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   194228篇
  免费   34113篇
  国内免费   18518篇
化学   117927篇
晶体学   1713篇
力学   8432篇
综合类   895篇
数学   16144篇
物理学   50231篇
无线电   51517篇
  2024年   622篇
  2023年   3668篇
  2022年   4684篇
  2021年   6112篇
  2020年   7237篇
  2019年   8067篇
  2018年   5936篇
  2017年   5607篇
  2016年   10166篇
  2015年   10638篇
  2014年   12189篇
  2013年   15124篇
  2012年   16128篇
  2011年   15718篇
  2010年   12565篇
  2009年   12451篇
  2008年   12504篇
  2007年   11212篇
  2006年   10378篇
  2005年   9189篇
  2004年   6992篇
  2003年   6192篇
  2002年   6599篇
  2001年   5250篇
  2000年   4595篇
  1999年   3996篇
  1998年   3094篇
  1997年   2668篇
  1996年   2857篇
  1995年   2288篇
  1994年   2136篇
  1993年   1707篇
  1992年   1614篇
  1991年   1420篇
  1990年   1103篇
  1989年   764篇
  1988年   625篇
  1987年   481篇
  1986年   467篇
  1985年   409篇
  1984年   297篇
  1983年   220篇
  1982年   171篇
  1981年   117篇
  1980年   90篇
  1979年   55篇
  1978年   42篇
  1977年   42篇
  1976年   42篇
  1974年   50篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion.  相似文献   
72.
研究了受外场驱动的两个二能级系统分别与两个单模量子化光场相互作用模型中纠缠演化及转移问题。该工作主要是对外场驱动的Landau-Zener模型进行了研究,采用旋转波近似的方法,通过数值计算详细分析了二能级系统初始状态、能级间的耦合常数以及驱动外场的参数对子系统间纠缠和转移特性的影响。结果表明,适当调节模型中的参数,可以使系统初始纠缠完全转移为光腔场间的纠缠,实现二能级系统与光场间的最大纠缠转移。  相似文献   
73.
JPC – Journal of Planar Chromatography – Modern TLC - A new high-performance thin-layer chromatographic (HPTLC) method has been developed for the simultaneous estimation of...  相似文献   
74.
A (di)graph is supereulerian if it contains a spanning eulerian sub(di)graph. This property is a relaxation of hamiltonicity. Inspired by this analogy with hamiltonian cycles and by similar results in supereulerian graph theory, we analyze a number of sufficient Ore type conditions for a digraph to be supereulerian. Furthermore, we study the following conjecture due to Thomassé and the first author: if the arc‐connectivity of a digraph is not smaller than its independence number, then the digraph is supereulerian. As a support for this conjecture we prove it for digraphs that are semicomplete multipartite or quasitransitive and verify the analogous statement for undirected graphs.  相似文献   
75.
76.
77.
This minireview describes the strategies for synthesis of fiuorinated surfactants potentially nonbioaccumulable.Various strategies have been focused on(Ⅰ) reducing the length of the perfluorocarbon chain,(Ⅱ) introducing hetero atoms into the fluorocarbon chain,(Ⅲ) introducing branch(herein and after branch means the fluoro-carbon chain section is not straight).In most cases,the surface tensions versus the surfactant concentrations have been assessed.These above strategies led to various highly fiuorinated(perfluorinated or not perfluorinated) surfactants whose chemical changes enabled to obtain novel alternatives to perfluorooctanoic acid(PFOA) and perfluorooctane sulphonate(PFOS).  相似文献   
78.
79.
80.
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   
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