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   300350篇
  免费   2289篇
  国内免费   519篇
化学   143864篇
晶体学   5023篇
力学   14815篇
综合类   11篇
数学   43792篇
物理学   95653篇
  2020年   1734篇
  2019年   1934篇
  2018年   10867篇
  2017年   11755篇
  2016年   7533篇
  2015年   3095篇
  2014年   3729篇
  2013年   9358篇
  2012年   10838篇
  2011年   20403篇
  2010年   12750篇
  2009年   12820篇
  2008年   17605篇
  2007年   21093篇
  2006年   6998篇
  2005年   12835篇
  2004年   8968篇
  2003年   8503篇
  2002年   6328篇
  2001年   6339篇
  2000年   4965篇
  1999年   3591篇
  1998年   2828篇
  1997年   2743篇
  1996年   2787篇
  1995年   2564篇
  1994年   2444篇
  1993年   2258篇
  1992年   2916篇
  1991年   2828篇
  1990年   2769篇
  1989年   2787篇
  1988年   2819篇
  1987年   2825篇
  1986年   2683篇
  1985年   3431篇
  1984年   3448篇
  1983年   2716篇
  1982年   2815篇
  1981年   2883篇
  1980年   2637篇
  1979年   2993篇
  1978年   2993篇
  1977年   3023篇
  1976年   2892篇
  1975年   2623篇
  1974年   2579篇
  1973年   2574篇
  1972年   1755篇
  1968年   1806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