全文获取类型
收费全文 | 2360篇 |
免费 | 676篇 |
国内免费 | 812篇 |
专业分类
化学 | 1491篇 |
晶体学 | 46篇 |
力学 | 251篇 |
综合类 | 87篇 |
数学 | 570篇 |
物理学 | 1403篇 |
出版年
2024年 | 20篇 |
2023年 | 53篇 |
2022年 | 88篇 |
2021年 | 58篇 |
2020年 | 44篇 |
2019年 | 78篇 |
2018年 | 65篇 |
2017年 | 59篇 |
2016年 | 71篇 |
2015年 | 83篇 |
2014年 | 143篇 |
2013年 | 116篇 |
2012年 | 129篇 |
2011年 | 124篇 |
2010年 | 106篇 |
2009年 | 145篇 |
2008年 | 177篇 |
2007年 | 132篇 |
2006年 | 128篇 |
2005年 | 140篇 |
2004年 | 163篇 |
2003年 | 139篇 |
2002年 | 93篇 |
2001年 | 98篇 |
2000年 | 109篇 |
1999年 | 97篇 |
1998年 | 106篇 |
1997年 | 120篇 |
1996年 | 102篇 |
1995年 | 91篇 |
1994年 | 90篇 |
1993年 | 83篇 |
1992年 | 83篇 |
1991年 | 95篇 |
1990年 | 68篇 |
1989年 | 77篇 |
1988年 | 36篇 |
1987年 | 29篇 |
1986年 | 17篇 |
1985年 | 23篇 |
1984年 | 31篇 |
1983年 | 31篇 |
1982年 | 31篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 6篇 |
1964年 | 4篇 |
1963年 | 5篇 |
1955年 | 6篇 |
排序方式: 共有3848条查询结果,搜索用时 187 毫秒
951.
952.
953.
本文研究了二甲亚砜(DMSO),二甲替甲酰胺(DMF)吡啶(py)等溶剂对[Co(acac)_2·2H_2O]载氧和氧化性能的影响.实验证明[Co(acac)_2·2H_2O]与O_2的反应第一步为可逆载氧,而第二步为不可逆载氧.用元素分析和波谱研究了[Co(acac)_2·2H_2O]在溶剂中的存在形态和热力学性质。用配位场理论计算了[Co(acac)_2·2H_2O]在溶剂中的各种配位场参数。动力学的研究表明,[Co(acac)_2·2H_2O]在DMF溶剂中O_2的反应发生一级半过程,一级为[Co(acac)_2·2H_2O]半级为O_2.反应的动力学方程为v=k[Co(acac)_2·2H_2O]·P_(o_2)~(0.41).反应的表观活化能为44.8千焦/摩尔,波谱的分析结果证实,氧化反应的主要产物为[Co(acac)_3] 相似文献
954.
955.
956.
957.
原子簇化合物[WS4Cu3Br(bipy)2]的晶体结构和非线性光学性质 总被引:1,自引:0,他引:1
The title cluster compound [WS4Cu3Br(bipy)2] has been synthesized by the reaction of (NH4)2[WS4], CuBr and 2,2′-bipy in DMF solution. Single crystal X-ray diffraction data show that the compound has a nest-shaped structure. Nonlinear optical properties (NLO) of the cluster were investigated by a Z-scan technique with a pulsed laser at 532nm. The cluster exhibits the strong NLO absorption and a self-defocusing effect (effective non-linear absorption coefficient, α2eff=7.3×10-11mW-1; effective non-linear refractive index, n2eff=3.9×10-11esu) when measured in a 6.0×10-4mol·dm-3 DMF solution. CCDC: 200397. 相似文献
958.
Ag-modified La0.6Sr0.4MnO3 catalysts were prepared and their catalytic performance for deep oxidation of CH4 and CH3OH at low concentrations were investigated. The results showed that the La0.6Sr0.4MnO3 host catalyst with the perovskite-type nano-crystallite structure displayed considerably high catalytic activity for deep oxidation of CH4 and CH3OH at low concentrations. Ag modification to the La0.6Sr0.4MnO3 host catalyst resulted in significant enhancement of the catalyst activity, making the T95 (the reaction temperature needed for conversion of 95%of CH4 or CH3OH) lowered down to 735K (for CH4) and 421K (for CH3OH) from 813 and 465 K over the Ag-free system under the reaction conditions:0.1MPa,CH4/O2/N2=2/12/86(molar ratio),GHSV=45000 h-1 and CH3OH/O2/N2= 0.2/1.0/98.8 (molar ratio),GHSV=58000 h-1,respectively.The carbon containing product was almost CO2 and the contents of HCHO and CO in the reaction exit gas were both under GC detectable limit in both cases.
The results of spectroscopic characterization indicated that modification by proper amount of Ag-dopant did not change the perovskite structure of the La0.6Sr0.4MnO3 host catalyst as a whole. Interaction of Ag-dopant with the surface of the host catalyst,La0.6Sr0.4MnO3,was in favor of high dispersion of the Ag component at the catalyst surface and led to the oxidation of part of the Mn3+species to Mn4+,resulting in an increase of amounts of the reducible Mnn+ species and a decrease of their reduction temperature. On the other hand, this interaction led also to enhancement of adsorption ability of the catalyst toward O2 at relatively low temperature. High activity of the Ag modified La0.6Sr0.4MnO3 catalyst for CH4 and CH3OH complete oxidation was closely related to high redox-activity of the catalyst and its prominent adsorption-activation ability to O2 at relatively low temperatures. 相似文献
The results of spectroscopic characterization indicated that modification by proper amount of Ag-dopant did not change the perovskite structure of the La0.6Sr0.4MnO3 host catalyst as a whole. Interaction of Ag-dopant with the surface of the host catalyst,La0.6Sr0.4MnO3,was in favor of high dispersion of the Ag component at the catalyst surface and led to the oxidation of part of the Mn3+species to Mn4+,resulting in an increase of amounts of the reducible Mnn+ species and a decrease of their reduction temperature. On the other hand, this interaction led also to enhancement of adsorption ability of the catalyst toward O2 at relatively low temperature. High activity of the Ag modified La0.6Sr0.4MnO3 catalyst for CH4 and CH3OH complete oxidation was closely related to high redox-activity of the catalyst and its prominent adsorption-activation ability to O2 at relatively low temperatures. 相似文献
959.
960.
如今社会在飞速发展,各行各业对人才的需求越来越大.从教育领域来讲,大量的教学实践证明新时代教育应突破传统的教学模式全面落实素质教育,以对学生的高阶思维能力和创新精神进行培养.小学生的思维模式和计算能力会在其学习数学知识的过程中得到锻炼,教师应在课堂教学中融入高阶思维,从多方面入手培养学生的创新能力,使学生可以对数学知识进行有效运用. 相似文献