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   13665篇
  免费   792篇
  国内免费   416篇
化学   8724篇
晶体学   95篇
力学   571篇
综合类   40篇
数学   2320篇
物理学   3123篇
  2023年   116篇
  2022年   164篇
  2021年   340篇
  2020年   403篇
  2019年   363篇
  2018年   304篇
  2017年   273篇
  2016年   522篇
  2015年   488篇
  2014年   492篇
  2013年   863篇
  2012年   946篇
  2011年   1091篇
  2010年   674篇
  2009年   658篇
  2008年   884篇
  2007年   830篇
  2006年   807篇
  2005年   681篇
  2004年   568篇
  2003年   453篇
  2002年   373篇
  2001年   210篇
  2000年   135篇
  1999年   126篇
  1998年   117篇
  1997年   122篇
  1996年   152篇
  1995年   107篇
  1994年   142篇
  1993年   106篇
  1992年   100篇
  1991年   79篇
  1990年   93篇
  1989年   76篇
  1988年   60篇
  1987年   63篇
  1986年   45篇
  1985年   72篇
  1984年   101篇
  1983年   56篇
  1982年   80篇
  1981年   48篇
  1980年   61篇
  1979年   65篇
  1978年   55篇
  1977年   42篇
  1976年   37篇
  1975年   29篇
  1974年   35篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
We investigate the possibility of phantom crossing in the dark energy sector and the solution for the Hubble tension between early and late universe observations. We use robust combinations of different cosmological observations, namely the Cosmic Microwave Background (CMB), local measurement of Hubble constant (H0), Baryon Acoustic Oscillation (BAO) and SnIa for this purpose. For a combination of CMB+BAO data that is related to early universe physics, phantom crossing in the dark energy sector was confirmed at a 95% confidence level and we obtained the constraint H0=71.03.8+2.9 km/s/Mpc at a 68% confidence level, which is in perfect agreement with the local measurement by Riess et al. We show that constraints from different combinations of data are consistent with each other and all of them are consistent with phantom crossing in the dark energy sector. For the combination of all data considered, we obtained the constraint H0=70.25±0.78 km/s/Mpc at a 68% confidence level and the phantom crossing happening at the scale factor am=0.8510.031+0.048 at a 68% confidence level.  相似文献   
2.
Advances in Data Analysis and Classification - In the original publication of the article, the line after equation (5) has been published incorrectly  相似文献   
3.
Journal of Dynamics and Differential Equations - In this paper we focus on a class of symmetric vector fields in the context of singularly perturbed fast-slow dynamical systems. Our main question...  相似文献   
4.
5.
The great challenge for modern research is to define the most efficient tools to make more sustainable the industrial production and manufacturing. Among the different aspects that require attention the replacement of toxic and/or non-renewable solvents it is certainly playing a crucial role. Dealing with widely used dipolar aprotic solvents, among the different alternatives proposed in the literature γ-valerolactone (GVL) plays a pivotal role covering different application area. In this contribution, the benefits derived from the use of GVL as a circular, safe, biomass-derived reaction medium are highlighted covering most recent publications (2021). The presentation has been divided into three major sections: (i) biomass valorization, (ii) materials synthesis, manufacturing and recycle and (iii) new synthetic methodologies.  相似文献   
6.
By linking the carbazole unit to the nitrogen atom of acridone through phenyl or pyridyl, two compounds, named 10-(4-(9H-carbazol-9-yl)phenyl)acridin-9(10H)-one (AC-Ph-Cz) and 10-(5-(9H-carbazol-9-yl)pyridin-2-yl)acridin-9(10H)-one (AC-Py-Cz) were designed and synthesized. These two materials, characterized with highly twisted and rigid structure, good thermal stability, and balanced carrier-transporting properties, were employed as host materials for green phosphorescent and thermally activated delayed fluorescent organic light-emitting diodes (OLEDs). The carbazole group, despite its small contribution to the highest occupied molecular orbitals (HOMOs) of these two materials, plays an essential role as an intramolecular host in energy delivering and improving the hole transporting ability of these two hosts. The incorporation of the electron-deficient pyridyl group as a linking group slightly improves the electron transporting capability of AC-Py-Cz. The green phosphorescent OLED (PhOLED) based on AC-Py-Cz exhibited excellent device performance with a turn-on voltage of 2.5 V, a maximum power efficiency and an external quantum efficiency (ηext) of 89.8 lm W−1 and 25.2 %, respectively, benefitting from the better charge-balancing ability of AC-Py-Cz host due to the presence of the pyridyl bridge. More importantly, all the devices based on these two hosts showed low efficiency roll-off at high brightness due to the suppressed non-radiative transition in the emitting layer. In particular, the AC-Py-Cz-hosted green PhOLED exhibited an efficiency roll-off of 1.6 % from the maximum next at a high brightness of 1000 cd m−2 and a roll-off of 15.9 % at an extremely high brightness of 10000 cd m−2. This study manifests that acridone-based host materials have great potential in fabricating OLEDs with low efficiency roll-off.  相似文献   
7.
Advances in Data Analysis and Classification - We propose two new outlier detection methods, for identifying and classifying different types of outliers in (big) functional data sets. The proposed...  相似文献   
8.
该文采用离子迁移谱(IMS)对20种假币用纸进行分析,通过快速检测假币用纸中的可挥发性组分,构建假币用纸的指纹谱图库。基于主成分分析(PCA)和层次聚类分析(HCA)对迁移时间8 ~ 17.5 ms范围的迁移谱信息进行处理,从而对假币用纸进行分类。PCA可将同种假币用纸聚类,HCA则可进一步将20种假币用纸准确分类,其对6个未知来源的半成品假币的分类正确率达83.33%。结果表明,IMS快速检测分析是比较和分类假币用纸的有效方法。  相似文献   
9.
10.
Journal of Solid State Electrochemistry - Electrochemical impedance spectroscopy (EIS) and voltammetry of immobilized particles (VIMP) measurements using air-saturated mineral water and...  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