全文获取类型
收费全文 | 1567篇 |
免费 | 30篇 |
国内免费 | 6篇 |
专业分类
化学 | 947篇 |
晶体学 | 9篇 |
力学 | 64篇 |
数学 | 276篇 |
物理学 | 307篇 |
出版年
2023年 | 12篇 |
2022年 | 51篇 |
2021年 | 49篇 |
2020年 | 41篇 |
2019年 | 35篇 |
2018年 | 24篇 |
2017年 | 19篇 |
2016年 | 65篇 |
2015年 | 48篇 |
2014年 | 51篇 |
2013年 | 80篇 |
2012年 | 91篇 |
2011年 | 111篇 |
2010年 | 50篇 |
2009年 | 63篇 |
2008年 | 89篇 |
2007年 | 95篇 |
2006年 | 60篇 |
2005年 | 51篇 |
2004年 | 41篇 |
2003年 | 37篇 |
2002年 | 36篇 |
2001年 | 31篇 |
2000年 | 16篇 |
1999年 | 22篇 |
1998年 | 10篇 |
1997年 | 15篇 |
1996年 | 22篇 |
1995年 | 24篇 |
1994年 | 22篇 |
1993年 | 19篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 10篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 6篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 12篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1966年 | 4篇 |
排序方式: 共有1603条查询结果,搜索用时 31 毫秒
1.
V. Vittoria R. Russo F. De Candia P. L. Magagnini B. Bresci 《Journal of Polymer Science.Polymer Physics》1991,29(9):1163-1168
The transport properties of a side-chain liquid-crystalline polymer forming a smectic A phase have been investigated using dichloromethane as a permeant. Samples differing in the isotropization enthaoly were analyzed. A. Correlation between this thermal parameter and sorption has been found, while the diffusion coefficient is substantially the same in all samples. The results obtained can be explained in terms of a biphasis model in which a disordered permeable phase is present within the liquid-crystalline phase, which is impermeable to the diffusant molecules. 相似文献
2.
Ilaria Fratoddi Chiara Battocchio Alessandra L. Groia Maria V. Russo 《Journal of polymer science. Part A, Polymer chemistry》2007,45(15):3311-3329
The reactivity of square planar palladium(II) and platinum(II) complexes in trans or cis configuration, namely trans or cis‐[dichlorobis(tributylphosphine)platinum(II)] and trans‐[dichlorobis(tributylphosphine)palladium(II)] with 1,1′‐bis(ethynyl) 4,4′‐biphenyl, DEBP, leading to π‐conjugated organometallic oligomeric and polymeric metallaynes, was investigated by a systematic variation of the reaction conditions. The formation of polymers and oligomers with defined chain length [? M(PBu3)2 (C?C? C6H4? C6H4? C?C? )]n (n = 3–10 for the oligomers, n = 20–50 for the polymers) depends on the configuration of the precursor Pt(II) and Pd(II) complexes, the presence/absence of the catalyst CuI, and the reaction time. A series of model reactions monitored by XPS, GPC, and NMR 31P spectroscopy showed the route to modulate the chain growth. As expected, the nature of the transition metal (Pt or Pd) and the molecular weight of the polymers markedly influence the photophysical characteristics of the polymetallaynes, such as optical absorption and emission behavior. Polymetallaynes with nanostructured morphology could be obtained by a simple casting procedure of polymer solutions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3311–3329, 2007 相似文献
3.
4.
We present here an ab-initio STO-3G and advanced semiempirical AM1 calculation for the structure and the conformational behavior of phenyltetrazine and bitetrazine molecules. Results for phenyltetrazine isomers show that in the absence of H-H interactions, the preferred conformation is the planar one. Instead, in the case of bitetrazines, the systems dominated by the lone pair-lone pair interactions are not planar. In the presence of direct H-H interaction as for 5-5-1,2,3,4 bitetrazine, the antiplanar conformation is the preferred one. Comparison with other systems (including one or more nitrogen lone pairs) shows that the compounds with the same ortho substituents have very similar conformational behavior irrespective of their composition. The AM1 results indicate that this method is able to give reliable conformational information for compounds in which H-H interactions are involved. A Fourier expansion of the torsional potential suggests that the first two terms fit the calculated torsional potentials well except in the case of two H-H interactions in the same molecule. 相似文献
5.
6.
Coated capillaries modified with a hydrophobic layer were developed. Linear hydrocarbons and ethylbenzene modified surfaces greatly improved the electrophoretic performance of the capillaries. The column efficiency for organic compounds reached as high as 327 000 theoretical plate numbers per meter on a 50 microm I.D. linear hydrocarbon (C6) surface treated fused-silica capillary column. This value did not change during 50 repeated analyses and the columns showed strong stability against 0.1 M NaOH and 0.1 M HCl. The relative standard deviation of the run-to-run, day-to-day, and capillary-to-capillary coating with hydrophobic layer showed values of < or =2.5%, and good reproducibility. The separations of four aromatic amines and six pharmacological amines at pH 2.5 is reported. 相似文献
7.
B. E. Krisyuk A. A. Popov G. E. Zaikov F. de Candia V. Vittoria R. Russo 《Colloid and polymer science》1987,265(3):220-225
The static modulus of elasticity (E) and the correlation time of rotation (
c
) of 2,-2,6,6-tetramethylpiperidine-1-oxyl are studied as a function of the temperature (210<T <350°K) for oriented films of isotactic polypropylene and polyethylene of high and low density.E and
c
change both upon heating and polymer orientation; this result indicates that sample properties are influenced by the microstructure of the amorphous phase where probes are localized. 相似文献
8.
C. Bagnasco P. Ciambelli S. Crescitelli G. Russo 《Reaction Kinetics and Catalysis Letters》1978,8(3):293-300
Cytalysts containing manganese, cobalt or nickel oxides supported on -alumina were physically characterized and tested for the oxidehydrogenation of ethylbenzene. The physical characterization shows surface spinel formation and/or metal oxide segregation for the systems cobalt-alumina and nickelalumina, but Mn2O3 segregation only for the manganese system. The catalytic activity data indicate a promoting effect of Mn2O3 and cobalt aluminate, while the presence of Co3O4 results in a lower activity.
, , -Al2O3, . / - , Mn2O3 . , Mn2O3 , Co3O4) .相似文献
9.
Stable polyacrylamide (polyAA)–montmorillonite adducts were prepared by two distinct processes: (1) free radical copolymerization of AA with alkaline clay previously treated with 2-(N-methyl-N,N-diethyl ammonium iodide)ethylacrylate (QD1) and (2) direct interactions of alkaline montmorillonite with various preformed copolymers of AA with QD1. The structure of the adducts as determined by Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry and X-ray diffraction was shown to consist of AA macromolecules inserted between lamellar layers whose spacing was larger than in the polymer-free clay. The polymer was strongly attached to the inorganic surfaces, probably due to cooperative formation of electrostatic bonding. The thermal stability of the organic polymers in the resulting complexes was substantially enhanced while the mobility of macromolecules decreased. 相似文献
10.
R. Russo 《Colloid and polymer science》1991,269(1):1-6
Solution casted films of segmented polyurethanes based on poly (ethylene adipate) glycol, 4,4diphenylmethanediisocyanate, and 1,4 butanediol were studied by thermal-mechanical methods including differential scanning calorimetry and mechanical hysteresis. Data demonstrate that, following thermal treatment at 70 °C for 15 min, these polymers show time-dependent thermal and mechanical properties. In fact, because 70 °C is a temperature greater than the melting point of soft segments (about 42 °C), the soft-segment crystals are melted and their crystallization is time dependent. The results are explained in terms of phase separation. In particular, the sample with better phase separation has a faster and larger recovery. 相似文献