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   239947篇
  免费   3461篇
  国内免费   660篇
化学   132536篇
晶体学   3881篇
力学   8998篇
综合类   16篇
数学   25419篇
物理学   73218篇
  2020年   2218篇
  2019年   2296篇
  2018年   2691篇
  2017年   2808篇
  2016年   4495篇
  2015年   2931篇
  2014年   4396篇
  2013年   10818篇
  2012年   8138篇
  2011年   9779篇
  2010年   6901篇
  2009年   6672篇
  2008年   8805篇
  2007年   8572篇
  2006年   8171篇
  2005年   7407篇
  2004年   6703篇
  2003年   6049篇
  2002年   5717篇
  2001年   6896篇
  2000年   5267篇
  1999年   3988篇
  1998年   3194篇
  1997年   3098篇
  1996年   3118篇
  1995年   2906篇
  1994年   2807篇
  1993年   2689篇
  1992年   3358篇
  1991年   3081篇
  1990年   3037篇
  1989年   3059篇
  1988年   3075篇
  1987年   3102篇
  1986年   2924篇
  1985年   3766篇
  1984年   3772篇
  1983年   2957篇
  1982年   3104篇
  1981年   3153篇
  1980年   2910篇
  1979年   3230篇
  1978年   3195篇
  1977年   3322篇
  1976年   3136篇
  1975年   2858篇
  1974年   2812篇
  1973年   2734篇
  1968年   1934篇
  1967年   2035篇
排序方式: 共有10000条查询结果,搜索用时 62 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.
Journal of Optimization Theory and Applications - We consider a distributionally robust formulation of stochastic optimization problems arising in statistical learning, where robustness is with...  相似文献   
7.
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   
8.
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   
9.
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   
10.
Differential Equations - Galathea traps for confining plasma in a magnetic field created by current-carrying conductors immersed in the plasma volume constitute a promising class of objects for...  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