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   145942篇
  免费   3187篇
  国内免费   400篇
化学   69588篇
晶体学   1146篇
力学   8484篇
数学   41305篇
物理学   29006篇
  2023年   566篇
  2022年   427篇
  2021年   752篇
  2020年   1048篇
  2019年   993篇
  2018年   11382篇
  2017年   11021篇
  2016年   8170篇
  2015年   2912篇
  2014年   2419篇
  2013年   4786篇
  2012年   8609篇
  2011年   15013篇
  2010年   8369篇
  2009年   8193篇
  2008年   10617篇
  2007年   12669篇
  2006年   4111篇
  2005年   4920篇
  2004年   4568篇
  2003年   4369篇
  2002年   3131篇
  2001年   1694篇
  2000年   1485篇
  1999年   1040篇
  1998年   851篇
  1997年   692篇
  1996年   930篇
  1995年   594篇
  1994年   606篇
  1993年   670篇
  1992年   640篇
  1991年   520篇
  1990年   486篇
  1989年   473篇
  1988年   415篇
  1987年   405篇
  1986年   379篇
  1985年   582篇
  1984年   520篇
  1983年   378篇
  1982年   467篇
  1981年   443篇
  1980年   389篇
  1979年   397篇
  1978年   362篇
  1976年   356篇
  1975年   325篇
  1974年   313篇
  1973年   345篇
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
71.
72.
73.
74.
75.
76.
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.  相似文献   
77.
Naphthalimide‐phthalimide derivatives (NDPDs) have been synthesized and combined with an iodonium salt, N‐vinylcarbazole, amine or 2,4,6‐tris(trichloromethyl)‐1,3,5‐triazine to produce reactive species (i.e., radicals and cations). These generated reactive species are capable of initiating the cationic polymerization of epoxides and/or the radical polymerization of acrylates upon exposure to very soft polychromatic visible lights or blue lights. Compared with the well‐known camphorquinone based systems used as references, the novel NDPD based combinations employed here demonstrate clearly higher efficiencies for the cationic polymerization of epoxides under air as well as the radical polymerization of acrylates. Remarkably, one of the NDPDs (i.e., NDPD2) based systems is characterized by an outstanding reactivity. The structure/reactivity/efficiency relationships of the investigated NDPDs were studied by fluorescence, cyclic voltammetry, laser flash photolysis, electron spin resonance spin trapping, and steady state photolysis techniques. The key parameters for their reactivity are provided. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 665–674  相似文献   
78.
79.
Thermal decarbonylation of the acyl compounds [Mn(CO)5(CORF)] (RF=CF3, CHF2, CH2CF3, CF2CH3) yielded the corresponding alkyl derivatives [Mn(CO)5(RF)], some of which have not been previously reported. The compounds were fully characterized by analytical and spectroscopic methods and by several single-crystal X-ray diffraction studies. The solution-phase IR characterization in the CO stretching region, with the assistance of DFT calculations, has allowed the assignment of several weak bands to vibrations of the [Mn(12CO)4(eq-13CO)(RF)] and [Mn(12CO)4(ax-13CO)(RF)] isotopomers and a ranking of the RF donor power in the order CF3<CHF2<CH2CF3≈CF2CH3. The homolytic Mn−RF bond cleavage in [Mn(CO)5(RF)] at various temperatures under saturation conditions with trapping of the generated RF radicals by excess tris(trimethylsilyl)silane yielded activation parameters ΔH and ΔS that are believed to represent close estimates of the homolytic bond dissociation thermodynamic parameters. These values are in close agreement with those calculated in a recent DFT study (J. Organomet. Chem. 2018 , 864, 12–18). The ability of these complexes to undergo homolytic Mn−RF bond cleavage was further demonstrated by the observation that [Mn(CO)5(CF3)] (the compound with the strongest Mn−RF bond) initiated the radical polymerization of vinylidene fluoride (CH2=CF2) to produce poly(vinylidene fluoride) in good yields by either thermal (100 °C) or photochemical (UV or visible light) activation.  相似文献   
80.
Journal of Solid State Electrochemistry - A novel material was developed using sol-gel chemistry and an environmental-friendly grafting process of clay nanoparticles. In a previous work of our...  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