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   301230篇
  免费   6034篇
  国内免费   3116篇
化学   162209篇
晶体学   4647篇
力学   14065篇
综合类   198篇
数学   33062篇
物理学   96199篇
  2021年   2615篇
  2020年   2975篇
  2019年   3201篇
  2018年   3978篇
  2017年   3962篇
  2016年   5698篇
  2015年   3825篇
  2014年   5684篇
  2013年   12762篇
  2012年   10489篇
  2011年   12638篇
  2010年   8938篇
  2009年   8734篇
  2008年   11370篇
  2007年   11484篇
  2006年   10714篇
  2005年   9538篇
  2004年   8632篇
  2003年   7737篇
  2002年   7601篇
  2001年   8470篇
  2000年   6563篇
  1999年   5223篇
  1998年   4530篇
  1997年   4521篇
  1996年   4250篇
  1995年   3874篇
  1994年   4037篇
  1993年   3592篇
  1992年   4049篇
  1991年   4022篇
  1990年   3870篇
  1989年   3669篇
  1988年   3759篇
  1987年   3625篇
  1986年   3428篇
  1985年   4502篇
  1984年   4729篇
  1983年   3949篇
  1982年   4061篇
  1981年   3978篇
  1980年   3946篇
  1979年   3909篇
  1978年   4212篇
  1977年   4130篇
  1976年   4202篇
  1975年   3877篇
  1974年   3920篇
  1973年   4071篇
  1972年   2863篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
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   
53.
54.
Russian Chemical Bulletin - Quantum chemical calculations and a comparative analysis of Raman spectra of 3,4,5-triphenyl-1-propyl-1,2-diphosphole (1),...  相似文献   
55.
Two new compounds of fluorine: (C2H5)4N[I2F] and (C2H5)4N[Br2F], have been easily synthesized in a nearly quantitative by a direct reaction of (C2H5)4NF, I2 and Br2. The products were isolated and characterized by elemental analysis and spectroscopic methods such as: Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). These compounds have been studied computationally with the Scalar ZORA relativistic level of theory using the ADF program package. The molecular parameters, and vibrational spectra were calculated. The excitation energies were found by timedependent perturbation density functional theory (TD-DFT). Molecule optimization, frequencies and excitation energies were calculated with standard Slatertype-orbital (STO) basis sets with triple-zeta quality double plus polarization functions (TZ2P) for all atoms. The FTIR, UV-Vis spectra and assignment of principal transitions and total density of state (TDOS) were extracted using the GaussSum 2.2 program. The comparison between experimental and calculated values showes that the experimental results correlate well with the predicted data.  相似文献   
56.
57.
58.
59.
Applied Magnetic Resonance - The suggested approach allowed us to derive analytical expressions for modeling the shape of solid-echo signal and its time evolution for a system of three-spin groups...  相似文献   
60.
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