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   132082篇
  免费   6030篇
  国内免费   4281篇
化学   59065篇
晶体学   1258篇
力学   10200篇
综合类   258篇
数学   38485篇
物理学   33127篇
  2023年   786篇
  2022年   1356篇
  2021年   1552篇
  2020年   1681篇
  2019年   1621篇
  2018年   11652篇
  2017年   11383篇
  2016年   7984篇
  2015年   2680篇
  2014年   2686篇
  2013年   3441篇
  2012年   7478篇
  2011年   13988篇
  2010年   8213篇
  2009年   8497篇
  2008年   9215篇
  2007年   11133篇
  2006年   2488篇
  2005年   3204篇
  2004年   3168篇
  2003年   3347篇
  2002年   2364篇
  2001年   1425篇
  2000年   1303篇
  1999年   1235篇
  1998年   1117篇
  1997年   1007篇
  1996年   1116篇
  1995年   922篇
  1994年   812篇
  1993年   798篇
  1992年   740篇
  1991年   671篇
  1990年   638篇
  1989年   553篇
  1988年   480篇
  1987年   490篇
  1986年   426篇
  1985年   474篇
  1984年   460篇
  1983年   410篇
  1982年   394篇
  1979年   377篇
  1978年   389篇
  1977年   358篇
  1976年   447篇
  1975年   406篇
  1974年   422篇
  1973年   438篇
  1972年   404篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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   
2.
3.
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   
4.
5.
6.
7.
Three‐dimensional (3D) nanometal films serving as current collectors have attracted much interest recently owing to their promising application in high‐performance supercapacitors. In the process of the electrochemical reaction, the 3D structure can provide a short diffusion path for fast ion transport, and the highly conductive nanometal may serve as a backbone for facile electron transfer. In this work, a novel polypyrrole (PPy) shell@3D‐Ni‐core composite is developed to enhance the electrochemical performance of conventional PPy. With the introduction of a Ni metal core, the as‐prepared material exhibits a high specific capacitance (726 F g?1 at a charge/discharge rate of 1 A g?1), good rate capability (a decay of 33 % in Csp with charge/discharge rates increasing from 1 to 20 A g?1), and high cycle stability (only a small decrease of 4.2 % in Csp after 1000 cycles at a scan rate of 100 mV s?1). Furthermore, an aqueous symmetric supercapacitor device is fabricated by using the as‐prepared composite as electrodes; the device demonstrates a high energy density (≈21.2 Wh kg?1) and superior long‐term cycle ability (only 4.4 % and 18.6 % loss in Csp after 2000 and 5000 cycles, respectively).  相似文献   
8.
9.
10.
A green and sustainable strategy synthesizes clinical medicine warfarin anticoagulant by using lipase‐supported metal–organic framework (MOF) bioreactors (see scheme). These findings may be beneficial for future studies in the industrial production of chemical, pharmaceutical, and agrochemical precursors.  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