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   51610篇
  免费   4614篇
  国内免费   2420篇
化学   35983篇
晶体学   479篇
力学   1877篇
综合类   187篇
数学   6379篇
物理学   13739篇
  2023年   653篇
  2022年   604篇
  2021年   1013篇
  2020年   1327篇
  2019年   1271篇
  2018年   1349篇
  2017年   1319篇
  2016年   2156篇
  2015年   1921篇
  2014年   2059篇
  2013年   3517篇
  2012年   3999篇
  2011年   4273篇
  2010年   2611篇
  2009年   2338篇
  2008年   3387篇
  2007年   3243篇
  2006年   2865篇
  2005年   2480篇
  2004年   2001篇
  2003年   1568篇
  2002年   1409篇
  2001年   1091篇
  2000年   981篇
  1999年   870篇
  1998年   687篇
  1997年   621篇
  1996年   777篇
  1995年   581篇
  1994年   584篇
  1993年   532篇
  1992年   484篇
  1991年   380篇
  1990年   303篇
  1989年   249篇
  1988年   239篇
  1987年   218篇
  1986年   209篇
  1985年   262篇
  1984年   198篇
  1983年   167篇
  1982年   142篇
  1981年   127篇
  1980年   107篇
  1979年   108篇
  1978年   92篇
  1977年   85篇
  1976年   81篇
  1975年   77篇
  1973年   89篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
This work demonstrates the analytical applicability of single ion-selective membranes (ISMs) and potentiometric sensor array to distinguish and detect cathinone derivatives. Potentiometric data from ISMs based on cation exchanger and varying content of calix[4]arene derivative were processed by principal component analysis (PCA). Such a combination of methods allowed discriminating various individual synthetic cathinones and their recognition from the mixture comprising primary amines (substituted amphetamines+aminoindane). Analytical parameters of ISM containing 1wt % of calix[4]arene derivative were sufficient to detect 1.0×10−4 mol.l−1 1-(4-fluorophenyl)-2-(ethylamino)butan-1-one and 2-(methylamino)-1-phenylbutan-1-one (buphedrone) in both model and saliva samples.  相似文献   
3.
Journal of Solid State Electrochemistry - The addition of nanocrystalline titanium dioxide (P90) to a cathode of Li/S cell enhances its voltammetric charge capacity by 19%, from which only a small...  相似文献   
4.
Fuzzy Optimization and Decision Making - Seepage equation in fissured porous media is a partial differential equation describing the variation of pressure of a given area over time. In traditional...  相似文献   
5.
Czechoslovak Mathematical Journal - We give a complete characterization of closed sets F ? ?2 whose distance function dF:= dist(·, F) is DC (i.e., is the difference of two convex...  相似文献   
6.
Doklady Mathematics - The paper studies the asymptotic behavior of the optimal control for the Poisson type boundary value problem in a domain perforated by holes of an arbitrary shape with...  相似文献   
7.
Three nonfused ring electron acceptors (NFREAs) TTC6,TT-C8T and TT-TC8 were purposefully designed and synthesized.The molecular geometry can be adjusted by the steric hindrance of lateral substituents.According to the DFT calculations,from TTC6 to TT-C8T and TT-TC8,planarity of the molecular backbone is gradually improved,accompanying with the enhancing of intramolecular charge transfer effect.As for TT-TC8,the two phenyl substituents are almost perpendicular to the molecular backbone,which endues the acceptor with good solubility and suppresses it to form over-aggregation.Multidirectional regular molecular orientation and closer molecular stacking are formed in TT-TC8 film.As a result,TT-TC8 based devices afford the highest PCE of 13.13%,which is much higher than that of TTC6 (4.41%) and TT-C8T (10.42%) and among the highest PCE values based on NFREAs.  相似文献   
8.
9.

Organisations are concerned about measuring the performance of the product/service they deliver to their customers. In all types of organisations, if a proper performance assessment is to be developed, it should be measured in different dimensions. At University, the new study programs include the development and assessment of transversal competences due to their importance in enhancing the abilities and improving the employability of students. The achievement of transversal competences can be assessed in different levels/stages; for example, the 1st and 2nd years of a Bachelor’s degree; the 3rd and 4th years of a Bachelor’s degree and at Master’s level. The purpose of this paper is to integrate the research into performance management in organisations to develop an approach consisting of four components (a methodology, a solid and integrated performance management framework, graphical diagrams and quantitative techniques) to assess and manage the achievement of transversal competences through the different levels of study using a consolidated approach. The proposal uses the Analytic Network Process (ANP) to model dependences and feedback among the elements of the competences.

  相似文献   
10.
Zhang  F.  Yi  S. H.  Niu  H. B.  Lu  X. G.  Wang  X. X. 《Fluid Dynamics》2021,56(3):383-392
Fluid Dynamics - To predict the boundary layer transition on swept wings, experimental and numerical researches were conducted to obtained the accurate boundary layer transition front and to...  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