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排序方式: 共有617条查询结果,搜索用时 15 毫秒
31.
Víctor I. Hernández Domingo I. García-Gutiérrez Juan A. Aguilar-Garib Román J. Nava-Quintero 《Ceramics International》2021,47(1):310-319
In the current study two different batches of X7R-0603 BME-MLCCs displayed dissimilar electrical performance, despite having the same chemical composition, tape casting, and sintering conditions; with the only difference between them being the ore deposits where the raw materials were extracted from to synthesize the BaTiO3. Specifically, they presented different electrical response to highly accelerated life tests (HALT). Although the chemical analysis of each slip showed the same composition, the trace elements of the BaTiO3 sources could have acted as dopants or produced different secondary phases. A search for precipitates in the two samples was conducted by means of Scanning (SEM) and Transmission Electron Microscopy (TEM) techniques. SEM observations confirmed the presence of precipitates formed within the structure of the MLCCs exhibiting the greatest decrement in their electrical resistance results during the HALT. In order to further characterize the observed precipitates, samples were prepared by Focused Ion Beam (FIB) lift-out method, to make TEM characterization of specific precipitates feasible. TEM studies were performed on the precipitates to obtain electron diffraction patterns and complementary Energy Dispersive X-Ray Spectroscopy (EDXS) chemical analysis. Based on the crystal and chemical data obtained, it can be concluded that the precipitates are a hexagonal anhydrous silicate oxyapatite phase with a stoichiometry of Ca3Y16Si10O13, and lattice parameters of a = 0.9353 nm and c = 0.6970 nm; this phase was not found in the JCPDS data base. Differences in raw materials coming from different ore deposits can produce undesired precipitates that affect the electrical performance of MLCCs. 相似文献
32.
Odacir Almeida Neves Estaner Claro Romão João Batista Campos Silva 《Numerical Heat Transfer, Part A: Applications》2013,63(10):730-748
This work presents a numerical study of the tri-dimensional convection-diffusion equation by the control-volume-based on finite-element method using quadratic hexahedral elements. Considering that the equation governing this problem in its main variable may represent several properties, including temperature, turbulent kinetic energy, viscous dissipation rate of the turbulent kinetic energy, specific dissipation rate of the turbulent kinetic energy, or even the concentration of a contaminant in a given medium, among others, the wide applicability of this problem is thus evidenced. Three cases of temperature distributions will be studied specifically in this work, in addition to one case of pollutant dispersion upon analysis of the concentration of a contaminant in a fixed flow point. Some comparisons will be carried out against works found in the open literature, while others will be done according to each phenomenon characteristics. 相似文献
33.
Estaner Claro Romão 《Numerical Heat Transfer, Part A: Applications》2013,63(9):669-698
This study addresses how to implement the Galerkin finite element and least square finite element methods using auxiliary equations to solve the partial differential equation numerically, which models the convection–diffusion–reaction, set on a steady 3D domain. In the spatial discretization, hexahedral elements with eight (linear element) and 27 (quadratic element) nodes were used, in which Lagrange interpolation functions were adopted in local coordinates. Turning all the formulation of the problem of global coordinates into local coordinates, the Gauss–Legendre quadrature method was used to integrate coefficients of the element matrices numerically. In addition to the formulation by the two methods, a computer code was implemented to simulate the phenomenon proposed. By using analytical solutions, sundry numerical error analysis was performed from L2 norm (domain–average error) and L∞ norm (domain–top error), thus validating the numerical results. A real case is proposed and assessed. 相似文献
34.
J. F. Román-Zamorano M. Flores-Acosta H. Arizpe-Chávez F. F. Castillón-Barraza M. H. Farías R. Ramírez-Bon 《Journal of Materials Science》2009,44(18):4781-4788
We have synthesized lead and lead sulfide nanoparticles embedded in a natural zeolite (clinoptilolite) matrix by a simple
hydrothermal process. The process steps involve the partial removing of the natural cations in clinoptilolite, the ion-exchange
process to enclose Pb ions and nanoparticles and finally a sulfuration process at different temperatures to obtain lead sulfide
phases in the zeolite matrix. The samples were studied by X-ray diffraction, diffuse reflectance spectroscopy, energy dispersive
X-ray spectroscopy, X-ray photon spectroscopy and transmission electron microscopy. The experimental results show the inclusion
of three Pb species with different valence states after the Pb ion-exchange step, namely Pb2+, Pb4+, and Pb0. At the end of the process, two simultaneous lead sulfide crystalline phases, PbS (Galena) and PbS2 (tetragonal) were synthesized in the clinoptilolite matrix. The optical absorption spectra of the samples show the exciton
absorption peaks typical of colloidal PbS nanoparticles. The average size of the PbS nanoparticles was about 10 nm and their
crystalline structure was determined from diffraction electron patterns. The high-pressure phase PbS2 was also identified and its formation was attributed to the influence of the special conditions of clinoptilolite matrix
as crystallization media to induce some selective nucleation process of this crystalline phase. 相似文献
35.
R. Chavan G. Chitarin R.S. Delogu A. Encheva A. Gallo E.R. Hodgson L.C. Ingesson A. Le-Luyer J.B. Lister Ph. Moreau J.-M. Moret S. Peruzzo J. Roméro D.S. Testa M. Toussaint G. Vayakis R. Vila 《Fusion Engineering and Design》2009,84(2-6):295-299
The current status of the ITER magnetics diagnostic is summarised. The various risks are discussed on the basis of when they could be present during ITER operation and appropriate mitigation is reviewed. An implementation risk or common mode operation failure risk to the magnetic diagnostic can only be mitigated by diversity. All identified risks are being handled with ongoing research and development to minimise these risks. A reasonable level of design and manufacturing diversity has been therefore introduced in the procurement and installation plans, in order to optimise overall reliability avoiding dispersion of resources. 相似文献
36.
Synthesis of porous hydroxyapatites by combination of gelcasting and foams burn out methods 总被引:2,自引:0,他引:2
Padilla S Román J Vallet-Regí M 《Journal of materials science. Materials in medicine》2002,13(12):1193-1197
The biocompatibility and the osteoconductive behavior of hydroxyapatite (OHAp) ceramics are well established. Bioceramics made of OHAp are available in dense and porous form. Recently it has been proved that the volume of bone ingrowth at early times is primarily interconnectivity dependent. A new method for the obtention of porous OHAp ceramics that combine the in situ polymerization (gel casting method) and the foams burn out is proposed. Four polyurethane foams with different cells/cm were used. The foams were fully filled of an OHAp polymerizable suspension that after gelled produced very homogeneous and strong green bodies. After different thermal treatments the green bodies yield porous OHAp ceramics that were a replica of the foams used. Materials used in this work were studied by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), N2 adsorption isotherm, particle size distribution, and Hg porosimetry. Porous pieces of OHAp obtained are constituted by polyhedral-like particles (0.45–1.0 m) that are surrounded by an interconnected network of pores. A bimodal distribution of the pores size between 30.8–58.6 and 1.0–1.2 m has been observed. The size of the interconnected pores (30.8–58.6 m) was controled as a function of the cells/cm of the foam while the volume of the small pores was modified as a function of the sintering time. The presence of pores could promote the bone ingrowth and also could be used to insert different drugs, which makes these porous pieces a potential candidate to be used as non-load-bearing bone implants and as drug delivery systems. 相似文献
37.
38.
G. J. Rom’an-Moguel F. Olvera S. Aguirre B. S’anchez 《JOM Journal of the Minerals, Metals and Materials Society》1988,40(9):38-40
Using a porous plug or a tuyere, a copper bath composed of electrical scrap may be oxidized or deoxidized through the application of gas injection. Dry air and a hydrocarbon were used in the tests at scales of 16 kg, 400 kg and 16 t. 相似文献
39.
Tharinger Deborah J.; Lambert Nadine M.; Bricklin Patricia M.; Feshbach Norma; Johnson Neal F.; Oakland Thomas D.; Paster Vera S.; Sanchez William 《Canadian Metallurgical Quarterly》1996,27(1):24
National, state, and local education reform agendas have been on a fast track for more than a decade. Although some psychologists have been active in promoting psychology and psychological services in education reform initiatives, knowledge about their efforts is fragmented. In order to educate psychologists about education reform, this article highlights the impetus for the recent education reform movement, briefly reviews the latest waves of education reform, and discusses the development of the National Education Goals. Then, an argument is made for the integration of education, health, and social reform initiatives; state-level education reform principles and initiatives are highlighted, illustrated by the systemic education reform mandate in Kentucky. Next, progress toward the development and implementation of an APA-sponsored response to the National Education Goals is discussed. Finally, objectives and roles for psychologists in advancing education reform are presented, and guidelines for the education and training of future psychologists are introduced. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
40.