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   565697篇
  免费   5848篇
  国内免费   1600篇
化学   272290篇
晶体学   7860篇
力学   29121篇
综合类   13篇
数学   95638篇
物理学   168223篇
  2021年   3741篇
  2020年   4184篇
  2019年   4521篇
  2018年   20250篇
  2017年   20523篇
  2016年   16450篇
  2015年   6835篇
  2014年   8873篇
  2013年   20495篇
  2012年   21483篇
  2011年   35901篇
  2010年   23062篇
  2009年   23337篇
  2008年   30411篇
  2007年   34373篇
  2006年   16559篇
  2005年   20703篇
  2004年   17301篇
  2003年   16092篇
  2002年   13633篇
  2001年   13739篇
  2000年   10545篇
  1999年   8058篇
  1998年   6750篇
  1997年   6446篇
  1996年   6350篇
  1995年   5644篇
  1994年   5530篇
  1993年   5344篇
  1992年   5927篇
  1991年   6041篇
  1990年   5767篇
  1989年   5585篇
  1988年   5623篇
  1987年   5496篇
  1986年   5205篇
  1985年   6678篇
  1984年   6817篇
  1983年   5415篇
  1982年   5502篇
  1981年   5472篇
  1980年   5076篇
  1979年   5471篇
  1978年   5613篇
  1977年   5430篇
  1976年   5370篇
  1975年   4935篇
  1974年   4900篇
  1973年   4946篇
  1972年   3484篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
113.
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   
114.
115.
116.
117.
118.
A model of the explosive fragmentation of a thin ring is developed which takes into account the statistical dispersion of the relative fracture deformation along the length of the ring. A formula is proposed for calculating the velocity of the boundary of the region near a plastic rupture in which the plastic flow of the ring material ceases. Methods for the numerical and analytical calculation of the average number of fragments of the ring are developed. The calculation results are compared with available experimental data.  相似文献   
119.
In this paper, we have significantly modified an existing model for calculating the zeta potential and streaming potential coefficient of porous media and tested it with a large, recently published, high-quality experimental dataset. The newly modified model does not require the imposition of a zeta potential offset but derives its high salinity zeta potential behaviour from Stern plane saturation considerations. The newly modified model has been implemented as a function of temperature, salinity, pH, and rock microstructure both for facies-specific aggregations of the new data and for individual samples. Since the experimental data include measurements on samples of both detrital and authigenic overgrowth sandstones, it was possible to model and test the effect of widely varying microstructural properties while keeping lithology constant. The results show that the theoretical model represents the experimental data very well when applied to model data for a particular lithofacies over the whole salinity, from 10?5 to 6.3 mol/dm3, and extremely well when modelling individual samples and taking individual sample microstructure into account. The new model reproduces and explains the extreme sensitivity of zeta and streaming potential coefficient to pore fluid pH. The low salinity control of streaming potential coefficient by rock microstructure is described well by the modified model. The model also behaves at high salinities, showing that the constant zeta potential observed at high salinities arises from the development of a maximum charge density in the diffuse layer as it is compressed to the thickness of one hydrated metal ion.  相似文献   
120.
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