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   1501499篇
  免费   32091篇
  国内免费   8377篇
化学   647483篇
晶体学   20430篇
力学   74408篇
综合类   107篇
数学   239836篇
物理学   363761篇
无线电   195942篇
  2021年   14776篇
  2020年   17365篇
  2019年   17500篇
  2018年   14048篇
  2016年   29831篇
  2015年   21834篇
  2014年   32736篇
  2013年   78503篇
  2012年   38581篇
  2011年   34811篇
  2010年   39640篇
  2009年   44851篇
  2008年   38481篇
  2007年   35432篇
  2006年   41392篇
  2005年   34387篇
  2004年   35678篇
  2003年   33796篇
  2002年   34748篇
  2001年   32917篇
  2000年   29837篇
  1999年   28165篇
  1998年   27141篇
  1997年   27056篇
  1996年   26748篇
  1995年   24572篇
  1994年   24048篇
  1993年   23400篇
  1992年   22899篇
  1991年   23088篇
  1990年   21930篇
  1989年   21599篇
  1988年   20767篇
  1987年   19570篇
  1986年   18352篇
  1985年   24920篇
  1984年   26146篇
  1983年   22127篇
  1982年   23591篇
  1981年   22797篇
  1980年   22060篇
  1979年   21826篇
  1978年   23168篇
  1977年   22709篇
  1976年   22242篇
  1975年   20912篇
  1974年   20535篇
  1973年   21049篇
  1972年   15219篇
  1967年   13035篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
Erosion and sediments transport processes have a great impact on industrial structures and on water quality. Despite its limitations, the Saint‐Venant‐Exner system is still (and for sure for some years) widely used in industrial codes to model the bedload sediment transport. In practice, its numerical resolution is mostly handled by a splitting technique that allows a weak coupling between hydraulic and morphodynamic distinct softwares but may suffer from important stability issues. In recent works, many authors proposed alternative methods based on a strong coupling that cure this problem but are not so trivial to implement in an industrial context. In this work, we then pursue 2 objectives. First, we propose a very simple scheme based on an approximate Riemann solver, respecting the strong coupling framework, and we demonstrate its stability and accuracy through a number of numerical test cases. However, second, we reinterpret our scheme as a splitting technique and we extend the purpose to propose what should be the minimal coupling that ensures the stability of the global numerical process in industrial codes, at least, when dealing with collocated finite volume method. The resulting splitting method is, up to our knowledge, the only one for which stability properties are fully demonstrated.  相似文献   
122.
Experimental and theoretical studies are performed in order to illuminate, for first time, the intercalation mechanism of polycyclic aromatic molecules into graphite oxide. Two representative molecules of this family, aniline and naphthalene amine are investigated. After intercalation, aniline molecules prefer to covalently connect to the graphene oxide matrix via chemical grafting, while napthalene amine molecules bind with the graphene oxide surface through π–π interactions. The presence of intercalated aromatic molecules between the graphene oxide layers is demonstrated by X‐ray diffraction, while the type of interaction between graphene oxide and polycyclic organic molecules is elucidated by X‐ray photoelectron spectroscopy. Combined quantum mechanical and molecular mechanical calculations describe the intercalation mechanism and the aniline grafting, rationalizing the experimental data. The present work opens new perspectives for the interaction of various aromatic molecules with graphite oxide and the so‐called “intercalation chemistry”.  相似文献   
123.
124.
125.
126.
127.
In this study, the functional interaction of HPLW peptide with VEGFR2 (Vascular Endothelial Growth Factor Receptor 2) was determined by using fast 15N‐edited NMR spectroscopic experiments. To this aim, 15N uniformly labelled HPLW has been added to Porcine Aortic Endothelial Cells. The acquisition of isotope‐edited NMR spectroscopic experiments, including 15N relaxation measurements, allowed a precise characterization of the in‐cell HPLW epitope recognized by VEGFR2.  相似文献   
128.
129.
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   
130.
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