首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1494篇
  免费   90篇
  国内免费   27篇
化学   1248篇
晶体学   12篇
力学   31篇
数学   99篇
物理学   221篇
  2024年   3篇
  2023年   14篇
  2022年   59篇
  2021年   69篇
  2020年   87篇
  2019年   87篇
  2018年   124篇
  2017年   86篇
  2016年   95篇
  2015年   66篇
  2014年   107篇
  2013年   147篇
  2012年   137篇
  2011年   123篇
  2010年   86篇
  2009年   60篇
  2008年   71篇
  2007年   54篇
  2006年   26篇
  2005年   35篇
  2004年   24篇
  2003年   15篇
  2002年   3篇
  2001年   5篇
  2000年   5篇
  1999年   4篇
  1998年   3篇
  1997年   3篇
  1996年   2篇
  1995年   1篇
  1994年   1篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1984年   1篇
  1976年   1篇
排序方式: 共有1611条查询结果,搜索用时 15 毫秒
21.
The hydrodistilled oils from the aerial parts of Ferula latisecta and Mozaffariania insignis, which is endemic to Iran, were analyzed by GC and GC/MS. (Z)-Ocimenone (32.4%), (E)-ocimenone (20.3%), and cis-pinocarvone (11.4%) were the main components among the 22 constituents characterized in the oil of F. latisecta, representing 87.7% of the total components detected. Twenty-five compounds were identified in the oil of M. insignis, representing 99.0% of the total oil, with octyl acetate (41.1%), β-pinene (30.3%), and α-pinene (23.9%) as the main constituents. The essential oils were examined for their potential antimicrobial activities. Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 561–563, November–December, 2006.  相似文献   
22.
Nitrogen doped nano porous graphene was used as an efficient sorbent in solid‐phase extraction process for simultaneous separation and pre‐concentration of metal ions lead (II), cadmium(II), and chromium(III)) in biological samples. Ultrasonic assisted in‐syringe dispersive micro solid phase extraction coupled with micro sampling atomic absorption spectrometry was utilized for the determination of metal ions. Nitrogen doped nano porous graphene was synthesized as a nano sorbent by chemical vapour deposition method. Methane and aniline were used as carbon and nitrogen sources. The characterization of sorbent was performed by field emission scanning electron microscope, transmission electron microscopy, atomic force microscope, fourier transform infrared, chemical element analysis and raman analysis. Effective parameters on the extraction efficiency such as pH, sorbent dosage, eluent volume and eluent concentration were optimized by central composite design and desirability function. Experimental results indicate that the optimal conditions for this extraction were pH = 6.4, 1.42 mg of sorbent, 100 μL of eluent, and 0.84 mol L‐1 of eluent concentration. The detection limits are as low as 1.5, 0.3 and 0.9 μg L‐1 for lead, cadmium, and chromium, respectively. The intra‐day precisions were 3.6, 4.38 and 2.94 and Inter‐day precision were 4.83, 5.26 and 4.52 for lead, cadmium, and chromium, respectively. Method performance was investigated by determination of mentioned heavy metals in complicated biological matrixes such as human plasma, urine and saliva samples with good recoveries.  相似文献   
23.
Microchimica Acta - Graphene oxide nanosheets were modified with magnetite nanoparticles, and a hyperbranched polyamidoamine dendrimer was then covalently attached to their surface. The resulting...  相似文献   
24.
In this work, we report a facile hydrothermal method for the preparation of three dimensional hollow ZnS nanostructures, using Zinc bis(salicyle aldehitato), Zn(Sal)2, thioacetamide (TAA) and thioglycolic acid (TGA) as Zn2+, sulfur source and capping agent, respectively. The ZnS solid and hollow sphere was produced from the self-assembly of nanoparticles with diameters of 11 ± 2 nm with TGA and TGA, TAA, respectively. Furthermore, with changing zinc precursor from Zn(Sal)2 to zinc acetate [Zn(OAC)2], ZnS nanorods were obtained. The products were characterized by XRD, SEM, TEM, selected area electron diffraction, and FT-IR spectra. The influence of surfactant (Polyethylene glycol) on the morphology of the products was also investigated. Possible formation mechanism and optical properties of these architectures were also reported.  相似文献   
25.
26.
27.
28.
A simple and green protocol, developed utilizing an efficient, heterogeneous and recyclable catalyst, i.e. zinc oxide nanoparticles (ZnO NPs)-mediated synthesis of N-arylhomophthalimides and benzannelated isoquinolinones, is reported. The structures of the desired products were characterized by FTIR, 1H NMR, 13C NMR, and HRMS techniques. The ZnO NPs exhibited excellent catalytic activity and the proposed methodology is capable of providing the desired products in good yield and purity.  相似文献   
29.
30.
Catalytic one‐pot condensation of benzil, aldehyde and ammonium acetate have been successfully carried out using 2‐hydroxyethylammonium formate (HEAF) grafted on a magnetic nanoparticles as a new heterogeneous catalyst. The as‐prepared catalyst was characterized by FT‐IR, TEM, FESEM, VSM, TGA and XRD. This catalyst indicated significant advantages, such as excellent yields, shorter reaction time, reusability of the catalyst and easy workup process.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号