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   18902篇
  免费   3398篇
  国内免费   1684篇
化学   13135篇
晶体学   179篇
力学   1039篇
综合类   67篇
数学   2025篇
物理学   7539篇
  2024年   63篇
  2023年   402篇
  2022年   711篇
  2021年   717篇
  2020年   740篇
  2019年   755篇
  2018年   738篇
  2017年   589篇
  2016年   983篇
  2015年   876篇
  2014年   1089篇
  2013年   1421篇
  2012年   1731篇
  2011年   1762篇
  2010年   1159篇
  2009年   1083篇
  2008年   1197篇
  2007年   1039篇
  2006年   990篇
  2005年   788篇
  2004年   602篇
  2003年   425篇
  2002年   434篇
  2001年   333篇
  2000年   276篇
  1999年   389篇
  1998年   276篇
  1997年   292篇
  1996年   284篇
  1995年   245篇
  1994年   209篇
  1993年   215篇
  1992年   143篇
  1991年   159篇
  1990年   129篇
  1989年   99篇
  1988年   88篇
  1987年   71篇
  1986年   68篇
  1985年   54篇
  1984年   57篇
  1983年   30篇
  1982年   32篇
  1981年   23篇
  1980年   26篇
  1978年   13篇
  1976年   16篇
  1975年   15篇
  1973年   15篇
  1968年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
871.
High‐performance liquid chromatography coupled with photodiode array detection has been extensively applied in many fields and the peaks among the analyzed samples can be shifted due to the variations of instrumental and experimental conditions. In multivariate analysis, retention time alignment is an important pretreatment step. Hence, the shifted peaks in high‐performance liquid chromatography coupled with photodiode array detection three‐dimensional spectra should be aligned for further analysis. Being motivated by this purpose, the interval correlated shifting method combined with the proposed data arrangement methods are recommended and employed on high‐performance liquid chromatography coupled with photodiode array detection data as a demonstration. We validate the alignment performance of the proposed method through comparison the consistency of the retention time before and after alignment. The obtained results demonstrated that the proposed method is capable of successful aligning the employed data. Additionally, the interval correlated shifting method combined with the data arrangement modes is implemented in an easy‐to‐use graphical user interface environment and so can be operated easily by users not familiar with programming languages.  相似文献   
872.
Ma  Lijiao  Xu  Ye  Zu  Yunfei  Liao  Qing  Xu  Bowei  An  Cunbin  Zhang  Shaoqing  Hou  Jianhui 《中国科学:化学(英文版)》2020,63(1):21-27
In order to meet the requirements for making organic solar cells(OSCs) through solution printing techniques, great efforts have been devoted into developing high performance OSCs with relatively thicker active layers. In this work, a thick-film(300 nm)ternary OSC with a power conversion efficiency of 14.3% is fabricated by introducing phenyl-C_(61)-butyric-acid-methyl ester(PC_(61)BM) into a PBDB-T-2Cl:BTP-4 F host blend. The addition of PC_(61)BM is found to be helpful for improving the hole and electron mobilities, and thus facilitates charge transport as well as suppresses charge recombination in the active layers, leading to the improved efficiencies of OSCs with relatively thicker active layers. Our results demonstrate the feasibility of employing fullerene derivative PC_(61)BM to construct a high-efficiency thick-film ternary device, which would promote the development of thick layer ternary OSCs to fulfill the requirements of future roll to roll production.  相似文献   
873.
Ma  Junyang  Xu  Wentao  Xie  Jin 《中国科学:化学(英文版)》2020,63(2):187-191
In this communication,we disclose the first example of metal-free and site-selective radical fluorination of readily available tertiary alkyl ethers,enabled by synergistic photocatalysis and organocatalysis.This catalytic combination allows for exclusive fluorination of tertiary C–O bonds under mild conditions even in the presence of competing reaction sites.The excellent functional group tolerance affords valuable access to sterically hindered alkyl fluorides through late-stage modification of complex molecules.The successful use of tertiary alkyl ethers in radical fluorination enhances the structural diversity of aliphatic fluorides that can be derived from naturally abundant alcohols.  相似文献   
874.
层状复合氢氧化物(LDHs)是一种层板金属元素和层间离子可调的无机层状材料,利用其独特的插层组装特性,基于静电、氢键、范德华力等相互作用力,功能性荧光客体分子可与LDHs纳米片复合构筑多功能荧光薄膜材料.LDHs薄膜基荧光材料用于荧光传感器,在有机挥发性气体(VOCs)、温度、压力、重要生物分子等的检测中显示了良好性能.本文总结了LDHs复合薄膜的制备方法以及近年来其在纳米荧光传感领域的进展,并对其未来发展做出了展望.  相似文献   
875.
Ma  Xiaoshuang  Ma  Guanyu  Qin  Lubing  Chen  Guangxu  Chen  Shaowei  Tang  Zhenghua 《中国科学:化学(英文版)》2020,63(12):1777-1784
Science China Chemistry - Despite the recent progress on controllable synthesis of alkynyl-protected Au nanoclusters, the effective synthetic means are very limited and the cluster formation...  相似文献   
876.

The main objective of the present numerical analysis is to predict the nonlinear frequency ratios associated with the nonlinear free vibration response of porous composite plates at microscale in the presence of different microstructural gradient tensors. To achieve this end, by taking cubic-type elements into account, isogeometric models of porous composite microplates are obtained with and without a central cutout and relevant to various porosity patterns of distribution along the plate thickness. The established unconventional models have the capability to capture the effects of various unconventional gradient tensors continuity on the basis of a refined shear deformable plate formulation. For the simply supported microsized uniform porous functionally graded material (U-PFGM) plate having the oscillation amplitude equal to the plate thickness, it is revealed that the rotation gradient tensor causes to reduce the frequency ratio about 0.73%, the dilatation gradient tensor causes to reduce it about 1.93%, and the deviatoric stretch gradient tensor leads to a decrease of it about 5.19%. On the other hand, for the clamped microsized U-PFGM plate having the oscillation amplitude equal to the plate thickness, these percentages are equal to 0.62%, 1.64%, and 4.40%, respectively. Accordingly, it is found that by changing the boundary conditions from clamped to simply supported, the effect of microsize on the reduction of frequency ratio decreases a bit.

  相似文献   
877.
Ma  Li  Wu  Bowen 《Nonlinear dynamics》2022,107(4):3749-3766
Nonlinear Dynamics - The main purpose of this paper is to investigate the finite-time stability of Hadamard fractional differential equations (HFDEs). Firstly, the standard definitions of...  相似文献   
878.
介绍了新型对开门高低温动态试验箱的研制过程,包括系统热负荷计算、复叠制冷循环系统的热力计算等。并根据系统的热力计算,进行了冷凝器和蒸发器的结构设计以及主要部件压缩机和通风机的设计选型。  相似文献   
879.
880.
为解决两端固定支撑弹性梁解的存在性及唯一性问题,运用Leray-Schauder延拓定理,研究一类非线性四阶常微分方程边值问题,当非线性项满足适当至多增长性条件时,得到解的存在性结果.进一步,当非线性项满足Lipschitz条件时,得到解的唯一性结果.  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