全文获取类型
收费全文 | 2363篇 |
免费 | 40篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 30篇 |
综合类 | 1篇 |
化学工业 | 255篇 |
金属工艺 | 27篇 |
机械仪表 | 38篇 |
建筑科学 | 21篇 |
矿业工程 | 1篇 |
能源动力 | 66篇 |
轻工业 | 28篇 |
水利工程 | 4篇 |
石油天然气 | 35篇 |
无线电 | 444篇 |
一般工业技术 | 286篇 |
冶金工业 | 868篇 |
原子能技术 | 14篇 |
自动化技术 | 290篇 |
出版年
2023年 | 11篇 |
2022年 | 52篇 |
2021年 | 32篇 |
2020年 | 28篇 |
2019年 | 28篇 |
2018年 | 40篇 |
2017年 | 33篇 |
2016年 | 29篇 |
2015年 | 42篇 |
2014年 | 42篇 |
2013年 | 123篇 |
2012年 | 60篇 |
2011年 | 55篇 |
2010年 | 69篇 |
2009年 | 50篇 |
2008年 | 55篇 |
2007年 | 50篇 |
2006年 | 55篇 |
2005年 | 51篇 |
2004年 | 45篇 |
2003年 | 44篇 |
2002年 | 46篇 |
2001年 | 26篇 |
2000年 | 41篇 |
1999年 | 53篇 |
1998年 | 282篇 |
1997年 | 163篇 |
1996年 | 120篇 |
1995年 | 88篇 |
1994年 | 68篇 |
1993年 | 73篇 |
1992年 | 26篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 34篇 |
1988年 | 25篇 |
1987年 | 27篇 |
1986年 | 27篇 |
1985年 | 38篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 13篇 |
1980年 | 19篇 |
1979年 | 11篇 |
1978年 | 9篇 |
1977年 | 30篇 |
1976年 | 56篇 |
1974年 | 9篇 |
1973年 | 9篇 |
排序方式: 共有2408条查询结果,搜索用时 15 毫秒
141.
Absract Samples of Cr3C2-NiCr cermet and NiCrBSi coatings formed by the high velocity oxy-fuel (HVOF) process on Superni 718 superalloy have been
corroded in the Na2SO4-V2O5 molten salt environment at 900 °C under cyclic conditions. The hot corrosion behavior of the coatings has been investigated
by means of thermogravimetric analysis, X-ray diffraction, scanning electron microscopy/energy dispersive spectroscopy, and
electron probe microanalyzer techniques. Efforts have been made to formulate the mode of corrosion attack. Both the coatings
protected the substrate superalloy Superni 718 completely. While protecting the superalloy, the Cr3C2-NiCr cermet coating partially oxidized along the splat boundaries up to the coating substrate interface, whereas only the
upper part of the coating, to about 100 μm from the surface, oxidized in the case of the NiCrBSi coating. The hot corrosion
resistance of both the coatings has been attributed to the formation of protective oxides of chromium/silicon at the surface
and at the splat boundaries of the coatings. 相似文献
142.
Spatial database operations are typically performed in two steps. In the filtering step, indexes and the minimum bounding rectangles (MBRs) of the objects are used to quickly determine a set of candidate objects. In the refinement step, the actual geometries of the objects are retrieved and compared to the query geometry or each other. Because of the complexity of the computational geometry algorithms involved, the CPU cost of the refinement step is usually the dominant cost of the operation for complex geometries such as polygons. Although many run-time and pre-processing-based heuristics have been proposed to alleviate this problem, the CPU cost still remains the bottleneck. In this paper, we propose a novel approach to address this problem using the efficient rendering and searching capabilities of modern graphics hardware. This approach does not require expensive pre-processing of the data or changes to existing storage and index structures, and is applicable to both intersection and distance predicates. We evaluate this approach by comparing the performance with leading software solutions. The results show that by combining hardware and software methods, the overall computational cost can be reduced substantially for both spatial selections and joins. We integrated this hardware/software co-processing technique into a popular database to evaluate its performance in the presence of indexes, pre-processing and other proprietary optimizations. Extensive experimentation with real-world data sets show that the hardware-accelerated technique not only outperforms the run-time software solutions but also performs as well if not better than pre-processing-assisted techniques. 相似文献
143.
Magan Lal Agrawal Rajesh Gupta Pramod R. Bhave 《Canadian Metallurgical Quarterly》2007,133(3):319-330
A water distribution network (WDN) is designed to meet time-varying demands with sufficient pressure, taking into consideration an appropriate demand during peak hours. Therefore, a network has inherent redundancy in the sense that under abnormal conditions such as those arising due to pipe breaks or pump failures, deficiency in supply during peak hours can be met through additional supply during off-peak periods. However, this necessitates a storage facility at the consumer end of the network, which is normally available in the form of a sump or an overhead tank in developing countries. Such a storage enables the consumer to store water during the off-peak period and then use it during the peak period. Reliability of a WDN is assessed herein considering nodal storage, and an iterative method is proposed for the optimal design of Level 1 redundant WDNs, i.e., networks that can sustain a single pipe failure without affecting consumer services either in part or in full. The method is illustrated through an example and the designs of a network with and without storage are compared. Provision of a nodal storage is found to reduce the total cost of the network. 相似文献
144.
MaryGail Perkins Steven W. Effler Feng Peng Donald Pierson David G. Smith Yogesh C. Agrawal 《Canadian Metallurgical Quarterly》2007,133(8):800-808
Characterization of the particle population for a location in a water supply reservoir, Kensico Reservoir, N.Y., is documented for a high turbidity event, from its onset, through alum treatment and its waning. Supporting in situ measurements included the beam attenuation coefficient at 670?nm (c670) and 660?nm (c660) [surrogates of turbidity (Tn)], particle concentrations (N) and size distributions (PSDs), and size class specific settling velocities (SVs). Laboratory measurements included chemical and morphometric analyses of individual particles, and routine measurements of Tn. The turbidity is shown to be primarily derived from clay minerals, mostly in the size range of 1.5–6?μm. An initial high c670 level (40?m?1;Tn ~ 100?NTU) decreased sevenfold in less than 1?week in response to alum treatment that largely eliminated the particle size classes responsible for the elevated turbidity. Successful SV experiments, made using a laser in situ scattering and transmissometry (LISST) instrument, for seven particle size classes in the range of 1.25–129?μm yielded SV values of 0.17–69.4?m?day?1. Size classes larger than ~ 5?μm settled much slower than Stokes law predictions, before alum treatment, indicating that these classes existed as porous flocs or aggregates. Decreases in SVs following treatment suggest changes in floc character consistent with increased porosity. In situ measurements of c670, N, PSDs, and SVs can contribute to the development and testing of a multiple particle size class model to simulate fate, transport, and impacts of suspended particles. 相似文献
145.
Pankaj Agrawal Silvia I. Oliveira E. M. Araújo Tomas J. A. Melo 《Journal of Materials Science》2007,42(13):5007-5012
In this work, the rheological, mechanical and morphological properties of nylon 6/polypropylene compatibilized blends were
investigated. Two types of polypropylene were used. One with MFI of 40 g/10 min (PP H103) and the other with MFI of 3.5 g/10 min
(PP H503). The compatibilizers used were polypropylene grafted with 6% of acrylic acid (PPgAA) and polypropylene grafted with
1% of maleic anhydride (PPgMA). The blends composition was 80/20 (wt%) for the PA6/PP binary blends and 80/10/10(wt%) for
the nylon 6/PPgAA/polypropylene and nylon 6/PPgMA/polypropylene ternary blends. Torque rheometry analysis showed that when
PPgAA and PPgMA were added to nylon 6/polypropylene blends, there was an increase in the torque, indicating that reactive
compatibilization has occurred. There is no influence of the polypropylene MFI on the mechanical properties of the uncompatibilized
and compatibilized blends. The impact strength of the blends containing PPgMA were greater than those of the blends containing
PPgAA. The blends containing PPgAA are unstable. SEM analysis showed that PPgMA improves considerably the adhesion between
PA6/PP phases, leading to good mechanical properties. 相似文献
146.
Elizabeth L. Wason Anurag A. Agrawal Mark D. Hunter 《Journal of chemical ecology》2013,39(8):1101-1111
The existence of predictable latitudinal variation in plant defense against herbivores remains controversial. A prevailing view holds that higher levels of plant defense evolve at low latitudes compared to high latitudes as an adaptive plant response to higher herbivore pressure on low-latitude plants. To date, this prediction has not been examined with respect to volatile organic compounds (VOCs) that many plants emit, often thus attracting the natural enemies of herbivores. Here, we compared genetically-based constitutive and herbivore-induced aboveground vegetative VOC emissions from plants originating across a gradient of more than 10° of latitude (>1,500 km). We collected headspace VOCs from Asclepias syriaca (common milkweed) originating from 20 populations across its natural range and grown in a common garden near the range center. Feeding by specialist Danaus plexippus (monarch) larvae induced VOCs, and field environmental conditions (temperature, light, and humidity) also influenced emissions. Monarch damage increased plant VOC concentrations and altered VOC blends. We found that genetically-based induced VOC emissions varied with the latitude of plant population origin, although the pattern followed the reverse of that predicted—induced VOC concentration increased with increasing latitude. This pattern appeared to be driven by a greater induction of sesquiterpenoids at higher latitudes. In contrast, constitutive VOC emission did not vary systematically with latitude, and the induction of green leafy volatiles declined with latitude. Our results do not support the prevailing view that plant defense is greater at lower than at higher latitudes. That the pattern holds only for herbivore-induced VOC emission, and not constitutive emission, suggests that latitudinal variation in VOCs is not a simple adaptive response to climatic factors. 相似文献
147.
In this paper, we describe an analytical model to determine contracting policies for a firm that purchases components from external suppliers. The model evaluates the tradeoff between the flexibility offered by short term contracts arid the fixed investments, improvement opportunities and price certainty associated with long term contracts. We show that long term contracts may not always be optimal, and discuss conditions under which short term contracts may be justified. During a recent survey of supply managers, we observed that managers often tend to participate in short term contracts, even though they claim to seek long term relationships with suppliers. Sensitivity analysis of our model provides some explanation for this observed inconsistency. We also discuss managerial implications of the analysis. 相似文献
148.
149.
Viscous potential flow analysis of Kelvin–Helmholtz instability with heat and mass transfer in presence of a horizontal electric field has been carried out. Stability criterion is given by a critical value of relative velocity of two fluids as well as critical value of the applied electric field. Various graphs with respect to physical parameters, such as wave-number, viscosity ratio, ratio of dielectric constants of two fluids, heat transfer coefficients have been drawn and effect of various parameters have been described. 相似文献
150.
Pramod S. Dobal Rasmi R. Das Ram S. Katiyar Dinesh C. Agrawal 《Journal of the American Ceramic Society》2000,83(8):1953-1956
Powder compacts of TiO2 and ZrO2 were prepared from their suspensions in water at different pH values, and micro-Raman spectroscopy was used to reveal the degree of mixing in each of them, with different sizes of the focused laser spot. The change in laser intensity and particle-size distributions led to a slight variation in the average composition, as determined using three different probe sizes. The Raman-estimated volume fractions of each constituent indicated that the aqueous suspensions in which the powders were well dispersed produced the most-uniform mixing. Powders that were flocculated in suspensions before mixing also resulted in a good mixture. The most-nonuniform mixing was observed when, in the individual suspensions, one of the constituents was dispersed and the other was flocculated. These results indicated that Raman spectroscopy can be useful for the rapid determination of the degree of mixing in powder mixtures. 相似文献