全文获取类型
收费全文 | 138570篇 |
免费 | 24211篇 |
国内免费 | 13494篇 |
专业分类
化学 | 109434篇 |
晶体学 | 1494篇 |
力学 | 6596篇 |
综合类 | 708篇 |
数学 | 14905篇 |
物理学 | 43138篇 |
出版年
2024年 | 371篇 |
2023年 | 2150篇 |
2022年 | 3853篇 |
2021年 | 4157篇 |
2020年 | 5294篇 |
2019年 | 6240篇 |
2018年 | 4701篇 |
2017年 | 4097篇 |
2016年 | 8077篇 |
2015年 | 8184篇 |
2014年 | 9236篇 |
2013年 | 11558篇 |
2012年 | 12127篇 |
2011年 | 11619篇 |
2010年 | 9295篇 |
2009年 | 9036篇 |
2008年 | 8878篇 |
2007年 | 7646篇 |
2006年 | 6947篇 |
2005年 | 6146篇 |
2004年 | 4965篇 |
2003年 | 4107篇 |
2002年 | 4572篇 |
2001年 | 3507篇 |
2000年 | 3203篇 |
1999年 | 2456篇 |
1998年 | 1796篇 |
1997年 | 1613篇 |
1996年 | 1590篇 |
1995年 | 1394篇 |
1994年 | 1247篇 |
1993年 | 1028篇 |
1992年 | 920篇 |
1991年 | 792篇 |
1990年 | 663篇 |
1989年 | 511篇 |
1988年 | 396篇 |
1987年 | 343篇 |
1986年 | 348篇 |
1985年 | 277篇 |
1984年 | 202篇 |
1983年 | 158篇 |
1982年 | 138篇 |
1981年 | 83篇 |
1980年 | 65篇 |
1979年 | 37篇 |
1978年 | 30篇 |
1976年 | 29篇 |
1975年 | 29篇 |
1957年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
42.
DFT mechanistic study of the H2‐assisted chain transfer copolymerization of propylene and p‐methylstyrene catalyzed by zirconocene complex 下载免费PDF全文
Cheng‐Gen Zhang Shu‐Yuan Yu Liaoyun Zhang Huayi Li Zhi‐Xiang Wang 《Journal of polymer science. Part A, Polymer chemistry》2015,53(4):576-585
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585 相似文献
43.
Synthesis,Electronic Properties and WOLED Devices of Planar Phosphorus‐Containing Polycyclic Aromatic Hydrocarbons 下载免费PDF全文
Dr. François Riobé Rózsa Szűcs Dr. Pierre‐Antoine Bouit Dr. Denis Tondelier Bernard Geffroy Fátima Aparicio Julia Buendía Prof. Luis Sánchez Prof. Régis Réau Prof. László Nyulászi Prof. Muriel Hissler 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(17):6547-6556
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs). 相似文献
44.
45.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献
46.
Amphiphilic block copolymer self‐assemblies of poly(NVP)‐b‐poly(MDO‐co‐vinyl esters): Tunable dimensions and functionalities 下载免费PDF全文
Guillaume G. Hedir A. Pitto‐Barry Andrew P. Dove Rachel K. O'Reilly 《Journal of polymer science. Part A, Polymer chemistry》2015,53(23):2699-2710
Functional, degradable polymers were synthesized via the copolymerization of vinyl acetate (VAc) and 2‐methylene‐1,3‐dioxepane (MDO) using a macro‐xanthate CTA, poly(N‐vinylpyrrolidone), resulting in the formation of amphiphilic block copolymers of poly(NVP)‐b‐poly(MDO‐co‐VAc). The behavior of the block copolymers in water was investigated and resulted in the formation of self‐assembled nanoparticles containing a hydrophobic core and a hydrophilic corona. The size of the resultant nanoparticles was able to be tuned with variation of the hydrophilic and hydrophobic segments of the core and corona by changing the incorporation of the macro‐CTA as well as the monomer composition in the copolymers, as observed by Dynamic Light Scattering, Static Light Scattering, and Transmission Electron Microscopy analyses. The concept was further applied to a VAc derivative monomer, vinyl bromobutanoate, to incorporate further functionalities such as fluorescent dithiomaleimide groups throughout the polymer backbone using azidation and “click” chemistry as postpolymerization tools to create fluorescently labeled nanoparticles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2699–2710 相似文献
47.
48.
49.
50.
Quantitative analysis of polyhexamethylene guanidine (PHMG) oligomers via matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with an ionic‐liquid matrix 下载免费PDF全文