全文获取类型
收费全文 | 9836篇 |
免费 | 1467篇 |
国内免费 | 1367篇 |
专业分类
化学 | 9279篇 |
晶体学 | 82篇 |
力学 | 31篇 |
综合类 | 89篇 |
数学 | 6篇 |
物理学 | 3183篇 |
出版年
2024年 | 36篇 |
2023年 | 99篇 |
2022年 | 364篇 |
2021年 | 366篇 |
2020年 | 390篇 |
2019年 | 443篇 |
2018年 | 322篇 |
2017年 | 374篇 |
2016年 | 520篇 |
2015年 | 501篇 |
2014年 | 534篇 |
2013年 | 956篇 |
2012年 | 775篇 |
2011年 | 601篇 |
2010年 | 587篇 |
2009年 | 617篇 |
2008年 | 612篇 |
2007年 | 659篇 |
2006年 | 608篇 |
2005年 | 523篇 |
2004年 | 453篇 |
2003年 | 378篇 |
2002年 | 311篇 |
2001年 | 179篇 |
2000年 | 208篇 |
1999年 | 161篇 |
1998年 | 162篇 |
1997年 | 155篇 |
1996年 | 128篇 |
1995年 | 147篇 |
1994年 | 92篇 |
1993年 | 100篇 |
1992年 | 75篇 |
1991年 | 61篇 |
1990年 | 39篇 |
1989年 | 28篇 |
1988年 | 26篇 |
1987年 | 28篇 |
1986年 | 8篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
991.
Masakatsu Kasuya Tatsuo Taniguchi Ryuhei Motokawa Michinari Kohri Keiki Kishikawa Takayuki Nakahira 《Journal of polymer science. Part A, Polymer chemistry》2013,51(19):4042-4051
We developed a novel fluorescence labeling technique for quantification of surface densities of atom transfer radical polymerization (ATRP) initiators on polymer particles. The cationic P(St‐CPEM‐C4DMAEMA) and anionic P(St‐CPEM) polymer latex particles carrying ATRP‐initiating chlorine groups were prepared by emulsifier‐free emulsion polymerization of styrene (St), 2‐(2‐chloropropionyloxy)ethyl methacrylate (CPEM), and N‐n‐butyl‐N,N‐dimethyl‐N‐(2‐methacryloyloxy)ethylammonium bromide (C4DMAEMA). ATRP initiators on the surface of polymer particles were converted into azide groups by sodium azide, followed by fluorescent labeling with 5‐(N,N‐dimethylamino)‐N′‐(prop‐2‐yn‐1‐yl)naphthalene‐1‐sulfonamide (Dansyl‐alkyne) by copper‐catalyzed azide‐alkyne cycloaddition (CuAAC). The reaction time required for both azidation of ATRP‐initiating groups and successive fluorescence labeling of azide groups with Dansyl‐alkyne by CuAAC were investigated in detail by FTIR and fluorescence spectral measurement, respectively. The ATRP initiator densities on the cationic P(St‐CPEM‐C4DMAEMA) and anionic P(St‐CPEM) particle surfaces were estimated to be 0.21 and 0.15 molecules nm?2, respectively, which gave close agreement with values previously determined by a conductometric titration method. The fluorescence labeling through click chemistry proposed herein is a versatile technique to quantify the surface ATRP initiator density both on anionic and cationic polymer particles. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4042–4051 相似文献
992.
993.
Xiaofeng Xu Wanzhu Cai Junwu Chen Yong Cao 《Journal of polymer science. Part A, Polymer chemistry》2011,49(5):1263-1272
Poly(2,7‐carbazole) neutral polymers (PC‐N, PC‐NOH, and PC‐P) and polyelectrolytes (PC‐NBr and PC‐SO3Na) with hydrophilic pendant groups of ammonium, phosphonate, and sulfonate were synthesized as interlayers for cathode modifications in bulk‐heterojunction photovoltaic cells (BHJ PVCs). The absorptions of the polymers were determined by the poly(2,7‐carbazole) backbone, showing absorption peaks at ~390 nm for their solutions and films. Because of large intermolecular interactions, excimer emissions with wavelengths higher than 500 nm were found in the photoluminescence spectra of the films of the polymers, which weakened the light emissions of the polymers. PC‐N, PC‐NBr, PC‐NOH, and PC‐P possessed comparable HOMO levels of ?5.23 eV and LUMO levels of ?2.4 eV, but HOMO and LUMO levels of PC‐SO3Na were up‐lying to ?4.91 and ?2.12 eV, respectively. PC‐N, PC‐NBr, PC‐NOH, and PC‐P were selected to construct thin interlayers in BHJ PVCs with PFO‐DBT35:PCBM = 1:4 as the active layer. Compared with traditional Al cathode, bilayer cathodes with the interlayers showed improvements of open‐circuit voltages and short‐circuit currents of the PVCs. PC‐NOH was the best for the photovoltaic performances and over 20% increase of power conversion efficiency (PCE) was achieved. The bilayer cathodes would have great potential to further elevate PCE of BHJ PVCs with other active layer materials. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
994.
Zheng Chen Daniel R. Dreyer Zong‐quan Wu Kelly M. Wiggins Zhenhua Jiang Christopher W. Bielawski 《Journal of polymer science. Part A, Polymer chemistry》2011,49(6):1421-1426
The synthesis and characterization of a novel family of main‐chain carbazole‐containing polymers using copper‐catalyzed azide‐alkyne cycloaddition chemistry is reported. The reactions were performed under mild conditions using readily available copper catalysts and ligands, which afforded polymeric products with Mws up to 18 kDa. Using a range of techniques, the polymers were found to exhibit a glass transition temperature (Tg) of 85 °C, high thermal stability (Td = 274 °C), and high photoluminescent quantum efficiency (?f = 0.29; λem = 448 nm), which underscore their potential for use in organic light‐emitting diodes or other emissive devices, particularly where efficient blue emission is of value. The approach described offers practical advantages over other synthetic methods used to prepare main‐chain carbazole‐containing polymers, especially with regard to the lack of need for rigorously inert conditions and the absence of byproducts generated during the polymerization reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
995.
We previously showed that in N,N‐dimethylformamide (DMF), poly(9‐anthracenylmethyl methacrylate) (PAMMA) and poly(2‐naphthylmethacrylate) selectively disperse semiconducting and metallic single‐walled carbon nanotubes (SWNTs), respectively. We have also proposed a new noncovalent polymer interaction based on photon induced dipole–dipole interaction to account for the metallicity‐based selectivity. In this article, we investigate two other polymethacrylates, that is, poly(benzyl methacrylate) (PBMA) and poly(methylmethacrylate)‐co‐(9‐anthracenylmethyl acrylate) (PMMA‐c‐PAMA) in the light of our previously proposed photon‐induced dipole–dipole interaction. We find that PBMA and PMM‐c‐PAMMA in DMF show no metallicity selectivity. The different selective behavior of the four polymers in DMF manifests the decisive influence of the side aromatic group in determining their metallicity selectivity. The nonpreferential energy transfer from PMMA‐c‐PAMA to SWNTs and the nonoverlap of PBMA fluorescence (in the ultraviolet range) with nanotube absorption account for their nonselectivity of specific nanotube species. Further, the parallel relationship between the diameters of extracted tube species and the affinity between polymers and solvents suggests the leading role of the polymeric conformation on the diameter selectivity. A sufficient (i.e., 2 weeks) standing time of the SWNTs solution after sonication, during which the polymers presumably optimize their conformation to the SWNTs, was found to be essential to the enrichment. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
996.
Rodion Yu. IliashenkoNikolay Yu. Gorobets Andrey O. Doroshenko 《Tetrahedron letters》2011,52(39):5086-5089
Two new unsymmetric derivatives of 1,2-bis-(5-phenyloxazol-2-yl)benzene (ortho-POPOP) were synthesized via microwave-assisted nucleophilic substitution of fluorine which appears to be significantly more efficient compared with conventional thermal activation. The compounds synthesized are characterized by high fluorescence Stokes shifts (6000-11,000 cm−1) in solvents of various polarity, intermediate-to-high fluorescence quantum yields and lifetimes in the range of several nanoseconds. 相似文献
997.
We present a revised assignment of the Raman active fundamental vibrations of TCNE which utilizes new information obtained from Raman studies of electron donor/acceptor complexes of TCNE. This new assignment is consistent with and supported by all available evidence from previous studies. 相似文献
998.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(3):319-327
Different kinds of porous organic polymers (POPs) bearing 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BDP) fluorophores have been developed to generate singlet oxygen upon light illumination. Herein, four imine‐linked POPs were prepared by copolymerization of amine and aldehyde with different ratios of di‐aldehyde A1 and A2. The POPs were investigated by a combination of techniques such as solid 13C NMR, FTIR, and nitrogen absorption–desorption isotherms and electronic microscopy. The results demonstrated that these POPs were prone to form hierarchical porous architectures. Scanning electron microscopy and transmission electron microscopy images revealed that the spherical morphologies showed different roughness, that is, BDP‐POPs with more BDP aldehyde A2 presented rougher surface. Finally, these POPs were used to generate singlet oxygen (1O2) monitored by 1,3‐diphenylisobenzofuran and bioimaging in HeLa cells. Our results indicated that the ability to generate 1O2 is dependent on the amount of BDP. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 319–327 相似文献
999.
1000.
A new fluorogenic probe for sodium new houttuyfonate (SNH) was proposed. 4‐Methylumbelliferyl‐2,4‐dinitrobenzenesulfonate (4‐MUDNBS) was a nonfluorescent compound and was synthesized via the one‐step reaction of 4‐methylumbelliferone (4‐MU) with 2,4‐dinitrobenzenesulfonyl chloride. In basic media, SNH was decomposed to produce sodium sulfite, which then reacted with 4‐MUDNBS to yield highly fluorescent 4‐MU, hence leading to the fluorescence increase of the reaction solution. A linear correlation existed between the emission intensity and the concentration of SNH within the range from 0.5 to 15 μg·mL−1 with a detection limit of 0.15 μg· mL−1 (3δ). The effect of substituents on the benzenesulfonyl moiety of the probe is discussed, and the presence of electronegative groups is favorable for the proposed cleavage reaction. 相似文献