全文获取类型
收费全文 | 16999篇 |
免费 | 2643篇 |
国内免费 | 3067篇 |
专业分类
化学 | 12463篇 |
晶体学 | 256篇 |
力学 | 994篇 |
综合类 | 274篇 |
数学 | 2234篇 |
物理学 | 6488篇 |
出版年
2024年 | 35篇 |
2023年 | 206篇 |
2022年 | 427篇 |
2021年 | 520篇 |
2020年 | 533篇 |
2019年 | 578篇 |
2018年 | 523篇 |
2017年 | 561篇 |
2016年 | 766篇 |
2015年 | 837篇 |
2014年 | 1043篇 |
2013年 | 1291篇 |
2012年 | 1357篇 |
2011年 | 1518篇 |
2010年 | 1222篇 |
2009年 | 1289篇 |
2008年 | 1392篇 |
2007年 | 1228篇 |
2006年 | 1210篇 |
2005年 | 1063篇 |
2004年 | 857篇 |
2003年 | 693篇 |
2002年 | 831篇 |
2001年 | 598篇 |
2000年 | 511篇 |
1999年 | 363篇 |
1998年 | 227篇 |
1997年 | 161篇 |
1996年 | 157篇 |
1995年 | 104篇 |
1994年 | 95篇 |
1993年 | 75篇 |
1992年 | 76篇 |
1991年 | 63篇 |
1990年 | 54篇 |
1989年 | 52篇 |
1988年 | 41篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 25篇 |
1984年 | 11篇 |
1983年 | 11篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 10篇 |
1979年 | 6篇 |
1978年 | 14篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
51.
52.
Tanmoy Dutta Yong Li Aaron L. Thornton Da‐Ming Zhu Zhonghua Peng 《Journal of polymer science. Part A, Polymer chemistry》2013,51(18):3818-3828
Donor‐acceptor conjugated polymers containing a new imide‐functionalized naphthodithiophene (INDT) as the acceptor unit and a 2,2'‐bithiophene with varied substituents as the donor unit have been synthesized. The bandgaps of these polymers depend strongly on the dihedral angle of the 2,2'‐bithiophene unit. The 3,3'‐dialkoxy substitution (polymers PDOR / PBOR ) leads to near planar bithiophene conformation due to the well‐known S–O short contact, while the 3,3'‐dialkyl substitution (polymer PDR ) results in significant twisting due to the steric effect. Consequently PDOR / PBOR shows the lowest bandgap of 1.82/1.85 eV while PDR has a bandgap of 2.38 eV. Bulk‐heterojunction solar cells of the polymer/fullerene blends have been fabricated. Preliminary results show that PBOR gives the best device performance with power conversion efficiencies as high as 2.45% in air without any thermal annealing treatment, indicating the promising potential of INDT‐containing conjugated polymers for efficient solar cells. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3818–3828 相似文献
53.
A highly convenient method for N-formylation of amines via treatment by formic acid in the presence of melamine trisulfonic acid as a catalyst has been developed. This method showed improvements over previous reports in terms of yield, reaction time and chemoselectivity. 相似文献
54.
55.
Coral reef-like PANI nanotubes composed of nanopaticles were successfully synthesized by a reactive template of manganese oxide.The structure was characterized by using SEM,TEM,and FT-IR,and the supercapacitive behaviors of these nanotubes were investigated with cyclic voltammetry(CV),and charge-discharge tests,respectively.A maximum specific capacitance of 533 F/g could be achieved in 1mol/L aqueous H2SO4 with the potential range of -0.2 to 0.8 V(vs.the saturated calomel electrode) in a half-cell setup configuration for PANI electrode,suggesting its potential application in the electrode material for electrochemical capacitors. 相似文献
56.
Cheng-Ling Pan Chang-Min Hou Lei Zhang Yong Fan Shao-Ding Sheng 《Mendeleev Communications》2012,22(2):109-110
The reaction of potassium pyridyl amido ligand {L = [N(R)(2-C5H3N-6-Me)]–, R = CH2But} with YbI2(thf)2 afforded the linear polymeric complex [K0.5(L)3YbiiK0.5]n, which was characterized by X-ray structure analysis. 相似文献
57.
A rapid,sensitive,selective and reliable strip assay based on DNA-functionalized gold nanoparticles for Hg2+ detection has been developed,with a detection limit 5 nmol/L.The measurement principle was based on thymine-Hg2+-thymine(T-Hg2+-T) coordination chemistry and streptavidin-biotin interaction.The major advantages of this assay are that results can be read visually without any instrument in less than 10 min and that it does not require any sample pretreatment. 相似文献
58.
59.
Da Quan Zhang Xing Jin Bin Xie Hyung Goun Joo Li Xin Gao Kang Yong Lee 《Surface and interface analysis : SIA》2012,44(1):78-83
The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10?4 mol.l?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
60.
The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275?K with pressures from 0 to 3.7?MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO2 hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO2 sorption was about 2.5?mmol of CO2 per gram of dry sorbent at 275?K. Similarly, the highest sorption was about 2.7?mmol for wet SG-B with R w =0.81. However, CO2 hydrate did not form on the wet surface of SG-C due to its large pore sizes. 相似文献