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   232253篇
  免费   3333篇
  国内免费   508篇
化学   127775篇
晶体学   3781篇
力学   8714篇
综合类   11篇
数学   24791篇
物理学   71022篇
  2020年   2155篇
  2019年   2201篇
  2018年   2619篇
  2017年   2699篇
  2016年   4351篇
  2015年   2895篇
  2014年   4328篇
  2013年   10801篇
  2012年   7829篇
  2011年   9592篇
  2010年   6535篇
  2009年   6353篇
  2008年   8700篇
  2007年   8562篇
  2006年   8034篇
  2005年   7207篇
  2004年   6449篇
  2003年   5860篇
  2002年   5608篇
  2001年   6707篇
  2000年   5153篇
  1999年   3870篇
  1998年   3073篇
  1997年   3010篇
  1996年   3007篇
  1995年   2802篇
  1994年   2710篇
  1993年   2627篇
  1992年   3208篇
  1991年   3009篇
  1990年   2972篇
  1989年   2942篇
  1988年   2975篇
  1987年   2975篇
  1986年   2826篇
  1985年   3671篇
  1984年   3664篇
  1983年   2922篇
  1982年   3041篇
  1981年   3112篇
  1980年   2853篇
  1979年   3153篇
  1978年   3166篇
  1977年   3274篇
  1976年   3072篇
  1975年   2802篇
  1974年   2736篇
  1973年   2703篇
  1972年   1811篇
  1968年   1828篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Russian Journal of General Chemistry - Aminophosphabetaines, i.e., isobutyl {[alkyl(dimethyl)ammonio]methyl}phosphonates with higher alkyl substituents at the nitrogen atom, were obtained by a...  相似文献   
2.
3.

The aim of this study is to develop and validate a sensitive and specific stability-indicating reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the quantitative determination of Sugammadex sodium together with its process and possible degradation impurities. The pKa value is 2.82. The chromatographic conditions have been optimized by the Hypersil Gold 250 mm X 4.6 mm, 3 µ RP-18 columns with gradient elution using a mobile phase composed of 0.1% phosphoric acid, acetonitrile, and methanol. The eluents were monitored at 205 nm with a flow rate of 1.0 mL/min with an injection volume of 20 µL. The optimized method produced symmetrical and sharp peaks with good separation between the process and degradation impurities. The forced degradation study was carried out under acid, base, oxidation, and thermal conditions to demonstrate the stability-indicating capability of the method. The method was validated as per the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) Q2 (R1) and showed excellent specificity, precision, linearity, accuracy, and robustness. The developed HPLC method was precise with a value of 0.25%. The relative standard deviation of accuracy represented by the recovery studies ranged between 89.5% and 104.6%. Linearity analyses indicated a correlation coefficient value of greater than 0.996 for Sugammadex and its known impurities. The LOD and LOQ values for Sugammadex ranged from 0.017% to 0.050%, and for its related impurities, they ranged from 0.015% to 0.055%. The stability of the analytical solution was evaluated and was stable for 75 h when stored at 5 °C. No chromatographic interference was observed during the degradation studies and also in the blank chromatogram.

  相似文献   
4.
Fan  K.  Lu  R. S.  Liang  K. K.  Hou  Z. C. 《High Energy Chemistry》2022,56(4):264-269
High Energy Chemistry - Modification of Polyvinylidene fluoride (PVDF) by radiation grafting is a research hotspot in recent years. In this study, the monomer 2-Hydroxyethyl methacrylate (HEMA) was...  相似文献   
5.
Journal of Applied Spectroscopy - Three simple, sensitive, precise, and rapid spectrophotometric methods are developed and optimized for the assay of vardenafil in pharmaceutical formulations. The...  相似文献   
6.
Russian Journal of General Chemistry - Tungstophosphatozincates with the Keggin anion structure Kt5[PW11O39Zn(H2O)]?nH2O, Kt = Rb+, Cs+, (CH3)4N+; (C2H5)4N+ were synthesized. Their...  相似文献   
7.
Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...  相似文献   
8.
Russian Journal of Organic Chemistry - A highly efficient green protocol has been proposed for the synthesis of symmetrical S-aryl arenesulfonothioates by irradiation of N-hydroxy arenesulfonamides...  相似文献   
9.
Optics and Spectroscopy - Optical investigations of crystals of solid solutions NdxGd1 – xCr3(BO3)4, 0.01 ≤ x ≤ 1, have been performed. Absorption spectra in the...  相似文献   
10.
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