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1.
Bowen Lv Zhaoliang Qu Baosheng Xu Yiguang Wang Daining Fang 《Ceramics International》2021,47(12):16547-16554
A numerical model is developed for surface crack propagation in brittle ceramic coatings, aiming at the intrinsic failure of rare-earth silicate environmental barrier coating systems (EBCs) under combustion conditions in advanced gas turbines. The main features of progressive degradation of EBCs in such conditions are captured, including selective silica vaporization in the top coat due to exposure to water vapor, diffusion path-dependent bond coat oxidation, as well as crack propagation during cyclic thermal loading. In light of these features, user-defined subroutines are implemented in finite element analysis, where surface crack growth is simulated by node separation. Numerical results are validated by existing experimental data, in terms of monosilicate layer thickening, thermal oxide growth, and fracture behaviors. The experimentally observed quasi-linear oxidation in the early stage is also elucidated. Furthermore, it is suggested that surface crack undergoes rapid propagation in the late stage of extended thermal cycling in water vapor and leads to catastrophic failure, driven by both thermal mismatch and oxide growth stresses. The latter is identified as the dominant mechanism of penetration. Based on detailed analyses of failure mechanisms, the optimization strategy of EBCs composition is proposed, balancing the trade-off between mechanical compliance and erosion resistance. 相似文献
2.
Tallison O. Abreu Roterdan F. Abreu Felipe F. do Carmo Wellington V. de Sousa Helenilson de O. Barros José E.V. de Morais João P.C. do Nascimento Marcelo A.S. da Silva Sergei Trukhanov Alex Trukhanov Larissa Panina Charanjeet Singh Antonio S.B. Sombra 《Ceramics International》2021,47(11):15424-15432
This work presents the dielectric properties of YNbO4 (YNO)–TiO2 composites in the microwave range. X-ray diffraction analysis demonstrates that the addition of TiO2 to YNO results in the formation of a Y(Nb0.5Ti0.5)2O6 phase. In the microwave range, the values of permittivity and dielectric loss did not present major changes with the increment of TiO2. Moreover, the addition of TiO2 results in an improvement in the thermal stability of YNO, with YNO63 demonstrating a resonant frequency of ?8.96 ppm.°C?1. We utilised numerical simulations to evaluate the behaviour of these materials as dielectric resonator antennae and it is found that they exhibit a reflection coefficient below ?10 dB at the resonant frequency, with a realised gain of 4.94 – 5.76 dBi, a bandwidth of 665–1050 MHz and a radiation efficiency above 84%. Our results indicate that YNO–TiO2 composites are interesting candidates for microwave operating devices. 相似文献
3.
气藏平均地层压力跟踪计算新方法 总被引:1,自引:0,他引:1
平均地层压力是产能评价和动态分析的基础,准确、快速获取平均地层压力对高效开发气藏意义重大。基于地层压力随时间变化的规律,分析了平均地层压力的变化规律。研究结果表明:平均地层压力等效点仅随时间发生改变,平均地层压力的下降速率等于或者近似等于井底流压的下降速率。从封闭弹性驱动气藏的物质平衡方程出发,考虑偏差系数和井底流压随平均地层压力的变化,推导建立了平均地层压力跟踪计算新方法,根据生产数据可迭代计算平均地层压力。方法验证结果显示,采气速度和采出程度共同影响模型的计算结果。应用实例表明,跟踪计算法与压力恢复试井和物质平衡法之间的相对误差均较小,满足工程计算精度要求,且跟踪计算法不需依托生产测试数据,节约了测试费用,避免了测试占产。 相似文献
4.
Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions. 相似文献
5.
6.
《International Journal of Hydrogen Energy》2022,47(16):9829-9834
A recent commentary by Santhosh and Ravindran on our paper (Int. J. Hydrogen Energy 2014, 39:10,606) demonstrated that the interaction between H2 and MXene (Sc2C and Ti2C) phases are not Kubas-type and should be of weak physisorption, and thus made a conclusion that 2D Sc2C and Ti2C are not suitable for practical hydrogen storage applications. In this responses, we recalculated hydrogen adsorption on 2D Sc2C and Ti2C by using different exchange-correlation functionals. And based on the calculated results, bare MXenes (especially the Ti2C) are suitable as hydrogen storage materials at temperatures of several tens degrees lower than room temperature. And the hydrogen adsorptions on the MXenes terminated with oxygen group were also investigated. Among the Ti2C, Sc2C and their oxygen-functional counterparts, the binding energy of H2 on Sc2CO2 surface is the closest to the ideal range of 0.16–0.42 eV/H2 at ambient conditions, and thus the Sc2C with oxygen group is expected to be more suitable as hydrogen storage materials. 相似文献
7.
《Advanced Powder Technology》2022,33(8):103695
Fe(III) ion can strongly inhibit the sulphidation amine flotation of smithsonite. However, its modification mechanism on smithsonite surface is still obscure. In this work, a systematic study of the modification of Fe(III) ion on smithsonite (1 0 1) surface was performed using DFT calculation. The optimal number of H2O ligands for Fe(III) ion hydrates in aqueous conditions was probed, and [Fe(OH)2(H2O)4]+ and [Fe(OH)4]? were identified as the major modification species, then their adsorption and bonding mechanisms were further revealed by analyzing the frontier orbitals, density of state, Mulliken population, and electron density. The calculated adsorption structures were consistent with the former experiment, and we found the O site that bonded to the C atom on smithsonite surface was the most favorable position for [Fe(OH)2(H2O)4]+ and [Fe(OH)4]? adsorptions. Besides, their adsorption mechanisms on smithsonite surface were principally due to the combined effect of FeO bond and hydrogen bonding. Simultaneously, hydrogen bonding greatly enhanced the stability of the adsorption structures. Moreover, the dominant orbital contribution for the bonding of FeO was primarily due to the orbital hybridization between Fe 3d and O 2p orbitals. This work can help in deeper understanding of the depression of Fe(III) ion on the sulphidation amine flotation of smithsonite. 相似文献
8.
9.
《International Journal of Hydrogen Energy》2022,47(65):28152-28164
The combustion characteristics of ammonia/methanol mixtures were investigated numerically in this study. Methanol has a dramatic promotive effect on the laminar burning velocity (LBV) of ammonia. Three mechanisms from literature and another four self-developed mechanisms constructed in this study were evaluated using the measured laminar burning velocities of ammonia/methanol mixtures from Wang et al. (Combust.Flame. 2021). Generally, none of the selected mechanisms can precisely predict the measured laminar burning velocities at all conditions. Aiming to develop a simplified and reliable mechanism for ammonia/methanol mixtures, the constructed mechanism utilized NUI Galway mechanism (Combust.Flame. 2016) as methanol sub-mechanism and the Otomo mechanism (Int. J. Hydrogen. Energy. 2018) as ammonia sub-mechanism was optimized and reduced. The reduced mechanism entitled ‘DNO-NH3’, can accurately reproduce the measured laminar burning velocities of ammonia/methanol mixtures under all conditions. A reaction path analysis of the ammonia/methanol mixtures based on the DNO-NH3 mechanism shows that methanol is not directly involved in ammonia oxidation, instead, the produced methyl radicals from methanol oxidization contribute to the dehydrogenation of ammonia. Besides, NOx emission analysis demonstrates that 60% methanol addition results in the highest NOx emissions. The most important reactions dominating the NOx consumption and production are identified in this study. 相似文献
10.
《International Journal of Hydrogen Energy》2022,47(93):39549-39562
In this study, first-principles calculations were performed to investigate the catalytic effect of NiN4-G on the dehydrogenation of MgH2. Side-on MgH2 can be adsorbed stably on the NiN4-G monolayer and is preferentially adsorbed on the NiN4 site compared with the graphene site. The hydrogen desorption process, in which MgH2 dissociated to the Mg atom on the NiN4 site or graphene site and an H2 molecule in the vacuum, should overcome lower barriers than pure MgH2. This is because the corresponding Mg–H bond is weakened owing to the electron transfer between the Mg atom and the substrate. The hydrogen desorption enthalpies of the (MgH2)5 cluster on the NiN4 active and graphene sites are significantly smaller (0.11 eV and 1.50 eV, respectively) when H2+H2 is released from the cluster compared with those of the undoped MgH2 cluster (2.48 eV). Therefore, the NiN4-G monolayer can provide the double effect of the NiN4 active and graphene sites on improving the dehydrogenation performance of MgH2. 相似文献