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   277884篇
  免费   19773篇
  国内免费   929篇
化学   180009篇
晶体学   3719篇
力学   10881篇
综合类   2篇
数学   28295篇
物理学   75680篇
  2023年   4449篇
  2021年   3818篇
  2020年   6165篇
  2019年   4128篇
  2018年   4714篇
  2017年   2965篇
  2016年   9027篇
  2015年   7726篇
  2014年   8505篇
  2013年   15884篇
  2012年   10966篇
  2011年   10990篇
  2010年   9667篇
  2009年   9541篇
  2008年   9953篇
  2007年   9841篇
  2006年   8579篇
  2005年   7976篇
  2004年   7096篇
  2003年   6289篇
  2002年   6220篇
  2001年   7240篇
  2000年   5391篇
  1999年   4241篇
  1998年   3578篇
  1997年   3638篇
  1996年   3355篇
  1995年   3250篇
  1994年   3012篇
  1993年   3182篇
  1992年   3360篇
  1991年   3386篇
  1990年   3188篇
  1989年   3143篇
  1988年   3237篇
  1987年   3094篇
  1986年   2960篇
  1985年   4044篇
  1984年   4215篇
  1983年   3463篇
  1982年   3837篇
  1981年   3738篇
  1980年   3629篇
  1979年   3647篇
  1978年   3868篇
  1977年   3760篇
  1976年   3983篇
  1975年   3571篇
  1974年   3693篇
  1973年   3927篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
101.
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   
102.
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   
103.
104.
105.
106.
107.
108.
109.
Sulfur hexafluoride (SF6) is considered as a potent greenhouse gas, whose effective degradation is challenging. Here we report a computational study on the nucleophilic activation of sulfur hexafluoride by N-heterocyclic carbenes and N-heterocyclic olefins. The result shows that the activation of SF6 is both thermodynamically and kinetically favorable at mild condition using NHOs with fluoro-substituted azolium and sulfur pentafluoride anion being formed. The Gibbs free energy barrier during the activation of SF6 has a linear relationship with the energy of HOMO of substrates, which could be a guideline for applying those compounds that feature higher energy in HOMO to activate SF6 in high efficiency.  相似文献   
110.
The present work reports new experimental and numerical results of the combustion properties of hydrogen based mixtures diluted by nitrogen and steam. Spherical expanding flames have been studied in a spherical bomb over a large domain of equivalence ratios, initial temperatures and dilutions at an initial pressure of 100 kPa (Tini = 296, 363, 413 K; N2/O2 = 3.76, 5.67, 9; %Steam = 0, 20, 30). From these experiments, the laminar flame speed SL0, the Markstein length L’, the activation energy Ea and the Zel'dovich β number have been determined. These parameters were also simulated using COSILAB® in order to verify the validity of the Mével et al. [1] detailed kinetic mechanism. Other parameters as the laminar flame thickness δ and the effective Lewis number Leeff were also simulated. These new results aim at providing an extended database that will be very useful in the hydrogen combustion hazard assessment for nuclear reactor power plant new design.  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