全文获取类型
收费全文 | 589篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
化学 | 355篇 |
晶体学 | 6篇 |
力学 | 16篇 |
数学 | 32篇 |
物理学 | 188篇 |
出版年
2021年 | 4篇 |
2019年 | 3篇 |
2018年 | 5篇 |
2016年 | 3篇 |
2015年 | 8篇 |
2014年 | 8篇 |
2013年 | 35篇 |
2012年 | 29篇 |
2011年 | 40篇 |
2010年 | 11篇 |
2009年 | 15篇 |
2008年 | 20篇 |
2007年 | 15篇 |
2006年 | 28篇 |
2005年 | 34篇 |
2004年 | 29篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 9篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 5篇 |
1994年 | 9篇 |
1993年 | 8篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 16篇 |
1984年 | 12篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1976年 | 7篇 |
1975年 | 3篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1931年 | 2篇 |
1897年 | 3篇 |
排序方式: 共有597条查询结果,搜索用时 62 毫秒
81.
Taís Vanessa Gabbay Alves Eraldo José Madureira Tavares Fauze Ahmad Aouada Charles Alberto Brito Negrão Marcos Enê Chaves Oliveira Anivaldo Pereira Duarte Júnior Carlos Emmerson Ferreira da Costa José Otávio Carréra Silva Júnior Roseane Maria Ribeiro Costa 《Journal of Thermal Analysis and Calorimetry》2011,106(3):717-724
This paper reports the thermal characterization of polyacrylamide-co-methylcellulose hydrogels and the constituent monomers (acrylamide and methylcellulose). Polymeric materials can be used
to produce hydrogels, which can be natural, synthetic, or a mixture. The hydrogels described here were obtained by free radical
polymerization, in the presence of N,N′-methylene-bis-acrylamide as a cross-linker agent. Four acrylamide concentrations were used for the synthesis of hydrogels:
3.6, 7.2, 14.7, and 21.7% (w/v). The materials so obtained were analyzed by TG, DTG, DSC, and FT-IR. The TG curves of acrylamide
and methylcellulose showed three mass loss events. In DSC curves, the acrylamide exhibited one melting peak at 84.5 °C, and
methylcellulose indicated one exothermic event. Nevertheless, acrylamide was considered more stable than methylcellulose.
The TG curves of the hydrogels exhibited three mass loss events, and on the DSC curves, three endothermic events were observed.
It was verified that the different acrylamide proportions influenced the thermic behavior of hydrogels, and that the authors
considered the 7.2% hydrogel a promising drug carrier system. The absorption bands were well defined, confirming the presence
of the functional groups in the samples. 相似文献
82.
H. Wabnitz Y. Mairesse L. J. Frasinski M. Stankiewicz W. Boutu P. Breger P. Johnsson H. Merdji P. Monchicourt P. Salières K. Varjú M. Vitteau B. Carré 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):305-311
We investigate the carrier-envelope phase dependence of the total ionization yield for single and double ionization of xenon.
We compare our results to theoretical calculations and to the phase dependent asymmetry in photoelectron emission. We observe
that the phase dependence of the photoion yields, regardless if single or double ionization, is at least 2-3 orders of magnitude
below the photoelectron emission signal. We conclude that total photoionization yields are only very weakly dependent on the
carrier envelope phase, and that they are not a useful means for measurement of the phase. It seems possible that the broad
bandwidth of few-cycle pulses facilitates multiphoton ionization, which leads to a randomization of strong field ionization
phase dependencies. Besides, we observe that the spatial asymmetry in photoelectron emission appears to be useful as an indicator
for the laser pulse duration in the few cycle regime. 相似文献
83.
84.
The discrete coagulation-fragmentation equations: Existence,uniqueness, and density conservation 总被引:6,自引:0,他引:6
The discrete coagulation-fragmentation equation describes the kinetics of cluster growth in which clusters can coagulate via binary interactions to form larger clusters or fragment to form smaller ones. These models have many applications in pure and applied science ranging from cluster formation in galaxies to the kinetics of phase transformations in binary alloys. Our results relate to existence, uniqueness, density conservation and continuous dependence and they generalise the corresponding results in [ref. 2] for the Becker-Doring equations for which the processes are restricted to clusters gaining or shedding one particle. Examples are given which illustrate the role of the assumptions on the kinetic coefficients and show the rich set of analytic phenomena supported by the general discrete coagulation-fragmentation equations. 相似文献
85.
The kinetics of oxidation of simple aliphatic sulphur compounds by potassium ferrate 总被引:1,自引:0,他引:1
Potassium ferrate (K2FeO4) is highly soluble in water and a very strong oxidizing agent(1, 2). Other properties include a strong bacteriacidal action which has been documented by Murmann and Robinson(1). These characteristics, and others, suggest that potassium ferrate would be useful in the advanced treatment of municipal waste water. The efficiency of oxidation of various organic compounds by potassium ferrate must be investigated before conclusions can be drawn.When K2FeO4 is placed into aqueous solution a purple colour is produced which disappears as K2FeO4 is reduced. At a spectrophotometric wavelength of 505 nm this affords a convenient method for measuring the decomposition kinetics of K2FeO4.Rate constants were obtained by algorithmic analysis of spectral absorbance data by the Cornell method(3). This work will present a mechanism of reaction for oxidation of simple aliphatic sulphur compounds by potassium ferrate. The oxidation of simple aliphatic sulphur compounds produces the corresponding sulphoxide or sulphone(4, 5) Compounds studied included dimethyl sulphoxide, diethylsulphide, dimethylsulphone, and 2,2-thiodiethanol. 相似文献
86.
Thermally stimulated discharge has been used in the past to diagnose and estimate the magnitude of electrical polarization in polymers. Nevertheless, molecular characterization of operative phenomena by this technique alone is often a difficult task. In the present work, infrared attenuated total reflection spectroscopy has been used to investigate the origin of thermally stimulated discharge currents near 200°C in externally unpolarized films of polyacrylonitrile (PAN). Spectroscopic analysis of thermally degraded films reveals some unsaturation of the PAN backbone and possibly the generation of cyanide ions. Opposite surfaces in a solvent-cast film give different spectra, indicating a gradient in chemical degradation products across the film thickness. Data suggest that nonuniform generation of charged species and unsaturated bonds gives rise to internal potentials in PAN. The origin of thermally stimulated currents in PAN near 200°C is thus believed to be associated with the onset of chemical degradation. 相似文献
87.
Phase conjugation via stimulated Brillouin scattering in CH4 gas has been used to correct amplifier aberrations in a Nd: YAG oscillator/amplifier system. The single amplifier stage has been used in two-pass and four-pass arrangements. Using the four-pass arrangement incorporating compensation for thermal birefringence, a single-frequency diffraction-limited output of 350 mJ, in a compressed 6 ns pulse is achieved at 15 Hz repetition rate. 相似文献
88.
J.J. Aubert G. Bassompierre K.H. Becks C. Best E. Böhm X. de Bouard F.W. Brasse C. Broll S. Brown J. Carr R.W. Clifft J.H. Cobb G. Coignet F. Combley G.R. Court J.M. Crespo P.F. Dalpiaz S.J. Wimpenny 《Physics letters. [Part B]》1980,95(2):306-310
The transverse momenta of charged hadrons produced in high energy muon-proton scattering have been studied. The average squared transverse momentum 〈p2⊥〉 shows a strong dependence on z = Eh/v characteristic of intrinsic momentum effects and a significant rise as a function of s = W2. The W2, q2, x and z dependences of the data are compared with the predictions of a perturbative QCD model. 相似文献
89.
Changes in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed. 相似文献
90.