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   2762篇
  免费   103篇
  国内免费   33篇
化学   2021篇
晶体学   35篇
力学   101篇
综合类   3篇
数学   174篇
物理学   564篇
  2024年   13篇
  2023年   23篇
  2022年   129篇
  2021年   183篇
  2020年   85篇
  2019年   90篇
  2018年   107篇
  2017年   64篇
  2016年   138篇
  2015年   105篇
  2014年   119篇
  2013年   221篇
  2012年   217篇
  2011年   227篇
  2010年   130篇
  2009年   107篇
  2008年   100篇
  2007年   96篇
  2006年   86篇
  2005年   69篇
  2004年   55篇
  2003年   57篇
  2002年   43篇
  2001年   25篇
  2000年   27篇
  1999年   18篇
  1998年   12篇
  1997年   14篇
  1996年   15篇
  1995年   8篇
  1994年   15篇
  1993年   18篇
  1992年   14篇
  1991年   17篇
  1990年   12篇
  1989年   14篇
  1988年   16篇
  1987年   12篇
  1986年   23篇
  1985年   20篇
  1984年   15篇
  1983年   10篇
  1982年   17篇
  1981年   13篇
  1980年   15篇
  1979年   12篇
  1977年   12篇
  1976年   12篇
  1975年   8篇
  1974年   5篇
排序方式: 共有2898条查询结果,搜索用时 15 毫秒
71.
72.
Cellulose - This present work evaluated the influence of oil palm frond cellulose nanocrystal (OPF-CNC) as a nanofiller to improve the barrier protection of the epoxy-Zn coating to lessen the...  相似文献   
73.
Benzoyl peroxide has been used as a mild and efficient reagent for the preparation of benzoyl ester of oxime in moderate to good yields.  相似文献   
74.
The reaction of different mercapto substituted heterocycles with o,o-dialkyl chlorphosphate or thiophosphates, gave the corresponding S- and N- alkylated derivatives instead of the expected phosphorylated products.  相似文献   
75.
Journal of Solid State Electrochemistry - Polypyrrole-Zr(IV) phosphate (PPyZP) composite cation exchange material was synthesized by chemical oxidative polymerization of pyrrole with the help of...  相似文献   
76.
In this paper, we suggest and analyze a Krasnoselski-Mann type iterative method to approximate a common element of solution sets of a hierarchical fixed point problem for nonexpansive mappings and a split mixed equilibrium problem. We prove that sequences generated by the proposed iterative method converge weakly to a common element of solution sets of these problems. Further, we derive some consequences from our main result. Furthermore, we extend the considered iterative method to a split monotone variational inclusion problem and deduce some consequences. Finally, we give a numerical example to justify the main result. The method and results presented in this paper generalize and unify the corresponding known results in this area.  相似文献   
77.
This paper reports a study on the effect of Al2O3 nanoparticles on the adhesion strength of steel-glass/epoxy composite joints bonded by a two-component structural acrylic adhesive. The addition of Al2O3 nanoparticles to the two-component acrylic adhesive led to a remarkable enhancement in the shear and tensile strength of the composite joints. The shear and tensile strength of the adhesive joints increased by addition of Al2O3 up to 1.5 wt%, which decreased by further addition of the nanofiller. Introduction of the nanoparticles caused a reduction in the peel strength of the joints. DSC analysis revealed that the glass transition temperature (Tg) of the adhesives rose by increasing the nanofiller content. The advancing water contact angle was decreased for adhesives containing nanoparticles. SEM micrographs indicated good dispersions of the Al2O3 nanoparticles within the acrylic matrix in the specimens with up to 1.5 wt% Al2O3 and revealed that addition of nanoparticles altered the fracture morphology from smooth to rough fracture surfaces.  相似文献   
78.
Gene silencing is one of the limiting factors for transgene expression in plants. But the plant viruses have learnt to suppress gene silencing by encoding the protein(s), called RNA silencing suppressor(s) (RSS). Hence, these proteins could be used to overcome the limitation for transgene expression. The RNAi suppressors, namely HC-Pro and P19, have been shown to enhance the transgene expression but other RSS proteins have not been screened for similar role. Moreover, none of RSSs from the DNA viruses are known for enhancing the expression of transgenes. The Mungbean Yellow Mosaic India Virus (MYMIV) belonging to the genus Begomovirus within the family of Geminiviridae encodes an RSS called the AC2 protein. Here, we used AC2 to elevate the expression of the transgenes. Upon introduction of MYMIV-AC2 in the silenced GFP transgenic tobacco lines, by either genetic hybridisation or transgenesis, the GFP expression was enhanced several fold in F1 and T0 lines. The GFP-siRNA levels were much reduced in F1 and T0 lines compared with those of the initial parental silenced lines. The enhanced GFP expression was also observed at the cellular level. This approach was also successful in enhancing the expression of another transgene, namely topoisomeraseII.  相似文献   
79.
80.
Cold expansion is a useful process for imposing compressive residual stresses around the holes in riveted and bolted connections. These stresses increase the fatigue life of holed parts. Distribution and amount of exerted residual stress dependent on various parameters as material, distance of adjacent holes, hole diameter, cold expansion ratio and plate thickness. In this study, experimental and numerical results for two different aluminum alloys and various holes distances are investigated and compared. Effects of mentioned parameters on the residual stress are studied.  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