全文获取类型
收费全文 | 199985篇 |
免费 | 24611篇 |
国内免费 | 18180篇 |
专业分类
化学 | 88653篇 |
晶体学 | 1351篇 |
力学 | 8477篇 |
综合类 | 962篇 |
数学 | 15299篇 |
物理学 | 53421篇 |
综合类 | 74613篇 |
出版年
2024年 | 838篇 |
2023年 | 3472篇 |
2022年 | 5554篇 |
2021年 | 5972篇 |
2020年 | 6036篇 |
2019年 | 5231篇 |
2018年 | 4949篇 |
2017年 | 4709篇 |
2016年 | 7039篇 |
2015年 | 7501篇 |
2014年 | 9503篇 |
2013年 | 11406篇 |
2012年 | 13375篇 |
2011年 | 15377篇 |
2010年 | 10601篇 |
2009年 | 10937篇 |
2008年 | 11072篇 |
2007年 | 10023篇 |
2006年 | 9115篇 |
2005年 | 8273篇 |
2004年 | 8804篇 |
2003年 | 6443篇 |
2002年 | 5995篇 |
2001年 | 5112篇 |
2000年 | 4418篇 |
1999年 | 6278篇 |
1998年 | 5587篇 |
1997年 | 5558篇 |
1996年 | 4915篇 |
1995年 | 4333篇 |
1994年 | 4030篇 |
1993年 | 3936篇 |
1992年 | 3501篇 |
1991年 | 3017篇 |
1990年 | 2714篇 |
1989年 | 2222篇 |
1988年 | 1650篇 |
1987年 | 1096篇 |
1986年 | 842篇 |
1985年 | 497篇 |
1984年 | 254篇 |
1983年 | 189篇 |
1982年 | 144篇 |
1981年 | 89篇 |
1980年 | 55篇 |
1979年 | 23篇 |
1977年 | 6篇 |
1974年 | 5篇 |
1966年 | 4篇 |
1957年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Lijuan Shen Li Li Sheng Lu Xiaohan Zhang Jie Liu Junlin An Guojun Zhang Bo Wu Fei Wang 《中国颗粒学报》2015,(3):10-15
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
63.
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
64.
The biodegradability of phtalic acid esters in marine and freshwater environments was characterized by their binding free energy with corresponding degrading enzymes. According to comprehensive biodegradation effects weights, the binding free energy values were converted into dimensionless efficacy coefficient using ratio normalization method. Then, considering comprehensive dual biodegradation effects value and the structural parameters of PAEs in both marine and freshwater environments, a 3D-QSAR pharmacophore model was constructed, five PAE derivatives (DBP−COOH, DBP−CHO, DBP−OH, DINP−NH2, and DINP−NO2) were screened out based on their environmental friendliness, functionality and stability. The prediction of biodegradation effects on five PAE derivatives by biodegradation models in marine and freshwater environment increased by 15.90 %, 15.84 %, 27.21 %, 12.33 %, and 8.32 %, and 21.57 %, 15.21 %, 20.99 %, 15.10 %, and 9.74 %, respectively. By simulating the photodegradation path of the PAE derivative molecular, it was found that DBP−OH can generate .OH and provides free radicals for the photodegradation of microplastics in the environment. 相似文献
65.
66.
67.
68.
张晓盼 《太原师范学院学报(自然科学版)》2015,(2):21-23
讨论二面体群的结构问题,利用GAP软件给出二面体群D2n的共轭类长素图,并完整给出当n以及n/2分别是奇数和偶数时的共轭类长素图情况. 相似文献
69.
Terahertz(THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional(1D) time-dependent Schr ¨odinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime. 相似文献
70.