年 | 2088篇 |
2005年 | 1741篇 |
2004年 | 1466篇 |
2003年 | 1100篇 |
2002年 | 1000篇 |
2001年 | 851篇 |
2000年 | 778篇 |
1999年 | 906篇 |
1998年 | 726篇 |
1997年 | 655篇 |
1996年 | 723篇 |
1995年 | 617篇 |
1994年 | 571篇 |
1993年 | 499篇 |
1992年 | 469篇 |
1991年 | 373篇 |
1990年 | 330篇 |
1989年 | 247篇 |
1988年 | 230篇 |
1987年 | 208篇 |
1986年 | 147篇 |
1985年 | 160篇 |
1984年 | 141篇 |
1983年 | 122篇 |
1982年 | 83篇 |
1981年 | 60篇 |
1980年 | 54篇 |
1979年 | 33篇 |
1978年 | 28篇 |
1976年 | 28篇 |
1975年 | 31篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
991.
A non-linear regression model was derived for the simultaneous determination of the rate constant in alkaline hydrolysis of esters and the initial concentration of esters based on the linear relationship between the frequency response of the surface acoustic wave sensor system and the conductivity of the solution. The model was tested theoretically and experimentally with the methyl-, ethyl-, and n-propyl-acetate systems. The corresponding rate constants estimated at 25 degrees C are 0.147, 0.103 and 0.0671 respectively. 相似文献
992.
Silver nanocomposite multilayer films were prepared through the in situ method. Multilayer thin films, prepared through the sequential electrostatic deposition of a positively charged third-generation poly(amidoamine) dendrimer (PAMAM) and negatively charged poly(styrenesulfonate) (PSS) and poly(acrylic acid) (PAA), were utilized as nanoreactors for the formation of silver nanoparticles. The silver ions were preorganized in layer-by-layer (LBL) films composed of PAMAM dendrimers and subsequently reduced with hydrogen to prepare the silver nanoparticles. The UV-vis spectrum and profilometer were used to characterize the regular growth of bilayers. UV-vis absorption from plasmon resonance at 435 nm and TEM images indicated the formation of the silver nanoparticles in the multilayer films. The silver nanocomposite LBL films were also constructed on the indium tin oxide-glass and investigated using cyclic voltammetry. The silver nanoparticles in the multilayer films have a stronger negative redox potential. The silver nanocomposite LBL films may have a potential application in the catalysis of reduction of 4-nitrophenol with sodium borohydride. 相似文献
993.
994.
Liu JM Yang TL Liang XS Wu AH Li LD Lin SQ 《Analytical and bioanalytical chemistry》2004,380(4):632-636
Luminescent 50-nm silicon dioxide nanoparticles containing both types of rhodamine 6G (R; particles denoted R-SiO2) were synthesized by the sol–gel method. In the presence of Pb(Ac)2 as a heavy atom perturber the particle can emit the intense and stable room-temperature phosphorescence (RTP) signal of R on a polyamide membrane, with exmax/emmax=470/635 nm for R. Our research indicates that the specific immune reaction between goat-anti-human IgG antibody labeled with R-SiO2 and human IgG can be carried out quantitatively on a polyamide membrane, and the phosphorescence intensity was enhanced after the immunoreaction. Thus a new method for solid-substrate room-temperature phosphorescence immunoassay (SS-RTP-IA) for determination of human IgG was established on the basis of antibody labeled with the nanoparticles containing binary luminescent molecules. The linear range of this method is 0.0624–20.0 pg spot–1 of human IgG (corresponding to a concentration range of 0.156–50.0 ng mL–1, sample volume 0.40 L spot–1). The regression equations of the working curves are Ip=71.27+7.208mIgG (pg spot–1) (r=0.9996). Detection limits calculated as 3Sb/k are 0.022 pg spot–1. Compared with the same IA using fluorescein isothiocyanate (FITC) as the marker the new method was more sensitive and had a wider linear range. After elevenfold replicate measurement RSD are 4.5 and 3.6% for samples containing 0.156 and 50.0 ng mL–1 IgG, respectively. This method is sensitive, accurate, and of high precision. 相似文献
995.
996.
997.
998.
Photosensitized oxidation of trialkylalkenes 2-methyl-2-pentene (1), 1-methylcyclohexene (2), trans-3-methyl-2-pentene (3), cis-3-methyl-2-pentene (4), and 2-methyl-2-butene (5) included in the internal framework of Na-ZSM-5 zeolites was investigated. The zeolite samples having adsorbed the alkenes were suspended in isooctane, and the sensitizer, tetraphenylporphyrin (TPP), was dissolved in the solution. Singlet oxygen produced in the solution diffused into the internal framework of the zeolites and reacted with alkenes. For all the substrates studied, the ene-type allylic hydroperoxides were obtained in a highly regioselective manner. The regiochemistry for 1-4 in favor of the allylic hydrogen abstraction from the largest substituents is in contrast to their photooxidation within the dye-supported zeolite Na-Y, where the secondary hydroperoxides are preferentially produced. The tight confinement of the alkenes within the narrow channels of the ZSM-5 zeolites is likely to be responsible for this selectivity. 相似文献
999.
[formula: see text] S-Nitrosoglutathione oxidized 4-substituted Hantzsch 1,4-dihydropyridines in CH3CN/H2O or CH3CN/phosphate aqueous buffer solution to give aromatic products in various yields. 相似文献
1000.