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   3661篇
  免费   576篇
  国内免费   451篇
化学   2815篇
晶体学   26篇
力学   176篇
综合类   34篇
数学   308篇
物理学   1329篇
  2024年   7篇
  2023年   82篇
  2022年   102篇
  2021年   91篇
  2020年   134篇
  2019年   138篇
  2018年   111篇
  2017年   107篇
  2016年   154篇
  2015年   153篇
  2014年   202篇
  2013年   281篇
  2012年   361篇
  2011年   392篇
  2010年   245篇
  2009年   218篇
  2008年   273篇
  2007年   246篇
  2006年   210篇
  2005年   167篇
  2004年   129篇
  2003年   95篇
  2002年   91篇
  2001年   83篇
  2000年   60篇
  1999年   64篇
  1998年   61篇
  1997年   59篇
  1996年   67篇
  1995年   74篇
  1994年   39篇
  1993年   25篇
  1992年   35篇
  1991年   30篇
  1990年   17篇
  1989年   16篇
  1988年   15篇
  1987年   6篇
  1986年   8篇
  1985年   10篇
  1984年   5篇
  1983年   3篇
  1982年   6篇
  1981年   7篇
  1980年   1篇
  1979年   4篇
  1974年   1篇
  1940年   1篇
  1902年   1篇
  1898年   1篇
排序方式: 共有4688条查询结果,搜索用时 31 毫秒
101.
CO and formaldehyde(HCHO)oxidation reactions were investigated over mesoporous Ag/Co3O4 catalysts prepared by one-pot(OP)and impregnation(IM)methods.It was found that the one-pot method was superior to the impregnation method for synthesizing Ag/Co3O4 catalysts with high activity for both reactions.It was also found that the catalytic behavior of mesoporous Co3O4 and Ag/Co3O4 catalysts for the both reactions was different.And the addition of silver on mesoporous Co3O4 did not always enhance the catalytic activity of final catalyst for CO oxidation at room temperature(20 C),but could significantly improve the catalytic activity of final catalyst for HCHO oxidation at low temperature(90 C).The high surface area,uniform pore structure and the pretty good dispersion degree of the silver particle should be responsible for the excellent low-temperature CO oxidation activity.However,for HCHO oxidation,the addition of silver played an important role in the activity enhancement.And the silver particle size and the reducibility of Co3O4 should be indispensable for the high activity of HCHO oxidation at low temperature.  相似文献   
102.
Tetrathiatriarylmethyl (TAM, trityl) radicals have found wide applications as spin probes/labels for EPR spectroscopy and imaging, and as polarizing agents for dynamic nuclear polarization. The high hydrophilicity of TAM radicals is essential for their biomedical applications. However, the synthesis of hydrophilic TAM radicals (e.g., OX063) is extremely challenging and has only been reported in the patent literature, to date. Herein, an efficient synthesis of a highly water-soluble TAM radical bis(8-carboxyl-2,2,6,6-tetramethylbenzo[1,2-d:4,5-d′]bis([1,3]dithiol-4-yl)-mono-(8-carboxyl-2,2,6,6-tetrakis(2-hydroxyethyl)benzo[1,2-d:4,5-d′]bis([1,3]dithiol-4-yl)methyl (TFO), which contains four additional hydroxylethyl groups, relative to the Finland trityl radical CT-03, is reported. Similar to OX063, TFO exhibits excellent properties, including high water solubility in phosphate buffer, low log P, low pKa, long relaxation times, and negligible binding with bovine serum albumin. On the other hand, TFO has a sharper EPR line and higher O2 sensitivity than those of OX063. Therefore, in combination with its facile synthesis, TFO should find wide applications in magnetic resonance related fields and this synthetic approach would shed new light on the synthesis of other hydrophilic TAM radicals.  相似文献   
103.
详细介绍了高温超导双饼线圈的加工工艺和流程,针对绕制时带材弯曲形变使临界电流退化的技术难点,重点阐述了其解决方法。在液氮温度、自场环境下对采用该加工工艺制作的YBCO双饼线圈及Bi2223/Ag双饼线圈进行低温实验,测试其V-I特性曲线。实验结果表明:该工艺制作的双饼线圈性能良好,工艺安全可靠,是合适的。同时,实验测量数据也为线圈在磁体中的进一步应用提供了可靠依据。  相似文献   
104.
A facile and simple catalyst‐free protocol has been developed for the condensation of 1,2‐diketones with aromatic 1,2‐diamines in polyethylene glycol (PEG), providing quinoxaline derivatives in good yields. The important features of the methodology are broad substrates scope, simple workup, catalyst free, environmentally benign, and no requirement for metal catalysts. It is noteworthy that the cyclization reaction of 1,2‐diketones with aliphatic 1,2‐diamines is also conducted smoothly to afford pyrazines in good yields under the standard conditions. In addition, PEG could be recovered easily and was reused without evident loss in activity  相似文献   
105.
106.
107.
108.
109.
Here we reported the radiolabeling and evaluation of a novel 131I-radiolabeled quercetin for the treatment of dedifferentiated thyroid cancers. The human thyroid cancer cell lines (FTC-133, TT and DRO) experienced much higher uptake of 131I-quercetin as compared to the free 131I. And the proliferation inhibition rate of 131I-quercetin on in vitro DRO cell line was 86.87 ± 7.15%. Biodistribution and SPECT analysis demonstrated that the injected radioactivity mainly accumulated in tumors. The tumor volume in the treatment group was dramatically inhibited in comparison with the control group.  相似文献   
110.
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