全文获取类型
收费全文 | 74850篇 |
免费 | 13903篇 |
国内免费 | 6405篇 |
专业分类
化学 | 66785篇 |
晶体学 | 813篇 |
力学 | 3062篇 |
综合类 | 459篇 |
数学 | 6547篇 |
物理学 | 17492篇 |
出版年
2024年 | 130篇 |
2023年 | 752篇 |
2022年 | 1255篇 |
2021年 | 1496篇 |
2020年 | 2694篇 |
2019年 | 3803篇 |
2018年 | 2211篇 |
2017年 | 1811篇 |
2016年 | 4947篇 |
2015年 | 5049篇 |
2014年 | 5407篇 |
2013年 | 6654篇 |
2012年 | 6103篇 |
2011年 | 5405篇 |
2010年 | 5114篇 |
2009年 | 5053篇 |
2008年 | 4787篇 |
2007年 | 4015篇 |
2006年 | 3623篇 |
2005年 | 3441篇 |
2004年 | 2921篇 |
2003年 | 2512篇 |
2002年 | 3150篇 |
2001年 | 2354篇 |
2000年 | 2226篇 |
1999年 | 1399篇 |
1998年 | 929篇 |
1997年 | 767篇 |
1996年 | 759篇 |
1995年 | 658篇 |
1994年 | 624篇 |
1993年 | 516篇 |
1992年 | 444篇 |
1991年 | 382篇 |
1990年 | 392篇 |
1989年 | 253篇 |
1988年 | 212篇 |
1987年 | 181篇 |
1986年 | 182篇 |
1985年 | 134篇 |
1984年 | 86篇 |
1983年 | 73篇 |
1982年 | 72篇 |
1981年 | 49篇 |
1980年 | 28篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1973年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
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
2.
Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon(WIRC) component of total suspended particulates(TSP),collected weekly during 2003,as well as from October 2005 to May 2006 at the WMO-GAW Mt.Waliguan(WLG) site.The overall average WIRC mass concentration was(1183±120)ng/m3(n = 79),while seasonal averages were 2081 ±1707(spring),454±205(summer),650±411(autumn),and 1019±703(winter) ng/m3.Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer,although WIRC concentrations were typically higher,especially in winter and spring.The δ13C PDB value(-25.3 ± 0.8)%.determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion.No seasonal change in δ13C PDB was evident.The average percent Modern Carbon(pMC) for 14C in WIRC for winter and spring was(67.2 ± 7.7)%(n = 29).Lower pMC values were associated with air masses transported from the area east of WLG,while higher pMC values were associated with air masses from the Tibetan Plateau,southwest of WLG.Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event. 相似文献
3.
Ionics - This study aims to explore the potential merits of palladium oxide sensing electrode. PdO is applied on a solid-state potentiometric sensor on an yttria-stabilized zirconia (YSZ)... 相似文献
4.
5.
6.
7.
A new secoiridoid, multiflorin (1) has been isolated from the EtOAc-soluble fraction of Jasminum multiflorum (Oleaceace). The structure of I was determined by application of spectral methods. 相似文献
8.
We employ a first-principles plane wave method with the
relativistic analytic pseudopotential of Hartwigsen, Goedecker and Hutter
(HGH) scheme in the frame of DFT to calculate
the equilibrium lattice parameters and the thermodynamic properties of
AlB2 compound with hcp structure. The obtained lattice parameters are in
good agreement with the available experimental data and those calculated by
others. Through the quasi-harmonic Debye model, obtained successfully are
the dependences of the
normalized lattice parameters a/a0 and c/c0 on pressure P, the normalized
primitive cell volume V/V0 on pressure P, the variation of the thermal
expansion α with pressure P and temperature T, as well as the Debye
temperature \ThetaD and the heat capacity CV on pressure P and
temperature T. 相似文献
9.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities. 相似文献
10.
Gang Wang Xiulin Zhu Zhenping Cheng Jian Zhu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(9):2912-2921
A series of (di)picolinic acids and their derivates are investigated as novel complexing tridentate or bidentate ligands in the iron‐mediated reverse atom transfer radical polymerization of methyl methacrylate in N,N‐dimethylformamide at 100 °C with 2,2′‐azobisisobutyrontrile as an initiator. The polymerization rates and polydispersity indices (1.32–1.8) of the resulting polymers are dependent on the structures of the ligands employed. Different iron complexes may be involved in iron‐mediated reverse atom transfer radical polymerization, depending on the type of acid used. 1H NMR spectroscopy has been used to study the structure of the resulting polymers. Chain‐extension reactions have been performed to further confirm the living nature of this catalytic system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2912–2921, 2006 相似文献