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排序方式: 共有429条查询结果,搜索用时 343 毫秒
91.
Mangesh T. Bore Timothy L. Ward Atsushi Fukuoka Abhaya K. Datye 《Catalysis Letters》2004,98(4):167-172
Spherical mesoporous silica particles prepared by evaporation induced self assembly (EISA) were used as templates to form Pt nanowires. Transmission electron microscope (TEM) images of these aerosol-derived silica particles reveal hexagonally ordered pores coiled within each particle, with no obvious termination of the pores on the external surface. Near the particle surface the pores are seen to run parallel to the surface, consistent with the external constraint of spherical geometry. For MCM-41 type mesoporous materials, the pores are straight and accessible at either end for pore filling, but for spherical silica particles prepared by EISA, the pores are not open to the external surface. Hence it is remarkable that Pt nanowires can be formed within the closed pores inside these spherical silica particles, where conventional mechanisms of pore filling would not be expected to be operative. These results suggest that the silica walls in these mesoporous silica allow transport of volatile Pt complexes during wet reduction in H2. The permeability to gases makes these spherical silica particles especially suitable for gas phase catalytic reactions, while at the same time confining metallic particles within the silica pores. 相似文献
92.
The idea of an activation complex is popular for explaining reaction rates, but the characteristics of reactions and catalysis may not be explained in this way. A predestined state for each reaction composed of surface atoms and adsorbed species is responsible for these features. Two single Sn atoms trapped in adjacent half-unit cells of an Si(111) 7 × 7 surface is an example of a predestined state. An isolated Sn atom in a half-unit cell does not migrate to other half-unit cells at room temperature, but when two single Sn atoms are in adjacent half-unit cells they undergo rapid combination to form an Sn2 dimer. In addition, these two single Sn atoms replace the center Si adatoms and an Si4 cluster is formed. The spatial distribution of molecules desorbing from surfaces may reflect the predestined states for the desorption processes. The spatial distribution in the temperature-programmed desorption (TPD) of NO on Pd(110) and Pd(211) surfaces and that in the temperature-programmed reaction (TPR) of NO + H2 were studied. N2 desorbing from Pd(110) by the recombination of N atoms obeys cos6
– cos7
but the N2 produced by a catalytic reaction of NO with H2 obeys cos. In contrast, the N2 desorbing with NO at 490 K in the TPD of Pd(110) shows a sharp off-normal distribution expressed by cos46( – 38). The adsorption of NO on Pd(211) predominantly occurs on the (111) terrace but the spatial distribution suggests that the predestined states for the reaction and desorption are formed on both the (111) terrace and (100) step surfaces. 相似文献
93.
Origins of peak broadening in a histogram of measured adhesive forces were studied. The adhesive forces were measured in water by pulsed-force-mode atomic force microscopy. One sample was prepared by a microcontact printing method on a sputtered gold film with fine grains, on which CH(3)- and COOH-terminated regions were produced. Gold surfaces of other samples were chemically modified homogeneously by a self-assembling method in solution. Their surfaces were, however, topographically different, i.e. (i) an Au(111)-terrace-rich gold film prepared by vacuum vapor deposition at high temperature and (ii) sputtered gold films on cover glass with different grain sizes obtained by different deposition time. These sample surfaces and the probe tip surface were all CH(3)-terminated by self-assembled monolayers with CH(3)(CH(2))(19)SH. The main origin of peak broadening in the histogram was the topographic effect. Namely, the change in the grain sizes and the change in multiplicity of contacts between the tip and convexities of the grains resulted in the distribution of the observed adhesive forces. 相似文献
94.
To tailor the characteristics of molecularly thin lubricant films, magnetic disk surfaces coated with nanometer-thick perfluoropolyether
AM3001 lubricant films were irradiated with 184.9 and 253.7 nm ultraviolet (UV) rays. We elucidated the effect of UV irradiation
on the interactions between the lubricant and the magnetic disk surface via surface energy, bonded lubricant thickness and
lubricant spreading measurements for films with and without UV irradiation. We found that UV irradiation decreased the dispersive
and polar surface energies of the lubricant films by 20 and 80%, respectively; increased bonded lubricant thickness; and decelerated
lubricant spreading. These results indicated that dispersion and polar interactions between lubricant molecules and the magnetic
disk surface were strengthened by UV irradiation. 相似文献
95.
Takamasa Fukuoka 《Polymer Engineering and Science》2000,40(12):2511-2523
For controlling a reactive extrusion process in the subsequent study. the model equations of reaction kinetics and shear viscosity were studied. We focused on a free radical reaction between the molten polyethylene and vinylsilane. The kinetics model was expressed as a reaction rate equation with an apparent rate constant. The shear dependent of reacted polyethylene was formulated by employing the modified Cross model proposed in our early study. In addition, the average molecular weight was considered to correlate the shear viscosity with the reaction kinetics, leading to a series of rheo‐kinetics formulas. The experiments were carried out in a specific batch mixer suitably designed for sampling in arbitrary periods. Their reaction conversions, molecular weight distributions, and shear viscosity were measured, respectively, with an induced coupled plasma (ICP) emission spectrochemical analyzer, a high temperature gel permeation chromatography (GPC), and a capillary rheometer. Determining the parameters in each model, a simulator is set to investigate an engineering extrusion process. 相似文献
96.
Linear polysaccharides are typically composed of repeating mono- or disaccharide units and are ubiquitous among living organisms. Polysaccharide diversity arises from chain-length variation, branching, and additional modifications. Structural diversity is associated with various physiological functions, which are often regulated by cognate polysaccharide-binding proteins. Proteins that interact with linear polysaccharides have been identified or developed, such as galectins and polysaccharide-specific antibodies, respectively. Currently, data is accumulating on the three-dimensional structure of polysaccharide-binding proteins. These proteins are classified into two types: exo-type and endo-type. The former group specifically interacts with the terminal units of polysaccharides, whereas the latter with internal units. In this review, we describe the structural aspects of exo-type and endo-type protein-polysaccharide interactions. Further, we discuss the structural basis for affinity and specificity enhancement in the face of inherently weak binding interactions. 相似文献
97.
This study presents an integrated method suitable for off-axis tension and compression testing in unidirectional composites,and its application to the testing of in-plane shear characterization.A new rotating-grip test fixture,incorporating the attractive features of the existing pinned-end fixture and hydraulic wedge grips,has been developed.The proposed gripping system consists of two sets of jaw faces,each with a pair of self-aligning bearings that allows for loading in the axial and radial directions.Fi... 相似文献
98.
Lauwereyns Johan; Koizumi Masashi; Sakagami Masamichi; Hikosaka Okihide; Kobayashi Shunsuke; Tsutsui Ken-ichiro 《Canadian Metallurgical Quarterly》2000,26(3):352
To study the operation of selective attention in a conflict situation with automatic processes, we trained 4 Japanese macaques; (Macaca fuscata) extensively on a manual go/no-go task. The monkey had to discriminate either the color, shape, motion direction, or location of a visual stimulus. In each trial, the behavioral meaning of the relevant feature (go or no-go) could either be congruent or incongruent with irrelevant features of the same stimulus. Reaction times were slowed, and error rates increased when irrelevant stimulus features were incongruent with the required response. The effects were obtained when the monkey attended to the color, shape, or motion direction, but not when it attended to the location of the stimulus. The effects were cumulative so that the interference from 1 incongruent feature was smaller than that from 2 incongruent features. We propose that the present paradigm provides a behavioral analogue of the human Stroop effect. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
99.
Nishino M 《Journal of nanoscience and nanotechnology》2006,6(6):1854-1856
Low dimensional strongly correlated systems have great potential for new quantum devices. Among them, quantum wires are actively investigated with development of new methods based on self-organized formation. For magnetic wires (chains), impurity doping, which causes inhomogeneity of magnetic interaction, can bring new magnetic properties to the systems. In the present study, the effect of inhomogeneity (defect) on magnetic chains with bond alternation is focused on. Defects induce local moments in the magnetic chains at low temperatures. However, depending on the relation of the distance between the defects, the magnetic profile is found to be drastically changed. 相似文献
100.
Microbial communities in the garbage composting with rice hull as an amendment revealed by culture-dependent and -independent approaches 总被引:5,自引:0,他引:5
Takaku H Kodaira S Kimoto A Nashimoto M Takagi M 《Journal of Bioscience and Bioengineering》2006,101(1):42-50
The diversity and succession of microbial communities during the garbage composting with rice hull as an amendment were studied by denaturing gradient gel electrophoresis (DGGE) and clone library analysis of PCR-amplified 16S ribosomal DNA (rDNA) with universal primers. Based on temperature changes, the composting process could be divided into thermophilic, cooling-down, and maturing stages. The DGGE profiles and clone library analysis revealed that the microbial community drastically changed during the composting process from the thermophilic to the maturing stages. The dominant bacterial group changed from the phylum Firmicutes in the thermophilic stage to the phylum Bacteroidetes in the maturing stage. This change in microbial communities may be significant for the composting process. The diversity of cultivated bacteria isolated from samples taken at various stages of the composting process was low. A total of 87 isolates were classified as belonging to only four different groups. These groups were also detected in the DGGE profiles and by the clone library analysis. Our study indicated that a combination of culture-dependent and -independent approaches could be very useful for monitoring both bacterial diversity and the succession of communities during the composting process. This study would be beneficial for assessing the ecological consequences of disposal of organic waste. 相似文献