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   108864篇
  免费   20324篇
  国内免费   11539篇
化学   75005篇
晶体学   1102篇
力学   7086篇
综合类   637篇
数学   12749篇
物理学   44148篇
  2024年   130篇
  2023年   2406篇
  2022年   2530篇
  2021年   3571篇
  2020年   4795篇
  2019年   4377篇
  2018年   3917篇
  2017年   3493篇
  2016年   5545篇
  2015年   5186篇
  2014年   6452篇
  2013年   8248篇
  2012年   10111篇
  2011年   10524篇
  2010年   6912篇
  2009年   6722篇
  2008年   7305篇
  2007年   6401篇
  2006年   5999篇
  2005年   4850篇
  2004年   3710篇
  2003年   2882篇
  2002年   2540篇
  2001年   2219篇
  2000年   1900篇
  1999年   2253篇
  1998年   1954篇
  1997年   1919篇
  1996年   1899篇
  1995年   1672篇
  1994年   1440篇
  1993年   1214篇
  1992年   1086篇
  1991年   966篇
  1990年   801篇
  1989年   619篇
  1988年   449篇
  1987年   369篇
  1986年   404篇
  1985年   319篇
  1984年   180篇
  1983年   157篇
  1982年   124篇
  1981年   78篇
  1980年   48篇
  1979年   12篇
  1974年   1篇
  1957年   33篇
  1923年   1篇
  1922年   1篇
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
11.
Juglandis Mandshuricae Cortex is the bark of Juglans mandshurica Maxim., which has been used as a folk medicine plant in China and India. In this study, an ultra-high performance liquid chromatography–quadrupole/orbitrap high-resolution mass spectrometry method was developed to clarify and quantify the chemical profiling of Juglandis Mandshuricae Cortex rapidly. A total of 113 compounds were characterized. Among them, seven flavonoids were simultaneously quantified in 15 min, including myricetin, myricetrin, taxifolin, kaempferol, quercetin, quercitrin, and naringenin. The method was validated for accuracy, precision, and the limits of detection and quantification. All calibration curves showed a good linear relationship (r > 0.9990) within test ranges. The intra- and inter-day relative standard deviations were less than 2.16%. Accuracy validation showed that the recovery was between 95.6 and 101.3% with relative standard deviation values below 2.85%. The validated method was successfully applied to determine the contents of seven flavones in Juglandis Mandshuricae Cortex from seven sources and the contents of these places were calculated respectively. This method provides a theoretical basis for further developing the medicinal value of Juglandis Mandshuricae Cortex.  相似文献   
12.
用电高峰期家用电器电压不足的问题,来源于实际生活情景,是帮助学生理解交、直流电路规律的很好素材.基于高中物理教学中恒定电流和交流电相关内容的知识、模型,讨论了家庭电路中用电器电压损失的两种来源,并对人教版新旧教材关于此问题的处理进行了对比和评价.  相似文献   
13.
14.
Theoretical and Mathematical Physics - By introducing shift relations satisfied by a matrix $$\boldsymbol{r}$$ , we propose a generalized Cauchy matrix scheme and construct a discrete second-order...  相似文献   
15.
Catalysis Surveys from Asia - Co3O4 catalyst derived from Co-MOFs demonstrated rich active sites in the catalytic reaction. In this paper, we prepared the rod-like Co3O4 catalysts by calcining...  相似文献   
16.
Wu  Yifei  Zhao  Xiaofei 《BIT Numerical Mathematics》2022,62(3):1049-1090
BIT Numerical Mathematics - In this paper, we introduce a novel class of embedded exponential-type low-regularity integrators (ELRIs) for solving the KdV equation and establish their optimal...  相似文献   
17.
Zhang  Jia-Rui  Zhang  Jia-Qi  Zheng  Zhao-Lin  Lin  Da  Shen  Yu-Jia 《Nonlinear dynamics》2022,108(2):1005-1026
Nonlinear Dynamics - Parametrically excited oscillators are used in several domains, in particular to improve the dynamical behaviour of systems like in the case of the parametric amplification or...  相似文献   
18.
Journal of Solid State Electrochemistry - In this study, hot pressing was evaluated as a method of cell fabrication to increase the energy density of next-generation all-solid-state batteries with...  相似文献   
19.
Based on the primal mixed variational formulation, a stabilized nonconforming mixed finite element method is proposed for the linear elasticity on rectangular and cubic meshes. Two kinds of penalty terms are introduced in the stabilized mixed formulation, which are the jump penalty term for the displacement and the divergence penalty term for the stress. We use the classical nonconforming rectangular and cubic elements for the displacement and the discontinuous piecewise polynomial space for the stress, where the discrete space for stress are carefully chosen to guarantee the well-posedness of discrete formulation. The stabilized mixed method is locking-free. The optimal convergence order is derived in the $L^2$-norm for stress and in the broken $H^1$-norm and $L^2$-norm for displacement. A numerical test is carried out to verify the optimal convergence of the stabilized method.  相似文献   
20.
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   
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