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   280672篇
  免费   12067篇
  国内免费   2143篇
化学   170506篇
晶体学   4713篇
力学   11158篇
综合类   20篇
数学   25498篇
物理学   82987篇
  2021年   2019篇
  2020年   3305篇
  2019年   4788篇
  2018年   3710篇
  2017年   3408篇
  2016年   7490篇
  2015年   6068篇
  2014年   7670篇
  2013年   14995篇
  2012年   11174篇
  2011年   12530篇
  2010年   10103篇
  2009年   10064篇
  2008年   11610篇
  2007年   10752篇
  2006年   9953篇
  2005年   9220篇
  2004年   8354篇
  2003年   7655篇
  2002年   7992篇
  2001年   9574篇
  2000年   7417篇
  1999年   4989篇
  1998年   3655篇
  1997年   3595篇
  1996年   3314篇
  1995年   3080篇
  1994年   2885篇
  1993年   2652篇
  1992年   3509篇
  1991年   3408篇
  1990年   3268篇
  1989年   3192篇
  1988年   3217篇
  1987年   3237篇
  1986年   3031篇
  1985年   3948篇
  1984年   3941篇
  1983年   3024篇
  1982年   3155篇
  1981年   3188篇
  1980年   2914篇
  1979年   3347篇
  1978年   3371篇
  1977年   3493篇
  1976年   3280篇
  1975年   2961篇
  1974年   2938篇
  1973年   2840篇
  1972年   1908篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Journal of Experimental and Theoretical Physics - Dzyaloshinskii–Moriya interaction, DMI in short, represents an antisymmetric type of magnetic interactions that favor orthogonal orientation...  相似文献   
2.
3.
Kinetics and Catalysis - The catalytic properties of a nickel phosphide catalyst supported on silica gel in the reductive amination of carbonyl compounds were studied in a flow reactor using...  相似文献   
4.
Yang  T. L.  Kao  C. L.  Kuo  C. E.  Yeh  H. C.  Li  W. J.  Li  H. T.  Chen  C. Y. 《Chemistry of Natural Compounds》2022,58(5):825-827
Chemistry of Natural Compounds - A novel bibenzyl derivative, hydrangchinenin (1), was isolated from the stems of Hydrangea chinensis Maxim. (Hydrangeaceae). Its structure was determined on the...  相似文献   
5.
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   
6.
7.

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   
8.
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   
9.
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   
10.
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   
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