全文获取类型
收费全文 | 4455篇 |
免费 | 628篇 |
国内免费 | 265篇 |
专业分类
化学 | 2627篇 |
晶体学 | 49篇 |
力学 | 47篇 |
综合类 | 21篇 |
数学 | 21篇 |
物理学 | 1163篇 |
无线电 | 1420篇 |
出版年
2024年 | 5篇 |
2023年 | 45篇 |
2022年 | 90篇 |
2021年 | 131篇 |
2020年 | 131篇 |
2019年 | 133篇 |
2018年 | 102篇 |
2017年 | 142篇 |
2016年 | 171篇 |
2015年 | 211篇 |
2014年 | 220篇 |
2013年 | 296篇 |
2012年 | 228篇 |
2011年 | 251篇 |
2010年 | 189篇 |
2009年 | 226篇 |
2008年 | 248篇 |
2007年 | 293篇 |
2006年 | 329篇 |
2005年 | 257篇 |
2004年 | 236篇 |
2003年 | 229篇 |
2002年 | 161篇 |
2001年 | 192篇 |
2000年 | 136篇 |
1999年 | 132篇 |
1998年 | 104篇 |
1997年 | 96篇 |
1996年 | 79篇 |
1995年 | 61篇 |
1994年 | 41篇 |
1993年 | 54篇 |
1992年 | 39篇 |
1991年 | 23篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1979年 | 6篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有5348条查询结果,搜索用时 618 毫秒
141.
Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2006,44(7):2139-2155
The synthesis and characterization by size exclusion chromatography, liquid chromatography, NMR, matrix‐assisted laser desorption/ionization, thermal analysis, and other techniques of well‐defined and narrow molecular weight distribution macrocyclic polystyrene (PS), poly(2‐vinylpyridine), poly(α‐methylstyrene), poly (2‐vinyl‐naphthalene) (P2VN), and poly(9,9‐dimethyl‐2‐vinylfluorene) (PDMVF) containing a single 1,4‐benzylidene, methylidene, or 9,10‐anthracenylidene unit are reviewed. The absorption and emission spectroscopy of PS, P2VN, and PDMVF is also discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2139–2155, 2006 相似文献
142.
Four polyphenylacetylene samples, synthesized using different C6H5OH/Mo molar ratios, were investigated thermoanalytically by modulated temperature differential scanning calorimetry (MTDSC) in order to clarify a non-reversible exothermic event observed between 473 and 523 K on normal DSC. A stepwise, non-reversible change in heat capacity suggests the presence of internal reactions within the sample, that are followed by decomposition with loss of volatile products. 相似文献
143.
A. N. Danilenko V. S. Romanova E. F. Kuleshova Z. N. Parnes E. E. Braudo 《Russian Chemical Bulletin》1998,47(11):2134-2136
The concentration dependences of heat capacities of aqueous solutions of several amino acid and peptide derivatives of fullerene
were measured by scanning differential calorimetry at 298 K. The heat capacities for the arginine, alanylalanine, and glycylvaline
derivatives dissolved in water depend slightly on concentration. The concentration dependences of the heat capacities of aqueous
solutions of the serine and alanine derivatives display extrema. The calculated contributions of hydration to the heat capacities
of the dissolved fullerene derivatives have both positive and negative signs.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2202–2204, November, 1998. 相似文献
144.
K. Asami 《Colloid and polymer science》1998,276(4):373-378
A dielectric imaging technique with a scanning dielectric microscope was applied to polystyrene microcapsules in an aqueous
environment to study the electrical properties of individual ones. The dielectric images obtained over a frequency range from
10 kHz to 10 MHz showed frequency dependence, which indicated dielectric dispersion (or relaxation) due to interfacial polarization
or the build up of charge on the boundaries between the microcapsule shell and the aqueous phases. The dielectric dispersion
was analyzed based on an equivalent electrical circuit model and a shell-sphere model in which a spherical core is covered
with an insulating shell.
Received: 26 September 1997 Accepted: 26 December 1997 相似文献
145.
A dual-electrode approach for highly selective detection of glucose based on diffusion layer theory: experiments and simulation 总被引:1,自引:0,他引:1
A dual-electrode configuration for the highly selective detection of glucose in the diffusion layer of the substrate electrode is presented. In this approach, a glassy carbon electrode (GCE, substrate) modified with a conductive layer of glucose oxidase/Nafion/graphite (GNG) was used to create an interference-free region in its diffusion layer by electrochemical depletion of interfering electroactive species. A Pt microelectrode (tip, 5 microm in radius) was located in the diffusion layer of the GNG-modified GCE (GNG-G) with the help of scanning electrochemical microscopy. Consequently, the tip of the electrode could sense glucose selectively by detecting the amount of hydrogen peroxide (H2O2) formed from the oxidization of glucose on the glucose oxidase layer. The influences of parameters, including tip-substrate distance, substrate potential, and electrolyzing time, on the interference-removing efficiency of this dual-electrode approach have been investigated systematically. When the electrolyzing time was 30 s, the tip-substrate distance was 1.8 a (9.0 microm) (where a is the radius of the tip electrode), the potentials of the tip and substrate electrodes were 0.7 V and 0.4 V, respectively, and a mixture of ascorbic acid (0.3 mM), uric acid (0.3 mM), and 4-acetaminophen (0.3 mM) had no influence on the glucose detection. In addition, the current-time responses of the tip electrode at different tip-substrate distances in a solution containing interfering species were numerically simulated. The results from the simulation are in good agreement with the experimental data. This research provides a concept of detection in the diffusion layer of a substrate electrode, as an interference-free region, for developing novel microelectrochemical devices. 相似文献
146.
J. Vzquez D. García-G. Barreda P.L. Lpez-Alemany P. Villares R. Jimnez-Garay 《Thermochimica Acta》2005,430(1-2):173-182
A method has been developed for analysing the evolution with time of the volume fraction transformed and for calculating the kinetic parameters at non-isothermal reactions in materials involving formation and growth of nuclei. By considering the assumptions of extended volume and random nucleation, a general expression of the fraction transformed as a function of time has been obtained in isothermal crystallization processes. Considering the mutual interference of regions growing from separate nuclei the Johnson–Mehl–Avrami equation has been deduced as a particular case. The application of the transformation rate equation to the non-isothermal processes has been carried out under the restriction of a nucleation which takes place early in the transformation and the nucleation frequency is zero thereafter. Under these conditions, the kinetic parameters have been deduced by using the techniques of data analysis of single-scan and multiple-scan. The theoretical method developed has been applied to the glass-crystal transformation kinetics of the semiconducting Ge0.13Sb0.23Se0.64 alloy. The kinetic parameters obtained according to both techniques differ by only about 2.5%, which confirms the reliability and accuracy of the single-scan technique when calculating the above-mentioned parameters in non-isothermal transformation processes. The phases at which the above-mentioned semiconducting glass crystallizes after the thermal process have been identified by X-ray diffraction. The diffractogram of the transformed material shows that microcrystallites of Sb2Se3 and GeSe are associated with the crystallization process, remaining a residual amorphous matrix. 相似文献
147.
M. A. da Silva P. J. A. Sobral T. G. Kieckbusch 《Journal of Thermal Analysis and Calorimetry》2006,84(2):435-439
Differential scanning calorimetry (DSC) was used
to determine phase transitions of freeze-dried camu-camu pulp in a wide range
of moisture content. Samples were equilibrated at 25°C over saturated
salt solutions in order to obtain water activities (aw)
between 0.11–0.90. Samples with aw>0.90
were obtained by direct water addition. At the low and intermediate moisture
content range, Gordon–Taylor model was able to predict the plasticizing
effect of water. In samples, with aw>0.90,
the glass transition curve exhibited a discontinuity and T’g was practically constant (–58.8°C), representing the glass transition
temperature of the maximally concentrated phase(Tg
). 相似文献
148.
CRYSTALLIZATION AND MELTING OF NYLON 610 总被引:1,自引:0,他引:1
Differential scanning calorimetry was used to study the crystallization andmelting of nylon 610. For nylon 610 crystallized from the melt state (260℃), the overall rateof bulk crystallization can be described by a simple Avrami equation with Avrami exponentn ≈ 2, independent of crystallization temperature. With the experimentally obtainedT_m~0 (235℃ ~ 255℃) of nylon 610, the fold surface free energy σ_e was determined to be35 ~38 erg/cm~2. The effects of annealing temperature and time on the melting of quenchednylon 610 were also investigated. For nylon 610 quenched at room temperature there isonly one DSC endotherm peak DSC scans on annealed samples exhibited an endothermpeak at approximately 10℃ above the annealing temperature. The size and position of theendothermic peak is strongly related to annealing temperature and time. An additionalthird melting was observed when quenched nylon 610 was annealed at high temperaturefor a sufficiently long residence time. The existence of the third melting peak suggests thatmore than one kind of distribution of lamella thickness may occur when quenched nylon610 is annealed. The implications of these results in terms of crystal thickening mechanismwere discussed. 相似文献
149.
《Arabian Journal of Chemistry》2022,15(12):104330
The present study was carried out to design and synthesize a number of novel aromatic carboxamide derivatives of dehydroabietylamine. The preliminary antifungal assay indicated that most of title compounds displayed moderate to good antifungal activity toward the six fungal strains in vitro. Compounds 3i, 3q, 4b and 4d showed significant antifungal activity against Sclerotinia sclerotiorum, with EC50 values ranging from 0.067 ~ 0.393 mg/L. Compounds 3i, 4b and 4d also showed pronounced mycelial growth inhibition activities against B. cinerea and A. solani. Furthermore, in the in vivo assay, compound 4b exhibited brilliant protective activity against S. sclerotiorum-infected rape leaves. Meanwhile, the in vivo bioassay on tomato plants infected by B. cinerea showed that compound 3i and 4d displayed excellent protective activity at 200 mg/L, which were near to boscalid. Primary mechanistic study revealed that 4b could inhibit sclerotia formation as well as reduce the exopolysaccharide level. SEM and TEM analysis indicated that 4b possessed a strong ability to destroy the surface morphology of mycelia, cell structure and seriously interfere with the growth of the fungal pathogen. In addition, 4b exhibited good inhibitory activity (IC50 = 23.3 ± 1.6 μM) toward succinate dehydrogenase (SDH). Molecular modeling study confirmed the binding modes between compound 4b and SDH. The above antifungal results and fungicidal mechanism study revealed that this class of dehydroabietylamine derivatives could be potential SDH inhibitors and lead compounds for novel fungicides development. 相似文献