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   462篇
  免费   30篇
  国内免费   13篇
化学   349篇
晶体学   5篇
力学   6篇
数学   29篇
物理学   116篇
  2024年   3篇
  2023年   10篇
  2022年   71篇
  2021年   60篇
  2020年   32篇
  2019年   30篇
  2018年   26篇
  2017年   18篇
  2016年   28篇
  2015年   16篇
  2014年   26篇
  2013年   27篇
  2012年   18篇
  2011年   25篇
  2010年   18篇
  2009年   10篇
  2008年   7篇
  2007年   11篇
  2006年   7篇
  2005年   4篇
  2004年   7篇
  2003年   2篇
  2002年   5篇
  2001年   3篇
  2000年   4篇
  1999年   2篇
  1994年   5篇
  1993年   3篇
  1992年   1篇
  1991年   3篇
  1990年   3篇
  1989年   3篇
  1988年   2篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
  1980年   2篇
  1976年   1篇
  1974年   1篇
  1973年   1篇
  1970年   1篇
  1967年   1篇
排序方式: 共有505条查询结果,搜索用时 0 毫秒
101.
The structures of 2‐[N‐(2‐chlorophenyl)carbamoyl]benzenesulfonamide and 2‐[N‐(4‐chlorophenyl)carbamoyl]benzenesulfonamide, both C13H11ClN2O3S, are stabilized by extensive intra‐ and intermolecular hydrogen bonds. In both structures, sulfonamide groups are hydrogen bonded via the N and O atoms and form chains of molecules. The carbamoyl groups are also hydrogen bonded, involving the O and N atoms, further strengthening the polymeric chains running along the c and a axes in the 2‐ and 4‐chloro derivatives, respectively. Carbamoylsulfonamide derivatives are novel compounds with a great potential for medicinal applications.  相似文献   
102.
Two series of Co and Ni based catalysts supported over commercial (ZrO2, CeO2, and Al2O3) nano supports were investigated for dry reforming of methane. The catalytic activity of both Co and Ni based catalysts were assessed at different reaction temperatures ranging from 500—800 °C; however, for stability the time on stream experiments were conducted at 700 °C for 6 h. Various techniques such as N2 adsorption‐desorption isotherm, temperature‐programmed reduction (H2‐TPR), temperature‐programmed desorption (CO2‐TPD), temperature‐programmed oxidation (TPO), X‐ray diffraction (XRD), thermogravimetric analysis (TGA) were applied for characterization of fresh and spent catalysts. The catalytic activity and stability tests clearly showed that the performance of catalyst is strongly dependent on type of active metal and support. Furthermore, active metal particle size and Lewis basicity are key factors which have significant influence on catalytic performance. The results indicated that Ni supported over nano ZrO2 exhibited highest activity among all tested catalysts due to its unique properties including thermal stability and reducibility. The minimum carbon deposition and thus relatively stable performance was observed in case of Co‐Al catalyst, since this catalyst has shown highest Lewis basicity.  相似文献   
103.
Journal of Thermal Analysis and Calorimetry - The aim of this study is to oversee the impact of various techniques on thermal performance of heat pipes and to comprehensively cover the progress...  相似文献   
104.
Graphene as a material for optoelectronic design applications has been significantly restricted owing to zero bandgap and non-compatible handling procedures compared with regular microelectronic ones. In this work, nitrogen-doped reduced graphene oxide (N-rGO) with tunable optical bandgap and enhanced electrical conductivity was synthesized via a microwave-assisted hydrothermal method. The properties of the synthesized N-rGO were determined using XPS, FTIR and Raman spectroscopy, UV/vis, as well as FESEM techniques. The UV/vis spectroscopic analysis confirmed the narrowness of the optical bandgap from 3.4 to 3.1, 2.5, and 2.2 eV in N-rGO samples, where N-rGO samples were synthesized with a nitrogen doping concentration of 2.80, 4.53, and 5.51 at.%. Besides, an enhanced n-type electrical conductivity in N-rGO was observed in Hall effect measurement. The observed tunable optoelectrical characteristics of N-rGO make it a suitable material for developing future optoelectronic devices at the nanoscale.  相似文献   
105.
Nanostructured ZnSe-graphene/TiO2 was synthesized by a hydrothermal-assisted approach. ZnSe-graphene/TiO2 exhibited favorable adsorption of rhodamine B, a wide wavelength absorption range, and efficien...  相似文献   
106.
Recently, the nanofluids report multidisciplinary applications in the various era of engineering like engine cooling, solar energy production, cooling of engineering devices, diesel generator performance etc. Owing to such novel applications, the aim of current communication is to report the significances of bio-convection for unsteady Eyring Powell nanofluid due to bidirectional oscillatory stretching surface. The enrollment of buoyancy forces and magnetic impact are worked out to inspect the stability and thermal on set of nanofluids. Heat transformation features are explored by utilizing thermal radiation. Further, the characteristics of chemical reaction and activation energy have been considered for physical significance. Unlike traditional approach, the governing equations are not altered into ordinary set of equation but only diminish the independent variables. This task makes the non-dimensional equations in highly complicated from which the convergent technique via HAM is successfully implemented. The physical outcomes of dominant variables on profiles of microorganisms, concentration, temperature, velocity and skin frictions are conferred graphically while local motile density, Sherwood and Nusselt numbers are deliberated through different tables. It is noted that the amplitude of bidirectional shear stresses and velocities periodically get increase for higher material parameter. This analysis emphasized that concentration distribution augments for rising values of activation energy variable, whereas conflicting situation occurs for temperature difference parameter. Moreover, motile microorganism's distributions are diminished by improved values of bio-convected Peclet and bio-convected Lewis numbers.  相似文献   
107.
Journal of Thermal Analysis and Calorimetry - Heat transportation advancement in liquid is a crucial work which can be easily obtained via utilization of hybrid nanoparticles. Therefore, main...  相似文献   
108.
109.
110.
In this article, common fixed point theorems for a pair of multivalued mappings satisfying a new Ciric-type rational F-contraction condition in complete dislocated metric spaces are established. An example is constructed to illustrate our results. An application to the system of integral equations is presented to support the usability of proved results. Our results combine, extend and infer several comparable results in the existing literature.  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