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   127601篇
  免费   26166篇
  国内免费   12051篇
化学   103282篇
晶体学   1344篇
力学   6578篇
综合类   654篇
数学   13234篇
物理学   40726篇
  2024年   237篇
  2023年   2076篇
  2022年   2854篇
  2021年   3497篇
  2020年   5042篇
  2019年   5857篇
  2018年   4165篇
  2017年   3603篇
  2016年   7706篇
  2015年   7628篇
  2014年   8575篇
  2013年   10781篇
  2012年   11430篇
  2011年   11087篇
  2010年   8706篇
  2009年   8523篇
  2008年   8536篇
  2007年   7207篇
  2006年   6587篇
  2005年   5743篇
  2004年   4679篇
  2003年   3837篇
  2002年   4454篇
  2001年   3451篇
  2000年   3114篇
  1999年   2399篇
  1998年   1817篇
  1997年   1741篇
  1996年   1732篇
  1995年   1443篇
  1994年   1267篇
  1993年   1070篇
  1992年   928篇
  1991年   850篇
  1990年   709篇
  1989年   540篇
  1988年   411篇
  1987年   336篇
  1986年   345篇
  1985年   284篇
  1984年   160篇
  1983年   127篇
  1982年   108篇
  1981年   62篇
  1980年   46篇
  1979年   13篇
  1977年   3篇
  1974年   2篇
  1957年   32篇
  1936年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D-QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH2, and DINP−NO2) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate .OH and provides free radicals for the photodegradation of microplastics in the environment.  相似文献   
62.
63.
64.
By tuning the length and rigidity of the spacer of bis(biurea) ligands L, three structural motifs of the A2L3 complexes (A represents anion, here orthophosphate PO43?), namely helicate, mesocate, and mono‐bridged motif, have been assembled by coordination of the ligand to phosphate anion. Crystal structure analysis indicated that in the three complexes, each of the phosphate ions is coordinated by twelve hydrogen bonds from six surrounding urea groups. The anion coordination properties in solution have also been studied. The results further demonstrate the coordination behavior of phosphate ion, which shows strong tendency for coordination saturation and geometrical preference, thus allowing for the assembly of novel anion coordination‐based structures as in transition‐metal complexes.  相似文献   
65.
66.
67.
68.
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics.  相似文献   
69.
70.
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