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   454515篇
  免费   4066篇
  国内免费   1099篇
化学   235574篇
晶体学   6696篇
力学   18930篇
综合类   13篇
数学   50329篇
物理学   148138篇
  2021年   4125篇
  2020年   4726篇
  2019年   5019篇
  2018年   5905篇
  2017年   5779篇
  2016年   9068篇
  2015年   5713篇
  2014年   8727篇
  2013年   20418篇
  2012年   15888篇
  2011年   19550篇
  2010年   13695篇
  2009年   13562篇
  2008年   17929篇
  2007年   17907篇
  2006年   16649篇
  2005年   14894篇
  2004年   13897篇
  2003年   12306篇
  2002年   12308篇
  2001年   13956篇
  2000年   10526篇
  1999年   8401篇
  1998年   6880篇
  1997年   6638篇
  1996年   6372篇
  1995年   5742篇
  1994年   5688篇
  1993年   5440篇
  1992年   6118篇
  1991年   6207篇
  1990年   5996篇
  1989年   5863篇
  1988年   5815篇
  1987年   5680篇
  1986年   5444篇
  1985年   6904篇
  1984年   7053篇
  1983年   5622篇
  1982年   5706篇
  1981年   5685篇
  1980年   5287篇
  1979年   5670篇
  1978年   5802篇
  1977年   5721篇
  1976年   5649篇
  1975年   5197篇
  1974年   5166篇
  1973年   5162篇
  1972年   3719篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
The concentrations of toxic elements (arsenic, cadmium, lead) in commercial algae Saccharina japonica and Ahnfeltia tobuchiensis from different habitats of the Sea of Japan have been determined. Bioaccumulation of heavy metals has been analyzed with respect to the habitat and growth conditions. The lead content of Sascharina japonica from all habitats and arsenic content of the same alga species from the Ol’ga Bay, Kievka Bay, and Tatar Strait have been found to exceed maximum permissible levels. Increased lead concentrations have been detected in Ahnfeltia tobuchiensis. Samples of Ahnfeltia tobuchiensis collected from the bottom layer contain more toxic elements than those from the upper layer.  相似文献   
23.
Nickel nanoparticles were deposited on the surface of highly oriented pyrolytical graphite by laser electrodispersion and precipitation from a solution of reverse micelles. The particles were studied using scanning tunneling microscopy and spectroscopy as well as Auger spectroscopy. The elemental composition of the nanoparticles and specific features of the electronic structure of their surface were determined. Adsorption of molecular hydrogen was also studied.  相似文献   
24.
An experimental ultraviolet (UV) polymerizable hybrid organic–inorganic protective coating, mainly intended for the surface protection of porous calcareous stone substrates, has been recently proposed and patented. The hybrid product evidenced an extraordinary hydrophobicity character, able to guarantee a high protection of the stone against water actions, as well as a high traspirability. Furthermore, it is able to equal the performance of commercial available coatings, with the important adjunctive advantage to be free solvent. The application of this product involves the use of a “dual curing” treatment, necessary to harden the coating applied on the substrate, representing this latter a technological limit. The dual curing treatment consists of 6 hr of exposure to a UV‐lamp plus 1 hr at 140°C in oven. In order to avoid this procedure, not easy to realize in situ, two different modifications of the composition of the hybrid product are proposed in this paper. The first one allows the photopolymerization of the hybrid coating only by sunlight exposure. The second one, even though requiring a UV exposure to photo‐polymerize the coating, does not need the subsequent thermal treatment at 140°C. Several experimental characterizations were performed on the newly developed hybrid products, in order to select an optimal composition for the formulations. The selected innovative products were, finally, applied on a calcareous stone substrate, typical of Apulia Region (Pietra Leccese, PL). Both coatings exhibit excellent water‐repellent action and a slight variation of the natural stone color. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
25.
26.
27.
Specific features of preparation of paint-and-varnish nickel–polymer coatings by joint cathodic electrodeposition of an amine-containing oligomeric electrolyte and nickel were studied. The coatings obtained exhibit layer-by-layer heterogeneity, with the lowest layer constituted by an intermetallic compound of nickel with iron. The coatings are characterized by higher degree of cross-linking compared to the polymer coatings without nickel. A paint-and-varnish formulation based on a nickel–polymer film-forming agent was developed for electrodeposition of corrosion- and wear-resistant coatings.  相似文献   
28.
29.
30.
Guo  L.  Zhang  S. T.  Lv  T. M.  Feng  W. J. 《Research on Chemical Intermediates》2015,41(6):3729-3742
Research on Chemical Intermediates - The electronic parameters of two azole molecules, namely benzoxazole (BOX) and benzothiazole (BTH), have been studied using DFT/B3LYP, MP2, and HF methods with...  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