全文获取类型
收费全文 | 355806篇 |
免费 | 4558篇 |
国内免费 | 1769篇 |
专业分类
化学 | 190891篇 |
晶体学 | 4439篇 |
力学 | 15039篇 |
综合类 | 64篇 |
数学 | 41949篇 |
物理学 | 109751篇 |
出版年
2020年 | 2920篇 |
2019年 | 3205篇 |
2018年 | 4139篇 |
2017年 | 4246篇 |
2016年 | 6329篇 |
2015年 | 4043篇 |
2014年 | 6215篇 |
2013年 | 15490篇 |
2012年 | 12374篇 |
2011年 | 14966篇 |
2010年 | 10718篇 |
2009年 | 10572篇 |
2008年 | 14167篇 |
2007年 | 14143篇 |
2006年 | 13374篇 |
2005年 | 12114篇 |
2004年 | 10940篇 |
2003年 | 9598篇 |
2002年 | 8839篇 |
2001年 | 10475篇 |
2000年 | 7721篇 |
1999年 | 5641篇 |
1998年 | 4726篇 |
1997年 | 4704篇 |
1996年 | 4481篇 |
1995年 | 4280篇 |
1994年 | 4346篇 |
1993年 | 4149篇 |
1992年 | 4605篇 |
1991年 | 4641篇 |
1990年 | 4408篇 |
1989年 | 4290篇 |
1988年 | 4241篇 |
1987年 | 4165篇 |
1986年 | 4056篇 |
1985年 | 5392篇 |
1984年 | 5504篇 |
1983年 | 4705篇 |
1982年 | 5033篇 |
1981年 | 4669篇 |
1980年 | 4459篇 |
1979年 | 4765篇 |
1978年 | 5000篇 |
1977年 | 4988篇 |
1976年 | 5037篇 |
1975年 | 4713篇 |
1974年 | 4792篇 |
1973年 | 4988篇 |
1972年 | 3649篇 |
1971年 | 2928篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Comparison of copolymer emulsions of fluorine and siloxane‐containing acrylates with core–shell structure for water‐repellent cotton fabrics coatings 下载免费PDF全文
J. Lin C. Zheng M. N. Zhu Y. Z. Chen P. P. Lu Q. Liu X. F. Cai J. W. Zhuang X. M. Cai L. P. Liao G. Y. Yuan C. L. Xu 《先进技术聚合物》2015,26(1):68-76
This paper described the synthesis of copolymer emulsions of fluorine and siloxane‐containing acrylates for water‐repellent cotton fabrics coatings. Chemical composition, morphology structure, and properties of the latex copolymers were investigated by Fourier transform infrared (FTIR), dynamic light scattering (DLS), gel permeation chromatography (GPC), and transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Effects of water‐repellent functional monomers (Rf) on surface morphology, water contact angle, and water‐repellent properties of the coated fabric surface were also studied. The results indicated that Rf greatly influenced molecular mass distribution of the latex copolymers, the molecular aggregation states and orientation of Rf on the coated fabric surface, and water‐repellency of coated cotton fabrics. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
992.
993.
Novel polymer composites PEN/PVDF were prepared from poly(arylene ether nitrile) (PEN) and poly(vinylidene fluoride) (PVDF) via solution mixing. Due to the toughening effect of PVDF, PEN/PVDF blends with 5 wt % PVDF exhibit higher tensile strength (106 MPa) and breaking elongation (8.09%) than pure PEN does. Because of introduction of PVDF and interfacial polarization, the dielectric constant of PEN/PVDF blends at 1 kHz and room temperature increases from 3.3 to 4.5 with increasing content of PVDF. The dissipation factor (tanδ) of PEN/PVDF blends is relatively low (<0.04) in a very wide frequency range from 250 Hz to 100 kHz. The PEN/PVDF blends show certain piezoelectric behavior (d 33 from 0.9 to 1 pC/N) due to the contribution of PVDF. After polarization, the piezoelectric coefficient d 33 somewhat increases. The results suggest that PEN/PVDF blends will have potential application in electronic information fields, especially in film capacitors. 相似文献
994.
995.
996.
A. A. Golovanov V. V. Bekin I. S. Odin A. Yu. Chertov O. B. Grigor’eva V. S. Pisareva 《Russian Journal of Organic Chemistry》2015,51(12):1688-1692
Nucleophilic addition of secondary heterocyclic amines (morpholine, piperidine, and piperazine) to the double or triple bond of (E)-1,5-diarylpent-2-en-4-yn-1-ones is controlled by the kinetic and thermodynamic factor, respectively. The regioselectivity of the addition of piperazine to these enynones is determined by the substituent nature in the benzene rings. Conjugated ketones with electron-donating substituents take up piperazine molecule at the double bond, and those with electron-withdrawing groups, at the triple bond. 相似文献
997.
The synthesis of an octavalent bolaamphiphile with D-glucose moiety as branching unit has been designed and accomplished via 1,3-dipolar cycloaddition of bis(tetra-O-propargylglucoside) and 8 equiv of 2-azidoethyl β-D-lactoside. 相似文献
998.
M. V. Moskalev A. A. Skatova V. A. Chudakova N. M. Khvoinova N. L. Bazyakina A. G. Morozov O. V. Kazarina A. V. Cherkasov G. A. Abakumov I. L. Fedushkin 《Russian Chemical Bulletin》2015,64(12):2830-2840
Digallane (dpp-bian)Ga—Ga(dpp-bian) (1) (dpp-bian is the 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) catalyzes the addition of 4-chloroaniline to some terminal alkynes RC≡CH (R = Bun, Ph, 4-MeC6H4). The reaction orders in each of the substrates were found for the reaction of phenylacetylene with 4-chloroaniline catalyzed by compound 1. The reaction of compound 1 with phenylacetylene in a molar ratio of 1: 10 led to 1-[N-(2,6-diisopropylphenyl)imino]-2-(1-phenylethylidene)acenaphthene (5) and the compound [C12H6(NC6H3Pr2 i)(PhC=CH2)(PhC=CH)]Ga(C≡CPh)2 (6). The reaction of digallane 1 with phenylacetylene and aniline in a stoichiometric ratio of 1: 2: 2 gave bis-anilide (dpp-bian)-Ga[N(H)Ph]2 (7) in 40% yield. The compound (PhC≡C)3Ga·THF (9) was obtained by the reaction of three equivalents of sodium phenylacetylide (prepared in situ from phenylacetylene and sodium) with one equivalent of GaCl3 in tetrahydrofuran. Compounds 5—7 and 9 were characterized by IR spectroscopy, 1H NMR spectroscopy was used to characterize products 5, 6, and 9, whereas EPR spectroscopy was used for amide 7. The structures of compounds 5—7 and 9 were determined by single crystal X-ray diffraction analysis. 相似文献
999.
Vasilieva E. A. Gainanova G. A. Bekmukhametova A. M. Karimova T. R. Saifutdinova M. N. Gavrilova E. L. Zakharova L. Ya. Sinyashin O. G. 《Russian Chemical Bulletin》2015,64(12):2897-2902
The solubilization capacities of binary systems based on cationic surfactants (cetyltrimethylammonium bromide and dodecanediyl-1,12-bis(hydroxyethylmethylhexadecylammonium bromide)) and new amphiphilic calix[4]resorcinol with amino acid residues at the upper rim and alkyl substituents at the lower rim with respect to the spectral probe Sudan I and the fluorescent labels (pyrene and prodan) were studied by spectrophotometry and fluorimetry. Critical aggregation concentrations were determined and aggregation numbers were calculated. The sizes of surfactant—calix[4]resorcinol complexes were determined by dynamic light scattering.
相似文献1000.
Xianwen Lou Bas F. M. de Waal Lech‐Gustav Milroy Joost L. J. van Dongen 《Journal of mass spectrometry : JMS》2015,50(5):766-770
In matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI TOF MS), analyte signals can be substantially suppressed by other compounds in the sample. In this technical note, we describe a modified thin‐layer sample preparation method that significantly reduces the analyte suppression effect (ASE). In our method, analytes are deposited on top of the surface of matrix preloaded on the MALDI plate. To prevent embedding of analyte into the matrix crystals, the sample solution were prepared without matrix and efforts were taken not to re‐dissolve the preloaded matrix. The results with model mixtures of peptides, synthetic polymers and lipids show that detection of analyte ions, which were completely suppressed using the conventional dried‐droplet method, could be effectively recovered by using our method. Our findings suggest that the incorporation of analytes in the matrix crystals has an important contributory effect on ASE. By reducing ASE, our method should be useful for the direct MALDI MS analysis of multicomponent mixtures. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献