全文获取类型
收费全文 | 5228篇 |
免费 | 350篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 106篇 |
综合类 | 5篇 |
化学工业 | 1528篇 |
金属工艺 | 175篇 |
机械仪表 | 153篇 |
建筑科学 | 195篇 |
矿业工程 | 12篇 |
能源动力 | 281篇 |
轻工业 | 557篇 |
水利工程 | 40篇 |
石油天然气 | 90篇 |
无线电 | 494篇 |
一般工业技术 | 960篇 |
冶金工业 | 298篇 |
原子能技术 | 39篇 |
自动化技术 | 678篇 |
出版年
2023年 | 51篇 |
2022年 | 139篇 |
2021年 | 176篇 |
2020年 | 142篇 |
2019年 | 205篇 |
2018年 | 287篇 |
2017年 | 208篇 |
2016年 | 217篇 |
2015年 | 181篇 |
2014年 | 211篇 |
2013年 | 456篇 |
2012年 | 250篇 |
2011年 | 318篇 |
2010年 | 268篇 |
2009年 | 268篇 |
2008年 | 235篇 |
2007年 | 185篇 |
2006年 | 193篇 |
2005年 | 125篇 |
2004年 | 117篇 |
2003年 | 154篇 |
2002年 | 112篇 |
2001年 | 85篇 |
2000年 | 96篇 |
1999年 | 79篇 |
1998年 | 115篇 |
1997年 | 65篇 |
1996年 | 53篇 |
1995年 | 48篇 |
1994年 | 42篇 |
1993年 | 32篇 |
1992年 | 22篇 |
1991年 | 30篇 |
1990年 | 20篇 |
1989年 | 21篇 |
1988年 | 25篇 |
1987年 | 43篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 25篇 |
1983年 | 27篇 |
1982年 | 16篇 |
1981年 | 18篇 |
1980年 | 27篇 |
1979年 | 14篇 |
1978年 | 21篇 |
1977年 | 21篇 |
1976年 | 27篇 |
1975年 | 21篇 |
1973年 | 19篇 |
排序方式: 共有5611条查询结果,搜索用时 0 毫秒
61.
This paper shows the wide application range (such as electrical self‐heating and electromagnetic shielding effectiveness) of composites consisting of conductive carbon black/aluminum flakes (CBA) filler and epoxy insulative matrix. The effect of CBA content on the network structure of epoxy matrix was investigated in detail. Static electrical conductivity increases linearly with the increase of filler concentration at the interface in epoxy composites. The large decrease of the conductivity as a function of the temperature is analyzed in terms of the negative temperature coefficient of conductivity (NTCC) effect. The influence of viscosity, surface energy and barrier highest energy on the NTCC behaviour in the composite is also considered. Based on these results, a new interpretation is proposed to explain the NTCC phenomena by computing the swelling force among conductive phases. The correlations of conductivity during the temperature cycling and activation energy were analyzed. The effects of dynamic ageing at various temperatures on the resistivity are reported. Current–voltage–temperature characteristics for epoxy with different contents of CBA were examined in detail. A model based on the law of energy conservation is proposed to calculate the specific heat and amount of heat dissipation. The static charge of the epoxy–CBA composites was estimated. The correlation between electromagnetic wave‐shielding effectiveness (EMS), conductivity and frequency of epoxy composites with different filler contents is also discussed. Furthermore, the effect of annealing on EMS of epoxy composites was examined. © 2002 Society of Chemical Industry 相似文献
62.
Rock phosphate fractions were examined for their porous structure by nitrogen adsorption. The pore size distribution and the shape of pores does not seem to depend on the particle size. The specific surface area values present two regions, one above and one below that of the particles with 125 μrn diameter. Particles of a given size were leached with dilute phosphoric acid (1.5 mass% P2O5) at 25°C. It was observed that there is a widening of the initial pores during leaching. The particles collected at the initial period of the reaction are pitted and those collected at the final period are disintegrated. 相似文献
63.
SiC‐ and B4C‐filled NBR rubber composites were prepared with various volume fractions of filler by a conventional roll‐mill method. The morphological structures of the NBR–SiC and NBR–B4C composites were analyzed by scanning electron microscopy. The dependence of room‐temperature volume resistivity (ρv) on the concentration of filler in the two systems was studied. In addition, variation in the number of current carriers (n), mobility carriers (μ), dielectric constant (ε), and dielectric loss factor (tan δ) on filler concentration in the two systems were investigated in detail. The applicability of composites as negative temperature coefficient (NTCR) linear thermistors was studied by the dependence of volume resistivity on temperature. The resistivity showed negative temperature dependence and changed linearly with temperature parallel. The conduction mechanism of the conductivity of the two composites was analyzed in terms of the computed activation energy and hopping energy. Change in volume resistivity as a function of frequency for the two systems was also investigated. Finally, the dependence of volume resistivity on applied pressure and possible real applications of these composites as transducers in pressure sensors were also studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2158–2165, 2007 相似文献
64.
Electrical conductivity of concrete containing silica fume 总被引:15,自引:0,他引:15
S. A. Abo El-Enein M. F. Kotkata G. B. Hanna M. Saad M. M. Abd El Razek 《Cement and Concrete Research》1995,25(8):1615-1620
The influence of silica fume on concrete properties represents an important technical research. In general, silica fume tends to improve both mechanical characteristics and durability of concrete. Thus the electrical properties of concrete containing silica fume can be studied to clarify its physical performance during hydration. The electrical conductivity of neat cement, mortar and concrete pastes was measured during setting and hardening. The ordinary Portland cement was partially replaced by different amounts of silica fume by weight. The changes in the electrical conductivity were reported during setting and hardening after gauging with water. The results of this study showed that the electrical conductivity can be used as an indication for the setting characteristics as well as the structural changes of the hardened pastes made with and without silica fume. 相似文献
65.
The response of lentil grown under rainfed conditions to directly applied and residual phosphorus (P) was described by a modified Mitscherlich equation, accounting for the effects of rainfall on (1) potential yield, and (2) the availability of soil-P to the crop. The response of lentil yield to directly applied and residual P was studied in two-course cereal–lentil rotational trials under rainfed conditions in a Mediterranean-type environment. Cereal crops were grown at different P application rates during 4 growing seasons at 3 sites, representing different rainfall zones in northwest Syria. Lentil (Lens culinaris Med.) was grown during 4 seasons at the same sites, each lentil crop following a cereal crop. In 3 out of 4 lentil-growing seasons, additional P was applied to lentil in subplots to compare the residual and direct effects of P application. The initial contents of extractable soil-P (P-Olsen) were low at all sites, in the range of 2–5 ppm P. Under the conditions of the experiments, lentil appeared to benefit slightly more from P applied to the preceding wheat crop (residual P) than from directly applied P. It is shown that the modified Mitscherlich equation could be used as a basis for P fertilizer recommendations for rainfed farming. As for lentil, it was concluded that a single application of P to the wheat crop in a wheat/lentil rotation could reduce the cost of lentil production, without reducing lentil yield. 相似文献
66.
Wool fabrics were exposed to ultraviolet (UV)–ozone treatment for different periods. After exposure, the fabrics were analyzed by Fourior transform infrared spectroscopy (FTIR). Also, the crystallinity and amorphousity regions were followed by an X‐ray diffraction technique. The results were correlated by mechanical properties measurements. After a certain period of exposure, the dyeability and printability were improved because these abilities are strongly related to the percentage ratio of crystallinity regions to amorphousity regions in wool fabrics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1469–1476, 2002 相似文献
67.
Ian A. Brummel Daniel E. Drury Andrew R. Kitahara Farid El Gabaly Jon F. Ihlefeld 《Journal of the American Ceramic Society》2021,104(2):711-721
Lithium zirconium phosphate (LiZr2P3O12) thin films have been prepared on platinized silicon substrates via a chemical solution deposition approach with processing temperatures between 700°C and 775°C. Films that were subject to a single high-temperature anneal were found to crystallize at temperatures above 725°C. Crystallization was observed in films annealed after each deposited layer at 700°C and above. In both cases, grain size was found to increase with annealing temperature. Ion conductivity was found to increase with annealing temperature in singly annealed films. In per-layer annealed films ion conductivity was found to initially increase then decrease with increasing annealing temperature. A maximum ion conductivity of 1.6 × 10−6 S/cm was observed for the singly annealed 775°C condition, while a maximum ion conductivity of 5.8 × 10−7 S/cm was observed for the 725°C per-layer annealed condition. These results are consistent with an increasing influence of cross-plane, internal interface resistance and vapor phase carrier loss in the per-layer annealed samples. This work demonstrates that post-deposition processing methods can strongly affect the ion conducting properties of LiZr2P3O12 thin films. 相似文献
68.
Hamza El Marouazi Benoit van der Schueren Damien Favier Anaëlle Bolley Samuel Dagorne Thierry Dintzer Izabela Janowska 《应用聚合物科学杂志》2021,138(44):51300
Four series of polylactide (PLA) based composite films containing horizontally aligned few layer graphene (FLG) flakes of high aspect ratio and adsorbed albumin are prepared. The mechanical and thermal properties varies with percentage, dispersion degree and size of FLG flakes. Great improvement up to 290% and 360% of tensile modulus and strength respectively were obtained for the composite containing high lateral size of FLG at 0.17% wt, and up to 60% and 80% for the composite with very well dispersed 0.02% wt FLG. The composites of PLA and PEG-PLLA containing very well dispersed FLG flakes at 0.07% wt are ductile showing enhancement of elongation at break up to respectively 80% and 88%. Relatively high electrical conductivity, 5 × 10−3 S/cm, is measured for PLA film charged with 3% of FLG. 相似文献
69.
This article investigates the prediction of the crack growth angle of an existing internal crack under mixed mode loading at the crack tip for an unfilled ethylene propylene diene terpolymer rubber (EPDM). For the realization of mixed mode loading, the cracks of the uniaxial loaded specimens were oriented with different angles to the loading direction. The energy density factor was used as a potential criterion for determining the crack growth angle. The determination of the strain energy density factor was carried out simulatively in Abaqus. The second-order Ogden model was used to describe the rubber-like material behavior. The relative local minimum of the strain energy density factor provides the possible growth angle. The experimental investigations show that the initial cracks grow orthogonally to the loading direction for the different crack orientation angles. For the crack orientation angle parallel to the load direction, the crack growth was observed because the strong stretching of the specimen caused strong necking in the crack region. The crack growth for the remaining crack orientation angles were induced due to shear loading at the crack tip. The predictive angle of different crack orientation angles shows very good accordance to the measured crack growth angles. 相似文献
70.
V. M. El’kin E. A. Kozlov E. V. Kakshina Yu. S. Moreva 《The Physics of Metals and Metallography》2006,101(3):208-217
A thermodynamically complete equation of two-phase (γ, α) state of cerium was derived in terms of a pseudobinary solid-solution model developed by Aptekar’ and Ponyatovskii. According to the model, unalloyed cerium is considered to be a substitutional solid solution whose components are represented by atoms with different electron configurations. The free energy of the individual phases (solid-solution components) is represented as a sum of three terms that describe the atomic interaction at T = 0 K, quasi-harmonic lattice vibrations, and the combined contribution of the anharmonicity and thermally excited electrons. The equation of state is shown to adequately describe the unusual behavior of cerium under the effect of static actions. In this work, calculations of the dynamic compression of cerium are performed. The calculations indicate that, up to the completion of the γ-α transition, the formation of the shockwave front in cerium is impossible and compression of cerium occurs in an isentropic wave of simple compression. As the pressure increases, a multiwave configuration with the participation of isentropic and shock waves is realized in cerium. The initial state in which the shock wave is propagated changes depending on the wave intensity; i.e., the initial state “slides” along the leading isentropic wave. The shock adiabat was shown to not pass through the very complex range of metastable existence of α-, α′-, and α″ phases. This provides prerequisites for experimental finding the α-ε transformation which can occur in the shock wave and is not masked with the preceding α-α′ and α′-α″ transformations. When assuming the absence of the α-ε transformation, the calculated coordinates of the point corresponding to the start of melting in the shock wave are p melt = 11.3 GPa and T melt = 1130 K. 相似文献