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   835篇
  免费   18篇
  国内免费   6篇
化学   394篇
晶体学   2篇
力学   23篇
数学   93篇
物理学   224篇
无线电   123篇
  2023年   12篇
  2022年   15篇
  2021年   7篇
  2020年   15篇
  2019年   16篇
  2018年   16篇
  2017年   9篇
  2016年   29篇
  2015年   15篇
  2014年   25篇
  2013年   35篇
  2012年   38篇
  2011年   39篇
  2010年   32篇
  2009年   31篇
  2008年   46篇
  2007年   43篇
  2006年   33篇
  2005年   30篇
  2004年   23篇
  2003年   21篇
  2002年   16篇
  2001年   12篇
  2000年   20篇
  1999年   14篇
  1998年   12篇
  1997年   19篇
  1996年   10篇
  1995年   11篇
  1994年   18篇
  1993年   13篇
  1992年   10篇
  1991年   12篇
  1990年   5篇
  1989年   6篇
  1988年   6篇
  1987年   6篇
  1986年   15篇
  1985年   11篇
  1984年   15篇
  1983年   10篇
  1982年   6篇
  1981年   11篇
  1980年   12篇
  1978年   6篇
  1977年   7篇
  1976年   6篇
  1972年   4篇
  1971年   6篇
  1970年   4篇
排序方式: 共有859条查询结果,搜索用时 265 毫秒
51.
The present study investigates the effect of hybrid fillers such as graphene nanoplatelets (GnPs) and Titanium di-oxide (TiO2) in polypropylene (PP) composites on the mechanical properties. The compatibilizing agent of Maleic anhydride grafted polypropylene (MAPP) are used in the polypropylene based composites to increase the interfacial adhesion between matrix and fillers. The experiments are designed according to L16 orthogonal array (OA) based design of experiments (DOE). The parameters selected for this study are GnPs, TiO2 and MAPP with four different levels are used.By using Orthogonal array and Taguchi based experimental design, the performance characteristics of tensile modulus, tensile strength, elongation at break and toughness can be analyzed with more objective through a small set of experiments.Taguchi based analysis are used to find out the optimal parameters to maximize the tensile properties for the GnPs and TiO2 reinforced PP hybrid composites. Further, analysis of variance (ANOVA) is investigated to identify the most significant parameters which influence the mechanical properties.From the analysis it was found that the optimal parameters of 3 ?wt% GnPs, 2 ?wt% TiO2 and 6 ?wt% MAPP for maximum tensile modulus and tensile strength. The most significant parameter for tensile modulus and tensile strength is GnPs followed by TiO2 and MAPP according to ANOVA analysis.  相似文献   
52.
Journal of Radioanalytical and Nuclear Chemistry - Efficient and selective extraction of 137Cs and 90Sr from high level liquid waste (HLLW) is of utmost importance in the back end nuclear fuel...  相似文献   
53.
The in situ Grignard Metalation Method (iGMM) is a straightforward one-pot procedure to quickly produce multigram amounts of Hauser bases R2N-MgBr which are valuable and vastly used metalation reagents and novel electrolytes for magnesium batteries. During addition of bromoethane to a suspension of Mg metal and secondary amine at room temperature in an ethereal solvent, a smooth reaction yields R2N-MgBr under evolution of ethane within a few hours. A Schlenk equilibrium is operative, interconverting the Hauser bases into their solvated homoleptic congeners Mg(NR2)2 and MgBr2 depending on the solvent. Scope and preconditions are studied, and side reactions limiting the yield have been investigated. DOSY NMR experiments and X-ray crystal structures of characteristic examples clarify aggregation in solution and the solid state.  相似文献   
54.
55.
Stereoselective and temporally controlled supramolecular polymerizations are ubiquitous in nature and are desirable attributes for the design of chiral, well-defined functional materials. Kinetically controlled, living supramolecular polymerization (LSP) has emerged recently for the synthesis of supramolecular polymers with controlled length and narrow dispersity. On the other hand, stringent design requirements for chiral-discriminating monomers precludes the stereoselective control of the supramolecular polymer structure. Herein, a synergetic stereo- and structural control of supramolecular polymerization by the realization of an unprecedented stereoselective seed-induced LSP is reported. Homochiral and seeded growth is demonstrated with bischromophoric naphthalene diimide (NDI) enantiomers with a chiral binaphthyl amine core, exhibiting strong self-recognition abilities and pathway complexity.  相似文献   
56.
Journal of Radioanalytical and Nuclear Chemistry - The speciation of iodine in environment must be known in order to properly assess its geological fate and to study potential remediation materials...  相似文献   
57.
58.
59.
A Kerr metric describing a rotating black hole is obtained on the three brane in a five-dimensional Randall-Sundrum brane world by considering a rotating five-dimensional black string in the bulk. We examine the causal structure of this space-time through the geodesic equations.  相似文献   
60.
A single step synthesis of 2-deaminoactinomycin D ( 3a ) and 2-deamino-2-nitroactinomycin D ( 2a ) arising from actinomycin D ( 1a, AMD ) is reported. Structural confirmation was made by nmr, ir and chemical conversion to known materials.  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