全文获取类型
收费全文 | 1839篇 |
免费 | 63篇 |
国内免费 | 160篇 |
专业分类
化学 | 1083篇 |
力学 | 202篇 |
综合类 | 3篇 |
数学 | 59篇 |
物理学 | 715篇 |
出版年
2016年 | 4篇 |
2015年 | 15篇 |
2014年 | 1篇 |
2013年 | 9篇 |
2012年 | 22篇 |
2011年 | 397篇 |
2010年 | 199篇 |
2009年 | 225篇 |
2008年 | 38篇 |
2007年 | 15篇 |
2006年 | 47篇 |
2005年 | 107篇 |
2004年 | 351篇 |
2003年 | 174篇 |
2002年 | 136篇 |
2001年 | 93篇 |
2000年 | 30篇 |
1999年 | 23篇 |
1998年 | 25篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 23篇 |
1992年 | 33篇 |
1991年 | 14篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1925年 | 2篇 |
排序方式: 共有2062条查询结果,搜索用时 15 毫秒
81.
A self-intermolecular cyclocondensation reaction of 3,4-dihydropyrimidine-2-thione(DHPM) to give a novel tricyclic structure containing DHPM core in the presence of diethyl azodicarboxylate(DEAD) and triphenylphosphine(TPP) at room temperature is reported. 相似文献
82.
Yiwei Zhang Yuming Zhou Lihui Wan Mengwei Xue Yongzheng Duan Xuan Liu .School of Chemistry Chemical Engineering Southeast University Nanjing Jiangsu China .Biochemical Environmental Engineering College Nanjing Xiaozhuang University Nanjing 《天然气化学杂志》2011,20(6):639-646
Catalytic dehydrogenation of isobutane has recently received considerable attention because of the increasing demand for isobutene.In this study,the synergistic effect between Sn and K on PtSnK/γ-Al2O3 catalysts has been investigated by changing the content of Sn.It was found that with the presence of potassium,suitable addition of Sn could not only increase the metal dispersion,but also reduce the catalyst acidity.In these cases,the synergistic effect could also strengthen the interactions between the metal and support,which resulted in an increase in both catalytic activity and stability.In our experiments,Pt-0.6SnK/Al catalyst exhibited the lowest deactivation rate (12.4%) and showed a selectivity to isobutene higher than 94% at the isobutane conversion of about 45.3% after running the reaction for 6 h.However,with the excessive loading of Sn,surface property of active sites and the interactions between metal and support were changed.As a result,the initial optimal ratio between the metallic function and acid function would be destroyed,which was disadvantageous to the reaction. 相似文献
83.
ZHAO Hai-feng WU Lei LU Ming HU Yu-lin HAN Xiao LI Zheng-qiang . Key Laboratory for Molecular Enzymology & Engineering Ministry of Education Jilin University Changchun P. R. China . Medical 《高等学校化学研究》2011,(3):450-454
Lipid-bound [VHb(406)] and lipid-free [VHb(402)] wide type Vitreoscilla hemoglobin were separated from E. coli BL21(DE3). The RZ is 3.30 for [VHb(406)] and 3.15 for [VHb(402)], respectively. VHb(406) shows a characteristic absorption band at 626 nm, while VHb(402) shows one at 644 nm, and it has more α-helix than VHb(402). Data of Raman spectra experiment shows under the excitation wavelength 488 nm, υ4 vibration of both VHb(402) and VHb(406) had a pure and strong signal at 1375 cm-1, which proves that iron... 相似文献
84.
HU Fang ZHANG Chun-hua ZHANG Song MING Xing CHEN Gang WEI Ying-jin WANG Chun-zhong . School of Materials Science Engineering Shenyang University of Technology Shenyang P. R. China . College of Physics State Key Laboratory of Superhard Materials Jilin University Changchun . College of Physical Science Technology Huanggang Normal University Huanggang 《高等学校化学研究》2011,(3):528-530
1 Introduction Low-dimensional nanostructures, such as nanorods, nanowires, and nanotubes, have received much attention for their superior optical, electrical, catalytic and magnetic properties. 相似文献
85.
SUI XinCe SHI Yan & FU ZhiFeng State Key Laboratory of Chemical Resource Engineering Beijing University of Chemical Technology Beijing China 《中国科学B辑(英文版)》2011,(3)
A novel copolymer network with acetal structure was prepared using bis[4-(vinyloxy)butyl](4-methyl-1,3-phenylene)biscarbamate(BECT)as the crosslinking agent.Firstly,a tri-copolymer of maleic anhydride(MAn),n-butyl vinyl ether(BVE)and 4-hydroxybutyl vinyl ether(HBVE)was synthesized via free-radical polymerization with 2,2′-azobisisobutyronitrile as the initiator.The tri-copolymer consisted of two sorts of alternating units,MAn-alt-BVE and MAn-alt-HBVE.The linear copolymer Poly((MAn-alt-BVE)-co-(MAn-alt-HBVE)... 相似文献
86.
CUI Tao TANG ShunLin ZHANG Lei & YU DaRen School of Energy Science Engineering Harbin Institute of Technology Harbin China Pharmaceutical College Heilongjiang University of Chinese Medicine Institution Harbin China 《中国科学B辑(英文版)》2011,(7)
Catalytic CO oxidation on platinum group metals exhibits nonlinear phenomena such as hysteresis and bifurcation.Elucidation of the nonlinear mechanisms is important for catalyst design and control of reaction routes.Previous studies have offered initial insights into the local bifurcation behavior of CO oxidation.However,since the bifurcation behavior of CO oxidation is determined by multiple parameters such as temperature,total flux,and CO fraction,it is difficult to predict the global bifurcation behavior... 相似文献
87.
WANG Wei & ZHU Jun-Jie State Key Laboratory of Analytical Chemistry for Life Science School of Chemistry Chemical Engineering Nanjing University Nanjing China 《中国科学B辑(英文版)》2011,(8)
This review presents a simple introduction on the unique properties and general synthesis of quantum dots (QDs) in which we lay emphasis on the optical applications in the biological system. The detection of biological molecules such as DNA, protein and enzyme, the cell-based analysis and in vivo animal imaging are mainly discussed. 相似文献
88.
SHANG Jing ZHAO FengWei ZHU Tong & LI Jia State Key Joint Laboratory of Environmental Simulation Pollution Control College of Environmental Sciences Engineering Peking University Beijing China 《中国科学B辑(英文版)》2011,(1)
Perylene tetracarboxylic diimide (PTCDI),widely used in organic photovoltaic devices,is an n-type semiconductor with strong absorption in the visible-light spectrum.There has been almost no study of the PTCDI-sensitized TiO2 composite used to photocatalytically degrade pollutants.In this study,PTCDIand copper phthalocyanine tetrasulfonic acid (CuPcTs)-sensitized TiO2 composites were prepared using a hydrothermal method.The morphologies and structures of the two composites were characterized by X-ray diffrac... 相似文献
89.
LI YouJi CHEN Wei LI LeiYong & MA MingYuan College of Chemistry Chemical Engineering Jishou University Jishou China 《中国科学B辑(英文版)》2011,(3)
TiO2-coated carbon felt(TCF)composite catalysts have been prepared via a supercritical treatment of titanium tetraisopropoxide(TTIP)as the precursor.The physical properties of the catalysts were characterized by means of thermogravimetric and differential thermal analysis(TG–DTA),X-ray diffraction(XRD),fluorescence spectroscopy,scanning electron microscopy (SEM),and BET surface areas techniques.The photocatalytic activities of the materials were evaluated using the degradation of Congo red(CR)as a probe rea... 相似文献
90.
CHEN YuJin SHI XiaoLing CAO MaoSheng & ZHU ChunLing School of Materials Science Engineering Beijing Institute of Technology Beijing China Micro-Nano Technologies Research Center Hunan University Changsha College of Science Harbin Engineering University Harbin College of Material Science Chemical Engineering 《中国科学G辑(英文版)》2009,(7)
CdS/α-Fe2O3 hierarchical nanostructures, where the CdS nanorods grow irregularly on the side surface of α-Fe2O3 nanorods, were synthesized via a three-step process. The diameters and lengths of CdS nanorods can be tuned by changing the ethylenediamine (EDA) and Cd ion concentrations. The magnetic investigations by superconducting quantum interference device indicate that the hierarchical nanostructures have an Morin transition at lower temperature (230 K) than that of the single bulk α-Fe2O3 materials (263 ... 相似文献