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   32789篇
  免费   1334篇
  国内免费   40篇
化学   22677篇
晶体学   235篇
力学   644篇
数学   4602篇
物理学   6005篇
  2023年   270篇
  2022年   205篇
  2021年   401篇
  2020年   577篇
  2019年   519篇
  2018年   707篇
  2017年   652篇
  2016年   1269篇
  2015年   1027篇
  2014年   1050篇
  2013年   2160篇
  2012年   2382篇
  2011年   2560篇
  2010年   1470篇
  2009年   1219篇
  2008年   2175篇
  2007年   2126篇
  2006年   1824篇
  2005年   1656篇
  2004年   1360篇
  2003年   1030篇
  2002年   927篇
  2001年   669篇
  2000年   567篇
  1999年   418篇
  1998年   305篇
  1997年   230篇
  1996年   351篇
  1995年   243篇
  1994年   232篇
  1993年   277篇
  1992年   250篇
  1991年   171篇
  1990年   166篇
  1989年   134篇
  1988年   142篇
  1987年   131篇
  1986年   122篇
  1985年   190篇
  1984年   148篇
  1983年   119篇
  1982年   119篇
  1981年   109篇
  1980年   83篇
  1979年   99篇
  1978年   85篇
  1977年   77篇
  1976年   80篇
  1975年   75篇
  1973年   86篇
排序方式: 共有10000条查询结果,搜索用时 15 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.
Structural Chemistry - In the present work, the energy contribution of the sulfur atom in a heterocycle and in a disulfide bond in solid and gas phases was calculated. To achieve this goal,...  相似文献   
4.
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   
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.
8.

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   
9.
Central European Journal of Operations Research - Sustainability practice within supply chains remains in an early development phase. Enterprises still need tools that support the integration of...  相似文献   
10.
Journal of Optimization Theory and Applications - This paper proposes and analyzes a globalized version of the Newton method for finding a singularity of the nonsmooth vector fields. Basically, the...  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