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   227389篇
  免费   27589篇
  国内免费   17424篇
化学   156667篇
晶体学   2705篇
力学   11850篇
综合类   1082篇
数学   26377篇
物理学   73721篇
  2023年   2645篇
  2022年   5176篇
  2021年   5809篇
  2020年   6999篇
  2019年   8058篇
  2018年   7090篇
  2017年   6597篇
  2016年   10897篇
  2015年   9910篇
  2014年   11979篇
  2013年   15502篇
  2012年   16195篇
  2011年   16148篇
  2010年   12893篇
  2009年   12706篇
  2008年   12723篇
  2007年   11306篇
  2006年   10346篇
  2005年   9156篇
  2004年   7655篇
  2003年   6588篇
  2002年   7197篇
  2001年   5925篇
  2000年   5089篇
  1999年   3962篇
  1998年   3252篇
  1997年   2873篇
  1996年   2818篇
  1995年   2440篇
  1994年   2398篇
  1993年   2083篇
  1992年   1936篇
  1991年   1866篇
  1990年   1747篇
  1989年   1531篇
  1988年   1287篇
  1987年   1248篇
  1986年   1215篇
  1985年   1177篇
  1984年   1090篇
  1983年   977篇
  1982年   925篇
  1981年   782篇
  1979年   828篇
  1978年   834篇
  1977年   823篇
  1976年   942篇
  1975年   835篇
  1974年   852篇
  1973年   865篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
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   
23.
The results of investigation of optical image detectors designed for the largest problem, near-VUV, range of the spectrum are presented. The possibility of using a dual-stage image detection system to appreciably lower the sensitivity threshold and make computer data processing feasible is considered. The integration of a UV module into a wideband image detector is studied.  相似文献   
24.
25.
26.
在中国科学技术大学夏季学期的研究型实验课程"化学科研基础训练"中开设"壳聚糖的制备与表征"综合实验,以龙虾壳为原料,通过除蛋白、脱盐、脱色、脱乙酰等一系列反应,制备得到目标产物壳聚糖。运用红外光谱、核磁共振仪、黏度法、滴定等对产品的结构及性能进行表征。  相似文献   
27.
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   
28.
Unsteady transitions of separation patterns in single expansion ramp nozzle   总被引:2,自引:0,他引:2  
Y. Yu  J. Xu  K. Yu  J. Mo 《Shock Waves》2015,25(6):623-633
  相似文献   
29.
30.
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   
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