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排序方式: 共有567条查询结果,搜索用时 15 毫秒
111.
Llorens I Lahera E Delnet W Proux O Braillard A Hazemann JL Prat A Testemale D Dermigny Q Gelebart F Morand M Shukla A Bardou N Ulrich O Arnaud S Berar JF Boudet N Caillot B Chaurand P Rose J Doelsch E Martin P Solari PL 《The Review of scientific instruments》2012,83(6):063104
Fluorescence detection is classically achieved with a solid state detector (SSD) on x-ray absorption spectroscopy (XAS) beamlines. This kind of detection however presents some limitations related to the limited energy resolution and saturation. Crystal analyzer spectrometers (CAS) based on a Johann-type geometry have been developed to overcome these limitations. We have tested and installed such a system on the BM30B/CRG-FAME XAS beamline at the ESRF dedicated to the structural investigation of very dilute systems in environmental, material and biological sciences. The spectrometer has been designed to be a mobile device for easy integration in multi-purpose hard x-ray synchrotron beamlines or even with a laboratory x-ray source. The CAS allows to collect x-ray photons from a large solid angle with five spherically bent crystals. It will cover a large energy range allowing to probe fluorescence lines characteristic of all the elements from Ca (Z = 20) to U (Z = 92). It provides an energy resolution of 1-2 eV. XAS spectroscopy is the main application of this device even if other spectroscopic techniques (RIXS, XES, XRS, etc.) can be also achieved with it. The performances of the CAS are illustrated by two experiments that are difficult or impossible to perform with SSD and the complementarity of the CAS vs SSD detectors is discussed. 相似文献
112.
Molecular approaches to the assessment of biodiversity in aquatic microbial communities 总被引:12,自引:0,他引:12
For the past 20 years, the increased development and routine application of molecular-based techniques has made it possible to carry out detailed evaluations of the biodiversity of aquatic microbial communities. It also offers great opportunities for finding out how this parameter responds to various environmental stresses. Most of these approaches involve an initial PCR amplification of a target, which is generally located within the ribosomal operon. The amplification is achieved by means of primers that are specific to the organisms of interest. The second step involves detecting sequence variations in the PCR fragments either by a cloning/sequencing analysis, which provides a complete characterization of the fragments, or by an electrophoretic analysis, which provides a visual separation of the mixture of fragments according to sequence polymorphism (denaturing or temperature gradient gel electrophoresis, single strand conformation polymorphism) or length polymorphism (terminal-restriction fragment length polymorphism, automated ribosomal intergenic spacer analysis). Other non-PCR-based methods are also commonly used, such as fluorescence in-situ hybridization and DNA re-association analysis. Depending on the technique used, the information gained can be quite different. Moreover, some of these analyses may be rather onerous in terms of time and money, and so not always suitable for screening large numbers of samples. The most widely used techniques are discussed in this paper to illustrate the principles, advantages and shortcomings of each of them. Finally, we will conclude by evaluating the techniques and discussing some emerging molecular techniques, such as real-time PCR and the microarray technique. 相似文献
113.
Thomas Voisin Lise Durand Nikhil Karnatak Sophie Le Gallet Marc Thomas Yannick Le Berre Jean-François Castagné Alain Couret 《Journal of Materials Processing Technology》2013,213(2):269-278
The determination and the homogeneity of the sample temperature during consolidation of powders by Spark Plasma Sintering (SPS) are addressed. Densifications were carried out in three different facilities differing by their constructors and their size. A structural transformation activated in a TiAl alloy was used as a marker of the sample temperature and finite element modeling were performed to evaluate the temperature at each point of the set-up. A good agreement between experimental and simulated data is exhibited. Alloys with identical microstructures were sintered and the homogeneity of the microstructure was better in the largest machines or when the sample was isolated by alumina disks.Large specimens with a diameter of 100 mm and a height of 60 mm were sintered, with the aim to achieve full densification and good microstructural control. On the basis of this temperature mastering, samples with complex shape were successfully densified. SEM post mortem observations confirmed the absence of porosities, and the expected microstructure as predicted by FEM calculations. 相似文献
114.
115.
Key Fatty Acid Combinations Define Vascular Smooth Muscle Cell Proliferation and Viability 总被引:1,自引:1,他引:0
High plasma concentrations of free fatty acids (FFA) and insulin are common features in atherosclerotic patients with type 2 diabetes. FFA, according to their nature, can have various effects on vascular smooth muscle cells (VSMC). These cells play important roles throughout atherosclerosis pathogenesis, from plaque development to plaque instability. Thus, this study aims to assess the impact of two FFA combinations and insulin on murine VSMC viability. The two combinations contain the same FFA but at different ratios, one being richer in saturated fatty acids (SFA) and the other having a higher proportion of monounsaturated fatty acids (MUFA). Both combinations inhibited VSMC proliferation due to their pro-apoptotic potential, with SFA being the major inducers of apoptosis. However, the presence of oleic acid (OLA) attenuated this impact in a dose-dependent manner. OLA had also the capacity to reduce apoptosis rates more strongly when combined with a SFA than when used alone in VSMC treatments. This effect was significant only for specific proportions of these FFA and was even more effective in presence of insulin. These results highlight the presence of a competition between pro-apoptotic and anti-apoptotic mechanisms in VSMC that is dependent on FFA ratios (saturated vs. monounsaturated) and on insulinemia. They also underline the importance of the presence of MUFA such as OLA in diets containing high proportions of SFA. 相似文献
116.
Impact-echo and multi-channel analysis of surface wave (MASW) methods were combined for a hybrid analysis of multi-channel surface wavefield data sets to iteratively solve for the thickness, elastic modulus, and Poisson's ratio of Portland cement and asphalt concrete plates. The time-frequency method was used to evaluate the plate thickness resonance frequency of the zero group velocity component of the first-order symmetric Lamb wave mode for use in the impact-echo analysis. It was observed that the thickness resonance frequency may not be resolved using focusing or amplifying signal processing techniques when plate/base interface conditions result in weak reflection amplitudes. Hybrid analysis results compared favourably against longitudinal resonant frequency tests of both cast cylinders and drilled cores from Portland cement concrete plates. It was shown that the hybrid analysis technique can be used to provide accurate compression wave velocity estimates used in impact-echo surveys. 相似文献
117.
Bin Luo Jean-Fran?ois Aujol Yann Gousseau Sa?d Ladjal Henri Ma?tre 《IEEE transactions on image processing》2007,16(10):2503-2514
We study the problem of finding the characteristic scale of a given satellite image. This feature is defined so that it does not depend on the spatial resolution of the image. This is a different problem than achieving scale invariance, as often studied in the literature. Our approach is based on the use of a linear scale space and the total variation (TV). The critical scale is defined as the one at which the normalized TV reaches its maximum. It is shown experimentally, both on synthetic and real data, that the computed characteristic scale is resolution independent. 相似文献
118.
Kenneth T. Stanton Kevin P. O’Flynn Shohei Nakahara Jean-François Vanhumbeeck John M. Delucca Bobby Hooghan 《Journal of materials science. Materials in medicine》2009,20(4):851-857
Glass of generic composition SiO2 · Al2O3 · P2O5 · CaO · CaF2 will crystallise predominantly to apatite and mullite upon heat-treatment. Such ceramics are bioactive, osseoconductive,
and have a high resistance to fracture. As a result, they are under investigation for use as biomedical device coatings, and
in particular for orthopaedic implants. Previous work has shown that the material can be successfully enamelled to titanium
with an interfacial reaction zone produced during heat treatment. The present study uses high angle annular dark field transmission
electron microscopy (HAADF-TEM) to conduct a detailed examination of this region. Results show evidence of complex interfacial
reactions following the diffusion of titanium into an intermediate layer and the production of titanium silicides and titanium
phosphides. These results confirm previously hypothesised mechanisms for the bonding of silicate bioceramics with titanium
alloys. 相似文献
119.
Philippe Gilles Walid El-Ahmar Jean-François Jullien 《International Journal of Pressure Vessels and Piping》2009,86(1):3-12
This study contributes to the NeT-TG1 European Network formed in 2002. The aim of this study is to predict, by numerical simulation, the residual stresses generated in a test plate by the fusion welding process. The experiment consisted in the deposit of a weld bead along the longitudinal centre-line of an austenitic 316L plate using an automatic Tungsten Inert Gas (TIG) welding process with 316L filler material. During and after thermal cycle, a large quantity of measurement data is obtained that serve to develop a comparison with the results of different numerical models. The comparative thermal and mechanical analysis allows assessment for the general ability of the numerical models to describe the structural behaviour. The importance of the heat-input rate and material characteristics is also investigated. The residual stresses were predicted by the finite element method using the program Code_Aster of EDF and SYSWELD of ESI-GROUP. Finally the numerical results are validated by comparison with experimentally measured data. 相似文献
120.
Vandenberghe Christian; Bentein Kathleen; Michon Richard; Chebat Jean-Charles; Tremblay Michel; Fils Jean-Fran?ois 《Canadian Metallurgical Quarterly》2007,92(4):1177
The authors examined the relationships between perceived organizational support, organizational commitment, commitment to customers, and service quality in a fast-food firm. The research design matched customer responses with individual employees' attitudes, making this study a true test of the service provider-customer encounter. On the basis of a sample of matched employee-customer data (N = 133), hierarchical linear modeling analyses revealed that perceived organizational support had both a unit-level and an employee-level effect on 1 dimension of service quality: helping behavior. Contrary to affective organizational commitment, affective commitment to customers enhanced service quality. The 2 subdimensions of continuance commitment to the organization--perceived high sacrifice and perceived lack of alternatives--exerted effects opposite in sign: The former fostered service quality, whereas the latter reduced it. The implications of these findings are discussed within the context of research on employee-customer encounters. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献