全文获取类型
收费全文 | 300078篇 |
免费 | 37026篇 |
国内免费 | 28284篇 |
专业分类
化学 | 191969篇 |
晶体学 | 3591篇 |
力学 | 18762篇 |
综合类 | 1840篇 |
数学 | 39799篇 |
物理学 | 109427篇 |
出版年
2023年 | 4034篇 |
2022年 | 6662篇 |
2021年 | 8348篇 |
2020年 | 9492篇 |
2019年 | 9423篇 |
2018年 | 9400篇 |
2017年 | 9028篇 |
2016年 | 12536篇 |
2015年 | 11126篇 |
2014年 | 14342篇 |
2013年 | 19584篇 |
2012年 | 22455篇 |
2011年 | 23827篇 |
2010年 | 17093篇 |
2009年 | 16730篇 |
2008年 | 18006篇 |
2007年 | 16283篇 |
2006年 | 15178篇 |
2005年 | 13011篇 |
2004年 | 10557篇 |
2003年 | 8711篇 |
2002年 | 8519篇 |
2001年 | 7240篇 |
2000年 | 6209篇 |
1999年 | 6092篇 |
1998年 | 5337篇 |
1997年 | 4871篇 |
1996年 | 4831篇 |
1995年 | 4213篇 |
1994年 | 3905篇 |
1993年 | 3389篇 |
1992年 | 3091篇 |
1991年 | 2898篇 |
1990年 | 2619篇 |
1989年 | 2227篇 |
1988年 | 1874篇 |
1987年 | 1665篇 |
1986年 | 1592篇 |
1985年 | 1553篇 |
1984年 | 1365篇 |
1983年 | 1180篇 |
1982年 | 1105篇 |
1981年 | 920篇 |
1979年 | 877篇 |
1978年 | 880篇 |
1977年 | 878篇 |
1976年 | 992篇 |
1975年 | 880篇 |
1974年 | 887篇 |
1973年 | 916篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
111.
Gurenkova Yu. S. Kornyakov I. V. Ostrovsky V. A. Skrylnikova M. A. Khramchikhin A. V. 《Russian Journal of General Chemistry》2020,90(7):1202-1206
Russian Journal of General Chemistry - 8-Phenyltetrazolo[5,1-b][1,3,4]thiadiazepine was obtained as a result of intermolecular cyclization of 1-amino-1H-tetrazole-5-thiol and 3-phenyl-2-propynal.... 相似文献
112.
Panpan Li Quanbin Liang Eugene Yau-Hin Hong Chin-Yiu Chan Yat-Hin Cheng Ming-Yi Leung Mei-Yee Chan Kam-Hung Low Hongbin Wu Vivian Wing-Wah Yam 《Chemical science》2020,11(42):11601
A class of acceptor–donor–acceptor chromophoric small-molecule non-fullerene acceptors, 1–4, with difluoroboron(iii) β-diketonate (BF2bdk) as the electron-accepting moiety has been developed. Through the variation of the central donor unit and the modification on the peripheral substituents of the terminal BF2bdk acceptor unit, their photophysical and electrochemical properties have been systematically studied. Taking advantage of their low-lying lowest unoccupied molecular orbital energy levels (from −3.65 to −3.72 eV) and relatively high electron mobility (7.49 × 10−4 cm2 V−1 s−1), these BF2bdk-based compounds have been employed as non-fullerene acceptors in organic solar cells with maximum power conversion efficiencies of up to 4.31%. Moreover, bistable resistive memory characteristics with charge-trapping mechanisms have been demonstrated in these BF2bdk-based compounds. This work not only demonstrates for the first time the use of a boron(iii) β-diketonate unit in constructing non-fullerene acceptors, but also provides more insights into designing organic materials with multi-functional properties.Boron(iii) β-diketonates have been demonstrated to serve as multi-functional materials in NFA-based OPVs and organic resistive memories. 相似文献
113.
114.
115.
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
116.
V. A. Bespalov V. M. Glazov E. A. Il’ichev Yu. A. Klimov S. V. Kuklev A. E. Kuleshov R. M. Nabiev G. N. Petrukhin B. G. Potapov G. S. Rychkov D. S. Sokolov V. V. Fandeev E. A. Fetisov S. S. Yakushov 《Technical Physics》2015,60(4):553-560
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
117.
118.
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
119.
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
120.
Xiaoxia Yang Hongyan Xie Zhiguang Xu Jiabing Feng Qiwei Fu Haidong Li Yongtang Jia 《Journal of polymer science. Part A, Polymer chemistry》2021,59(9):813-823
An efficient, atom-economic, oxygen-tolerant, and water-tolerant strategy has been established to synthesize cyano-rich polyesters. Four kinds of organic bases, 1,1,3,3-tetramethylguanidine (TMG), 4-dimethylaminopyridine, triethylamine, and 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) were explored for accelerating Michael addition polymerization of malononitrile and 1,4-butandiol diacrylate. TMG can promote the polymerization efficiently under mild conditions to quantitatively afford polyester with high-molecular weight and moderate polydispersity. The comparison of the kinetic studies of TMG and TBD reveals that TMG shows better catalytic performance, while the catalysis of TBD brings about oligomers in spite of the higher efficiency at early age of the polymerization. Moreover, other diacrylate compounds could also be quantitatively polymerized to afford polyesters with high molecular weight. When dimethacrylate is chose as the monomer, the polymerization becomes sluggish. All the afforded polyesters display programmable thermal and mechanical properties that are closely related to their chemical structures. 相似文献