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21.
In this paper, we take a quasi-Newton approach to nonlinear eigenvalue problems (NEPs) of the type M(λ)v =?0, where \(M:\mathbb {C}\rightarrow \mathbb {C}^{n\times n}\) is a holomorphic function. We investigate which types of approximations of the Jacobian matrix lead to competitive algorithms, and provide convergence theory. The convergence analysis is based on theory for quasi-Newton methods and Keldysh’s theorem for NEPs. We derive new algorithms and also show that several well-established methods for NEPs can be interpreted as quasi-Newton methods, and thereby, we provide insight to their convergence behavior. In particular, we establish quasi-Newton interpretations of Neumaier’s residual inverse iteration and Ruhe’s method of successive linear problems. 相似文献
22.
23.
The gas‐phase thermal chlorination of CHCl3 has been studied up to high conversions by photometry and gas chromatography in a conditioned static quartz reaction vessel between 573 and 635 K. The initial pressures of both CHCl3 and Cl2 ranged from about 10–100 Torr, and the initial total pressure was varied between about 30–190 Torr. The reaction is rather complex because the produced CCl4 is not stable. The rate of consumption of Cl2 therefore increases in the course of time. This acceleration is explained quantitatively in terms of a radical mechanism and its kinetic and thermodynamic parameters. This reaction model is based on a known model for the pyrolysis of CCl4 to which only one reaction couple involving CHCl3 has been added. Analyses of the rates of the homogeneous elementary steps show that the primary source of Cl atoms is the second‐order dissociation of Cl2, which is rapidly superseded by a secondary source, the first‐order dissociation of the CCl4 primary product. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 466–472, 2000 相似文献
24.
Giuseppe Vasapollo Antonio Scarpa Giuseppe Mele Ludovico Ronzini Bassam El Ali 《应用有机金属化学》2000,14(11):739-743
Palladium acetate [Pd(OAc)2] and 1,4‐bis(diphenylphosphino)butane (dppb) catalyse regioselective cyclocarbonylation of bisallyl derivatives of bisphenols affording seven‐membered ring bislactones in good yields. Double cyclocarbonylation reactions carried out using different conditions afforded bislactones with two different ring sizes (7–6 and 7–5‐membered). Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
25.
Pascale De Meuter Jo Amelrijckx Hubert Rahier Bruno Van Mele 《Journal of Polymer Science.Polymer Physics》1999,37(20):2881-2892
The slow isothermal crystallization of concentrated amorphous starch systems is measured by Modulated Differential Scanning Calorimetry (MDSC). It can be followed continuously by the evolution (stepwise decrease) of the MDSC heat capacity signal (Cp), as confirmed with data from X-ray diffractometry, Dynamic Mechanical Analysis, Raman spectroscopy, and conventional Differential Scanning Calorimetry. Isothermal MDSC measurements enable a systematic study of the slow crystallization process of a concentrated starch system, such as a pregelatinized waxy corn starch with 24 wt % water and 76 wt % starch. After isothermal crystallization, a broad melting endotherm with a bimodal distribution is observed, starting about 10°C beyond the crystallization temperature. The bulk glass transition temperature (Tg) decreases about 15°C during crystallization. The isothermal crystallization rate goes through a maximum as a function of crystallization time. The maximum rate is characterized by the time at the local extreme in the derivative of Cp (tmax), or by the time to reach half the decrease in Cp (t1/2). Both tmax and t1/2 show a bell-shaped curve as a function of crystallization temperature. The temperature of maximum crystallization rate, for the system studied, lies as high as 75°C. This is approximately 65°C above the initial value of Tg. Normalized Cp curves indicate the temperature dependence of the starch crystallization mechanism. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2881–2892, 1999 相似文献
26.
Photocontrolled variations in the wetting capability of photochromic polymers enhanced by surface nanostructuring 总被引:2,自引:0,他引:2
Athanassiou A Lygeraki MI Pisignano D Lakiotaki K Varda M Mele E Fotakis C Cingolani R Anastasiadis SH 《Langmuir : the ACS journal of surfaces and colloids》2006,22(5):2329-2333
The wetting characteristics of surfaces of polymers doped with photochromic spiropyran molecules can be tuned when irradiated with laser beams of properly chosen photon energy. The hydrophilicity is enhanced upon UV laser irradiation since the embedded nonpolar spiropyran molecules convert to their polar merocyanine isomers. The process is reversed upon green laser irradiation. Structuring of the photochromic polymeric surfaces with soft lithography enhances significantly the hydrophobicity of the system, indicating that the water droplets on the patterned features interact with air that is trapped in the microcavities, thus creating superhydrophobic air-water contact areas. Furthermore, the light-induced wettability variations of the structured surfaces are enhanced by a factor of 3 compared to those on the flat surfaces. This significant enhancement is attributed to the photoinduced reversible volume changes to the imprinted gratings, which additionally contribute to the wettability changes due to the light-induced photochromic interconversions. 相似文献
27.
The waveguiding properties and amplified spontaneous emission (ASE) of a blend of light-emitting gain-conjugated polymers were investigated. ASE-induced line narrowing occurs for excitation fluences larger than 100 microJ cm(-2), with a maximum optical-gain coefficient of 8 cm(-1). Energy transfer between the host and guest polymers, significantly reducing the self-absorption, leads to a loss coefficient of the waveguide as low as 0.3 cm(-1), which is believed to be the lowest value reported for active organic gain slabs and a highly polarized emission, with a polarization contrast up to 0.65. These results indicate that gain-conjugated polymer blends are state-of-the-art organic materials for lasing devices. 相似文献
28.
We show that, in the present inclusive searches for the Higgs boson at the LHC, a fermiophobic Higgs mimics the standard-model-like Higgs if its mass is around 125 GeV. For that mass the order-of-magnitude reduction of fermiophobic Higgs production cross sections is compensated by a corresponding increase in the Higgs branching fraction into γγ , while the WW?, ZZ?, Zγ signal yields are predicted to be somewhat smaller. The excess seen in the ATLAS and CMS fermiophobic Higgs boson searches in the γγ channel, including the exclusive vector-boson-fusion analysis, could point to a fermiophobic rather than a standard-model Higgs boson. If the Higgs boson will turn out to be fermiophobic, many of our present ideas of new physics should be revised. 相似文献
29.
Marius Ciprian Rusu Christophe Block Guy Van Assche Bruno Van Mele 《Journal of Thermal Analysis and Calorimetry》2012,110(1):287-294
Photo-DSC was used to investigate the cure kinetics of a photo-initiated resin. The exothermal photo-polymerization reactions were performed in isothermal mode. The irradiation of photo-initiated resin was studied under different conditions of temperature, UV lamp intensity, and reaction atmosphere (nitrogen and air). The results obtained by photo-DSC allowed us to determine kinetic data of the photo-polymerized reactions: the global activation energy and reaction enthalpy, and the conversion as a function of time and temperature. Modulated temperature DSC measurements were carried out to verify whether vitrification occurs during polymerization. The conversion at the top and bottom of irradiated samples was obtained by FT-IR spectroscopy before and after photo-polymerization. A non-homogenous photo-polymerization into the material was observed, probably because of the light absorptions effects within the uppermost layers. 相似文献
30.
Influence of the Degree of Dehydroxylation of Kaolinite on the Properties of Aluminosilicate Glasses
The degree of dehydroxylation of kaolinite, DTG and DIR, respectively, is characterized by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). The
relation between DTG and DIR based on the infrared absorptions at 3600–3700, 915, 810, and 540 cm−1 is established. Three regions can clearly be distinguished: the dehydroxylation region (DTG<0.9), the metakaolinite region (0.9<DTG<1) and the ‘spinel’ region(DTG=1). The effect of the degree of dehydroxylation of kaolinite on the amount of reactive material is measured by the reaction
enthalpy, ΔH, of the low-temperature reaction of the dehydroxylated kaolinite with a potassium silicate solution using differential scanning
calorimetry (DSC). |ΔH| increases almost linearly with DTG in the dehydroxylation region. In the metakaolinite region, ΔH and thus the amount of reactive material, becomes constant. |ΔH| is sharply decreasing when metakaolinite transforms into other phases in the ‘spinel’ region. No significant differences
in the reactivity of the dehydroxylates is detected with DSC. According to FTIR, the use of partially dehydroxylated kaolinite
is not influencing the molecular structure of the low-temperature synthesized aluminosilicates, but residual kaolinite is
retrieved as an additive.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献