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991.
Naoki Shinozaki Ryoji Takahashi Satoshi Sato Toshiaki Sodesawa 《Journal of Sol-Gel Science and Technology》2007,43(3):275-282
The bending strength and the Young’s modulus of bimodal porous silica gels having different porosity were evaluated. The porosity
of the gel increased by aging the gel under basic conditions, and decreased with increasing the calcination temperature. The
mesopores disappeared on calcination at 1,050 °C, whereas continuous macropores retained their morphology up to 1,050 °C for
all the samples. Both the bending strength and the Young’s modulus of the bimodal porous silica gels were expressed as power-law
functions of the bulk density, and no effect of bimodal pore structures on mechanical properties was observed. We also found
linear correlation between the bending strength and the elasticity. The bimodal porous silica had higher strength and elastic
modulus compared with other porous materials at the same porosity probably due to the presence of homogeneous micrometer-scale
macropores. 相似文献
992.
In the second part of this general study, the carbon fiber–PEEK interfacial shear strength is measured by means of a fragmentation test on single-fiber composites. Different thermal treatments (continuous cooling from the melt, isothermal treatments and long melting temperature time) are applied to these model composites prior to testing. The results are systematically compared with the previously determined reversible work of adhesion between carbon fiber and PEEK. It is shown that physical interactions at the interface determine, to a large extent, the magnitude of the interfacial shear strength between both materials. However, it appears that the magnitude of the stress transfer from the matrix to the fiber is affected either by the existence of an interfacial layer or by a preferential orientation of the polymer chains near the fiber surface. The results obtained on systems that have been subjected to isothermal treatments (isothermal crystallization of PEEK) seem to confirm the existence of a transcrystalline interphase, the properties of which are dependent upon the crystallization rate of the matrix and the interfacial adhesion energy. 相似文献
993.
Electro-conductive resins, convenient for casting and coating applications were investigated in this paper.Electrical conductivity of epoxy and polyurethane resins, filled with two different grades of synthetic graphite (different average size) was studied. It was found that all the investigated composites became electro-conductive when filled with 22-vol% of the filler.The impact strength of epoxy and polyurethane resins filled with graphite was also investigated. A decrease in impact strength with an increase in filler content was observed in all cases. The highest values of impact strength were found for polyurethane/graphite KS 6 composites.The strength of adhesion of the filled resins to aluminum was also determined. A decrease in the strength of adhesive joints to aluminum foils with an increase in filler content was observed in all cases. The strongest adhesive joints were found for the epoxy/graphite KS 6 composites. 相似文献
994.
Summary Elution strengths of 11 common HPLC solvents on a polymeric C18 phase were compared using a marker set of polycyclic aromatic hydrocarbons. Naphthalene, pyrene, benzo[ghi]perylene, and three larger naphthologues of 8, 10, and 12 rings (constituting a naphthalene zigzag series) were chosen because they span the solvent strength range up to and including the strongest solvents, tetrahydrofuran (THF) and chlorobenzene. Four pairs of similarly shaped isomers were used to probe solvent selectivity. With the exception of THF, HPLC solvent strength correlated with observed red shifts of fluorescence band maxima in each solvent. For THF, the pure solvent and blended mixtures behaved quite differently. 相似文献
995.
The aim of the last part of this general study is to analyze the influence of the interfacial properties and, more precisely, the adhesion energy, between carbon fibers and PEEK on the final performance of unidirectional composites. A set of mechanical properties, i.e. interlaminar shear strength, longitudinal tensile and compressive and transverse tensile properties, of different unidirectional laminates with the same content (60% by volume) of carbon fibers is determined. It is first shown that the interlaminar shear strength is constant, whatever the type of materials. Therefore, this test is not appropriate to characterize the strength of the fiber–matrix interface in PEEK-based composites. On the contrary, in agreement with previous work on other systems, it appears that the ultimate properties (longitudinal tensile and compressive as well as transverse tensile strengths and strains) of the laminates increase with the interfacial adhesion energy, whereas the stiffness of these composites remains unaffected in all cases. 相似文献
996.
Tsuguyuki?Saito Masahiro?Yanagisawa Akira?IsogaiEmail author 《Cellulose (London, England)》2005,12(3):305-315
Linter cellulose was suspended in water and oxidized by the NaClO/NaBr/2,2,6,6-tetramehylpiperidine-1-oxy radical (TEMPO)
system at pH 10.5 (TEMPO-mediated oxidation), and the oxidized products were separated into several fractions by filtration
and centrifugation, depending on their particle sizes and apparent water-solubility. The major fraction (>ca. 80 mass % of
the original linter cellulose) is the filter paper-trapped fibers, which can form inter-fiber hemiacetal linkages when handsheets
are prepared thereof. Size-exclusion chromatographic analysis with multi-angle laser light scattering detection (SEC–MALLS)
of these fibrous fractions dissolved in 0.5% LiCl/N,N-dimethylacetamide (DMAc) showed that some depolymerization occurred on cellulose chains during the TEMPO-mediated oxidation.
On the other hand, the apparently water-soluble fractions (<ca. 20 mass % of the original linter cellulose) in the TEMPO-oxidized
linter cellulose consisted of small amounts of colloidal particles having the cellulose I crystal structure, which came off
from linter cellulose by the TEMPO-mediated oxidation and were mixed in the apparently water-soluble fraction even after filtration
using 0.45 μm membrane. The presence of such colloidal cellulose crystals in the water-soluble fractions of the TEMPO-oxidized
linter cellulose brings about anomalous bimodal SEC-elution patterns and extremely large molecular-mass values calculated
from the SEC–MALLS data. Truly water-soluble cellouronic acid and/or over-oxidized compounds having glucuronic acid and hexeneuronic
acid units are also present in the water-soluble fractions. 相似文献
997.
Summary Statistical copolymers of styrene and acrylonitrile have been separated by high performance precipitation chromatography according to the increase in acrylonitrile content. The separation mechanism was strongly depending on the combination of stationary phase and eluent composition. By applying a typical normal phase gradient from n-heptane (precipitation) to dichloromethane the polymers were adsorbed, after dissolution of the polar groups of the stationary phases. The elution curves became broader with increasing acrylonitrile content of the polymer. By the addition of 20% methanol to the dichloromethane the adsorption could be minimized and copolymer elution was dependent solely on solubility and independent of stationary phase polarity. Separation according to chemical composition was also possible without precipitation with a large pore silica and a normal phase gradient from dichloromethane to the same eluent containing 2.75% methanol.Part I see reference 19 相似文献
998.
Richard M. Kettler David J. Wesolowski Donald A. Palmer 《Journal of solution chemistry》1995,24(4):385-407
The dissociation quotient of benzoic acid was determined potentiometrically in a concentration cell fitted with hydrogen electrodes. The hydrogen ion molality of benzoic acid/benzoate solutions was measured relative to a standard aqueous HCl solution at seven temperatures from 5 to 250°C and at seven ionic strengths ranging from 0.1 to 5.0 molal (NaCl). The molal dissociation quotients and selected literature data were fitted in the isocoulombic (all anionic) form by a six-term equation. This treatment yielded the following thermodynamic quantities for the acid dissociation equilibrium at 25°C and 1 bar: logKa=–4.206±0.006, H
a
o
=0.3±0.3 kJ-mol–1, S
a
o
=–79.6±1.0 J-mol–1-K–1, and C
p;a
o
=–207±5 J-mol–1-K–1. A five-term equation derived to describe the dependence of the dissociation constant on solvent density is accurate to 250°C and 200 MPa. 相似文献
999.
SiO2/ZnO复合纳米粒子的制备及表征 总被引:10,自引:1,他引:10
采用双注控制沉积法(Controlled Double-Jet Precipitation,CDJP)将反应物添加到含有SiO2的溶液中,通过直接的表面反应来制备单分散的SiO2/ZnO复合纳米粒子,并对其进行了表征。透射电镜(TEM)观察表明,SiO2表面有一层ZnO纳米颗粒或薄层。对复合纳米粒子SiO2/ZnO进行X射线衍射(XRD)分析,复合颗粒的衍射峰与单独的氧化锌的衍射峰完全一致。能量弥散X射线法(EDX)分析表明,复合颗粒中含有Zn、Si、O元素。荧光光谱表明有ZnO的吸收峰。 相似文献
1000.
The rates of oxidation of Cu(I) in air saturated solutions was measured as a function of pH, temperature (5–45°C), and ionic strength (0.5 to 6m) in NaCl and NaCl–NaClO4 solutions. In pure NaCl solutions, the effect of pH is independent of ionic strength and temperature. The overall rate constant is given by logk=12.32+0.12(pH)–2064/T–3.69I1/2+ 0.73I The energy of activitation was 39±2 kJ-mol–1 and is independent of ionic strength. At a constant ionic strength (I=1, 3 and 6m) in NaCl–NaClO4 mixtures the Cl– dependence of the rates is attributed to the oxidation of the various forms of Cu(I) in the solution. The rate constants for the oxidation of the various species are found to be functions of ionic strength. At a constant ionic strength (I=1) in NaCl–NaClO4 solutions, the effect of temperature is independent of the chloride concentration. The effect of Mg2+ and HCO
3
–
on the oxidation rate was determined as a function of chloride concentration (1 to 6m) at 25°C and pH=8. The addition of Mg2+ causes the rate to decrease and the addition of HCO
3
–
causes the rate to increase. The possible causes of these effects are discussed. Empirical equations for the rate of oxidation of Cu(I) in Na-Mg-Cl-HCO3 solutions as a function of composition are used to make reliable estimates of the oxidation in seawater and Red Sea waters. 相似文献