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71.
《Ceramics International》2021,47(24):34695-34703
Li4x/3Zn2–2xTi1+2x/3O4 microwave dielectric ceramics with a spinel phase were prepared via a high-temperature solid-phase method. P–V–L theory, vibration spectra, and XPS were utilized to establish the links between the intrinsic and extrinsic factors and the microwave dielectric properties. According to the characterization, the change in permittivity (εr) was ascribed to the increase in the average bond ionicity of Ti–O(AfiTi-O) and the polar mode of the lattice vibration; the change in quality factor(Q × f) resulted from the change in the Ti–O lattice energy (AUTi-O) and existence of oxygen vacancy; the increase in temperature coefficient of the resonance frequency (τf) was triggered by the increase in the Ti–O bond energy. The Li0.6Zn1.1Ti1.3O4 ceramics (x = 0.45) sintered at 1125 °C finally obtained optimal microwave dielectric constants of εr = 17.3, Q × f = 76,318 GHz and τf = -58 ppm/°C. 相似文献
72.
Maximilian Dyga Andreas Keller Hans Hasse 《American Institute of Chemical Engineers》2022,68(4):e17573
Formaldehyde is an important chemical that is mostly handled in aqueous solutions, which generally also contain methanol; furthermore, also solutions of formaldehyde in other alcohols are used. The density of these solutions is an important thermophysical property. The available models of the density of formaldehyde-containing solutions, however, all have shortcomings, such as a poor accuracy or a limited range of applicability. Therefore, in the present work, a new model of the density in systems of the type (formaldehyde + water + alcohol) was developed. The alcohols that are presently included in the new model are methanol, 1-propanol, and isoprenol; an extension to other alcohols is straightforward. The model was developed using literature data and extensive new density data measured in this work covering binary, ternary, and quarternary solutions of formaldehyde in water, methanol, 1-propanol, and isoprenol at temperatures of K and formaldehyde concentrations of 0.06 − 0.30 g g−1. 相似文献
73.
《Ceramics International》2022,48(10):14349-14359
The influence of heat-treatment temperatures (700 °C, 900°C, 1200 °C) on the phase, physical properties, crystallization rate, and in vitro properties of the solution combustion synthesized silicon-doped calcium phosphates (CaPs) were investigated. The thermodynamic aspects (enthalpy, entropy, and free energy) of the synthesis process and the crystallographic properties of the final samples were first predicted and then confirmed using density functional theory (DFT). Results demonstrated that the crystallization rate was controlled by the fuel(s) type (glycine, citric acid, and urea) and the amounts of Si4+ ions (0, 0.1, 0.4 mol). The highest calculated crystallization rate values of the un-doped, 0.1, and 0.4 mol Si-doped samples were 64%, 22%, 38%, respectively. The obtained results from the DFT simulation revealed that crystal growth in the direction of c-axis of hydroxyapatite (HAp) structure could change the stability of (001) surface of (HAp). Also, the computational data confirmed the adsorption of Si–OH groups on the (001) surface of HAp during the SCS process with an adsorption energy of 1.53 eV. AFM results in line with DFT simulation showed that the observed change in the surface roughness of Si-doped CaPs from 2 to 8 nm could be related to the doping of Si4+ ions onto the surface of CaPs. Besides, the theoretical and experimental investigation showed that crystal growth and doping of Si4+ ions could decrease the activation energy of oxygen reduction reaction (ORR). Furthermore, the results showed that the crystallized HAp structure could have great potential to efficiently reduce oxidative stress in human body. 相似文献
74.
《Ceramics International》2022,48(14):20096-20101
A series of Mn2+-doped Mg1-xMnxTa2O6 (x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ceramics were synthesized by solid-state reaction method. The influence of introducing Mn–O bonds as a partial replacement for Mg–O bonds on the lattice and microwave dielectric properties was systematically investigated. XRD and Rietveld refinement confirm that Mn2+ occupies the 2a Wyckoff position and forms a pure trirutile phase. Moreover, based on the chemical bond theory, the dielectric constant is mainly affected by the ionicity of the Ta–O bond. The lattice and dielectric properties remain relatively stable with Mn2+ doping below 0.1, but excessive Mn2+ doping leads to pronounced distortion of the lattice, which is not beneficial for lattice stability and microwave dielectric properties. Introducing an appropriate amount of Mn–O bonds with high bond dissociation energy facilitates MgO6 octahedron stability, which improves the thermal stability of the lattice. Accordingly, the microwave dielectric properties for 0.06 Mn2+-doped MgTa2O6 ceramics were determined: εr = 28, Q × f = 105,000 GHz (at 7.5 GHz), τf = 19.5 ppm/°C. 相似文献
75.
《Ceramics International》2022,48(13):18278-18285
We report the improved energy storage density and efficiency after 2.5% of Samarium substitution in ferroelectric Pb[(Mg1/3Nb2/3)0.80Ti0.20]O3 (PMNT) electroceramic. The microstructure and surface morphology were analyzed and correlated with various functional properties. The energy storage density, leakage current density, ferroelectric and dielectric properties were investigated thoroughly, indicating that Samarium's substitution significantly modified the microstructure, the dielectric strength, breakdown electric field, and turned ferroelectric PMNT to relaxor ferroelectrics. Due to the relaxor nature, the gap between remanent polarization and maximum polarization increases with the substitution of Samarium in PMNT matrix, which further increases the recoverable energy storage density and energy efficiency. A nearly 100% increase in recoverable energy density and efficiency was obtained at an electric field strength of 35 kV/cm at room temperature (~296 K). The electroceramic shows maximum energy density near the ferroelectric phase transition temperature (325 K–345 K) region and provides a moderate energy storage density for possible applications in power microelectronics. 相似文献
76.
《Ceramics International》2022,48(12):17359-17368
In this work, 0.7BaTiO3-0.3Sr0.2Bi0.7TiO3 (0.7BT-0.3SBT) ceramics with 0.15 mol% various rare-earth oxides doped are designed and synthesized by the conventional solid-state route. All prepared samples exhibited a single perovskite phase and dense microstructure with fine grain size (0.2–0.5 μm) after sintering at 1180 °C. Especially, the Gd-doped 0.7BT-0.3SBT ceramics exhibited excellent energy storage performances; the corresponding recoverable energy density and efficiency were 3.2 J/cm3 and 91.5% under an electric field of 330 kV/cm, respectively. Meanwhile, doping with Gd caused the BT-based ceramics to possess excellent temperature (30–150 °C) and outstanding frequency stabilities (10–1000 Hz). Moreover, the pulsed charge-discharge experiments revealed that a high power density of 59 MW/cm3 and a fast discharge speed of 110 ns with outstanding temperature stability could be synchronously obtained in the Gd-doped composition. All these features are attractive for pulsed power applications. 相似文献
77.
Jordana Cox 《Review of Communication》2019,19(2):127-146
ABSTRACTIn response to the latest “crisis” in the humanities, advocates have marched, rallied, fundraised, and—especially—argued. This essay contends that communication scholars can support the growing “case for the humanities” by analyzing argumentative strategies, and more specifically, by offering ethical argumentative strategies that avoid replicating structures of domination. In particular, we look to Mari Lee Mifsud's theorization of rhetoric as gift, which follows Henry W. Johnstone in conceptualizing argument as something other than winning over an adversary. We place Mifsud's theorization of the gift in conversation with the methods of the digital public humanities (DPH), which acknowledge and offer abundant resources for meaning-making. Through the methods of DPH, we offer a response to the humanities “crisis” that activates the humanities’ already broad constituencies by giving resources for humanistic inquiry rather than seeking to capture adversaries. Our case study is Photogrammar, a DPH project for organizing, searching, and visualizing the New Deal and World War II era photographs funded by the U.S. federal government. The project forefronts visual, nonlinear, and interactive argumentation in order to engage publics in generative humanistic inquiry. By enlisting participants and sharing expertise, Photogrammar shows how humanities advocates can deepen attachments to the humanities and build broad constituencies of collaborators and allies. 相似文献
78.
In [1] a procedure for bias-free estimation of the autocorrelation function is introduced for equidistantly sampled data with randomly occurring samples being invalid. The method incorporates sample-and-hold interpolation of the missing data points. The occurring dynamic error of the primary estimate of the correlation function is treated by a deconvolution procedure with two parameters and with , which are the on-diagonal and the aside-diagonal parameters of a specific correction matrix (at all lag times except zero). The parameters and were obtained as a function of the probability α of a sample to be valid by numerical simulation. However, explicit expressions for the parameters and can be derived, which might improve the usability of the deconvolution procedure in [1]. 相似文献
79.
80.
By using first-principles calculations we studied the electronic, optical and magnetic properties of ZnO co-doped with Eu and Pm. In this calculation, we used Wien2k code based on full potential linearized augmented plane waves (FP-LAPW) method with the modified Becke-Johnson (mBJ) approximation. This correction gives good band gap compared to experimental band gap. The introduction of Eu and Pm codoping leads to an increase in the band gap. Electrons can transit easily from the valence band to the conduction band, which results in an enhancement of visible light absorption in a wider absorption range. Absorption spectra reach a high value in visible and infrared light regions. With the significance of the obtained results, the studied compounds may potentially find spintronic and optoelectronic applications. 相似文献