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   493072篇
  免费   6295篇
  国内免费   2211篇
化学   256058篇
晶体学   6074篇
力学   22762篇
综合类   68篇
数学   60199篇
物理学   156417篇
  2021年   4029篇
  2020年   4714篇
  2019年   5190篇
  2018年   6968篇
  2017年   7149篇
  2016年   10087篇
  2015年   6132篇
  2014年   9702篇
  2013年   22892篇
  2012年   18402篇
  2011年   22085篇
  2010年   16196篇
  2009年   15897篇
  2008年   20129篇
  2007年   20091篇
  2006年   18679篇
  2005年   16577篇
  2004年   15093篇
  2003年   13194篇
  2002年   12214篇
  2001年   14721篇
  2000年   10797篇
  1999年   8082篇
  1998年   6756篇
  1997年   6645篇
  1996年   6352篇
  1995年   5794篇
  1994年   5849篇
  1993年   5617篇
  1992年   6207篇
  1991年   6408篇
  1990年   6036篇
  1989年   5908篇
  1988年   5651篇
  1987年   5702篇
  1986年   5509篇
  1985年   7120篇
  1984年   7243篇
  1983年   6024篇
  1982年   6252篇
  1981年   5849篇
  1980年   5657篇
  1979年   6063篇
  1978年   6226篇
  1977年   6265篇
  1976年   6266篇
  1975年   5846篇
  1974年   5900篇
  1973年   6003篇
  1972年   4457篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Chen  C. Y.  Kao  C. L.  Huang  S. T.  Kuo  C. E.  Song  P. L.  Li  W. J.  Hsu  L. T.  Li  H. T. 《Chemistry of Natural Compounds》2022,58(1):107-109
Chemistry of Natural Compounds -  相似文献   
62.
Gawad  Dina A.  Elnaggar  Mai M.  Belal  Tarek S. 《Chromatographia》2022,85(7):617-628
Chromatographia - The present work deals with the optimization, validation and application of a versatile HPLC–DAD method for concurrent estimation of nine antimicrobials and proton pump...  相似文献   
63.
Photo-catalytic elimination of organic contaminants plays a significant role in wastewater treatment. Developing a highly efficient photo-catalyst is one of the leading research topic. Herein, we reported the fabrication of a novel nanoporous NiO@SiO2 photo-catalyst by a simple ion-exchange method to eliminate the reactive dyes. The synthesized NiO@SiO2 catalyst exhibited fast photo-degradation and excellent adsorption capability and could efficiently remove Red FN-3GL dye from wastewater, due to a high loading of NiO and a large specific surface area, abundant electron-withdrawing groups, as well as narrow bandgap energy. In addition, the NiO@SiO2 photo-catalyst also displayed a high capability to remove reactive dyes over a wide range of pH values (pH 3–9). The prominent adsorption and photo-degradation of dyes were strongly dependent on the surface charge of the catalyst and the generation of hydroxyl radicals (OH?) by the catalyst, respectively. Furthermore, the NiO@SiO2 photo-catalyst also exhibited excellent recyclability, thus demonstrating the feasibility of practical applications in industries. The strategy of covering the metal oxide to nanoporous silica is a promising method for developing active photo-catalysts and applying them in the wastewater treatments.  相似文献   
64.
Crystallography Reports - The molecular structure of 2-chloro-3-(1'-napthyl)-5,5-dimethyl-2- cyclohexenone was determined by single crystal X-ray diffraction. The compound crystallized in a...  相似文献   
65.
Statistical Inference for Stochastic Processes - The class of autoregressive (AR) processes is extensively used to model temporal dependence in observed time series. Such models are easily...  相似文献   
66.

The machining process is primarily used to remove material using cutting tools. Any variation in tool state affects the quality of a finished job and causes disturbances. So, a tool monitoring scheme (TMS) for categorization and supervision of failures has become the utmost priority. To respond, traditional TMS followed by the machine learning (ML) analysis is advocated in this paper. Classification in ML is supervised based learning method wherein the ML algorithm learn from the training data input fed to it and then employ this model to categorize the new datasets for precise prediction of a class and observation. In the current study, investigation on the single point cutting tool is carried out while turning a stainless steel (SS) workpeice on the manual lathe trainer. The vibrations developed during this activity are examined for failure-free and various failure states of a tool. The statistical modeling is then incorporated to trace vital signs from vibration signals. The multiple-binary-rule-based model for categorization is designed using the decision tree. Lastly, various tree-based algorithms are used for the categorization of tool conditions. The Random Forest offered the highest classification accuracy, i.e., 92.6%.

  相似文献   
67.
Premchand  V. P.  Balaram  Bipin  Mani  Ajith K.  Narayanan  M. D.  Sajith  A. S. 《Nonlinear dynamics》2022,110(1):573-588
Nonlinear Dynamics - Optimisation procedures for nonlinear vibrating systems are made cumbersome due to the fact that the regimes of periodic response are not known beforehand. Moreover, such...  相似文献   
68.
Radiophysics and Quantum Electronics - Under coupling, a large group of chaotic spiking–bursting oscillating neurons can undergo neuronal regularization. This aspect has been studied in...  相似文献   
69.
Chen  R. J.  Chen  W.  Kong  F. L. 《Analysis Mathematica》2022,48(1):19-28

Restricted testing conditions were considered recently. For the maximal operator, Hytönen, Li and Sawyer [8] first obtained parental testing condition. Later, they [9] showed that it suffices to restrict testing to doubling cubes. Chen and Lacey [3] gave a similar restricted testing condition. In our paper, we discuss a version of the latter in the multilinear setting.

  相似文献   
70.
Journal of Experimental and Theoretical Physics - The yields of alpha particles and neutrons from the promising 11B(p, 3α) fusion reaction and the reference 11B(p, n)11C nuclear reaction,...  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