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   102260篇
  免费   15017篇
  国内免费   11222篇
化学   70300篇
晶体学   1271篇
力学   6424篇
综合类   874篇
数学   12004篇
物理学   37626篇
  2024年   310篇
  2023年   1886篇
  2022年   3219篇
  2021年   3407篇
  2020年   3644篇
  2019年   3645篇
  2018年   3235篇
  2017年   2966篇
  2016年   4385篇
  2015年   4600篇
  2014年   5438篇
  2013年   7201篇
  2012年   8769篇
  2011年   8895篇
  2010年   6345篇
  2009年   6138篇
  2008年   6646篇
  2007年   5889篇
  2006年   5601篇
  2005年   4894篇
  2004年   3896篇
  2003年   3057篇
  2002年   2866篇
  2001年   2409篇
  2000年   2202篇
  1999年   2176篇
  1998年   1780篇
  1997年   1526篇
  1996年   1555篇
  1995年   1348篇
  1994年   1326篇
  1993年   1106篇
  1992年   955篇
  1991年   833篇
  1990年   688篇
  1989年   597篇
  1988年   445篇
  1987年   397篇
  1986年   353篇
  1985年   362篇
  1984年   238篇
  1983年   200篇
  1982年   172篇
  1981年   135篇
  1980年   105篇
  1979年   68篇
  1978年   67篇
  1976年   62篇
  1975年   67篇
  1973年   65篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
993.
994.
Taking a typical local and industry-orientated applied chemistry major as an example with focusing on the major changes in the form and content of the petrochemical industry, the way to reform the core curriculum system and teaching contents is presented. Based on the changing tendency of refinement of the petrochemical industry, a complete curriculum system with distinctive industry characteristics is set up according to the principles of the emerging engineering education (3E) with several reasonable suggestions. A new model for the construction of a 3E major in chemistry-related majors is suggested. It is a good reference for the construction of curriculum systems for other local and industry-orientated colleges who want to make 3E reform.  相似文献   
995.
996.
997.
A racemic glycidyl butyrate resolving strain, preliminarily identified as a Rhizopus sp., had been isolated from soil. Its extracellular lipase was found to enantioselectively hydrolyze the (S)-enantiomer of the chiral ester, with optimal activities at pH 5.3 and 42°C. Higher en antioselectivity of theenzyme was observed at lower temperatures, while the best anantioselectivity was obtained at pH 5.5–6.0, with an, E value (enantiomeric ratio) of 57.  相似文献   
998.
The syntheses, structure solutions, and physicochemical and catalytic characterizations of the novel zeolites SSZ-53 and SSZ-59 are described. SSZ-53 and SSZ-59 were synthesized under hydrothermal conditions with the [1-(4-fluorophenyl)cyclopentylmethyl]trimethyl ammonium cation and 1-[1-(4-chlorophenyl)cyclopentylmethyl]-1-methyl azocanium cation, respectively, as structure-directing agents. The framework topology of SSZ-53 was solved with the FOCUS method, and the structure of SSZ-59 was determined by model building. Rietveld refinement of synchrotron X-ray powder diffraction data confirms each proposed model. SSZ-53 and SSZ-59 each possess a one-dimensional channel system delimited by 14-membered rings. Results from transmission electron microscopy, electron diffraction, catalytic experiments (spaciousness index and constraint index tests), and argon and hydrocarbon adsorption experiments are consistent with the proposed structures.  相似文献   
999.
The equilibrium geometrical structures of small AlmFen clusters have been determined through ab initio calculation of the cluster total energy at the UB3LYP/Lanl2dz level. For dimers of iron and aluminum, the dissociation energies, the equilibrium atomic distances, and the vibrational frequencies were calculated. The agreement between calculations and experiments is reasonable. The ground stable geometrical structures of Fe4, FeAl3, Fe3Al and Fe2Al2 clusters favor three-dimension configurations, but Al4 tetramers are planar structures. The Al-rich tetramers are more stable than the other two composition tetramers. This is different from that of bulk alloys.  相似文献   
1000.
Ultraviolet absorption spectra and infrared absorption spectra of 5′-carboxy-2′-hydroxychalcone and eleven derivatives substituted at side benzene nucleus are measured to elucidate the spectroscopic effects of the 5′-carboxyl group in this series of compounds.  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